1016 results found
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Observation of electroweak production of W gamma with two jets in proton-proton collisions at root s=13 TeV, PHYSICS LETTERS B, Vol: 811, ISSN: 0370-2693
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurements of the W boson rapidity, helicity, double-differential cross sections, and charge asymmetry in pp collisions at root s=13 TeV, PHYSICAL REVIEW D, Vol: 102, ISSN: 2470-0010
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the dilepton final state in proton-proton collisions at root s=13 TeV, PHYSICAL REVIEW D, Vol: 102, ISSN: 2470-0010
Akerib DS, Akerlof CW, Akimov DY, et al., 2020, The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs, EUROPEAN PHYSICAL JOURNAL C, Vol: 80, ISSN: 1434-6044
Akerib DS, Akerlof CW, Akimov DY, et al., 2020, The LUX-ZEPLIN (LZ) experiment, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, Vol: 953, Pages: 1-22, ISSN: 0168-9002
We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850’ level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements.
MICE collaboration, 2020, Demonstration of cooling by the Muon Ionization Cooling Experiment, Nature, Vol: 578, Pages: 53-59, ISSN: 0028-0836
The use of accelerated beams of electrons, protons or ions has furthered the development of nearly every scientific discipline. However, high-energy muon beams of equivalent quality have not yet been delivered. Muon beams can be created through the decay of pions produced by the interaction of a proton beam with a target. Such 'tertiary' beams have much lower brightness than those created by accelerating electrons, protons or ions. High-brightness muon beams comparable to those produced by state-of-the-art electron, proton and ion accelerators could facilitate the study of lepton-antilepton collisions at extremely high energies and provide well characterized neutrino beams1-6. Such muon beams could be realized using ionization cooling, which has been proposed to increase muon-beam brightness7,8. Here we report the realization of ionization cooling, which was confirmed by the observation of an increased number of low-amplitude muons after passage of the muon beam through an absorber, as well as an increase in the corresponding phase-space density. The simulated performance of the ionization cooling system is consistent with the measured data, validating designs of the ionization cooling channel in which the cooling process is repeated to produce a substantial cooling effect9-11. The results presented here are an important step towards achieving the muon-beam quality required to search for phenomena at energy scales beyond the reach of the Large Hadron Collider at a facility of equivalent or reduced footprint6.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Probing the chiral magnetic wave in pPb and PbPb collisions at root S-NN=5.02 TeV using charge-dependent azimuthal anisotropies, Physical Review C: Nuclear Physics, Vol: 100, Pages: 064908-1-064908-17, ISSN: 0556-2813
Charge-dependent anisotropy Fourier coefficients (vn) of particle azimuthal distributions are measured in pPb and PbPb collisions at √sNN=5.02TeV with the CMS detector at the LHC. The normalized difference in the second-order anisotropy coefficients (v2) between positively and negatively charged particles is found to depend linearly on the observed event charge asymmetry with comparable slopes for both pPb and PbPb collisions over a wide range of charged particle multiplicity. In PbPb, the third-order anisotropy coefficient v3 shows a similar linear dependence with the same slope as seen for v2. The observed similarities between the v2 slopes for pPb and PbPb, as well as the similar slopes for v2 and v3 in PbPb, are compatible with expectations based on local charge conservation in the decay of clusters or resonances, and constitute a challenge to the hypothesis that, at LHC energies, the observed charge asymmetry dependence of v2 in heavy ion collisions arises from a chiral magnetic wave.
The Muon Ionization Cooling Experiment (MICE) collaboration has developed theMICE Analysis User Software (MAUS) to simulate and analyze experimental data. It serves asthe primary codebase for the experiment, providing for offline batch simulation and reconstructionas well as online data quality checks. The software provides both traditional particle-physicsfunctionalities such as track reconstruction and particle identification, and accelerator physicsfunctions, such as calculating transfer matrices and emittances. The code design is object orientated,but has a top-level structure based on the Map-Reduce model. This allows for parallelization tosupport live data reconstruction during data-taking operations. MAUS allows users to develop in either Python or C++ and provides APIs for both. Various software engineering practices fromindustry are also used to ensure correct and maintainable code, including style, unit and integrationtests, continuous integration and load testing, code reviews, and distributed version control. Thesoftware framework and the simulation and reconstruction capabilities are described
Collaboration TMICE, Adams D, Adey D, et al., 2019, First particle-by-particle measurement of emittance in the Muon Ionization Cooling Experiment, The European Physical Journal C - Particles and Fields, Vol: 79, Pages: 1-15, ISSN: 1124-1861
The Muon Ionization Cooling Experiment (MICE) collaboration seeks to demonstrate the feasibility of ionization cooling, the technique by which it is proposed to cool the muon beam at a future neutrino factory or muon collider. The emittance is measured from an ensemble of muons assembled from those that pass through the experiment. A pure muon ensemble is selected using a particle-identification system that can reject efficiently both pions and electrons. The position and momentum of each muon are measured using a high-precision scintillating-fibre tracker in a 4 T solenoidal magnetic field. This paper presents the techniques used to reconstruct the phase-space distributions in the upstream tracking detector and reports the first particle-by-particle measurement of the emittance of the MICE Muon Beam as a function of muon-beam momentum.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement of prompt psi(2S) production cross sections in proton-lead and proton-proton collisions at root s(NN)=5.02 TeV, Physics Letters B, Vol: 790, Pages: 509-532, ISSN: 0370-2693
Measurements of prompt meson production cross sections in proton–lead (pPb) and proton–proton (pp) collisions at a nucleon–nucleon center-of-mass energy of are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 and 28.0 , respectively. The nuclear modification factor is measured for prompt in the transverse momentum range and the center-of-mass rapidity range . The results on are compared to the corresponding modification factor for prompt mesons. The results point to different nuclear effects at play in the production of the excited charmonium state compared to the ground state, in the region of backward rapidity and for .
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement of nuclear modification factors of gamma(1S)), gamma(2S), and gamma(3S) mesons in PbPb collisions at root s(NN)=5.02 TeV, Physics Letters B, Vol: 790, Pages: 270-293, ISSN: 0370-2693
The cross sections for ϒ(1S), ϒ(2S), and ϒ(3S) production in lead–lead (PbPb) and proton–proton (pp) collisions at TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, , derived from the PbPb-to- ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, . The suppression of ϒ(1S) is larger than that seen at , although the two are compatible within uncertainties. The upper limit on the of integrated over , rapidity and centrality is 0.096 at 95% confidence level, which is the strongest suppression observed for a quarkonium state in heavy ion collisions to date.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for t(t)over-barH production in the H -> b(b)over-bar decay channel with leptonic t(t)over-bar decays in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2019, ISSN: 1029-8479
A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair (tt⎯⎯H), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy √=13 TeV. The data correspond to an integrated luminosity of 35.9 fb−1 recorded with the CMS detector at the CERN LHC. Candidate tt⎯⎯H events are selected that contain either one or two electrons or muons from the tt⎯⎯ decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed tt⎯⎯H signal strength relative to the standard model cross section, μ = σ/σSM, under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on μ of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 ± 0.24(stat) ± 0.38(syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Non-Gaussian elliptic-flow fluctuations in PbPb collisions at root S-NN=5.02 TeV, Physics Letters B, Vol: 789, Pages: 643-665, ISSN: 0370-2693
Event-by-event fluctuations in the elliptic-flow coefficient are studied in PbPb collisions at TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions for charged particles with transverse momentum and pseudorapidity are determined for different collision centrality classes. The moments of the distributions are used to calculate the coefficients based on cumulant orders 2, 4, 6, and 8. A rank ordering of the higher-order cumulant results and nonzero standardized skewness values obtained for the distributions indicate non-Gaussian initial-state fluctuations. Bessel–Gaussian and elliptic power fits to the flow distributions are studied to characterize the initial-state spatial anisotropy.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of medium-induced modifications of jet fragmentation in Pb-Pb collisions at root s(NN)=5.02 TeV using isolated photon-tagged jets, Physical Review Letters, Vol: 121, ISSN: 0031-9007
Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with pjetT>30 GeV/c in events containing an isolated photon with pγT>60 GeV/c, using charged tracks with transverse momentum ptrkT>1 GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial pT and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) pT particles, with a transition around 3 GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of differential cross sections for Z boson production in association with jets in proton- proton collisions at v s=13TeV, The European Physical Journal C, Vol: 78, ISSN: 1434-6044
The production of a Z boson, decaying to two charged leptons, in association with jets in proton-proton collisions at a centre-of-mass energy of 13TeV is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19fb-1. The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the Z boson, the jet kinematic variables (transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the Z boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes one-loop corrections. The third is a fixed-order calculation with next-to-next-to-leading order accuracy for the process with a Z boson and one parton in the final state. The fourth combines the fully differential next-to-next-to-leading order calculation of the process with no parton in the final state with next-to-next-to-leading logarithm resummation and parton showering.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for black holes and sphalerons in high-multiplicity final states in proton-proton collisions a root s=13 TeVt, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search in energetic, high-multiplicity final states for evidence of physics beyond the standard model, such as black holes, string balls, and electroweak sphalerons, is presented. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected with the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV in 2016. Standard model backgrounds, dominated by multijet production, are determined from control regions in data without any reliance on simulation. No evidence for excesses above the predicted background is observed. Model-independent 95% confidence level upper limits on the cross section of beyond the standard model signals in these final states are set and further interpreted in terms of limits on semiclassical black hole, string ball, and sphaleron production. In the context of models with large extra dimensions, semiclassical black holes with minimum masses as high as 10.1 TeV and string balls with masses as high as 9.5 TeV are excluded by this search. Results of the first dedicated search for electroweak sphalerons are presented. An upper limit of 0.021 is set at 95% confidence level on the fraction of all quark-quark interactions above the nominal threshold energy of 9 TeV resulting in the sphaleron transition.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurements of Higgs boson properties in the diphoton decay channel in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
Measurements of Higgs boson properties in the H → γγ decay channel are reported. The analysis is based on data collected by the CMS experiment in proton-proton collisions at √=13 TeV during the 2016 LHC running period, corresponding to an integrated luminosity of 35.9 fb−1. Allowing the Higgs mass to float, the measurement yields a signal strength relative to the standard model prediction of 1.18 − 0.14 + 0.17 = 1.18 − 0.11 + 0.12 (stat) − 0.07 + 0.09 (syst) − 0.06 + 0.07 (theo), which is largely insensitive to the exact Higgs mass around 125 GeV. Signal strengths associated with the different Higgs boson production mechanisms, couplings to bosons and fermions, and effective couplings to photons and gluons are also measured.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the top quark mass with lepton plus jets final states using pp collisions at root s=13 TeV, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
The mass of the top quark is measured using a sample of tt⎯⎯ events collected by the CMS detector using proton-proton collisions at √=13 TeV at the CERN LHC. Events are selected with one isolated muon or electron and at least four jets from data corresponding to an integrated luminosity of 35.9fb−1. For each event the mass is reconstructed from a kinematic fit of the decay products to a tt⎯⎯ hypothesis. Using the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in qq⎯⎯⎯′ decays. The measurement is calibrated on samples simulated at next-to-leading order matched to a leading-order parton shower. The top quark mass is found to be 172.25±0.08(stat+JSF)±0.62(syst)GeV. The dependence of this result on the kinematic properties of the event is studied and compared to predictions of different models of tt⎯⎯ production, and no indications of a bias in the measurements are observed.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the groomed jet mass in PbPb and pp collisions at root s(NN)=5:02 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A measurement of the groomed jet mass in PbPb and pp collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS detector at the LHC is presented. Jet grooming is a recursive procedure which sequentially removes soft constituents of a jet until a pair of hard subjets is found. The resulting groomed jets can be used to study modifications to the parton shower evolution in the presence of the hot and dense medium created in heavy ion collisions. Predictions of groomed jet properties from the pythia and herwig++ event generators agree with the measurements in pp collisions. When comparing the results from the most central PbPb collisions to pp data, a hint of an increase of jets with large jet mass is observed, which could originate from additional medium-induced radiation at a large angle from the jet axis. However, no modification of the groomed mass of the core of the jet is observed for all PbPb centrality classes. The PbPb results are also compared to predictions from the jewel and q-pythia event generators, which predict a large modification of the groomed mass not observed in the data.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state with two bquarks and two tau leptons in proton-proton collisions at root s=13 TeV The CMS Collaboration, PHYSICS LETTERS B, Vol: 785, Pages: 462-488, ISSN: 0370-2693
A search for an exotic decay of the Higgs boson to a pair of light pseudoscalar bosons is performed for the first time in the final state with two b quarks and two τ leptons. The search is motivated in the context of models of physics beyond the standard model (SM), such as two Higgs doublet models extended with a complex scalar singlet (2HDM + S), which include the next-to-minimal supersymmetric SM (NMSSM). The results are based on a data set of proton–proton collisions corresponding to an integrated luminosity of , accumulated by the CMS experiment at the LHC in 2016 at a center-of-mass energy of . Masses of the pseudoscalar boson between 15 and are probed, and no excess of events above the SM expectation is observed. Upper limits between 3 and 12% are set on the branching fraction assuming the SM production of the Higgs boson. Upper limits are also set on the branching fraction of the Higgs boson to two light pseudoscalar bosons in different 2HDM + S scenarios. Assuming the SM production cross section for the Higgs boson, the upper limit on this quantity is as low as 20% for a mass of the pseudoscalar of in the NMSSM.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Study of jet quenching with isolated-photon plus jet correlations in PbPb and pp collisions at root s(NN)=5.02 TeV, PHYSICS LETTERS B, Vol: 785, Pages: 14-39, ISSN: 0370-2693
Measurements of azimuthal angle and transverse momentum ( ) correlations of isolated photons and associated jets are reported for and PbPb collisions at . The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with and an associated jet with , the photon+jet azimuthal correlation and imbalance in PbPb collisions are studied as functions of collision centrality and . The results are compared to reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio decreases significantly for PbPb data relative to the reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with is observed to be shifted towards lower values in central PbPb collisions compared to collisions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Pseudorapidity and transverse momentum dependence of flow harmonics in pPb and PbPb collisions, PHYSICAL REVIEW C, Vol: 98, ISSN: 2469-9985
Measurements of azimuthal angular correlations are presented for high-multiplicity pPb collisions at √sNN=5.02TeV and peripheral PbPb collisions at √sNN=2.76TeV. The data used in this work were collected with the Compact Muon Solenoid (CMS) detector at the European Organization for Nuclear Research (CERN) Large Hadron Collider (LHC). Fourier coefficients as functions of transverse momentum and pseudorapidity are studied using the scalar product method; four-, six-, and eight-particle cumulants; and the Lee-Yang zero technique. The influence of event plane decorrelation is evaluated using the scalar product method and found to account for most of the observed pseudorapidity dependence.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for new physics in dijet angular distributions using proton-proton collisions at root s=13 TeV and constraints on dark matter and other models, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton–proton collisions at √=13TeV. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9fb−1. The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani–Hamed–Dimopoulos–Dvali model of extra dimensions. In the Giudice–Rattazzi–Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling q=1.0.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for Z gamma resonances using leptonic and hadronic final states in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search is presented for resonances decaying to a Z boson and a photon. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1, and collected with the CMS detector at the LHC in 2016. Two decay modes of the Z boson are investigated. In the leptonic channels, the Z boson candidates are reconstructed using electron or muon pairs. In the hadronic channels, they are identified using a large-radius jet, containing either light-quark or b quark decay products of the Z boson, via jet substructure and advanced b quark tagging techniques. The results from these channels are combined and interpreted in terms of upper limits on the product of the production cross section and the branching fraction to Zγ for narrow and broad spin-0 resonances with masses between 0.35 and 4.0 TeV, providing thereby the most stringent limits on such resonances.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for a heavy resonance decaying into a Z boson and a Z or W boson in 2l2q final states at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search has been performed for heavy resonances decaying to ZZ or ZW in 2ℓ2q final states, with two charged leptons (ℓ = e, μ) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of s√=13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W′ bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for top squarks decaying via four-body or chargino-mediated modes in single-lepton final states in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for the pair production of the lightest supersymmetric partner of the top quark (t~1) is presented. The search focuses on a compressed scenario where the mass difference between the top squark and the lightest supersymmetric particle, often considered to be the lightest neutralino (χ~01), is smaller than the mass of the W boson. The proton-proton collision data were recorded by the CMS experiment at a centre-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb−1. In this search, two decay modes of the top squark are considered: a four-body decay into a bottom quark, two additional fermions, and a χ~01; and a decay via an intermediate chargino. Events are selected using the presence of a high-momentum jet, significant missing transverse momentum, and a low transverse momentum electron or muon. Two analysis techniques are used, targeting different decay modes of the t~1: a sequential selection and a multivariate technique. No evidence for the production of top squarks is found, and mass limits at 95% confidence level are set that reach up to 560 GeV, depending on the m(t~1)−m(χ~01) mass difference and the decay mode.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the Z/gamma* -> tau tau cross section in pp collisions at root s=13 TeV and validation of tau lepton analysis techniques, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
A measurement is presented of the Z/γ∗→ττ cross section in pp collisions at s√=13 TeV, using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.3 fb−1. The product of the inclusive cross section and branching fraction is measured to be σ(pp→Z/γ∗+X)B(Z/γ∗→ττ)=1848±12(stat)±67 (syst \,+\,lumi) pb, in agreement with the standard model expectation, computed at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. The measurement is used to validate new analysis techniques relevant for future measurements of τ lepton production. The measurement also provides the reconstruction efficiency and energy scale for τ decays to hadrons+ντ final states, determined with respective relative uncertainties of 2.2 and 0.9%.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for additional neutral MSSM Higgs bosons in the tau tau final state in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search is presented for additional neutral Higgs bosons in the τ τ final state in proton-proton collisions at the LHC. The search is performed in the context of the minimal supersymmetric extension of the standard model (MSSM), using the data collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes production of the Higgs boson in association with b quarks. No significant deviation above the expected background is observed. Model-independent limits at 95% confidence level (CL) are set on the product of the branching fraction for the decay into τ leptons and the cross section for the production via gluon fusion or in association with b quarks. These limits range from 18 pb at 90 GeV to 3.5 fb at 3.2 TeV for gluon fusion and from 15 pb (at 90 GeV) to 2.5 fb (at 3.2 TeV) for production in association with b quarks, assuming a narrow width resonance. In the m h hod + scenario these limits translate into a 95% CL exclusion of tan β > 6 for neutral Higgs boson masses below 250 GeV, where tan β is the ratio of the vacuum expectation values of the neutral components of the two Higgs doublets. The 95% CL exclusion contour reaches 1.6 TeV for tan β = 60.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for third-generation scalar leptoquarks decaying to a top quark and a tau lepton at root s=13 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
A search for pair production of heavy scalar leptoquarks (LQs), each decaying into a top quark and a τ lepton, is presented. The search considers final states with an electron or a muon, one or two τ leptons that decayed to hadrons, and additional jets. The data were collected in 2016 in proton–proton collisions at s√=13TeV with the CMS detector at the LHC, and correspond to an integrated luminosity of 35.9fb−1. No evidence for pair production of LQs is found. Assuming a branching fraction of unity for the decay LQ→tτ, upper limits on the production cross section are set as a function of LQ mass, excluding masses below 900GeV at 95% confidence level. These results provide the most stringent limits to date on the production of scalar LQs that decay to a top quark and a τ lepton.
We report a measurement of the lifetime of the Ω0c baryon using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment. The sample consists of about 1000 Ω−b→Ω0cμ−¯νμX signal decays, where the Ω0c baryon is detected in the pK−K−π+ final state and X represents possible additional undetected particles in the decay. The Ω0c lifetime is measured to be τΩ0c=268±24±10±2 fs, where the uncertainties are statistical, systematic, and from the uncertainty in the D+ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.
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