J. Hauser

The Collider Detector at Fermilab (CDF) is a 5000 t magnetic detector built to study 2 TeV pp collisions at the Fermilab Tevatron. Event analysis is based on charged particle tracking, magnetic momentum analysis and fine-grained calorimetry. The combined electromagnetic and hadron calorimetry has approximately uniform granularity in rapidity-azimuthal angle and extends down to 2° from the beam direction. Various tracking chambers cover the calorimeter acceptance and extend charged particle tracking down to 2 mrad from the beam direction. Charged particle momenta are analyzed in a 1.5 T solenoidal magnetic field, generated by a superconducting coil which is 3 m in diameter and 5 m in length. The central tracking chamber measures particle momenta with a resolution better then δpT/pT2 = 2 × 10−3 (GeV/c)−1 in the region 40° < θ < 140° and δPT/pT2 ≤ 4 × 10−3 for 21° < θ < 40° and 140° < θ < 159°. The calorimetry, which has polar angle coverage from 2° to 178° and full azimuthal coverage, consists of electromagnetic shower counters and hadron calorimeters, and is segmented into about 5000 projective “towers” or solid angle elements. Muon coverage is provided by drift chambers in the region 56° < θ < 124°, and by large forward toroid systems in the range 3° < θ < 16° and 164° < θ < 177°. Isolated high momentum muons can be identified in the intermediate angular range by a comparison of the tracking and calorimeter information in many cases. A custom front-end electronics system followed by a large Fastbus network provides the readout of the approximately 100 000 detector channels. Fast Level 1 and Level 2 triggers make a detailed pre-analysis of calorimetry and tracking information; a Level 3 system of on-line processors will do parallel processing of events. This paper provides a summary of the aspects of the detector which are relevant to its physics capabilities, with references to more detailed descriptions of the subsystems.

We report a revised determination of charmed-D-meson absolute branching fractions based on complete reconstruction of DD¯ events at the ψ(3770). Two backgrounds, Cabibbo-suppressed and multi-π0 D decays, are addressed in detail. The first measurement of the decay D0→K−π+π0π0 establishes the sensitivity to hitherto unobserved multi-π0 modes. Removal of both backgrounds reduces the values of our previously reported branching fractions by (21-24)%, leaving their ratios largely unchanged. The new values are unable to account fully for a reported deficit in charm production in B-meson decay.Received 24 June 1987DOI:https://doi.org/10.1103/PhysRevLett.60.89©1988 American Physical Society

We present measurements of the pseudorapidity (η) distribution of charged particles (dNchdη) produced within |η|≤3.5 in proton-antiproton collisions at √s of 630 and 1800 GeV. We measure dNchdη at η=0 to be 3.18±0.06(stat)±0.10(syst) at 630 GeV, and 3.95±0.03 (stat)±0.13(syst) at 1800 GeV. Many systematic errors in the ratio of dNchdη at the two energies cancel, and we measure 1.26±0.01±0.04 for the ratio of dNchdη at 1800 GeV to that at 630 GeV within |η|≤3. Comparing to lower-energy data, we observe an increase faster than ln(s) in dNchdη at η=0.Received 2 October 1989DOI:https://doi.org/10.1103/PhysRevD.41.2330©1990 American Physical Society

Measurements of inclusive transverse-momentum spectra for charged particles produced in proton-antiproton collisions at \ensuremath{\surd}2 of 630 and 1800 GeV are presented and compared with data taken at lower energies.

A search for the top quark in p\ifmmode\bar\else\textasciimacron\fi{}p collisions at a center-of-mass energy of 1.8 TeV using the Collider Detector at Fermilab is described. A study of events selected by requiring an energetic electron, missing transverse energy, and two or more jets excludes at 95% confidence level the standard-model production and decay of tt\ifmmode\bar\else\textasciimacron\fi{} pairs if the top-quark mass is between 40 and 77 GeV/${c}^{2}$. The observed electron + multijet data are consistent with W-boson production.

A new technique is applied to data collected at the $\ensuremath{\psi}(3770)$ resonance to derive charmed-$D$-meson branching fractions without relying on the measurement of $D$-production cross sections. Measurements are presented for three decay modes of the ${D}^{0} ({K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}, {D}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}, \mathrm{and} {K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}$ and four decay modes of the ${D}^{+} ({K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+},{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0},{K}_{S}^{0}{\ensuremath{\pi}}^{+}, \mathrm{and} {K}_{S}^{0}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0})$. The resulting branching fractions are significantly larger than previous measurements.

We have determined mW=79.91±0.39 GeV/c2 from an analysis of W→eν and W→μν data from the Collider Detector at Fermilab in p¯p collisions at a c.m. energy of √s =1.8 TeV. This result, together with the world-average Z mass, determines the weak mixing angle to be sin2θW=0.232±0.008. Bounds on the top-quark mass are discussed.Received 13 August 1990DOI:https://doi.org/10.1103/PhysRevLett.65.2243©1990 American Physical Society

Evidence is presented for a narrow state, called \ensuremath{\xi}, in the decay modes J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\xi}, \ensuremath{\xi}\ensuremath{\rightarrow}${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, and \ensuremath{\xi}\ensuremath{\rightarrow}${K}_{S}^{0}$${K}_{S}^{0}$. In the ${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$ mode, the \ensuremath{\xi} has a mass of 2.230\ifmmode\pm\else\textpm\fi{}0.006\ifmmode\pm\else\textpm\fi{}0.014 GeV/${c}^{2}$, a width of \ensuremath{\Gamma}${=0.026}_{\mathrm{\ensuremath{-}}0.016}^{+0.020}$\ifmmode\pm\else\textpm\fi{} 0.017 GeV/${c}^{2}$, a product branching ratio of ${(4.2}_{\mathrm{\ensuremath{-}}1.4}^{+1.7}$\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}10 $^{\mathrm{\ensuremath{-}}5}$, and a statistical significance of \ensuremath{\sim}4.5 standard deviations. In the ${K}_{S}^{0}$${K}_{S}^{0}$ mode, it has a mass of 2.232\ifmmode\pm\else\textpm\fi{}0.007\ifmmode\pm\else\textpm\fi{}0.007 GeV/${c}^{2}$, a width of \ensuremath{\Gamma}${=0.018}_{\mathrm{\ensuremath{-}}0.015}^{+0.023}$\ifmmode\pm\else\textpm\fi{} 0.010 GeV/${c}^{2}$, a product branching ratio of ${(3.1}_{\mathrm{\ensuremath{-}}1.3}^{+1.6}$\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}10 $^{\mathrm{\ensuremath{-}}5}$, and a statistical significance of \ensuremath{\sim}3.6 standard deviations. Limits on \ensuremath{\xi} decay to other final states are presented.

Measurements of the semileptonic branching ratios of charmed ${D}^{+}$ and ${D}^{0}$ mesons are presented, from data collected at the $\ensuremath{\psi}(3770)$ in the Mark III detector at SPEAR. From a sample of events kinematically selected as charmed ${D}^{+}{D}^{\ensuremath{-}}$ or ${D}^{0}{\overline{D}}^{0}$ pairs, the branching ratios $R({D}^{+}\ensuremath{\rightarrow}{e}^{+}+X)=(17.0\ifmmode\pm\else\textpm\fi{}1.9\ifmmode\pm\else\textpm\fi{}0.7)%$ and $R({D}^{0}\ensuremath{\rightarrow}{e}^{+}+X)=(7.5\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\pm\else\textpm\fi{}0.4)%$ are obtained. The ratio of these measurements can be interpreted as the ratio of ${D}^{+}$ and ${D}^{0}$ lifetimes $\frac{{\ensuremath{\tau}}^{+}}{{\ensuremath{\tau}}^{0}}={2.3}_{\ensuremath{-}0.4\ensuremath{-}0.1}^{+0.5+0.1}$ by neglect of the contribution of Cabibbo-suppressed decays to the total decay width.

Measurements of the exclusive branching fractions B(${D}^{0}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${e}^{+}$${\ensuremath{\nu}}_{e}$) and B(${D}^{0}$\ensuremath{\rightarrow}${K}^{\mathrm{\ensuremath{-}}}$${e}^{+}$${\ensuremath{\nu}}_{e}$), using data collected at the \ensuremath{\psi}(3770) with the Mark III detector at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR, are used to determine the ratio of the Kobayashi-Maskawa matrix elements \ensuremath{\Vert}${V}_{\mathrm{cd}}$/${V}_{\mathrm{cs}}$${\ensuremath{\Vert}}^{2}$ =0.057${\ifmmode\pm\else\textpm\fi{}}_{0.015}^{+0.038}$\ifmmode\pm\else\textpm\fi{}0.005.

A search for tt\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}e\ensuremath{\mu}+X in pp\ifmmode\bar\else\textasciimacron\fi{} collisions at s\ensuremath{\surd}\ifmmode\bar\else\textasciimacron\fi{} TeV is described. The production and decay of top-quark--antiquark pairs is considered in the context of the standard model. The analysis is based on data with an integrated luminosity of 4.4 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ recorded with the Collider Detector at Fermilab. An upper limit on the tt\ifmmode\bar\else\textasciimacron\fi{} cross section is obtained, and the top quark in the mass range 28--72 GeV/${c}^{2}$ is excluded at the 95% C.L. The same limits apply to a possible fourth-generation, charge -(1/3, b' quark, decaying via the charged current.

Results from a partial-wave analysis of the decay J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}^{\ifmmode\pm\else\textpm\fi{}}$${\mathrm{\ensuremath{\pi}}}^{\ensuremath{\mp}}$ in the ${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}^{\ifmmode\pm\else\textpm\fi{}}$${\mathrm{\ensuremath{\pi}}}^{\ensuremath{\mp}}$ invariant-mass range 1.35--1.6 GeV/${\mathit{c}}^{2}$ are presented. Within the isobar model, the data in this mass range are best described by a mixture of ${0}^{\mathrm{\ensuremath{-}}+}$ and ${1}^{++}$ amplitudes, corresponding to the ${\mathit{K}}^{\mathrm{*}}$K\ifmmode\bar\else\textasciimacron\fi{}+c.c (P wave), ${\mathit{K}}^{\mathrm{*}}$K\ifmmode\bar\else\textasciimacron\fi{}+c.c (S wave), and ${\mathit{a}}_{0}$(980) \ensuremath{\pi} (S wave) channels. These results show that \ensuremath{\eta}(1430) is not a ${\mathit{J}}^{\mathit{P}\mathit{C}}$=${0}^{\mathrm{\ensuremath{-}}+}$ ${\mathit{a}}_{0}$(980)\ensuremath{\pi} resonance, but a mixture of overlapping states.

We have determined mW=79.91±0.39 GeV/c2 from an analysis of W→eν and W→μν data from the Collider Detector at Fermilab in ¯pp collisions at √s=1.8 TeV. From this result and the world-average Z mass, the weak mixing angle is determined to be sin2θW=0.232±0.008. An upper bound on the top-quark mass derived from this result is discussed.Received 13 August 1990DOI:https://doi.org/10.1103/PhysRevD.43.2070©1991 American Physical Society

An analysis of ${Z}^{0}$\ensuremath{\rightarrow}${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ and ${Z}^{0}$\ensuremath{\rightarrow}${\ensuremath{\mu}}^{+}$${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$ data from the Collider Detector at Fermilab in p\ifmmode\bar\else\textasciimacron\fi{}p collisions at \ensuremath{\surd}s =1.8 TeV yields a mass of the ${Z}^{0}$ boson of ${M}_{Z}$=90.9\ifmmode\pm\else\textpm\fi{}0.3 (stat+syst)\ifmmode\pm\else\textpm\fi{}0.2 (scale) GeV/${c}^{2}$ and a width of ${\ensuremath{\Gamma}}_{z}$=3.8\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}1.0 GeV.

We present measurements of the two-body decays of the J/\ensuremath{\psi} into a vector and a pseudoscalar meson. The data, taken with the Mark III detector at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR, consist of 5.8\ifmmode\times\else\texttimes\fi{}${10}^{6}$ produced J/\ensuremath{\psi}'s. The branching ratios for the J/\ensuremath{\psi} decays into \ensuremath{\rho}\ensuremath{\pi}, \ensuremath{\rho}\ensuremath{\eta}, \ensuremath{\rho}\ensuremath{\eta}', \ensuremath{\omega}${\ensuremath{\pi}}^{0}$, \ensuremath{\omega}\ensuremath{\eta}, \ensuremath{\omega}\ensuremath{\eta}', \ensuremath{\varphi}\ensuremath{\eta}, \ensuremath{\varphi}\ensuremath{\eta}', and ${K}^{\mathrm{*}}$K are measured; an upper limit on J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\varphi}${\ensuremath{\pi}}^{0}$ is obtained. Using the measured branching ratios we obtain parameters of a phenomenological model of J/\ensuremath{\psi} decays, indicating that the \ensuremath{\eta} and \ensuremath{\eta}' are consistent with being composed only of light and strange quarks. The model is used to obtain the mixing angle in the pseudoscalar nonet. The \ensuremath{\omega}${\ensuremath{\pi}}^{0}$ electromagnetic form factor is determined. The upper limit on J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\varphi}${\ensuremath{\pi}}^{0}$ is used to study the contributions from electromagnetic doubly--Okubo-Zweig-Iizuka--suppressed decays of the J/\ensuremath{\psi}. .AE

Dalitz plot analyses of four Kππ decays of the D0 and D+ mesons are presented. The relative amounts of K̄∗π, K̄ϱ and non-resonant Kππ in each decay mode are determined, and isospin amplitudes and phases are derived. These results are compared with predictions from QCD. The K−π+π+ mode has a non-uniform, non-resonant contribution; attempts to fit this distribution are described.

This paper describes the design, construction and performance of the Mark III, a new general purpose large solid angle spectrometer at SPEAR, the SLAC 2–8 GeV e+e− storage ring. The detector has been designed for the study of exclusive final states in e+e− annihilation, which requires large solid angle coverage combined with charged particle momentum resolution, particle identification, and photon detection efficiency at low energies.

Inclusive jet production at $\sqrt{s}=1.8$ TeV has been measured in the CDF detector at the Fermilab Tevatron $\overline{p}p$ Collider. Jets with transverse energies (${E}_{t}$) up to 250 GeV have been observed. The ${E}_{t}$ dependence of the inclusive jet cross section is consistent with leading-order quantum-chromodynamic calculations, and comparison with lower-energy data shows deviations from scaling consistent with QCD. A lower limit of 700 GeV (95% confidence level) is placed on the quark compositeness scale parameter ${\ensuremath{\Lambda}}_{c}$ associated with an effective contact interaction.

An experiment utilizing the decay \ensuremath{\varphi}\ensuremath{\rightarrow}${K}_{S}$${K}_{L}$ is proposed for measuring the ratio \ensuremath{\epsilon}'/\ensuremath{\epsilon} of CP-violating parameters in the kaon system. It appears one can probe values of \ensuremath{\epsilon}'/\ensuremath{\epsilon} down to ${10}^{\mathrm{\ensuremath{-}}3}$ with ${10}^{9}$ \ensuremath{\varphi}'s. An asymmetry measurement of the relative times of ${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ and ${\ensuremath{\pi}}^{0}$${\ensuremath{\pi}}^{0}$ decays is capable of testing the phase difference ${\ensuremath{\varphi}}_{+\mathrm{\ensuremath{-}}}$-${\ensuremath{\varphi}}_{00}$ to \ifmmode\pm\else\textpm\fi{}${1.6}^{0}$ (3\ensuremath{\sigma}), with ${10}^{10}$ \ensuremath{\varphi}'s. Far fewer \ensuremath{\varphi}'s (perhaps ${10}^{8}$) can be useful in constraining some parameters of the kaon system associated with CPT violations.

An analysis of high-transverse-momentum electrons using data from the Collider Detector at Fermilab (CDF) of ¯pp collisions at √s=1800 GeV yields values of the production cross section times branching ratio for W and Z0 bosons of σ(¯pp→WX→eνX)=2.19±0.04(stat)±0.21(syst) nb and σ(¯pp→Z0X→e+e−X)=0.209±0.013(stat)±0.017(syst) nb. Detailed descriptions of the CDF electron identification, background, efficiency, and acceptance are included. Theoretical predictions of the cross sections that include a mass for the top quark larger than the W mass, current values of the W and Z0 masses, and higher-order QCD corrections are in good agreement with these measured values.Received 13 November 1990DOI:https://doi.org/10.1103/PhysRevD.44.29©1991 American Physical Society

Measurements of the branching ratios of ten Cabibbo-suppressed hadronic weak decays of the ${D}^{+}$ and ${D}^{0}$ are presented from data collected with the Mark III detector SPEAR. In addition to the previously observed channels ${D}^{0}$\ensuremath{\rightarrow}${K}^{\mathrm{\ensuremath{-}}}$${K}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$, we report new measurements of ${D}^{0}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$, and ${D}^{+}$\ensuremath{\rightarrow}K${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$${K}^{+}$, ${\ensuremath{\pi}}^{0}$${\ensuremath{\pi}}^{+}$, K${\ifmmode\bar\else\textasciimacron\fi{}}^{\mathrm{*}0}$(892)${K}^{+}$, \ensuremath{\varphi}${\ensuremath{\pi}}^{+}$, ${K}^{\mathrm{\ensuremath{-}}}$${K}^{+}$${\ensuremath{\pi}}^{+}$, and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{+}$.

We present an analysis of the decay J/ψ→γ4π in the final states γπ+π−π+π− and γπ+π0π−π0. The branching fractions obtained are B(J/ψ→γπ+π−π+π−)= (3.05±0.08±0.45)×10−3 and B(J/ψ→γπ+π0π−πo)=( 8.3±0.2±3.1)×10−3 for m4π less than 2 GeV/c2. The 4π invariant-mass distributions extend from 1.0 to 3.0 GeV/c2, showing peaks at approximately 1.55 and 1.8 GeV/c2. In an analysis of the 4π final state we find that ≊50% of the events below 2 GeV/c2 are pseudoscalar ρρ, the product branching fraction of which is determined to be &→ρρ)= (4.7±0.3±0.9)×10−3. No other significant ρρ component is found, and upper limits on the product branching fraction B(J/ψ→γX)B(X→ρρ) are presented for the theta(1690) and the gT states near 2.2 GeV/c2.Received 29 July 1985DOI:https://doi.org/10.1103/PhysRevD.33.1222©1986 American Physical Society

We describe a two level FASTBUS based trigger processor designed and built for the CDF detector at the Fermilab pp collider. The Level 1 decision is based on the global energy deposition in the calorimeters as well as on the presence of muon candidates and stiff tracks in the central drift chamber. The Level 1 decision is made in the 3.5 μs between beam crossings, incurring no deadtime while reducing a raw event rate of 50–75 kHz to a few kHz. The remaining events are passed on to Level 2. The Level 2 decision is driven by the topology of the event, operating on calorimeter clusters, central stiff tracks and muon candidates. Level 2 is designed to reduce the rate to 1–100 Hz, incurring less than 10% deadtime, before initiating readout of all the detector elements. A large fraction of the trigger hardware is used for both the Level 1 and Level 2 decisions.

The series of upgrades to the Large Hadron Collider, culminating in the High Luminosity Large Hadron Collider, will enable a significant expansion of the physics program of the CMS experiment. However, the accelerator upgrades will also make the experimental conditions more challenging, with implications for detector operations, triggering, and data analysis. The luminosity of the proton-proton collisions is expected to exceed $2-3\times10^{34}$~cm$^{-2}$s$^{-1}$ for Run 3 (starting in 2022), and it will be at least $5\times10^{34}$~cm$^{-2}$s$^{-1}$ when the High Luminosity Large Hadron Collider is completed for Run 4. These conditions will affect muon triggering, identification, and measurement, which are critical capabilities of the experiment. To address these challenges, additional muon detectors are being installed in the CMS endcaps, based on Gas Electron Multiplier technology. For this purpose, 161 large triple-Gas Electron Multiplier detectors have been constructed and tested. Installation of these devices began in 2019 with the GE1/1 station and will be followed by two additional stations, GE2/1 and ME0, to be installed in 2023 and 2026, respectively. The assembly and quality control of the GE1/1 detectors were distributed across several production sites around the world. We motivate and discuss the quality control procedures that were developed to standardize the performance of the detectors, and we present the final results of the production. Out of 161 detectors produced, 156 detectors passed all tests, and 144 detectors are now installed in the CMS experiment. The various visual inspections, gas tightness tests, intrinsic noise rate characterizations, and effective gas gain and response uniformity tests allowed the project to achieve this high success rate.

We report the results of a search for the leptonic decay ${\mathrm{D}}^{+}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\mu}}}^{+}$${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$ using the Mark III detector at the SLAC ${\mathrm{e}}^{+}$${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR. A data sample of 9.3 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ collected at the \ensuremath{\psi}(3770) resonance yields no signal events, corresponding to a 90%-confidence-level upper limit of 7.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ on the branching ratio B(${\mathrm{D}}^{+}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\mu}}}^{+}$${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$). This represents an upper limit on the pseudoscalar decay constant ${\mathrm{f}}_{\mathrm{D}}$ of 290 MeV/${\mathrm{c}}^{2}$.

The decays J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ and J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, 2.0 GeV/${c}^{2}$, have been studied. Measurements are presented for B(\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}f(1270))B(f(1270)\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$), B(\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}f(1270))B(f(1270)\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$), B(\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}f'(1525))B(f'(1525)\ensuremath{\rightarrow}${\mathrm{K}}^{+}$${\mathrm{K}}^{\mathrm{\ensuremath{-}}}$), and B(\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}theta)B(theta(1270)\ensuremath{\rightarrow}${\mathrm{K}}^{+}$${\mathrm{K}}^{\mathrm{\ensuremath{-}}}$). A higher-mass structure is observed in the ${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ channel. The spin of the theta(1720) is established with high confidence. The polarization structure of the f(1270), f'(1525), and theta(1720) have been determined.

Pairs of $\ensuremath{\tau}$ leptons produced at $\sqrt{s}=3.77$ GeV have been studied in $e\ensuremath{\mu}$, $\mathrm{ee}$, and $\ensuremath{\mu}\ensuremath{\mu}$ final states. The leptonic branching ratios have been measured to be $B(\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\nu}\ensuremath{\nu})=(18.2\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}0.5)%$ and $B(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}\ensuremath{\nu})=(18.0\ifmmode\pm\else\textpm\fi{}1.0\ifmmode\pm\else\textpm\fi{}0.6)%$. Limits have been set for the two-body decays $\ensuremath{\tau}\ensuremath{\rightarrow}\mathrm{eG}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}G$, where $G$ is a light Goldstone boson.

We present evidence for the radiative decay J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\omega}\ensuremath{\omega} with a branching fraction of (1.76\ifmmode\pm\else\textpm\fi{}0.09\ifmmode\pm\else\textpm\fi{}0.45)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$. The \ensuremath{\omega}\ensuremath{\omega} invariant-mass distribution peaks at 1.8 GeV/${c}^{2}$, just above threshold. Analysis of angular correlations indicates that \ensuremath{\omega}\ensuremath{\omega} system below 2 GeV/${c}^{2}$ is predominantly pseudoscalar. Upper limits are presented for the branching fractions of \ensuremath{\omega}\ensuremath{\omega} decays of the \ensuremath{\theta}(1690), the ${g}_{T}$ states near 2.2 GeV/${c}^{2}$, and the ${\ensuremath{\eta}}_{c}$.

From a study of 2.7\ifmmode\times\else\texttimes\fi{}${10}^{6}$ J/\ensuremath{\psi} decays with the Mark III detector at the SLAC storage ring SPEAR, we have obtained new measurements of the two-body decays of the J/\ensuremath{\psi} into a vector and a pseudoscalar meson. We present branching ratios for decays to \ensuremath{\rho}\ensuremath{\pi}, ${\mathrm{KK}}^{\mathrm{*}}$(892), \ensuremath{\varphi}\ensuremath{\eta}, the previously unobserved modes \ensuremath{\varphi}\ensuremath{\eta}', \ensuremath{\omega}\ensuremath{\eta}, \ensuremath{\omega}\ensuremath{\eta}', \ensuremath{\omega}${\ensuremath{\pi}}^{0}$, ${\ensuremath{\rho}}^{0}$\ensuremath{\eta}, and new upper limits on ${\ensuremath{\rho}}^{0}$\ensuremath{\eta}' and \ensuremath{\varphi}${\ensuremath{\pi}}^{0}$. In the decay J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\eta}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$, we observe ${\ensuremath{\rho}}^{0}$-\ensuremath{\omega} interference. The collection of measured branching ratios are simultaneously fit to a simple model of J/\ensuremath{\psi} decays which includes strong and electromagnetic amplitudes and allows for violation of SU(3) invariance. Using this model, we calculate the strange- and nonstrange-quark content of the \ensuremath{\eta} and \ensuremath{\eta}' and conclude that (35\ifmmode\pm\else\textpm\fi{}18)% of the \ensuremath{\eta}' wave function can be attributed to an additional component, e.g., gluonium or radial excitation. The measurement of the \ensuremath{\omega}${\ensuremath{\pi}}^{0}$ branching ratio, when combined with that of the \ensuremath{\gamma}${\ensuremath{\pi}}^{0}$ decay mode of the \ensuremath{\omega}, yields a determination of the \ensuremath{\omega}${\ensuremath{\pi}}^{0}$ electromagnetic-form-factor ratio \ensuremath{\Vert}f(${q}^{2}$=${m}_{J/\ensuremath{\psi}}$${\mathrm{}}^{2}$)/f(${q}^{2}$=0) \ensuremath{\Vert}=0.038\ifmmode\pm\else\textpm\fi{}0.006.

We present the dijet invariant-mass distribution in the region between 60 and 500 GeV, measured in 1.8-TeV $\overline{p}p$ collisions in the Collider Detector at Fermilab. Jets are restricted to the pseudorapidity interval $|\ensuremath{\eta}|&lt;0.7$. Data are compared with QCD calculations; axigluons are excluded with 95% confidence in the region $120&lt;{M}_{A}&lt;210$ GeV for axigluon width ${\ensuremath{\Gamma}}_{A}=\frac{N{\ensuremath{\alpha}}_{s}{M}_{A}}{6}$, with $N=5$.

We present a study of the radiative decay J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\varphi}\ensuremath{\varphi} in the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ and \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}_{\mathit{L}}^{0}$ final states. A pseudoscalar state is observed in the \ensuremath{\varphi}\ensuremath{\varphi} invariant-mass spectrum at 2.22 GeV/${\mathit{c}}^{2}$ with a width of 150 MeV/${\mathit{c}}^{2}$. The product branching ratios are B(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}X)B(X\ensuremath{\rightarrow}\ensuremath{\varphi}\ensuremath{\varphi})=(3.3\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ for the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ mode and B(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}X)B(X\ensuremath{\rightarrow}\ensuremath{\varphi}\ensuremath{\varphi})=(2.7\ifmmode\pm\else\textpm\fi{}0.6 \ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ for the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}_{\mathit{L}}^{0}$ mode. No evidence for ${2}^{++}$ states below 2.4 GeV/${\mathit{c}}^{2}$ is found in this radiative J/\ensuremath{\psi} decay mode.

Using the Collider Detector at Fermilab, the W-boson differential cross section d\ensuremath{\sigma}/${\mathit{dP}}_{\mathit{T}}$ is measured using W\ensuremath{\rightarrow}e\ensuremath{\nu} events in proton-antiproton collisions at \ensuremath{\surd}s =1.8 TeV. A next-to-leading-order theoretical calculation agrees well with the data. The cross section (\ensuremath{\sigma}) for ${\mathit{P}}_{\mathit{T}}$&gt;50 GeV/c is measured to be 423\ifmmode\pm\else\textpm\fi{}58(stat)\ifmmode\pm\else\textpm\fi{}108(syst) pb.

From a study of 2.7\ifmmode\times\else\texttimes\fi{}${10}^{6}$ J/\ensuremath{\psi} decays with the Mark III detector at the SLAC storage ring SPEAR, we determine branching ratios for decays of the ${\ensuremath{\eta}}_{c}$ to \ensuremath{\eta}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$, ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$${K}^{\ensuremath{\mp}}$${K}_{S}$, ${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$, ${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, pp\ifmmode\bar\else\textasciimacron\fi{}, the previously unobserved modes \ensuremath{\eta}'${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$, ${\ensuremath{\pi}}^{0}$${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}K^{\ifmmode\pm\else\textpm\fi{}}$${\ensuremath{\pi}}^{\ensuremath{\mp}}$, ${K}^{\mathrm{*}0}$K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}$, and new upper limits on \ensuremath{\rho}\ensuremath{\rho}, \ensuremath{\omega}\ensuremath{\omega}, \ensuremath{\delta}\ensuremath{\pi}, ${A}_{2}$\ensuremath{\pi}, f\ensuremath{\eta}, and \ensuremath{\eta}KK. When combined, the different measurements of the ${\ensuremath{\eta}}_{c}$ mass yield 2980.2\ifmmode\pm\else\textpm\fi{}1.6 MeV/${c}^{2}$. In the decays ${\ensuremath{\eta}}_{c}$\ensuremath{\rightarrow}vector+vector, a strong increase of the decay rate with the number of strange quarks in the final state is observed.

New results are obtained for the decays J/\ensuremath{\psi}\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ and J/\ensuremath{\psi}\ensuremath{\rightarrow}${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$. The first observation of the decay J/\ensuremath{\psi}\ensuremath{\rightarrow}${K}_{S}^{0}$${K}_{L}^{0}$ is reported. Branching ratios are measured to be (1.58\ifmmode\pm\else\textpm\fi{}0.20\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, (2.39\ifmmode\pm\else\textpm\fi{}0.24\ifmmode\pm\else\textpm\fi{}0.22)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, and (1.01\ifmmode\pm\else\textpm\fi{}0.16\ifmmode\pm\else\textpm\fi{}0.09)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, respectively. The corresponding electromagnetic form factors are ${\mathrm{\ensuremath{\Vert}}}^{2}$=(11.9\ifmmode\pm\else\textpm\fi{}1.5\ifmmode\pm\else\textpm\fi{}0. 9)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ and ${\mathrm{\ensuremath{\Vert}}}^{2}$=(20.9\ifmmode\pm\else\textpm\fi{}2.1\ifmmode\pm\else\textpm\fi{}1. 5) \ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$. The ${K}_{S}^{0}$-${K}_{L}^{0}$ transition form factor \ensuremath{\Vert} $^{2}$=(8.9\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ is obtained. A 90%-confidence-level upper limit of 5.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ is given for the branching ratio for the decay J/\ensuremath{\psi}\ensuremath{\rightarrow}${K}_{S}^{0}$${K}_{S}^{0}$. These form factors are substantially larger than expectations based on vector dominance and indicate large ${\mathrm{SU}}_{3}$-symmetry-breaking effects.

The CMS collaboration considers upgrading the muon forward region which is particularly affected by the high-luminosity conditions at the LHC. The proposal involves Gas Electron Multiplier (GEM) chambers, which are able to handle the extreme particle rates expected in this region along with a high spatial resolution. This allows to combine tracking and triggering capabilities, which will improve the CMS muon High Level Trigger, the muon identification and the track reconstruction. Intense R&D has been going on since 2009 and it has lead to the development of several GEM prototypes and associated detector electronics. These GEM prototypes have been subjected to extensive tests in the laboratory and in test beams at the CERN Super Proton Synchrotron (SPS). This contribution will review the status of the CMS upgrade project with GEMs and its impact on the CMS performance.

Triple-GEM detector technology was recently selected by CMS for a part of the upgrade of its forward muon detector system as GEM detectors provide a stable operation in the high radiation environment expected during the future High-Luminosity phase of the Large Hadron Collider (HL-LHC). In a first step, GEM chambers (detectors) will be installed in the innermost muon endcap station in the $1.6<\left|\eta\right|<2.2$ pseudo-rapidity region, mainly to control level-1 muon trigger rates after the second LHC Long Shutdown. These new chambers will add redundancy to the muon system in the $\eta$-region where the background rates are high, and the bending of the muon trajectories due to the CMS magnetic field is small. A novel construction technique for such chambers has been developed in such a way where foils are mounted onto a single stack and then uniformly stretched mechanically, avoiding the use of spacers and glue inside the active gas volume. We describe the layout, the stretching mechanism and the overall assembly technique of such GEM chambers.

We have measured the cross section as a function of invariant mass for isolated electron pairs produced in p¯p collisions at s=1.8 TeV for pair masses M>30 GeV/c2. We find good agreement between the measured distribution and the standard-model prediction for the Drell-Yan production mechanism. Additional heavy neutral vector bosons (Z′) are excluded for MZ'<387 GeV/c2 (95% confidence level) assuming standard-model couplings. A lower limit of 2.2 TeV (95% confidence level) is placed on the electron-quark compositeness scale parameter Λ−LL associated with an effective contact interaction.Received 16 July 1991DOI:https://doi.org/10.1103/PhysRevLett.67.2418©1991 American Physical Society

An analysis of W- and Z-boson production using data from the Collider Detector at Fermilab at \ensuremath{\surd}s =1.8 TeV yields \ensuremath{\sigma}(W\ensuremath{\rightarrow}ev)/\ensuremath{\sigma}(Z\ensuremath{\rightarrow}ee)=10.2\ifmmode\pm\else\textpm\fi{}0.8(stat)\ifmmode\pm\else\textpm\fi{}0.4(syst). The width of the W boson, \ensuremath{\Gamma}(W), and a limit on the top-quark mass independent of decay mode are extracted from this measurement.

The cross section for the production and subsequent decay to electron and neutrino of the W intermediate vector boson has been measured in 1.8-TeV p\ifmmode\bar\else\textasciimacron\fi{}p collisions at the Fermilab Tevatron Collider. An analysis of events with missing transverse energy greater than 25 GeV and with an electron of transverse energy greater than 15 GeV from a datum sample of 25.3 ${\mathrm{nb}}^{\mathrm{\ensuremath{-}}1}$ gives \ensuremath{\sigma}B=2.6\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\pm\else\textpm\fi{}0.5 nb.

In a study of 2.7 million Jψ decays with the Mark III, a new magnetic detector at SPEAR, we have observed the sequential decay Jψ→γηc, ηc→φφ. The product branching fraction is (1.02±0.25±0.14)×10−4, where the quoted errors are statistical and systematic, respectively. Analysis of the final-state angular distributions provides the first experimental determination that the spin and parity of the ηc are 0−.Received 9 April 1984DOI:https://doi.org/10.1103/PhysRevLett.52.2126©1984 American Physical Society

The charged-particle fractional momentum distribution within jets, D(z), has been measured in dijet events from 1.8-TeV p\ifmmode\bar\else\textasciimacron\fi{}p collisions in the Collider Detector at Fermilab. As expected from scale breaking in quantum chromodynamics, the fragmentation function D(z) falls more steeply as dijet invariant mass increases from 60 to 200 GeV/${\mathit{c}}^{2}$. The average fraction of the jet momentum carried by charged particles is 0.65\ifmmode\pm\else\textpm\fi{}0.02(stat)\ifmmode\pm\else\textpm\fi{}0.08(syst).

We report a new measurement of the D∗ branching ratios, using data obtained with the Mark III detector at the e+e− storage ring SPEAR at s=4.14 GeV. A fit to the recoil mass squared spectrum of D mesons reconstructed through the decay modes K−π+π+ and K−π+ is used to extract the D∗+ → γD+, π0D+, π+D0 and D∗0 → γD0, π0D0 branching ratios.

The reactions J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\omega}KK\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi} and J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\varphi}KK\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi} have been studied in a sample of 5.8\ifmmode\times\else\texttimes\fi{}${10}^{6}$ produced J/\ensuremath{\psi} decays. The systems ${K}^{\ifmmode\pm\else\textpm\fi{}}$${K}_{S}^{0}$${\ensuremath{\pi}}^{\ensuremath{\mp}}$ and ${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{0}$ produced in association with an \ensuremath{\omega} have enhancements in the mass distribution near 1.44 GeV/${c}^{2}$. The observed angular distributions are consistent with ${J}^{P}$${=1}^{+}$ and do not favor a ${J}^{P}$${=0}^{\mathrm{\ensuremath{-}}}$ assignment. No signal is seen at the nominal ${f}_{1}$(1285) mass. The reverse pattern is observed in the KK\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi} system produced in association with a \ensuremath{\varphi}, which shows an enhancement near 1.280 GeV/${c}^{2}$, and no evidence for structure at 1.4 GeV/${c}^{2}$.

A search was made for heavy stable charged particles produced in 1.8-TeV proton-antiproton collisions. No such particles were found in 26.2 ${\mathrm{nb}}^{\mathrm{\ensuremath{-}}1}$ of data. Cross-section limits are presented and mass limits of the order of 100 GeV are set for particles containing excited quarks in higher color representations.

The weak hadronic decay ${D}^{0}\ensuremath{\rightarrow}{\overline{K}}^{0}{K}^{+}{K}^{\ensuremath{-}}$ is observed in a data sample of 9.3 ${\mathrm{pb}}^{\ensuremath{-}1}$ collected with the Mark III detector at the $\ensuremath{\psi}(3770)$ resonance. An analysis of the ${K}^{+}{K}^{\ensuremath{-}}$ subsystem suggests that while the decay proceeds in part through the ${\overline{K}}^{0}\ensuremath{\varphi}$ channel, providing evidence for the presence of nonspectator amplitudes in ${D}^{0}$ decays, a significant fraction of the decays occurs through both higher- and lower-mass ${K}^{+}{K}^{\ensuremath{-}}$ systems. A limit is set on the decay ${D}^{0}\ensuremath{\rightarrow}{\overline{K}}^{0}{K}^{0}$, also thought to proceed by nonspectator processes.

We have measured dijet angular distributions at \ensuremath{\surd}s =1.8 TeV with the Collider Detector at Fermilab and the Tevatron p\ifmmode\bar\else\textasciimacron\fi{}p Collider and find agreement with leading-order QCD. By comparing the distribution for the highest dijet invariant masses with the prediction of a model of quark compositeness, we set a lower limit on the associated scale parameter ${\ensuremath{\Lambda}}_{c}$ at 330 GeV (95% C.L.).

In this work the design of a constant fraction discriminator (CFD) to be used in the VFAT3 chip for the read-out of the triple-GEM detectors of the CMS experiment, is described. A prototype chip containing 8 CFDs was implemented using 130 nm CMOS technology and test results are shown.

We present a study of the decay sequence Jψ→γX, X→γρ0, ρ0→π+π−, based on 5.8 × 106 produced Jψ collected by the Mark III detector at the SLAC storage ring SPEAR. In the γρ0 mass spectrum, we find two peaks with masses and widths consistent with the axial-vector mesons f1(1285) and f1(1420) that have recently been observed in two-photon collisions. Fits to the angular distributions confirm that the first peak is an axial-vector state, but are unable to distinguish between the f1(1420) or the pseudoscalar η(1430) for the high-mass peak. Product branching fractions for both objects are presented.Received 17 October 1989DOI:https://doi.org/10.1103/PhysRevD.41.1410©1990 American Physical Society

The B0 B¯ 0 average mixing parameter χ has been extracted from eμ and ee events produced in pp¯ collisions at √s =1.8 TeV. In a sample of 900 eμ events, the like-sign to opposite-sign charge ratio R is measured to be 0.556±0.048(stat)+0.035−0.042(syst). In the absence of mixing, the expected value of R would be 0.23±0.06. The corresponding number for 212 ee events is 0.573±0.116(stat)±0.047(syst) with an expected nonmixing value of 0.24±0.07. The observed excess in R leads to a combined determination of χ=0.176±0.031(stat+syst) ±0.032 (model), where the last uncertainty is due to Monte Carlo modeling.Received 6 August 1991DOI:https://doi.org/10.1103/PhysRevLett.67.3351©1991 American Physical Society

Measurements of inclusive transverse-momentum spectra for ${K}_{S}^{0}$ mesons produced in proton-antiproton collisions at $\sqrt{s}$ of 630 and 1800 GeV are presented and compared with data taken at lower energies. The ratio, as a function of ${p}_{T}$, of the cross section for ${K}_{S}^{0}$ to that for charged hadrons is very similar to what is observed at lower energies. At 1800 GeV, we calculate the strangeness-suppression factor $\ensuremath{\lambda}=0.40\ifmmode\pm\else\textpm\fi{}0.05$.

The high-luminosity phase of the Large Hadron Collider (HL-LHC) will result in ten times higher particle background than measured during the first phase of LHC operation. In order to fully exploit the highly-demanding operating conditions during HL-LHC, the Compact Muon Solenoid (CMS) Collaboration will use Gas Electron Multiplier (GEM) detector technology. The technology will be integrated into the innermost region of the forward muon spectrometer of CMS as an additional muon station called GE1∕1. The primary purpose of this auxiliary station is to help in muon reconstruction and to control level-1 muon trigger rates in the pseudo-rapidity region 1.6≤|η|≤2.2. The new station will contain trapezoidal-shaped GEM detectors called GE1∕1 chambers. The design of these chambers is finalized, and the installation is in progress during the Long Shutdown phase two (LS-2) that started in 2019. Several full-size prototypes were built and operated successfully in various test beams at CERN. We describe performance measurements such as gain, efficiency, and time resolution of these prototype chambers, developed after years of R&D, and summarize their behavior in different gas compositions as a function of the applied voltage.

A search for the lepton family number violating decay D0→μe is reported. No signal is observed in a data sample of 9.3 pb−1 collected at the ζ (3770) resonance with the MARK III detector, where 0.18±0.06±0.05 background events are expected. A 90% confidence level upper limit on the branching fraction B(D0→μe) of 1.5 × 10−4 is obtained.

This contribution introduces a new type of Micropattern Gaseous Detector, the Fast Timing Micropattern (FTM) detector, utilizing fully Resistive WELL structures. The structure of the prototype will be described in detail and the results of the characterization study performed with an X-ray gun will be presented, together with the first results on time resolution based on data collected with muon/pion test beams.

DEPFET Active Pixel Sensors (APS) have been introduced as focal plane detectors for X-ray astronomy already in 1996. Fabricated on high resistivity, fully depleted silicon and back-illuminated they can provide high quantum efficiency and low noise operation even at very high read rates. In 2009 a new type of DEPFET APS, the DSSC (DEPFET Sensor with Signal Compression) was developed, which is dedicated to high-speed X-ray imaging at the European X-ray free electron laser facility (EuXFEL) in Hamburg. In order to resolve the enormous contrasts occurring in Free Electron Laser (FEL) experiments, this new DSSC-DEPFET sensor has the capability of nonlinear amplification, that is, high gain for low intensities in order to obtain single-photon detection capability, and reduced gain for high intensities to achieve high dynamic range for several thousand photons per pixel and frame. We call this property "signal compression".

We present a detailed examination of the heavy flavor properties of jets produced at the Fermilab Tevatron collider. The data set, collected with the Collider Detector at Fermilab, consists of events with two or more jets with transverse energy ET>~15GeV and pseudorapidity |η|<~1.5. The heavy flavor content of the data set is enriched by requiring that at least one of the jets (lepton-jet) contains a lepton with a transverse momentum larger than 8GeV/c. Jets containing hadrons with heavy flavor are selected via the identification of secondary vertices. The parton-level cross sections predicted by the HERWIG Monte Carlo generator program are tuned within theoretical and experimental uncertainties to reproduce the secondary-vertex rates in the data. The tuned simulation provides new information on the origin of the discrepancy between the bb¯ cross section measurements at the Tevatron and the next-to-leading order QCD prediction. We also compare the rate of away-jets (jets recoiling against the lepton-jet) containing a soft lepton (pT>~2GeV/c) in the data to that in the tuned simulation. We find that this rate is larger than what is expected for the conventional production and semileptonic decay of pairs of hadrons with heavy flavor.Received 2 December 2003DOI:https://doi.org/10.1103/PhysRevD.69.072004©2004 American Physical Society

Gas Electron Multipliers (GEM) are a proven position sensitive gas detector technology which nowadays is becoming more widely used in High Energy Physics. GEMs offer an excellent spatial resolution and a high particle rate capability, with a close to 100% detection efficiency. In view of the high luminosity phase of the CERN Large Hadron Collider, these aforementioned features make GEMs suitable candidates for the future upgrades of the Compact Muon Solenoid (CMS) detector. In particular, the CMS GEM Collaboration proposes to cover the high-eta region of the muon system with large-area triple-GEM detectors, which have the ability to provide robust and redundant tracking and triggering functions. In this contribution, after a general introduction and overview of the project, the construction of full-size trapezoidal triple-GEM prototypes will be described in more detail. The procedures for the quality control of the GEM foils, including gain uniformity measurements with an x-ray source will be presented. In the past few years, several CMS triple-GEM prototype detectors were operated with test beams at the CERN SPS. The results of these test beam campaigns will be summarised.

The two-jet differential cross section ${\mathit{d}}^{3}$\ensuremath{\sigma}(p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}jet 1+jet 2+X)/${\mathit{dE}}_{\mathit{t}}$d${\mathrm{\ensuremath{\eta}}}_{1}$d${\mathrm{\ensuremath{\eta}}}_{2}$, averaged over -0.6\ensuremath{\le}${\mathrm{\ensuremath{\eta}}}_{1}$\ensuremath{\le}0.6, at \ensuremath{\surd}s =1.8 TeV, has been measured in the Collider Detector at Fermilab. The predictions of leading-order quantum chromodynamics for most choices of structure functions show agreement with the data.

Presented are the main design features of the large Cathode Strip Chambers (CSCs) for the CMS Endcap Muon System as well as the performance results obtained with the two full-scale 3.4×1.5 m2 six-plane prototypes. The prototype performance was within the baseline requirements: (a) higher than 99% efficiency of muon track finding at the trigger level with more than 92% probability for bunch crossing identification and better than 2 mm spatial resolution, and (b) better than 150 μm spatial resolution in off-line.

The production rate of charged D* mesons in jets has been measured in 1.8-TeV p¯p collisions at the Fermilab Tevatron with the Collider Detector at Fermilab. In a sample of approximately 32 300 jets with a mean transverse energy of 47 GeV obtained from an exposure of 21.1 nb−1, a signal corresponding to 25.0±7.5(stat)±2.0(syst) D*±→K∓π±π± events is seen above background. This corresponds to a ratio N(D*++D*−)/N(jet) =0.10±0.03±0.03 for D* mesons with fractional momentum z greater than 0.1.Received 10 October 1989DOI:https://doi.org/10.1103/PhysRevLett.64.348©1990 American Physical Society

Abstract We describe the algorithm that is used to find and fit charged particle trajectories in the Mark III detector at SPEAR. The computer program uses a novel non-numerical pattern recognition technique analogous to that used by the digital hardware in the experiment's track finding trigger processor. The technique is both fast and efficient. The complete reconstruction of events is performed at a rate of 37 ms per track on an IBM 3081K, compared with 91 ms per track with a more conventional technique. A preliminary fit of all tracks, suitable for online monitoring, is available after 15 ms per track. Similar techniques are also applicable to future experiments operating in high multiplicity environments. The organization of the algorithms is such as to lead to simple implementation on vector processors.

We report the first observation of the decay Ds+→K¯ 0K+ and a new measurement of the decay Ds+→K¯ (892)0K+. The data were collected at √s=4.14 GeV with the Mark III detector at the SLAC e+e− storage ring at SPEAR. We obtain the relative branching fractions B(D+s→K¯0K+/ B(Ds+→φπ+)=0.92±0.32±0.20 and B(Ds+→K¯*0K+)/ B(Ds+→φπ+)=0.84±0.30±0.22, using our new determination of σB(Ds+→φπ+). A search for the Cabibbo-suppressed decay D+s→K0π+ yields a limit B(Ds+→K0π+)/B(Ds+→φπ+)<0.21 at the 90% confidence level.Received 17 May 1989DOI:https://doi.org/10.1103/PhysRevLett.63.1211©1989 American Physical Society

A measurement of the QCD jet-broadening parameter ⟨QT⟩ is described for high-ET jet data in the central calorimeter of the Collider Detector at Fermilab. As an alternate approach to clustering analysis, this method involves the use of a global event parameter which is free from the ambiguities associated with the definition and separation of individual clusters. The parameter QT is defined as the scalar sum of the transverse momentum perpendicular to the transverse thrust axis. Parton-level QCD predictions are made for ⟨QT⟩ as a function of ET, the total transverse energy in the events, and suggest that a measurement would show a dependence on the running of the strong coupling constant αs. Comparisons are made to first-order QCD parton-level calculations, as well as to fully evolved and hadronized leading-log simulations. The data are well described by the QCD predictions.Received 25 January 1991DOI:https://doi.org/10.1103/PhysRevD.44.601©1991 American Physical Society

We report a study of the hadronic branching fractions of the ${D}_{s}^{+}$ meson, which is used to extract an upper limit on the absolute branching fraction for ${D}_{s}^{+}$\ensuremath{\rightarrow}\ensuremath{\varphi}${\ensuremath{\pi}}^{+}$. A search is made for fully reconstructed events from the reaction ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${D}_{s}^{\mathrm{*}\ifmmode\pm\else\textpm\fi{}}$${D}_{s}^{\ensuremath{\mp}}$, ${D}_{s}^{\mathrm{*}\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\rightarrow}\ensuremath{\gamma}${D}_{s}^{\ifmmode\pm\else\textpm\fi{}}$, using seven exclusive ${D}_{s}^{+}$ decay modes. The data sample of 6.30\ifmmode\pm\else\textpm\fi{}0.46 ${\mathrm{ppb}}^{\mathrm{\ensuremath{-}}1}$ was collected at \ensuremath{\surd}s\ifmmode\bar\else\textasciimacron\fi{}=4.14 GeV with the Mark III detector at the SLAC ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR. No candidate events are observed. The measured relative ${D}_{s}^{+}$ branching fractions and \ensuremath{\sigma}B(${D}_{s}^{+}$\ensuremath{\rightarrow}\ensuremath{\varphi}${\ensuremath{\pi}}^{+}$) are used to establish the limit B(${D}_{s}^{+}$\ensuremath{\rightarrow}\ensuremath{\varphi}${\ensuremath{\pi}}^{+}$)4.1% at 90% confidence level.

We report on the development and test of a fast three-dimensional Track-Finder for the Level-1 trigger of the CMS endcap muon system. System tests included four types of custom circuit boards clocked at 40MHz, optical links, and a high-speed custom auxiliary backplane in a VME crate. The hardware results, calculated using field-programmable gate arrays, programmable logic devices, and memory lookup tables, agreed bit-for-bit with software simulations for both random patterns and realistic tracks.

Two CMS production Cathode Strip Chambers were tested for aging effects in a high-radiation environment at the Gamma Irradiation Facility at CERN. The chambers were irradiated over a large area: in total, about 2.1 m2 or 700 m of wire in each chamber. The 40% Ar+50% CO2+10% CF4 gas mixture was provided by an open-loop gas system for one of the chambers and by a closed-loop re-circulating gas system for the other. After an accumulation of 0.3–0.4 C/cm of a wire, equivalent to about 30–50 years of operation at peak LHC luminosity, no significant changes in gas gain, chamber efficiency and wire signal noise were observed for either of the two chambers. The only consistent signs of aging were a small increase in dark current from ∼2 to ∼10 nA per plane of 600 wires and a decrease of strip-to-strip resistance from 1000 to 10–100 GΩ. Disassembly of the chambers revealed deposits on the cathode planes, while the anode wires remained fairly clean.

After the Phase-2 high-luminosity upgrade to the Large Hadron Collider (LHC), the collision rate and therefore the background rate will significantly increase, particularly in the high $\eta$ region. To improve both the tracking and triggering of muons, the Compact Muon Solenoid (CMS) Collaboration plans to install triple-layer Gas Electron Multiplier (GEM) detectors in the CMS muon endcaps. Demonstrator GEM detectors were installed in CMS during 2017 to gain operational experience and perform a preliminary investigation of detector performance. We present the results of triple-GEM detector performance studies performed in situ during normal CMS and LHC operations in 2018. The distribution of cluster size and the efficiency to reconstruct high $p_T$ muons in proton--proton collisions are presented as well as the measurement of the environmental background rate to produce hits in the GEM detector.

A simple network of comparators applied to the strip signals of a cathode strip chamber allows quick hit localization to within a halfstrip width, or ± a quarter-strip. A six-plane chamber with 6.4 mm wide strips was tested in a high-energy muon beam. The chamber was placed behind a 30 cm thick iron block. We show that patterns of hits localized to within a halfstrip allowed us to identify 300 GeV/c muon tracks with 99% probability and 0.7 mm spatial resolution in the presence of bremsstrahlung radiation. This technique of finding muon tracks will be used in the cathode strip chambers of the CMS Endcap Muon System.

The charge asymmetry of leptons from W-boson decay has been measured using p\ifmmode\bar\else\textasciimacron\fi{}p data from the Collider Detector at Fermilab at \ensuremath{\surd}s =1.8 TeV. The observed asymmetry is well described by most of the available parton distributions.

After a brief overview of the CMS EMU electronics system, results on radiation induced single event effects, total ionization dose and displacement effects will be reported. These results are obtained by irradiating the components on electronics boards with 63MeV protons and 1MeV neutrons. During the proton irradiation, the electronics board was fully under power, all components on the board were active and the data were read out in the same way as designed for CMS. No deterioration of analog performance for each of the three CMOS ASICs on the tested board was observed, up to a dose of 10krad. Each of the tested FPGAs survived beyond the dose of 30krad. No single event latch-up was detected for the CMOS ASICs up to a proton fluence of 2×1012cm−2. Single Event Upsets (SEU) in FPGAs were detected and their cross-sections measured. SEU mitigation with triple module redundancy and voting was implemented and tested.

A large cylindrical drift chamber has been constructed for the MARK III detector at SPEAR. The inner layer has a high density of sense wires for the measurement of kinks, vees, and dEdx. The outer layers have a cell design with three sense wires, giving uniform drift behavior and left/right ambiguity resolution within a cell. The chamber has both current division and stereo layers for longitudinal position measurement.

In order to cope with the harsh environment expected from the high luminosity LHC, the CMS forward muon system requires an upgrade. The two main challenges expected in this environment are an increase in the trigger rate and increased background radiation leading to a potential degradation of the particle ID performance. Additionally, upgrades to other subdetectors of CMS allow for extended coverage for particle tracking, and adding muon system coverage to this region will further enhance the performance of CMS. Following an extensive R&D program, CMS has identified triple-foil gas electron multiplier (GEM) detectors as a solution for the first muon station in the region 1.6<|η|<2.2, while continuing R&D is ongoing for additional regions.

Gas Electron Multiplier (GEM) technology, in particular triple-GEM, was selected for the upgrade of the CMS endcap muon system following several years of intense effort on R&D. The triple-GEM chambers (GE1/1) are being installed at station 1 during the second long shutdown with the goal of reducing the Level-1 muon trigger rate and improving the tracking performance in the harsh radiation environment foreseen in the future LHC operation [1]. A first installation of a demonstrator system started at the beginning of 2017: 10 triple-GEM detectors were installed in the CMS muon system with the aim of gaining operational experience and demonstrating the integration of the GE1/1 system into the trigger. In this context, a dedicated Detector Control System (DCS) has been developed, to control and monitor the detectors installed and integrating them into the CMS operation. This paper presents the slice test DCS, describing in detail the different parts of the system and their implementation.

The CMS muon system in the region with 2.03<|η|<2.82 is characterized by a very harsh radiation environment which can generate hit rates up to 144 kHz/cm2 and an integrated charge of 8 C/cm2 over ten years of operation. In order to increase the detector performance and acceptance for physics events including muons, a new muon station (ME0) has been proposed for installation in that region. The technology proposed is Triple—Gas Electron Multiplier (Triple-GEM), which has already been qualified for the operation in the CMS muon system. However, an additional set of studies focused on the discharge probability is necessary for the ME0 station, because of the large radiation environment mentioned above. A test was carried out in 2017 at the Cern High energy AcceleRator Mixed (CHARM) facility, with the aim of giving an estimation of the discharge probability of Triple-GEM detectors in a very intense radiation field environment, similar to the one of the CMS muon system. A dedicated standalone Geant4 simulation was performed simultaneously, to evaluate the behavior expected in the detector exposed to the CHARM field. The geometry of the detector has been carefully reproduced, as well as the background field present in the facility. This paper presents the results obtained from the Geant4 simulation, in terms of sensitivity of the detector to the CHARM environment, together with the analysis of the energy deposited in the gaps and of the processes developed inside the detector. The discharge probability test performed at CHARM will be presented, with a complete discussion of the results obtained, which turn out to be consistent with measurements performed by other groups.

An analysis of the forward-backward asymmetry in ${\mathit{Z}}^{0}$ decays using data from the Collider Detector at Fermilab at \ensuremath{\surd}s =1.8 TeV yields ${\mathit{A}}_{\mathit{F}\mathit{B}}$=[5.2\ifmmode\pm\else\textpm\fi{}5.9(stat)\ifmmode\pm\else\textpm\fi{}0.4(syst)]% and ${\mathrm{sin}}^{2}$\ensuremath{\theta}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{W}}$ =0.${228}_{\mathrm{\ensuremath{-}}0.015}^{+0.017}$(stat)\ifmmode\pm\else\textpm\fi{}0.002(syst).

We determine the resonant substructure of ${\mathit{D}}^{0}$\ensuremath{\rightarrow}${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ decays using a five-dimensional maximum-likelihood technique to extract the relative fractions and phases of the amplitudes contributing to this final state. We find that two-body decay modes account for at least 76% of all decays. We obtain branching ratios for several decay modes including B(${\mathit{D}}^{0}$\ensuremath{\rightarrow}${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{a}}_{1}^{+}$) =(9.0\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}1.7)%, B(${\mathit{D}}^{0}$\ensuremath{\rightarrow}K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}\mathrm{\ensuremath{\rho}}^{0}$)=(1.9\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}0.7)%, and B(${\mathit{D}}^{0}$\ensuremath{\rightarrow}${\mathit{K}}_{1}$(1270${)}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{+}$) =(1.8\ifmmode\pm\else\textpm\fi{}0.5 \ifmmode\pm\else\textpm\fi{}0.8)%. For the decay mode ${\mathit{D}}^{0}$\ensuremath{\rightarrow}K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}\mathrm{\ensuremath{\rho}}^{0}$, the K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}$ and ${\mathrm{\ensuremath{\rho}}}^{0}$ are found to be polarized with their spins oriented in the direction of their motion as seen from the ${\mathit{D}}^{0}$ frame.

The CMS Collaboration has been developing large-area triple-gas electron multiplier (GEM) detectors to be installed in the muon Endcap regions of the CMS experiment in 2019 to maintain forward muon trigger and tracking performance at the High-Luminosity upgrade of the Large Hadron Collider (LHC); 10 preproduction detectors were built at CERN to commission the first assembly line and the quality controls (QCs). These were installed in the CMS detector in early 2017 and participated in the 2017 LHC run. The collaboration has prepared several additional assembly and QC lines for distributed mass production of 160 GEM detectors at various sites worldwide. In 2017, these additional production sites have optimized construction techniques and QC procedures and validated them against common specifications by constructing additional preproduction detectors. Using the specific experience from one production site as an example, we discuss how the QCs make use of independent hardware and trained personnel to ensure fast and reliable production. Preliminary results on the construction status of CMS GEM detectors are presented with details of the assembly sites involvement.

A novel approach which uses Fiber Bragg Grating (FBG) sensors has been utilized to assess and monitor the flatness of Gaseous Electron Multipliers (GEM) foils. The setup layout and preliminary results are presented.

We report a search for the decay ${D}^{0}$\ensuremath{\rightarrow}${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ based on a data sample of 9.6 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ collected at the \ensuremath{\psi}(3770) resonance with the Mark III detector at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR. We find no evidence for this flavor-changing weak-neutral-current decay and set an upper limit on the branching ratio of B(${D}^{0}$\ensuremath{\rightarrow}${e}^{+}$${e}^{\ensuremath{-}}$)1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ at the 90% confidence level. This limit constrains various extensions of the standard model.

In the Compact Muon Solenoid (CMS) experiment, muon detection in the forward direction is accomplished by cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using 36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge (MTCC) exercise conducted by the CMS experiment in 2006. In contrast to earlier studies that used muon beams to illuminate a very small chamber area (<0.01m2), results presented in this paper were obtained by many installed CSCs operating in situ over an area of ≈23m2 as a part of the CMS experiment. The efficiency of finding two-dimensional trigger primitives within six-layer chambers was found to be 99.93±0.03%. These segments, found by the CSC electronics within 800 ns after the passing of a muon through the chambers, are the input information for the Level-1 muon trigger and, also, are a necessary condition for chambers to be read out by the Data Acquisition System.

The Compact Muon Solenoid (CMS) detector is one of the two general-purpose detectors at the CERN LHC. LHC will provide exceptional high instantaneous and integrated luminosity after second long shutdown. The forward region |η| ≥ 1:5 of CMS detector will face extremely high particle rates in tens of kHz/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and hence it will affect the momentum resolution, efficiency and longevity of the muon detectors. Here, η is pseudorapidity defined as η = −ln(tan(θ/2)), where θ is the polar angle measured from z-axis. To overcome these issues the CMSGEM collaboration has proposed to install new large size rate capable Triple Gas Electron Multiplier (GEM) detectors in the forward region of CMS muon system. The first set of Triple GEM detectors will be installed in the GE1/1 region (1:6 < |η| < 2.2) of the muon endcap during the long shutdown 2 (LS2) of the LHC. Towards this goal, full size CMS Triple GEM detectors have been fabricated and tested at the CERN SPS, H2 and H4 test beam facility. The GEM detectors were operated with two gas mixtures: Ar/CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (70/30) and Ar/CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /CF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> (45/15/40). In 2014, good quality data was collected during test beam campaigns. In this paper, the performance of the detectors is summarized based on their tracking efficiency and time resolution.

The decay \ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\nu} is studied in \ensuremath{\tau} pair production by ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ annihilation at \ensuremath{\surd}s =3.77 GeV, 0.20 GeV above \ensuremath{\tau}\ensuremath{\tau} threshold. The branching fraction is measured to be B(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\nu})=(23.0\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\pm\else\textpm\fi{}1.7)%. The measured distribution of the helicity angle of the charged pion from the \ensuremath{\rho} decay agrees with the theoretical prediction.

The CMS experiment at LHC will upgrade its forward muon spectrometer by incorporating Triple-GEM detectors. This upgrade referred to as GEM Endcap (GE1/1), consists of adding two back-to-back Triple-GEM detectors in front of the existing Cathode Strip Chambers (CSC) in the innermost ring of the endcap muon spectrometer. Before the full installation of 144 detectors in 2019–2020, CMS will first install ten single chamber prototypes during the early 2017. This pre-installation is referred as the slice test. These ten detectors will be read-out by VFAT2 chips [1]. On-detector there is also a FPGA mezzanine card which sends VFAT2 data optically to the μTCA back-end electronics. The correct and safe operation of the GEM system requires a sophisticated and powerful online Detector Control System, able to monitor and control many heterogeneous hardware devices. The DCS system developed for the slice test has been tested with CMS Triple-GEM detectors in the laboratory. In this paper we describe the newly developed DCS system and present the first results obtained in the GEM assembly and quality assurance laboratory.

We report on the construction and first operating experience of a novel detector designed to measure with high accuracy the spatial position of charged particle trajectories and of electromagnetic showers from electrons or photons. This position detector was constructed of two layers of 2 mm thick scintillating fibers with a 15° angle between layers. The photon readout used a newly developed multianode photomultiplier. The device was inserted in a prototype electromagnetic calorimeter for the CDF collaboration and studied at a Fermilab test beam facility. The position detector yielded a spatial resolution for electromagnetic showers of 400 μm for 100 GeV electrons.

We report on the results of testing two six-layer 0.6 × 0.6 m2 cathode strip chamber (CSC) prototypes in a muon beam at CERN. The prototypes were designed to simulate sections of the end-cap muon system of the Compact Muon Solenoid (CMS) detector which will be installed at the Large Hadron Collider (LHC). We measured the spatial and time resolutions of each chamber for different gains, different orientations with respect to the beam direction and different strength magnetic fields. The single-layer spatial resolution of a prototype with a strip pitch of 15.88 mm ranged from 78 to 468 μm, depending on whether the particle passed between two cathode strips or through the center of a strip; its six-layer resolution was found to be 44 μm. The single-layer spatial resolution of a prototype with a strip pitch of 6.35 mm ranged from 54 to 66 μm; its six-layer resolution was found to be 23 μm. The efficiency for collecting an anode wire signal from one of six layers within a 20 ns time window appropriate for the LHC was found to be greater than 95% in normal running conditions.

We present a novel application of Fiber Bragg Grating (FBG) sensors in the construction and characterisation of Micro Pattern Gaseous Detector (MPGD), with particular attention to the realisation of the largest triple (Gas electron Multiplier) GEM chambers so far operated, the GE1/1 chambers of the CMS experiment at LHC. The GE1/1 CMS project consists of 144 GEM chambers of about 0.5 m 2 active area each, employing three GEM foils per chamber, to be installed in the forward region of the CMS endcap during the long shutdown of LHC in 2108-2019. The large active area of each GE1/1 chamber consists of GEM foils that are mechanically stretched in order to secure their flatness and the consequent uniform performance of the GE1/1 chamber across its whole active surface. So far FBGs have been used in high energy physics mainly as high precision positioning and re-positioning sensors and as low cost, easy to mount, low space consuming temperature sensors. FBGs are also commonly used for very precise strain measurements in material studies. In this work we present a novel use of FBGs as flatness and mechanical tensioning sensors applied to the wide GEM foils of the GE1/1 chambers. A network of FBG sensors have been used to determine the optimal mechanical tension applied and to characterise the mechanical tension that should be applied to the foils. We discuss the results of the test done on a full-sized GE1/1 final prototype, the studies done to fully characterise the GEM material, how this information was used to define a standard assembly procedure and possible future developments.

A bstract Sphaleron and instanton solutions of the Standard Model provide violation of baryon and lepton numbers and could lead to spectacular events at the LHC or future colliders. Certain models of new physics can also lead to sphaleron-like vacuum transitions. This nonperturbative physics could be relevant to the generation of the matter-antimatter asymmetry of the universe. We have developed BaryoGEN, an event generator that facilitates the exploration of sphaleron-like transitions in proton-proton collisions with minimal assumptions. BaryoGEN outputs standard Les Houches Event files that can be processed by PYTHIA, and the code is publicly available. We also discuss various approaches to experimental searches for such transitions in proton-proton collisions.

For the High Luminosity LHC CMS is planning to install new large size Triple-GEM detectors, equipped with a new readout system in the forward region of its muon system (1.5<|η|<2.2). In this note we report on the status of the project, the main achievements regarding the detectors as well as the electronics and readout system.

A small magnetic flux probe is described. It exhibits a magnetometer-like response over the frequency range of 20 Hz to 200 kHz with an effective antenna height of 1 m. The E-field equivalent noise floor of this device is approximately 10 mu V/m square root Hz at 10 kHz. A switchable high-pass filter is included to allow the measurement of very low frequency fields in the presence of strong 50-400-Hz power-line fields. The distinguishing features of this probe are its method of winding and shielding. Both the theory of operation and practical construction are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Motivated by recent evidence for the decay $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\nu}$, a search for this decay has been carried out in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation at $\sqrt{s}=3.77$ GeV. No evidence for the decay is found; an upper limit of 2.5% at the 90% confidence level is set on the branching fraction $B(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\nu})$.

A search for the decay of the charmed meson ${D}^{0}\ensuremath{\rightarrow}{\overline{K}}^{0}{e}^{+}{e}^{\ensuremath{-}}$ is presented, based on data collected at the $\ensuremath{\psi}(3770)$ resonance with the Mark III detector at the SLAC storage ring SPEAR. No evidence for this process is found, resulting in an upper limit on the decay branching ratio of 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ at the 90% confidence level.

Presented are the main design features and performance results of the Cathode Strip Chambers for the CMS Endcap Muon system. Although the strips are unusually wide (up to 16mm) for the cathode-to-anode wire distance of 5mm, the six-plane structure of these chambers yields a spatial resolution of about 80μm, essentially uniform and independent of the strip width. In addition, the net spatial resolution of about one-tenth of the strip width at the hardware trigger level (300ns) is obtained using a simple network of comparators. Time resolution achieved at the trigger level is ∼4ns (rms) that allows unambiguous tagging of bunch crossings which occur every 25ns. Aging test results, including those obtained with a recirculating gas system, are discussed; only minor aging affects were observed. The aging studies were performed with large-scale chambers; 700m of wire were irradiated for a dose up to 0.4C/cm of the total accumulated charge.

The Compact Muon Solenoid (CMS) experiment at the LHC is planning an upgrade of its muon detection system aiming to extend the muon detection capabilities in the forward region with the installation of new muon stations based on Gas Electron Multiplier (GEM) and Resistive Plate Chambers (RPC) technologies during the so-called Phase-2 upgrade scenario. With the imminent increase on luminosity to 5 × 1034cm-2s-1 and center of mass collision energy of 14 TeV an unprecedented and hostile radiation environment will be created, the most affected detectors will be the ones located in the forward region where the intense flux of neutrons and photons could potentially degrade the detector performance. Using FLUKA simulation the expected radiation environment is estimated for the regions of interest, possible shielding scenarios are proposed and the effect on the detector performance is discussed.

Gas Electron Multiplier (GEM) technology is being considered for the forward muon upgrade of the CMS experiment in Phase 2 of the CERN LHC. Its first implementation is planned for the GE1/1 system in the $1.5 < \mid\eta\mid < 2.2$ region of the muon endcap mainly to control muon level-1 trigger rates after the second long LHC shutdown. A GE1/1 triple-GEM detector is read out by 3,072 radial strips with 455 $\mu$rad pitch arranged in eight $\eta$-sectors. We assembled a full-size GE1/1 prototype of 1m length at Florida Tech and tested it in 20-120 GeV hadron beams at Fermilab using Ar/CO$_{2}$ 70:30 and the RD51 scalable readout system. Four small GEM detectors with 2-D readout and an average measured azimuthal resolution of 36 $\mu$rad provided precise reference tracks. Construction of this largest GEM detector built to-date is described. Strip cluster parameters, detection efficiency, and spatial resolution are studied with position and high voltage scans. The plateau detection efficiency is [97.1 $\pm$ 0.2 (stat)]\%. The azimuthal resolution is found to be [123.5 $\pm$ 1.6 (stat)] $\mu$rad when operating in the center of the efficiency plateau and using full pulse height information. The resolution can be slightly improved by $\sim$ 10 $\mu$rad when correcting for the bias due to discrete readout strips. The CMS upgrade design calls for readout electronics with binary hit output. When strip clusters are formed correspondingly without charge-weighting and with fixed hit thresholds, a position resolution of [136.8 $\pm$ 2.5 stat] $\mu$rad is measured, consistent with the expected resolution of strip-pitch/$\sqrt{12}$ = 131.3 $\mu$rad. Other $\eta$-sectors of the detector show similar response and performance.

We have searched for the inclusive reaction ${\mathit{D}}_{\mathit{s}}^{\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\rightarrow}${\mathit{e}}^{\ifmmode\pm\else\textpm\fi{}}$X using a tagged sample of 68 ${\mathit{D}}_{\mathit{s}}^{\ifmmode\pm\else\textpm\fi{}}$ produced in the reaction ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{D}}_{\mathit{s}}^{\ifmmode\pm\else\textpm\fi{}}$${\mathit{D}}_{\mathit{s}}^{\mathrm{*}\ensuremath{\mp}}$ at a center-of-mass energy of 4.14 GeV. The tagged sample consists of the decays ${\mathit{D}}_{\mathit{s}}^{+}$\ensuremath{\rightarrow}\ensuremath{\varphi}${\mathrm{\ensuremath{\pi}}}^{+}$, ${\mathit{D}}_{\mathit{s}}^{+}$\ensuremath{\rightarrow}K\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}0}$${\mathit{K}}^{+}$, and ${\mathit{D}}_{\mathit{s}}^{+}$\ensuremath{\rightarrow}K\ifmmode\bar\else\textasciimacron\fi{} $^{0}$${\mathit{K}}^{+}$. We determine B(${\mathit{D}}_{\mathit{s}}^{+}$\ensuremath{\rightarrow}${\mathit{e}}^{+}$X)=0.${05}_{\mathrm{\ensuremath{-}}0.05}^{+0.05}$\ifmmode\pm\else\textpm\fi{}0.02, which corresponds to a limit of B(${\mathit{D}}_{\mathit{s}}^{+}$\ensuremath{\rightarrow}${\mathit{e}}^{+}$X)0.20, at the 90% confidence level.

We report on results of tests of the 16-channel Hamamatsu R5900-M16 photomultiplier tube for gain uniformity and stability, pixel uniformity, linearity, cross-talk, and quantum efficiency. These parameters are essential to our application; i.e., the read out of signals which are generated by the passage of ionizing particles through the scintillating strips of an electromagnetic shower maximum detector and which are carried to the photodetector by optical fibers. In all respects the R5900-M16 tube performance is found to be superior to that of earlier generations of multianode photomultiplier tubes.

Presented are the main design features of the large cathode strip chambers (CSCs) for the CMS endcap muon system as well as the performance results obtained with the first large-scale prototype. The 3.4×1.2 m2 six-plane prototype has been reliably operated over one year and the cosmic-ray tests showed that it was capable of detecting muons with ∼80 μm spatial and ∼5 ns time resolutions.

The production, installation, and testing of 468 cathode strip chambers for the endcap muon system of the CMS experiment played a critical role in the preparation of the endcap muon system for the final commissioning. Common testing procedures and sets of standard equipment were used at 5 international assembly centers. The chambers were then thoroughly retested after shipment to CERN. Final testing was performed after chamber installation on the steel disks in the CMS detector assembly building. The structure of the detector quality control procedure is presented along with the results of chamber performance validation tests.