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Register a new userOn the application of photon+jet events for setting the absolute jet energy scale and determining the gluon distribution at the LHC
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We study the impact of new set of cuts, proposed in our previous works, on the improvement of accuracy of the jet energy calibration with p p ->photon+Jet+X process at LHC. Monte Carlo events produced by the PYTHIA 5.7 generator are used for this aim. The selection criteria for photon+jet event samples that would provide a good balance of photon Pt with jet Pt and would allow to reduce the background are described. The distributions of these events over photon Pt and jet pseudorapidity are presented. The features of photon+jet events in the barrel region of the CMS detector (|eta^{jet}| < 1.4) are exposed. The efficiency of the cuts used for background suppression is demonstrated. It is shown that the samples of photon+jet events, gained with the cuts for the jet energy calibration, may have enough statistics for determining the gluon distribution inside a proton in the region of x > 2*10^{-4} and of Q^2 by two orders higher than that studied at HERA.
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A possibility of jet energy scale setting by help of ``p p -> Z0+jet+X process at LHC is studied. The effect of new set of cuts, proposed in our previous works, on the improvement of the Pt balance between Z0 boson and jet is demonstrated. The distributions of the selected events over Z0 transverse momentum and jet pseudorapidity are presented. A possibility of background events suppression by use of the Z0+jet events selection criteria is shown. It is also found that the samples of Z0+jet events, gained with the cuts for the jet energy calibration, may have enough statistics for determining the gluon distribution inside a proton in the region of 2*10^{-4} < x < 1.0$ with 0.9*10^3 < Q^2 < 4*10^4 (GeV/c)^2. Monte Carlo events produced by the PYTHIA 5.7 generator are used here.
The consequences of application of new set of criteria, proposed in our previous works, for the improvement of a jet energy calibration accuracy with the process p~p->photon+jet+X at Tevatron and for a reduction of background events contribution are studied. The efficiencies of the used selection criteria are estimated. The distributions of these events over photon Pt and jet pseudorapidity are presented. The features of photon+jet events in the central calorimeter region of the D0 detector (|eta|<0.7) are investigated. It is also shown that the samples of photon+jet events, selected with the cuts used for the jet energy calibration, may have the statistics sufficient for determining the gluon distribution function of a proton in the region of 2*10^{-3}< x < 1.0 and the values of Q^2 by one order higher than that reached in the experiments at HERA. Monte Carlo events produced by the PYTHIA 5.7 generator are used for this aim.
It is shown that the samples of Z0+jet events, collected at the LHC with the integrated luminosity L_{int}=20 fb^{-1}, may have enough statistics for determining the gluon distribution inside a proton in the region of 2*10^{-4} < x < 1.0 at Q^2 values in the interval of 0.9*10^3 < Q^2 < 4*10^4 ~(GeV/c)^2. A possibility of the background events suppression by use of the Z^0+jet events selection criteria is also demonstrated.
The number of photon+jet and Z+jet events suitable for a determination of gluon distribution function in a proton at Tevatron Run II and during the low luminosity runs at future LHC experiments are estimated for various intervals of x and Q^2. These numbers allow to extract gluon distribution in new kinematic regions of 2 * 10^{-3} < x < 1.0 with 1.6*10^3 < Q^2 < 2*10^4 ~(GeV/c)^2 at Tevatron and of 2* 10^{-4} < x < 1.0$ with 1.6*10^3 < Q^2 < 2*10^5 ~(GeV/c)^2 at LHC. The contributions of background events in different Q^2 intervals are also given.
The DZERO detector is used to study proton-antiproton collisions at the 1800 GeV and 630 GeV center-of-mass energies available at the Fermilab Tevatron. To measure jets, the detector uses a sampling calorimeter composed of uranium and liquid argon as the passive and active media respectively. Understanding the jet energy calibration is not only crucial for precision tests of QCD, but also for the measurement of particle masses and the determination of physics backgrounds associated with new phenomena. This paper describes the energy calibration of jets observed with the DZERO detector at the two proton-antiproton center-of-mass energies in the transverse energy and pseudorapidity range ET>8 GeV and pseudorapidity<3.
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