Dijet events are studied in the proton--proton collision dataset recorded at $\sqrt{s}=$13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb$^{-1}$ and 33.5 fb$^{-1}$ respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The dataset is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W' bosons, W* bosons, and a range of masses and couplings in a Z' dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity.
The number of events as a function of the dijet invariant mass, compared to background prediction from fit and corresponding uncertainties, in the region defined by |y*|<0.6
The number of events as a function of the dijet invariant mass, compared to background prediction from fit and corresponding uncertainties, in the region defined by |y*|<1.2 optimized for the W* search.
The number of events normalized to bin width as a function of the chi angular separation between the two jets, compared to background prediction from Monte Carlo simulation and corresponding uncertainties, in [3.4-3.7] TeV dijet invariant mass region
This Letter presents a search for new physics manifested as anomalous triple gauge boson couplings in WW and WZ diboson production in proton-proton collisions. The search is performed using events containing a W boson that decays leptonically and a W or Z boson whose decay products are merged into a single reconstructed jet. The data, collected at sqrt(s) = 8 TeV with the CMS detector at the LHC, correspond to an integrated luminosity of 19 inverse femtobarns. No evidence for anomalous triple gauge couplings is found and the following 95% confidence level limits are set on their values: lambda ([-0.011, 0.011]), Delta kappa[gamma] ([-0.044, 0.063]), and Delta g[1,Z] ([-0.0087, 0.024]). These limits are also translated into their effective field theory equivalents: c[WWW] / Lambda^2 ([-2.7, 2.7] TeV^{-2}), c[B] / Lambda^2 ([-14, 17] TeV^{-2}), and c[W] / Lambda^2 ([-2.0, 5.7] TeV^{-2}).
One-dimensional 95% CL limits on anomalous trilinear gauge couplings from the W V -> l nu q q channel.
Measurements of the electroweak production of a $W$ boson in association with two jets at high dijet invariant mass are performed using $\sqrt{s} = 7$ and $8$ TeV proton-proton collision data produced by the Large Hadron Collider, corresponding respectively to 4.7 and 20.2 fb$^{-1}$ of integrated luminosity collected by the ATLAS detector. The measurements are sensitive to the production of a $W$ boson via a triple-gauge-boson vertex and include both the fiducial and differential cross sections of the electroweak process.
Integrated fiducial cross-sections for QCD+EW and EW-only $Wjj$ production in the inclusive region with $m_{jj} > 1.5$ TeV.
Integrated fiducial cross-sections for QCD+EW $Wjj$ production in the forward-lepton region.
Integrated fiducial cross-sections for QCD+EW and EW-only $Wjj$ production in the signal region with $m_{jj} > 1.0$ TeV.
Normalized double-differential cross sections for top quark pair (t t-bar) production are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the dilepton e+/- mu-/+ final state. The t t-bar cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and t t-bar system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured t t-bar cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.
The measured normalized $t\bar{t}$ double-differential cross sections in different bins of $y(t)$ and $p_{T}(t)$, along with their relative statistical and systematic uncertainties expressed as percentages.
The correlation matrix of statistical uncertainties for the normalized $t\bar{t}$ double-differential cross sections as a function of $y(t)$ and $p_{T}(t)$. The values are expressed as percentages. For bin indices see Table 5.
Sources and values of the relative systematic uncertainties in percent of the measured normalized $t\bar{t}$ double-differential cross sections as a function of $y(t)$ and $p_{T}(t)$. For bin indices see Table 5.
Measurements of the production cross section of a $Z$ boson in association with jets in proton-proton collisions at $\sqrt{s} = 13$ TeV are presented, using data corresponding to an integrated luminosity of 3.16 fb$^{-1}$ collected by the ATLAS experiment at the CERN Large Hadron Collider in 2015. Inclusive and differential cross sections are measured for events containing a $Z$ boson decaying to electrons or muons and produced in association with up to seven jets with $p_T > 30$ GeV and $|y| <2.5$. Predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements for up to two additional partons interfaced with parton shower and fixed-order predictions at next-to-leading order and next-to-next-to-leading order are compared with the measured cross sections. Good agreement within the uncertainties is observed for most of the modelled quantities, in particular with the generators which use next-to-leading-order matrix elements and the more recent next-to-next-to-leading-order fixed-order predictions.
Measured fiducial cross sections for successive exclusive jet multiplicities in the electron channel. The statistical, systematic, and luminosity uncertainties are given.
Measured fiducial cross sections for successive exclusive jet multiplicities in the muon channel. The statistical, systematic, and luminosity uncertainties are given.
Measured fiducial cross sections for successive exclusive jet multiplicities in the combined electron and muon channels. The statistical, systematic, and luminosity uncertainties are given.
The production of opposite-charge $W$-boson pairs in proton-proton collisions at $\sqrt{s}$ = 13 TeV is measured using data corresponding to 3.16 fb$^{-1}$ of integrated luminosity collected by the ATLAS detector at the CERN Large Hadron Collider in 2015. Candidate $W$-boson pairs are selected by identifying their leptonic decays into an electron, a muon and neutrinos. Events with reconstructed jets are not included in the candidate event sample. The cross-section measurement is performed in a fiducial phase space close to the experimental acceptance and is compared to theoretical predictions. Agreement is found between the measurement and the most accurate calculations available.
The measured fiducial cross section P P --> WW --> $e^\pm \mu^\mp$.
Detailed breakdown of the systematic uncertainties in the fiducial cross-section measurement as a result of the simultaneous fit to signal and control regions. Summarised in Table 4 of the paper.
Systematic uncertainty correlation matrix for the fiducial cross section.
A measurement is presented of the cross section for the electroweak production of a Z boson and a photon in association with two jets in proton-proton collisions at sqrt(s)= 8 TeV. The Z bosons are identified through their decays to electron or muon pairs. The measurement is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 inverse femtobarns. The electroweak contribution has a significance of 3.0 standard deviations, and the measured fiducial cross section is 1.86 +0.90/-0.75 (stat) +0.34/-0.26 (syst) +/- 0.05 (lumi) fb, while the summed electroweak and quantum chromodynamic total cross section in the same region is observed to be 5.94 +1.53/-1.35 (stat) +0.43/-0.37 (syst) +/- 0.13 (lumi) fb. Both measurements are consistent with the leading-order standard model predictions. Limits on anomalous quartic gauge couplings are set based on the Z gamma mass distribution.
The measured fiducial cross section of EW ZGamma+2Jets process.
Detailed measurements of $t$-channel single top-quark production are presented. They use 20.2 fb$^{-1}$ of data collected by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of 8 TeV at the LHC. Total, fiducial and differential cross-sections are measured for both top-quark and top-antiquark production. The fiducial cross-section is measured with a precision of 5.8 % (top quark) and 7.8 % (top antiquark), respectively. The total cross-sections are measured to be $\sigma_{\mathrm{tot}}(tq) = 56.7^{+4.3}_{-3.8}\;$pb for top-quark production and $\sigma_{\mathrm{tot}}(\bar{t}q) = 32.9^{+3.0}_{-2.7}\;$pb for top-antiquark production, in agreement with the Standard Model prediction. In addition, the ratio of top-quark to top-antiquark production cross-sections is determined to be $R_t=1.72 \pm 0.09$, with an improved relative precision of 4.9 % since several systematic uncertainties cancel in the ratio. The differential cross-sections as a function of the transverse momentum and rapidity of both the top quark and the top antiquark are measured at both the parton and particle levels. The transverse momentum and rapidity differential cross-sections of the accompanying jet from the $t$-channel scattering are measured at particle level. All measurements are compared to various Monte Carlo predictions as well as to fixed-order QCD calculations where available.
Predicted and observed event yields for the signal region (SR). The multijet background prediction is obtained from a binned maximum-likelihood fit to the $E_{\mathrm{T}}^{\mathrm{miss}}$ distribution. All the other predictions are derived using theoretical cross-sections, given for the backgrounds in Sect. 6 and for the signal in Sect. 1. The quoted uncertainties are in the predicted cross-sections or in the number of multijet events, in case of the multijet process.
Definition of the fiducial phase space.
The seven input variables to the NN ordered by their discriminating power. The jet that is not $b$-tagged is referred to as $\textit{untagged}~$jet.
Light-by-light scattering ($\gamma\gamma\rightarrow\gamma\gamma$) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead (Pb) ions. Using 480 $\mu$b$^{-1}$ of Pb+Pb collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, the ATLAS Collaboration reports evidence for the $\gamma\gamma\rightarrow\gamma\gamma$ reaction. A total of 13 candidate events are observed with an expected background of 2.6$\pm$0.7 events. After background subtraction and analysis corrections, the fiducial cross section of the process $\textrm{Pb+Pb}\,(\gamma\gamma)\rightarrow \textrm{Pb}^{(\ast)}\textrm{+}\textrm{Pb}^{(\ast)}\,\gamma\gamma$, for photon transverse energy $E_{\mathrm{T}}>$3 GeV, photon absolute pseudorapidity $|\eta|<$2.4, diphoton invariant mass greater than 6 GeV, diphoton transverse momentum lower than 2 GeV and diphoton acoplanarity below 0.01, is measured to be 70 $\pm$ 24 (stat.) $\pm$ 17 (syst.) nb, which is in agreement with Standard Model predictions.
Detector-level diphoton invariant mass distribution
Detector-level diphoton acoplanarity distribution
The measured total fiducial cross section
This paper reports the measurement of J/psi meson production in proton-proton (pp) and proton-lead (pPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV by the CMS experiment at the LHC. The data samples used in the analysis correspond to integrated luminosities of 28 inverse picobarns and 35 inverse nanobarns for pp and pPb collisions, respectively. Prompt and nonprompt J/psi mesons, the latter produced from the decay of B mesons, are measured in their dimuon decay channels. Differential cross sections are measured in the transverse momentum range of 2 < pt < 30 GeV/c, and center-of-mass rapidity ranges of abs(y[CM]) < 2.4 (pp) and -2.87 < y[CM] < 1.93 (pPb). The nuclear modification factor, R[pPb], is measured as functions of both pt and y[CM]. Small modifications of the J/psi cross sections are observed in pPb relative to pp collisions. The ratio of J/psi production cross sections in p-going and Pb-going directions, R[FB], studied as functions of pt and y[CM], shows a significant decrease for increasing transverse energy deposited at large pseudorapidities. These results, which cover a wide kinematic range, provide new insight on the role of cold nuclear matter effects on prompt and nonprompt J/psi production.
Differential cross section (multiplied by the dimuon branching fraction) of prompt J/$\psi$ mesons in pp collisions at forward $y_{\mathrm{CM}}$.
Differential cross section (multiplied by the dimuon branching fraction) of prompt J/$\psi$ mesons in pp collisions at backward $y_{\mathrm{CM}}$.
Differential cross section (multiplied by the dimuon branching fraction) of prompt J/$\psi$ mesons in pPb collisions at forward $y_{\mathrm{CM}}$.
Forum