Top Quarks from Tevatron to the LHC

Nature

In the version of this article initially published, CMS Collaboration author names, affiliations and acknowledgements were omitted and have now been included in the HTML and PDF versions of the article.

European Physical Journal C

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.

Nature physics

Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be , and …

Journal of High Energy Physics

A search for supersymmetry is presented in events with a single charged lepton, electron or muon, and multiple hadronic jets. The data correspond to an integrated luminosity of 138 fb− 1 of proton-proton collisions at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the CERN LHC. The search targets gluino pair production, where the gluinos decay into final states with the lightest supersymmetric particle (LSP) and either a top quark-antiquark () pair, or a light-flavor quark-antiquark () pair and a virtual or on-shell W boson. The main backgrounds, pair and W+ jets production, are suppressed by requirements on the azimuthal angle between the momenta of the lepton and of its reconstructed parent W boson candidate, and by top quark and W boson identification based on a machine-learning technique. The number of observed events is consistent with the expectations from standard model …

The second-order () and third-order () Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/, as well as prompt (2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of = 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb recorded with the CMS detector. The J/ and (2S) mesons are reconstructed using their dimuon decay channel. The and coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured values for prompt J/ mesons are found to be larger than those for nonprompt J/ mesons. The prompt J/ values at high are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ meson and prompt (2S) and values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.

The European Physical Journal C

Measurements of Higgs boson production, where the Higgs boson decays into a pair of τ leptons, are presented, using a sample of proton-proton collisions collected with the CMS experiment at a center-of-mass energy of, corresponding to an integrated luminosity of 138 fb-1. Three analyses are presented. Two are targeting Higgs boson production via gluon fusion and vector boson fusion: a neural network based analysis and an analysis based on an event categorization optimized on the ratio of signal over background events. These are complemented by an analysis targeting vector boson associated Higgs boson production. Results are presented in the form of signal strengths relative to the standard model predictions and products of cross sections and branching fraction to τ leptons, in up to 16 different kinematic regions. For the simultaneous measurements of the neural network based analysis and the …

Symmetry

The class of two-interacting-qubit spin–boson models with vanishing transverse fields on the spin-pair is studied. The model can be mapped exactly into two independent standard single-impurity spin–boson models where the role of the tunneling parameter is played by the spin–spin coupling. The dynamics of the magnetization are analyzed for different levels of (an)isotropy. The existence of a decoherence-free subspace, as well as of different classical regimes separated by a critical temperature, and symptoms of quantum (first-order and Kosterlitz–Thouless type) phase transitions in the Ohmic regime are brought to light.

IPPOG Annual Report 2021 with two parts. The first part corresponds to an introduction of the collaboration along with a description of the main activities in 2021. The second part provides a summary of main activities of the IPPOG members in 2021.

The European Physical Journal C

A search is presented for slepton pairs produced in proton–proton collisions at a center-of-mass energy of 13. The search is carried out in events containing two leptons in the final state, on the assumption that each slepton decays primarily to a lepton and a neutralino. Events are considered in which each lepton decays to one or more hadrons and a neutrino, or in which one of the leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for slepton pair production in various models for slepton masses between 90 and 200 and neutralino masses of 1, 10, and 20. In the case of purely left-handed slepton production and …

The azimuthal anisotropy of Υ (1S) mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon centerof-mass energy of 8.16 TeV. The Υ (1S) mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the Υ (1S) mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of Υ (1S) transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for Υ (1S) mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV.

Abstract The ATLAS and CMS Collaborations both use POWHEG+ PYTHIA8 for their nominal Monte-Carlo simulations. Presented here is a second iteration of agreed-upon common settings for such a setup, in order to ease comparison and combination of ATLAS and CMS results. Validation of each experiment's ability to reproduce identical samples is shown, and subsequent comparisons are made to publicly available unfolded data. An additional common setup, using the SHERPA Monte-Carlo generation package, is similarly validated and compared.

Journal of High Energy Physics

The charge-parity (CP) structure of the Yukawa interaction between the Higgs (H) boson and the top quark is measured in a data sample enriched in the t H and tH associated production, using 138 fb− 1 of data collected in proton-proton collisions at= 13 TeV by the CMS experiment at the CERN LHC. The study targets events where the H boson decays via H→ WW or H→ ττ and the top quarks decay via t→ Wb: the W bosons decay either leptonically or hadronically, and final states characterized by the presence of at least two leptons are studied. Machine learning techniques are applied to these final states to enhance the separation of CP-even from CP-odd scenarios. Two-dimensional confidence regions are set on κ t and t, which are respectively defined as the CP-even and CP-odd top-Higgs Yukawa coupling modifiers. No significant fractional CP-odd contributions, parameterized by the quantity|| are observed; the …

Journal of Instrumentation

The Large Hadron Collider at CERN will undergo an upgrade in order to increase its luminosity to 7.5× 1034 cm− 2s− 1. The increased luminosity during this High-Luminosity running phase, starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square 50 μm× 50 μm and rectangular 100 μm× 25 μm pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS during the High-Luminosity running phase. A spatial resolution of approximately 3.4 μm (2 μm) is obtained using the modules with 50 μm× 50 μm (100 μm× 25 μm) pixels at the optimal angle …

Physical Review D

For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of s NN= 8.16 TeV, almost 300 times higher than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the epos-lhc generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology, the epos-lhc, qgsjet ii, and hijing predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.

Encuentros multidisciplinares

En este artículo se presenta el origen, la estructura, la organización, los objetivos, así como las actividades principales de la Asociación Española para el Avance de la Ciencia (AEAC), junto con una reflexión final sobre las dimensiones éticas de la investigación científica. Como se puede comprobar en el desarrollo de las distintas secciones, se trata de una organización única a nivel nacional en su objetivo declarado de establecer un puente permanente entre ciencia y sociedad. La consideración de la ciencia como un derecho de la ciudadanía y la defensa del conocimiento científico como herramienta de progreso y justicia social son rasgos que singularizan a la AEAC y que se manifiestan en las acciones y actividades que se desarrollan en su seno

Journal of High Energy Physics

A search is reported for heavy resonances and quantum black holes decaying into eμ, eτ, and μτ final states in proton-proton collision data recorded by the CMS experiment at the CERN LHC during 2016–2018 at= 13 TeV, corresponding to an integrated luminosity of 138 fb− 1. The eμ, eτ, and μτ invariant mass spectra are reconstructed, and no evidence is found for physics beyond the standard model. Upper limits are set at 95% confidence level on the product of the cross section and branching fraction for lepton flavor violating signals. Three benchmark signals are studied: resonant τ sneutrino production in R parity violating supersymmetric models, heavy Z′ gauge bosons with lepton flavor violating decays, and nonresonant quantum black hole production in models with extra spatial dimensions. Resonant τ sneutrinos are excluded for masses up to 4.2 TeV in the eμ channel, 3.7 TeV in the eτ channel, and 3 …

Physics Letters B

The first measurements of the Fourier coefficients (V n Δ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8 nb− 1 of ultra-peripheral proton-lead (pPb) collisions at s NN= 8.16 TeV using 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 V n Δ coefficients are presented in ranges of event multiplicity and transverse momentum (p T) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean p T of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, V 1 Δ is negative, V 2 Δ is positive, and V 3 …

Physics Letters B

A precise measurement of the invisible width of the Z boson produced in proton-proton collisions at a center-of-mass energy of 13 TeV is presented using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 36.3 fb− 1. The result is obtained from a simultaneous fit to kinematic distributions for two data samples of Z boson plus jets: one dominated by Z boson decays to invisible particles and the other by Z boson decays to muon and electron pairs. The invisible width is measured to be 523±3 (stat)±16 (syst) MeV. This result is the first precise measurement of the invisible width of the Z boson at a hadron collider, and is the single most precise direct measurement to date, competitive with the combined result of the direct measurements from the LEP experiments.

Journal of High Energy Physics

A search for the exotic decay of the Higgs boson to a pair of light pseudoscalars, each of which subsequently decays into a pair of photons, is presented. The search uses data from proton-proton collisions at= 13 TeV recorded with the CMS detector at the LHC that corresponds to an integrated luminosity of 132 fb− 1. The analysis probes pseudoscalar bosons with masses in the range 15–62 GeV, coming from the Higgs boson decay, which leads to four well-isolated photons in the final state. No significant deviation from the background-only hypothesis is observed. Upper limits are set on the product of the Higgs boson production cross section and branching fraction into four photons. The observed (expected) limits range from 0.80 (1.00) fb for a pseudoscalar boson mass of 15 GeV to 0.26 (0.24) fb for a mass of 62 GeV at 95% confidence level.