3,060 research outputs found
Photon Cross Sections at Ecm = 2 TeV
Photon production rates have been studied by the D0 and CDF experiments in
Run II of the Fermilab Tevatron Collider. Measurements of the inclusive
isolated photon cross section and the di-photon cross section are presented,
based on integrated luminosities of 0.3 fb-1 and 0.2 fb-1, respectively. The
results are compared to perturbative QCD calculations in various
approximations.Comment: 4 pages 2 figures, presented at XLIrst Rencontres de Moriond on ``QCD
and High Energy Hadronic Interactions'', La Thuile, Italy, March 18-25, 2006,
on behalf of the CDF and D0 collaboration
Dijet azimuthal decorrelations for in perturbative QCD
We point out an inconsistency in perturbative QCD predictions previously used
for dijet azimuthal decorrelations for azimuthal angles of between the two jets. We show how the inconsistency arises and
how the calculations can be modified to provide more accurate results that
exhibit a smaller scale dependence and give a better description of the data
than the inconsistent results. We also explain how the quality of the
predictions strongly depends on a perceivedly minor detail in the definition of
the dijet phase space and give recommendations for future measurements.Comment: 12 pages, 4 figures, 3 tables, submitted to JHE
A new quantity for studies of dijet azimuthal decorrelations
We introduce a new measurable quantity, , for studies of the
rapidity and transverse momentum dependence of dijet azimuthal decorrelations
in hadron-hadron collisions. In pQCD, is computed as a ratio
of three-jet and dijet cross sections in which the parton distribution
functions cancel to a large extent. At the leading order, is
proportional to , and the transverse momentum dependence of can
therefore be exploited to determine . We compute the NLO pQCD theory
predictions and non-perturbative corrections for at the LHC
and the Tevatron and investigate the corresponding uncertainties. From this, we
estimate the theory uncertainties for determinations based on
at both colliders. The potential of
measurements for tuning Monte Carlo event generators is also demonstrated.Comment: 20 pages, 11 figures, 1 table, submitted to JHE
Direct determination of the gluon density in the proton from jet cross sections in deep-inelastic scattering
A QCD analysis of jet production in deep-inelastic scattering is presented. The studies are based on recent measurements of jet cross sections in the H1 experiment at HERA which are directly sensitive to the gluon density in the proton. The inclusion of H1 data on the inclusive deep-inelastic scattering cross section enables us to perform a consistent, simultaneous determination of the quark and gluon densities in the proton. The gluon density has been determined at fairly large values of at a scale of the order of the transverse jet energies \mu^2_f = 200\GeV^2. The result is consistent with indirect determinations from HERA structure function data and extends their range of sensitivity to larger -values
Progress in the Understanding of Dijet Production in Deep-Inelastic Scattering
Recent results on dijet production in deep-inelastic scattering from the H1
experiment at the ep-collider HERA are presented. Internal jet structure has
been studied in terms of jet shapes and subjet multiplicities in the Breit
frame. Both observables are seen to be well described by QCD models. We observe
a broadening of the jets towards the proton direction and at lower transverse
jet energies. Dijet rates and dijet cross sections have been measured over a
wide range of four momentum transfers (5 < Q^2 < 5000 GeV^2) and transverse jet
energies (25 < E^2_t,Breit < 1200 GeV^2) with different jet algorithms.
Perturbative QCD calculations in next-to-leading order in the strong coupling
constant give a good description of the data.Comment: 8 pages, 3 figures, to appear in the proceedings of the 6th
International Workshop on Deep Inelastic Scattering and QCD (DIS98), Brussels
199
QCD Tests in Hadronic Final States
Various QCD studies based on jet observables in hadronic final states in
deep-inelastic scattering and hadron-hadron collisions are presented. Measured
quantities are event shape variables, jet rates and jet cross sections. QCD
analyses have been performed to determine the value of the strong coupling
constant , the gluon density in the proton and to test power
corrections.Comment: 6 pages, 10 figures, to appear in the proceedings of the 29th
International Conference on High Energy Physics (ICHEP'98), Vancouver,
Canada, 199
Determination of the Strong Coupling Constant and Multijet Cross Section Ratio Measurements
Concepts and results of determinations of the strong coupling constant in
hadron collisions are discussed. A recent alpha_s result from the inclusive jet
cross section in pp-bar collisions at sqrt(s)=1.96 TeV is presented which is
based on perturbative QCD calculations beyond next-to-leading order. Emphasis
is put on the consistency of the conceptual approach. Conceptual limitations in
the approach of extracting alpha_s from cross section data are discussed and
how these can be avoided by using observables that are defined as ratios of
cross sections. For one such observable, the multijet cross section ratio R3/2,
preliminary results are presented.Comment: 4 pages, 2 figures, proceedings of DIS201
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