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

Stairway to discovery: a report on the CMS programme of cross section measurements from millibarns to femtobarns

International audienceThe Large Hadron Collider at CERN, delivering proton-proton collisions at much higher energies and far higher luminosities than previous machines, has enabled a comprehensive programme of measurements of the standard model (SM) processes by the CMS experiment. These unprecedented capabilities facilitate precise measurements of the properties of a wide array of processes, the most fundamental being cross sections. The discovery of the Higgs boson and the measurement of its mass became the keystone of the SM. Knowledge of the mass of the Higgs boson allows precision comparisons of the predictions of the SM with the corresponding measurements. These measurements span the range from one of the most copious SM processes, the total inelastic cross section for proton-proton interactions, to the rarest ones, such as Higgs boson pair production. They cover the production of Higgs bosons, top quarks, single and multibosons, and hadronic jets. Associated parameters, such as coupling constants, are also measured. These cross section measurements can be pictured as a descending stairway, on which the lowest steps represent the rarest processes allowed by the SM, some never seen before

Search for long-lived heavy neutral leptons in proton-proton collision events with a lepton-jet pair associated with a secondary vertex at s\sqrt{s} = 13 TeV

International audienceA search for long-lived heavy neutral leptons (HNLs) using proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ collected at $\sqrt{s}$ = 13 TeV with the CMS detector at the CERN LHC is presented. Events are selected with a charged lepton originating from the primary vertex associated with the proton-proton interaction, as well as a second charged lepton and a hadronic jet associated with a secondary vertex that corresponds to the semileptonic decay of a long-lived HNL. No excess of events above the standard model expectation is observed. Exclusion limits at 95% confidence level are evaluated for HNLs that mix with electron and/or muon neutrinos. Limits are presented in the mass range of 1-16.5 GeV, with excluded square mixing parameter values reaching as low as 2 $\times$ 10$^{-7}$. For masses above 11 GeV, the presented limits exceed all previous results in the semileptonic decay channel, and for some of the considered scenarios are the strongest to date

Study of WH production through vector boson scattering and extraction of the relative sign of the W and Z couplings to the Higgs boson in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search for the production of a W boson and a Higgs boson through vector boson scattering (VBS) is presented, using CMS data from proton-proton collisions at $\sqrt{s}$ = 13 TeV collected from 2016 to 2018. The integrated luminosity of the data sample is 138 fb$^{-1}$. Selected events must be consistent with the presence of two jets originating from VBS, the leptonic decay of the W boson to an electron or muon, and a Higgs boson decaying into a pair of b quarks, reconstructed as either a single merged jet or two resolved jets. A measurement of the process as predicted by the standard model (SM) is performed alongside a study of beyond-the-SM (BSM) scenarios. The SM analysis sets an observed (expected) 95% confidence level upper limit of 14.3 (9.0) on the ratio of the measured VBS WH cross section to that expected by the SM. The BSM analysis, conducted within the so-called $\kappa$ framework, excludes all scenarios with $\lambda_\mathrm{WZ}$ $\lt$ 0 that are consistent with current measurements, where $\lambda_\mathrm{WZ}$ = $\kappa_\mathrm{W}/\kappa_\mathrm{Z}$ and $\kappa_\mathrm{W}$ and $\kappa_\mathrm{Z}$ are the HWW and HZZ coupling modifiers, respectively. The signficance of the exclusion is beyond 5 standard deviations, and it is consistent with the SM expectation of $\lambda_\mathrm{WZ}$ = 1

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 nuclear modifications of B+^+ meson production in pPb collisions at sNN\sqrt{s_\mathrm{NN}} = 8.16 TeV

International audienceNuclear medium effects on B$^+$ meson production are studied using the binary-collision scaled cross section ratio between events of different multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV, corresponding to an integrated luminosity of 175 nb$^{-1}$, were used. The scaling factors in the ratio are determined using a novel approach based on the Z $\to$$\mu^+\mu^-$ cross sections measured in the same events. The scaled ratio for B$^+$ is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor

Search for long-lived heavy neutral leptons in proton-proton collision events with a lepton-jet pair associated with a secondary vertex at s\sqrt{s} = 13 TeV

International audienceA search for long-lived heavy neutral leptons (HNLs) using proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ collected at $\sqrt{s}$ = 13 TeV with the CMS detector at the CERN LHC is presented. Events are selected with a charged lepton originating from the primary vertex associated with the proton-proton interaction, as well as a second charged lepton and a hadronic jet associated with a secondary vertex that corresponds to the semileptonic decay of a long-lived HNL. No excess of events above the standard model expectation is observed. Exclusion limits at 95% confidence level are evaluated for HNLs that mix with electron and/or muon neutrinos. Limits are presented in the mass range of 1-16.5 GeV, with excluded square mixing parameter values reaching as low as 2 $\times$ 10$^{-7}$. For masses above 11 GeV, the presented limits exceed all previous results in the semileptonic decay channel, and for some of the considered scenarios are the strongest to date