Performance of electron-photon triggers at the first trigger level (L1) with Run II and Run III data collected by the CMS experiment at the CERN LHC

Από την αρχή της Run III το 2022, ο Μεγάλος Επιταχυντής Αδρονίων (LHC) συγκρούει δέσμες πρωτονίων σε ενέργειες κέντρου μάζας 13.6 TeV. Η φωτεινότητα με την οποία τις συγκρούει έχει αυξηθεί σε σχέση με την Run II (2015-2018), οδηγώντας έτσι σε γεγονότα με κατά μέσο όρο 60 ταυτόχρονες συγκρούσεις πρωτονίων ανά διασταύρωση δέσμης. Το σύστημα σκαναλισμού (trigger system) του CMS πρέπει να ανταπεξέλθει αυτών των απαιτητικών συνθηκών, ώστε να συμβαδίζει η απόδοση του συστήματος με το ευρύ φάσμα ερευνών φυσικής που μελετάται στο πείραμα CMS. Σε αυτή την εργασία, παρουσιάζεται η επίδοση του πρώτου επιπέδου (Level-1) σκανδαλισμού ηλεκτρονίων και φωτονίων. Πιο συγκεκριμένα, παρουσιάζονται οι θέσεις, η ενέργεια και η διακριτική ικανότητα των θέσεων των superclusters ηλεκτρονίων και φωτονίων στο Level-1, καθώς και οι ρυθμοί καταγραφής δεδομένων στο Level-1. Η απόδοση του Level-1 σκανδαλισμού ηλεκτρονίων και φωτονίων πραγματοποιείται με την μέθοδο “Tag and Probe” και υπολογίζεται σαν συνάρτηση της εγκάρσιας ενέργειας των αντικειμένων και σαν συνάρτηση των αριθμών ανακατασκευασμένων κορυφών που υπάρχουν στα γεγονότα, για διάφορα κατώφλια ενέργειας στο Level1. Επίσης, γίνεται μια εκτενής αναφορά στα ECAL Spikes, δηλαδή στα ανώμαλα σήματα που δίνουν τα Avalhance Photodiodes (APDs) στην κεντρική περιοχή του ηλεκτρομαγνητικού θερμοδιμέτρου, και παρουσιάζονται τα ποσοστά τους ανάμεσα στα συνολικά αντικείμενα ηλεκτρονίων και φωτονίων στα γεγονότα. Οι μελέτες έχουν διεξαχθεί με τα δεδομένα που συλλέχθηκαν από τις περιόδους 2018 και 2022 με τον ανιχνευτή CMS στον LHC του CERN, τα οποία αποτελούνται από 58.9f b−1 και 31.5f b−1 ολοκληρωμένης φωτεινότητας, αντίστοιχα. Τέλος, η σύγκριση των δύο περιόδων δείχνει ότι παρά το γεγονός ότι στην Run III οι συνθήκες έχουν επιδεινωθεί αρκετά, λόγω της αυξημένης ενέργειας και φωτεινότητας, η απόδοση παραμένει υψηλή, ενώ σε κάποιες περιπτώσεις είναι ακόμα και καλύτερη από τη Run II.At the start of Run III in 2022, the Large Hadron Collider (LHC) delivered proton-proton collisions at a center-of-mass energy of 13.6 TeV. Instantaneous luminosity has been increased since Run II (2015-2018), leading to events with up to a mean of about 60 simultaneous p-p collisions per bunch crossing. The CMS trigger system has to overcome these challenging conditions, in order to keep up with the broad physics program that the CMS experiment conducts. In this thesis, the performance of the CMS Level-1 electron and photon trigger is presented. The Level-1 position, energy, and resolution of the electromagnetic calorimeter (ECAL) superclusters are shown, as well as, the Level-1 rates. The L1 trigger efficiency is computed via the “Tag and Probe” method as a function of transverse energy and number of vertices for several L1 energy thresholds. Also, the ECAL spikes, which are anomalous signals in the ECAL Barrel region due to the Avalanche Photodiodes (APDs), are studied in detail, and their contamination is presented. These studies are performed with both the 2018 and 2022 data collected with the CMS experiment at the CERN LHC, with an integrated luminosity of 59.8f b−1 and 31.5f b−1, respectively. Finally, the comparison of the two data-taking periods is presented, showing that, although the conditions are more challenging in Run III, the performance remains the same, and even better in some cases, than in Run II. Ke

Test of lepton flavor universality in semileptonic Bc+^+_\text{c} meson decays in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA measurement of the ratio of branching fractions $R$(J/$\psi$) = $\mathcal{B}$(B$^+_\text{c}$$\to$ J/$\psi$$\tau^+\nu_\tau$)/$\mathcal{B}$(B$^+_\text{c}$$\to$ J/$\psi$$\mu^+\nu_\mu$) in the J/$\psi$$\to$$\mu^+\mu^-$, $\tau^+$$\to$$\mu^+\mu_\tau\overline{\nu}_\tau$ decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding to an integrated luminosity of 59.7 fb$^{-1}$. The measured ratio, $R$(J/$\psi$) = 0.17$^{+ 0.18}_{- 0.17}$ (stat) $^{+ 0.21}_{- 0.22}$ (syst) $^{+ 0.19}_{- 0.18}$ (theo) = 0.17 $\pm$ 0.33, agrees with the value of 0.2582 $\pm$ 0.0038 predicted by the standard model, which assumes lepton flavor universality

Observation of the Ξb−\Xi^-_\mathrm{b}→\toψ\psi(2S)Ξ−\Xi^- decay and studies of the Ξb∗0\Xi_\mathrm{b}^{\ast{}0} baryon in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceThe first observation of the decay $\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$ and measurement of the branching ratio of $\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$ to $\Xi^-_\mathrm{b}$$\to$ J/$\psi$$\Xi^-$ are presented. The J/$\psi$ and $\psi$(2S) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016-2018, corresponding to an integrated luminosity of 140 fb$^{-1}$. The branching fraction ratio is measured to be $\mathcal{B}$($\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$)/$\mathcal{B}$($\Xi^-_\mathrm{b}$$\to$ J/$\psi$$\Xi^-$) = 0.84$^{+0.21}_{-0.19}$ (stat) $\pm$ 0.10 (syst) $\pm$ 0.02 ($\mathcal{B}$), where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the $\Xi_\mathrm{b}^{\ast{}0}$ baryon mass and natural width are also presented, using the $\Xi_\mathrm{b}^-\pi^+$ final state, where the $\Xi^-_\mathrm{b}$ baryon is reconstructed through the decays J/$\psi \Xi^-$, $\psi$(2S)$\Xi^-$, J/$\psi \Lambda$K$^-$, and J/$\psi \Sigma^0$K$^-$. Finally, the fraction of the $\Xi^-_\mathrm{b}$ baryons produced from $\Xi_\mathrm{b}^{\ast{}0}$ decays is determined

Search for CPCP violation in D0^0→\to KS0^0_\mathrm{S}KS0^0_\mathrm{S} decays in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search is reported for charge-parity D$^0$$\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$$CP$ violation in D$^0$$\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ decays, using data collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 fb$^{-1}$, which consists of about 10 billion events containing a pair of ẖadrons, nearly all of which decay to charm hadrons. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays D$^{*+}$$\to$ D$^0\pi^+$ and D$^{*-}$$\to$ D$^0\pi^-$. The D$^0$$\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$$CP$ asymmetry in D$^0$$\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ is measured to be $A_{CP}$( K$^0_\mathrm{S}$K$^0_\mathrm{S}$) = (6.2 $\pm$ 3.0 $\pm$ 0.2 $\pm$ 0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the D$^0$ $\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ $CP$ asymmetry in the D$^0$ $\to$ K$^0_\mathrm{S}\pi^+\pi^-$ decay. This is the first D$^0$ $\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ $CP$ asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state

Search for heavy neutral leptons in final states with electrons, muons, and hadronically decaying tau leptons in proton-proton collisions at s\sqrt{s} =13 TeV

International audienceA search for heavy neutral leptons (HNLs) of Majorana or Dirac type using proton-proton collision data at $\sqrt{s}$ =13 TeV is presented. The data were collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. Events with three charged leptons (electrons, muons, and hadronically decaying tau leptons) are selected, corresponding to HNL production in association with a charged lepton and decay of the HNL to two charged leptons and a standard model (SM) neutrino. The search is performed for HNL masses between 10 GeV and 1.5 TeV. No evidence for an HNL signal is observed in data. Upper limits at 95% confidence level are found for the squared coupling strength of the HNL to SM neutrinos, considering exclusive coupling of the HNL to a single SM neutrino generation, for both Majorana and Dirac HNLs. The limits exceed previously achieved experimental constraints for a wide range of HNL masses, and the limits on tau neutrino coupling scenarios with HNL masses above the W boson mass are presented for the first time

Search for long-lived particles using displaced vertices and missing transverse momentum in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016-2018, corresponding to a total integrated luminosity of 137 fb$^{-1}$. This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 $\mu$m, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gauge-mediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 $\mu$m

Searches for pair-produced multijet resonances using data scouting in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceSearches for pair-produced multijet signatures using data corresponding to an integrated luminosity of 128 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}$ = 13 TeV are presented. A data scouting technique is employed to record events with low jet scalar transverse momentum sum values. The electroweak production of particles predicted in $R$-parity violating supersymmetric models is probed for the first time with fully hadronic final states. This is the first search for prompt hadronically decaying mass-degenerate higgsinos, and extends current exclusions on $R$-parity violating top squarks and gluinos

Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at sNN\sqrt{s_\mathrm{NN}} = 5.02 TeV

International audienceThis Letter presents the first measurements of the groomed jet radius $R_\mathrm{g}$ and the jet girth $g$ in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables $R_\mathrm{g}$ and $g$ provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb$^{-1}$ and 301 pb$^{-1}$, respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum $p_\mathrm{T}^\gamma$ 100 GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum $p_\mathrm{T}^\text{jet}$ such that $p_\mathrm{T}^\text{jet}/p_\mathrm{T}^\gamma$$>$ 0.4. The measured $R_\mathrm{g}$ and $g$ distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with $p_\mathrm{T}^\text{jet}/p_\mathrm{T}^\gamma$$>$ 0.8, i.e., those that closely balance the photon $p_\mathrm{T}^\gamma$, are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with $p_\mathrm{T}^\text{jet}/p_\mathrm{T}^\gamma$$>$ 0.4 reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements

Search for long-lived particles using displaced vertices and missing transverse momentum in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016-2018, corresponding to a total integrated luminosity of 137 fb$^{-1}$. This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 $\mu$m, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gauge-mediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 $\mu$m

The CMS Statistical Analysis and Combination Tool: COMBINE

International audienceThis paper describes the COMBINE software package used for statistical analyses by the CMS Collaboration. The package, originally designed to perform searches for a Higgs boson and the combined analysis of those searches, has evolved to become the statistical analysis tool presently used in the majority of measurements and searches performed by the CMS Collaboration. It is not specific to the CMS experiment, and this paper is intended to serve as a reference for users outside of the CMS Collaboration, providing an outline of the most salient features and capabilities. Readers are provided with the possibility to run COMBINE and reproduce examples provided in this paper using a publicly available container image. Since the package is constantly evolving to meet the demands of ever-increasing data sets and analysis sophistication, this paper cannot cover all details of COMBINE. However, the online documentation referenced within this paper provides an up-to-date and complete user guide