Professor Amanda Cooper-Sarkar

Abstract:

New ZEUS data are added into the NLO QCD analysis of the ZEUS-JETS PDF fit. The addition of high-Q2 NC and CC e- p inclusive cross-section data improves the determination of the u-valence quark at high x. The addition of high-Q2 CC e+p inclusive cross-section data improves the determination of the d-valence quark at high x. The addition of lower-Q2 NC e+ p inclusive cross-section data, run at three difierent proton beam energies, improves the determination of the sea and gluon PDFs at small x. The new PDF fit is called the ZEUS09 PDF fit.

Abstract:

Deeply virtual Compton scattering, γ*p→γp has been measured in e+p collisions at HERA with the ZEUS detector using an integrated luminosity of 61.1 pb-1. Cross sections are presented as a function of the photon virtuality, Q2, and photon-proton centre-of-mass energy, W, for a wide region of the phase space, Q2 > 1.5GeV2 and 40 < W < 170GeV. A subsample of events in which the scattered proton is measured in the leading proton spectrometer, corresponding to an integrated luminosity of 31.3 pb-1, is used for the first direct measurement of the differential cross section as a function of t, where t is the square of the four-momentum transfer at the proton vertex. © SISSA 2009.

Abstract:

Direct measurements of the proton structure function FL have been performed in deep inelastic ep scattering at low x at HERA. The FL values are extracted by the H1 and ZEUS collaborations from the cross sections measured at fixed x and Q2 but different y values. This is achieved by using data sets collected with three different proton beam energies. The H1 and ZEUS results are consistent with each other and exhibit a non-zero FL. The measurements are also consistent with the previous indirect determinations of FL by H1. The results confirm DGLAP NLO and NNLO QCD predictions for FL(x,Q2), derived from previous HERA data, which are dominated by a large gluon density at low x.

Abstract:

We provide an assessment of the state of the art in various issues related to experimental measurements, phenomenological methods and theoretical results relevant for the determination of parton distribution functions (PDFs) and their uncertainties, with the specific aim of providing benchmarks of different existing approaches and results in view of their application to physics at the LHC. We discuss higher order corrections, we review and compare different approaches to small x resummation, and we assess the possible relevance of parton saturation in the determination of PDFS at HERA and its possible study in LHC processes. We provide various benchmarks of PDF fits, with the specific aim of studying issues of error propagation, non-gaussian uncertainties, choice of functional forms of PDFs, and combination of data from different experiments and different processes. We study the impact of combined HERA (ZEUS-H1) structure function data, their impact on PDF uncertainties, and their implications for the computation of standard candle processes, and we review the recent F L determination at HERA. Finally, we compare and assess methods for luminosity measurements at the LHC and the impact of PDFs on them.