Inclusive dijet production at large pseudorapidity intervals (delta_eta) between the two jets has been suggested as a regime for observing BFKL dynamics. We have measured the dijet cross section for large delta_eta in ppbar collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic cross section increases strongly with the size of delta_eta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of a_{BFKL}(20GeV)=1.65+/-0.07.
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
We present new measurements of differential cross sections for Z/gamma*(->mumu)+jet+X production in a 1 fb-1 data sample collected with the D0 detector in proton anti-proton collisions at sqrt{s}=1.96 TeV. Results include the first measurements differential in the Z/gamma* transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/gamma* transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.
Measured cross section as a function of the jet transverse momentum.
Measured cross section as a function of the jet rapidity.
Measured cross section as a function of the Z0 transverse momentum.
We present a measurement of the fraction of inclusive $W$+jets events produced with net charm quantum number $\pm1$, denoted $W$+$c$-jet, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using approximately 1~fb$^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron Collider. We identify the $W$+jets events via the leptonic $W$ boson decays. Candidate $W$+$c$-jet events are selected by requiring a jet containing a muon in association with a reconstructed $W$ boson and exploiting the charge correlation between this muon and $W$ boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of $W$+$c$-jet events in the inclusive $W$+jets sample for jet $p_{T}>20$ GeV and pseudorapidity $|\eta|<2.5$ to be 0.074$\pm0.019$(stat.)$\pm^{0.012}_{0.014}$(syst.), in agreement with theoretical predictions. The probability that background fluctuations could produce the observed fraction of $W$+$c$-jet events is estimated to be $2.5\times 10^{-4}$, which corresponds to a 3.5 $\sigma$ statistical significance.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (E NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (MU NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (LEPTON NU) channel for various jet PT ranges.
We determine the fraction of events with double parton (DP) scattering in a single ppbar collision at sqrt{s}=1.96 TeV in samples of photon + 3 jet and photon + b/c jet + 2 jet events collected with the D0 detector and corresponding to an integrated luminosity of about 8.7 fb^{-1}. The DP fractions and effective cross sections (sigma_eff) are measured for both event samples using the same kinematic selections. The measured DP fractions range from 0.21 to 0.17, with effective cross sections in the photon + 3 jet and photon + b/c jet + 2 jet samples of sigma_eff^incl = 12.7 +- 0.2 (stat) +- 1.3 (syst) mb and sigma_eff^HF = 14.6 +- 0.6 (stat) +- 3.2 (syst) mb, respectively.
The effective cross sections measured for the inclusive and heavy flavour event samples.
This Letter describes a model-independent search for the production of new resonances in photon + jet events using 20 inverse fb of proton--proton LHC data recorded with the ATLAS detector at a centre-of-mass energy of sqrt(s) = 8 TeV. The photon + jet mass distribution is compared to a background model fit from data; no significant deviation from the background-only hypothesis is found. Limits are set at 95% credibility level on generic Gaussian-shaped signals and two benchmark phenomena beyond the Standard Model: non-thermal quantum black holes and excited quarks. Non-thermal quantum black holes are excluded below masses of 4.6 TeV and excited quarks are excluded below masses of 3.5 TeV.
Invariant mass of the photon+jet pair for events passing the final selections. The number of observed events and the fit background estimates are given in each bin, where the fit estimates are rounded to the nearest integer.
The 95% CL upper limits on SIG*BR*A*EPSILON for a hypothetical signal with a Gaussian-shaped M(GAMMA JET) distribution as a function of the signal mass M(G) for four values of the relative width SIGMA(G) / M(G).
Acceptance (A), efficiency (EPSILON), cross-section (SIG) and limits in number of events for the quantum black hole (QBH) benchmark model, as a function of the threshold mass M(th). Uncertainties on the cross section are on the order of 1%. The limits include statistical uncertainties only. Expected limits include the 68% uncertainty band. Acceptance was calculated using parton-level quantities by imposing criteria that apply directly to kinematic selections (photon/jet |eta|, photon/jet transverse momentum, Delta(eta), Delta(R)). All other selections, which in general correspond to event and object quality criteria, were used to calculate the efficiency based on the events included in the acceptance.
The production of a W boson in association with a single charm quark is studied using 4.6 fb^-1 of pp collision data at sqrt(s)=7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26 -0.30 at Q^2=1.9 GeV^2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W^+ + bar{c})/sigma(W^- + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-bar{s} quark asymmetry.
Measured integrated cross sections of the production of a W boson with a single c-jet, a D meson or a D* meson times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured integrated cross section ratios of the production of W+ and W- bosons associated with a single c-jet, a D meson or a D* meson in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured differential cross sections as function of the lepton pseudo-rapidity of the production of a W boson with a single c-jet times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. The cross sections are defined for OS-SS events.
This Letter presents a search for quantum black-hole production using 20.3 inverse fb of data collected with the ATLAS detector in pp collisions at the LHC at sqrt(s) = 8 TeV. The quantum black holes are assumed to decay into a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton+jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.
The combined 95% CL upper limits on the cross section times branching fraction (SIG*BR) for Quantum Black Holes decaying to a lepton and jet, as a function of the threshold mass, Mth.
Numbers of observed events and expected background events for electron+jet channel, along with acceptance (A), experimental efficiency (EPSILON), cumulative efficiency (A*EPSILON), total cross section (SIG*BR) and 95% CL observed upper limit, for various values of the threshold mass, Mth. The leading order cross sections have a statistical precision of the order of 1%. The uncertainties on the predicted background include both statistical and systematic components. Acceptance is calculated using generator-level quantities by imposing selection criteria that apply directly to phase space (electron/jet eta, electron/jet pT, Delta(eta), Delta(phi), <eta>, and Minv). All other selections, which in general correspond to event and object quality criteria, are used to calculate the efficiency on the events included in the acceptance. The cumulative signal efficiency is the product of the acceptance and experimental efficiency.
Numbers of observed events and expected background events for muon+jet channel, along with acceptance (A), experimental efficiency (EPSILON), cumulative efficiency (A*EPSILON), total cross section (SIG*BR) and 95% CL observed upper limit, for various values of the threshold mass, Mth. The leading order cross sections have a statistical precision of the order of 1%. The uncertainties on the predicted background include both statistical and systematic components. Acceptance is calculated using generator-level quantities by imposing selection criteria that apply directly to phase space (muon/jet eta, muon/jet pT, Delta(eta), Delta(phi), <eta>, and Minv). All other selections, which in general correspond to event and object quality criteria, are used to calculate the efficiency on the events included in the acceptance. The cumulative signal efficiency is the product of the acceptance and experimental efficiency.
This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma(W+ \ge n) / sigma(W+ \ge n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n \le 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.
The measured cross section times branching ratio for W+jets in the electron channel as a function of corrected jet multiplicity.
The measured cross section times branching ratio for W+jets in the muon channel as a function of corrected jet multiplicity.
The measured cross section ratio for W+jets in the electron channel as a function of corrected jet multiplicity.
A search for events with large missing transverse momentum, jets, and at least two tau leptons has been performed using 2 fb^-1 of proton-proton collision data at sqrt(s) = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95% CL visible cross section upper limit for new phenomena is set. A 95% CL lower limit of 32 TeV is set on the GMSB breaking scale Lambda independent of tan(beta). These limits provide the most stringent tests to date in a large part of the considered parameter space.
The observed PT spectrum of the leading TAU candidates and the estimated SM background after pre-selection of candidate events, soft multi-jet rejection and the requirement of two or more TAUS and no light leptons.
The distribution of the effective mass of the two leading TAU candidates in data (with statistical uncertainties only) and the estimated SM background after pre-selection of candidate events, soft multi-jet rejection and the requirement of two or more TAUS and no light leptons.
The distribution of the sum of the transverse masses of the two leading TAU candidates in data (with statistical uncertainties only) and the estimated SM background after pre-selection of candidate events, soft multi-jet rejection and the requirement of two or more TAUS and no light leptons.
This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.
Percentage D*+- production rate R in Z and PT bins.
Percentage D*+- production rate R integrated over jet PT 25-70 GeV as a function of Z.
D*+- production rate R integrated over jet PT=25-70 GeV and Z=0.3-1.0.
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