The production of Z bosons in pPb collisions at sqrt(s[NN]) = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.
Differential cross section of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Forward-backward asymmetry (AFB) distribution of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Differential cross section of the Z bosons in pPb collisions as a function of transverse momentum in the fiducial region for the combined leptonic decay channel.
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Distributions of transverse momentum $p_T^{ll}$ and the angular variable $\phi^*_\eta$ of Drell--Yan lepton pairs are measured in 20.3 fb$^{-1}$ of proton--proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in proton--proton collisions at $\sqrt{s}=7$ TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of $\phi^*_\eta < 1$ the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of $\phi^*_\eta$ this is not generally the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of $p_T^{ll}$ and the fixed-order prediction of DYNNLO falls below the data at high values of $p_T^{ll}$. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the $\phi^*_\eta$ and $p_T^{ll}$ distributions as a function of lepton-pair mass and rapidity.
Fiducial cross sections at Born level in the electron- and muon-pair channels as well as the combined value. The statistical and systematic uncertainties are given as a percentage of the cross section. An additional uncertainty of 2.8% on the integrated luminosity, which is fully correlated between channels and among all $m_{\ell\ell}$ bins, pertains to these measurements. The individual uncertainty sources after the combination are not necessarily orthogonal and also do not include uncertainties uncorrelated between bins of $m_{\ell\ell}$. Therefore their quadratic sum may not give the total systematic uncertainty.
The values of $(1/\sigma)\,\mathrm{d}\sigma/\mathrm{d}\phi^*_{\eta}$ in each bin of $\phi^*_{\eta}$ for the electron and muon channels separately (for various particle-level definitions) and for the Born-level combination in the kinematic region $46\textrm{ GeV} \leq m_{\ell\ell} < 66\textrm{ GeV},\ 0 \leq |y_{\ell\ell}| < 0.8$. The associated statistical and systematic (both uncorrelated and correlated between bins of $\phi^*_{\eta}$) are provided in percentage form.
The values of $(1/\sigma)\,\mathrm{d}\sigma/\mathrm{d}\phi^*_{\eta}$ in each bin of $\phi^*_{\eta}$ for the electron and muon channels separately (for various particle-level definitions) and for the Born-level combination in the kinematic region $46\textrm{ GeV} \leq m_{\ell\ell} < 66\textrm{ GeV},\ 0.8 \leq |y_{\ell\ell}| < 1.6$. The associated statistical and systematic (both uncorrelated and correlated between bins of $\phi^*_{\eta}$) are provided in percentage form.
A first measurement of the top quark spin asymmetry, sensitive to the top quark polarisation, in t-channel single top quark production is presented. It is based on a sample of pp collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 inverse-femtobarns. A high-purity sample of t-channel single top quark events with an isolated muon is selected. Signal and background components are estimated using a fit to data. A differential cross section measurement, corrected for detector effects, of an angular observable sensitive to the top quark polarisation is performed. The differential distribution is used to extract a top quark spin asymmetry of 0.26 +/- 0.03 (stat) +/- 0.10 (syst), which is compatible with a p-value of 4.6% with the standard model prediction of 0.44.
The normalized differential cross section as a function of unfolded $\cos\theta_{\mu}^{*}$ for top quark.
The normalized differential cross section as a function of unfolded $\cos\theta_{\mu}^{*}$ for top antiquark.
The normalized differential cross section as a function of unfolded $\cos\theta_{\mu}^{*}$ for top quark and antiquark.
A $6.8 \ {\rm nb^{-1}}$ sample of $pp$ collision data collected under low-luminosity conditions at $\sqrt{s} = 7$ TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with $p_\mathrm{T} > 20$ GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in $\Delta\eta^F$, the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, $\tilde{\xi}$, of the fractional momentum loss of the proton assuming single diffractive dissociation ($pp \rightarrow pX$). Model comparisons indicate a dominant non-diffractive contribution up to moderately large $\Delta\eta^F$ and small $\tilde{\xi}$, with a diffractive contribution which is significant at the highest $\Delta\eta^F$ and the lowest $\tilde{\xi}$. The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions.
The cross section differential in the forward rapidity gap size, DELTA(C=RAPGAP), for events with at least two jets of pt > 20 GeV found by the anti-kt jet algorithm with R=0.6.
The cross section differential in the forward rapidity gap size, DELTA(C=RAPGAP), for events with at least two jets of pt > 20 GeV found by the anti-kt jet algorithm with R=0.4.
The cross section differential in the fraction of the proton four-momentum carried by the Pomeron, LOG10(C=XI), for events with at least two jets of pt > 20 GeV found by the anti-kt jet algorithm with R=0.6.
The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for $t\bar{t}$ events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti-$k_t$ jet with radius parameter $R=1.0$ and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.
Fiducial particle-level differential cross-section, with statistical and systematic uncertainties, as a function of the top-jet candidate p_T.
Parton-level differential cross-section, with statistical and systematic uncertainties, as a function of the hadronically decaying top quark p_T.
The individual systematic uncertainties calculated as a percentage of the particle-level differential cross-section $d\sigma_{tt} / d p_{T,ptcl}$ in each bin. Variations on the two sides ("UP" and "DOWN") are separately quoted with their respective signs. Uncertainties smaller than 0.1% are neglected.
We present a measurement of b jet transverse momentum (pt) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based estimate of the nuclear modification factor is found to be 1.22 +/- 0.15 (stat + syst pPb) +/- 0.27 (syst PYTHIA) averaged over all jets with pt between 55 and 400 GeV/c and with abs(eta[lab]) < 2. We also compare this result to predictions from models using perturbative calculations in quantum chromodynamics.
Distributions of the JP tagger discriminator before applying the SSV tagger selection.
Distributions of the JP tagger discriminator after applying the SSV tagger selection.
Distributions of the b-tagging efficiency as a function of the mistag rate of light jets for pp collisions in a PYTHIA simulation.
Jet multiplicity distributions in top quark pair (t t-bar) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the dilepton decay channels (e+ e-, mu+ mu-, and e+/- mu-/+). The absolute and normalized differential cross sections for t t-bar production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential t t-bar b and t t-bar b b-bar cross sections are presented for the first time as a function of the kinematic properties of the leading additional b jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.
Absolute differential ttbar cross sections as a function of the jet multiplicity for jets with pt > 30GeV, along with their statistical and systematic uncertainties. The results are presented at the particle level in the visible phase space of the ttbar decay products and the additional jets.
Normalized differential ttbar cross sections as a function of the jet multiplicity for jets with pt > 30GeV, along with their statistical and systematic uncertainties. The results are presented at the particle level in the visible phase space of the ttbar decay products and the additional jets.
Absolute differential ttbar cross sections as a function of the jet multiplicity for jets with pt > 60GeV, along with their statistical and systematic uncertainties. The results are presented at the particle level in the visible phase space of the ttbar decay products and the additional jets.
The four-lepton ($4\ell$, $\ell = e, \mu$) production cross section is measured in the mass range from 80 to 1000 GeV using 20.3 fb$^{-1}$ of data in $pp$ collisions at $\sqrt{s}=8$ TeV collected with the ATLAS detector at the LHC. The $4\ell$ events are produced in the decays of resonant $Z$ and Higgs bosons and the non-resonant $ZZ$ continuum originating from $q\bar q$, $gg$, and $qg$ initial states. A total of 476 signal candidate events are observed with a background expectation of $26.2 \pm 3.6$ events, enabling the measurement of the integrated cross section and the differential cross section as a function of the invariant mass and transverse momentum of the four-lepton system. In the mass range above $180$ GeV, assuming the theoretical constraint on the $q\bar q$ production cross section calculated with perturbative NNLO QCD and NLO electroweak corrections, the signal strength of the gluon-fusion component relative to its leading-order prediction is determined to be $\mu_{gg}=2.4 \pm 1.0 (stat.) \pm 0.5 (syst.)\pm 0.8 (theory)$.
The measured differential cross-section distributions in unit of fb/TeV of $m_{4\ell}$ unfolded into the fiducial phase space, and compared to theory predictions. The first uncertainty is statistical, the second is systematic uncertainties.
The measured differential cross-section distributions in unit of fb/TeV of $p_{T}^{4\ell}$ unfolded into the fiducial phase space, and compared to theory predictions. The first uncertainty is statistical, the second is systematic uncertainties.
Measured cross sections in the fiducial phase space ($\sigma^\mathrm{fid}$) and extended phase space ($\sigma^\mathrm{ext}$), compared to their SM predictions. One should note that the non-resonant $gg$-induced signal cross section is only calculated at LO approximation.
Differential cross sections for the production of at least four jets have been measured in proton-proton collisions at $\sqrt{s} = 8$ TeV at the Large Hadron Collider using the ATLAS detector. Events are selected if the four anti-$k_{t}$ R=0.4 jets with the largest transverse momentum ($p_{T}$) within the rapidity range $|y|<2.8$ are well separated ($dR^{\rm min}_{4j}>0.65$), all have $p_{T}>64$ GeV, and include at least one jet with $p_{T} >100$ GeV. The dataset corresponds to an integrated luminosity of 20.3 $fb^{-1}$. The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT1, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All uncertainties are given in %. The first uncertainty quoted is due to the number of data events. DSYS:mcstat is the statistical uncertainty due to the number of MC simulation events. The other columns, denoted with DSYS, correspond to the experimental systematic uncertainties arising from JES, JER, unfolding and luminosity, respectively.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT2, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All other details are as for pT1.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT3, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All other details are as for pT1.
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