This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV $<p_T<$ 2.5 TeV and pseudorapidity $|\eta| < 2.1$ from an integrated luminosity of 33 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collisions are reconstructed with the ATLAS detector at the Large Hadron Collider. Charged-particle tracks with $p_T > 500$ MeV and $|\eta| < 2.5$ are used to probe the detailed structure of the jet. The fragmentation properties of the more forward and the more central of the two leading jets from each event are studied. The data are unfolded to correct for detector resolution and acceptance effects. Comparisons with parton shower Monte Carlo generators indicate that existing models provide a reasonable description of the data across a wide range of phase space, but there are also significant differences. Furthermore, the data are interpreted in the context of quark- and gluon-initiated jets by exploiting the rapidity dependence of the jet flavor fraction. A first measurement of the charged-particle multiplicity using model-independent jet labels (topic modeling) provides a promising alternative to traditional quark and gluon extractions using input from simulation. The simulations provide a reasonable description of the quark-like data across the jet $p_T$ range presented in this measurement, but the gluon-like data have systematically fewer charged particles than the simulations.
$\langle n_{ch} \rangle$, forward jet.
$\langle n_{ch} \rangle$, central jet.
$\langle \zeta \rangle$, forward jet.
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.
Transverse mass distribution for events satisfying all selection criteria in the electron channel.
Transverse mass distribution for events satisfying all selection criteria in the muon channel.
Upper limits at the 95% CL on the cross section for SSM $W^\prime$ production and decay to the electron+neutrino channel as a function of the $W^\prime$ pole mass.
This Letter presents the observation and measurement of electroweak production of a same-sign $W$ boson pair in association with two jets using 36.1 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of $69 \pm 7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is $\sigma^{\mathrm {fid.}}=2.89^{+0.51}_{-0.48} \mathrm{(stat.)} ^{+0.29}_{-0.28} \mathrm{(syst.)}$ fb.
Measured fiducial cross section.
The $m_{jj}$ distribution for events meeting all selection criteria for the signal region. Signal and individual background distributions are shown as predicted after the fit. The last bin includes the overflow. The highest value measured in a candidate event in data is $m_{jj}=3.8$ TeV.
The $m_{ll}$ distribution for events meeting all selection criteria for the signal region as predicted after the fit. The fitted signal strength and nuisance parameters have been propagated, with the exception of the uncertainties due to the interference and electroweak corrections for which a flat uncertainty is assigned. The last bin includes the overflow. The highest value measured in a candidate event in data is $m_{ll}=824$ GeV.
This paper reports on a search for the electroweak diboson ($WW/WZ/ZZ$) production in association with a high-mass dijet system, using data from proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV. The data, corresponding to an integrated luminosity of 35.5 fb$^{-1}$, were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The search is performed in final states in which one boson decays leptonically, and the other boson decays hadronically. The hadronically decaying $W/Z$ boson is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. The electroweak production of $WW/WZ/ZZ$ in association with two jets is measured with an observed (expected) significance of 2.7 (2.5) standard deviations, and the fiducial cross section is measured to be $45.1 \pm 8.6(\mathrm{stat.}) ^{+15.9} _{-14.6} (\mathrm{syst.})$ fb.
Summary of predicted and measured fiducial cross sections for EW $VVjj$ production. The three lepton channels are combined. For the measured fiducial cross sections in the merged and resolved categories, two signal-strength parameters are used in the combined fit, one for the merged category and the other one for the resolved category; while for the measured fiducial cross section in the inclusive fiducial phase space, a single signal-strength parameter is used. For the SM predicted cross section, the error is the theoretical uncertainty (theo.). For the measured cross section, the first error is the statistical uncertainty (stat.), and the second error is the systematic uncertainty (syst.).
Summary of predicted and measured fiducial cross sections for EW $VVjj$ production. in the three lepton channels. The measured values are obtained from a simultaneous fit where each lepton channel has its own signal-strength parameter, and in each lepton channel the same signal-strength parameter is applied to both the merged and resolved categories. For the SM predicted cross section, the error is the theoretical uncertainty (theo.). For the measured cross section, the first error is the statistical uncertainty (stat.), and the second error is the systematic uncertainty (syst.).
A measurement of fiducial and differential cross-sections for $W^+W^-$ production in proton-proton collisions at $\sqrt{s}=$13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of $36.1$ fb$^{-1}$ is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as $WW\rightarrow e^{\pm}\nu\mu^{\mp}\nu$. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.
Measured fiducial cross-section as a function of the jet-veto $p_{T}$ threshold. The value at the jet-veto $p_{T}$ threshold of 35GeV corresponds to the nominal fiducial cross section measured in this publication.
Statistical correlation between bins in data for the measured fiducial cross-section as a function of the jet-veto $p_{T}$ threshold. The value at the jet-veto $p_{T}$ threshold of 35GeV corresponds to the nominal fiducial cross section measured in this publication.
Total correlation between bins in data for the measured fiducial cross-section as a function of the jet-veto $p_{T}$ threshold. The value at the jet-veto $p_{T}$ threshold of 35GeV corresponds to the nominal fiducial cross section measured in this publication.
This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of $20.2~\mbox{fb$^{-1}$}$. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.
The correction factors, $C_{W^±,i}$ with their associated systematic uncertainties as a function of $|\eta_{\mu}|$, for $W^+$ and $W^−$
The integrated global correction factor $C_{W^±}$, for $W^+$ and $W^−$
Cross-sections (differential in $\eta_{\mu}$) and asymmetry, as a function of $|\eta_{\mu}|$). The central values are provided along with the statistical and dominant systematic uncertainties: the data statistical uncertainty (Data Stat.), the $E_T^{\textrm{miss}}$ uncertainty, the uncertainties related to muon reconstruction (Muon Reco.), those related to the background, those from MC statistics (MC Stat.), and modelling uncertainties. The uncertainties of the cross-sections are given in percent and those of the asymmetry as an absolute difference from the nominal.
A search for the production of three massive vector bosons in proton--proton collisions is performed using data at $\sqrt{s}=13\,TeV$ recorded with the ATLAS detector at the Large Hadron Collider in the years 2015--2017, corresponding to an integrated luminosity of $79.8\,\text{fb}^{-1}$. Events with two same-sign leptons $\ell$ (electrons or muons) and at least two reconstructed jets are selected to search for $WWW\to\ell\nu\ell\nu qq$. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for $WWW\to\ell\nu\ell\nu\ell\nu$, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for $WWZ\to\ell\nu qq \ell\ell$. Finally, events with four leptons are analysed to search for $WWZ\to\ell\nu\ell\nu\ell\ell$ and $WZZ\to qq \ell\ell\ell\ell$. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.0 standard deviations, where the expectation is 3.1 standard deviations.
Measurement of the $WWW$ cross section.
Measurement of the $WWZ$ cross section.
The inclusive production rates of isolated, prompt photons in $p$+Pb collisions at $\sqrt{s_\mathrm{NN}} = 8.16$ TeV are studied with the ATLAS detector at the Large Hadron Collider using a dataset with an integrated luminosity of 165 nb$^{-1}$ recorded in 2016. The cross-section and nuclear modification factor $R_{p\mathrm{Pb}}$ are measured as a function of photon transverse energy from 20 GeV to 550 GeV and in three nucleon-nucleon centre-of-mass pseudorapidity regions, (-2.83,-2.02), (-1.84,0.91), and (1.09,1.90). The cross-section and $R_{p\mathrm{Pb}}$ values are compared with the results of a next-to-leading-order perturbative QCD calculation, with and without nuclear parton distribution function modifications, and with expectations based on a model of the energy loss of partons prior to the hard scattering. The data disfavour a large amount of energy loss and provide new constraints on the parton densities in nuclei.
The measured cross sections for prompt, isolated photons with rapidity in (1.09,1.90).
The measured cross sections for prompt, isolated photons with rapidity in (−1.84,0.91).
The measured cross sections for prompt, isolated photons with rapidity in (−2.83,−2.02).
This paper presents measurements of $W^{\pm}Z$ production cross sections in $pp$ collisions at a centre-of-mass energy of 13 TeV. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1 fb$^{-1}$. The $W^{\pm}Z$ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu \ell \ell}^{\textrm{fid.}} = 63.7 \pm 1.0$ (stat.) $\pm 2.3$ (syst.) $\pm 1.4$ (lumi.) fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of $61.5^{+1.4}_{-1.3}$ fb. Cross sections for $W^+Z$ and $W^-Z$ production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of $W$ and $Z$ bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the $W$ and $Z$ bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.
The measured $W^{\pm}Z$ 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 modelling uncertainty, the third is luminosity uncertainty.
The measured $W^{+}Z$ 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 modelling uncertainty, the third is luminosity uncertainty.
The measured $W^{-}Z$ 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 modelling uncertainty, the third is luminosity uncertainty.
A measurement of the associated production of a top-quark pair ($t\bar{t}$) with a vector boson ($W$, $Z$) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using $36.1$ fb$^{-1}$ of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The $t\bar{t}Z$ and $t\bar{t}W$ production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are $\sigma_{t\bar{t}Z} = 0.95 \pm 0.08_{\mathrm{stat.}} \pm 0.10_{\mathrm{syst.}}$ pb and $\sigma_{t\bar{t}W} = 0.87 \pm 0.13_{\mathrm{stat.}} \pm 0.14_{\mathrm{syst.}}$ pb in agreement with the Standard Model predictions. The measurement of the $t\bar{t}Z$ cross section is used to set constraints on effective field theory operators which modify the $t\bar{t}Z$ vertex.
The result of the simultaneous fit to the $t\bar{t}Z$ and $t\bar{t}W$ cross sections.
68% confidence level (CL) contours of the measured $t\bar{t}Z$ and $t\bar{t}W$ cross sections.
95% confidence level (CL) contours of the measured $t\bar{t}Z$ and $t\bar{t}W$ cross sections.
Forum