Abstract Measurements of inclusive and normalized differential cross sections of the associated production of top quark-antiquark and bottom quark-antiquark pairs, t t ¯ b b ¯ $$ ...\textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ , are presented. The results are based on data from proton-proton collisions collected by the CMS detector at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb −1. The cross sections are measured in the lepton+jets decay channel of the top quark pair, using events containing exactly one isolated electron or muon and at least five jets. Measurements are made in four fiducial phase space regions, targeting different aspects of the t t ¯ b b ¯ $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ process. Distributions are unfolded to the particle level through maximum likelihood fits, and compared with predictions from several event generators. The inclusive cross section measurements of this process in the fiducial phase space regions are the most precise to date. In most cases, the measured inclusive cross sections exceed the predictions with the chosen generator settings. The only exception is when using a particular choice of dynamic renormalization scale, μ R = 1 2 ∏ i = t , t ¯ , b , b ¯ m T , i 1 / 4 $$ {\mu}_{\textrm{R}}=\frac{1}{2}{\prod}_{i=\textrm{t},\overline{\textrm{t}},\textrm{b},\overline{\textrm{b}}}{m}_{\textrm{T},i}^{1/4} $$ , where m T , i 2 = m i 2 + p T , i 2 $$ {m}_{\textrm{T},i}^2={m}_i^2+{p}_{\textrm{T},i}^2 $$ are the transverse masses of top and bottom quarks. The differential cross sections show varying degrees of compatibility with the theoretical predictions, and none of the tested generators with the chosen settings simultaneously describe all the measured distributions.
Abstract An inclusive search for long-lived exotic particles (LLPs) decaying to final states with a pair of muons is presented. The search uses data corresponding to an integrated luminosity of 36.6 ...fb −1 collected by the CMS experiment from the proton-proton collisions at s $$ \sqrt{s} $$ = 13.6 TeV in 2022, the first year of Run 3 of the CERN LHC. The experimental signature is a pair of oppositely charged muons originating from a secondary vertex spatially separated from the proton-proton interaction point by distances ranging from several hundred μm to several meters. The sensitivity of the search benefits from new triggers for displaced dimuons developed for Run 3. The results are interpreted in the framework of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons, and of an R-parity violating supersymmetry model, in which long-lived neutralinos decay to a pair of muons and a neutrino. The limits set on these models are the most stringent to date in wide regions of lifetimes for LLPs with masses larger than 10 GeV.
Abstract The hydrodynamic flow-like behavior of charged hadrons in high-energy lead-lead collisions is studied through multiparticle correlations. The elliptic anisotropy values based on different ...orders of multiparticle cumulants, v 2{2k}, are measured up to the tenth order (k = 5) as functions of the collision centrality at a nucleon-nucleon center-of-mass energy of s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV. The data were recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 0.607 nb −1. A hierarchy is observed between the coefficients, with v 2{2} > v 2{4} ≳ v 2{6} ≳ v 2{8} ≳ v 2{10}. Based on these results, centrality-dependent moments for the fluctuation-driven event-by-event v 2 distribution are determined, including the skewness, kurtosis and, for the first time, superskewness. Assuming a hydrodynamic expansion of the produced medium, these moments directly probe the initial-state geometry in high-energy nucleus-nucleus collisions.
Abstract The production of prompt Λ c + $$ {\Lambda}_{\textrm{c}}^{+} $$ baryons is measured via the exclusive decay channel Λ c + → p K − π + $$ {\Lambda}_{\textrm{c}}^{+}\to ...p{\textrm{K}}^{-}{\pi}^{+} $$ at a center-of-mass energy per nucleon pair of 5.02 TeV, using proton-proton (pp) and lead-lead (PbPb) collision data collected by the CMS experiment at the CERN LHC. The pp and PbPb data were obtained in 2017 and 2018 with integrated luminosities of 252 and 0.607 nb −1, respectively. The measurements are performed within the Λ c + $$ {\Lambda}_{\textrm{c}}^{+} $$ rapidity interval |y| < 1 with transverse momentum (p T) ranges of 3–30 and 6–40 GeV/c for pp and PbPb collisions, respectively. Compared to the yields in pp collisions scaled by the expected number of nucleon-nucleon interactions, the observed yields of Λ c + $$ {\Lambda}_{\textrm{c}}^{+} $$ with p T > 10 GeV/c are strongly suppressed in PbPb collisions. The level of suppression depends significantly on the collision centrality. The Λ c + $$ {\Lambda}_{\textrm{c}}^{+} $$ /D0 production ratio is similar in PbPb and pp collisions at p T > 10 GeV/c, suggesting that the coalescence process does not play a dominant role in prompt Λ c + $$ {\Lambda}_{\textrm{c}}^{+} $$ baryon production at higher p T.
Abstract A measurement of the Higgs boson (H) production via vector boson fusion (VBF) and its decay into a bottom quark-antiquark pair ( b b ¯ $$ \textrm{b}\overline{\textrm{b}} $$ ) is presented ...using proton-proton collision data recorded by the CMS experiment at s $$ \sqrt{s} $$ = 13 TeV and corresponding to an integrated luminosity of 90.8 fb −1. Treating the gluon-gluon fusion process as a background and constraining its rate to the value expected in the standard model (SM) within uncertainties, the signal strength of the VBF process, defined as the ratio of the observed signal rate to that predicted by the SM, is measured to be μ Hb b ¯ qqh = 1.01 − 0.46 + 0.55 $$ {\mu}_{\textrm{Hb}\overline{\textrm{b}}}^{\textrm{qqh}}={1.01}_{-0.46}^{+0.55} $$ . The VBF signal is observed with a significance of 2.4 standard deviations relative to the background prediction, while the expected significance is 2.7 standard deviations. Considering inclusive Higgs boson production and decay into bottom quarks, the signal strength is measured to be μ Hb b ¯ incl . = 0.99 − 0.41 + 0.48 $$ {\mu}_{\textrm{Hb}\overline{\textrm{b}}}^{\textrm{incl}.}={0.99}_{-0.41}^{+0.48} $$ , corresponding to an observed (expected) significance of 2.6 (2.9) standard deviations.
Abstract The polarization of τ leptons is measured using leptonic and hadronic τ lepton decays in Z → τ + τ − events in proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV recorded by CMS at the ...CERN LHC with an integrated luminosity of 36.3 fb −1. The measured τ − lepton polarization at the Z boson mass pole is P τ Z $$ {\mathcal{P}}_{\tau}\left(\textrm{Z}\right) $$ = −0.144 ± 0.006 (stat) ± 0.014 (syst) = −0.144 ± 0.015, in good agreement with the measurement of the τ lepton asymmetry parameter of A τ = 0.1439 ± 0.0043 = − P τ Z $$ -{\mathcal{P}}_{\tau}\left(\textrm{Z}\right) $$ at LEP. The τ lepton polarization depends on the ratio of the vector to axial-vector couplings of the τ leptons in the neutral current expression, and thus on the effective weak mixing angle sin2 θ W eff $$ {\theta}_{\textrm{W}}^{\textrm{eff}} $$ , independently of the Z boson production mechanism. The obtained value sin2 θ W eff $$ {\theta}_{\textrm{W}}^{\textrm{eff}} $$ = 0.2319 ± 0.0008(stat) ± 0.0018(syst) = 0.2319 ± 0.0019 is in good agreement with measurements at e + e − colliders.
Abstract A search for resonances in events with the γ+jet final state has been performed using proton-proton collision data collected at s $$ \sqrt{s} $$ = 13 TeV by the CMS experiment at the LHC. ...The total data analyzed correspond to an integrated luminosity of 138 fb −1. Models of excited quarks and quantum black holes are considered. Using a wide-jet reconstruction for the candidate jet, the γ+jet invariant mass spectrum measured in data is examined for the presence of resonances over the standard model continuum background. The background is estimated by fitting this mass distribution with a functional form. The data exhibit no statistically significant deviations from the expected standard model background. Exclusion limits at 95% confidence level on the resonance mass and other parameters are set. Excited light-flavor quarks (excited bottom quarks) are excluded up to a mass of 6.0 (3.8) TeV. Quantum black hole production is excluded for masses up to 7.5 (5.2) TeV in the Arkani-Hamed-Dimopoulos-Dvali (Randall-Sundrum) model. These lower mass bounds are the most stringent to date among those obtained in the γ+jet final state.
Abstract A search for direct production of low-mass dimuon resonances is performed using s $$ \sqrt{s} $$ = 13 TeV proton-proton collision data collected by the CMS experiment during the 2017–2018 ...operation of the CERN LHC with an integrated luminosity of 96.6 fb −1. The search exploits a dedicated high-rate trigger stream that records events with two muons with transverse momenta as low as 3 GeV but does not include the full event information. The search is performed by looking for narrow peaks in the dimuon mass spectrum in the ranges of 1.1–2.6 GeV and 4.2–7.9 GeV. No significant excess of events above the expectation from the standard model background is observed. Model-independent limits on production rates of dimuon resonances within the experimental fiducial acceptance are set. Competitive or world’s best limits are set at 90% confidence level for a minimal dark photon model and for a scenario with two Higgs doublets and an extra complex scalar singlet (2HDM+S). Values of the squared kinetic mixing coefficient ε 2 in the dark photon model above 10 −6 are excluded over most of the mass range of the search. In the 2HDM+S, values of the mixing angle sin(θ H) above 0.08 are excluded over most of the mass range of the search with a fixed ratio of the Higgs doublets vacuum expectation tan β = 0.5.
Abstract A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been ...performed using proton-proton collision data collected at $${\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V}}$$ s = 13 Te V by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$ fb - 1 . The 95% confidence level upper limit set on the branching fraction of the 125 $$\,\text {Ge}\hspace{-.08em}\text {V}$$ Ge V Higgs boson to invisible particles, $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$ B ( H → inv ) , is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$ B ( H → inv ) searches carried out at $${\sqrt{s}=7}$$ s = 7 , 8, and 13 $$\,\text {Te}\hspace{-.08em}\text {V}$$ Te V in complementary production modes. The combined upper limit at 95% confidence level on $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$ B ( H → inv ) is 0.15 (0.08 expected).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at ...the LHC corresponding to an integrated luminosity of 138 fb −1 at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of signal events with exactly one or more than one b quark jet. Results are also interpreted in a lepton-flavor-universal model with Z′ boson couplings to a bb quark pair (g b), an sb quark pair (g b δ bs), and any same-flavor charged lepton (g ℓ ) or neutrino pair (g ν ), with |g ν | = |g ℓ |. For a Z′ boson with a mass m Z ′ $$ {m}_{{\textrm{Z}}^{\prime }} $$ = 350 GeV (2 TeV) and |δ bs | < 0.25, the majority of the parameter space with 0.0057 < |g ℓ | < 0.35 (0.25 < |g ℓ | < 0.43) and 0.0079 < |g b | < 0.46 (0.34 < |g b | < 0.57) is excluded at 95% confidence level. Finally, constraints are set on a Z′ model with parameters consistent with low-energy b → sℓℓ measurements. In this scenario, most of the allowed parameter space is excluded for a Z′ boson with 350 < m Z ′ $$ {m}_{{\textrm{Z}}^{\prime }} $$ < 500 GeV, while the constraints are less stringent for higher m Z ′ $$ {m}_{{\textrm{Z}}^{\prime }} $$ hypotheses. This is the first dedicated search at the LHC for a high-mass dimuon resonance produced in association with multiple b quark jets, and the constraints obtained on models with this signature are the most stringent to date.
