Measurement Of Dijet Cross Sections Research Articles

Determination of diffractive PDFs from a global QCD analysis of inclusive diffractive DIS and dijet cross-section measurements at HERA

We present an updated set of {\tt SKMHS} diffractive parton distribution functions (PDFs). In addition to the diffractive deep-inelastic scattering (diffractive DIS) data sets, the recent diffractive dijet cross sections measurements by the H1 experiment from the HERA collider are added to the data sample. The new set of diffractive PDFs, entitled {\tt SKMHS23} and {\tt SKMHS23-dijet}, are presented at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) accuracy in perturbative QCD. Since the gluons directly contribute to jet production through the boson-gluon fusion process, the data on diffractive dijet production in inclusive DIS help to constrain the gluon density, allowing for the determination of both the quark and gluon densities with better accuracy. The NLO and NNLO theory predictions calculated using both {\tt SKMHS23} and {\tt SKMHS23-dijet} are compared to the analyzed data showing excellent agreements. The effect arising from the inclusion of diffractive dijet data and higher order QCD corrections on the extracted diffractive PDFs and data/theory agreements are clearly examined and discussed.

Determination of αs in NNLO QCD using H1 jet cross section measurements

Measurements of jet cross sections in neutral current deep-inelastic scattering (NC DIS) using data taken with the H1 detector at HERA are accomplished by the precision measurement of double-differential inclusive jet, dijet and trijet cross sections at low photon virtualities 5.5 < Q2 < 80 GeV2, and by extending previous inclusive jet measurements in the range 150 < Q2 < 15000 GeV2 to low transverse jet momenta 5 < PT < 7 GeV. The strong coupling constant at the Z-boson mass, αs(mZ), is determined in next-to-next-to-leading order (NNLO) QCD using H1 inclusive jet and dijet cross section measurements. Complementary, αs(mZ) is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The running of the strong coupling is tested at different values of the renormalisation scale and the results are found to be in agreement with the QCD expectations.

Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector

Double-differential dijet cross sections measured in pp collisions at the LHC with a 7 TeV centre-of-mass energy are presented as functions of dijet mass and rapidity separation of the two highest-pT jets. These measurements are obtained using data corresponding to an integrated luminosity of 4.5/fb, recorded by the ATLAS detector in 2011. The data are corrected for detector effects so that cross sections are presented at the particle level. Cross sections are measured up to 5 TeV dijet mass using jets reconstructed with the anti-kt algorithm for values of the jet radius parameter of 0.4 and 0.6. The cross sections are compared with next-to-leading-order perturbative QCD calculations by NLOJET++ corrected to account for non-perturbative effects. Comparisons with POWHEG predictions, using a next-to-leading-order matrix element calculation interfaced to a parton-shower Monte Carlo simulation, are also shown. Electroweak effects are accounted for in both cases. The quantitative comparison of data and theoretical predictions obtained using various parameterizations of the parton distribution functions is performed using a frequentist method. An example setting a lower limit on the compositeness scale for a model of contact interactions is presented, showing that the unfolded results can be used to constrain contributions to dijet production beyond that predicted by the Standard Model.

Hard QCD Results with Jets at the LHC

Hard QCD results in proton-proton collisions at sqrt(s) = 7 TeV with jets from data recorded up to the end of 2010 by the CMS and ATLAS experiments at the LHC are reported. Inclusive jet and di-jet cross section measurements as well as observables sensitive to multi-jet activity are shown and compared to simulations based on leading log parton showers as well as NLO QCD predictions. Novel approaches to identify highly boosted massive final states by exploiting the jet substructure are tested on the dominant QCD background.

QCD jet physics with the CMS detector at the LHC

We present QCD studies with jets collected by the CMS experiment at the Large Hadron Collider (LHC) at 7 TeV center of mass energy, including inclusive jet and dijet cross section measurements, the dijet polar and azimuthal angular distributions, and jet and event shapes. The data are compared to QCD predictions at NLO and NNLO and we show the sensitivity to physics processes beyond the Standard Model.

Measurement of dijet cross sections in ep interactions with a leading neutron at HERA

Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.

Measurement of dijet cross sections in photoproduction at HERA

Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e^+p data with an integrated luminosity of 34.9 pb^(-1). Jets are selected using the inclusive k_T algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x_p and photon longitudinal momentum fraction x_gamma in the ranges 0.05<x_p<0.6 and 0.1<x_gamma<1. The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.

Measurement of dijet cross sections for events with a leading neutron in photoproduction at HERA

Differential cross sections for dijet photoproduction in association with a leading neutron using the reaction e + + p → e + + n +jet+jet+ X r have been measured with the ZEUS detector at HERA using an integrated luminosity of 6.4 pb −1 . The fraction of dijet events with a leading neutron in the final state was studied as a function of the jet kinematic variables. The cross sections were measured for jet transverse energies E T jet >6 GeV, neutron energy E n >400 GeV, and neutron production angle θ n <0.8 mrad. The data are broadly consistent with factorization of the lepton and hadron vertices and with a simple one-pion-exchange model.

Measurement of di-jet cross-sections in photoproduction and photon structure

The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x γ is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section d σ/dlog( x γ ) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb −1. Using a restricted data sample at high transverse jet energy, E T,jet>6 GeV, the effective parton density f γ ,eff (x γ)= q(x γ)+ q ̄ (x γ)+9/4 g(x γ) in the photon in leading order QCD is measured down to x γ = 0.05 from which the gluon density in the photon is derived.

Measurement of dijet cross-sections in low ${\rm Q}^2$ ep collisions and the extraction of an effective parton density for the virtual photon

The triple-differential dijet cross-section, \({\rm d}^3 \sigma_{ep}/{\rm d} Q^2{\rm d} \overline{E_t}^2 {\rm d}x^{jets}_\gamma\), is measured with the H1 detector at HERA as a function of the photon virtuality \(Q^2\), the fraction of the photon's momentum carried by the parton entering the hard scattering, \(\x^{jets}_\gamma\), and the square of the mean transverse energy, \(\overline{E_t}^2\), of the two highest \(E_t\) jets. Jets are found using a longitudinal boost-invariant \(k_T\) clustering algorithm in the \(\gamma^* p\) center of mass frame. The measurements cover the ranges \(1.6 < Q^2 < 80\) GeV\(^2\) in virtuality and \(0.1 < y < 0.7\) in inelasticity y. The results are well described by leading order QCD models which include the effects of a resolved component to the virtual photon. Models which treat the photon as point-like fail to describe the data. An effective leading order parton density for the virtual photon is extracted as a function of the photon virtuality, the probing scale and the parton momentum fraction. The \(x_{\gamma}\) and probing scale dependences of the parton density show characteristic features of photon structure, and a suppression of this structure with increasing \(Q^2\) is seen.

Di-jet cross section in photoproduction and gluon density in the photon

We report on a new measurement of di-jet cross section in photoproduction, using an integrated luminosity of £ ≅ 7.2 pb −1 taken with the H1 detector at HERA. A leading order effective parton density of the photon is deduced, which extends down to small parton fractional energies of x γ = 0.04. This allows a measurement, in a largely unexplored kinematic domain, of the gluon density in the photon which is compared to QCD-inspired models and to a recent H1 measurement using charged tracks.

Measurement of dijet cross-sections in low

The triple-differential dijet cross-section, ${\rm d}^3 \sigma_{ep}/{\rm d} Q^2{\rm d} \overline{E_t}^2 {\rm d}x^{jets}_\gamma$ , is measured with the H1 detector at HERA as a function of the photon virtuality $Q^2$ , the fraction of the photon's momentum carried by the parton entering the hard scattering, $\x^{jets}_\gamma$ , and the square of the mean transverse energy, $\overline{E_t}^2$ , of the two highest $E_t$ jets. Jets are found using a longitudinal boost-invariant $k_T$ clustering algorithm in the $\gamma^* p$ center of mass frame. The measurements cover the ranges $1.6 < Q^2 < 80$ GeV $^2$ in virtuality and $0.1 < y < 0.7$ in inelasticity y. The results are well described by leading order QCD models which include the effects of a resolved component to the virtual photon. Models which treat the photon as point-like fail to describe the data. An effective leading order parton density for the virtual photon is extracted as a function of the photon virtuality, the probing scale and the parton momentum fraction. The $x_{\gamma}$ and probing scale dependences of the parton density show characteristic features of photon structure, and a suppression of this structure with increasing $Q^2$ is seen.