M. Déjardin

We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of K0 transforming into K0 and K0 into K0 as a function of the neutral-kaon eigentime t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time t=0 was tagged by the kaon charge in the reaction pp→K±π∓K0(K0) at rest, whereas the strangeness of the kaon at the decay time t=τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry〈R(K0t=0→e+π−νt=τ)−R(K0t=0→e−π+νt=τ)R(K0t=0→e+π−νt=τ)+R(K0t=0→e−π+νt=τ)〉=(6.6±1.3stat±1.0syst)×10−3was measured over the interval 1τS<τ<20τS, thus leading to evidence for time-reversal non-invariance.

We use fits to recent published CPLEAR data on neutral kaon decays to π+π− and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.

The EPR-type strangeness correlation in the K0K0 system produced in the reaction pp→K0K0 at rest has been tested using the CPLEAR detector. The strangeness was tagged via strong interaction with absorbers away from the creation point. The results are consistent with the QM non-separability of the wave function and exclude a spontaneous wave-function factorisation at creation (CL >99.99%).

We report on the multiple wavelength laser monitoring system designed for the compact muon solenoid (CMS) lead tungstate crystal calorimeter. Results are presented for the test-beam performance of the system designed to achieve ⩽0.2% relative optical transmittance inter-calibration for 75 848 lead tungstate crystals. The system cycles continuously over the calorimeter to follow each crystal's evolution under the irradiation and recovery periods foreseen during operation at the LHC.

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at $ \sqrt {s} = 7\;{\text{TeV}} $ is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 pb−1. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398GeV/c 2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c 2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.

A measurement of the top-antitop production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV has been performed at the LHC with the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three or more hadronic jets. The kinematic properties of the events are used to separate the top-antitop signal from W+jets and QCD multijet background events. The measured cross section is 173 + 39 - 32 (stat. + syst.) pb, consistent with standard model expectations.

The charge asymmetry in the production of top quark and antiquark pairs is measured in proton-proton collisions at a center-of-mass energy of 8 TeV. The data, corresponding to an integrated luminosity of 19.6 inverse femtobarns, were collected by the CMS experiment at the LHC. Events with a single isolated electron or muon, and four or more jets, at least one of which is likely to have originated from hadronization of a bottom quark, are selected. A template technique is used to measure the asymmetry in the distribution of differences in the top quark and antiquark absolute rapidities. The measured asymmetry is A[c,y] = [0.33 +/- 0.26 (stat) +/- 0.33 (syst)]%, which is the most precise result to date. The results are compared to calculations based on the standard model and on several beyond-the-standard-model scenarios.

The high-luminosity phase of operation of the CERN Large Hadron Collider (HL-LHC) will pose new challenges to the detectors and their readout electronics. In particular, the Compact Muon Solenoid (CMS) barrel electromagnetic calorimeter will require a full redesign of the electronic readout chain in order to cope with the increase in luminosity and trigger rate. In this framework, a new application-specific integrated circuit (ASIC) integrating A/D conversion, lossless data compression, and high-speed transmission has been developed and tested. The ASIC, named Lisboa-Torino Ecal Data Transmission Unit (LiTE-DTU), is designed in a commercial CMOS 65-nm process and embeds two 12-bit, 160-MS/s analog-to-digital converters (ADCs), a data selection and compression logic, and a 1.28-Gb/s output serial link. The high-speed 1.28-GHz clock is generated internally from the 160-MHz input by a clock multiplication phase-locked loop (PLL). The circuit has been designed implementing radiation-tolerant techniques in order to work in the harsh environment of the HL-LHC upgrade. The LiTE-DTU is currently in the preproduction phase. A sample of 600 chips has been tested and incorporated into front-end (FE) boards for systems performance testing.

We have improved by two orders of magnitude the limit currently available for the CPT violation parameter Re(δ). To this purpose we have analyzed the full sample of neutral-kaon decays to eπν recorded in the CPLEAR experiment, where the strangeness of the neutral kaons was tagged at production and decay time. An appropriate function of the measured decay rates, including information from the analysis of π+π− decay channel, gives directly Re(δ). The result Re(δ)=(3.0±3.3stat±0.6syst)×10−4 is compatible with zero. Values for the parameters Im(δ), Re(x−) and Im(x+) were also obtained.

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.

The CPLEAR collaboration has constructed a detector at CERN for an extensive programme of CP-, T- and CPT-symmetry studies using K0 and K0 produced by the annihilation of p's in a hydrogen gas target. The K0 and K0 are identified by their companion products of the annihilation K±π∓ which are tracked with multiwire proportional chambers, drift chambers and streamer tubes. Particle identification is carried out with a liquid Cherenkov detector for fast separation of pions and kaons and with scintillators which allow the measurement of time of flight and energy loss. Photons are measured with a lead/gas sampling electromagnetic calorimeter. The required antiproton annihilation modes are selected by fast online processors using the tracking chamber and particle identification information. All the detectors are mounted in a 0.44 T uniform field of an axial solenoid of diameter 2 m and length 3.6 m to form a magnetic spectrometer capable of full on-line reconstruction and selection of events. The design, operating parameters and performance of the subdetectors are described.

Data from the CPLEAR experiment, together with the most recent world averages for some of the neutral-kaon parameters, were constrained with the Bell–Steinberger (or unitarity) relation, allowing the T-violation parameter Re(ϵ) and the CPT-violation parameter Im(δ) of the neutral-kaon mixing matrix to be determined with an increased accuracy: Re(ϵ)=(164.9±2.5)×10−5, Im(δ)=(2.4±5.0)×10−5. Moreover, the constraint allows the CPT-violation parameter for the neutral-kaon semileptonic decays, Re(y), to be determined for the first time. The ΔS≠ΔQ parameters Re(x−) and Im(x+) are given with an increased accuracy. The quantity Re(y+x−), which enters the T-violation CPLEAR asymmetry previously published, is determined to be (−0.2±0.3)×10−3. The value obtained for Re(δ) is in agreement with the one resulting from a previous unconstrained fit and has a slightly smaller error.

LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

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.

We test the Principle of Equivalence for particles and antiparticles, using CPLEAR data on tagged K0 and K0bar decays into pi^+ pi^-. For the first time, we search for possible annual, monthly and diurnal modulations of the observables |eta_{+-}| and phi_{+-}, that could be correlated with variations in astrophysical potentials. Within the accuracy of CPLEAR, the measured values of |eta_{+-}| and phi_{+-} are found not to be correlated with changes of the gravitational potential. We analyze data assuming effective scalar, vector and tensor interactions, and we conclude that the Principle of Equivalence between particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10^{-9}, respectively, for scalar, vector and tensor potentials originating from the Sun with a range much greater than the distance Earth-Sun. We also study energy-dependent effects that might arise from vector or tensor interactions. Finally, we compile upper limits on the gravitational coupling difference between K0 and K0bar as a function of the scalar, vector and tensor interaction range.

The CP violation parameter η+− is determined through the eigentime-dependent asymmetry in the rates of initially tagged K0 and K0 decaying to π+π−. The obtained values are |η+−| = (2.312 ± 0.043stat. ± 0.030syst. ± 0.011τs) × 10−3 and Φ+− = 42.7° ± 0.9stat.° ± 0.6syst.° ± 0.9Δm° with Δ = (527.4 ± 2.9) × 107h̵gs−1 measured in the same experiment using the semileptonic decay channel.

We report a measurement of the CP violation parameter η+− from the time-dependent asymmetry between the decay rates of initially tagged K0 and K0. The results are based on the complete data sample collected by the CPLEAR collaboration. With Δm=(530.1±1.4)×107ℏs−1 and τS=(89.34±0.08) ps, the values obtained are |η+−|=(2.264±0.023stat±0.026syst±0.007τS)×10−3 and φ+−=43.19°±0.53°stat±0.28°syst±0.42°Δm.

We report on a new measurement of the KL–KS mass difference Δm using the CPLEAR full data sample of neutral-kaon decays to eπν. The result is Δm=(0.5295±0.0020stat±0.0003syst)×1010 ℏ/s. It includes earlier data reported in R. Adler et al., CPLEAR Collaboration, Phys. Lett. B 363 (1995) 237. A measurement of the ΔS=ΔQ violating parameter Re(x) is also obtained.

We report the first determination of CP violation parameters from parameter from particle—antiparticle asymmetry in the decay of neutral kaons into two charged pions. Observation of such an asymmetry is direct proof of CP violation. A fit to the asymmetry enabled a determination of the parameter η+− to be made, yielding the result |η+−|=[2.32±0.14 (stat.)±0.03 (syst.)]×10−3 and σ+−=42.3°±4.4° (stat.)±0.4° (syst.), with an additional uncertainty of ±1.0° due to the error on the present published value of Δm, the KL0-KS0 mass difference. The magnitudes of both statistical and systematic errors will be significantly reduced in the future.

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.

We present a new measurement of the KL-KS mass difference (Δm) using semileptonic decays of neutral kaons. The measurement yields Δm = (0.5274 ± 0.0029stat. ± 0.0005syst.) × 1010ħ/s.

The ratio of the branching fractions for pp→K+K− and pp→π+π− was determined with the CPLEAR detector, by stopping antiprotons in a gaseous hydrogen target at 15 bar pressure. It was found to be BR(K+K−)/BR(π+π−)=0.205± 0.016. The fraction of P-wave annihilation at rest at this target density was deduced to be (38±9)%.

The neutral kaon regeneration amplitude in carbon at momenta between 250 and 750 MeV/c was determined by measuring the interference of inherent and coherently regenerated KS amplitudes. This interference appears in the rates of initially pure (tagged) K0 and K0 decaying to π+π− after crossing a carbon absorber.

The CPLEAR experiment measured time-dependent decay-rate asymmetries of K0 and K0 decaying to π+π−π0 in order to study the interference between the decay amplitudes of KS0 — either CP-violating or CP-conserving — and the CP-conserving KL0 decay amplitude. From the analysis of the complete data set we find for the CP-violating parameter η+−0, Re(η+−0) = (−2 ± 7 stat. −1+4 syst.) × 10−3, Im(η+−0) = (−2 ± 9 stat. −1+2 syst.) × 10−3 and for the CP-conserving parameter λ, Re(λ) = (+28 ± 7 stat. ± 3 syst.) × 10−3, Im(λ) = (−10 ± 8 stat. ± 2 syst.) × 10−3. From the latter, the branching ratio of the CP-conserving K0S → π+π−π0 decay is deduced to be B = (2.5−1.0+1.3 stat. −0.6+0.5 syst.) × 10−7.

The CPLEAR experiment measured the eigentime-dependent asymmetry in the rates of initially tagged K0 and K0 decaying to π0π0π0 in order to study the interference between the CP-violating KS and the CP-conserving KL decay amplitudes. Without assuming CPT invariance, we obtain for the CP-violation parameter η000 the values Re(η000)=0.18±0.14stat.±0.06syst. and Im(η000)=0.15±0.20stat.±0.03syst.. Requiring Re(η000) to be equal to Re(ϵ) we obtain Im(η000)=−0.05±0.12stat.±0.05syst.. The corresponding upper limit for the branching ratio of the KS→π0π0π0 decay is deduced to be BKS→π0π0π0<1.9×10−5 at the 90% confidence level.

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.

The best estimation of ϕ+− (the phase of the CP violation parameter η+−) and of Δm (the KL - KS mass difference) is obtained by averaging the results of different experiments, taking into account the different correlation, existing for most of the experiments, between the measurement of ϕ+− and Δm. Including the recent measurements, we obtain the average values 〈Δm〉 = (530.7 ± 1.3) × 107 ħ/s and 〈ϕ+−〉 = 43.82° ± 0.63°. This value of ϕ+− is in good agreement with the superweak phase ϕSW = 43.49° ± 0.08°.

The incoming LHC upgrade to HL-LHC calls for a change of the ECAL front-end electronics design in order to maintain the present performance of the detector while facing a higher instantaneous luminosity and to optimize the timing resolution while using the existing crystals and APDs.The design of the new front-end electronics is based on the cascading of two ASIC: a fast, dual gain trans-impedance amplifier designed in a 130 nm CMOS process (named CATIA) and a dual ADC designed in a 65 nm CMOS process.The latest test-beam and laboratory test results of CATIA coupled with an ADC will be presented.

The CPT-violation parameters Re(δ) and Im(δ) determined recently by CPLEAR are used to evaluate the K0–K̄0 mass and decay-width differences, as given by the difference between the diagonal elements of the neutral-kaon mixing matrix (M−iΓ/2). The results – (MK0K0−MK̄0K̄0)=(−1.5±2.0)×10−18 GeV and (ΓK0K0−ΓK̄0K̄0)=(3.9±4.2)×10−18 GeV – are consistent with CPT invariance. The CPT invariance is also shown to hold within a few times 10−3–10−4 for many of the amplitudes describing neutral-kaon decays to different final states.

Neutral-kaon decays to πeν were analysed to determine the q2 dependence of the K0e3 electroweak form factor f+. Based on 365612 events, this form factor was found to have a linear dependence on q2 with a slope λ+=0.0245±0.0012stat±0.0022syst.

Located between the on-detector front-end electronics and the global data acquisition system (DAQ), the off-detector electronics of the CMS electromagnetic calorimeter (ECAL) is involved in both detector readout and trigger system. Working at 40 MHz, the trigger part must, within ten clock cycles, receive and deserialize the data of the front-end electronics, encode the trigger primitives using a nonlinear scale, assure time alignment between channels using a histogramming technique and send the trigger primitives to the regional trigger. In addition, it must classify trigger towers in three classes of interest and send this classification to the readout part. The readout part must select the zero suppression level to be applied depending on the regions of interest determined from the trigger tower classification, deserialize front-end data coming from high-speed (800 Mb/s) serial links, check their integrity, apply zero suppression, build the event and send it to the DAQ, monitor the buffer occupancy and send back pressure to the trigger system when required, provide data spying and monitoring facilities for the local DAQ. The system, and especially the data link speed, the latency constraints and the bit-error rate requirements have been validated on prototypes. Part of the system is about to go to production.

A search is performed for the production of a massive W′ boson decaying to a top and a bottom quark. The data analysed correspond to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in proton-proton collisions at $$ \sqrt{s}=8 $$ TeV. The hadronic decay products of the top quark with high Lorentz boost from the W′ boson decay are detected as a single top flavoured jet. The use of jet substructure algorithms allows the top quark jet to be distinguished from standard model QCD background. Limits on the production cross section of a right-handed W′ boson are obtained, together with constraints on the left-handed and right-handed couplings of the W′ boson to quarks. The production of a right-handed W′ boson with a mass below 2.02 TeV decaying to a hadronic final state is excluded at 95% confidence level. This mass limit increases to 2.15 TeV when both hadronic and leptonic decays are considered, and is the most stringent lower mass limit to date in the tb decay mode.

The time-dependent rate asymmetry of initial K0 and K0 decaying into π+π−π0 was measured in order to reveal the CP-violating amplitude of the KS → π+π−π0 decay. For the real and the imaginary parts of η+−0, we find Re(η+−0) = (6 ± 13stat. ± 1syst.) × 10−3 and Im(η+−0) = (−2 ± 18stat. ± 3syst.) × 10−3 which correspond to |η+−0| < 0.037 with CL.

The interference between CP-conserving Ks and KL → π+π−π0 decay amplitudes was observed by studying the decay rate asymmetries between initial K0 and K0 separately for the phase space regions ECM(π+) > ECM(π−) and ECM(π+) < ECM(π−). For the parameter λ we found Re(λ) = 0.036 ± 0.010(stat.)−0.003+0.002(syst.) and Im(λ) consistent with zero, leading to a branching ratio B = [4.1−1.9+2.5(stat.)−0.6+0.5(syst.)] × 10−7 for the CP-conserving KS → π+π−π0 decay.

The ratio R between the branching fractions of pp → KSKS and pp → KSKL for antiprotons annihilating at rest in gaseous hydrogen at 27 bar pressure was measured with the CPLEAR detector to be R(27 bar) = 0.037 ± 0.002. The fraction of P-wave annihilation at rest at this target density was deduced to be 0.45 ± 0.06. A value of R was also measured at 15 bar, with less statistics, yielding R(15 bar) = 0.041 ± 0.009.

The CPLEAR set-up (modified) has been used to determine the KL–KS mass difference by a method where neutral-kaon strangeness oscillations are monitored through kaon strong interactions, rather than semileptonic decays, thus requiring no assumptions on CPT invariance for the decay amplitudes. The result, Δm=(0.5343±0.0063stat±0.0025syst)×1010ℏ/s, provides a valuable input for CPT tests.

Two-charged-pion correlations were studied in $$\bar p$$ p(→2π*2π− nπ0,n≥0) annihilations at rest with the CPLEAR detector at the Low-Energy Antiproton Ring (LEAR). A strong enhancement was found in the production of pairs of like-sign pions with a small value of the relative fourmomentumQ, with respect to pairs of unlike-sign pions. The observed enhancement was interpreted as a consequence of the Bose-Einstein symmetrization of the two-pion wave function. The data are well represented by a correlation function parametrized as a double-Gaussian; an exponential parametrization is also statistically acceptable. The value of the correlation strength is found to be >1. The high-quality large data samples together with the ability for K± identification and final-state separation allowed the study of systematic effects impacting on theQ dependence of the correlation function and on the extracted space parameters of the pion sources.

The CP-violation parameter η00 is determined through the eigentime-dependent asymmetry in the rates of initially tagged K0 and K0 decaying to π0 π0. From the analysis of the complete data set we obtain the values |η00|=[2.47±0.31stat.±0.24syst.]×10−3 and φ00=42.00±5.6stat.0±1.9syst.0.

Maintaining the required performance of the CMS electromagnetic calorimeter (ECAL) barrel at the High-Luminosity Large Hadron Collider (HL-LHC) requires the replacement of the entire on-detector electronics. 12240 new very front end (VFE) cards will amplify and digitize the signals of 62100 lead-tungstate crystals instrumented with avalanche photodiodes. The VFE cards host five channels of CATIA pre-amplifier ASICs followed by LiTE-DTU ASICs, which digitize signals with 160MS/s and 12bit resolution. We present the strategy and infrastructure developed for achieving the required reliability of less than 0.5% failing channels over the expected lifetime of 20 years. This includes the choice of standards, design for reliability and manufacturing, as well as factory acceptance tests, reception testing, environmental stress screening and calibration of the VFE cards.

Bose-Einstein (BE) correlations between like-sign charged pions were studied in pp annihilations at rest into four-prong events, using data taken with the CPLEAR detector at LEAR (CERN). A strong enhancement was found in the production of pairs of like-sign pions of similar momenta, with respect to the pairs of unlike-sign pions. The observed BE- enhancement was used to extract the values for the strength λ of the effect and the radius r of the pion emitting source. The extracted value of λ >l is of relevant importance and clearly does not depend on the assumed parametrization of the correlation function. The influence of the normalization and fitting procedure, the detector resolution, the resonances production and decay and the neutral-pion multiplicity cuts, on the size of the pion source and the strength of the effect was investigated.

The CMS ECAL barrel electronics will be upgraded for the HL-LHC to meet the latency and bandwidth requirements of the Phase-II Level-1 trigger system. The new front-end electronics will mitigate the increasing noise from the avalanche photodiodes (APDs), discriminate against anomalous APD signals and provide improved timing information. The foreseen solution is to replace the current Charge-Sensitive-Amplifier with a Trans-Impedance Amplifier, which should provide the extra bandwidth needed to maintain the integrity of the detector signal shape. The first ASIC prototype, called CATIA, has been successfully designed in TSMC 130 nm CMOS technology and its test results will be presented.

Located between the on-detector front-end electronics and the global data acquisition system (DAQ), the off-detector electronics of the CMS electromagnetic calorimeter (ECAL) is involved in both detector readout and trigger system. Working at 40 MHz, the trigger part must, within 10 clock cycles, receive and deserialise the data of the front-end electronics, encode the trigger primitives using a non linear scale, assure time alignment between channels using a histogramming technique and send the trigger primitives to the regional trigger. In addition, it must classify trigger towers in three classes of interest and send this classification to the readout part. The readout part must select the zero suppression level to apply depending on the regions of interest determined from the trigger tower classification, deserialise front-end data coming from high-speed (800 Mbit/s) serial links, check their integrity, apply zero suppression, build the event and send it to the DAQ, monitor the buffer occupancy and send back pressure to the trigger system when required, provide data spying and monitoring facilities for the local DAQ. The system, and especially the data link speed, the latency constraints and the bit error rate requirements have been validated on prototypes. Part of the system is about to go to production.

Abstract By highlighting a particular example of track fitting with geometrical and kinematical constraints of events from a particle physics experiment simulated annealing and backprop neural networks are investigated as alternative optimization methods. The two methods are different in the way that simulated annealing suffers from the enormous amount of function evaluations required while a trained neural network requires negligible computing time. This makes the former unpractical to use in analysis of large amounts of data, but we find that using any of these methods to compute start values has significant impact on the convergence of the constrained fits. Further, it enables us to reduce and estimate the effects introduced by the optimization algorithm. For our case of kinematic and geometric fitting of p p → K 0 K ± π ± Monte Carlo events we find that the rate of non-convergence, in the case that the standard analytical minimization did not work using the measured values as the start values, changes up to 40% when making a second attempt with start values from a global optimizer.

Abstract We are presenting here the track detector constructed by Saclay/DPhPE for PS195 which will be installed at LEAR in March 1989.

Antiproton annihilation at rest in gaseous hydrogen (16 bar pressure) to the final states ρ(770)X andf 2(1270)X, whereX stands for one or more neutral mesons, has been studied at LEAR using the CPLEAR detector. Relative branching ratios are given forX =π 0,2π 0, 3π 0 ω in the ρ case, and forX =π 0, η in thef 2 case. The annihilation channel $$\bar pp \to \rho 3\pi ^0 $$ has not been measured before. The fraction of P-wave annihilation is deduced from the ratiof 2 π 0/ρπ 0 to be 0.38±0.07, in good agreement with the result previously obtained by CPLEAR from the ratioK + K -/π + π -.

The CPLEAR experiment uses tagged K0 and K0 produced in pp annihilation at rest to measure CP-, T- and CPT-violation parameters in the neutral kaon system. The results of these measurements and some implications are reported.

The CPLEAR experiment uses tagged K0 and K̄0 produced in pp̄ annihilation at rest to measure CP-, T- and CPT-violation parameters in the neutral kaon system. The results of these measurements and some implications are reported.

A search for massive resonances decaying to a Z boson and a photon is performed in events with a hadronically decaying Z boson candidate, separately in light-quark and b quark decay modes, identified using jet substructure and advanced b tagging techniques. Results are based on samples of proton-proton collisions collected with the CMS detector at the LHC at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 2.7 inverse femtobarns, respectively. The results of the search are combined with those of a similar search in the leptonic decay modes of the Z boson, based on the same data sets. Spin-0 resonances with various widths and with masses in a range between 0.2 and 3.0 TeV are considered. No significant excess is observed either in the individual analyses or the combination. The results are presented in terms of upper limits on the production cross section of such resonances and constitute the most stringent limits to date for a wide range of masses.

The inelastic hadronic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of 12.6 +/- 0.4 inverse nanobarns, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton-lead collisions with hadronic activity produced in the pseudorapidity ranges 3<abs(eta)<5 and/or -5<abs(eta)<-3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be sigma[inel,pPb]=2061 +/- 3 (stat) +/- 34 (syst) +/- 72 (lum) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of sigma[inel,pPb] is compatible with that expected from the proton-proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.

A measurement of the ttbar production cross section at sqrt(s)=13 TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.3 inverse femtobarns, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be sigma(ttbar)= 835 +/- 3 (stat) +/- 23 (syst) +/- 23 (lum) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m[t]), the value of m[t] is found to be 172.7+2.4-2.7 GeV.

The CPLEAR experiment at CERN measures the time dependent decay rate asymmetries of initially pure K0 and K0 states to study CP,T and CPT symmetries in the neutral kaon system. The latest results on η+−, Δm and x are reported, as well as direct tests of T violation and CPT violation in K0-K0 oscillations. Our results are consistent with CPT invariance and allow for an improved limit on the K0-K0 mass difference. Further, a possible loss of quantum coherence of the neutral kaon system has been tested to a level near the Planck scale.

We present the physics results of the CP{ and CPT{violation measurements performed by CPLEAR.CPLEAR has experimentally determined, for the rst time, the violation of T invariance and is able to disentangle all the CP{ and CPT{violating quantities from each other.This allows each of the CPT violating parameters to bedetermined with a precision of a few 10 4 and, in particular, the mass and width equality b e t w een the K 0 and K 0 to be tested down to the level of 10 19 GeV.Moreover, the precision of the CPLEAR measurements allows us to probe for the rst time physics on a scale approaching the Planck mass.

We study ππ correlations in the exclusive reactions pp → 2π+2π− and pp → 2π+2π−π0 at rest with complete reconstruction of the kinematics for each event. A new analysis technique has been developed which is model independent. With this new technique, which relies on double-differential distributions, no reference sample is needed to extract the correlation signal. The correlations are studied as a function of the four-pion invariant mass.

The CMS electromagnetic calorimeter consists of about 76000 lead tungstate crystals. A brief description of the readout electronics chain of the calorimeter is given. About 15000 Very Front End (VFE) cards amplify, shape and digitize the signals of the photo-detectors attached to the crystals. The production and the test program for these VFE cards are presented. The test program includes the power on test, the burn in and the calibration of the read out channels. Preliminary results of the tests performed on 420 pre-series VFE cards are presented.

The method for studying semileptonic neutral kaon decays at CPLEAR is presented together with a preliminary data analysis. For the first time a direct determination of T violation is shown to be possible and low statistics results are given. From the same data the KL-KS mass difference, Δm, the CP violation parameter of KS, ϵs, and the parameter x testing the ΔS = ΔQ rule are also obtained.

Physics in Collision 19, pp. 320-335 (2000) No AccessSTUDIES OF THE CP, T AND CPT SYMMETRIES IN THE NEUTRAL KAON SYSTEMR. LE GACR. LE GACCentre de Physique des Particules de Marseille, CNRS/IN2P3–Université de la Méditerranée, 163 avenue de Luminy, Case 907, F–13288 MARSEILLE, Francehttps://doi.org/10.1142/9789812792648_0022Cited by:0 (Source: Crossref) PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: In this contribution, we review the experimental results on the studies of the CP, T and CPT symmetries in the neutral kaon system. FiguresReferencesRelatedDetails Recommended Physics in Collision 19Metrics History PDF download

The CPLEAR experiment at CERN has directly studied matter and antimatter symmetries via the measurement of the time evolution of K0 and K̄0. The CPT violation parameter Re(δ) was directly measured with a precision of a few 10−4 while Im(δ) is determined from the Bell-Steinberger relation, with a precision of 10−5. The mass and decay-width equality between the K0 and K̄0 were tested down to the level of 10−18 GeV.

Using strangeness tagging at production time, CPLEAR measures time-dependent decay rate asymmetries between $K^0$ and $\bar{K}^0$, for picnic and semileptonic decays. Parameters describing CP, T, and CPT violation can be obtained with high precision. In the semileptonic channels neutral kaons are strangeness tagged also at the decay time, by the lepton charge, thus allowing the difference between the transition rates of $\bar{K}^0 \to K^0$ and $K^0 \to \bar{K}^0$ to be measured. In this way CPLEAR obtains the first direct measurement of T violation. By fitting the semileptonic rates under the constraint of the unitarity relation, we prove that in the reported measurement T violation is not mocked by CPT-violation effects in the decay amplitudes. Other CPLEAR measurements, only in part reported here, contribute to the experimental accuracy of the unitarity relation.

The CPLEAR experiment at CERN measured the CP and CPT violation parameters and determined in a direct way the T violation. The results allow the determination of the CPT violation parameters in the neutral kaon mixing with a precision better than a few 10−4. The mass equality between K0 and K̃0 is tested down to the level of 10−19 GeV. In addition, physics on a scale close to the Planck mass is probed for the first time.

A measurement of the branching ratio for KS→e+e− decay was performed with the CPLEAR detector at LEAR. Full event reconstruction together with calorimeter e/π separation allowed for powerful background rejection and high signal acceptance. The analysis on the complete set of data yields the result: BR(KS→e+e−)<1.4⋅10−7 (90% CL), an improvement on the current experimental limit by a factor of 20.

Using strangeness tagging at production time, CPLEAR measures K0/K̄0 time-dependent asymmetries in pionic and semileptonic kaon decays. From those, a set of parameters describing CP, T and CPT violation in neutral kaon mixing and decay can be determined. Strangeness tagging at decay time with the lepton charge allows for time-reversal violation to be directly observed with a significance of more than three standard deviations. The precision on each of the CPT violation parameters is discussed. The mass equality of the K0 and K̄0 is tested within 4.×10−19 GeV.

A measurement of the branching ratio for Ks → e+e− decay was performed with the CPLEAR detector at LEAR. Full event reconstruction together with calorimeter e/π separation allowed for powerful background rejection and high signal acceptance. Analysis of data taken up to 1994 yields the result: Br(Ks → e+e−) < 4.2 · 10−7 (90 % CL).

The CPLEAR experiment at CERN uses time-dependent decay-rate asymmetries between K0 and K̄0 to measure η+−. The analysis and the systematic errors are discussed. The preliminary results from all our data are φ+− = 43.50 ± 0.50stat ± 0.5syst ± 0.4Δm and |η+−| = (2.316 ± 0.025stat ± 0.028syst ± 0.009τS) × 10−3. The dominant part in the systematic error of φ+− is due to the regeneration correction. A dedicated experiment was performed to reduce this error considerably.

The CPLEAR experiment at CERN studies theCP, T andCPT symmetries in the neutral-kaon system by measuring the rate asymmetries between the decays of initially pure K0 and $$\overline {K^0 } $$ states. Using data taken between 1990 and mid 1994, precise measurements of |η+-|,φ +- and Δm are reported. The comparison of φ+- the superweak phase gives one of the most sensitive tests ofCPT invariance and leads to a new limit on the $$K^0 - \overline {K^0 } $$ mass difference.

Studies of the practices of the documentalists in the information retrieval on the Web by the means of social navigation (Dourish and Chalmers).

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation R. Adler, T. Alhalel, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, C. P. Bee, O. Behnke, J. Bennet, V. Bertin, F. Blanc, P. Bloch, Ch. Bula, P. Carlson, M. Carroll, J. Carvalho, E. Cawley, S. Charalambous, M. Chardalas, G. Chardin, M. B. Chertok, M. Danielsson, A. Cody, S. Dedoussis, M. Dejardin, J. Derre, M. Dodgson, J. Duclos, A. Ealet, B. Eckart, C. Eleftheriadis, I. Evangelou, L. Faravel, P. Fassnacht, J. L. Faure, C. Felder, R. Ferreira‐Marques, W. Fetscher, M. Fidecaro, A. Filipc̆ic̆, D. Francis, J. Fry, E. Gabathuler, R. Gamet, D. Garreta, T. Geralis, H.‐J. Gerber, A. Go, P. Gumplinger, C. Guyot, A. Haselden, P. J. Hayman, F. Henry‐Couannier, R. W. Hollander, E. Hubert, K. Jansson, H. U. Johner, K. Jon‐And, P. R. Kettle, C. Kochowski, P. Kokkas, R. Kreuger, T. Lawry, R. Le Gac, F. Leimgruber, A. Liolios, E. Machado, P. Maley, I. Mandić, N. Manthos, G. Marel, M. Mikuž, J. Miller, F. Montanet, T. Nakada, A. Onofre, B. Pagels, P. Pavlopoulos, F. Pelucchi, J. Pinto da Cunha, A. Policarpo, G. Polivka, H. Postma, R. Rickenbach, B. L. Roberts, E. Rozaki, T. Ruf, L. Sacks, L. Sakeliou, P. Sanders, C. Santoni, K. Sarigiannis, M. Schäfer, L. A. Schaller, A. Schopper, P. Schune, A. Soares, L. Tauscher, C. Thibault, F. Touchard, C. Touramanis, F. Triantis, D. A. Tröster, E. Van Beveren, C. W. E. Van Eijk, S. Vlachos, P. Weber, O. Wigger, C. Witzig, M. Wolter, C. Yeche, D. Zavrtanik, D. Zimmerman; CP, T, and CPT tests in neutral Kaon decays using tagged K0, K0at LEAR. AIP Conf. Proc. 10 May 1995; 334 (1): 816–821. https://doi.org/10.1063/1.48110 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

L'objet de cette these est la mise en uvre d'un detecteur constitue de six chambres a derive cylindriques concentriques. Il est destine a detecter le passage de particules chargees et de reconstruire leurs trajectoires dans un volume de 2 metres de long et de 50 cm de diametre. Dans une premiere partie, je presente les aspects theoriques du probleme qui est etudie dans l'experience ou prend place ce detecteur (violation de cp: chapitre 1). Puis, j'expose les differentes methodes experimentales envisageables pour etudier ce probleme theorique (chapitre 2). Je presente alors, l'experience dans laquelle prend place le detecteur (ps195: chapitre 3), et ensuite je detaille l'etude de ce detecteur central (chapitre 4): les contraintes experimentales et leurs consequences sur les caracteristiques mecaniques et electroniques; la fabrication des six chambres a derive qui constituent ce detecteur; la mise en uvre du detecteur dans l'experience; l'etude de la resolution et de l'efficacite de reconstruction des trajectoires realisee avec ce detecteur. Enfin, pour illustrer le fonctionnement du detecteur central, je presente les premiers resultats de physique obtenus grace a l'etude de la desintegration du k0 en pi-plus-pi-moins

We describe the status of experiment PS195, which is under way on LEAR at CERN to study CP violation starting with pure K0 or K̄0 states. Early results on backgrounds and systematic effects agree with expectations from the original proposal. An asymmetry in particle‐anti‐particle partial decay rates has been seen for the first time.

The CPLEAR experiment is aiming at precise CP violation tests using initially pure K0- andK0 beams from the intense source provided by the annihilation of the LEAR p-beam in hydrogen. The strangeness tagging efficiency and the systematic errors have been studied and found to be in agreement with the design specifications. The measurement of the differential time asymmetry of the π+π− decays allowed the direct observation of differences in the decay rates of particles and antiparticles. The CP violating parameters were determined as |ν±| = (2.32 ± 0.14) · 10−3 and ψ± = 42.3° ± 4.4°. First results in the reconstruction and analysis of the neutral kaon decays into two neutral pions and the Ke3 decay are presented.