K. Cankoçak

DELPHI (DEtector with Lepton, Photon and Hadron Identication) is a detector for e + e physics, designed to provide high granularity o v er a 4 solid angle, allowing an eective particle identication.It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989.This article reviews its performance.

Weak isosinglet Neutral Heavy Leptons (v m) have been searched for using data collected by the DELPHI detector corresponding to 3.3 × 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived v m production giving monojet or acollinear jet topologies, and for long-lived v m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 → v m?) of about 1.3 × 10−6 at 95% confidence level for v m masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the v m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region ( $3\leq|\eta|\leq5$ ), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h≈5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as $\frac{a}{\sqrt{E}}\oplus{b}$ . The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.

Experimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the Bπ and B∗π distribution of Q= m(B∗∗) − m(B(∗)) − m(π) using Z0 decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B∗∗→ B(∗)π is measured to be 284 ± 5 (stat.) ± 15 (syst.) MeV/c2, and the Gaussian width of the signal is 79 ± 5 (stat.) ± 8 (syst.) MeV/c2. This signal can be described as a single resonance of mass m = 5732 ± 5 (stat.) ± 20 (syst.) MeV/c2 and full width Γ = 145 ± 28 MeV/c2. The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-meson sector. The production rate of B∗∗ per b-jet is found to be 0.27 ± 0.02 (stat.) ± 0.06 (syst.).

A 10 kilo-tonne dual-phase liquid argon TPC is one of the detector options considered for the Deep Underground Neutrino Experiment (DUNE). The detector technology relies on amplification of the ionisation charge in ultra-pure argon vapour and oers several advantages compared to the traditional single-phase liquid argon TPCs. A 4.2 tonne dual-phase liquid argon TPC prototype, the largest of its kind, with an active volume of 3x1x1 $m^3$ has been constructed and operated at CERN. In this paper we describe in detail the experimental setup and detector components as well as report on the operation experience. We also present the first results on the achieved charge amplification, prompt scintillation and electroluminescence detection, and purity of the liquid argon from analyses of a collected sample of cosmic ray muons.

During the 1992 running period of the LEP e+e− collider, the DELPHI experiment accumulated approximately 24 pb− of data at the Z0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass mt = 157−48+36(expt.)−20+19(Higgs) GeV, and for the effective mixing angle sin2 θefflept = 0.2328 ± 0.0013 (expt.)−0.0003+0.0001(Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.

Extensive measurements have been made with pions, electrons and muons on four production wedges of the compact muon solenoid (CMS) hadron barrel (HB) calorimeter in the H2 beam line at CERN with particle momenta varying from 20 to 300 GeV/c. The time structure of the events was measured with the full chain of preproduction front-end electronics running at 34 MHz. Moving-wire radioactive source data were also collected for all scintillator layers in the HB. The energy dependent time slewing effect was measured and tuned for optimal performance.

Abstract The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly read out by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.

An analysis of inclusive production of K0 and the meson resonances K*±(892), ρ0(770),f 0(975) andf 2(1270) in hadronic decays of the Z0 is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962±0.060 K0 mesons, 0.712±0.067 K*±(892) and 1.21±0.15ρ0(770) per hadronic Z0 decay. The average multiplicities off 0(975) for scaled momentum,x p , in the range 0.05≤x p ≤0.6 and off 2(1270) for 0.05≤x p ≤1.0 are 0.098±0.016 and 0.170±0.043 respectively. Thef 0(975) and ρ0(770)x p -spectra have similar shapes. Thef 2(1270)/ρ0(770) ratio increases withx p . The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K0 momentum spectrum at low momentum, describes the K*±(892) and ρ0(770)x p -spectrum shapes, but significantly overestimates their production rates.

This analysis, based on a sample of 170000 hadronic Z0 decays, provides a measurement of the K± and p/p differential cross sections which is compared to string- and cluster fragmentation models. The total multiplicities for K± and p/p per hadronic event were found to be: NK = 2.26 ± 0.18 and Np = 1.07 ± 0.14. The positions ξ* of the maxima of the differential cross sections as a function of ξ = ln(1/xp) for K± and p/p were determined to be 2.63 ± 0.07 and 2.96 ± 0.16 respectively. A comparison of the ξ* values for various identified particles measured at LEP with the prediction of the Modified Leading Logarithm Approximation with Local Parton Hadron Duality model has been performed. The measured ξ* position as a function of the hadron mass, after corrections due to particle decays, is in agreement with the model calculation.

In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb−1, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e+e− → WW process of 3.67−0.85+0.97 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44 (stat.) ± 0.09 (syst.) ± 0.03 (LEP) GeV/c2. Alternatively, if mW is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV (V ≡ γ, Z) couplings.

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.

We investigated the darkening of two high OH- content quartz fibres irradiated with 24 GeV protons at the Cern PS facility IRRAD. The two tested fibres have a 0.6 mm quartz core diameter, one with hard plastic cladding (qp) and the other with quartz cladding (qq). These fibres were exposed at about 1.25 Grad in 3 weeks. The fibres became opaque below 380 nm and in the range 580–650 nm. The darkening under irradiation and damage recovery after irradiation as a function of dose and time are similar to what we observed with electrons. The typical attenuation at 455 nm are 1.44±0.22 and 2.20±0.15dB/m at 100 Mrad for qp and qq fibres, respectively. The maximum damage recovery is also observed near this wavelength.

The RADiCAL Collaboration is conducting R\&D on high performance electromagnetic (EM) calorimetry to address the challenges expected in future collider experiments under conditions of high luminosity and/or high irradiation (FCC-ee, FCC-hh and fixed target and forward physics environments). Under development is a sampling calorimeter approach, known as RADiCAL modules, based on scintillation and wavelength-shifting (WLS) technologies and photosensor, including SiPM and SiPM-like technology. The modules discussed herein consist of alternating layers of very dense (W) absorber and scintillating crystal (LYSO:Ce) plates, assembled to a depth of 25 $X_0$. The scintillation signals produced by the EM showers in the region of EM shower maximum (shower max) are transmitted to SiPM located at the upstream and downstream ends of the modules via quartz capillaries which penetrate the full length of the module. The capillaries contain DSB1 organic plastic WLS filaments positioned within the region of shower max, where the shower energy deposition is greatest, and fused with quartz rod elsewhere. The wavelength shifted light from this spatially-localized shower max region is then propagated to the photosensors. This paper presents the results of an initial measurement of the time resolution of a RADiCAL module over the energy range 25 GeV $\leq$ E $\leq$ 150 GeV using the H2 electron beam at CERN. The data indicate an energy dependence of the time resolution that follows the functional form: $\sigma_{t} = a/\sqrt{E} \oplus b$, where a = 256 $\sqrt{GeV}$~ps and b = 17.5 ps. The time resolution measured at the highest electron beam energy for which data was currently recorded (150 GeV) was found to be $\sigma_{t}$ = 27 ps.

A sample of events enriched in bb̄ quark pairs was selected in the data recorded by the DELPHI experiment at LEP during 1992 and 1993, by the presence of secondary decay vertices from short-lived particles. Using this sample, the average multiplicities of Ks0, K±, p(p̄), Λ(Λ) and of charged particles in bb̄ events have been measured, distinguishing the component from fragmentation and the component coming from the decay of b-hadrons. The measurement of the average charge multiplicity in bb̄ events was used to compute the mean fractional beam energy carried by the primary b-hadron, and the difference in charged particle multiplicity between bb̄ events and light quark (uū, dd̄, ss̄) events.

J/ψ mesons have been reconstructed from their decay to μ+μ− and e+e−, using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 ± 17 J/ψ were found, 5.4 ± 2.3 ψ′ were obtained in the channel J/ψ (→μ+μ−)π+π− and 6.4 ± 2.7 χc in the channel J/ψ ( → μ+μ−)γ. As the dominant source of Jψ mesons is from bquarks, the following branching ratios: Br(b → J/ψ X) = (1.12 ± 0.12 (stat) ± 0.10 (syst.))%, Br(b → ψ′ X) = (0.48 ± 0.22 (stat.± 0.10 (syst.))%, Br(b → χc1 X) = (1.4 ± 0.6 (stat.)−0.2+0.4 (syst.))% were measured. From the proper time distribution of the J/ψ sample, the average lifetime of b-hadrons decaying into J/ψ was found to be: τB = 1.50−0.21+0.24 (stat.) ± 0.03 (syst.) ps. A search for completely reconstructed B meson decays to final states including a J/ψ gave a signal of 15 ± 5 events.

An analysis is reported on the channele + e −→μ+μ−(nγ), n=1,2..., using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross sections of the radiative photons as a function of photon energy and of the angle between the photon and the muon are presented. No significant deviations from expectations are observed. The data are also used to extract the muon-pair cross section and asymmetry below the Z0 peak by using those events with relatively hard initial state radiative photon(s). The measured cross section and asymmetry show no significant deviation from the Standard Model expectations. These results together with the DELPHI cross section and asymmetry measurements at the LEP energies from the 1990 to 1992 running periods are used to determine limits on the Z0-Z′ gauge boson mixing angle θZ′ and on the Z′ mass. There is no indication of the existence of a Z′; the limits obtained on the mixing angle substantially improve upon existing limits. The 95% confidence level allowed ranges of θZ′ in various models are: $$\begin{gathered} - 0.0070 \leqslant \theta _{Z'} \leqslant 0.0078,E_6 (\chi )\bmod el, \hfill \\ - 0.0075 \leqslant \theta _{Z'} \leqslant 0.0095,E_6 (\psi )\bmod el, \hfill \\ - 0.029 \leqslant \theta _{Z'} \leqslant 0.029,E_6 (\eta )\bmod el, \hfill \\ - 0.0068 \leqslant \theta _{Z'} \leqslant 0.0082,L - R(1.)\bmod el, \hfill \\ - 0.0057 \leqslant \theta _{Z'} \leqslant 0.0077,L - R(\sqrt 2 )\bmod el. \hfill \\ \end{gathered} $$

In a sample of 3.02 million hadronic Z0 decays collected by the DELPHI detector, 270 Jψ→ ℓ+ℓ− candidates have been selected. A search for fully reconstructed Bc± mesons has yielded one Bc±→Jψπ± candidate, no Bc±→Jψℓ±νℓ candidates, and one Bc±→Jψ, π+π−π± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z0→ Bc±X) × Br(Bc±→Jψπ±) < (1.05 to 0.84) × 10−4 and Br(Z0→ Bc±X) × Br(Bc±→Jψℓ±νℓ) < (5.8 to 5.0) × 10−5, where the ranges quoted correspond to the range of predicted Bc± lifetimes from 0.4 to 1.4 ps, and Br(Z0→ Bc±X) × Br(Bc±→Jψπ+π−π±) < 1.75 × 10−4, constant over the range of predicted Bc± lifetimes.

A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the∑ ± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models.

Measurements are presented of short range three-particle correlations in e+e− annihilations at LEP using data collected by the DELPHI detector. At small values of the four-momentum difference, strong three-particle correlations are observed for like-sign (+++ and −−−) and for unlike-sign (++− and +−−) pion combinations which are not a consequence of two-particle correlations. A possible explanation of the observed effects in like-sign combinations is the existence of higher order Bose-Einstein interference, which significantly changes the particle distributions in jets.

Two-particle correlations in invariant mass are studied separately for like-sign and unlike-sign pions. Strong correlations are observed only at small masses. The correlations decrease very rapidly for like-sign pions and slowly for unlike-sign pions, manifesting different particle dynamics. The like-sign correlations exhibit a power-law behaviour as a function of mass, compatible with the previously observed intermittency effect. The predictions of the parton shower model (JETSET 7.3) deviate significantly from the data. However, good agreement is obtained with the mass correlations, both for the unlike-sign and for the like-sign pairs if the production of the η′ and ρ0 mesons is reduced and Bose-Einstein correlations are included in the model. The value of the Bose-Einstein correlation strength is consistent with unity for pions which are produced directly or in the decays of short-lived resonances.

A search for fully reconstructed Λb0 beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the Λc+π− channel and one in the Λc+a1− channel over a small background. The Λb0 beauty baryon mass is measured to be (5668 ± 16 (stat.) ± 8 (syst.)) MeV/c2.

Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree levelb→u and one-loop penguinb→s, d transitions. Evidence for charmlessB decays was obtained in two body hadronic modes. The branching ratios ofB 0 toπ + π − orK + π − andB − toρ 0 π − orK*0 π − were found to be (2.8 −1.0 +1.5 ±0.2)×10−5 and (1.7 −0.8 +1.2 ±0.2)×10−4 respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectators quark, was measured to be 0.58±0.18. Upper limits were set at 90% confidence level on the branching ratios for three and four body charmless hadronic decays in the range of (1–3)×10−4, for inclusive radiativeb→sγ decays at 5.4×10−4, for the exclusive radiative decaysB 0 →K*(892)0 γ andB 0 →φ(1020)γ at 2.1×10−4 and 7.0×10−4 respectively, and for dineutrino decays $$b \to s\nu \bar \nu $$ , in the exclusive channels $$B_d^0 \to K^* (892)^0 \nu \bar \nu $$ and $$B_s^0 \to \phi (1020)\nu \bar \nu $$ at 1.0×10−3 and 5.4×10−3 respectively. The limits on dineutrino decays constrain theories with a newU(1) gauge boson coupling predominantly to the third family of fermions.

The partial decay width of theZ to $$b\bar b$$ quark pairs has been measured by the DELPHI detector at LEP.b-hadrons, containingb-quarks, were tagged by leptons with high transverse momentum relative to the hadron or by tracks with large impact parameters to the primary vertex. The ratio of the numbers of events with a single such tag to those with two tags was used to estimate the efficiency of the method and to reduce the systematic uncertainty. Combining all methods, the value: $$\begin{gathered} \frac{{\Gamma _{b\bar b} }}{{\Gamma _{had} }} = 0.2210 \pm 0.0033 \pm 0.0003(model) \hfill \\ \pm 0.0014(\Gamma _{c\bar c} ) \hfill \\ \end{gathered} $$ was found, where the third error corresponds to a±8% uncertainty on the $$c\bar c$$ production width. A maximum likelihood in to the single and di-lepton distributions gave the branching fraction of the decays ofb-quarks to leptons as: $$\begin{gathered} BR(b \to l) = (11.06 \pm 0.39 \pm 0.19(model) \hfill \\ \pm 0.12(\Gamma _{c\bar c} ))\% . \hfill \\ \end{gathered} $$

During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450 000 Z0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z0 resonance. Model independent fits to the cross sections and leptonic forward- backward asymmetries yield the following Z0 parameters: the mass and total width MZ = 91.187 ± 0.009 GeV, ΓZ = 2.486 ± 0.012 GeV, the hadronicf and leptonic partials widths Γhad = 1.725 ± 0.012 GeV, Γℓ = 83.01 ± 0.52 MeV, the invisible width Γinv = 512 ± 10 MeV, the ratio of hadronic to leptonic partial widths Rℓ = 20.78 ± 0.15, and the Born level hadronic peak cross section σ0 = 40.90 ± 0.28 nb. Using these results and the value of αs determined from DELPHI data, the number of light neutrino species is determined to be 3.08 ± 0.05. The individual leptonic widths are found to be: Γe = 82.93 ± 0.70 MeV, Γμ = 83.20 ± 1.11 MeV and Γτ = 82.89 ± 1.31 MeV. Using the measured leptonic forward-backward asymmetries and assuming lepton universality, the squared vector and axial-vector couplings of the Z0 to charged leptons are found to be gVℓ2 = (1.47 ± 0.51) × 10−3 and gAℓ2 = 0.2483 ± 0.0016. A full Standard Model fit to the data yields a value of the top mass mt = 115−82+52 (expt.)−24+52(Higgs) GeV, corresponding to a value of the weak mixing angle sin2 θefflept = 0.2339±0.0015 (expt.)−0.0004+0.0001 (Higgs). Values are obtained for the variables S and T, or ϵ1 and ϵ3 which parameterize electroweak loop effects.

The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that is not contained by the barrel (HCAL HB) and electromagnetic (ECAL EB) calorimeters. Due to space limitation the barrel calorimeters do not contain completely the hadronic shower and an outer calorimeter (HO) was designed, constructed and inserted in the muon system of CMS to measure the energy leakage. Testing and calibration of the HO was carried out in a 300 GeV/c test beam that improved the linearity and resolution. HO will provide a net improvement in missing E T measurements at LHC energies. Information from HO will also be used for the muon trigger in CMS.

Abstract The 3×1×1 m 3 demonstrator is a dual phase liquid argon time projection chamber that has recorded cosmic rays events in 2017 at CERN. The light signal in these detectors is crucial to provide precise timing capabilities. The performance of the photon detection system, composed of five PMTs, are discussed. The collected scintillation and electroluminescence light created by passing particles has been studied in various detector conditions. In particular, the scintillation light production and propagation processes have been analyzed and compared to simulations, improving the understanding of some liquid argon properties.

The first measurement of like-sign charged kaon correlations in hadronic decays of the Z0 is presented, based on data collected by the DELPHI detector. The charged kaons are identified by means of ring imaging Cherenkov detectors. A significant enhancement at small values of the four-momentum difference is observed in the ratio of like-sign to unlike-sign KK pairs and in the ratio of like-sign pairs to a simulated reference sample. An update of the measurement of Ks0Ks0 interference is also presented. An enhancement is found in the production of pairs of Ks0 of similar momenta, as compared with a simulated reference sample. The measured Bose-Einstein correlation parameters λ and r are similar for charged and neutral kaon pairs. The value of the Bose-Einstein correlation strength λ is consistent with unity.

A sample of Z0→τ+τ− events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels $$ev\bar v$$ , $$\mu v\bar v$$ , πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=−0.148±0.022 and for the Z0 polarisationP Z=−0.136±0.027. These results are used to determine the ratio of vector to axial-vector effective couplings for taus $$\bar v_\tau /\bar a_\tau = 0.074 \pm 0.011$$ , and for electrons $$\bar v_e /\bar a_e = 0.068 \pm 0.014$$ , compatible with e-τ universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons $$\bar v_l /\bar a_l = 0.072 \pm 0.008$$ is obtained, implying a value of the effective weak mixing angle sin2θ eff lept =0.2320±0.0021.

We analyze effects of the $CP$-odd soft phases in the MSSM on the pair productions of colored superpartners in $pp$ collisions at the LHC energies. We find that, among all pair-production processes, those of the scalar quarks in the first and second generations are particularly sensitive to the $CP$-odd phases, more precisely, to the phases of the gluinos and neutralinos. We compute pair-production cross sections, classify various production modes according to their dependencies on the gluino and neutralino phases, perform a detailed numerical analysis to determine individual as well as total cross sections, and give a detailed discussion of 2. electric dipole moment (EDM) bounds. We find that pair productions of first and second generation squarks serve as a viable probe of the $CP$ violation sources in the gaugino sector of the theory even if experiments cannot determine chirality, flavor and electric charge of the squarks produced.

The Large Hadron Collider (LHC) is going to start taking data with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> luminosity, and reach the designed value of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in 2013. The LHC luminosity will continue to improve each year, reaching to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in 2023. We call this high luminosity era the Super-LHC (SLHC). Hadronic Endcap (HE) calorimeters of the CMS experiment cover the pseudorapidity range of 1.4 ≪ η ≪ 3 on both sides of the CMS detector, contributing to superior jet and missing transverse energy resolutions. As the integrated luminosity of the LHC increases, the scintillator tiles used in the CMS Hadronic Endcap calorimeter will lose their efficiency. The CMS collaboration plans to substitute Quartz plates for the scintillator tiles of the original design. Various tests have proved Quartz to be radiation hard, but the light produced by Quartz comes from Cerenkov process, which yields drastically fewer photons than scintillation. To increase the light collection efficiency, we propose to treat the Quartz plates with radiation hard wavelength shifters, p-terphenyl or 4% gallium doped zinc oxide. The test beam studies revealed a substantial light collection increase on pTp or ZnO:Ga deposited Quartz plates. We constructed a 20 layer calorimeter prototype with pTp coated plates, and tested the hadronic and the electromagnetic capabilities at the CERN H2 area. Here we report the results of these test beams as well as radiation damage studies performed on p-Terphenyl.

The forward-backward asymmetry of the processe + e −→Z→b $$b\bar b$$ has been measured using events collected by the DELPHI experiment during the 1991 and 1992 LEP runs. This data sample corresponded to 884 000 hadronicZ decays at a centre-of-mass energy $$\sqrt s \sim M_Z $$ . The tagging of b-quark events was performed using two approaches; the first was based on the semileptonic decay channelsb→X+μ andb→X+e, the second used a lifetime tag with jet-charge reconstruction. The results of these two methods were combined to give $$A_{FB}^{b\bar b} = 0.107 \pm 0.011(stat. + syst. + mixing).$$ With the semileptonic sample, the forward-backward asymmetry of the processe + e −→Z→ $$c\bar c$$ was also measured to be $$A_{FB}^{c\bar c} = 0.083 \pm 0.022(stat.) \pm 0.016(syst.).$$ The effective value of the Weinberg mixing angle derived from these measurements was $$sin^2 \theta _{eff}^{lep} = 0.2294 \pm 0.0021.$$

The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result of ττ = 291.8 ± 3.3 (stat.) ± 2.0(sys.) fs while the decay length distribution of three-prong decays gives the result ττ = 286.7 ± 4.9 (stat.) ±3.3 (sys.) fs. Combining the results presented here with previous DELPHI measurements, we get ττ = 291.4 ± 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 ± 0.009, compatible with lepton universality.

This letter reports the results of the measurement of single photon production in the reaction e + e !+ i n visible particles at centre-of-mass energies p s = 130 and 136 GeV and an integrated luminosity of 5.83 pb 1 , collected with the DELPHI detector at LEP.The signal is compatible with the prediction of the Standard Model for the process e + e !, and the number of neutrino families has been determined to be N = 3 : 1 0 : 6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specic model.

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb−1 at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events (e, μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits me∗ > 62.5 GeV/c2, mμ∗ > 62.6 GeV/c2 and mτ∗ > 62.2 GeV/c2 at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λml∗ of the coupling of the excited charged lepton to its mass were derived.

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is αs(MZ) = 0.124−0.007+0.006(exp) ± 0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence.

Two measurements of $$\Gamma _{b\bar b} /\Gamma _{had} $$ are presented. Both measurements use 250000Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, $$\Gamma _{b\bar b} /\Gamma _{had} $$ is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018 $$\Gamma _{c\bar c} $$ .

Due to an expected increase in radiation damage under super-LHC conditions, we propose to substitute the scintillator tiles in the original design of the hadronic endcap (HE) calorimeter with quartz plates. Quartz is proved to be radiation hard by the radiation damage tests with electron, proton, neutron and gamma beams. Using wavelength shifting fibers, it is possible to collect efficiently the Cherenkov light generated in quartz plates. This paper summarizes the results from various test beams, bench tests, and Geant4 simulations done on methods of collecting light from quartz plates, as well as radiation hardness tests on quartz material.

Abstract What is the luminosity needed for discovering new physics if the electroweak scale is to remain stable? In this work we study this question, with the pertinent example of a real singlet scalar which couples to the Higgs field at the renormalizable level. Observing that the electroweak scale remains stable if the two scalars couple in a see-sawic fashion through a mass-degeneracy-driven unification linkup among quartic couplings at a given scale, we show by detailed simulation studies of the $$pp\rightarrow (\mathrm{singlet\ scalar}) \rightarrow Z Z \rightarrow 4\ell $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>p</mml:mi> <mml:mi>p</mml:mi> <mml:mo>→</mml:mo> <mml:mo>(</mml:mo> <mml:mrow> <mml:mi>singlet</mml:mi> <mml:mspace /> <mml:mi>scalar</mml:mi> </mml:mrow> <mml:mo>)</mml:mo> <mml:mo>→</mml:mo> <mml:mi>Z</mml:mi> <mml:mi>Z</mml:mi> <mml:mo>→</mml:mo> <mml:mn>4</mml:mn> <mml:mi>ℓ</mml:mi> </mml:mrow> </mml:math> channel that the HL-LHC, which is expected to deliver an integrated luminosity of $$3~\mathrm{ab^{-1}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mspace /> <mml:msup> <mml:mi>ab</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , has no significant excess of signal over the background in the 800–2000 GeV mass range. The FCC-hh, on the other hand, can discover scalars up to a mass of 870 GeV with an integrated luminosity $$20~\mathrm{ab^{-1}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>20</mml:mn> <mml:mspace /> <mml:msup> <mml:mi>ab</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . Observation at $$3\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> (discovery at $$5\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> ) of a new scalar with a minimum mass 800 GeV requires at least $$2~\mathrm{ab^{-1}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mspace /> <mml:msup> <mml:mi>ab</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ( $$5.2~\mathrm{ab^{-1}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5.2</mml:mn> <mml:mspace /> <mml:msup> <mml:mi>ab</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ) integrated luminosity, showing that the new physics that does not destabilize the electroweak scale is accessible only at very high luminosities, and can be tested already in the early stages of the FCC-hh operation period.

Abstract We report the results of the analyses of the cosmic ray data collected with a 4 tonne (3×1×1 m 3 ) active mass (volume) Liquid Argon Time-Projection Chamber (TPC) operated in a dual-phase mode. We present a detailed study of the TPC's response, its main detector parameters and performance. The results are important for the understanding and further developments of the dual-phase technology, thanks to the verification of key aspects, such as the extraction of electrons from liquid to gas and their amplification through the entire one square metre readout plain, gain stability, purity and charge sharing between readout views.

A search for pair production of the lightest chargino at s=130.4and136.3 GeV has been carried out using the data sample corresponding to the 5.92 pb−1 recorded by the DELPHI detector during the high energy run of LEP in the last period of 1995. The theoretical reference model has been the Minimal Supersymmetric Standard Model with R-parity conservation. The three topologies expected for the decay of a pair of charginos, namely two acoplanar leptons plus missing energy (ℓℓ), two jets and an isolated lepton plus missing energy (jjℓ) and missing energy in a hadronic environment (s), were investigated. No evidence of a signal was found. Lower mass limits were derived for various scenarios, including the case of a low mass difference between the chargino and the neutralino and of a light sneutrino. The mass limits range between 56.3 GeV/c2 and the kinematic limit.

Kaon production in one prong tau decays has been studied using data collected with the DELPHI detector at the LEP collider. Charged kaons were identified over a large momentum range by the DELPHI barrel Ring Imaging Cherenkov detector. The following branching ratios have been determined: BR(τ→Kντ)=(0.85±0.18)%, BR(τ→Kντ≥0 neutrals)=(1.54±0.24)%, BR(τ→Kντ≥1 neutrals)=(0.69±0.25)%. The result for the exclusive branching ratio is consistent with the Standard Model prediction based on τ-μ-e universality. In addition, tau decay into K∗− was studied in the channel K∗−→K−π0. The result BR(τ→K∗−ντ)×BR(K∗−→K−π0)=(0.57±0.23)% was obtained.

K0SK0S correlations have been studied in a sample of 717 511 hadronic events collected by the DELPHI detector at LEP during 1992. An enhancement is found in the production of pairs of K0S of similar momenta, as compared with a Monte Carlo simulated reference sample. The measured values for the strength of the correlation and the radius of the emitting source of kaons are λ = 1.13 ± 0.54 (stat) ± 0.23 (syst) and r = 0.90 ± 0.19 (stat) ± 0.10 (syst) fm. This enhancement is consistent with the hypothesis that K0SK0S pairs display an enhancement, regardless of whether they come from a K0K̄0 or from a K0K0 (K̄0K̄0) system.

Strange beauty meson Bs0 have been reconstructed through exclusive hadronic final states, using the data collected in 1992 by the DELPHI experiment at the LEP collider. The analysis relies on the combined use of accurate tracking and of the hadron identification capabilities of DELPHI. Three Bs0 decay candidates have been selected over a negligible background using theDs−π+, Ds−a1+ (1260) and JΨφ decay modes, with identified kaons in the final state. The Bs0 meson mass is measured to be mBs = (5374± 16± 2) MeV/ c2.

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z0 decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, τcharged/τneutral, was 1.09 −0.10 +0.11 (stat.)±0.08 (syst.). By making assumptions about the B s 0 and Λ b 0 states, the B+ and B0 meson lifetimes were determined to be τB+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and τB+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was: τB+/τB0 = 1.06 −0.11 +0.13 ±0.10. The mean B lifetime was also deduced to be < τ > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps.

The time dependent mixing of Bd0–Bd0 mesons has been observed by using the correlations between the charge of D∗ mesons and the weighted mean charge of particles in each hemisphere. From a reconstructed D∗± sample corresponding to about 1.7 million hadronic Z0 decays, the mass difference between the two Bd0 mass eigenstates has been measured to be ̵Δm = 0.50±0.12 (stat.) ± 0.06 (syst.)h̵/ps or, converting into eV/c2: Δm = [3.29 ± 0.79 (stat) ± 0.39 (syst.)] 10−4 eV/c2.

A search for pair production of neutral heavy Higgs bosons decaying into $$b\bar b$$ has been carried out in a study of hadronic decays of the Z boson into four jet final states using data taken by DELPHI in 1991 and 1992. The two production mechanisms present in the two Higgs doublets scheme, bremsstrahlung production of hZ* and associated production of hA, may lead to four beauty jets well recognizable using the precise microvertex detector measurements. No evidence for a signal was found, leading to limits on BR(Z→hA→4b) from 3.5 to 5.5×10−4 at 95% contidence level, depending on the mass of the ligthest Higgs. When combined with the results of the recent DELPHI standard Higgs search, this result allows the kinematical limit to be reached for the masses of h and A in the minimal supersymmetric extension of the Standard Model (MSSM) scheme. It also allows the tanβ≤1 domain to be explored, and a region above the kinematic limit for direct hA production is constrained by considering virtual hA production. Results are also given in the general two-doublet scheme.

The production of multihadronic states in γγ collisions at LEP has been studied with the DELPHI detector. The analyzed data correspond to an integrated luminosity of about 32pb−1, collected in the LEP runs of 1990–1992. Minimum bias data and a sample of events with jets at highp T have been selected under the requirement that no scattered electron or positron is observed. The two data sets have been compared to Monte Carlo predictions. The non-perturbative contribution described by the vector meson dominance Model and direct $$q\bar q$$ production from pointlike photons described by the quark parton model were found to be insufficient to reproduce the data. It has been necessary to include a third interaction component, which is due to perburbative hard scattering of the partonic constituents of the photon. Several parametrisations of the quark and gluon densities of the photon have been tested. The interplay with the cut in jet transverse momentum, which is necessary for the separation of the perturbative and non-perturbative regions, is discussed. The data favour parametrisations with rather soft partonic content of the photon.

The decayB *→B γ has been observed with the DELPHI detector at LEP, where theB * meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB *-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c2. 95% confidence level upper limits at 6 MeV/c2 are placed on both the isospin (i.e.B +-B 0) and theB s -B ud splitting of the mass difference. The production ratio ofB * toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB * cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB * energy of 〈x E 〉=0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB * polarisation states is measured to be σL/(σL + σT) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).

A measurement of the Δ++(1232) inclusive production in hadronic decays of the Z at LEP is presented, based on 1.3 million hadronic events collected by the DELPHI detector in the 1994 LEP running period. The DELPHI ring imaging Cherenkov counters are used for identifying hadrons. The average Δ++(1232) multiplicity per hadronic event is 0.079 ± 0.015 which is more than a factor of two below the JETSET, HERWIG and UCLA model predictions. It agrees with a recently proposed universal mass dependence of particle production rates in e+e− annihilations.

The study of the properties of inclusive production ofD s mesons and of events in which a ϕ and a muon are present in the same jet provides two independent measurements of the probability,f s w , for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ 0 decays. The combined value of these measurements isf s w =0.19±0.06±0.08. From the flight distance distributions ofD s and of (ϕ-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB s 0 meson lifetime. Combining these measurements with a previous result based on the study ofD s-μ events, theB s 0 meson lifetime is measured to be: 0.96±0.37 ps.

An excess of events containing, in a jet, a samesign Ξ∓−ℓ∓ pair as compared to those with an oppositesign Ξ∓−ℓ± pair has been observed in an analysis of 1.7 million hadronic Z0 decays collected by the DELPHI detector at LEP between 1991 and 1993 inclusive. The probability for this signal to come from non B-baryon decays is less than 5×10−4. The measured production fraction corresponds to: per lepton species, averaged for electrons and muons and assuming that the two channels have an equal contribution. Semileptonic decays of Λ b baryons can account for less than 10% of these events and the major part of the signal has to originate from Ξ b semileptonic decays. Using the subsample of these events where the Ξ∓ trajectory has been measured in the Vertex Detector, the lifetime of B-baryons producing a Ξ∓ in their semileptonic decay final state is found to be: $$\tau (B - baryon \to \Xi ^ - \ell ^ - X) = 1.5_{ - 0.4}^{ + 0.7} \pm 0.3ps.$$

For the first time, multihadronic production from single tagged γγ collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared (〈Q2〉 = 0.06 (GeV/c2)2). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (ϱ, ω or π), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content.

The performance of the High-density Projection Chamber (HPC), the barrel electromagnetic calorimeter of the DELPHI experiment, is described. The detector adopts the time projection technique in order to obtain exceptionally fine spatial granularity in the three coordinates (/spl sim/2/spl times/20 mrad/sup 2/ in /spl theta//spl times//spl phi/ with nine samplings along the shower axes), using a limited number of readout channels (18432). Among the various topics concerning the HPC construction and operation, major emphasis is given to the aspects related to the calibration in energy of the calorimeter, based mainly on the analysis of the detector response to /sup 83m/Kr decays, and to the treatment of ageing in the readout proportional counters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, rapidity correlations of Λ-Λ, proton-proton, and Λ-proton pairs are compared with each other and with the predictions of the string fragmentation model. For Λp pairs, the additional correlation with respect to charged kaons is also analysed.

A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c 2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks.

From the data recorded with the DELPHI detector at LEP in the years 1991–1992, 46497 events were selected having a high-momentum muon in hadron jets. A fit to the average electric charge sum of the jets recoiling against a b-quark jet tagged by a high-PT muon results in an average mixing parameter of χ=0.144±0.014(stat.)+0.0170.011(syst.).

A total of about 900 000 Z0→ qq decays have been analyzed to measure the B0B0 mixing probability. Two different b tagging techniques have been used: events with two leptons and events with one lepton and one Λ. From a combination of the two methods the average mixing parameter, χ, was determined to be (12.1±1.6(stat.)±0.4(syst.)±0.4(model)%.

A sample of 25000 Z0 → τ+τ− events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eνν) = (17.51 ± 0.39)% and B(τ → μνν) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be gμge= 1.000 ± 0.013, satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lνν) = (17.50 ± 0.25)%.

Received 24 October 2007DOI:https://doi.org/10.1103/PhysRevD.76.119903©2007 American Physical Society

A search with the DELPHI detector at LEP for excited leptons (e∗, μ∗, τ∗ and ν∗) decaying through γ, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb−1 at an e+e− centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits me∗ > 79.6 GeV/c2, mμ∗ > 79.6 GeV/c2, mτ∗ > 79.4 GeV/c2 and mν∗ > 56.4 GeV/c2 at 95% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio λmℓ∗ of the coupling of the excited lepton to its mass.

The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives τB = 1.582 ± 0.011 (stat.) ± 0.027 (syst.) ps. Combining this result with the previous result based on charged particle impact parameter distributions yields τB = 1.575 ± 0.010 (stat.) ± 0.026 (syst.) ps.

As part of its HL-LHC upgrade program, the CMS collaboration is replacing its existing endcap calorimeters with a high-granularity calorimeter (CE). The new calorimeter is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic and hadronic compartments. Due to its compactness, intrinsic time resolution, and radiation hardness, silicon has been chosen as active material for the regions exposed to higher radiation levels. The silicon sensors are fabricated as 20 cm (8") wide hexagonal wafers and are segmented into several hundred pads which are read out individually. As part of the sensor qualification strategy, 8" sensor irradiation with neutrons has been conducted at the Rhode Island Nuclear Science Center (RINSC) and followed by their electrical characterisation in 2020-21. The completion of this important milestone in the CE's R&D program is documented in this paper and it provides detailed account of the associated infrastructure and procedures. The results on the electrical properties of the irradiated CE silicon sensors are presented.

Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given.

A measurement of the mass difference,Δm d , between the two physical B 0 states has been obtained from the analysis of the impact parameter distribution of a lepton emitted at large transverse momentum (p t ) relative to the jet axis and from the analysis of the flight distance distribution of secondary vertices tagged by either a highp t lepton or an identified kaon. In the opposite hemisphere of the event, the charge of the initial quark has been evaluated using a highp t lepton, a charged kaon or the mean jet charge. With 1.7 million hadronic Z0 decays recorded by DELPHI between 1991 and 1993,Δm d is found to be: $$\Delta m_d = 0.531_{ - 0.046}^{ + 0.050} (stat.) \pm 0.078 (syst.) ps^{ - 1} .$$ .

A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider. Samples of events with a D meson and a lepton in the same jet are selected where $$\bar D^{^0 } \ell ^ + $$ and D*ℓ+ events originate mainly from the semileptonic decays of B+ and B0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into $$\bar D^{^{**} } \ell ^ + v$$ , the following B meson lifetimes and lifetime ratio are measured: $$\begin{gathered} \tau (B^ + ) = 1.61_{ - 0.16}^{ + 0.16} (stat.) \pm 0.12(syst.) ps \hfill \\ \tau (B^0 ) = 1.61_{ - 0.13}^{ + 0.14} (stat.) \pm 0.08(syst.) ps \hfill \\ \tau (B^ + )/\tau (B^0 ) = 1.00_{ - 0.15}^{ + 0.17} (stat.) \pm 0.10(syst.) \hfill \\ \end{gathered} $$ and an average lifetime of B+ and B0 mesons is obtained: $$\tau (B) = 1.61_{ - 0.07}^{ + 0.08} (stat.) \pm 0.05(syst.) ps$$

The production and decay of beauty baryons (b-baryons) have been studied using 1.7×106 Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify theb-baryons. The first method used pairs of a Λ and a lepton to tag theb-baryon decay. The second method associated fully reconstructed ΛC baryons with leptons. The third analysis reconstructed theb-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: The averageb-baryon lifetime was determined to be:

The inclusive production of the f′2(1525) in hadronic Z0 decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f′2(1525) → K+K−. The average number of f′2(1525) produced per hadronic Z decay, 〈f′2〉 = 0.020 ± 0.005 (stat) ± 0.006 (syst), and the momentum distribution of the f′2(1525) have both been measured. The mass and width of the f′2(1525) are found to be 〈Mf′2〉 = 1535 ± 5 (stat) ± 4 (syst) MeV/c2, (Tf′2;) = 60 ± 20 (stat) ± 19 (syst) MeV/c2

The forward-backward asymmetries for the processes $$e^ + e^ - \to c\bar c$$ and $$e^ + e^ - \to b\bar b$$ at theZ resonance are measured using identifiedD *± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D *+→D 0π+ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be: $$\begin{gathered} A_{FB}^{c\bar c} = 0.077 \pm 0.029(stat) \pm 0.012(sys), \hfill \\ A_{FB}^{b\bar b} = 0.059 \pm 0.062(stat) \pm 0.024(sys). \hfill \\ \end{gathered} $$ Constraining theb asymmetry to the value measured by DELPHI using independent analyses, the charm asymmetry is determined to be: $$A_{FB}^{c,const} = 0.068 \pm 0.027(stat) \pm 0.011(sys).$$ . This result corresponds to an effective electroweak mixing angle measured using charm quark events of: $$\sin ^2 \theta _{eff}^{lept} = 0.2307 \pm 0.0062(stat) \pm 0.0026(sys).$$

The installation and commissioning of the Hadron Calorimeter system of the CMS detector is described and the performance of the various monitoring systems, the progress in the calibration work and the current plans for the HCAL calorimeter are summarized.

Due to an expected increase in radiation damage under super-LHC conditions, we propose to substitute the scintillator tiles in the original design of the CMS hadronic endcap (HE) calorimeter with quartz plates. Quartz is proved to be radiation hard by various tests, but the light produced by quartz comes from Cerenkov process, and it is 100 times less than scintillation photons. To enhance the light production we treated the quartz plates with p-Terphenyl, and constructed a 20 layers calorimeter prototype. Here, we report the test beam results for hadronic and electromagnetic capabilities of the calorimeter prototype as well as radiation damage results for p-Terphenyl.

The interference between initial and final state radiation in the processe + e −→μ + μ − at √s≈MZ has been studied by measuring the forward-backward asymmetry as a function of the acoplanarity angle between the final state muons. The interference is expected to be sensitive to the space-time separation of the initial and final state radiation. The measured asymmetry distribution has been compared to theoretical predictions using thekoralz generator, with and without $${\mathcal{O}}(\alpha )$$ interference. The magnitude of the interference between initial and final state radiation was found to be of the order predicted and to follow the expected distribution. Using the theoretical predictions, a value of $$\Gamma _{\rm Z} = 2.50 \pm 0.21 (stat.) \pm 0.06 (syst.) GeV.$$ has been extracted. The interpretation of this result is discussed. There is an additional uncertainty in the estimate ofΓ Z from as yet uncalculated higher order interference terms. By assuming a value ofΓ Z consistent with the world average, the data were used to estimate the size of these uncalculated corrections.

A search for high mass photon pairs from the processes $$e^ + e^ - \to \ell ^ + \ell ^ - \gamma \gamma $$ , $$e^ + e^ - \to q\bar q\gamma \gamma $$ and $$e^ + e^ - \to \nu \bar \nu \gamma \gamma $$ with the DELPHI detector at LEP I is reported. From a data sample containing 3.5 million hadronic Z0 decays, collected by DELPHI during the years 1991 to 1994, 79 events with two charged leptons and two isolated photons were selected with photon pair masses above 10 GeV/c2, where 76±6 events were predicted from standard sources. In the same data sample, no $$\nu \bar \nu \gamma \gamma $$ candidates were found and no accumulation of events was visible forγγ masses above 10 GeV/c2 in the $$q\bar q\gamma \gamma $$ channel. Upper limits at 95% confidence level on the Z0 branching ratios for the three different channels were extracted from the data. In the mass regionm γγ >30 GeV/c2 the limits obtained are between 3×10−6 and 4×10−6.

A measurement of the strange quark forward-backward asymmetry at the Z0 peak was performed using 718,000 multihadronic Z0 decays collected by the DELPHI detector at LEP in 1992. Thes-quark was tagged by the presence of high momentum charged kaons identified by the Ring Imaging Cherenkov detector and byΛ 0;s decaying intopπ−. Thes-quark purity obtained was estimated for the two hadrons to be 43%. The averages-quark asymmetry was found to be 0.131±0.035 (stat.) ±0.013 (syst.). The forward-backward asymmetry was measured for unresolvedd-ands-quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combinedd-ands-quark purity was 69% and their asymmetry was found to be 0.112±0.031 (stat.) ±0.054 (syst.).

We compute the rates for pp annihilation into chargino pairs via the Drell-Yan process taking into account the effects of supersymmetric soft phases, at a proton-proton collider. In particular, the phase of the \ensuremath{\mu} parameter gains direct accessibility via the production of dissimilar charginos. The phases of the trilinear soft masses do not have a significant effect on the cross sections.

A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K+, K0, p, Λ and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.

The hadronic photon structure functionF 2 γ has been measured in theQ 2 range from 4 to 30 GeV2/c 4 and down tox values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with severalF 2 γ parameterizations with special emphasis on their lowx behaviour. A result on theQ 2 evolution ofF 2 γ is presented.

The readout proportional chambers of the HPC electromagnetic calorimeter in the DELPHI experiment are affected by large ageing. In order to study the calorimeter long-term behaviour, one HPC module was extracted from DELPHI in 1992 and was brought to a test area where it was artificially aged during a period of two years; an ageing level exceeding that expected for the HPC at the end of the LEP era was reached. During this period the performance of the module was periodically tested by means of dedicated beam tests whose results are discussed in this paper. These show that ageing has no significant effects on the response linearity and on the energy resolution for electromagnetic showers, once the analog response loss is compensated for by increasing the chamber gain through the anode voltage.

An upper limit for BR(Z0 → 3g) is obtained from a correlation method, which distinguishes statistically between quark and gluon jets by using the difference in their charged particle multiplicity distributions. From the sample of threefold symmetric three-jet events collected by the DELPHI experiment at LEP during 1991–1994, the 95% confidence level upper limit is deduced to be: BR(Z0 → 3g) ≤ 1.6 × 10−2 for the JADE and BR(Z0 → 3g) ≤ 1.5 × 10−2 for the DURHAM jet-finder.

A search has been made for direct production of heavy quarkonium states in more than 3 million hadronicZ 0 decays in the 1991–1994 DELPHI data. PromptJ/ψ, ψ(2S) andΓ candidates have been searched for through their leptonic decay modes using criteria based on the kinematics and decay vertex positions. New upper limits are set at the 90% confidence level forBr(Z 0→(Qq)X)/Br(Z 0→ hadrons) for various strong production mechanisms ofJ/ψ andΓ; these range down to 0.9×10−4. The limits are set in the presence of a small excess (∼1% statistical probability of a background fluctuation) in the sum of candidates from promptJ/ψ, ψ(2S),γ(1S),γ(2S) andγ(3S) relative to the estimated background.

We compute the rates for $q \bar{q}$ annihilation into charginos and neutralinos by taking into account the effects of supersymmetric soft phases. In particular, the phase of the $\mu$ parameter gains direct accessibility via the production of dissimilar charginos and neutralinos. The phases of the trilinear soft masses do not have a significant effect on the cross sections. Our results can be important for sparticle searches at the LHC.

A search with the DELPHI detector at LEP for excited leptons ($e^*$, $\mu^*$, $\tau^*$ and $\nu^*$) decaying through $\gamma$, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb$^{-1}$ at an $e^+e^-$ centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits $m_{e^*} 79.6 $ GeV/$c^2$, $m_{\mu^*} 79.6$ GeV/$c^2$, $m_{\tau^*} 79.4$ GeV/$c^2$ and $m_{\nu^*} 56.4$ GeV/$c^2$ at 95\% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio $\lambda/m_{\ell^*}$ of the coupling of the excited lepton to its mass.

In this thesis a report is given on hardware work done on the DELPHI detector and a measurement of the inclusive branching ratios of decays. A sample of 16454 events collected by the DELPHI experiment at LEP in 1992 is used to measure the inclusive branching ratios of decays. The results are B( 1 charged particle) = 84.38 0.27 0.35 , B( 3 charged particles) = 14.90 0.27 0.23 and B( 5 charged particles) = 0.51 0.12 0.11 .

From a sample of 1.5 millionZ 0→qq decays collected by the DELPHI detector during 1991, 1992 and 1993, the production cross section for isolated final state photons is measured and is compared with theO(α, α s) matrix element calculations implemented in the EEPRAD and GNJETS Monte Carlo generators. The observed photon yield is used to derive the electroweak couplings of charge 2/3 (u-type) and charge 1/3 (d-type) quarks to theZ 0 boson. The measured valuesc 2/3=0.91 −0.36 +0.25 andc 1/3=1.62 −0.17 +0.24 are compatible with the Standard Model prediction,c 2/3=1.145 andc 1/3=1.477.