C. Biino

We present the results of a study of muon pairs with invariant masses greater than 4.05 GeV/${c}^{2}$ produced in high-energy pion-nucleon interactions. The production cross section together with the inferred pion and nucleon structure functions are reported and compared with other experiments and with QCD predictions. The transverse-momentum distributions are also presented. Finally, the full angular distribution in cos\ensuremath{\theta} and \ensuremath{\varphi} is given as a function of mass, Feynman x, and transverse momentum. Longitudinal photon polarization is seen in the lower portion of the mass range at high ${x}_{\ensuremath{\pi}}$. This result is compared with a higher-twist model.

A precision measurement of the ratio RK of the rates of kaon leptonic decays K±→e±ν and K±→μ±ν with the full data sample collected by the NA62 experiment at CERN in 2007–2008 is reported. The result, obtained by analysing ∼150000 reconstructed K±→e±ν candidates with 11% background contamination, is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation.

A bstract The NA62 experiment reports the branching ratio measurement $$ \mathrm{BR}\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right)=\left({10.6}_{-3.4}^{+4.0}\left|{}_{\mathrm{stat}}\right.\pm {0.9}_{\mathrm{syst}}\right)\times {10}^{-11} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>BR</mml:mi> <mml:mfenced> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mn>10.6</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mfenced> <mml:msub> <mml:mrow /> <mml:mtext>stat</mml:mtext> </mml:msub> </mml:mfenced> <mml:mo>±</mml:mo> <mml:msub> <mml:mn>0.9</mml:mn> <mml:mtext>syst</mml:mtext> </mml:msub> </mml:mrow> </mml:mfenced> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> </mml:math> at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare K + → $$ {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay, observed with a significance of 3.4 σ . The experiment achieves a single event sensitivity of (0 . 839 ± 0 . 054) × 10 − 11 , corresponding to 10.0 events assuming the Standard Model branching ratio of (8 . 4 ± 1 . 0) × 10 − 11 . This measurement is also used to set limits on BR( K + → π + X ), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample.

The NA62 experiment at CERN reports searches for $K^+\to\mu^+N$ and $K^+\to\mu^+\nu X$ decays, where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set. The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of ${\cal O}(10^{-8})$ of the neutrino mixing parameter $|U_{\mu4}|^2$ for $N$ masses in the range 200-384 MeV/$c^2$ and lifetime exceeding 50 ns. The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for $X$ masses in the range 10-370 MeV/$c^2$ are reported for the first time, ranging from ${\cal O}(10^{-5})$ to ${\cal O}(10^{-7})$. An improved upper limit of $1.0\times 10^{-6}$ is established at 90% CL on the $K^+\to\mu^+\nu\nu\bar\nu$ branching fraction.

We have performed a search for the 1P1 state of charmonium resonantly formed in p¯p annihilations, close to the center of gravity of the 3PJ states. We report results from the study of the J/ψ+π0 and J/ψ+2π final states. We have observed a statistically significant enhancement in the p¯+p→J/ψ+π0 cross section at √s ≃3526.2 MeV. This enhancement has the characteristics of a narrow resonance of mass, total width, and production cross section consistent with what is expected for the 1P1 state. In our search we have found no candidates for the reactions p¯+p→J/ψ+π0+π0 and p¯+p→J/ψ+π++π−.Received 10 July 1992DOI:https://doi.org/10.1103/PhysRevLett.69.2337©1992 American Physical Society

Cross sections for the reaction pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ have been measured at s=8.9,12.4, and 13.0 ${\mathrm{GeV}}^{2}$. The cross sections have been analyzed to obtain the proton electromagnetic form factors in the timelike region. We find that ${\mathit{G}}_{\mathit{M}}$(${\mathit{q}}^{2}$)\ensuremath{\propto}${\mathit{q}}^{\mathrm{\ensuremath{-}}4}$${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}^{2}$(${\mathit{q}}^{2}$) for ${\mathit{q}}^{2}$\ensuremath{\ge}5 (GeV/c${)}^{2}$.

The NA62 experiment at the CERN SPS reports the first search for $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ using the decay-in-flight technique, based on a sample of $1.21\times10^{11}$ $K^+$ decays collected in 2016. The single event sensitivity is $3.15\times 10^{-10}$, corresponding to 0.267 Standard Model events. One signal candidate is observed while the expected background is 0.152 events. This leads to an upper limit of $14 \times 10^{-10}$ on the $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ branching ratio at 95\% CL.

A search for heavy neutral lepton (N) production in K+→e+N decays using the data sample collected by the NA62 experiment at CERN in 2017–2018 is reported. Upper limits of the extended neutrino mixing matrix element |Ue4|2 are established at the level of 10−9 over most of the accessible heavy neutral lepton mass range 144–462 MeV/c2, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The |Ue4|2 range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c2.

The results of a search for $\pi^0$ decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of $4.12\times10^8$ tagged $\pi^0$ mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60--110 MeV/$c^2$. The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay $\pi^0 \to \gamma \nu \overline{\nu}$, improving the current limit by more than three orders of magnitude.

A sample of 3120 K±→π±μ+μ− decay candidates with (3.3±0.7)% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio was measured to be BR=(9.62±0.25)×10−8. The form factor W(z), where z=(Mμμ/MK)2, was parameterized according to several models. In particular, the slope of the linear form factor W(z)=W0(1+δz) was measured to be δ=3.11±0.57. Upper limits of 2.9×10−2 and 2.3×10−2 on possible charge asymmetry and forward–backward asymmetry were established at 90% CL. An upper limit BR(K±→π∓μ±μ±)<1.1×10−9 was established at 90% CL for the rate of the lepton number violating decay.

The NA62 experiment at CERN reports a search for the lepton number violating decays K+→π−e+e+ and K+→π−μ+μ+ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2×10−10 and 4.2×10−11 are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.

The NA62 experiment at the CERN SPS reports a study of a sample of $4 \times10^{9}$ tagged $\pi^0$ mesons from $K^+ \to \pi^+ \pi^0 (\gamma)$, searching for the decay of the $\pi^0$ to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of $4.4 \times10^{-9}$ is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay $K^+ \to \pi^+ X$, where $X$ is a particle escaping detection with mass in the range 0.110-0.155 GeV$/c^2$ and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming $X$ to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

We report on a study of the χ1(3P1) and χ2(3P2) states of charmonium formed in antiproton-proton annihilations. An energy scan through the resonances, performed with a very narrow momentum-band beam of antiprotons intersecting a hydrogen jet target, enables us to perform very precise measurements of the mass and the total width of the two resonances. From a sample of 513 χ1 and 585 χ2 events we find Mχ1 = (3510.53±0.13) MeV/c2, Mχ2 = (3556.15±0.14) MeV/c2, Γχ1 = (0.88±0.14) MeV and Γχ2 = (1.98±0.18) MeV. From our measurement of the quantity Γ(R → pp) × BR(R → Jψ → e+ e−), using known branching ratios, we obtain Λ(χ1 → pp) = (69±13) eV and Λ(χ2 → pp) = (180±31) eV.

The NA62 experiment at CERN, aimed to measure K+→π+νν¯ branching fraction (O(10−10)), relies on a Neon based RICH detector for π/μ separation, time measurement and level 0 trigger. The experimental requirements for this detector are: a muon contamination in pion samples lower than 5×10−3 in the momentum range 15–35 GeV/c and a time resolution on the charged track better than 100 ps. A prototype of such a detector was built and tested in 2009; it consists of a full length (≈18m) Ne filled vessel equipped with a spherical mirror and 414 PMs on its focal plane, located about 17 m upstream of the mirror. This prototype was tested at CERN SPS on a positive hadron beam, in the required momentum range, to measure the π/μ separation and to confirm the time resolution obtained with a previous prototype; the μ misidentification probability is about 0.7% and the time resolution is better than 100 ps in the whole momentum range.

A study of the dynamics of the rare decay K±→π±γγ has been performed on a sample of 232 decay candidates, with an estimated background of 17.4±1.1 events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 Collaboration at CERN. The combined model-independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2 is BMI(z>0.2)=(0.965±0.063)×10−6, and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is B(Kπγγ)=(1.003±0.056)×10−6. A detailed comparison of the results with the previous measurements is performed.

A bstract A search for the K + → π + X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K + → $$ {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV /c 2 and 154–260 MeV /c 2 , and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR( K + → π + X ), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.

During the latest decade, experiments have been performed at the CERN SPS to investigate the use of high-energy channeled nuclei in bent crystals for extraction, beam splitting and beam bending. An understanding of channeling in a bent crystal with extraction and deflection efficiencies for different energies, crystal types and ions has been developed. Furthermore, the long-standing question of radiation damage has been addressed with encouraging outcome. This makes extrapolations possible for the construction of, e.g., an extraction device for the LHC at CERN, RHIC at Brookhaven or new splitting elements in high-energy beams.We present the main results obtained and discuss existing and future applications of bent crystals in high-energy physics.

We report new measurements for the mass, width, and branching ratios for the $\frac{J}{\ensuremath{\psi}}$ and the ${\ensuremath{\psi}}^{\ensuremath{'}}$. These charmonium states are formed exclusively in $\overline{p}p$ annihilations at the Fermilab Antiproton Accumulator ring, where stochastically cooled antiprotons are brought into collision with the protons of an internal hydrogen gas jet target. The antiproton energy is precisely controlled and measured allowing an accurate measurement of the resonance parameters. From the shape of the excitation curves we find that the widths of $\frac{J}{\ensuremath{\psi}}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$ are $\ensuremath{\Gamma}(\frac{J}{\ensuremath{\psi}})=99\ifmmode\pm\else\textpm\fi{}12\ifmmode\pm\else\textpm\fi{}6$ keV and $\ensuremath{\Gamma}({\ensuremath{\psi}}^{\ensuremath{'}})=306\ifmmode\pm\else\textpm\fi{}36\ifmmode\pm\else\textpm\fi{}16$ keV, and that the mass of the $\frac{J}{\ensuremath{\psi}}$ is 3096.87 \ifmmode\pm\else\textpm\fi{} 0.03 MeV/${\mathit{c}}^{2}$. For the $\frac{J}{\ensuremath{\psi}}$ we obtain $B(\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}\overline{p}p)B(\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})=({1.14}_{\ensuremath{-}0.12}^{+0.16}\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$; for the ${\ensuremath{\psi}}^{\ensuremath{'}}$ we obtain $B({\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\overline{p}p)[B({\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})+B({\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}X})B(\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})]=({1.17}_{\ensuremath{-}0.12}^{+0.14}\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.

The distributions of quarks in the pion and nucleon are extracted from measurements of the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}N\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}X$ at 253 GeV/c in a naive Drell-Yan analysis, as well as QCD-corrected analyses at leading-log and next-to-leading-log order. As ${x}_{\ensuremath{\pi}}\ensuremath{\rightarrow}1$ the pion structure function shows a term that varies as $\frac{1}{{m}_{\ensuremath{\mu}\ensuremath{\mu}}^{4}}$, which we interpret as a higher-twist effect. Additionally, the angular distribution of the ${\ensuremath{\mu}}^{+}$ in the muon-pair rest frame tends towards ${sin}^{2}\ensuremath{\theta}$ as ${x}_{\ensuremath{\pi}}\ensuremath{\rightarrow}1$ and as ${m}_{\ensuremath{\mu}\ensuremath{\mu}}\ensuremath{\rightarrow}0$ in a manner consistent with higher-twist effects. When the strongly mass-dependent higher-twist effects are included as part of the pion structure function, the nucleon structure function agrees well with leading-twist results from deeply inelastic lepton-hadron scattering. A significant advance of the present work is the extension of the analysis to low masses by the subtraction of the $\frac{J}{\ensuremath{\psi}}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$ resonances from the continuum. Our analysis covers the kinematic range $0.4&lt;{x}_{\ensuremath{\pi}}&lt;1.0$ and $0.02&lt;{x}_{N}&lt;0.33$ with $3.0&lt;{m}_{\ensuremath{\mu}\ensuremath{\mu}}&lt;8.55$ GeV/${\mathit{c}}^{2}$. Cross sections for ${\ensuremath{\psi}}^{\ensuremath{'}}$ production are presented in an appendix.

A precision test of lepton flavour universality has been performed by measuring the ratio RK of kaon leptonic decay rates K+ --> e+nu and K+ --> mu+nu in a sample of 59813 reconstructed K+ --> e+nu candidates with (8.71 +- 0.24)% background contamination. The result RK = (2.487 +- 0.013) * 10^{-5} is in agreement with the Standard Model expectation.

The NA48 collaboration is preparing a new experiment at CERN aiming to study CP violation in the K0-K0 system with an accuracy of 2 × 10−4 in the parameter Re(ϵ′/ϵ). Decays in two π0's will be recorded by a quasi-homogeneous liquid krypton calorimeter. A liquid krypton calorimeter has been chosen to combine good energy, position and time resolution with precise charge calibration and long-term stability. The prototype calorimeter incorporating the final design of the electrode read-out structure is presented in this paper. An energy resolution of ≃3.5%√E with a constant term smaller than 0.5% has been obtained. The time resolution was found to be better than 300 ps above 15 GeV.

We present the first high-statistics study of the ηη system over the mass range 1000–3000 MeV/c2. The experiment was performed at the Fermilab Antiproton Accumulator, and the data sample consists of six-photon final states produced in antiproton-proton annihilations at s in the range 2950–3620 MeV. We find evidence for three states with masses 1488 ± 10 MeV/c2, 1748 ± 10 MeV/c2 and 2104 ± 20 MeV/c2 respectively.

The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.

A RICH prototype has been constructed and tested. The detector was cylindrical, 17 m long and 60 cm diameter, filled with neon gas at atmospheric pressure. A spherical mirror with 17 m focal length was used and 96 photomultipliers were placed in the mirror focal plane. The prototype was exposed to a 200GeV/c momentum negative beam derived from the CERN SPS in the 2007 fall. The performances of the detector in terms of Cherenkov angle resolution, number of photoelectrons and time resolution are presented.

A bstract The NA62 experiment reports an investigation of the $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> mode from a sample of K + decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0 . 389 ± 0 . 024) × 10 − 10 , corresponding to 2.2 events assuming the Standard Model branching ratio of (8 . 4 ± 1 . 0) × 10 − 11 . Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1 . 78 × 10 − 10 for the $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of ( $$ {0.48}_{-0.48}^{+0.72} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mn>0.48</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.48</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.72</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) × 10 − 10 , are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.

The NA62 experiment at CERN, designed to study the ultra-rare decay $K^+ \to \pi^+\nu\overline{\nu}$, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to $\mu^+\mu^-$ pairs is reported, based on a sample of $1.4 \times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV$/c^2$.

A bstract The NA62 experiment at CERN, designed to study the ultra-rare decay K + → π + $$ \nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ + μ − pairs is reported, based on a sample of 1 . 4 × 10 17 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV /c 2 .

The first results from an experiment to deflect a beam of fully stripped, ultrarelativistic ${\mathrm{Pb}}^{82+}$ ions of $400\mathrm{GeV}/c$ per unit of charge, equivalent to $33\mathrm{TeV}/c$, by means of a bent crystal are reported. Deflection efficiencies are as high as 14%, in agreement with theoretical estimates. In a second experiment a bent crystal was used to extract $270\mathrm{GeV}/c$-per-charge ${\mathrm{Pb}}^{82+}$ $(22\mathrm{TeV}/c)$ ions from a coasting beam in the CERN-SPS, and a high extraction efficiency of up to 10% was found. These represent the first measurements to demonstrate applications of bent crystals in high energy heavy ion beams.

Experimental results for the bremsstrahlung energy loss of 149, 207, and 287 GeV electrons in thin Ir, Ta, and Cu targets are presented. For each target and energy, a comparison between simulated values based on the Landau-Pomeranchuk-Migdal (LPM) suppression of incoherent bremsstrahlung is shown. For the electron energies investigated, the LPM effect enters the quantum regime where the recoil imposed on the electron by the emitted photon becomes important. Good agreement between simulations based on Migdal's theory and data from the experiment is found, indicating that the LPM suppression is well understood also in the quantum regime. Results from a comparison between simulations with the ``threshold'' energy ${E}_{\mathrm{LPM}}$ as a free parameter and the data are shown. This analysis reproduces the expected trend as a function of nominal radiation length, but yields values that tend to be low compared to Migdal's theory.

As a by-product to the study of muon pairs produced by 255-Ge V/c pions, data from Fermilab yield upper limits on the decay ${D}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and on ${D}^{0}\ensuremath{-}{\overline{D}}^{0}$ mixing. An unrestricted sample of 122 630 unlike-sign muon pairs allows a 90%-C.L. (confidence level) upper limit of 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ to be placed on the branching ratio of the charm-changing neutral-current decay ${D}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. From a sample of 3973 like-sign muon pairs, the ratio $r=\frac{\ensuremath{\Gamma}({\overline{D}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}X)}{\ensuremath{\Gamma}({\overline{D}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}X)}$ is determined to be $r&lt;5.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ at 90% C.L.

The production of ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ pairs with large longitudinal momentum has been studied in ${\ensuremath{\pi}}^{\ensuremath{-}}N$ collisions. The data confirm an earlier result that most of the pair production takes place via longitudinally polarized virtual photons as ${x}_{\mathrm{F}}\ensuremath{\rightarrow}1$. The transverse-momentum distribution of the muon pairs shows a marked narrowing in the same limit. The distribution of valence quarks in the pion is extracted, and indicates a nonzero probability of having a single quark carry all available longitudinal momentum. These results are compared with a QCD model of pion structure which includes the effect of higher-twist corrections.

The spin alignment of 2.2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ J/\ensuremath{\psi} particles produced in 252-GeV \ensuremath{\pi}N interactions has been measured via their decay to ${\ensuremath{\mu}}^{+}$${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$ in an experiment at Fermilab. Whereas J/\ensuremath{\psi}'s are produced unpolarized over most of the kinematic range, they are found to become longitudinally polarized as ${x}_{F}$\ensuremath{\rightarrow}1.

The response of the CMS barrel calorimeter (electromagnetic plus hadronic) to hadrons, electrons and muons over a wide momentum range from 2 to 350 GeV/c has been measured. To our knowledge, this is the widest range of momenta in which any calorimeter system has been studied. These tests, carried out at the H2 beam-line at CERN, provide a wealth of information, especially at low energies. The analysis of the differences in calorimeter response to charged pions, kaons, protons and antiprotons and a detailed discussion of the underlying phenomena are presented. We also show techniques that apply corrections to the signals from the considerably different electromagnetic (EB) and hadronic (HB) barrel calorimeters in reconstructing the energies of hadrons. Above 5 GeV/c, these corrections improve the energy resolution of the combined system where the stochastic term equals 84.7±1.6% and the constant term is 7.4±0.8%. The corrected mean response remains constant within 1.3% rms.

Searches for the lepton number violating K þ → π -μ þ e þ decay and the lepton flavor violatingand π 0 → μ -e þ decays are reported using data collected by the NA62 experiment at CERN in 2017-2018.No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level:and Bðπ 0 → μ -e þ Þ < 3.2 × 10 -10 .These results improve by 1 order of magnitude over previous results for these decay modes.

Using a silicon vertex detector, we measure the charged particle pseudorapidity distribution over the range 1.5 to 5.5 using data collected from PbarP collisions at root s = 630 GeV. With a data sample of 3 million events, we deduce a result with an overall normalization uncertainty of 5%, and typical bin to bin errors of a few percent. We compare our result to the measurement of UA5, and the distribution generated by the Lund Monte Carlo with default settings. This is only the second measurement at this level of precision, and only the second measurement for pseudorapidity greater than 3.

The central calorimeter in Fermilab experiment E760++ has been designed to measure the topology and energies of electrons and photons in the decay of charmonium formed in pp annihilation. The calorimeter is composed of 1280 lead-glass Cherenkov counters read out with photomultiplier tubes. This paper discusses design criteria for the calorimeter and describes how these criteria were met. Data from tests in low energy (10–84 MeV) and medium energy (1–4 GeV) beams are presented showing a spatial resolution of 9 mm, an energy resolution of (3.0 ± 0.3)%√E[GeV] + (1.5 ± 0.5)%, and an effective energy threshold below 10 MeV.

Experiment R704, the last to be performed at the CERN-ISR, has successfully applied a new method to study (cc) states formed directly in antiproton-proton annihilations. The novelty of the method rests on the capability to build a highly performing annihilation source by letting a cold

Performance tests of some aspects of the CMS ECAL were carried out on modules of the "barrel" sub-system in 2002 and 2003. A brief test with high energy electron beams was made in late 2003 to validate prototypes of the new Very Front End electronics. The final versions of the monitoring and cooling systems, and of the high and low voltage regulation were used in these tests. The results are consistent with the performance targets including those for noise and overall energy resolution, required to fulfil the physics programme of CMS at the LHC.

Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.

The GigaTracKer (GTK) is the beam spectrometer of the CERN NA62 experiment. The detector features challenging design specifications, in particular a peak particle flux reaching up to 2.0 MHz/mm$^2$, a single hit time resolution smaller than 200 ps and, a material budget of 0.5% X$_0$ per tracking plane. To fulfill these specifications, novel technologies were especially employed in the domain of silicon hybrid time-stamping pixel technology and micro-channel cooling. This article describes the detector design and reports on the achieved performance.

The first measurement of the branching ratio of the ultra-rare $K^+ \to \pi^+\nu\bar\nu$ decay and the searches for production of feebly interacting particles predicted by dark scalar models from the NA62 experiment at CERN are presented. The results of a search for in-flight decays of dark photon to $\ell^+\ell^-$ pairs with data collected in beam-dump mode in 2021 are also reported.

The GigaTracKer is a hybrid silicon pixel detector designed for the fixed-target experiment NA62 at the CERN SPS aiming to measure the branching ratio of the very rare kaon decay $K^+ \rightarrow \pi^+\nu \bar{\nu}$ with 10\% precision. The detector has to provide measurements of momentum, direction and time of beam particles arriving at a rate of 750 MHz. The tracking system consists of four stations installed in vacuum ($\sim10^{-6}$ mbar), $60.8 \times 27\ \text{mm}^2$ each, with a total material budget of less than 2X$_0$. Each station is cooled with a microchannel cooling plate used for the first time in a high energy physics experiment. The beam particles are tracked in 4 dimensions by means of time-stamping pixels ($300\times300\ \mu \text{m}^{2}$) with the single hit time resolution reaching 115 ps. This performance has to be maintained despite the beam irradiation amounting to a yearly fluence of $4.5 \times 10^{14}\ 1MeV\ n_{\text{eq}}/200\ \text{days}$. The detector has been fully operational since 2016. We describe the GigaTracKer design and performance in the 2016-2022 years of NA62 data taking.

A bstract The NA48/2 experiment at CERN reports the first observation of the K ± → π 0 π 0 μ ± ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV 2 / c 4 is measured to be (0.65 ± 0.03) × 10 − 6 . The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10 − 6 , in agreement with chiral perturbation theory predictions.

Abstract The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023.

Results from five distinct bending experiments performed recently in the H8 beam at CERN are presented. Firstly, deflection of a positive pion beam at 200 GeV/c is compared to the “standard” 450-GeV/c proton beam for a bending angle of 3.1 mrad along the (111) plane in a 50 mm silicon crystal. Second, deflection of negative pions at 200 GeV/c is investigated for the same crystal, for incidence along the (111) plane as well as the 〈110〉 axis. Small deflection effects are seen, but no negative particles are bent through the full bending angle of the crystal. Third, the first results from beam deflection at high energy using a germanium crystal are shown. Slightly higher deflection efficiencies than for silicon are seen for large bending angles, but significantly smaller than expected for such a crystal with higher atomic number. Fourth, deflection efficiencies using a strongly irradiated silicon crystal have been measured for the first time, and a small reduction in efficiency is seen in the irradiated region. Finally, deflection of positive particles using axial alignment of a bent silicon crystal has been investigated at 450 GeV/c. Qualitatively similar behaviour as in previous experiments at 12 GeV/c is seen; the beam splits into several beams corresponding to the different planes, and even weak planes are observed.

A new measurement has been made of the rate of pair-production in a 3.2 mm thick tungsten crystal, exposed to photons with energies in the range 10 to 150 GeV, for angles of incidence up to 10 mrad from the crystal axis. A strong enhancement of the pair-production rate is observed when the beam is aligned along the 〈100〉 crystal axis, as compared to a random orientation. This effect can be exploited in the NA48 CP-violation experiment by using a thin crystal rather than an amorphous material to convert photons, thus minimising the scattering of kaons in the converter.

The E760 Collaboration has studied the reaction p¯p→χ2→γγ using a hydrogen gas jet target in the Fermilab antiproton acumulator ring. The following values are obtained for the branching ratio and partial width to two photons; B(χ2→γγ)=(1.60±0.45)×10−4 and Γ(χ2→γγ)=321±95 eV.Received 2 October 1992DOI:https://doi.org/10.1103/PhysRevLett.70.2988©1993 American Physical Society

Experimental results for the radiative energy loss of 149, 207, and 287 GeV electrons in a thin Ir target are presented. From the data we conclude that at high energies the radiation length increases in accordance with the Landau-Pomeranchuk-Migdal (LPM) theory and thus electrons become more penetrating the higher the energy. The increase of the radiation length as a result of the LPM effect has a significant impact on the behavior of high-energy electromagnetic showers.

Fermilab experiment E-760 studies the resonant formation of charmonium states in proton-antiproton interactions using a hydrogen gas-jet target in the Antiproton Accumulator ring at Fermilab. Precision measurements of the mass and width of the charmonium states χc1,χc2, a direct measurement of the ψ’ width, and a new precision measurement of the J/ψ mass are presented.Received 3 February 1992DOI:https://doi.org/10.1103/PhysRevLett.68.1468©1992 American Physical Society

The E760 Collaboration performed an experiment in the Antiproton Accumulator at Fermilab to study the two photon decay of the ηc(1 1S0) charmonium state formed in p¯p annihilations. This resulted in a new measurement of the mass Mηc=2988.3+3.3−3.1 MeV/c2 and of the product B(ηc→p¯p)×Γ(ηc→γγ) =(8.1+2.9−2.0) eV. We performed a search for the process p¯p→η′c(2 1S0)→γγ over a limited range of center-of-mass energies. Since no signal was observed, we derived upper limits on the product of branching ratios B(η′c→p¯p)×B(η′c→γγ) in the center-of-mass energy range 3584≤ √s ≤3624 MeV. We observed no signal for the nonresonant process p¯+p→γ+γ and obtain upper limits.Received 20 April 1995DOI:https://doi.org/10.1103/PhysRevD.52.4839©1995 American Physical Society

We report on a study of the angular distribution in the reaction ¯pp→χc2→Jψγ→e+e−γ. Using a sample of 1904 events, we find that the contribution of helicity zero in the formation process is B20<0.22 (90% C.L.), and that the normalized quadrupole amplitude in the radiative decay is a2=−0.14±0.06. The normalized radiative decay octupole amplitude a3 is found to be consistent with zero.Received 5 March 1993DOI:https://doi.org/10.1103/PhysRevD.48.3037©1993 American Physical Society

The ratio of sea to valence quarks for nucleons in tungsten has been measured for the fractional momentum range 0.04${x}_{N}$0.36. The determination is based on the relative production rate of muon pairs by ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ beams on a tungsten target. The results provide the most accurate determination to date of this ratio in the region ${x}_{N}$0.1 and ${Q}^{2}$&gt;20 ${\mathrm{GeV}}^{2}$, and are in good agreement with earlier measurements.

From 56 days of data taking in 2002, the NA48/1 experiment observed 6316 Ξ0→Σ+e−ν¯e candidates (with the subsequent Σ+→pπ0 decay) and 555 Ξ0¯→Σ+¯e+νe candidates with background contamination of 215±44 and 136±8 events, respectively. From these samples, the branching ratios BR(Ξ0→Σ+e−ν¯e)=(2.51±0.03stat±0.09syst)×10−4 and BR(Ξ0¯→Σ+¯e+νe)=(2.55±0.14stat±0.10syst)×10−4 were measured allowing the determination of the CKM matrix element |Vus|=0.209−0.028+0.023. Using the Particle Data Group average for |Vus| obtained in semileptonic kaon decays, we measured the ratio g1/f1=1.20±0.05 of the axial-vector to vector form factors.

Ensuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered.

The effects of space charge due to slowly drifting ions can be relevant for detectors operated at high intensity, or for relatively low values of the bias voltage. Accurate measurements have been obtained with the liquid krypton calorimeter of the NA48 experiment, from data collected in 1997. The build-up of space charge takes place during the first part of the beam extraction burst, and causes a dependence of the response on the transverse coordinate of the axis of electromagnetic showers, and a small reduction of average amplitude. The effects are well reproduced by a computation, where the only free parameter is the value of the ion mobility. The model can be applied a wide range of operating conditions, and generalized to detectors with different geometry and active medium.

The LHCb Vertex Locator (VELO) is used to reconstruct beam-gas interaction vertices which allows one to obtain precise profiles of the LHC beams.In LHCb, this information is combined with the profile of the reconstructed beam-beam collisions and with the LHC beam currents to perform precise measurements of the luminosity.This beam-gas imaging (BGI) method also allows one to study the transverse beam shapes, beam positions and angles in real time.Therefore, a demonstrator beam-gas vertex detector (BGV) based on scintillating fibre modules has been built and installed in LHC Ring 2 at point 4.

The muon collider represents one of the most promising solutions for a future machine exploring the high energy frontier, but several challenges due to the 2.2 $\mu$sec muon lifetime at rest have to be carefully considered. The LEMMA project is investigating the possibility of producing low emittance muon/antimuon pairs from the e$^+$e$^-$ annihilation process at threshold energy, resulting in small transverse emittance beams without any additional beam cooling. However most of the measurements available are performed at higher $\sqrt{s}$ values. It is therefore necessary to measure muons production in positron annihilation at threshold energy and compare the experimental results with the predictions in this specific energy regime. Apart from being a topic of physical interest by itself, these near to threshold measurements can have a sizeable impact on the estimation of the ultimate luminosity achievable in a muon collider with the LEMMA injection scheme.

Abstract Large apecture forward spectrometers with planar geometry perpendicular to the beam line are the natural detectors to accomodate the expected forward peaking of Beauty particle production at high energy hadron colliders. We have designed, built and tested a prototype planar silicon strip vertex detector for triggering such a spectrometer system. The test system consisted of 43 000 channels, configured in six planes, each with four quadrants, perpendicular to the beam line and installed inside the SPS-collider vacuum pipe at the center of an interaction region. Events recorded with the rf shield of the silicon system 1.5 mm from the circulating beams show negligible event-unrelated background.

Abstract A tracking detector composed of aluminized mylar drift tubes is under development for the Fermilab experiment 760. A prototype chamber has been constructed. Results on the longitudinal coordinate determined by charge division are given. Spatial resolution values below 2 mm (rms) were found, corresponding to

The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 1013 and 1.3× 1014 cm−2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb−1 and 3000 fb−1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.

This paper reports on the charged pion production yields measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction. An experimental accuracy ranging from 5 to 10%, depending on the beam momentum, has been achieved, limited mainly by the knowledge of the beam acceptance. These results will be relevant in the calculation of neutrino fluxes in present and future neutrino beams.

We present measurements of the 2π0 mass spectrum in proton—antiproton annihilations. The f2 (1520) resonance is strongly produced in the 3π0 channel. Its production along with an η is observed, but strongly suppressed. Other features are seen in the data, including the f2 (1270) and structures at 2000 MeV/c2 and above.

This paper reports on the charged K/π production ratios and on the shape of the pT distributions of π fluxes measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction and with pT values up to 600 MeV/c. An experimental accuracy of about 3% has been achieved. These results will reduce the uncertainty on the estimation of the νe component of neutrino beams.

We have observed exclusive decays of the ψ′ in an experiment where the ψ′ is formed in antiproton-proton annihilations. We report the branching ratios B(ψ′→e+e−)=(8.3±0.5stat±0.7syst)×10−3, B(ψ′→J/ψπ+π−)=0.283±0.021stat±0.020syst, B(ψ′→J/ψπ0π0)=0.184±0.019stat±0.013syst, B(ψ′→J/ψη)=0.032±0.010stat±0.002syst. Received 3 September 1996DOI:https://doi.org/10.1103/PhysRevD.55.1153©1997 American Physical Society

We present experimental results giving evidence for the strong reduction—a factor of more than 20—of nuclear-charge changing interactions for 18 TeV In49+ ions channeled through a silicon crystal bent to 7.5, 11.9 and 19.8 mrad. A very small fraction of the deflected ions suffer electromagnetic or nuclear interactions leading to proton loss while traversing the 60 mm long crystal, even though its thickness corresponds to about 0.13 nuclear interaction lengths for an amorphous material. By considering the deflected ions only, we show experimentally that the nuclear-charge pickup reaction believed to be induced by virtual photons is a short-range phenomenon.

The decay asymmetries of the weak radiative hyperon decays Ξ0→Λγ and Ξ0→Σ0γ have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52 000 Ξ0→Λγ and 15 000 Ξ0→Σ0γ decays, we obtain for the decay asymmetries αΞ0→Λγ=−0.704±0.019stat±0.064syst and αΞ0→Σ0γ=−0.729±0.030stat±0.076syst, respectively. These results are in good agreement with previous experiments, but more precise.

Differential cross sections for pp elastic scattering have been measured for very small momentum transfers at six different incident antiproton momenta in the range 3.7 to 6.2 GeV/c by the detection of recoil protons at scattering angles close to 90°. Forward scattering parameters σT, b, and ϱ have been determined. For the ϱ-parameter, up to an order of magnitude higher level of precision has been achieved compared to that in earlier experiments. It is found that existing dispersion theory predictions are in disagreement with our results for the ϱ-parameter.

Experimental results on high-energy beam deflection by means of a bent germanium crystal are presented. Record deflection efficiencies of 60% have been found for 450 GeV/c protons at small angles. The results obtained with 200 and 450 GeV/c positively charged particles are well described by a classical model, giving confidence in predictions for other crystals and different beam momenta.

We have performed an experiment in the Antiproton Accumulator at Fermilab to study two-body neutral final states formed in ¯pp annihilations. Differential cross sections are determined in the center-of-mass energy range 2.911<√s<3.686 GeV for the final states π0π0, ηπ0, ηη, π0γ, and γγ. The energy dependence of differential cross sections at 90° in the center of mass is studied to test the predictions of phenomenological QCD scaling hypotheses which predict power-law dependence.Received 30 December 1996DOI:https://doi.org/10.1103/PhysRevD.56.2509©1997 American Physical Society

Abstract Experimental results for pair production by 20–150 GeV photons in a Ge crystal cooled to 100 K are presented. The results include total and differential enhancements for incidence of the photons along the (1 1 0) plane with angles 0–4.5 mrad to the 〈1 1 0〉 axis. For the first time, a comparison can be made with theoretical results which for incidence along the plane predict pronounced structural changes of a resonance type in the pair production yield as a function of angle to the axis. These changes originate from the coherent interaction with the strong field of the atomic strings in the crystal. Furthermore, results for pair production by 5–55 GeV photons in W and Ir crystals at temperatures between 100 and 300 K are presented. These results are for total enhancements with photons incident along the strongest axes in these materials, i.e. the 〈1 1 1〉 axis in W and the 〈1 1 0〉 axis in Ir. A clear disagreement with theoretical curves calls for improved calculations.

The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20 -170 GeV.The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences.This is significant as the theoretical description of CB and CPP is an area of active debate and development.With the approach used in this paper, both the measured cross sections and polarization observables are predicted very well.This indicates a proper understanding of CB and CPP up to energies of 170 GeV.Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements.New technologies for high-energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment.Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal.Our measurements and our calculations indicate low photon polarizations for the high-energy SOS photons.

The NA62 experiment will begin taking data in 2015. Its primary purpose is a 10% measurement of the branching ratio of the ultrarare kaon decay $K^+ \to \pi^+ \nu \bar{ \nu }$, using the decay in flight of kaons in an unseparated beam with momentum 75 GeV/c.The detector and analysis technique are described here.

Presented are experimental results for the difference in pair production probability (the asymmetry) for 5–150 GeV photons polarized parallel and perpendicular to a (110) plane in a 1.5 mm thick diamond 〈100〉 crystal. The photons are produced by interaction of 150 GeV electrons with an aligned diamond 〈100〉 crystal of 0.5 mm thickness. A significant asymmetry is found over the whole energy range, which corresponds to a high degree of linear polarization of the photons as well as a difference in the refractive index. This proof-of-principle result gives the possibility of producing high energy photons with circular polarization by use of a crystal. This might open for several opportunities in high energy physics like for instance the investigation of the contribution of the gluons to the spin of the nucleon.

A proportional chamber made with aluminized mylar drift tubes is described. The design is optimized for lightness and good performance in drift time and charge division on resistive sense wires. The design makes it possible to minimize the effect of failures, since a broken wire does not prevent the rest of the chamber from operation, and allows a very low weight. The use of resistive wire, not common to other detectors of this kind, makes it possible to measure the longitudinal coordinate by comparing the charges collected at the two anode ends. The design of the chamber is described, its readout characteristics are examined, and preliminary results are reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The CERN-NA-59 experiment examined a wide range of electromagnetic processes for multi-GeV electrons and photons interacting with oriented single crystals. The various types of crystals and their orientations were used for producing photon beams and for converting and measuring their polarisation. The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised photon beams. A new crystal polarimetry technique was established for measuring the linear polarisation of the photon beam. The polarimeter is based on the dependence of the coherent pair production (CPP) cross section in oriented single crystals on the direction of the photon polarisation with respect to the crystal plane. Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set of synthetic Diamond crystals were used as analyzers of the linear polarisation. A birefringence phenomenon, the conversion of the linear polarisation of the photon beam into circular polarisation, was observed. This was achieved by letting the linearly polarised photon beam pass through a 10 cm thick Silicon single crystal that acted as a “quarter wave plate” (QWP) as suggested by Cabibbo et al.

The Electromagnetic Calorimeter (ECAL) of the Compact Muon Solenoid (CMS) experiment at the LHC is a hermetic, fine grained, homogeneous calorimeter, containing 75,848 lead tungstate scintillating crystals. We highlight the key role of the ECAL in the discovery and elucidation of the Standard Model Higgs boson during LHC Run I. We discuss, with reference to specific examples from LHC Run I, the challenges of operating a crystal calorimeter at a hadron collider. Particular successes, chiefly in terms of achieving and maintaining the required detector energy resolution in the harsh radiation environment of the LHC, are described. The prospects for LHC Run II (starting in 2015) are discussed, building upon the experience gained from Run I. The high luminosity upgrade of the LHC (HL-LHC) is expected to be operational from about 2025 to 2035 and will provide instantaneous and integrated luminosities of around 5 × 1034/cm2/s and 3000/fb respectively. We outline the challenges that ECAL will face and motivate the evolution of the detector that is thought to be necessary to maintain its performance throughout LHC and High-Luminosity LHC operation.

A prototype electromagnetic calorimeter containing 180 litres of liquid krypton has been tested in electron and muon beams at the CERN SPS. The main features of this detector are its active shower medium, a granularity of 2 cm with tower readout, and the use of the initial current readout technique with an effective shaping time of about 60 ns. An energy resolution for electrons of 4.1%√E[GeV] with a constant term of 0.4% and a noise contribution of 50 MeV has been achieved. The calorimeter has a spatial resolution of 4.5 mm√E[GeV] with a constant term of 0.3 mm and a time resolution of about 0.5 ns for energies larger than 10 GeV.

Abstract A threshold gas Cherenkov counter is used in Fermilab Experiment 760 to tag electrons in the detection of charmonium states. Mechanical structures and mirrors were built with carbon-fiber-epoxy composites, resulting in a light weight detector covering 2π in azimuthal angle. The counter is operated at atmospheric pressure with different gases, CO 2 and Freon 13, respectively in the two cells at small and large polar angles, to maximize pion rejection. Design considerations, construction details, and performance of the counter are described.

We report the first observation of the (radiative) decay $\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\gamma}$. Our data are from an experiment in which $\frac{J}{\ensuremath{\psi}}$ is formed in antiproton-proton annihilations. The observed rate is consistent with a QED calculation based on final state radiation. Our measurement gives a branching ratio for this mode of (8.8\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ for $\ensuremath{\gamma}$ energy&gt;100 MeV.

The weak radiative decay Ξ0→Λe+e− has been detected for the first time. We find 412 candidates in the signal region, with an estimated background of 15±5 events. We determine the branching fraction B(Ξ0→Λe+e−)=[7.6±0.4(stat)±0.4(syst)±0.2(norm)]×10−6, consistent with an internal bremsstrahlung process, and the decay asymmetry parameter αΞΛee=−0.8±0.2, consistent with that of Ξ0→Λγ. The charge conjugate reaction Ξ0¯→Λ¯e+e− has also been observed.

We compare experimental results and computer simulations on the reduction of inelastic interactions for 33 TeV Pb82+ ions channeled in a bent silicon crystal. The comparison shows that a very small fraction of the initially channeled ions suffer nuclear interactions while traversing the 60 mm long crystal under perfect alignment, even though its thickness would correspond to about 1.2 nuclear interaction lengths for an amorphous material. This result indicates that a bent crystal approach to extraction of high energy, fully stripped ions from e.g. RHIC or LHC might be feasible.

The distribution of the energy released in a silicon detector placed on the downstream side of thick germanium single crystals bombarded by 20–180 GeV gamma rays along directions close to the 〈110〉 axis or along a random direction has been investigated. A large enhancement of the shower for axial incidence of the gamma rays has been found. The response of the system composed of a germanium crystal and a silicon detector to single gamma rays as a function of their energy has been deduced and compared with existing Monte Carlo simulations.

Abstract We have built a prototype 40 cm long atmospheric pressure threshold Cherenkov counter and tested it with Freon 13 at STP. With 1–4 Gev/ c electrons we measure an average number of 6 photoelectrons/incident particle. Below π threshold the π rejection is measured to be 4 × 10 −3 , with a corresponding electron efficiency of 0.96.

NA62, an experiment at the CERN SPS to measure the branching ratio for the decay K+ -> pi+ nu nu-bar with ~10% precision, will observe ~10^13 K+ decays in its fiducial volume, and will thus also be able to carry out a rich program to search for forbidden K+ and pi0 decays, including in particular K+ decays that violate the conservation of lepton flavor and/or number. NA62's potential performance in searches for a number of forbidden K+ and pi0 decays is discussed, with initial sensitivity estimates.

Na59 Experiment at CERN-SPS aims for obtaining circularly polarized high energy photons (~100GeV) starting from an unpolarized electron beam. The basic principle of operation was predicted in 1962 by Cabbibo and has remained untested up to now. Among other physics goals, Na59 collaboration investigates usage of crystals for high energy photon polarimetry. This paper presents the experiment and summarizes some of the results obtained as of Autumn 2000.

The Gigatracker is the NA62 beam tracker. It is made of three 63.1mm×29.3mm stations of 300μm×300μm hybrid silicon pixel detectors installed in vacuum (∼10−6mbar). The beam particles, flowing at 750MHz, are traced in 4-dimensions by mean of time-stamping pixels with a design resolution of 200ps. This performance has to be maintained despite the beam irradiation amounting to a yearly fluence of 2×10141MeVneq∕cm2. The detector material minimization is paramount, as the detector faces the full beam. The station material budget is reduced to 0.5%X0 by using (HEP world first) micro-channels cooling. We will describe the detector design and performances during the NA62 runs.

This work introduces an experimental test of the new proposal for a low–emittance muon accelerator (LEMMA). A low–emittance muon beam is obtained from the e$^+$ e$^-$ → μ$^+$ μ$^-$ annihilation process at the threshold energy of 45 GeV eliminating the need for a dedicated muon cooling system. A series of two testbeam campaigns were carried out at CERN to validate this concept. The experimental setup is presented together with first preliminary results from the obtained data.

Effects of new physics in flavor could be found both in Flavor Changing Neutral Current (FCNC) processes and in Lepton Flavor Violation (LFV) modes. The former offer the possibility to deeply test the standard model in a clean environment, while the latter are sensitive to contribution from several models beyond the standard model. In the Kaon sector both FCNC and LFV will be investigated in the NA62 experiment. In addition the kaons sector is an ideal place where to look for new particles and tiny effects, in the region of hundreds of MeV/c2. In this paper prospects for exotic searches in NA62 will be presented, together with recent results from NA48/2 and NA62-RK on LFV kaon decays modes.

The investigation of the energy frontier in physics requires novel concepts for future colliders. The idea of a muon collider is very appealing since it would allow to study particle collisions at up to tens of TeV energy, while offering a cleaner experimental environment with respect to hadronic colliders. One key element in the muon collider design is the low-emittance muon production. Recently,the Low EMittance Muon Accelerator (LEMMA) collaboration has explored the muon pair production close to its kinematic threshold by annihilating 45 GeV positrons with electrons in a low Z material target. In this configuration, muons are emerging from the target with a naturally low-emittance. In this paper we describe the performance of a system, to study this production mechanism, that consists in several segmented absorbers with alternating active layers composed of fast Cherenkov detectors together with a muon identification technique based on this detector. Passive layers were made of tungsten. We collected data corresponding to muon and electron beams produced at the H2 line in the North Area of the European Organization for Nuclear Research (CERN) in September 2018.

New results on the deflection of fully stripped 32.8 TeV/c Pb ions in a bent Si crystal at the CERN-SPS are reported. Deflection efficiencies above 10% have been measured for deflection angles in the range 4–9 mrad. The effect of particle losses due to interaction in the crystal and other systematic errors have been carefully investigated. The experimental results are in agreement with theoretical calculations.

The CMS experiment at the LHC will comprise a large silicon strip tracker. This article highlights some of the results obtained in the R&D studies for the optimization of its silicon sensors. Measurements of the capacitances and of the high voltage stability of the devices are presented before and after irradiation to the dose expected after the full lifetime of the tracker.

A sample of more than one million K±→π+π−e±ν ( Ke4 ) decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003–2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of Ke4γ decays, is measured to be BR(Ke4)=(4.257±0.016exp±0.031ext)×10−5 with a total relative error of 0.8% . This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the ππ scattering lengths conducted on the same data sample. The overall form factor normalization fs=5.705±0.017exp±0.031ext is obtained with a total relative precision of 0.6% .

The branching ratio (BR) for the decay K + → π + ν ν is a sensitive probe for new physics.The NA62 experiment at the CERN SPS will measure this BR to within about 10%.To reject the dominant background from channels with final state photons, the large-angle vetoes (LAVs) must detect photons of energy as low as 200 MeV with an inefficiency of less than 10 -4 , as well as provide energy and time measurements with resolutions of 10% and 1 ns for 1 GeV photons.The LAV detectors make creative reuse of lead glass blocks recycled from the OPAL electromagnetic calorimeter barrel.We describe the mechanical design and challenges faced during construction, the characterization of the lead glass blocks and the development of front-end electronics to allow simultaneous time and energy measurements over an extended dynamic range using the timeover-threshold technique.