Slide 1

29.6.2005Low x meeting, Sinai 20051 Alice Valkrov on behalf of H1 collaboration LOW x meeting 2005, Sinaia H1 measurements of the structure of diffraction and tests of factorisation Slide 2 29.6.2005Low x meeting, Sinai 20052 2 HERA: ~ 10% of low-x DIS events are diffractive study QCD structure of high energy diffraction with virtual photon e e DIS: Probe structure of proton F 2 Diffractive DIS: Probe structure of color singlet exchange F 2 D HERA experiments and diffraction Slide 3 29.6.2005Low x meeting, Sinai 20053 Momentum fraction of proton carried by color singlet exchange: Momentum fraction of color singlet carried by struck quark: Large rapidity gap between leading proton p and X W max Diffraction kinematics Slide 4 29.6.2005Low x meeting, Sinai 20054 QCD factorisation inclusive dijet hard scattering QCD matrix element, perturbatively calculated, process dependent Universal diffractive parton densities identical for all processes get PDFs from inclusive diffraction predict cross sections for exclusive diffraction universal hard scattering cross section (same as in inclusive DIS) diffractive parton distribution function s obey DGLAP universal for diffractive ep DIS (inclusive, di-jets, charm) proven for DIS (J.Collins (1998)) not proven for photoproduction! Slide 5 29.6.2005Low x meeting, Sinai 20055 diff = flux(x P ) object (,Q 2 ) Results from inclusive diffraction Q2Q2 Reduced cross section from inclusive diffractive data get diffractive PDFs from a NLO (LO) DGLAP QCD Fit to inclusive data from 6.5 GeV 2 to 120 GeV 2 extrapolation of the Fit to lower Q 2 to higher Q 2 gives a reasonably good description of inclusive data from 3.5 GeV 2 1600 GeV 2 Regge factorisation is an additional assumption, there is no PROOF!! pomeron flux factor pomeron PDF Slide 6 29.6.2005Low x meeting, Sinai 20056 Diffractive Parton Densities determined from NLO QCD analysis of diffractive structure function more sensitive to quarks gluons from scaling violation, poorer constraint gluon carries about 75% of pome- ron momentum large uncertainty at large z P Assuming factorisation holds, the jet and HQ cross sections give better constraint on the gluon density Slide 7 29.6.2005Low x meeting, Sinai 20057 Jet and HQ production Hard scale is E T of the jet or HQ mass Direct access to gluon density Can reconstruct z P in dijet events tests of universality of PDFs (=QCD factorisation) test of DGLAP evolution Slide 8 29.6.2005Low x meeting, Sinai 20058 Charm cross section (DIS) NLO calculations HVQDIS (Harris & Smith) Good agreement within experimental & theoretical uncertainties. Good description of diffractive D* production in DIS (2GeV 2 29.6.2005Low x meeting, Sinai 200512 Direct and resolved processes at HERA x - fraction of photons momentum in hard subprocess DIS (Q 2 >5GeV 2 ) and direct photoproduction (Q 2 0): photon directly involved in hard scattering x =1 Resolved photoproduction: photon fluctuates into hadronic system, which takes part in hadronic scattering dominant at Q 2 0 x