The multiplicities of positive and negative pions, kaons and unidentified hadrons produced in deep-inelastic scattering are measured in bins of the Bjorken scaling variable x, the relative virtual-photon energy y and the fraction of the virtual-photon energy transferred to the final-state hadron z. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam of both electric charges and a liquid hydrogen target. These measurements cover the kinematic domain with photon virtuality Q^2 > 1 (GeV/c)^2, 0.004 < x < 0.4, 0.1 < y < 0.7 and 0.2 < z < 0.85, in accordance with the kinematic domain used in earlier published COMPASS multiplicity measurements with an isoscalar target. The calculation of radiative corrections was improved by using the Monte Carlo generator DJANGOH, which results in up to 12% larger corrections in the low-x region.

The current status of the R&D performed for the ePIC-dRICH detector at the EIC is presented. A special focus will be given to the beam test results obtained with the dRICH prototype SiPM optical readout. A large-area readout plane consisting of a total of 1280 3 x3 mm2 2 SiPM sensors was built and tested with particle beams at CERN-PS in October 2023. The modular photodetector is based on a novel EIC-driven prototype photodetection unit (PDU) developed by INFN, which integrates 256 SiPM pixel sensors, cooling and TDC electronics in a volume of roughly 5x5x 14 cm3. 3 . The data have been collected with a complete chain of front-end and readout electronics based on the ALCOR chip, developed by INFN Torino. The features of the PDU and the performance of the full dRICH SiPM prototype system will be highlighted.

We present a mixed-signal ASIC, called ALCOR (A Low-power Chip for Optical sensor Readout), designed for the readout and digitization of signals from Silicon Photomultipliers (SiPMs) in the framework of the dualradiator RICH (dRICH) detector of the electron-Proton/Ion Collider (ePIC) experiment at the Electron-Ion Collider (EIC). ALCOR features 32 channels arranged in an 8x4 matrix. The amplifier input stage is a low impedance current conveyor based on a regulated common-gate topology. The versatile front-end is able to work with positive or negative input polarity signals and includes four gain settings and two discriminators with 6-bit DAC programmable thresholds. Each channel also incorporates quad-buffered low-power TDCs based on analogue interpolation providing precise timestamping with a 25-50 ps time bin. ALCOR is designed in a 110 nm CMOS technology and the power consumption is about 10-12 mW per channel. The ASIC has been extensively tested in the laboratory standalone and coupled to different SiPM models to assess its functionality and performance. The results have been validated in a beam test campaign with a prototype of the dRICH detector and 1280 3 x 3 mm(2) SiPM sensors.

New results are presented on a high-statistics measurement of Collins and Sivers asymmetries of charged hadrons produced in deep inelastic scattering of muons on a transversely polarised $^6$LiD target. The data were taken in 2022 with the COMPASS spectrometer using the 160 \gevv\ muon beam at CERN, balancing the existing data on transversely polarised proton targets. The first results from about two-thirds of the new data have total uncertainties smaller by up to a factor of three compared to the previous deuteron measurements. Using all the COMPASS proton and deuteron results, both the transversity and the Sivers distribution functions of the $u$ and $d$ quark, as well as the tensor charge in the measured $x$-range are extracted. In particular, the accuracy of the $d$ quark results is significantly improved.

Several spectrometer upgrades are planned for future phases of the AMBER (NA66) experiment at CERN. Among these upgrades, the replacement of some aging Multi-Wire Proportional Chambers has motivated a R&D program to develop a Micro-Pattern Gaseous Detector and its frontend electronics. The results of testing the first small Micromegas prototype with the TIGER-based front-end are presented.

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised 6LiD (deuteron) and NH3 (proton) targets is presented. All available data collected in the years 2003–2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160GeV/c at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from e+e− annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of π+π− pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range x>0.032, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of π+π− measured on the 6LiD target can be interpreted as indication for a cancellation of u and d-quark transversity distributions.

The production of vector mesons in deep inelastic scattering is an interesting yet scarcely explored channel to study the transverse spin structure of the nucleon and the spin-dependence of fragmentation. The COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced rho(0) mesons. The analysis is based on the data set collected in deep inelastic scattering in 2010 using a 160 GeV/c mu(+) beam impinging on a transversely polarized NH3 target. The rho(0) mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-xvariable, the transverse momentum of the pair and the fraction of the energy z carried by the pair. Indications for positive Collins and Sivers asymmetries are observed. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).

We present the development and testing of a Micromegas detector prototype and its front end intended to be a candidate for the substitutions of some of the Multiwire Proportional Chambers in the future AMBER (NA66) experiment at CERN. Results of the test of the first small size prototype are discussed.

We present the study of the production of double J/ψ mesons using COMPASS data collected with a 190 GeV/c π^- beam scattering off NH_3, Al and W targets. Kinematic distributions of the collected double J/ψ events are analysed, and the double J/ψ production cross section is estimated for each of the COMPASS targets. The results are compared to predictions from single- and double-parton scattering models as well as the pion intrinsic charm and the tetraquark exotic resonance hypotheses. It is demonstrated that the single parton scattering production mechanism gives the dominant contribution that is sufficient to describe the data. An upper limit on the double intrinsic charm content of pion is evaluated. No significant signatures that could be associated with exotic tetraquarks are found in the double J/ψ mass spectrum.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ρ ^0 meson muoproduction at COMPASS using 160 GeV/c polarised μ ^+ and μ ^- beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/c^2 < W < 17.0 GeV/c^2, 1.0 (GeV/c)^2 < Q^2 < 10.0 (GeV/c)^2 and 0.01 (GeV/c)^2 < p_T^2 < 0.5 (GeV/c)^2. Here, W denotes the mass of the final hadronic system, Q^2 the virtuality of the exchanged photon, and p_T the transverse momentum of the ρ ^0 meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons (γ^*_T → V^_L) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive ρ ^0 production.

We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile their experimental findings. We study the nonresonant contributions to the $\pi^-\pi^-\pi^+$ final state using pseudo-data generated on the basis of a Deck model. Subjecting pseudo-data and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the $J^{PC} = 1^{-+}$ amplitude and also for amplitudes with other $J^{PC}$ quantum numbers. We investigate for the first time the amplitude of the $\pi^-\pi^+$ subsystem with $J^{PC} = 1^{--}$ in the $3\pi$ amplitude with $J^{PC} = 1^{-+}$ employing the novel freed-isobar analysis scheme. We reveal this $\pi^-\pi^+$ amplitude to be dominated by the $\rho(770)$ for both the $\pi_1(1600)$ and the nonresonant contribution. We determine the $\rho(770)$ resonance parameters within the three-pion final state. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the $J^{PC} = 1^{-+}$ amplitude.

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions h1q are nowadays well established. Several possible channels to access these functions were originally proposed. One candidate is the measurement of the polarisation of Λ hyperons produced in SIDIS off transversely polarised nucleons, where the transverse polarisation of the struck quark might be transferred to the final-state hyperon. In this article, we present the COMPASS results on the transversity-induced polarisation of Λ and Λ¯ hyperons produced in SIDIS off transversely polarised protons. Within the experimental uncertainties, no significant deviation from zero was observed. The results are discussed in the context of different models taking into account previous experimental results on h1u and h1d.

We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile their experimental findings. We study the nonresonant contributions to the $\pi^-\pi^-\pi^+$ final state using pseudo-data generated on the basis of a Deck model. Subjecting pseudo-data and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the $J^{PC} = 1^{-+}$ amplitude and also for amplitudes with other $J^{PC}$ quantum numbers. We investigate for the first time the amplitude of the $\pi^-\pi^+$ subsystem with $J^{PC} = 1^{--}$ in the $3\pi$ amplitude with $J^{PC} = 1^{-+}$ employing the novel freed-isobar analysis scheme. We reveal this $\pi^-\pi^+$ amplitude to be dominated by the $\rho(770)$ for both the $\pi_1(1600)$ and the nonresonant contribution. We determine the $\rho(770)$ resonance parameters within the three-pion final state. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the $J^{PC} = 1^{-+}$ amplitude.

By the end of 2016 more than 10 Million core-hours of computing resources have been delivered by several commercial cloud providers to the four LHC experiments to run their production workloads, from simulation to full chain processing. In this paper we describe the experience gained at CERN in procuring and exploiting commercial cloud resources for the computing needs of the LHC experiments. The mechanisms used for provisioning, monitoring, accounting, alarming and benchmarking will be discussed, as well as the involvement of the LHC collaborations in terms of managing the workflows of the experiments within a multicloud environment.

In a commercial cloud environment, exhaustive resource profiling is beneficial to cope with the intrinsic variability of the virtualised environment, allowing to promptly identify performance degradation. In the context of its commercial cloud initiatives, CERN has acquired extensive experience in benchmarking commercial cloud resources. Ultimately, this activity provides information on the actual delivered performance of invoiced resources. In this report we discuss the experience acquired and the results collected using several fast benchmark applications adopted by the HEP community. These benchmarks span from open-source benchmarks to specific user applications and synthetic benchmarks. The workflow put in place to collect and analyse performance metrics is also described.

The current tier-0 processing at CERN is done on two managed sites, the CERN computer centre and the Wigner computer centre. With the proliferation of public cloud resources at increasingly competitive prices, we have been investigating how to transparently increase our compute capacity to include these providers. The approach taken has been to integrate these resources using our existing deployment and computer management tools and to provide them in a way that exposes them to users as part of the same site. The paper will describe the architecture, the toolset and the current production experiences of this model.

The degradation of signal in silicon sensors is studied under conditions expected at the CERN High-Luminosity LHC. 200 μm thick n-type silicon sensors are irradiated with protons of different energies to fluences of up to 3 · 1015 neq/cm2. Pulsed red laser light with a wavelength of 672 nm is used to generate electron-hole pairs in the sensors. The induced signals are used to determine the charge collection efficiencies separately for electrons and holes drifting through the sensor. The effective trapping rates are extracted by comparing the results to simulation. The electric field is simulated using Synopsys device simulation assuming two effective defects. The generation and drift of charge carriers are simulated in an independent simulation based on PixelAV. The effective trapping rates are determined from the measured charge collection efficiencies and the simulated and measured time-resolved current pulses are compared. The effective trapping rates determined for both electrons and holes are about 50% smaller than those obtained using standard extrapolations of studies at low fluences and suggest an improved tracker performance over initial expectations.

Jet multiplicity distributions in top quark pair () events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7. The measurement is performed in the dilepton decay channels (, , and ). The absolute and normalized differential cross sections for production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential and cross sections are presented for the first time as a function of the kinematic properties of the leading additional jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.

Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of [Formula: see text] is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb[Formula: see text] is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range [Formula: see text] in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about [Formula: see text] is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at [Formula: see text]. In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.