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CMS Silicon Strip Tracker Performance in Run 3
No full textThe CMS tracking system is the world's largest silicon tracker, comprising 1,856 pixel and 15,148 strip modules. In these proceedings, we present the performance of the silicon strip tracker during data taking in LHC Run 3, based on proton-proton collisions at the center-of-mass energy of 13.6 TeV. Key performance metrics as signal-to-noise ratio, hit efficiency, resolution, evolution of bad module components will be shown. The results demonstrate that the tracker maintained excellent performance throughout Run 3 so far, ensuring high-quality tracking crucial for CMS physics analyses
Recent advancements in the tau reconstruction and identification techniques in CMS
No full textTau leptons play a crucial role in studies of the Higgs boson and searches for Beyond the Standard Model physics at the present LHC and in its high luminosity upgrade. This talk presents the latest advancements in the reconstruction and identification of hadronic decays of tau leptons at the CMS experiment, both at the online and offline levels. The tau identification algorithm deployed for the early Run 3 data-taking period, based on a deep convolutional neural network with domain adaptation, showcases significantly improved discrimination of genuine hadronic tau decays against mis-identified quark and gluon jets, electrons, and muons. During live data-taking, a simplified version of the algorithm is used to select events with tau leptons at the High Level Trigger (HLT). The performance and calibration of both algorithms using early Run 3 data are presented. Many CMS physics analyses involving tau leptons are expected to benefit from these improvements. Alternative approaches to identify hadronic taus combined with jet flavour, based on graph neural networks and particle transformers, are also covered. Additionally, the dedicated techniques used to reconstruct and identify displaced tau leptons originating from long-lived particle decays using graph neural networks are discussed
Investigation of charm hadronisation and early magnetic field in ultrarelativistic heavy-ion collisions via D-meson spin alignment with ALICE
No full textHeavy quarks, i.e. charm and beauty, are produced in the early stages of heavy-ion collisions and are sensitive to the large initial orbital angular momentum and strong magnetic field. Under these conditions, charm quarks can be polarised. This polarisation is expected to be further transferred to the final-state hadrons during the hadronisation process and can be probed by measuring the spin density matrix element of spin-1 mesons, such as D mesons. In these proceedings, we report the first measurement of prompt D-meson spin alignment in Pb–Pb collisions with respect to the direction orthogonal to the reaction plane. A deviation from the unpolarised value, , is observed for GeV/ and with a significance of . The measured spin alignment of prompt D mesons is compared to that of inclusive J/ mesons measured at forward rapidity. Additionally, the first measurement of the parameter of D mesons in pp collisions based on the first data samples collected during LHC Run 3 is also reported
Exotic hadron production in and Pb collisions at LHCb
No full textIn the last decade, hadron spectroscopy has unveiled a wealth of states that do not have the properties expected of particles composed of two or three valence quarks. Foremost among these is the X(3872), which is thought to contain a pair plus two light quarks. In heavy ion collisions, these multiquark states are especially sensitive to a range of phenomena that can suppress or enhance their production. With a full range of precision vertexing, tracking, and particle ID capabilities covering forward rapidity, the LHCb experiment is especially well suited to measurements of both prompt and non-prompt exotic hadrons. This talk will present recent LHCb measurements of exotic hadrons, including the first measurement of the nuclear modification factor of the exotic hadron X(3872) in pPb collisions
Performance and efficiency of a transformer-based quark/gluon jet tagger in the ATLAS experiment
No full textA deep-learning approach based on the transformer architecture is developed to distinguish between jets originating from quarks and gluons. The algorithm operates on jets with transverse momentum GeV and pseudorapidity and pseudorapidity and takes as input several properties derived from the jet constituents, using information from the ATLAS detector's tracker and calorimeter. The algorithm's performance is evaluated by analyzing dijet data events from proton-proton collisions at and TeV during Run 2 and Run 3 of the Large Hadron Collider. Two methods are used to obtain distributions from quark- or gluon-initiated jets in data: a matrix method fully based on Monte Carlo simulation and a new approach named `jet topics' which has less dependence on the modelling of the physics process under study. The quark and gluon identification efficiencies measured in data for the 50% quark-identification-efficiency working point vary from the simulated ones for quark-initiated (gluon-initiated) jets by factors of 0.88-1.30 (0.61-1.05) with uncertainties of 10%-70% (10%-95%). The uncertainties estimated with the jet topics method are smaller than those estimated with the matrix method, with up to 20% less systematic uncertainty in some phase-space regions. The advances in jet identification reported here provide a robust tool for precision Standard Model measurements and searches for new physics at the LHC
"All Charm" Tetraquark
No full textThe exact nature of these exotic hadrons is far from established. Some models describe them as tightly bound tetraquarks or pentaquarks, others as loosely bound pairs of standard hadrons, and still others as both simultaneously. In a paper published in the journal Nature, the CMS collaboration has taken an important step in disentangling the true nature of exotic hadrons by reporting the first measurement of the quantum properties of a family of three “all-charm” tetraquarks
NNLO+NNLL Predictions for Heavy-Jet Mass and C-parameter in Higgs Decays to Quarks and Gluons
No full textWe consider the resummation of large logarithmic corrections arising in the two-particle limit at next-to-next-to-leading logarithmic (NNLL) accuracy for the heavy-jet mass and -parameter distributions in the decay of a Higgs boson to quarks and gluons: , , and . We demonstrate how the matched NNLO+NNLL results clarify the relative contributions of key hadronic Higgs-decay channels (, , ) yielding reduced uncertainties for both event-shape observables -- especially for heavy-jet mass -- while revealing substantial effects that shift the -parameter peak in gluonic decays
