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≲Q2<2000GeV2 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 EjetT>7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range −3<ηjet<0 . The variable xobsγ , 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- xobsγ events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- xobsγ contribution relative to that at high xobsγ . 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
BASILE, MAURIZIO;CIFARELLI, LUISA;CONTIN, ANDREA;PALMONARI, FEDERICO;RINALDI, LORENZO;SARTORELLI, GABRIELLA;ZICHICHI, ANTONINO;
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≲Q2<2000GeV2 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 EjetT>7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range −3<ηjet<0 . The variable xobsγ , 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- xobsγ events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- xobsγ contribution relative to that at high xobsγ . 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
