Correlations between mean transverse momentum $[p_{\rm T}]$ and anisotropic flow coefficients $v_{\rm 2}$ or $v_{\rm 3}$ are measured as a function of centrality in Pb$-$Pb and Xe$-$Xe collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and 5.44 TeV, respectively, with ALICE. In addition, the recently proposed higher-order correlation between $[p_{\rm T}]$, $v_{\rm 2}$, and $v_{\rm 3}$ is measured for the first time, which shows an anticorrelation for the presented centrality ranges. These measurements are compared with hydrodynamic calculations using IP-Glasma and $\rm T_{R}ENTo$ initial-state shapes, the former based on the Color Glass Condensate effective theory with gluon saturation, and the latter a parameterized model with nucleons as the relevant degrees of freedom. The data are better described by the IP-Glasma rather than the $\rm T_{R}ENTo$ based calculations. In particular, Trajectum and JETSCAPE predictions, both based on the $\rm T_{R}ENTo$ initial state model but with different parameter settings, fail to describe the measurements. As the correlations between $[p_{\rm T}]$ and $v_{\rm n}$ are mainly driven by the correlations of the size and the shape of the system in the initial state, these new studies pave a novel way to characterize the initial state and help pin down the uncertainty of the extracted properties of the quark$-$gluon plasma recreated in relativistic heavy-ion collisions.
Centrality dependence of $\rho\left(v_{2}^{2}, [p_{\rm T}] \right)$ and $\rho\left(v_{3}^{2}, [p_{\rm T}] \right)$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV
Centrality dependence of $\rho\left(v_{2}^{2}, [p_{\rm T}] \right)$ in Xe--Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV
Centrality dependence of $\rho\left(v_{3}^{2}, [p_{\rm T}] \right)$ in Xe--Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV
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/$\psi$ 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/$\psi$ mesons into pairs of oppositely charged muons - with a statistical significance above five standard deviations. We measured the inclusive fiducial cross section to be 272 $^{+141}_{-104}$ (stat) $\pm$ 17 (syst) fb, and compared it to theoretical expectations for triple-J/$\psi$ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross sections, double- and triple-parton scattering are the dominant contributions for the measured process.
Dimuon invariant mass ($m$), proper decay-length ($L$), transverse momentum ($p_{T}$), rapidity ($y$), and azimuthal angle ($\phi$) of each of the three $J/\psi$ candidates measured in the six triple-$J/\psi$ events passing our selection criteria.
Measured DPS effective cross section
$pp \rightarrow J/\psi J/\psi J/\psi X~$ fiducial cross section
The cross sections for inclusive and Mueller-Navelet dijet production are measured as a function of the rapidity separation between the jets in proton-proton collisions at $\sqrt{s} =$ 2.76 TeV for jets with transverse momentum $p_\mathrm{T}$$\gt$ 35 GeV and rapidity $\vert y\vert$$\lt$ 4.7. Various dijet production cross section ratios are also measured. A veto on additional jets with $p_\mathrm{T}$$\gt$ 20 GeV is introduced to improve the sensitivity to the effects of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution. The measurement is compared with the predictions of various Monte Carlo models based on leading-order and next-to-leading-order calculations including the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi leading-logarithm (LL) parton shower as well as the LL BFKL resummation.
Summary of the systematic uncertainties on the cross section dσincl/d∆y.
Summary of the systematic uncertainties on the cross section dσMN/d∆y.
Summary of the systematic uncertainties on the ratio Rincl.
Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of 87.9 $_{-7.3}^{+7.5}$ (stat) $_{-6.0}^{+7.3}$ (syst) fb for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations and the most precise determination to date. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as 2.37 $_{-0.42}^{+0.56}$ (stat) ${}_{-0.13}^{+0.27}$ (syst). Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be 0.54 $\pm$ 0.16 (stat) $\pm$ 0.06 (syst), in agreement with SM predictions.
Numerical results of inclusive cross section measurements. Each row represents a measurement: "tZq" for fully inclusive, "tZq_top" for the top quark channel, "tZq_antitop" for the top antiquark channel, "ratio" for the ratio measurement. The columns are the central value, statistical error up/down, systematic error up/down. All values are in fb, except for the ratio (dimensionless).
Numerical representation of impact plot.
Simulated signal, total background, and observed data in the signal category with exactly 1 b jet and 2-3 jets for the three data-taking years combined. For the uncertainty on the signal and background, both the total (systematic+statistical) and statistical uncertainties are provided. The uncertainty on the data is the (statistical) Poisson uncertainty. Note that this is the prefit version.
Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets originating from bottom (b) or charm (c) quarks. An overview of the algorithms used to identify c jets is described and a novel method to calibrate them is presented. This new method adjusts the entire distributions of the outputs obtained when the algorithms are applied to jets of different flavours. It is based on an iterative approach exploiting three distinct control regions that are enriched with either b jets, c jets, or light-flavour and gluon jets. Results are presented in the form of correction factors evaluated using proton-proton collision data with an integrated luminosity of 41.5 fb$^{-1}$ at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment in 2017. The closure of the method is tested by applying the measured correction factors on simulated data sets and checking the agreement between the adjusted simulation and collision data. Furthermore, a validation is performed by testing the method on pseudodata, which emulate different miscalibration conditions. The calibrated results enable the use of the full distributions of heavy-flavour identification algorithm outputs, e.g. as inputs to machine-learning models. Thus, they are expected to increase the sensitivity of future physics analyses.
The shape calibration SF values as a function of CvsL and CvsB for DeepCSV-based c taggers for c jets
The shape calibration SF values as a function of CvsL and CvsB for DeepCSV-based c taggers for b jets
The shape calibration SF values as a function of CvsL and CvsB for DeepCSV-based c taggers for light-flavour jets
Proton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks (t) and Higgs bosons (H). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. No significant excess above the background prediction is observed. Upper limits on the branching fractions ($\mathcal{B}$) of the top quark decaying to a Higgs boson and an up (u) or charm quark (c) are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019 (0.031)% for $\mathcal B$(t $\to$ Hu) and 0.073 (0.051)% for $\mathcal{B}$(t $\to$ Hc). These are the strictest upper limits yet determined.
Expected and observed 95\% CL upper limits on the branching fraction of the top quark decaying to the Higgs boson and a light-flavor quark (either an up or a charm quark)
A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a Z boson. The search uses proton-proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$, at a center-of-mass energy $\sqrt{s} =$ 13 TeV. No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits on dark photon and axion-like particle production, based on two specific models, are reported.
Exclusion limit for BrHXX_Br2Xee
Exclusion limit for BrHXX_Br2Xmumu
Exclusion limit for BrHXX_Br2Xll
Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass $125$ GeV decays into four leptons ($\ell =$$e$,$\mu$). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: $H \rightarrow XX/ZX \rightarrow 4\ell$, where the new boson $X$ has a mass between 1 and 60 GeV. The search uses $pp$ collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into $XX/ZX$, improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where $X$ is interpreted to be a dark boson.
Distribution of $\langle m_{\ell\ell}\rangle$ for events selected in the HM $H\to XX \to 4\ell$ $\, ( 15 \,\text{GeV} < m_{X} < 60 \,\text{GeV})$ analysis. (Pre-fit background expectations and signal templates for $m_{Z_d} = 20 \,\text{GeV}$, $35 \,\text{GeV}$, and $55 \,\text{GeV}$ are given. The latter's yields are normalized with $\sigma(pp\to H\to Z_dZ_d\to 4\ell) =\frac{1}{10}\sigma_{\textrm{SM}}(pp\to H\to ZZ^*\to 4\ell)$.
Distribution of $\langle m_{\ell\ell}\rangle$ for events selected in the LM $H\to XX \to 4\mu$ $( 1 \,\text{GeV} < m_{X} < 15 \, \text{GeV} )$ analysis. The regions of 2 GeV to 4.4 GeV, and 8 GeV to 12 GeV are each excluded by the quarkonia veto. No data events pass this selection. Background expectations are pre-fit. Signal templates for $m_{Z_d} = 2 \,\text{GeV}$, $6 \,\text{GeV}$, and $15 \,\text{GeV}$ are given. All signal yields are normalized with $\sigma(pp\to H\to aa\to 4\mu) = \frac{1}{10}\sigma_{\textrm{SM}}(pp\to H\to ZZ^*\to 4\mu) = 0.15 \text{ fb}$ .
Distribution of $m_{34}$ for data and background events in the mass range $115 \,\text{GeV} < m_{4\ell} < 130 \,\text{GeV}$ after the $H\to ZX\to 4\ell$ selection. The background yield for the $H \to ZZ^* \to 4\ell$ process is post-fit and constrained to $1.2 \pm 0.16$ times the Standard Model expectation. Three $H \to ZZ_d \to 4\ell$ signal templates are shown for $Z_d$ masses of $m_{Z_d} = 20 \,\text{GeV}$, $35 \,\text{GeV}$, and $55 \,\text{GeV}$. They are normalized to a branching ratio of $\textrm{BR}(H\rightarrow ZZ_d \rightarrow 4\ell) = \frac{1}{10}\textrm{BR}(H\rightarrow ZZ^*\rightarrow 4\ell)$.
A search for long-lived particles (LLPs) produced in association with a Z boson is presented. The study is performed using data from proton-proton collisions with a center-of-mass energy of 13 TeV recorded by the CMS experiment during 2016-2018, corresponding to an integrated luminosity of 117 fb$^{-1}$. The LLPs are assumed to decay to a pair of standard model quarks that are identified as displaced jets within the CMS tracker system. Triggers and selections based on Z boson decays to electron or muon pairs improve the sensitivity to light LLPs (down to 15 GeV). This search provides sensitivity to beyond the standard model scenarios which predict LLPs produced in association with a Z boson. In particular, the results are interpreted in the context of exotic decays of the Higgs boson to a pair of scalar LLPs (H $\to$ SS). The Higgs boson decay branching fraction is constrained to values less than 6% for proper decay lengths of 10-100 mm and for LLP masses between 40 and 55 GeV. In the case of low-mass ($\approx$ 15 GeV) scalar particles that subsequently decay to a pair of b quarks, the search is sensitive to branching fractions $\mathcal{B}$(H $\to$ SS) $\lt$ 20% for proper decay lengths of 10-50 mm. The use of associated production with a Z boson increases the sensitivity to low-mass LLPs of this analysis with respect to gluon fusion searches. In the case of 15 GeV scalar LLPs, the improvement corresponds to a factor of 2 at a proper decay length of 30 mm.
Distributions of the median-log10 impact parameter significance tagging variable for data and for four signal samples, where the decay lengths of the signal range from 1 to 1000 mm.
Distributions of the median-log10 track angle tagging variable for data and for four signal samples, where the decay lengths of the signal range from 1 to 1000 mm.
Distributions of the alpha max tagging variable for data and for four signal samples, where the decay lengths of the signal range from 1 to 1000 mm.
The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb$^{-1}$ of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields $\sigma_{\text{tot}}$(pp $\to$ WZ) = 50.6 $\pm$ 0.8 (stat) $\pm$ 1.5 (syst) $\pm$ 1.1 (lumi) $\pm$ 0.5 (theo) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading order in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.
Distribution of the three leading leptons flavour in the CR-ZZ with uncertainties evaluated after the inclusive cross section fit
Distribution of the jet multiplicity in the CR-ttZ with uncertainties evaluated after the inclusive cross section fit
Distribution of the three leading leptons flavour in the CR-conv with uncertainties evaluated after the inclusive cross section fit
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