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  1. Abstract

    The CERN LHC provided proton and heavy ion collisions during its Run 2 operation period from 2015 to 2018. Proton-proton collisions reached a peak instantaneous luminosity of 2.1× 1034cm-2s-1, twice the initial design value, at √(s)=13 TeV. The CMS experiment records a subset of the collisions for further processing as part of its online selection of data for physics analyses, using a two-level trigger system: the Level-1 trigger, implemented in custom-designed electronics, and the high-level trigger, a streamlined version of the offline reconstruction software running on a large computer farm. This paper presents the performance of the CMS high-level trigger system during LHC Run 2 for physics objects, such as leptons, jets, and missing transverse momentum, which meet the broad needs of the CMS physics program and the challenge of the evolving LHC and detector conditions. Sophisticated algorithms that were originally used in offline reconstruction were deployed online. Highlights include a machine-learning b tagging algorithm and a reconstruction algorithm for tau leptons that decay hadronically.

     
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    Free, publicly-accessible full text available November 1, 2025
  2. A<sc>bstract</sc>

    Diboson production in association with jets is studied in the fully leptonic final states, pp → (Z/γ*)(Z/γ*) + jets → 22′ + jets, (,′ = e orμ) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb1collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentumpT, pseudorapidityη, invariant mass and ∆ηof the highest-pTand second-highest-pTjets, and as a function of invariant mass of the four-lepton system for events with various jet multiplicities. These differential cross sections are compared with theoretical predictions that mostly agree with the experimental data. However, in a few regions we observe discrepancies between the predicted and measured values. Further improvement of the predictions is required to describe the ZZ+jets production in the whole phase space.

     
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    Free, publicly-accessible full text available October 1, 2025
  3. A<sc>bstract</sc>

    A search for Higgs boson pair (HH) production in association with a vector boson V (W or Z boson) is presented. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb1. Both hadronic and leptonic decays of V bosons are used. The leptons considered are electrons, muons, and neutrinos. The HH production is searched for in the$$ \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}} $$bb¯bb¯decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set at 294 (124) times the standard model prediction. Constraints are also set on the modifiers of the Higgs boson trilinear self-coupling,kλ, assumingk2V= 1, and vice versa on the coupling of two Higgs bosons with two vector bosons,k2V. The observed (expected) 95% confidence intervals of these coupling modifiers are37.7 <kλ< 37.2 (30.1 <kλ< 28.9) and12.2 <k2V< 13.5 (7.2 <k2V< 8.9), respectively.

     
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    Free, publicly-accessible full text available October 1, 2025
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  7. Abstract

    Using proton–proton collision data corresponding to an integrated luminosity of$$140\hbox { fb}^{-1}$$140fb-1collected by the CMS experiment at$$\sqrt{s}= 13\,\text {Te}\hspace{-.08em}\text {V} $$s=13TeV, the$${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} $$Λb0J/ψΞ-K+decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the$${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} $$Λb0ψ(2S)Λdecay, is measured to be$$\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} )/\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} ) = [3.38\pm 1.02\pm 0.61\pm 0.03]\%$$B(Λb0J/ψΞ-K+)/B(Λb0ψ(2S)Λ)=[3.38±1.02±0.61±0.03]%, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in$$\mathcal {B}({{{\uppsi }} ({2\textrm{S}})} \rightarrow {{\text {J}/\uppsi }} {{{\uppi }} ^{{+}}} {{{\uppi }} ^{{-}}} )$$B(ψ(2S)J/ψπ+π-)and$$\mathcal {B}({{{\Xi }} ^{{-}}} \rightarrow {{\Lambda }} {{{\uppi }} ^{{-}}} )$$B(Ξ-Λπ-).

     
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    Free, publicly-accessible full text available October 1, 2025
  8. A search is described for the production of a pair of bottom-type vectorlike quarks (BVLQs) with mass greater than 1000 GeV. EachBVLQ decays into abquark and a Higgs boson, abquark and aZboson, or atquark and aWboson. This analysis considers both fully hadronic final states and those containing a charged lepton pair from aZboson decay. The products of theHbbboson decay and of the hadronicZorWboson decays can be resolved as two distinct jets or merged into a single jet, so the final states are classified by the number of reconstructed jets. The analysis uses data corresponding to an integrated luminosity of138fb1collected in proton-proton collisions ats=13TeVwith the CMS detector at the LHC from 2016 to 2018. No excess over the expected background is observed. Lower limits are set on theBVLQ mass at the 95% confidence level. These depend on theBVLQ branching fractions and are 1570 and 1540 GeV for 100%BbHand 100%BbZ, respectively. In most cases, the mass limits obtained exceed previous limits by at least 100 GeV.

    <supplementary-material><permissions><copyright-statement>© 2024 CERN, for the CMS Collaboration</copyright-statement><copyright-year>2024</copyright-year><copyright-holder>CERN</copyright-holder></permissions></supplementary-material></sec> </div> <a href='#' class='show open-abstract' style='margin-left:10px;'>more »</a> <a href='#' class='hide close-abstract' style='margin-left:10px;'>« less</a> <div class="actions" style="padding-left:10px;"> <span class="reader-count"> Free, publicly-accessible full text available September 1, 2025</span> </div> </div><div class="clearfix"></div> </div> </li> <li> <div class="article item document" itemscope itemtype="http://schema.org/TechArticle"> <div class="item-info"> <div class="title"> <a href="https://par.nsf.gov/biblio/10552265-performance-cms-electromagnetic-calorimeter-pp-collisions-tev" itemprop="url"> <span class='span-link' itemprop="name">Performance of the CMS electromagnetic calorimeter in pp collisions at √ s = 13 TeV</span> </a> </div> <div> <strong> <a class="misc external-link" href="https://doi.org/10.1088/1748-0221/19/09/P09004" target="_blank" title="Link to document DOI">https://doi.org/10.1088/1748-0221/19/09/P09004  <span class="fas fa-external-link-alt"></span></a> </strong> </div> <div class="metadata"> <span class="authors"> <span class="author" itemprop="author">Hayrapetyan, A</span> <span class="sep">; </span><span class="author" itemprop="author">Tumasyan, A</span> <span class="sep">; </span><span class="author" itemprop="author">Adam, W</span> <span class="sep">; </span><span class="author" itemprop="author">Andrejkovic, JW</span> <span class="sep">; </span><span class="author" itemprop="author">Bergauer, T</span> <span class="sep">; </span><span class="author" itemprop="author">Chatterjee, S</span> <span class="sep">; </span><span class="author" itemprop="author">Damanakis, K</span> <span class="sep">; </span><span class="author" itemprop="author">Dragicevic, M</span> <span class="sep">; </span><span class="author" itemprop="author">Escalante_Del_Valle, A</span> <span class="sep">; </span><span class="author" itemprop="author">Hussain, PS</span> <span class="sep">; </span><span class="author">et al</span></span> <span class="year">( <time itemprop="datePublished" datetime="2024-09-01">September 2024</time> , Journal of Instrumentation) </span> </div> <div style="cursor: pointer;-webkit-line-clamp: 5;" class="abstract" itemprop="description"> <title>Abstract

    The operation and performance of the Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL) are presented, based on data collected in pp collisions at √s=13 TeV at the CERN LHC, in the years from 2015 to 2018 (LHC Run 2), corresponding to an integrated luminosity of 151 fb-1. The CMS ECAL is a scintillating lead-tungstate crystal calorimeter, with a silicon strip preshower detector in the forward region that provides precise measurements of the energy and the time-of-arrival of electrons and photons. The successful operation of the ECAL is crucial for a broad range of physics goals, ranging from observing the Higgs boson and measuring its properties, to other standard model measurements and searches for new phenomena. Precise calibration, alignment, and monitoring of the ECAL response are important ingredients to achieve these goals. To face the challenges posed by the higher luminosity, which characterized the operation of the LHC in Run 2, the procedures established during the 2011–2012 run of the LHC have been revisited and new methods have been developed for the energy measurement and for the ECAL calibration. The energy resolution of the calorimeter, for electrons from Z boson decays reaching the ECAL without significant loss of energy by bremsstrahlung, was better than 1.8%, 3.0%, and 4.5% in the |η| intervals [0.0,0.8], [0.8,1.5], [1.5, 2.5], respectively. This resulting performance is similar to that achieved during Run 1 in 2011–2012, in spite of the more severe running conditions.

     
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    Free, publicly-accessible full text available September 1, 2025
  9. Abstract

    The performance of muon tracking, identification, triggering, momentum resolution, and momentum scale has been studied with the CMS detector at the LHC using data collected at √(sNN) = 5.02 TeV in proton-proton (pp) and lead-lead (PbPb) collisions in 2017 and 2018, respectively, and at √(sNN) = 8.16 TeV in proton-lead (pPb) collisions in 2016. Muon efficiencies, momentum resolutions, and momentum scales are compared by focusing on how the muon reconstruction performance varies from relatively small occupancy pp collisions to the larger occupancies of pPb collisions and, finally, to the highest track multiplicity PbPb collisions. We find the efficiencies of muon tracking, identification, and triggering to be above 90% throughout most of the track multiplicity range. The momentum resolution and scale are unaffected by the detector occupancy. The excellent muon reconstruction of the CMS detector enables precision studies across all available collision systems.

     
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    Free, publicly-accessible full text available September 1, 2025