A search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016-2018, corresponding to a total integrated luminosity of 137 fb$^{-1}$. This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 $\mu$m, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gauge-mediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 $\mu$m.
Distributions of $S_{\mathrm{ML}}$ for data, simulated background and signal events with $n_{\mathrm{track}}$ of 3. The distributions are shown for split-SUSY signals with a gluino mass of 2000 GeV and neutralino mass of 1900 GeV. Different gluino proper decay lengths are shown as $c\tau$ in the legend. All distributions are normalized to unity.
Distributions of $S_{\mathrm{ML}}$ for data, simulated background and signal events with $n_{\mathrm{track}}$ of 3. The distributions are shown for split-SUSY signals with a gluino mass of 2000 GeV and neutralino mass of 1800 GeV. Different gluino proper decay lengths are shown as $c\tau$ in the legend. All distributions are normalized to unity.
Distributions of $S_{\mathrm{ML}}$ for data, simulated background and signal events with $n_{\mathrm{track}}$ of 4. The distributions are shown for split-SUSY signals with a gluino mass of 2000 GeV and neutralino mass of 1900 GeV. Different gluino proper decay lengths are shown as $c\tau$ in the legend. All distributions are normalized to unity.
The first search for narrow resonances decaying to three well-separated hadronic jets is presented. The search uses proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ at $\sqrt{s}$ = 13 TeV, collected at the CERN LHC. No significant deviations from the background predictions are observed between 1.75-9.00 TeV. The results provide the first mass limits on a right-handed boson Z$_{\mathrm{R}}$ decaying to three gluons, an excited quark decaying via a vector boson to three quarks, as well as updated limits on a Kaluza-Klein gluon decaying via a radion to three gluons.
Observed and expected (background-only fitted) invariant mass spectra of trijet events. Data spectra from three years are fitted separately and the sum is shown in the figure. The fitting function used is ${ d N}/{ d m} = p_{0}(1-x)^{p_{1}}/x^{\sum_{i=2}^{3} p_{i}\log^{i-2}(x)}$. The fitted parameters are $p_{1} = 7.350, p_{2} = 6.926, p_{3} = 0.388$ for 2016, $p_{1} = 8.308, p_{2} = 5.931, p_{3} = 0.167$ for 2017 and $p_{1} = 8.770, p_{2} = 5.617, p_{3} = 0.106$ for 2018. $p_{0}$ is the normalization parameter and its exact value is irrelevant.
Expected and observed limits at 95% CL on $\sigma \mathcal{B} (X \to ggg) \mathcal{A}$ for a 3-body decay trijet resonance with $\Gamma_{X}\sim 3\% m_{X}$. The acceptance $\mathcal{A}$ is defined as $\mathcal{A} = N$(events with $m_{X}^{GEN} > 85\% m_{X}^{input}$) / $N$(events generated in the full phase space defined by the CMS default generator settings). Only 2016 data are used to derive limits below 2.0 TeV because of higher trigger thresholds in 2017 and 2018. Theoretical predictions assuming SM-like couplings are depicted with the red curve.
Expected and observed limits at 95% CL on $\sigma \mathcal{B} (X \to ggg) \mathcal{A}$ for a 3-body decay trijet resonance with $\Gamma_{X}\sim 0.01\% m_{X}$. The acceptance $\mathcal{A}$ is defined as $\mathcal{A} = N$(events with $m_{X}^{GEN} > 85\% m_{X}^{input}$) / $N$(events generated in the full phase space defined by the CMS default generator settings). Only 2016 data are used to derive limits below 2.0 TeV because of higher trigger thresholds in 2017 and 2018. Theoretical predictions are depicted with the red curve.
A test of lepton flavor universality in B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$ and B$^{\pm}$$\to$ K$^{\pm}$e$^+$e$^-$ decays, as well as a measurement of differential and integrated branching fractions of a nonresonant B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$ decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded in 2018, by the CMS experiment at the LHC, using a special high-rate data stream designed for collecting about 10 billion unbiased b hadron decays. The ratio of the branching fractions $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$) to $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}$e$^+$e$^-$) is determined from the measured double ratio $R$(K) of these decays to the respective branching fractions of the B$^\pm$$\to$ J/$\psi$K$^\pm$ with J/$\psi$$\to$$\mu^+\mu^-$ and e$^+$e$^-$ decays, which allow for significant cancellation of systematic uncertainties. The ratio $R$(K) is measured in the range 1.1 $\lt q^2 \lt$ 6.0 GeV$^2$, where $q$ is the invariant mass of the lepton pair, and is found to be $R$(K) = 0.78$^{+0.47}_{-0.23}$, in agreement with the standard model expectation $R$(K) $\approx$ 1. This measurement is limited by the statistical precision of the electron channel. The integrated branching fraction in the same $q^2$ range, $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$) = (12.42 $\pm$ 0.68) $\times$ 10$^{-8}$, is consistent with the present world-average value and has a comparable precision.
The differential $\text{B}^+ \to \text{K}^+\mu^+\mu^-$ branching fraction measured in the individual $q^2$ bins. The uncertainties in the yields are statistical uncertainties from the fit, while the branching fraction uncertainties include both the statistical and systematic components.
Differential branching fraction $d\mathcal{B}/dq^2$, with theoretical predictions obtained with the HEPFiT, SuperIso, Flavio, and EOS packages. The HEPFiT predictions are available only for $q^2 < 8\ \mathrm{GeV}^2$.
Relative uncertainties in the differential branching fraction measurement of $\mathrm{B}^+\to\mathrm{K}^+\mu^+\mu^-$ per $q^2$ bin.
The first evidence for the standard model production of a top quark in association with a W boson and a Z boson is reported. The measurement is performed in multilepton final states, where the Z boson is reconstructed via its decays to electron or muon pairs and the W boson decays either to leptons or hadrons. The analysed data were recorded by the CMS experiment at the CERN LHC in 2016-2018 in proton-proton collisions at $\sqrt{s}$ = 13 TeV, and correspond to an integrated luminosity of 138 fb$^{-1}$. The measured cross section is 354 $\pm$ 54 (stat) $\pm$ 95 (syst) fb, and corresponds to a statistical significance of 3.4 standard deviations.
Expected yields for signal and background processes and observed number of events in the signal and control regions
Postfit b jet multiplicity distribution in the $\text{SR}_\text{4l}$
Postfit score of the tWZ output node from the multiclass classifier in $\text{SR}_\text{3l,3j}$ for events with exactly 1 b jet
Using proton-proton collision data corresponding to an integrated luminosity of 140 fb$^{-1}$ collected by the CMS experiment at $\sqrt{s}$ = 13 TeV, the $\Lambda_\text{b}^0$$\to$ J/$\psi\Xi^-$K$^+$ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the $\Lambda_\text{b}^0$$\to$$\psi$(2S)$\Lambda$ decay, is measured to be $\mathcal{B}$($\Lambda_\text{b}^0$$\to$ J/$\psi\Xi^-$K$^+$)/$\mathcal{B}$( $\Lambda_\text{b}^0$$\to$$\psi$(2S)$\Lambda$) = [3.38 $\pm$ 1.02 $\pm$ 0.61 $\pm$ 0.03]%, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in $\mathcal{B}$($\psi$(2S) $\to$ J/$\psi\pi^+\pi^-$) and $\mathcal{B}$($\Xi^-$ $\to$ $\Lambda\pi^-$).
The measured branching fraction ratio
Measurements of inclusive and normalized differential cross sections of the associated production of top quark-antiquark and bottom quark-antiquark pairs, ttbb, 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 ttbb 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, $\mu_\mathrm{R}=\frac{1}{2} \prod_{i=\mathrm{t, \bar{t}, b, \bar{b}}} m_{\mathrm{T},i}^{1/4}$, where $m_{\mathrm{T},i}^2=m_i^2+p^2_{\mathrm{T},i}$ 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.
Fiducial cross sections from the measurements of all observables, compared to predictions from different ttbb simulation approaches. For each of the normalized differential measurements the fiducial cross section in the respective phase space is also determined. In the paper only one representative observable is quoted for each fiducial phase space, while here the measured cross section with the uncertainties from the fit to the respective observable is summarized.
Compatibility of normalized differential cross section measurements with modeling predictions. The compatibility is quantified with z scores for each of the theoretical predictions, given the unfolded normalized differential cross sections and their covariances. A lower value indicates a better agreement between prediction and measurement. A value of z = 2 indicates a p-value of 5%. In the calculation of the z score only the measurement uncertainties and the statistical uncertainties of the modeling predictions are taken into account
Normalized differential cross section of $|\eta(\mathrm{b}^{\mathrm{add.}}_{1})|$ in $\geq 6$ jets: $\geq 4 \mathrm{b}$ phase space.
Diboson production in association with jets is studied in the fully leptonic final states, pp $\to$ (Z$\gamma^*$)(Z/$\gamma^*$)+jets $\to$ 2$\ell$2$\ell'$+jets, ($\ell,\ell'$ = e or $\mu$) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentum $p_\mathrm{T}$, pseudorapidity $\eta$, invariant mass and $\Delta\eta$ of the highest-$p_\mathrm{T}$ and second-highest-$p_\mathrm{T}$ jets, and as a function of invariant mass of the four-lepton system for events with various jet multiplicities. These differential cross sections are compared with theoretical predictions that mostly agree with the experimental data. However, in a few regions we observe discrepancies between the predicted and measured values. Further improvement of the predictions is required to describe the ZZ+jets production in the whole phase space.
Differential cross sections normalized to the fiducial cross section as a function of the invariant mass of the four-lepton system, in the on-shell ZZ region
Differential cross sections normalized to the fiducial cross section as a function of the number of jets with $p_T > 30$ GeV
Differential cross sections normalized to the fiducial cross section as a function of the $p_T$ of the highest-$p_T$ jet
A study of the anomalous couplings of the Higgs boson to vector bosons, including $CP$-violation effects, has been conducted using its production and decay in the WW channel. This analysis is performed on proton-proton collision data collected with the CMS detector at the CERN LHC during 2016-2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of 138 fb$^{-1}$. The different-flavor dilepton (e$\mu$) final state is analyzed, with dedicated categories targeting gluon fusion, electroweak vector boson fusion, and associated production with a W or Z boson. Kinematic information from associated jets is combined using matrix element techniques to increase the sensitivity to anomalous effects at the production vertex. A simultaneous measurement of four Higgs boson couplings to electroweak vector bosons is performed in the framework of a standard model effective field theory. All measurements are consistent with the expectations for the standard model Higgs boson and constraints are set on the fractional contribution of the anomalous couplings to the Higgs boson production cross section.
Expected profiled likelihood on $f_{a2}$ using Approach 1. The signal strength modifiers are treated as free parameters. Axis scales are varied to improve the visibility of important features.
Observed profiled likelihood on $f_{a2}$ using Approach 1. The signal strength modifiers are treated as free parameters. Axis scales are varied to improve the visibility of important features.
Expected profiled likelihood on $f_{\Lambda1}$ using Approach 1. The signal strength modifiers are treated as free parameters. Axis scales are varied to improve the visibility of important features.
A search for exotic decays of the Higgs boson (H) with a mass of 125 GeV to a pair of light pseudoscalars $\mathrm{a}_1$ is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or $\tau$ leptons. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (CL) on the Higgs boson branching fraction to $\mu\mu$bb and to $\tau\tau$bb, via a pair of $\mathrm{a}_1$s. The limits depend on the pseudoscalar mass $m_{\mathrm{a}_1}$ and are observed to be in the range (0.17-3.3) $\times$ 10$^{-4}$ and (1.7-7.7) $\times$ 10$^{2}$ in the $\mu\mu$bb and $\tau\tau$bb final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine model-independent upper limits on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$ $\to$ $\ell\ell$bb) at 95% CL, with $\ell$ being a muon or a $\tau$ lepton. For different types of 2HDM+S, upper bounds on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, $\mathcal{B}($H $\to$ $\mathrm{a}_1\mathrm{a}_1$) values above 0.23 are excluded at 95% CL for $m_{\mathrm{a}_1}$ values between 15 and 60 GeV.
Observed and expected upper limits at 95% CL on B($\text{H} \rightarrow \text{a}_{1}\text{a}_{1} \rightarrow \mu\mu$bb) as functions of $m_{\text{a}_{1}}$. The inner and outer bands indicate the regions containing the distribution of limits located within 68 and 95% confidence intervals, respectively, of the expectation under the background-only hypothesis.
Observed and expected upper limits at 95% CL on B($\text{H} \rightarrow \text{a}_{1}\text{a}_{1} \rightarrow \tau\tau$bb) in percent as functions of $m_{\text{a}_{1}}$, for the combination of the $\mu\tau_{\text{h}}$, $e\tau_{\text{h}}$, and $e\mu$ channels. The inner and outer bands indicate the regions containing the distribution of limits located within 68 and 95% confidence intervals, respectively, of the expectation under the background-only hypothesis.
Observed and expected upper limits at 95% CL on B($\text{H} \rightarrow \text{a}_{1}\text{a}_{1} \rightarrow ll$bb) in percent, where $l$ stands for muons or $\tau$ leptons, obtained from the combination of the $\mu\mu$bb and $\tau\tau$bb channels. The results are obtained as functions $m_{\text{a}_{1}}$ for 2HDM+S models, independent of the type and tan $\beta$ parameter. The inner and outer bands indicate the regions containing the distribution of limits located within 68 and 95% confidence intervals, respectively, of the expectation under the background-only hypothesis.
A search is presented for baryon number violating interactions in top quark production and decay. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC with an integrated luminosity of 138 fb$^{-1}$. Candidate events are selected by requiring two oppositely-charged leptons (electrons or muons) and exactly one jet identified as originating from a bottom quark. Multivariate discriminants are used to separate the signal from the background. No significant deviation from the standard model prediction is observed. Upper limits are placed on the strength of baryon number violating couplings. For the first time the production of single top quarks via baryon number violating interactions is studied. This allows the search to set the most stringent constraints to date on the branching fraction of the top quark decay to a lepton, an up-type quark (u or c), and a down-type quark (d, s, or b). The results improve the previous bounds by three to six orders of magnitude based on the fermion flavor combination of the baryon number violating interactions.
The observed upper limits on the branching fractions of the top quark BNV decays are shown with circle and triangle shapes for electron and muon couplings, respectively. The observed limits corresponding to the $C_t$ and $C_s$ coefficients are shown with filled and open markers, respectively. The yellow light (green dark) bands indicate the range within plus or minus one (two) standard deviations bands around the expected limits.
Energy correlators that describe energy-weighted distances between two or three particles in a jet are measured using an event sample of $\sqrt{s}$ = 13 TeV proton-proton collisions collected by the CMS experiment and corresponding to an integrated luminosity of 36.3 fb$^{-1}$. The measured distributions reveal two key features of the strong interaction: confinement and asymptotic freedom. By comparing the ratio of the two measured distributions with theoretical calculations that resum collinear emissions at approximate next-to-next-to-leading logarithmic accuracy matched to a next-to-leading order calculation, the strong coupling is determined at the Z boson mass: $\alpha_\mathrm{S}(m_\mathrm{Z})$ = 0.1229$^{+0.0040}_{-0.0050}$, the most precise $\alpha_\mathrm{S}(m_\mathrm{Z})$ value obtained using jet substructure observables.
Unfolded E2C distributions in data compared to MC predictions.
Unfolded E2C distributions in data compared to MC predictions.
Unfolded E2C distributions in data compared to MC predictions.
A search for Higgs boson pair (HH) production in association with a vector boson V (W or Z boson) is presented. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. All hadronic and leptonic decays of V bosons are used. The leptons considered are electrons, muons, and neutrinos. The HH production is searched for in the $\mathrm{b\bar{b}b\bar{b}}$ decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set at 294 (124) times the standard model prediction. Constraints are also set on the modifiers of the Higgs boson trilinear self-coupling, $\kappa_{\lambda}$, assuming $\kappa_{2\mathrm{V}}$ = 1 and vice versa on the coupling of two Higgs bosons with two vector bosons, $\kappa_{2\mathrm{V}}$. The observed (expected) 95% confidence intervals of these coupling modifiers are -37.7 $\lt$ $\kappa_{\lambda}$ $\lt$ 37.2 (-30.1 $\lt$ $\kappa_{\lambda}$ $\lt$ 8.9) and -12.2 $\lt$ $\kappa_{2\mathrm{V}}$ $\lt$ 13.5 (-7.2 $\lt$ $\kappa_{2\mathrm{V}}$ $\lt$ 8.9), respectively.
The VHH cross section limits per channel and combined for SM value couplings.
The VHH cross section limits per channel and combined for $\kappa_{\lambda}$ = 5.5.
Upper 95% CL limits on VHH signal cross section scanned over the $\kappa_{\lambda}$ parameter while fixing the $\kappa_{2V}$ and $\kappa_{V}$ to their SM-predicted values.
A search is performed for charged-lepton flavor violating processes in top quark (t) production and decay. The data were collected by the CMS experiment from proton-proton collisions at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb$^{-1}$. The selected events are required to contain one opposite-sign electron-muon pair, a third charged lepton (electron or muon), and at least one jet of which no more than one is associated with a bottom quark. Boosted decision trees are used to distinguish signal from background, exploiting differences in the kinematics of the final states particles. The data are consistent with the standard model expectation. Upper limits at 95% confidence level are placed in the context of effective field theory on the Wilson coefficients, which range between 0.024-0.424 TeV$^{-2}$ depending on the flavor of the associated light quark and the Lorentz structure of the interaction. These limits are converted to upper limits on branching fractions involving up (charm) quarks, t$\to$e$\mu$u (t$\to$e$\mu$c), of 0.032 (0.498)$\times$10$^{-6}$, 0.022 (0.369)$\times$10$^{-6}$, and 0.012 (0.216)$\times$10$^{-6}$ for tensor-like, vector-like, and scalar-like interactions, respectively.
The expected and observed upper limits on CLFV Wilson coefficients. The Limits on the Wilson coefficients are extracted from the upper limits on the cross sections.
The expected and observed upper limits on top quark CLFV branching fractions. The Limits on the top quark CLFV branching fractions are extracted from the upper limits on the Wilson coefficients.
A measurement is presented of the primary Lund jet plane (LJP) density in inclusive jet production in proton-proton collisions. The analysis uses 138 fb$^{-1}$ of data collected by the CMS experiment at $\sqrt{s}$ = 13 TeV. The LJP, a representation of the phase space of emissions inside jets, is constructed using iterative jet declustering. The transverse momentum $k_\mathrm{T}$ and the splitting angle $\Delta R$ of an emission relative to its emitter are measured at each step of the jet declustering process. The average density of emissions as function of $\ln(k_\mathrm{T}$/GeV) and $\ln(R/\Delta R)$ is measured for jets with distance parameters $R$ = 0.4 or 0.8, transverse momentum $p_\mathrm{T} \gt$ 700 GeV, and rapidity $\vert y\vert \lt $ 1.7. The jet substructure is measured using the charged-particle tracks of the jet. The measured distributions, unfolded to the level of stable particles, are compared with theoretical predictions from simulations and with perturbative quantum chromodynamics calculations. Due to the ability of the LJP to factorize physical effects, these measurements can be used to improve different aspects of the physics modeling in event generators.
Primary Lund jet plane density for AK4 jets in a one-dimensional representation with bin indices for MC tuning purposes. The mapping between the bin indices and the physical binning can be imported from the XML file attached to this HepData record using the TUnfoldBinningXML class of ROOT (qualitatively, it corresponds to slicing the Lund plane horizontally from low kT to high kT). All systematic uncertainties are bin-to-bin fully correlated (allowing for sign-changes bin-to-bin), with the exception of the statistical uncertainties from data and MC, for which a separate correlation matrix is provided in this HepData record.
Correlation matrix associated to the statistical covariance matrix of the data and MC for the primary Lund jet plane density for AK4 jets in a one-dimensional representation with bin indices. The mapping between the bin indices and the physical binning can be imported from the XML file attached to this HepData record using the TUnfoldBinningXML class of ROOT (qualitatively, it corresponds to slicing the Lund plane horizontally from low kT to high kT).
Primary Lund jet plane density for AK8 jets in a one-dimensional representation with bin indices for MC tuning purposes. The mapping between the bin indices and the physical binning can be imported from the XML file attached to this HepData record using the TUnfoldBinningXML class of ROOT (qualitatively, it corresponds to slicing the Lund plane horizontally from low kT to high kT). All systematic uncertainties are bin-to-bin fully correlated (allowing for sign-changes bin-to-bin), with the exception of the statistical uncertainties from data and MC, for which a separate correlation matrix is provided in this HepData record.
A search for long-lived heavy neutrinos (N) in the decays of \PB mesons produced in proton-proton collisions at $\sqrt{s}$ = 13 TeV is presented. The data sample corresponds to an integrated luminosity of 41.6 fb$^{-1}$ collected in 2018 by the CMS experiment at the CERN LHC, using a dedicated data stream that enhances the number of recorded events containing B mesons. The search probes heavy neutrinos with masses in the range 1 $\lt$$m_\mathrm{N}$$\lt$ 3 GeV and decay lengths in the range 10$^{-2}$$\lt$$c\tau$$\lt$ 10$^{4}$ mm, where $\tau_\mathrm{N}$ is the N proper mean lifetime. Signal events are defined by the signature B $\to$$\ell_\mathrm{B}$NX; N $\to$$\ell^{\pm} \pi^{\mp}$, where the leptons $\ell_\mathrm{B}$ and $\ell$ can be either a muon or an electron, provided that at least one of them is a muon. The hadronic recoil system, X, is treated inclusively and is not reconstructed. No significant excess of events over the standard model background is observed in any of the $\ell^{\pm}\pi^{\mp}$ invariant mass distributions. Limits at 95% confidence level on the sum of the squares of the mixing amplitudes between heavy and light neutrinos, $\vert V_\mathrm{N}\vert^2$, and on $c\tau$ are obtained in different mixing scenarios for both Majorana and Dirac-like N particles. The most stringent upper limit $\vert V_\mathrm{N}\vert^2$ $\lt$ 2.0$\times$10$^{-5}$ is obtained at $m_\mathrm{N}$ = 1.95 GeV for the Majorana case where N mixes exclusively with muon neutrinos. The limits on $\vert V_\mathrm{N}\vert^2$ for masses 1 $\lt$ $m_\mathrm{N}$ $\lt$ 1.7 GeV are the most stringent from a collider experiment to date.
Expected and observed 95% CL upper limits on $|V_\mathrm{N}|^2$ as a function of $m_\mathrm{N}$ for the mixing scenario ($r_e$, $r_\mu$, $r_\tau$) = (0.0, 1.0, 0.0) and in the Majorana scenario.
Expected and observed 95% CL upper limits on $|V_\mathrm{N}|^2$ as a function of $m_\mathrm{N}$ for the mixing scenario ($r_e$, $r_\mu$, $r_\tau$) = (0.0, 0.5, 0.5) and in the Majorana scenario.
Expected and observed 95% CL upper limits on $|V_\mathrm{N}|^2$ as a function of $m_\mathrm{N}$ for the mixing scenario ($r_e$, $r_\mu$, $r_\tau$) = (0.5, 0.5, 0.0) and in the Majorana scenario.
The J/$\psi$$\to$$\mu^+\mu^-\mu^+\mu^-$ decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb${-1}$. Normalizing to the J/$\psi$$\to$$\mu^+\mu^-$ decay mode leads to a branching fraction [10.1$^{+3.3}_{-2.7}$ (stat) $\pm$ 0.4 (syst) ]$\times$ 10$^{-7}$, a value that is consistent with the standard model prediction.
$\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu\mu\mu$ branching fraction
$\mathcal{B}(\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu\mu\mu)$ / $\mathcal{B}(\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu)$ ratio
A search for ZZ and ZH production in the $\mathrm{b\bar{b}b\bar{b}}$ final state is presented, where H is the standard model (SM) Higgs boson. The search uses an event sample of proton-proton collisions corresponding to an integrated luminosity of 133 fb$^{-1}$ collected at a center-of-mass energy of 13 TeV with the CMS detector at the CERN LHC. The analysis introduces several novel techniques for deriving and validating a multi-dimensional background model based on control samples in data. A multiclass multivariate classifier customized for the $\mathrm{b\bar{b}b\bar{b}}$ final state is developed to derive the background model and extract the signal. The data are found to be consistent, within uncertainties, with the SM predictions. The observed (expected) upper limits at 95% confidence level are found to be 3.8 (3.8) and 5.0 (2.9) times the SM prediction for the ZZ and ZH production cross sections, respectively.
Expected and observed ZZ and ZH signal strengths and their corresponding 95% CL upper limits. The upper limits are obtained from a fit to the SvB signal probabilities under the hypothesis of no ZZ->4b or ZH->4b signal.
The production of $W^{\pm}Z$ events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb$^{-1}$. The $W^{\pm}Z$ candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu \ell \ell}^{\textrm{fid.}} = 63.2 \pm 3.2$ (stat.) $\pm 2.6$ (sys.) $\pm 1.5$ (lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is $53.4^{+3.6}_{-2.8}$ fb. The extrapolation of the measurement from the fiducial to the total phase space yields $\sigma_{W^{\pm}Z}^{\textrm{tot.}} = 50.6 \pm 2.6$ (stat.) $\pm 2.0$ (sys.) $\pm 0.9$ (th.) $\pm 1.2$ (lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of $48.2^{+1.1}_{-1.0}$ pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent $W^+Z$ and $W^-Z$ cross sections and their ratio.
The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity uncertainty, the second is the luminosity uncertainty.
The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity uncertainty, the second is the luminosity uncertainty.
The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity uncertainty, the second is the luminosity uncertainty.
We study charged particle production in proton-antiproton collisions at 300 GeV, 900 GeV, and 1.96 TeV. We use the direction of the charged particle with the largest transverse momentum in each event to define three regions of eta-phi space; toward, away, and transverse. The average number and the average scalar pT sum of charged particles in the transverse region are sensitive to the modeling of the underlying event. The transverse region is divided into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The center-of-mass energy dependence of the various components of the event are studied in detail. The data presented here can be used to constrain and improve QCD Monte Carlo models, resulting in more precise predictions at the LHC energies of 13 and 14 TeV.
Average charged particle pT sum for charged particles with pT > 0.5 GeV and |eta| < 0.8 in the TransMIN region as defined by the leading charged particle, as a function of the transverse momentum of the leading charged-particle pTmax, at 300 GeV.
We present the first measurements of femtoscopic correlations between the K$^0_{\rm S}$ and K$^{\rm \pm}$ particles in pp collisions at $\sqrt{s}=7$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely via the $a_0(980)$ resonance. The extracted kaon source radius and correlation strength parameters for K$^0_{\rm S}$K$^{\rm -}$ are found to be equal within the experimental uncertainties to those for K$^0_{\rm S}$K$^{\rm +}$. Results of the present study are compared with those from identical-kaon femtoscopic studies also performed with pp collisions at $\sqrt{s}=7$ TeV by ALICE and with a K$^0_{\rm S}$K$^{\rm \pm}$ measurement in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. Combined with the Pb-Pb results, our pp analysis is found to be compatible with the interpretation of the $a_0(980)$ having a tetraquark structure instead of that of a diquark.
Raw K0s K+ correlation function for all kT
Raw K0s K+ correlation function for kT < 0.85 GeV/c
Raw K0s K+ correlation function for kT > 0.85 GeV/c
A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV collected with the ATLAS detector at the LHC during 2015-2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for $pp \to W^\prime \to \ell\nu$ are extracted ($\ell = e$ or $\mu$). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. Gauge bosons with a mass below 6.0 TeV and 5.1 TeV are excluded in the electron and muon channels, respectively, in a model with a resonance that has couplings to fermions identical to those of the Standard Model $W$ boson. Cross-section limits are also provided for resonances with several fixed $\Gamma / m$ values in the range between 1% and 15%. Model-independent limits are derived in single-bin signal regions defined by a varying minimum transverse mass threshold. The resulting visible cross-section upper limits range between 4.6 (15) pb and 22 (22) ab as the threshold increases from 130 (110) GeV to 5.1 (5.1) TeV in the electron (muon) channel.
First measurements of the W -> lnu and Z/gamma* -> ll (l = e, mu) production cross sections in proton-proton collisions at sqrt(s) = 7 TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W -> lnu and 179 Z/gamma* -> ll candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb-1. The measured total W and Z/gamma*-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are $\stotW$ * BR(W -> lnu) = 9.96 +- 0.23(stat) +- 0.50(syst) +- 1.10(lumi) nb and $\stotZg$ * BR(Z/gamma* -> ll) = 0.82 +- 0.06(stat) +- 0.05(syst) +- 0.09(lumi) nb (within the invariant mass window 66 < m_ll < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 +- 0.9(stat) +- 0.4(syst). In addition, measurements of the W+ and W- production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.
Measured total cross-section ratio R_{W-/Z} = sigma (W- -> e- nubar) / sigma (Z/gamma^* -> e+ e-).
Jet shapes have been measured in inclusive jet production in proton-proton collisions at sqrt(s) = 7 TeV using 3 pb^{-1} of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and non-perturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.
Measured Differential Jet Shape RHO as a function of r for jet transverse momentum from 60 to 80 GeV and absolute values of the jet rapidity from 0 to 0.3. This is additional data, not in the paper.
Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb-1 recorded at the Large Hadron Collider. The anti-kt algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable $\chi$. The results are compared to expectations based on next-to-leading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.
Dijet double-differential cross sections in the |rapidity(max)| range 520 to 800, using a jet resolution R value of 0.4. The four (sys) errors are respectively, the Absolute JES, the Relative JES, the Unfolding and the Luminosity uncertainties.
Measurements are presented from proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase-space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo models, including a new AMBT1 PYTHIA 6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the Monte Carlo models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT >100 MeV, is measured to be 3.483 +- 0.009 (stat) +- 0.106 (syst) at sqrt(s) = 0.9 TeV and 5.630 +- 0.003 (stat) +- 0.169 (syst) at sqrt(s) = 7 TeV.
Average transverse momentum in proton-proton collisions at a centre-of mass energy of 900 GeV as a function of the number of charged particles in the event for events with the number of charged particles >=1 having transverse momentum >500 MeV and absolute(pseudorapidity) <2.5.
The production of $J/\psi$ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of $355pb^{-1}$ collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured $J/\psi$ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.
Normalized differential cross-section $\frac{d\ln\sigma\left(pp\rightarrow J/\psi D^+ X \right)}{d \left| \Delta \phi/\pi \right|}$ for $2<y(J/\psi)<4$, $p_T(J/\psi)<12$ GeV/$c$, $2<y(D^+)<4$, $3<p_T(D^+)<12$ GeV/$c$ region.
This Letter reports a measurement of the cross section for producing pairs of central prompt isolated photons in proton-antiproton collisions at a total energy of 1.96 TeV using data corresponding to 9.5/fb integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured differential cross section is compared to three calculations derived from the theory of strong interactions. These include a prediction based on a leading order matrix element calculation merged with parton shower, a next-to-leading order, and a next-to-next-to-leading order calculation. The first and last calculations reproduce most aspects of the data, thus showing the importance of higher-order contributions for understanding the theory of strong interaction and improving measurements of the Higgs boson and searches for new phenomena in diphoton final states.
The measured differential cross sections for the photon $E_T$ (two entries per event) , together with the predictions from the Sherpa Monte Carlo.
We present a study of the production of K_s^0 and Lambda^0 in inelastic pbar-p collisions at sqrt(s)= 1800 and 630 GeV using data collected by the CDF experiment at the Fermilab Tevatron. Analyses of K_s^0 and Lambda^0 multiplicity and transverse momentum distributions, as well as of the dependencies of the average number and <p_T> of K_s^0 and Lambda^0 on charged particle multiplicity are reported. Systematic comparisons are performed for the full sample of inelastic collisions, and for the low and high momentum transfer subsamples, at the two energies. The p_T distributions extend above 8 GeV/c, showing a <p_T> higher than previous measurements. The dependence of the mean K_s^0(Lambda^0) p_T on the charged particle multiplicity for the three samples shows a behavior analogous to that of charged primary tracks.
Average PT of LAMBDA at a centre of mass 630 GeV for the SOFT data sample.
During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450 000 Z 0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z 0 resonance. Model independent fits to the cross sections and leptonic forward- backward asymmetries yield the following Z 0 parameters: the mass and total width M Z = 91.187 ± 0.009 GeV, Γ Z = 2.486 ± 0.012 GeV, the hadronicf and leptonic partials widths Γ had = 1.725 ± 0.012 GeV, Γ ℓ = 83.01 ± 0.52 MeV, the invisible width Γ inv = 512 ± 10 MeV, the ratio of hadronic to leptonic partial widths R ℓ = 20.78 ± 0.15, and the Born level hadronic peak cross section σ 0 = 40.90 ± 0.28 nb. Using these results and the value of α s determined from DELPHI data, the number of light neutrino species is determined to be 3.08 ± 0.05. The individual leptonic widths are found to be: Γ e = 82.93 ± 0.70 MeV, Γ μ = 83.20 ± 1.11 MeV and Γ τ = 82.89 ± 1.31 MeV. Using the measured leptonic forward-backward asymmetries and assuming lepton universality, the squared vector and axial-vector couplings of the Z 0 to charged leptons are found to be g V ℓ 2 = (1.47 ± 0.51) × 10 −3 and g A ℓ 2 = 0.2483 ± 0.0016. A full Standard Model fit to the data yields a value of the top mass m t = 115 −82 +52 (expt.) −24 +52 (Higgs) GeV, corresponding to a value of the weak mixing angle sin 2 θ eff lept = 0.2339±0.0015 (expt.) −0.0004 +0.0001 (Higgs). Values are obtained for the variables S and T , or ϵ 1 and ϵ 3 which parameterize electroweak loop effects.
LEPTON+ LEPTON- cross sections from the 1990 data set. Data are corrected for t-channel subtraction, and to full solid angle but not for momenta and accollinearity cuts. Additional systematic uncertainty, excluding luminosity, is 0.6 pct.
To assess the properties of the quark-gluon plasma formed in heavy-ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the magnitudes of the flow harmonics. The analysis uses data samples of lead-lead and proton-lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02 TeV, corresponding to total integrated luminosities of $22 ~\mu b^{-1}$ and $28~nb^{-1}$, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the $2^{nd}$-, 3$^{rd}$-, and 4$^{th}$-order harmonics are measured as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution in the lead-lead collisions, which only weakly depends on the charged-particle momentum range. In the proton-lead collisions, the modified Pearson correlation coefficient measured for the second harmonics shows only weak centrality dependence. The data is qualitatively described by the predictions based on the hydrodynamical model.
The $cov(v_{3}^{2},[p_{T}])$ for Pb+Pb collisions for the $p_T$ 0.5-2 GeV interval as a function $N_{ch}$.
Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using $p+$Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Charged particles are reconstructed over pseudorapidity $|\eta|<2.3$ and transverse momentum between $0.1$ GeV and $22$ GeV in a dataset corresponding to an integrated luminosity of $1$ $\mu b^{-1}$. The results are presented in the form of charged-particle nuclear modification factors, where the $p+$Pb charged-particle multiplicities are compared between central and peripheral $p+$Pb collisions as well as to charged-particle cross sections measured in pp collisions. The $p+$Pb collision centrality is characterized by the total transverse energy measured in $-4.9<\eta<-3.1$, which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the $p+$Pb collision are carried out using the Glauber model and two Glauber-Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around $3$ GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus.
$R_{pPb}$ as a function of $p_{T}$ extracted from the invariant yields for six rapidity ranges, for eight centrality intervals, and for different geometrical models used to calculate $\langle T_{Pb} \rangle$.
A summary of the constraints from the ATLAS experiment on $R$-parity conserving supersymmetry is presented. Results from 22 separate ATLAS searches are considered, each based on analysis of up to 20.3 fb$^{-1}$ of proton-proton collision data at the centre-of-mass energy of $\sqrt{s}$ = 7 and 8 TeV at the Large Hadron Collider. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, in which the lightest supersymmetric particle is a neutralino, taking into account constraints from previous precision electroweak and flavour measurements as well as from dark matter related measurements. The results are presented in terms of constraints on supersymmetric particle masses and are compared to limits from simplified models. The impact of ATLAS searches on parameters such as the dark matter relic density, the couplings of the observed Higgs boson, and the degree of electroweak fine-tuning is also shown. Spectra for surviving supersymmetry model points with low fine-tunings are presented.
A search is performed for resonant and non-resonant Higgs boson pair production in the $\gamma\gamma b\bar{b}$ final state. The data set used corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling ($\kappa_\lambda = \lambda_{HHH} / \lambda_{HHH}^{\rm SM}$) is constrained at 95% confidence level to $-8.2 < \kappa_\lambda < 13.2$. For resonant Higgs boson pair production through X $\rightarrow$ HH $\rightarrow$ $\gamma\gamma b\bar{b}$, the limit is presented, using the narrow-width approximation, as a function of $m_X$ in the range 260 GeV $< m_X <$ 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range.
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the Large Hadron Collider (LHC) and correspond to an integrated luminosity of 315 nb^-1 collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% CL the q* mass interval 0.30 < mq* < 1.26 TeV, extending the reach of previous experiments.
A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a centre-of-mass energy sqrt(s) = 7TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<|eta|<1.81 in the transverse energy range 15 < E_T <100 GeV. The results are based on an integrated luminosity of 880 nb-1, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading order perturbative QCD calculations.
The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |eta|<2.5 and pT>500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at eta = 0 is measured to be 1.333 +/- 0.003 (stat.) +/- 0.040 (syst.), which is 5-15% higher than the Monte Carlo models predict.
The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at sqrt(s) = 7 TeV. The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb-1, is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|eta|<1.37 and 1.52<|eta|<2.37) and with an angular separation Delta R>0.4, is 44.0 (+3.2) (-4.2) pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins--Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.
A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb$^{-1}$ of proton-proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a $b$-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the $tq\gamma$ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tu\gamma$ coupling of 36 fb (78 fb) and on the branching ratio for $t\rightarrow \gamma u$ of $2.8\times 10^{-5}$ ($6.1\times 10^{-5}$). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tc\gamma$ coupling of 40 fb (33 fb) and on the branching ratio for $t\rightarrow \gamma c$ of $22\times 10^{-5}$ ($18\times 10^{-5}$).
A search for decays of the Higgs and Z boson to pairs of J/$\psi$ or $\Upsilon$(nS) (n=1, 2, 3) mesons, with their subsequent decay to $\mu^+\mu^-$ pairs, is presented. The analysis uses data from proton-proton collisions at $\sqrt{s}=$ 13 TeV, collected with the CMS detector at the LHC in 2017 and corresponding to an integrated luminosity of 37.5 fb$^{-1}$. While an observation of such a decay with this sample would indicate the presence of physics beyond the standard model, no significant excess is observed. Upper limits at 95% confidence level are placed on the branching fractions of these decays. In the J/$\psi$ pair channel, the limits are 1.8$\times$10$^{-3}$ and 2.2$\times$10$^{-6}$ for the Higgs and Z boson, respectively, while in the combined $\Upsilon$(nS) pair channel, the limits are 1.4$\times$ 10$^{-3}$ and 1.5$\times$10$^{-6}$, respectively, when the mesons from the Higgs and Z boson decay are assumed to be unpolarized. When fully longitudinal and transverse polarizations are considered the limits reduce by about 22-29% and increase by about 10-13%, respectively.
Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in PbPb collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_\mathrm{NN}} =$ 2.76 and 5.02 TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.
Mixed higher-order flow harmonic $v_4\{\Psi_{22}\}$ from the scalar-product method at 5.02 TeV as a function of PT in the 0-20% centrality range.
Mixed higher-order flow harmonic $v_4\{\Psi_{22}\}$ from the scalar-product method at 5.02 TeV as a function of PT in the 20-60% centrality range.
Mixed higher-order flow harmonic $v_4\{\Psi_{22}\}$ from the scalar-product method at 2.76 TeV as a function of PT in the 0-20% centrality range.
A search for supersymmetry in the context of general gauge-mediated (GGM) breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 inverse picobarns recorded by the CMS experiment at the LHC. The search is performed using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for GGM supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squark, gluino, and neutralino masses, excluding supersymmetry parameter space that was inaccessible to previous experiments.
95 PCT CL upper limits to cross section and the GGM acceptance as a function of Gluino mass for Squark mass 400 GeV and Neutralino mass 150 GeV.
Measurements of jet characteristics from inclusive jet production in proton-proton collisions at a centre-of-mass energy of 7 TeV are presented. The data sample was collected with the CMS detector at the LHC during 2010 and corresponds to an integrated luminosity of 36 inverse picobarns. The mean charged hadron multiplicity, the differential and integral jet shape distributions, and two independent moments of the shape distributions are measured as functions of the jet transverse momentum for jets reconstructed with the anti-kT algorithm. The measured observables are corrected to the particle level and compared with predictions from various QCD Monte Carlo generators.
The measured differential jet shape $\rho(r)$ for jets with 600 GeV $< p_{\mathrm{T}} <$ 1000 GeV and 0 <|y|< 0.5. The CF in the table refers to unfolding correction factor from {\sc pythia6} Tune Z2. The systematic uncertainties from different sources, jet energy scale (JES), unfolding, and single particle response (SPR), are also presented.
A measurement of the J/psi and psi(2S) production cross sections in pp collisions at sqrt(s)=7 TeV with the CMS experiment at the LHC is presented. The data sample corresponds to an integrated luminosity of 37 inverse picobarns. Using a fit to the invariant mass and decay length distributions, production cross sections have been measured separately for prompt and non-prompt charmonium states, as a function of the meson transverse momentum in several rapidity ranges. In addition, cross sections restricted to the acceptance of the CMS detector are given, which are not affected by the polarization of the charmonium states. The ratio of the differential production cross sections of the two states, where systematic uncertainties largely cancel, is also determined. The branching fraction of the inclusive B to psi(2S) X decay is extracted from the ratio of the non-prompt cross sections to be: BR(B to psi(2S) X) = (3.08 +/- 0.12(stat.+syst.) +/- 0.13(theor.) +/- 0.42(BR[PDG])) 10^-3
The non-prompt fraction (FB) of J/PSI times branching ratio to MU+ MU- from B-HADRON decays in the |rapidity| bin 0.9-1.2.
Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |eta|<0.5 to |eta|<2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distribution at sqrt(s) = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with sqrt(s) is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies.
Fully corrected charged hadron multiplicity spectrum for |pseudorapidity| < 2.4 and PT > 500 MeV at a centre-of-mass energy of 7000 GeV.
Measurements are presented of electroweak boson production using data from $pp$ collisions at a centre-of-mass energy of $\sqrt{s} = 8\mathrm{\,Te\kern -0.1em V}$. The analysis is based on an integrated luminosity of $2.0\mathrm{\,fb}^{-1}$ recorded with the LHCb detector. The bosons are identified in the $W\rightarrow\mu\nu$ and $Z\rightarrow\mu^{+}\mu^{-}$ decay channels. The cross-sections are measured for muons in the pseudorapidity range $2.0 < \eta < 4.5$, with transverse momenta $p_{\rm T} > 20{\mathrm{\,Ge\kern -0.1em V\!/}c}$ and, in the case of the $Z$ boson, a dimuon mass within $60 < M_{\mu^{+}\mu^{-}} < 120{\mathrm{\,Ge\kern -0.1em V\!/}c^{2}}$. The results are \begin{align*} \sigma_{W^{+}\rightarrow\mu^{+}\nu} &= 1093.6 \pm 2.1 \pm 7.2 \pm 10.9 \pm 12.7{\rm \,pb} \, , \sigma_{W^{-}\rightarrow\mu^{-}\bar{\nu}} &= \phantom{0}818.4 \pm 1.9 \pm 5.0 \pm \phantom{0}7.0 \pm \phantom{0}9.5{\rm \,pb} \, , \sigma_{Z\rightarrow\mu^{+}\mu^{-}} &= \phantom{00}95.0 \pm 0.3 \pm 0.7 \pm \phantom{0}1.1 \pm \phantom{0}1.1{\rm \,pb} \, , \end{align*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the $W$ and $Z$ boson cross-sections with centre-of-mass energy is studied using previously reported measurements with $1.0\mathrm{\,fb}^{-1}$ of data at $7\mathrm{\,Te\kern -0.1em V}$. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
Correlation coefficients of differential cross-section measurements as a function of $\eta^{\mu^{+}}$. The beam energy and luminosity uncertainties, which are fully correlated between cross-section measurements, are excluded.
An angular analysis of the $B^{0}\rightarrow K^{*0}(\rightarrow K^{+}\pi^{-})\mu^{+}\mu^{-}$ decay is presented. The dataset corresponds to an integrated luminosity of $3.0\,{\mbox{fb}^{-1}}$ of $pp$ collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine $C\!P$-averaged observables and $C\!P$ asymmetries, taking account of possible contamination from decays with the $K^{+}\pi^{-}$ system in an S-wave configuration. The angular observables and their correlations are reported in bins of $q^2$, the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for $q^2$-dependent decay amplitudes in the region $1.1<q^{2}<6.0\mathrm{\,Ge\kern -0.1em V}^{2}/c^{4}$, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of $C\!P$-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions.
Likelihood correlation matrix $4.0 <q^2< 6.0~{\rm GeV}^2/c^4$.
The production of $\Upsilon$ mesons in $pp$ collisions at $\sqrt=7$ and $8\,\mathrm{TeV}$ is studied with the LHCb detector using data samples corresponding to an integrated luminosity of $1\,\mathrm{fb}^{-1}$ and $2\,\mathrm{fb}^{-1}$ respectively. The production cross-sections and ratios of cross-sections are measured as functions of the meson transverse momentum $p_T$ and rapidity $y$, for $p_T<30\,\mathrm{GeV}/c$} and $2.0<y<4.5$.
The ratio of differential cross-section $\mathrm{d} \sigma ( pp \to ( \Upsilon \to \mu^+ \mu^- ) X ) / \mathrm{d}y$ for $\sqrt{s}=8$ and $\sqrt{s}=7$ TeV and $p_T < 30$ GeV/$c$.
The production of $W$ and $Z$ bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 fb$^{-1}$. The $W$ boson is identified using its decay to a muon and a neutrino, while the $Z$ boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of $W+$jet and $Z$+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.
The correlation matrix for the systematic uncertainties on the $W^+j$, $W^-j$ and $Zj$ production cross-section measurements presented in Tables 2 and 5 in bins of $\eta^{\rm jet}$. The first four rows/columns correspond to the $W^+j$ cross-section in bins of $\eta^{\rm jet}$, the middle four correspond to the $W^-j$ cross-section in bins of $\eta^{\rm jet}$ and the final four correspond to the $Zj$ cross-section in bins of $\eta^{\rm jet}$. The matrix is used to calculate the ratios of $Wj$ to $Zj$ production and the charge ratio and asymmetry of $Wj$ production in the total fiducial region.
The correlation matrix for the systematic uncertainties on the $W^+j$, $W^-j$ and $Z^0 j$ production cross-section measurements presented in Tables 2 and 5 in bins of $\eta^{\rm jet}$. The matrix is used to calculate the ratios of $Wj$ to $Z^0 j$ production and the charge ratio and asymmetry of $Wj$ production in the total fiducial region.
A search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. The search for heavy resonances is performed over the mass range 0.2-2.5 TeV for the $\tau^+\tau^-$ decay with at least one $\tau$-lepton decaying into final states with hadrons. The data are in good agreement with the background prediction of the Standard Model. In the $M_{h}^{125}$ scenario of the Minimal Supersymmetric Standard Model, values of $\tan\beta>8$ and $\tan\beta>21$ are excluded at the 95% confidence level for neutral Higgs boson masses of 1.0 TeV and 1.5 TeV, respectively, where $\tan\beta$ is the ratio of the vacuum expectation values of the two Higgs doublets.
Expected 95% CL upper limits on the scalar boson production cross section times ditau branching fraction as a function of the scalar boson mass and the fraction of the b-associated production. The limits are calculated from a statistical combination of the 1l1tau_h and 2tau_h channels.
Expected 95% CL upper limits on the scalar boson production cross section times ditau branching fraction as a function of the scalar boson mass and the fraction of the b-associated production. The limits are calculated from a statistical combination of the 1l1tau_h and 2tau_h channels.
Expected 95% CL upper limits on the scalar boson production cross section times ditau branching fraction as a function of the scalar boson mass and the fraction of the b-associated production. The limits are calculated from a statistical combination of the 1l1tau_h and 2tau_h channels.
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