1,721,654 research outputs found
The CMS statistical analysis and combination tool: COMBINE
Full text linkThis paper describes the Combine software package used for statistical analyses by the CMS Collaboration. The package, originally designed to perform searches for a Higgs boson and the combined analysis of those searches, has evolved to become the statistical analysis tool presently used in the majority of measurements and searches performed by the CMS Collaboration. It is not specific to the CMS experiment, and this paper is intended to serve as a reference for users outside of the CMS Collaboration, providing an outline of the most salient features and capabilities. Readers are provided with the possibility to run Combine and reproduce examples provided in this paper using a publicly available container image. Since the package is constantly evolving to meet the demands of ever-increasing data sets and analysis sophistication, this paper cannot cover all details of Combine. However, the online documentation referenced within this paper provides an up-to-date and complete user
guide
Review of top quark mass measurements in CMS
Full text linkThe top quark mass is one of the most intriguing parameters of the standard model (SM). Its value indicates a Yukawa coupling close to unity, and the resulting strong ties to Higgs physics make the top quark mass a crucial ingredient for understanding essential aspects of the electroweak sector of the SM. This review offers the first comprehensive overview of the top quark mass measurements performed by the CMS Collaboration using the data collected at centre-of-mass energies of 7, 8, and 13 TeV. Moreover, a detailed description of the top quark event reconstruction is provided and dedicated studies of the dominant uncertainties in the modelling of the signal processes are discussed. The interpretation of the experimental results on the top quark mass in terms of the SM Lagrangian parameter is challenging and is a focus of an ongoing discussion in the theory community. The CMS Collaboration has performed two main types of top quark mass measurements, addressing this challenge from different perspectives: highly precise ‘direct’ measurements, based on reconstructed top quark decay products and relying exclusively on Monte-Carlo simulations, as well as ‘indirect’ measurements, where the simulations are employed to determine parton-level cross sections that are compared to fixed-order perturbative calculations. Recent mass extractions using Lorentz-boosted top quarks open a new avenue of measurements based on top quark decay products contained in a single particle jet, with promising prospects for accurate theoretical interpretations
Measurement of inclusive jet cross sections in pp and PbPb collisions at sqrt(s_NN) = 2.76 TeV
No full textInclusive jet spectra from pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76TeV, collected with the CMS detector at the CERN Large Hadron Collider, are presented. Jets are reconstructed with three different distance parameters (R=0.2, 0.3, and 0.4) for transverse momentum (pT) greater than 70GeV/c and pseudorapidity |η|<2. Next-to-leading-order quantum chromodynamic calculations with nonperturbative corrections are found to overpredict jet production cross sections in pp for small distance parameters. The jet nuclear modification factors for PbPb compared to pp collisions, show a steady decrease from peripheral to central events, along with a weak dependence on the jet pT. They are found to be independent of the distance parameter in the measured kinematic range. ©2017 CERN, for the CMS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation
Enriching the physics program of the CMS experiment via data scouting and data parking
Full text linkSpecialized data-taking and data-processing techniques were introduced by the CMS experiment in Run 1 of the CERN LHC to enhance the sensitivity of searches for new physics and the precision of standard model measurements. These techniques, termed data scouting and data parking, extend the data-taking capabilities of CMS beyond the original design specifications. The novel data-scouting strategy trades complete event information for higher event rates, while keeping the data bandwidth within limits. Data parking involves storing a large amount of raw detector data collected by algorithms with low trigger thresholds to be processed when sufficient computational power is available to handle such data. The research program of the CMS Collaboration is greatly expanded with these techniques. The implementation, performance, and physics results obtained with data scouting and data parking in CMS over the last decade are discussed in this Report, along with new developments aimed at further improving low-mass physics sensitivity over the next years of data taking
Searches for Higgs boson production through decays of heavy resonances
No full textThe discovery of the Higgs boson has led to new possible signatures for heavy resonance searches at the LHC. Since then, search channels including at least one Higgs boson plus another particle have formed an important part of the program of new physics searches. In this report, the status of these searches by the CMS Collaboration is reviewed. Searches are discussed for resonances decaying to two Higgs bosons, a Higgs and a vector boson, or a Higgs boson and another new resonance. All analyses use proton–proton collision data collected at √s=13TeV in the years 2016–2018. A combination of the results of these searches is presented together with constraints on different beyond-the-standard model scenarios, including scenarios with extended Higgs sectors, heavy vector bosons and extra dimensions. Studies are shown for the first time by CMS on the validity of the narrow-width approximation in searches for the resonant production of a pair of Higgs bosons. The potential for a discovery at the High Luminosity LHC is also discussed
Performance of heavy-flavour jet identification in Lorentz-boosted topologies in proton-proton collisions at sqrt(s) = 13 TeV
Full text linkMeasurements in the highly Lorentz-boosted regime provoke increased interest in probing
the Higgs boson properties and in searching for particles beyond the standard model at the LHC. In the CMS Collaboration, various boosted-object tagging algorithms, designed to identify hadronic jets originating from a massive particle decaying to bb or cc, have been developed and deployed across a range of physics analyses. This paper highlights their performance on simulated events, and summarizes novel calibration techniques using proton-proton collision data collected at √ s = 13 TeV during the 2016–2018 LHC data-taking period. Three dedicated methods are used for the calibration in multijet events, leveraging either achine learning techniques, the presence of muons within energetic boosted jets, or the reconstruction of hadronically decaying high-energy Z bosons. The calibration results, obtained through a combination of these approaches, are presented and discusse
Measurement of differential cross sections for the production of a Z boson in association with jets in proton-proton collisions at sqrt(s) = 13 TeV
Full text linkmeasurement is presented of the production of Z bosons that decay into two electrons or muons in
association with jets, in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were
recorded by the CMS Collaboration at the LHC with an integrated luminosity of 35.9 fb −1 . The differential
cross sections are measured as a function of the transverse momentum (p T ) of the Z boson and the
transverse momentum and rapidities of the five jets with largest pT . The jet multiplicity distribution is
measured for up to eight jets. The hadronic activity in the events is estimated using the scalar sum of the p T
of all the jets. All measurements are unfolded to the stable-particle level and compared with predictions
from various Monte Carlo event generators, as well as with expectations at leading and next-to-leading
orders in perturbative quantum chromodynamics
Performance of reconstruction and identification of tau leptons decaying to hadrons and nu_tau in pp collisions at sqrt(s) = 13 TeV
No full textThe algorithm developed by the CMS Collaboration to reconstruct and identify tau leptons produced in proton-proton collisions at root s = 7 and 8 TeV, via their decays to hadrons and a neutrino, has been significantly improved. The changes include a revised reconstruction of pi(0) candidates, and improvements in multivariate discriminants to separate tau leptons from jets and electrons. The algorithm is extended to reconstruct tau leptons in highly Lorentz-boosted pair production, and in the high-level trigger. The performance of the algorithm is studied using proton-proton collisions recorded during 2016 at root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). The performance is evaluated in terms of the efficiency for a genuine tau lepton to pass the identification criteria and of the probabilities for jets, electrons, and muons to be misidentified as tau leptons. The results are found to be very close to those expected from Monte Carlo simulation
Measurements of Higgs boson production cross section in the four-lepton final state in proton-proton collisions at sqrt(s) = 13.6 TeV
Full text linkThe measurements of the Higgs boson (H) production cross sections performed by the CMS Collaboration in the four-lepton (4l, l = e, μ) final state at a center-of-mass energy √s = 13.6 TeV are presented. These measurements are based on data collected with the CMS detector at the CERN LHC in 2022, corresponding to an integrated luminosity of 34.7 fb−1. Cross sections are measured in a fiducial region closely matching the experimental acceptance, both inclusively and differentially, as a function of the transverse momentum and the absolute value of the rapidity of the four-lepton system. The H → ZZ → 4l inclusive fiducial cross section is measured to be 2.89+0.53−0.49(stat)+0.29−0.21(syst) fb, in agreement with the standard model expectation of 3.09+0.27−0.24 fb
Observation of nuclear modifications in W+- boson production in pPb collisions at sqrt(s_NN) = 8.16 TeV
Full text link.
The production of W± bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of √sNN=8.16TeV. Measurements are performed in the W±→μ±νμ channel using a data sample corresponding to an integrated luminosity of 173.4±6.1nb−1, collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame |ημlab|25GeV/c. The W± boson differential cross sections, muon charge asymmetry, and the ratios of W± boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits
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