The dependence of dijet production on the virtuality of the exchanged photon, Q(2), has been studied by measuring dijet cross sections in the range 0 less than or similar to Q(2) < 2000 GeV(2) with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb(-1). Dijet cross sections were measured for jets with transverse energy E(T)(jet) > 7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3 < eta(jet) < 0. The variable x(gamma)(obs), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q(2) dependence of the ratio of low- to high-x(gamma)(obs) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low-x(gamma)(obs) contribution relative to that at high x(gamma)(obs). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q(2), provide a qualitative description of the data.

The dependence of dijet production on the virtuality of the exchanged photon, Q(2), has been studied by measuring dijet cross sections in the range 0 less than or similar to Q(2) < 2000 GeV(2) with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb(-1). Dijet cross sections were measured for jets with transverse energy E(T)(jet) > 7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3 < eta(jet) < 0. The variable x(gamma)(obs), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q(2) dependence of the ratio of low- to high-x(gamma)(obs) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low-x(gamma)(obs) contribution relative to that at high x(gamma)(obs). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q(2), provide a qualitative description of the data.

The dependence of dijet production on photon virtuality in ep collisions at HERA

CAPUA, Marcella;MASTROBERARDINO, Anna;Schioppa M;TASSI, Enrico;
2004

Abstract

The dependence of dijet production on the virtuality of the exchanged photon, Q(2), has been studied by measuring dijet cross sections in the range 0 less than or similar to Q(2) < 2000 GeV(2) with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb(-1). Dijet cross sections were measured for jets with transverse energy E(T)(jet) > 7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3 < eta(jet) < 0. The variable x(gamma)(obs), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q(2) dependence of the ratio of low- to high-x(gamma)(obs) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low-x(gamma)(obs) contribution relative to that at high x(gamma)(obs). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q(2), provide a qualitative description of the data.
The dependence of dijet production on the virtuality of the exchanged photon, Q(2), has been studied by measuring dijet cross sections in the range 0 less than or similar to Q(2) < 2000 GeV(2) with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb(-1). Dijet cross sections were measured for jets with transverse energy E(T)(jet) > 7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3 < eta(jet) < 0. The variable x(gamma)(obs), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q(2) dependence of the ratio of low- to high-x(gamma)(obs) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low-x(gamma)(obs) contribution relative to that at high x(gamma)(obs). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q(2), provide a qualitative description of the data.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11770/126843
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