Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente

Trapping in irradiated p-on-n silicon sensors at fluences anticipated at the HL-LHC outer tracker

The degradation of signal in silicon sensors is studied under conditions expected at the CERN High-Luminosity LHC. 200 $\mu$m thick n-type silicon sensors are irradiated with protons of different energies to fluences of up to $3 \cdot 10^{15}$ neq/cm$^2$. Pulsed red laser light with a wavelength of 672 nm is used to generate electron-hole pairs in the sensors. The induced signals are used to determine the charge collection efficiencies separately for electrons and holes drifting through the sensor. The effective trapping rates are extracted by comparing the results to simulation. The electric field is simulated using Synopsys device simulation assuming two effective defects. The generation and drift of charge carriers are simulated in an independent simulation based on PixelAV. The effective trapping rates are determined from the measured charge collection efficiencies and the simulated and measured time-resolved current pulses are compared. The effective trapping rates determined for both electrons and holes are about 50% smaller than those obtained using standard extrapolations of studies at low fluences and suggests an improved tracker performance over initial expectations

Pseudorapidity distributions of charged hadrons in xenon-xenon collisions at root S-NN=5.44 TeV

Measurements of the pseudorapidity distributions of charged hadrons produced in xenon-xenon collisions at a nucleon-nucleon centre-of-mass energy of root S-NN = 5.44 TeV are presented. The measurements are based on data collected by the CMS experiment at the LHC. The yield of primary charged hadrons produced in xenon-xenon collisions in the pseudorapidity range vertical bar eta vertical bar <3.2 is determined using the silicon pixel detector in the CMS tracking system. For the 5% most central collisions, the chargedhadron pseudorapidity density in the midrapidity region vertical bar eta vertical bar <0.5 is found to be 1 187 +/- 36 (syst), with a negligible statistical uncertainty. The rapidity distribution of charged hadrons is also presented in the range vertical bar y vertical bar <3.2 and is found to be independent of rapidity around y = 0. Existing Monte-Carlo event generators are unable to simultaneously describe both results. Comparisons of charged-hadron multiplicities between xenon-xenon and lead-lead collisions at similar collision energies show that particle production at midrapidity is strongly dependent on the collision geometry in addition to the system size and collision energy. (C) 2019 The Author(s). Published by Elsevier B.V.Peer reviewe

Search for Dark Matter Particles Produced in Association with a Top Quark Pair at s =13 TeV

A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at s=13 TeV. The data correspond to an integrated luminosity of 35.9 fb-1 recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses

Strange hadron production in pp and pPb collisions at root(NN)-N-s=5.02 TeV

The transverse momentum (pT) distributions of Lambda, Xi(-), and Omega(-) baryons, their antiparticles, and K-S(0) mesons are measured in proton-proton (pp) and proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV over a broad rapidity range. The data, corresponding to integrated luminosities of 40.2 nb(-1) and 15.6 mu b(-1) for pp and pPb collisions, respectively, were collected by the CMS experiment. The nuclear modification factor R-pPb, which is defined as the ratio of the particle yield in pPb collisions and a scaled pp reference, is measured for each particle. A strong dependence on particle species is observed in the pT range from 2 to 7 GeV, where R-pPb for K-S(0) is consistent with unity, while an enhancement ordered by strangeness content and/or particle mass is observed for the three baryons. In pPb collisions, the strange hadron production is asymmetric about the nucleon-nucleon center-of-mass rapidity. Enhancements, which depend on the particle type, are observed in the direction of the Pb beam. The results are compared with predictions from EPOS LHC, which includes parametrized radial flow. The model is in qualitative agreement with the R-pPb data, but fails to describe the dependence on particle species in the yield asymmetries measured away from midrapidity in pPb collisions.Peer reviewe

Observation of the Lambda(0)(b) -> J/psi Lambda phi decay in proton-proton collisions at root s=13 TeV

The observation of the Lambda(0)(b) -> J/psi Lambda phi decay is reported using proton-proton collision data collected at root s = 13TeV by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity of 60fb(-1). The ratio of the branching fractions B(Lambda(0)(b) -> J/psi Lambda phi)/B(Lambda(0)(b) > psi(2S)Lambda) is measured to be (8.26 +/- 0.90 (stat) +/- 0.68 (syst) +/- 0.11 (B)) x 10(-2), where the first uncertainty is statistical, the second is systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of phi and psi(2S) decays to the reconstructed final states. (C) 2020 The Author. Published by Elsevier B.V.Peer reviewe

Determination of the strong coupling constant alpha(S)(m(Z)) from measurements of inclusive W-+/- and Z boson production cross sections in proton-proton collisions at root s=7 and 8 TeV

Twelve measurements of inclusive cross sections of W-+/- and Z boson production, performed in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, are compared with perturbative quantum chromodynamics calculations at next-to-next- to-leading order (NNLO) accuracy obtained with the CT14, HERAPDF2.0, MMHT14, and NNPDF3.0 parton distribution functions (PDFs). Data and theory agree well for all PDF sets, taking into account the experimental and theoretical uncertainties. A novel procedure is employed to extract the strong coupling constant at the Z pole mass from a detailed comparison of all the experimental fiducial cross sections to the corresponding NNLO theoretical predictions, yielding alpha S (m(Z)) = 0.1163(-0.0031)(+0.0024) (CT14), 0.1072(-0.0040)(+0.0043) (HERAPDF2.0), 0.1186 +/- 0. 0025 (MMHT14), and 0.1147 +/- 0.0023 (NNPDF3.0). Using the results obtained with the CT14 and MMHT14 PDFs, which yield the most robust and stable alpha(S)(mZ) extractions, a value alpha(S)(m(Z)) = 0.1175(-0.0028)(+0.0025) is determined.Peer reviewe

Search for supersymmetry with a compressed mass spectrum in the vector boson fusion topology with 1-lepton and 0-lepton final states in proton-proton collisions at p root s=13 TeV

A search for supersymmetric particles produced in the vector boson fusion topology in proton-proton collisions is presented. The search targets final states with one or zero leptons, large missing transverse momentum, and two jets with a large separation in rapidity. The data sample corresponds to an integrated luminosity of 35.9 fb(-1) of proton-proton collisions at root s = 13TeV collected in 2016 with the CMS detector at the LHC. The observed dijet invariant mass and lepton-neutrino transverse mass spectra are found to be consistent with the standard model predictions. Upper limits are set on the cross sections for chargino ((chi) over tilde (+/-)(1)) and neutralino ((chi) over tilde (0)(2)) production with two associated jets. For a compressed mass spectrum scenario in which the (chi) over tilde (+/-)(1) and (chi) over tilde (0)(2) decays proceed via a light slepton and the mass difference between the lightest neutralino chi(0)(1) and the mass-degenerate particles (chi) over tilde (+/-)(1) and (chi) over tilde (0)(2) is 1 (30) GeV, the most stringent lower limit to date of 112 (215) GeV is set on the mass of these latter two particles.Peer reviewe

Description and performance of track and primary-vertex reconstruction with the CMS tracker

A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For tbar t events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of pT > 0.9GeV is 94% for pseudorapidities of |η| < 0.9 and 85% for 0.9 < |η| < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of pT = 100GeV emitted at |η| < 1.4, the resolutions are approximately 2.8% in pT, and respectively, 10μm and 30μm in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10–12μm in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung

Measurement of single-diffractive dijet production in proton-proton collisions at root s=8 TeV with the CMS and TOTEM experiments

A Publisher's Erratum to this article was published on 03 May 2021. https://doi.org/10.1140/epjc/s10052-021-08863-wPeer reviewe