8,076 research outputs found

    First Search for Exclusive Diphoton Production at High Mass with Tagged Protons in Proton-Proton Collisions at √s =13 TeV

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    A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp → pγγp with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb−1 collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeVat the LHC. Events are selected with a diphoton invariant mass above 350 GeVand with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons match the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% confidence level are |ζ1| \u3c 2.9 × 10−13 GeV−4 and |ζ2| \u3c 6.0 × 10−13 GeV−4

    Measurements of jet multiplicity and jet transverse momentum in multijet events in proton–proton collisions at √s = 13TeV

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    Multijet events at large transverse momentum (pT) are measured at √ s = 13 TeV using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 36.3 fb−1. The multiplicity of jets with pT \u3e 50 GeV that are produced in association with a high-pT dijet system is measured in various ranges of the pT of the jet with the highest transverse momentum and as a function of the azimuthal angle difference Δφ1,2 between the two highest pT jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest pT jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower

    Two-particle azimuthal correlations in γp interactions using pPb collisions at √s\u3csub\u3eNN\u3c/sub\u3e=8.16TeV

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    The first measurements of the Fourier coefficients (VnΔ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8nb−1of ultra-peripheral proton-lead (pPb) collisions at √sNN=8.16 TeVusing the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This γp system provides a set of unique initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The VnΔ coefficients are presented in ranges of event multiplicity and transverse momentum (pT) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean pT of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, V1Δ is negative, V2Δ is positive, and V3Δ consistent with 0. For each multiplicity and pT range, V2Δ is larger for γp events. The γp data are consistent with model predictions that have no collective effects

    Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions

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    The structure of nucleons is multidimensional and depends on the transverse momenta, spatial geometry, and polarization of the constituent partons. Such a structure can be studied using high-energy photons produced in ultraperipheral heavy-ion collisions. The first measurement of the azimuthal angular correlations of exclusively produced events with two jets in photon-lead interactions at large momentum transfer is presented, a process that is considered to be sensitive to the underlying nuclear gluon polarization. This study uses a data sample of ultraperipheral lead-lead collisions at √sNN = 5.02 TeV, corresponding to an integrated luminosity of 0.38 nb−1, collected with the CMS experiment at the LHC. The measured second harmonic of the correlation between the sum and difference of the two jet transverse momentum vectors is found to be positive, and rising, as the dijet transverse momentum increases. Awell-tuned model that has been successful at describing a wide range of proton scattering data from the HERA experiments fails to describe the observed correlations, suggesting the presence of gluon polarization effects

    Erratum: Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV

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    In Fig. 3, the y axis titles were mistakenly written showing a single-differential cross section in either dimuon pT or rapidity, when in fact the cross section is normalized by both the pT and rapidity ranges used for a given measurement point. The corrected version is shown in the new Fig. 3 provided below

    Observation of Same-Sign \u3ci\u3eWW\u3c/i\u3e Production from Double Parton Scattering in Proton-Proton Collisions at √s=13 TeV

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    The first observation of the production of W±W± bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 138 fb−1 recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign W bosons decaying leptonically is 80.7 ± 11.2(stat)+9.5-8.6 (syst) ± 12.1(model) fb, whereas the measured fiducial cross section is 6.28 ± 0.81(stat) ± 0.69(syst) ± 0.37(model) fb. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis

    Search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state in proton-proton collisions at √s=13 TeV

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    A search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZHboson pairs in the all-jets final state is presented. The analysis is based on proton-proton collision data recorded by the CMS detector in 2016–2018 at a centre-of-mass energy of 13TeVat the CERN LHC, corresponding to an integrated luminosity of 138fb−1. The search is sensitive to resonances with masses between 1.3and 6 TeV, decaying to bosons that are highly Lorentz-boosted such that each of the bosons forms a single large-radius jet. Machine learning techniques are employed to identify such jets. No significant excess over the estimated standard model background is observed. A maximum local significance of 3.6 standard deviations, corresponding to a global significance of 2.3 standard deviations, is observed at masses of 2.1 and 2.9TeV. In a heavy vector triplet model, spin-1 Z\u27 and W\u27 resonances with masses below 4.8 TeVare excluded at the 95% confidence level (CL). These limits are the most stringent to date. In a bulk graviton model, spin-2 gravitons and spin-0 radions with masses below 1.4 and 2.7 TeV, respectively, are excluded at 95% CL. Production of heavy resonances through vector boson fusion is constrained with upper cross section limits at 95% CLas low as 0.1fb

    Search for Higgs Boson Decay to a Charm Quark-Antiquark Pair in Proton-Proton Collisions at √s =13 TeV

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    A search for the standard model Higgs boson decaying to a charm quark-antiquark pair, H → c[], produced in association with a leptonically decaying V (W or Z) boson is presented. The search is performed with proton-proton collisions at √s = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb−1. Novel charm jet identification and analysis methods using machine learning techniques are employed. The analysis is validated by searching for Z → c[] in VZ events, leading to its first observation at a hadron collider with a significance of 5.7 standard deviations. The observed (expected) upper limit on σ(VH)B(H → c[]) is 0.94 (0.50+0.22−0.15 )pb at 95% confidence level (C.L.), corresponding to 14 (7.6+3.4−2.3 ) times the standard model prediction. For the Higgs-charm Yukawa coupling modifier, κc, the observed (expected) 95% C.L. interval is 1.1 \u3c |κc| \u3c 5.5 (|κc| \u3c 3.4), the most stringent constraint to date

    Probing Heavy Majorana Neutrinos and the Weinberg Operator through Vector Boson Fusion Processes in Proton-Proton Collisions at √s = 13 TeV

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    The first search exploiting the vector boson fusion process to probe heavy Majorana neutrinos and the Weinberg operator at the LHC is presented. The search is performed in the same-sign dimuon final state using a proton-proton collision dataset recorded at √s = 13 TeV, collected with the CMS detector and corresponding to a total integrated luminosity of 138 fb−1. The results are found to agree with the predictions of the standard model. For heavy Majorana neutrinos, constraints on the squared mixing element between the muon and the heavy neutrino are derived in the heavy neutrino mass range 50 GeV– 25 TeV; for masses above 650 GeV these are the most stringent constraints from searches at the LHC to date. A first test of the Weinberg operator at colliders provides an observed upper limit at 95% confidence level on the effective μμ Majorana neutrino mass of 10.8 GeV

    Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States with Two Photons in Proton-Proton Collisions at √s =13 TeV

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    Proton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks (t) and Higgs bosons (H). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb−1. No significant excess above the background prediction is observed. Upper limits on the branching fractions (Ɓ) of the top quark decaying to a Higgs boson and an up (u) or charm (c) quark are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019% (0.031%) for Ɓ(t → Hu) and 0.073% (0.051%) for Ɓ(t → Hc). These are the strictest upper limits yet determined
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