A measurement of the dijet production cross section is reported based on proton-proton collision data collected in 2016 at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of up to 36.3 fb$^{-1}$. Jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm for distance parameters of $R$ = 0.4 and 0.8. Cross sections are measured double-differentially (2D) as a function of the largest absolute rapidity $\lvert y_\text{max}\rvert$ of the two jets with the highest transverse momenta $p_\mathrm{T}$ and their invariant mass $m_{1,2}$, and triple-differentially (3D) as a function of the rapidity separation $y^*$, the total boost $y_\mathrm{b}$, and either $m_{1,2}$ or the average $p_\mathrm{T}$ of the two jets. The cross sections are unfolded to correct for detector effects and are compared with fixed-order calculations derived at next-to-next-to-leading order in perturbative quantum chromodynamics. The impact of the measurements on the parton distribution functions and the strong coupling constant at the mass of the Z boson is investigated, yielding a value of $\alpha_\mathrm{S}(m_\mathrm{Z})$ = 0.1179 $\pm$ 0.0019.
Double-differential dijet cross section for anti-$k_\text{T}$ jets with R = 0.4 as a function of the dijet invariant mass ($m_{1,2}$) and the absolute rapidity of the outermost jet ($\left| y \right|_\text{max}$)
Electroweak corrections to double-differential dijet cross section for anti-$k_\text{T}$ jets with R = 0.4 as a function of the dijet invariant mass ($m_{1,2}$) and the absolute rapidity of the outermost jet ($\left| y \right|_\text{max}$)
Nonperturbative corrections to double-differential dijet cross section for anti-$k_\text{T}$ jets with R = 0.4 as a function of the dijet invariant mass ($m_{1,2}$) and the absolute rapidity of the outermost jet ($\left| y \right|_\text{max}$)
We report measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for inclusive jet and dijet production in polarized proton-proton collisions at midrapidity and center-of-mass energy $\sqrt{s}$ = 510 GeV, using the high luminosity data sample collected by the STAR experiment in 2013. These measurements complement and improve the precision of previous STAR measurements at the same center-of-mass energy that probe the polarized gluon distribution function at partonic momentum fraction 0.015 $\lesssim x \lesssim$ 0.25. The dijet asymmetries are separated into four jet-pair topologies, which provide further constraints on the $x$ dependence of the polarized gluon distribution function. These measurements are in agreement with previous STAR measurements and with predictions from current next-to-leading order global analyses. They provide more precise data at low dijet invariant mass that will better constraint the shape of the polarized gluon distribution function of the proton.
Parton jet $p_T$ vs $A_{LL}$ values with associated uncertainties.
Parton dijet $M_{inv}$ vs $A_{LL}$ values with associated uncertainties, for topology A.
Parton dijet $M_{inv}$ vs $A_{LL}$ values with associated uncertainties, for topology B.
We report high-precision measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for midrapidity inclusive jet and dijet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s}=200\,\mathrm{GeV}$. The new inclusive jet data are sensitive to the gluon helicity distribution, $\Delta g(x,Q^2)$, for gluon momentum fractions in the range from $x \simeq 0.05$ to $x \simeq 0.5$, while the new dijet data provide further constraints on the $x$ dependence of $\Delta g(x,Q^2)$. The results are in good agreement with previous measurements at $\sqrt{s}=200\,\mathrm{GeV}$ and with recent theoretical evaluations of prior world data. Our new results have better precision and thus strengthen the evidence that $\Delta g(x,Q^2)$ is positive for $x > 0.05$.
Jet yield versus jet transverse momentum $p_{T}$ at the detector level and at the parton level. Table includes data for the JP2 trigger conditions and the corresponding simulations.
Jet yield versus jet transverse momentum $p_{T}$ at the detector level and at the parton level. Table includes data for the JP1 trigger conditions and the corresponding simulations.
Dijet yield versus the dijet $M_{inv}$ at the detector level and at the parton level. Table includes data for the JP1 and JP2 trigger conditions and the corresponding simulations.
We report the first measurement of the longitudinal double-spin asymmetry $A_{LL}$ for mid-rapidity di-jet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s} = 200$ GeV. The di-jet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. $A_{LL}$ results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-$x > 0.05$.
Data simulation comparison (with arbitrary normalization). Di-jet invariant mass.
Data simulation comparison (with arbitrary normalization). Difference between jet pseudorapidities.
Data simulation comparison (with arbitrary normalization). Difference between jet azimuthal angles.
A measurement of the jet activity in ttbar events produced in proton-proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb^-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The ttbar events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, POWHEG, ALPGEN and SHERPA. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval < 0.8 having a transverse momentum greater than Q, as a function of Q.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval 0.8-1.5 having a transverse momentum greater than Q, as a function of Q.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval 1.5-2.1 having a transverse momentum greater than Q, as a function of Q.
Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kT algorithm with parameters R=0.4 and R=0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 inverse picobarns. Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading jets. The measurements are performed in the jet rapidity range |y|<4.4, covering jet transverse momenta from 20 GeV to 1.5 TeV and dijet invariant masses from 70 GeV to 5 TeV. The data are compared to expectations based on next-to-leading order QCD calculations corrected for non-perturbative effects, as well as to next-to-leading order Monte Carlo predictions. In addition to a test of the theory in a new kinematic regime, the data also provide sensitivity to parton distribution functions in a region where they are currently not well-constrained.
Inclusive jet PT distribution for the |y| range 0.0-0.3 and R=0.4.
Inclusive jet PT distribution for the |y| range 0.3-0.8 and R=0.4.
Inclusive jet PT distribution for the |y| range 0.8-1.2 and R=0.4.
A measurement of jet activity in the rapidity interval bounded by a dijet system is presented. Events are vetoed if a jet with transverse momentum greater than 20 GeV is found between the two boundary jets. The fraction of dijet events that survive the jet veto is presented for boundary jets that are separated by up to six units of rapidity and with mean transverse momentum 50 < pT(avg) < 500 GeV. The mean multiplicity of jets above the veto scale in the rapidity interval bounded by the dijet system is also presented as an alternative method for quantifying perturbative QCD emission. The data are compared to a next-to-leading order plus parton shower prediction from the POWHEG-BOX, an all-order resummation using the HEJ calculation and the PYTHIA, HERWIG++ and ALPGEN event generators. The measurement was performed using pp collisions at sqrt(s)=7 TeV using data recorded by the ATLAS detector in 2010.
The Gap Fraction as a function of the mean transverse momentum of the boundary jets for boundary jets having a rapidity difference in the range [1,2], using a jet veto Q0 = 20 GeV. Data are shown for two dijet selections: (i) the dijet system is defined as the two leading-pT jets in the event (ii) the dijet system is defined as the most forward-backward jets in the event.
The Gap Fraction as a function of the mean transverse momentum of the boundary jets for boundary jets having a rapidity difference in the range [2,3], using a jet veto Q0 = 20 GeV. Data are shown for two dijet selections: (i) the dijet system is defined as the two leading-pT jets in the event (ii) the dijet system is defined as the most forward-backward jets in the event.
The Gap Fraction as a function of the mean transverse momentum of the boundary jets for boundary jets having a rapidity difference in the range [3,4], using a jet veto Q0 = 20 GeV. Data are shown for two dijet selections: (i) the dijet system is defined as the two leading-pT jets in the event (ii) the dijet system is defined as the most forward-backward jets in the event.
Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full dataset (L=36/pb) acquired by the ATLAS detector during the 2010 sqrt(s)=7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high energy regime.
Distribution for the maxPT jet (P=3) from 110 to 160 GeV.
Distribution for the maxPT jet (P=3) from 160 to 210 GeV.
Distribution for the maxPT jet (P=3) from 210 to 260 GeV.
Using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally-segmented electromagnetic and hadronic calorimeters. The underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.
Asymmetry in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.
Asymmetry in 7 TeV P-P collisions.
DeltaPhi distribution in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.
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.
CHI distribution for mass bin 340 to 520 GeV.
CHI distribution for mass bin 520 to 800 GeV.
CHI distribution for mass bin 800 to 1200 GeV.