Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

the readout ASIC of the CMS barrel MIP Timing Detector

We thank the MTD sensor team for providing the SiPMs and sensor modules used in the measurements and more generally the MTD project for all the support provided to the TOFHIR2 development. We also thank the CMS collaboration for creating the conditions that made this work possible. We thank the Microelectronics Group at CERN for all the support and advice in the development of TOFHIR2, as well as for making available the radiation tolerant bandgap block and the TMRG tool. We thank Federico Faccio, Giulio Borghello and André David for helping in the preparation of the radiation tests. In particular we are thankful to Federico Faccio for the extrapolation of the heavy-ion SEE data to the LHC environment presented in this paper. We also thank the coordinators of the CERN X-ray irradiation facility and of the Heavy Ion Facility (HIF) in Louvain-la-Neuve for making available these facilities and for the help provided. Publisher Copyright: © 2024 IOP Publishing Ltd and Sissa Medialab.The CMS detector will be upgraded for the HL-LHC to include a MIP Timing Detector (MTD). The MTD will consist of barrel and endcap timing layers, BTL and ETL respectively, providing precision timing of charged particles. The BTL sensors are based on LYSO:Ce scintillation crystals coupled to SiPMs with TOFHIR2 ASICs for the front-end readout. A resolution of 30-60 ps for MIP signals at a rate of 2.5 Mhit/s per channel is expected along the HL-LHC lifetime. We present an overview of the TOFHIR2 requirements and design, simulation results and measurements with TOFHIR2 ASICs. The measurements of TOFHIR2 associated to sensor modules were performed in different test setups using internal test pulses or blue and UV laser pulses emulating the signals expected in the experiment. The measurements show a time resolution of 24 ps initially during Beginning of Operation (BoO) and 58 ps at End of Operation (EoO) conditions, matching well the BTL requirements. We also showed that the time resolution is stable up to the highest expected MIP rate. Extensive radiation tests were performed, both with x-rays and heavy ions, showing that TOFHIR2 is not affected by the radiation environment during the experiment lifetime.publishersversionpublishe