31.08.20091Hadron Structure 2009 Factorisation in diffraction Alice Valkárová Charles University, Prague Representing H1 and ZEUS experiments Hadron structure.

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Hadron Structure 2009 Factorisation in diffraction Alice Valkárová Charles University, Prague Representing H1 and ZEUS experiments Hadron structure ´09 Tatranská Štrba

HERA/LHC workshop May Hadron Structure HERA collider experiments 27.5 GeV electrons/positrons on 920 GeV protons → √s=318 GeV two experiments: H1 and ZEUS HERA I: 16 pb -1 e-p, 120 pb –1 e+p HERA II: ∼ 550 pb -1, ∼ 40% polarisation of e+,e- closed July 2007, still lot of excellent data to analyse…… e DIS: Probe structure of proton → F 2 Diffractive DIS: Probe structure of color singlet exchange → F 2 D

HERA/LHC workshop May Hadron Structure W ´ HERA: ~ 10% of low-x DIS events are diffractive Diffraction and diffraction kinematics momentum fraction of color singlet exchange fraction of exchange momentum, coupling to γ* t 4-momentum transfer squared MyMy Two classes of diffractive events: Q 2 ~0 → photoproduction Q 2 >>0 → deep inelastic scattering (DIS)

HERA/LHC workshop May Hadron Structure ) Proton Spectrometers: ZEUS: LPS ( ) H1: FPS ( ),VFPS ( ) t measurement access to high x IP range free of p-dissociation background at low x IP small acceptance  low statistics ☠ 2) Large Rapidity Gap, H1, ZEUS: Require no activity beyond η max t not measured, very good acceptance at low x IP p-diss background ~ 20% ☠ diff. non-diff e p Diffractive Event Selection e

HERA/LHC workshop May Hadron Structure What is QCD factorisation? Factorisation holds for inclusive and non-inclusive processes when: photon is point-like (Q 2 is high enough) higher twist corrections are negligible It allows to extract DPDFs from the (DIS) data → DPDFs – obey DGLAP, universal for diff. ep DIS (inclusive,dijet,charm) → universal hard scattering cross section (same as in inclusive DIS) H1 and ZEUS –QCD fits assuming Regge factorisation for DPDF pomeron PDFpomeron flux factor

HERA/LHC workshop May Hadron Structure How to profit from factorisation? to extract DPDFs from inclusive DIS and to estimate cross sections for dijet and D* production – then compare with data tests of factorisation to extract DPDFs from inclusive and semi-inclusive DIS (dijets,D*) – only semi-inclusive data are sensitive to gluon contribution, mainly at large z IP Used by H1 and ZEUS semi-inclusive data dijets in DIS 4 < Q 2 < 80 GeV < y < 0.7 x IIP < 0.03 P* tjet1 > 5.5 GeV P* tjet2 > 4 GeV -3. < η* jets < 0. EPJ C52 (2007) 813 JHEP (2007)

HERA/LHC workshop May Hadron Structure H1 QCD inclusive+dijet fit Largest difference Largest difference JHEP 0710:042,2007 A B A Inclusive fits A and B Fit jets uses dijets in DIS No difference for quarks, large difference for gluons at large z IP. jets Fit A Fit B

HERA/LHC workshop May Hadron Structure ZEUS QCD inclusive+dijet fit ZEUS fit C is the fit with same conditions as H1 fit B The results of fits of both experiments are similar.

HERA/LHC workshop May Hadron Structure pp  γ*p Exporting DPDFs from HERA to Tevatron….. x IP integrated effective DPDFs from CDF single diff. dijets (run I) Factorisation broken by β-dependent factor ~ 10, S ~ 0.1 Factorisation in hadron-hadron collisions Must be understood for LHC…e.g. CEP Higgs, (S=1-3%), related to underlying event….. Succesfully explained by terms of rescattering and absorption (see Kaidalov,Khoze,Martin,Ryskin:Phys.Lett.B567 (2003),61)

HERA/LHC workshop May Hadron Structure Tests of factorisation - HERA dijets in DIS – factorisation holds – H1 → ZEUS → D* in DIS and photoproduction - EPJ C52 (2007) 813 H1 Coll. EPJ C50 (2007) 1 R γp DIS = (data/theory) γp /(data/theory) DIS R γp DIS =1.15 ± 0.40 (stat.) ± 0.09 (syst.) JHEP (2007) within large errors no evidence for suppression, factorisation holds ZEUS Coll. EPJ C51 (2007) 301 H1 double ratio what about dijets in photoproduction????

HERA/LHC workshop May Hadron Structure Photoproduction, γ ⋆ p, Q 2 →0 direct photoproduction (Q 2 ≃ 0): photon directly involved in hard scattering x γ =1 (at parton level) resolved photoproduction (Q 2 ≃ 0): photon fluctuates into hadronic system, which takes part in hadronic scattering,dominant at Q 2 ≃ 0 x γ <1 (at parton level) x γ - fraction of photon’s momentum in hard subprocess In LO!

HERA/LHC workshop May Hadron Structure Photoproduction as hadronic process resolved contribution expected to be suppressed by factor 0.34 see Kaidalov et al. Typical models that describe suppression at Tevatron assume secondary interactions of spectators as the cause: HERA resolved photoproduction Secondary interactions between spectators

HERA/LHC workshop May Hadron Structure H1: E tjet1 > 5 GeV suppression of factor ~0.5 ZEUS: E tjet1 > 7.5 GeV weak (if any) suppression ( ) Neither collaboration sees difference between the resolved and direct regions, in contrast to theory! Possible explanation of differences between H1 and ZEUS (DIS 2007) Different phase space of both analyses ……..? DIS 07….

HERA/LHC workshop May Hadron Structure H1 – double ratio, E t dependence? Double ratio of Data/NLO for photoproduction and DIS → Figure extracted from published results Double ratio is within errors E t dependent! Very useful – full or partial cancellation of many uncertainties (energy scales for data, DPDFs used…etc ).

HERA/LHC workshop May Hadron Structure New H1 analysis -two cut scenarios To crosscheck previous H1 results To approach closest to ZEUS cuts Tagged dijet photoproduction, data 99/00, three times larger statistics, LRG

HERA/LHC workshop May Hadron Structure Integrated survival probabilities (ISP) No difference in survival probabilities for resolved and direct regions of x γ, like in previous H1 and ZEUS analyses Within errors no difference in ISP using different DPDFs Lower E t cut scenario

HERA/LHC workshop May Hadron Structure Higher E t cut scenario Now much more „direct-like“ events than in low E t analysis, peak at higher x γ Integrated survival probabilities (ISP) Larger ISP than for lower E t cut scenario → more close to ZEUS results!!!

HERA/LHC workshop May Hadron Structure Published data: EPJ C55 (2008) 177 Very good description → no evidence for suppression for ZEUS combined fit and H1 fit jets. New ZEUS fit-comparison with old data

HERA/LHC workshop May Hadron Structure Ratio diffractive to inclusive Proposed by Kaidalov et al. Phys.Lett B567 (2003) 61 Distribution of x γ sensitive to gap survival. H1 - measured in same kinematic range with same method as diffractive cross sections Acceptance corrections – PYTHIA Problem → describes low E t inclusive data with inclusion of multiple interactions only, large hadronisation corrections! With such a low E t jets problems also with NLO description of data – see for example H1 inclusive jet paper (EPJ C 129 (2003) 497) Full or partial cancellation of PDF uncertainties, scales…..

HERA/LHC workshop May Hadron Structure Ratio diffractive to inclusive comparison to MC models - RAPGAP/PYTHIA very different phase space for incl.& diffr. large sensitivity to multiple interactions (MI) for inclusive dijets better agreement of data ratio with PYTHIA MI z IP < 0.8 E p =820 GeV E p =930 GeV

HERA/LHC workshop May Hadron Structure Summary for dijets in photoproduction gap survival probability: significantily less than 1. for events with low E t leading jets, for higher E t (DPDF H1 fit jets 2007) ~ 0.8, consistent with ZEUS results (ZEUS combined fit 2009) ~ 1. hint that suppression is dependent on E t of the leading jet, → evidence that gap destruction becomes less likely as E t increases the evidence that suppression is not different for direct and resolved events remains (from theory not expected ) ratio diffractive dijets/inclusive dijets measured for the first time – the multiple interactions play important role for inclusive dijets → interpretation difficult

HERA/LHC workshop May Hadron Structure Backup

HERA/LHC workshop May Hadron Structure Tests of factorisation - HERA dijets in DIS – factorisation holds – H1 → ZEUS → D* in DIS and photoproduction - EPJ C52 (2007) 813 H1 Coll. Eur.Phys. J C50,1,(2007) R γp DIS = (data/theory) γp /(data/theory) DIS R γp DIS =1.15 ± 0.40 (stat.) ± 0.09 (syst.) JHEP (2007) within large errors no evidence for suppression, factorisation holds DIS ZEUS coll. EPJ C51 (2007) 301

HERA/LHC workshop May Hadron Structure Lower E t cut scenario Another hint of E t harder slope for data than NLO Hadronization corrections δ hadr =MC(hadr)/MC(parton)