P. Kokkas

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.

An already existing, sub-critical arrangement made of natural uranium and water moderator has been exposed to a low intensity (≈ 109 ppp) proton beam from CERN-PS at several kinetic energies from 600 MeV to 2.75 GeV. The energy delivered by the hadronic cascade induced by the beam in the device has been measured by the temperature rise of small sampling blocks of uranium located in several different positions inside the device and counting the fissions in thin probe foils of natural uranium. We find typically G ≈ 30 in reasonable agreement with calculations, where G is the ratio of the energy produced in the device to the energy delivered by the beam. This result opens the way to the realisation of the so-called Energy Amplifier, a practical device to produce energy from thorium or depleted uranium targets exposed to an intense high energy proton beam. Results show that the optimal kinetic is ≥ 1 GeV, below which G decreases but is still acceptable in the energy range explored

The goal of the DIRAC experiment at CERN (PS212) is to measure the $\pi^+\pi^-$ atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the $S$-wave $\pi\pi$ scattering lengths combination $|a_0-a_2|$. Based on part of the collected data we present a first result on the lifetime, $\tau=[2.91 ^{+0.49}_{-0.62}]\times 10^{-15}$ s, and discuss the major systematic errors. This lifetime corresponds to $|a_0-a_2|=0.264 ^{+0.033}_{-0.020} m_{\pi}^{-1}$.

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 summarize here the results of the TARC experiment whose main purpose is to demonstrate the possibility of using Adiabatic Resonance Crossing (ARC) to destroy efficiently Long-Lived Fission Fragments (LLFFs) in accelerator-driven systems and to validate a new simulation developed in the framework of the Energy Amplifier programme. An experimental set-up was installed in a CERN PS proton beam line to study how neutrons produced by spallation at relatively high energy (En⩾1MeV) slow down quasi-adiabatically with almost flat isolethargic energy distribution and reach the capture resonance energy of an element to be transmuted where they will have a high probability of being captured. Precision measurements of energy and space distributions of spallation neutrons (using 2.5 and 3.5 GeV/c protons) slowing down in a 3.3 m×3.3 m×3 m lead volume and of neutron capture rates on LLFFs 99Tc, 129I, and several other elements were performed. An appropriate formalism and appropriate computational tools necessary for the analysis and understanding of the data were developed and validated in detail. Our direct experimental observation of ARC demonstrates the possibility to destroy, in a parasitic mode, outside the Energy Amplifier core, large amounts of 99Tc or 129I at a rate exceeding the production rate, thereby making it practical to reduce correspondingly the existing stockpile of LLFFs. In addition, TARC opens up new possibilities for radioactive isotope production as an alternative to nuclear reactors, in particular for medical applications, as well as new possibilities for neutron research and industrial applications.

The DIRAC experiment at CERN has achieved a sizeable production of π+π− atoms and has significantly improved the precision on its lifetime determination. From a sample of 21 227 atomic pairs, a 4% measurement of the S-wave ππ scattering length difference |a0−a2|=(0.2533−0.0078+0.0080|stat|syst−0.0073+0.0078)Mπ+−1 has been attained, providing an important test of Chiral Perturbation Theory.

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 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.

Energy and space distributions of spallation neutrons (from 2.5 and 3.57 GeV/c CERN proton beams) slowing down in a 3.3 × 3.3 × 3 m3 lead volume and neutron capture rates on long-lived fission fragments 99Tc and 129I demonstrate that Adiabatic Resonance Crossing (ARC) can be used to eliminate efficiently such nuclear waste and validate innovative simulation.

The DIRAC spectrometer has been commissioned at CERN with the aim of detecting $\pi^+ \pi^-$ atoms produced by a 24 GeV/$c$ high intensity proton beam in thin foil targets. A challenging apparatus is required to cope with the high interaction rates involved, the triggering of pion pairs with very low relative momentum, and the measurement of the latter with resolution around 0.6 MeV/$c$. The general characteristics of the apparatus are explained and each part is described in some detail. The main features of the trigger system, data-acquisition, monitoring and setup performances are also given.

The armed invasion of Ukraine by the Russian Federation has adversely affected the relations between Russia and Western countries. Among other aspects, it has put scientific cooperation and collaboration into question and changed the scientific landscape significantly. Cooperation between some Western institutions and their Russian and Belarusian partners were put on hold after February 24, 2022. The CERN Council decided at its meeting in December 2023 to terminate cooperation agreements with Russia and Belarus that date back a decade. CERN is an international institution with UN observer status, and has so far played a role in international cooperation which was independent of national political strategies. We argue that the Science4Peace idea still has a great value and scientific collaboration between scientists must continue, since fundamental science is by its nature an international discipline. A ban of scientists participating in international cooperation and collaboration is against the traditions, requirements and understanding of science. We call for measures to reactivate the peaceful cooperation of individual scientists on fundamental research in order to stimulate international cooperation for a more peaceful world in the future. Specifically, we plead for finding ways to continue this cooperation through international organizations, such as CERN and JINR.

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.

The goal of the DIRAC experiment at CERN is to measure with high precision the lifetime of the $\pi^+\pi^-$ atom ($A_{2\pi}$), which is of order $3\times10^{-15}$ s, and thus to determine the s-wave $\pi\pi$-scattering lengths difference $|a_{0}-a_{2}|$. $A_{2\pi}$ atoms are detected through the characteristic features of $\pi^+\pi^-$ pairs from the atom break-up (ionization) in the target. We report on a first high statistics atomic data sample obtained from p Ni interactions at 24 GeV/$c$ proton momentum and present the methods to separate the signal from the background.

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 Transmutation by Adiabatic Resonance Crossing (TARC) experiment was carried out as PS211 at the CERN PS from 1996 to 1999. Energy and space distributions of spallation neutrons (produced by 2.5 and 3.57 GeV/c CERN proton beams) slowing down in a 3.3×3.3×3 m3 lead volume and neutron capture rates on long-lived fission fragments 99Tc and 129I demonstrate that Adiabatic Resonance Crossing (ARC) can be used to eliminate efficiently such nuclear waste and validate innovative simulation.

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°.

An automated recognition system has been developed which identifies, counts and classifies nuclear tracks on solid state nuclear track detectors (SSNTD). Special care is taken for overlapping tracks, allowing analysis of films with high track densities up to 60,000 tracks/cm2. The performance of the proposed method, with a counting error of 3% for a track density of 30,000 tracks/cm2, is superior to conventional track counting techniques when evaluating either CR-39 or Lexan SSNTDs. The recognition system evaluates each image in less than 2 s with a PC-486 at 66 MHz, allowing its integration in an on-line automated track detection set-up.

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.

The multilevel trigger system of the DIRAC experiment at CERN is presented. It includes a fast first level trigger as well as various trigger processors to select events with a pair of pions having a low relative momentum typical of the physical process under study. One of these processors employs the drift chamber data, another one is based on a neural network algorithm and the others use various hit-map detector correlations. Two versions of the trigger system used at different stages of the experiment are described. The complete system reduces the event rate by a factor of 1000 with respect to detectors’ single rates, the detection efficiency of events in the relative momentum range of interest being ⩾95%.

The CMS preshower is a fine grain detector that comprises 4288 silicon sensors, each containing 32 strips. The raw data are transferred from the detector to the counting room via 1208 optical fibres. Each fibre carries a 600-byte data packet per event. The maximum average level-1 trigger rate of 100 kHz results in a total data flow of ~72 GB/s from the preshower. For the readout of the preshower, 56 links to the CMS DAQ have been reserved, each having a bandwidth of 200 MB/s (2 kB/event). The total available downstream bandwidth of GB/s necessitates a reduction in the data volume by a factor of at least 7. A modular VME-based system is currently under development. The main objective of each VME board in this system is to acquire on-detector data from at least 22 optical links, perform on-line data reduction and pass the concentrated data to the CMS DAQ. The principle modules that the system is based on are being developed in collaboration with the TOTEM experiment.

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.

Abstract The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum; such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5.

The CPLEAR experiment will measure CP violation parameters in the neutral kaon system, using a low energy antiproton beam from the Low Energy Antiproton Ring (LEAR) at CERN. One of its subdetectors, the Particle Identification Detector (PID), makes a fast separation of pions and kaons, which is essential for the experiment. This article describes the design of the PID and its performance during beam tests and during initial runs at LEAR. A pion rejection efficiency of 99.7% for the first level trigger (after 60 ns) is found in the relevant momentum region.

The CMS Endcap Preshower (ES) sub-detector comprises 4288 silicon sensors, each containing 32 strips. The data are transferred from the detector to the counting room via 1208 optical fibres running at 800Mbps. Each fibre carries data from two, three or four sensors. For the readout of the Preshower, a VME-based system, the Endcap Preshower Data Concentrator Card (ES-DCC), is currently under development. The main objective of each readout board is to acquire on-detector data from up to 36 optical links, perform on-line data reduction via zero suppression and pass the concentrated data to the CMS event builder. This document presents the conceptual design of the Reduction Algorithms as well as their implementation in the ES-DCC FPGAs. These algorithms, as implemented in the ES-DCC, result in a data-reduction factor of 20.

The use of accelerator driven system (ADS) like for instance the Energy Amplifier concept (EA) proposed by C. Rubbia and his group might be one of the solutions to solve the energy problem and in particular to answer the question: what could we do with the nuclear waste produced by the present nuclear reactors? We present in this paper the EA concept, which is illustrated by two experiments performed at the CERN-PS facility. One of them is the TARC (Transmutation by Adiabatic Resonance crossing) experiment which is designed to demonstrate the high efficiency offered by the EA to destroy the long-lived fission fragments.

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.

A search for the decay KS → e+e− was performed within the framework of the CPLEAR experiment. Full event reconstruction together with e/π separation allowed powerful background rejection and high signal acceptance. The analysis of 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.

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.

To measure the CP violation in the neutral kaon system with initially pure K0 and K0 beams from the annihilation reaction pp → π± K∓ K0 (K0) a good separation of pions and kaons is necessary. The properties of a particle-identification device making this separation possible and consisting of a scintillator Cherenkov scintillator sandwich are presented.

The expected particle fluence in the inner part of the CMS Preshower is calculated to be 1.6×1014cm−2 for neutrons and 0.4×1014cm−2 for charged hadrons. Since the error of the calculation is high and/or unexpected accidental beam misalignments might happen we have irradiated Preshower silicon sensors to fluences up to 5×1014n/cm2 to verify that they hold voltages necessary to reach the full charge collection efficiency. All irradiated sensors showed no signs of breakdown up to 1000V, the maximum voltage applied. All but one display a sufficiently stable charge collection efficiency up to 1000V. No noisy channels were observed at the extreme voltages. The measured charge collection efficiency was 71±12% and 59±12% for sensors irradiated to 3×1014 and 5×1014n/cm2, respectively. These values are consistent with the extrapolation from previous measurements made on sensors irradiated to 2.3×1014n/cm2. The work presents the results of static and dynamic measurements and shows that our design and the technology are very robust.

During the first years of the LHC operation a large amount of jet data was recorded by the ATLAS and CMS experiments. In this review several measurements of jet-related observables are presented, such as multi-jet rates and cross sections, ratios of jet cross sections, jet shapes and event shape observables. All results presented here are based on jet data collected at a centre-of-mass energy of 7 TeV. Data are compared to various Monte Carlo generators, as well as to theoretical next-to-leading-order calculations allowing a test of perturbative Quantum Chromodynamics in a previously unexplored energy region.

The analysis of 150 GeV/c muon data collected during a test of a CMS Preshower prototype is presented. The test took place in 2004 in the H4 beam at CERN. The muon signal extraction is possible after pedestal subtraction and common mode correction. The results of a Geant-4-based simulation, developed for the Preshower prototype test, are also presented. The results of the simulation are found to be in excellent agreement with the data. It is also demonstrated that by combining the results of the data analysis and simulation an absolute calibration of the CMS Preshower detector system can be performed.

A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π0s with momentum pπ0 ≤ 800 MeV/c. The main purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K0 → π0π0 → 4γ and K0 → π0π0π0 → 6γ. This requires a position-sensitive photon detector with high spatial granularity in r−, ϕ−, and z−coordinates. The ECAL - a barrel without end-caps located inside a magnetic field of 0.44 T - consists of 18 identical concentric layers. Each layer of 13 radiation length (X0) contains a converter plate followed by small cross-section high-gain tubes of 2640 mm active length which are sandwiched by passive pick-up strip plates. The ECAL, with a total of 6X0 has an energy resolution of α(E)E ≈ 13%(E(GeV)and a position resolution of 4.5 mm for the shower foot. The shower topology allows separation of electrons from pions. The design, construction, read-out electronics, and performance of the detector are described.

The CMS Preshower is a fine grain detector that comprises 4288 silicon sensors, each containing 32 strips. The data are transferred from the detector to the counting room via 1208 optical fibres running at 800 Mbps. This enormous total data flow of about 1 Tbps necessitates a significant reduction in the data volume. For the readout of the Preshower, a VME-based system is currently under development. The main objective of each readout board is to acquire on-detector data from up to 36 optical links, perform online data reduction and pass the concentrated data to the CMS event builder. The principle modules that the system is based on are being developed in collaboration with the TOTEM experiment.

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.

Measurements of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta are presented for seven regions of leading jet transverse momentum.The analysis is based on data collected during 2012 with the CMS experiment, corresponding to an integrated luminosity of 19.7 fb -1 of proton-proton collisions at √ s = 8 TeV.The dijet azimuthal decorrelation is sensitive to the radiation of additional gluons and probes the dynamics of multijet production.The results are compared to fixed-order predictions of perturbative Quantum Chromodynamics, and to simulations using various Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions.

During the first years of the LHC operation a large amount of jet data was recorded by the ATLAS and CMS experiments. In this review several measurements of jet-related observables are presented, such as multi-jet rates and cross sections, ratios of jet cross sections, jet shapes and event shape observables. All results presented here are based on jet data collected at a center-of-mass energy of 7 TeV. Data are compared to various Monte Carlo generators, as well as to theoretical next-to-leading-order calculations allowing a test of perturbative Quantum Chromodynamics in a previously unexplored energy region.

During the first years of the LHC operation a large amount of jet data was recorded by the ATLAS and CMS experiments. In this review several measurements of jet-related observables are presented, such as multi-jet rates and cross sections, ratios of jet cross sections, jet shapes and event shape observables. All results presented here are based on jet data collected at a center-of-mass energy of 7 TeV. Data are compared to various Monte Carlo generators, as well as to theoretical next-to-leading-order calculations allowing a test of perturbative Quantum Chromodynamics in a previously unexplored energy region.

The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum. Such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5.

We have designed and tested a gas-sampling calorimeter of high granularity as a prototype for the electromagnetic calorimeter of the CPLEAR experiment. The prototype calorimeter, consisting of 18 layers of 1.5 mm thin lead converters interleaved with a total of 1152 high-gain tubes and 2304 pick-up strips, was tested in a tagged photon beam with photons in the energy range of 50 to 350 MeV. It well fulfilled the requirements of a good detection efficiency for photons above 50 MeV with a spatial resolution σ ≈ 5 mm for the photon conversion point and an energy resolution σ(E)/E ≈ 15%/√E[GeV].

Developing silicon strip sensors for the CMS Preshower detector we have noticed that some strips have a noise higher than the average and not correlated to a high leakage current. In order to investigate this effect we have developed a set-up for noise measurement on wafers and diced sensors that does not require bonding. The set-up is based on the DeltaStream chip coupled to a probe card. We have tested 45 sensors and found that the strips with an above average noise have a higher relative current increase as a function of voltage, ΔI/(IΔV). We also observed that, on these strips, the breakdown occurs within about 60V from the voltage at which the noise is observed. We describe our measurement method and present the results.

In the TARC experiment the differential neutron flux φ(E,r⃗) of a spallation of 2.5 and 3.5 GeV/c proton in large lead block is measured in the range between 0.1 eV and 1.5 MeV. A new technique, using small quantities (less than 0.1 gram) of material, is used for measuring the transmutation rate as a function of neutron energy in the range between 0.1 eV up to a few keV. The method is applied to a target of 86 mg (99Tc) mixed with 1.7 g of Aluminum. From these measurements the energy profile of the capture cross section can be extracted.

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 analysis of muon and electron data collected during a test of a CMS Preshower prototype is presented. First the absolute energy calibration of the modules is performed, by extracting the muon signal and combining it with Monte Carlo results. Then the total energy deposition of electrons is evaluated, taking into account the previous energy calibration of the modules. Monte Carlo results are in excellent agreement with data.

A compact, portable PC-based X-ray imaging system has been developed based on a 2D silicon microstrip sensor and particle physics readout electronics. The sensor is housed in a specially built hybrid, which also hosts the front-end electronics. The control and the readout electronics used are based on the standard PCI and PMC architectures and were originally developed for High Energy Physics Experiments. The use of PCI based electronics and the development of the control software for the PC-Linux platform led to a compact, portable, low cost imaging system. The system was initially tested and evaluated with beta particles from a 90Sr radioactive source, gamma rays from an 241Am radioactive source and cosmic rays, and it displayed consistent response. It was then operated using a compact X-ray machine with Mo tube and images of various targets were reconstructed offline using the ROOT data analysis package.

A compact trigger emulation module for evaluating electronic systems for LHC applications has been built using off-the-shelf components. The emulator, which is based on an FPGA, generates both programmable and true-random trigger patterns in compliance with the LHC triggering rules. For the true-random trigger part, the source of randomness is the avalanche effect on a transistor emitter-base diode. The system can be used either as a plug-in module for VME systems or as a standalone device controlled via a standard USB link by a PC running LabVIEW.

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.

The low-energy QCD predictions to be tested by the DIRAC experiment are revised. The experimental method, the setup characteristics and capabilities, along with first experimental results are reported. Preliminary analysis shows good detector performance: alignment error via $Λ$ mass measurement $m_Λ= 1115.6 MeV/c^2$ with $σ= 0.92 MeV/c^2$, $p π^-$ relative momentum resolution $σ_Q \approx 2.7 MeV/c$, and evidence for $π^+ π^-$ low momentum Coulomb correlation.

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.

The CPLEAR experiment at CERN studies Time Reversal, CP and CPT symmetries in theneutralkaonsystem,whichissofartheonlysystemwhereCPviolationhasbeenobserved. Inthe so-called 'golden channels', proton-antiproton annihilation produces a neutral kaon, a charged kaon andachargedpion. Thestrangenessoftheneutralkaonistaggedwiththechargeoftheaccompanying kaon. Decay rate asymmetries between K 0 and K 0 are measured. Symmetry violating parameters connectedtoTimeReversal,CPandCPTsymmetriesareextractedfromdecaystovariousnalstates.

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.