Dijet photoproduction at HERA and the structure of the photon

Abstract

The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb −1 . The events were required to have a virtuality of the incoming photon, Q 2 , of less than 1 GeV 2 and a photon-proton centre-of-mass energy in the range 134 < W γp < 277 GeV. Each event contains at least two jets satisfying transverse-energy requirements of E jet1 T > 14 GeV and E jet2 T > 11 GeV and pseudorapidity requirements of −1 < η jet1,2 < 2.4. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.

Simulations of photo-nuclear dijets with PYTHIA 8 and their sensitivity to nuclear PDFs

“…Here E i T and η i refer to the transverse energies and pseudorapidities of the jets, y is the inelasticity of the ep scattering and E e the energy of the electron beam. Figure 3 show comparisons between the ZEUS measurement [3] for the dijet photoproduction in ep collisions at HERA and the PYTHIA 8 simulation with direct-enhanced (x obs γ > 0.75) and resolvedenhanced (x obs γ < 0.75) event samples. The (sub-)leading jet were required to have E T > 14(11) GeV and the invariant mass of the photon-proton system were constrained to 134 < W γp < 277 GeV range.…”

“…Figure 3: Dijet photoproduction as a function of η jet2 for events with x obs γ < 0.75 (left) and x obs γ > 0.75 (right) with three different photon PDF set, CJKL (red) [4], GRV (green) [5] and SaSgam (orange) [6]. Data from ZEUS [3].…”

Measurement of inclusive jet and dijet production inppcollisions ats=7 TeVusing the ATLAS detector

“…The energy and the position of the jet are next corrected for instrumental effects such as dead material and noncompensation. This jet energy scale (JES) correction is calculated using isolated jets 4 in the Monte Carlo simulation as a function of energy and pseudorapidity of the reconstructed jet. The JES correction factor ranges from about 2.1 for low-energy jets with p T ¼ 20 GeV in the central region jyj < 0:3 to less than 1.2 for high-energy jets in the most forward region 3:6 jyj < 4:4.…”

“…They are an important tool for understanding the strong interaction and searching for physics beyond the standard model (see, for example, Refs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]).…”

Inclusive and diffractive dijet photoproduction at the Electron-Ion Collider in NLO QCD

“…Provided that the jet transverse momenta p T are sufficiently large, this process allows one to probe the microscopic quark-gluon structure of the proton and the real photon in quantum chromodynamics (QCD) as well as the strong interaction dynamics in the regime of perturbative QCD (pQCD). The predictions of next-to-leading order (NLO) pQCD provide a good description of the dijet photoproduction cross section measured at HERA as a function of various jet observables in a wide range of p T [4,5,6,7]. This serves as an important test of the QCD factorization and universality of parton distribution functions (PDFs).…”