304 Search Results

Diboson production in association with jets is studied in the fully leptonic final states, pp → (Z/γ$$^{*}$$)(Z/γ$$^{*}$$) + jets → 2ℓ2ℓ′ + jets, (ℓ, ℓ′ = e or μ) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb$$^{−1}$$ collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentum p$$_{T}$$, pseudorapidity η, invariant mass and ∆η of the highest-p$$_{T}$$ and second-highest-p$$_{T}$$ jets, and as a function of invariant mass of the four-lepton system formore » 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.« less

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

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 fb$$^{−1}$$. 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 $$ \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}} $$ decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set atmore » 294 (124) times the standard model prediction. Constraints are also set on the modifiers of the Higgs boson trilinear self-coupling, k$$_{λ}$$, assuming k$$_{2V}$$ = 1, and vice versa on the coupling of two Higgs bosons with two vector bosons, k$$_{2V}$$. The observed (expected) 95% confidence intervals of these coupling modifiers are −37.7 < k$$_{λ}$$ < 37.2 (−30.1 < k$$_{λ}$$ < 28.9) and −12.2 < k$$_{2V}$$ < 13.5 (−7.2 < k$$_{2V}$$ < 8.9), respectively.[graphic not available: see fulltext]« less

A search for electroweak production of a single vectorlike $T$ quark in association with a bottom ( $b$ ) quark in the all-hadronic decay channel is presented. This search uses proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected by the CMS experiment at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . The $T$ quark is assumed to have charge $2/3$ and decay to a top ( $t$ ) quark and a Higgs ( $H$ ) ormore » $Z$ boson. Hadronic decays of the $t$ quark and the $H$ or $Z$ boson are reconstructed from the kinematic properties of jets, including those containing $b$ hadrons. No deviation from the standard model prediction is observed in the reconstructed $tH$ and $tZ$ invariant mass distributions. The 95% confidence level upper limits on the product of the production cross section and branching fraction of a $T$ quark produced in association with a $b$ quark and decaying via $tH$ or $tZ$ range from 1260 to 68 fb for $T$ quark masses of 600–1200 GeV.« less

The polarizations of prompt and non-prompt Image 2 and $\mathrm{\psi }\left(\mathrm{2S}\right)$ mesons are measured in proton-proton collisions at $\sqrt{s}=13$  TeV, using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 ${\text{fb}}^{-1}$ . Based on the analysis of the dimuon decay angular distributions in the helicity frame, the polar anisotropy, ${\lambda }_{\vartheta }$ , is measured as a function of the transverse momentum,more » $p_{\mathrm{T}}$ , of the charmonium states, in the 25–120 and 20–100 GeV ranges for the Image 2 and $\mathrm{\psi }\left(\mathrm{2S}\right)$ , respectively. The non-prompt polarizations agree with predictions based on the hypothesis that, for $p_{\mathrm{T}}\gtrsim 25\text{GeV}$ , the non-prompt Image 2 and $\mathrm{\psi }\left(\mathrm{2S}\right)$ are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for $p_{\mathrm{T}}$ exceeding 30 times the Image 2 mass, where ${\lambda }_{\vartheta }$ tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at $\sqrt{s}=7$  TeV, the prompt polarizations show a significant variation with $p_{\mathrm{T}}$ , at low $p_{\mathrm{T}}$ .« less

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 √(s$$_{NN}$$) = 5.02 TeV in proton-proton (pp) and lead-lead(PbPb) collisions in 2017 and 2018, respectively, and at √(s$$_{NN}$$) = 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,more » 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.« less

The operation and performance of the Compact Muon Solenoid(CMS) electromagnetic calorimeter (ECAL) are presented, based ondata 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 of151 fb$$^{-1}$$. The CMS ECAL is a scintillating lead-tungstatecrystal calorimeter, with a silicon strip preshower detector in theforward region that provides precise measurements of the energy andthe time-of-arrival of electrons and photons. The successfuloperation 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 andmore » searches for newphenomena. Precise calibration, alignment, and monitoring of theECAL response are important ingredients to achieve these goals. Toface the challenges posed by the higher luminosity, whichcharacterized the operation of the LHC in Run 2, the proceduresestablished during the 2011–2012 run of the LHC have been revisitedand new methods have been developed for the energy measurement andfor the ECAL calibration. The energy resolution of the calorimeter,for electrons from Z boson decays reaching theECAL without significant loss of energy by bremsstrahlung, wasbetter 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 resultingperformance is similar to that achieved during Run 1 in 2011–2012,in spite of the more severe running conditions.« less

Computing demands for large scientific experiments, such as the CMS experiment at the CERN LHC, will increase dramatically in the next decades. To complement the future performance increases of software running on central processing units (CPUs), explorations of coprocessor usage in data processing hold great potential and interest. Coprocessors are a class of computer processors that supplement CPUs, often improving the execution of certain functions due to architectural design choices. We explore the approach of Services for Optimized Network Inference on Coprocessors (SONIC) and study the deployment of this as-a-service approach in large-scale data processing. In the studies, we takemore » a data processing workflow of the CMS experiment and run the main workflow on CPUs, while offloading several machine learning (ML) inference tasks onto either remote or local coprocessors, specifically graphics processing units (GPUs). With experiments performed at Google Cloud, the Purdue Tier-2 computing center, and combinations of the two, we demonstrate the acceleration of these ML algorithms individually on coprocessors and the corresponding throughput improvement for the entire workflow. This approach can be easily generalized to different types of coprocessors and deployed on local CPUs without decreasing the throughput performance. We emphasize that the SONIC approach enables high coprocessor usage and enables the portability to run workflows on different types of coprocessors.« less

The production of a pair of τ leptons via photon–photon fusion, $${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$$, is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptonsmore » are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of $${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$$ is $$\sigma^\text{fid}_\text{obs} = 12.4 ^{+3.8}_{-3.1}\,\textrm{fb}$$. Constraints are set on the contributions to the anomalous magnetic moment ($${a_{\unicode{x03C4}}}$$) and electric dipole moments ($${d_{\unicode{x03C4}}}$$) of the τ lepton originating from potential effects of new physics on the $$\unicode{x03B3}\unicode{x03C4}\unicode{x03C4}$$ vertex: $${a_{\unicode{x03C4}}} = 0.0009_{-0.0031}^{+0.0032}$$ and $$|{d_{\unicode{x03C4}}}| \lt 2.9\times 10^{-17}\,{e}\,\textrm{cm}$$ (95% confidence level), consistent with the standard model.« less

A search is described for the production of a pair of bottom-type vectorlike quarks ( $B$ VLQs) with mass greater than 1000 GeV. Each $B$ VLQ decays into a $b$ quark and a Higgs boson, a $b$ quark and a $Z$ boson, or a $t$ quark and a $W$ boson. This analysis considers both fully hadronic final states and those containing a charged lepton pair from a $Z$ boson decay. The products of the $H\to bb$ boson decay and of the hadronic $Zmore »$ or $W$ boson 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 of $138{\mathrm{fb}}^{-1}$ collected in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ with the CMS detector at the LHC from 2016 to 2018. No excess over the expected background is observed. Lower limits are set on the $B$ VLQ mass at the 95% confidence level. These depend on the $B$ VLQ branching fractions and are 1570 and 1540 GeV for 100% $B\to bH$ and 100% $B\to bZ$ , respectively. In most cases, the mass limits obtained exceed previous limits by at least 100 GeV.« less