21.1.2009LISHEP Rio de Janeiro1 Factorization in diffraction Alice Valkárová Charles University, Prague On behalf of H1 and ZEUS collaborations.

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LISHEP Rio de Janeiro1 Factorization in diffraction Alice Valkárová Charles University, Prague On behalf of H1 and ZEUS collaborations

LISHEP Rio de Janeiro2 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: ∼ 500 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

LISHEP Rio de Janeiro3 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)

LISHEP Rio de Janeiro4 Dijets in diffractive ep scattering photon directly involved in hard scattering x γ =1 (at parton level), due to hadronization and resolution not exactly true for measured x γ 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 LO QCD DIS, direct PHPresolved PHP Pointlike photon Resolved photon

LISHEP Rio de Janeiro5 What is QCD factorization? Is it possible to factorize hard diffractive processes into two parts? non-perturbative Diffractive Parton Density Functions (DPDFs) of an colorless object perturbatively calculable partonic cross section proven for DIS (J.Collins (1998)), Q 2 >>0 not proven for photoproduction, Q 2 ~0 ?

LISHEP Rio de Janeiro6 QCD factorization Hard scattering QCD matrix element,perturbatively calculated, process dependent Universal diffractive parton densities, identical for all processes direct PH, DISResolved PH Factorization ensures: Get DPDFs from inclusive measurement and predict the cross sections for exclusive processes (dijet production, D* production) It is not fulfilled in the case of Tevatron dijet production! Multi-pomeron exchange, remnant interactions, screening? x IP integrated effective DPDFs from CDF single diff. dijets (run I)

LISHEP Rio de Janeiro7 Photoproduction as hadronic process resolved contribution expected to be suppressed by factor 0.34 (Kaidalov,Khoze,Martin,Ryskin:Phys.Lett.B567 (2003),61) Rescattering leads to factorization breaking and rapidity gap fill up suppression of cross section ~ 1 – (rapidity gap survival probability) HERA resolved photoproduction Secondary interactions between spectators Factorization broken by β dependent factor ~ 10

LISHEP Rio de Janeiro8 Questions….. Is factorization valid for diffractive dijets and D* production in DIS and photoproduction? How large is the suppression in comparison to no breaking ? Does breaking of factorization occur in both PH direct and resolved dijet production? Comparison of the value of suppression to theory and hadron-hadron collisions at Tevatron and LHC. Questions…

LISHEP Rio de Janeiro9 Dijets in diffractive DIS, H1 For z IP < 0.4 NLO predictions using fits 2006 A and B agree with data very well Combined QCD fit for inclusive and dijet DIS data….. A B jets Largest difference published, JHEP,0710:042 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.

LISHEP Rio de Janeiro10 Data 99/00 Eur.Phys.J.C52: 83 (2007) Dijets in diffractive DIS, ZEUS E* tjet1 > 5 GeV 5 < Q 2 < 100 GeV 2 Conclusions: the best agreement of data and NLO for H fit B and MRW 2006 H1, ZEUS: for DIS dijets factorization holds….. R=data/NLO(ZEUS LPS)

LISHEP Rio de Janeiro11 D* production-DIS, photoproduction H1 Coll. Eur.Phys. J C50,1,(2007) ZEUS Coll.,Nucl.Phys. B672,3(2003) R γp DIS = (data/theory) γp /(data/theory) DIS R γp DIS =1.15 ± 0.40 (stat.) ± 0.09 (syst.) Within large errors no evidence for a suppression of the photoproduction component…… DIS

LISHEP Rio de Janeiro12 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 ……..? Dijet factorization tests in 2007

LISHEP Rio de Janeiro13 H1 analysis – data 99/00 Tagged photoproduction, luminosity 3x larger than for 97 diffractive events found by Large Rapidity Gap method (LRG)

LISHEP Rio de Janeiro14 Two cut scenarios To crosscheck previous H1 results To approach closest to ZEUS cuts 2 programs for NLO calculations, 3 sets of DPDFs: Frixione/Ridolfi → H Fit A H Fit B H Fit Jets Kramer/Klasen → H Fit B (thanks to Michael K.)

LISHEP Rio de Janeiro15 No difference in survival probabilities for resolved and direct regions of x γ, previous H1 and ZEUS analyses confirmed! Lower E t cut Higher E t cut Hadronization corrections δ hadr =MC(hadr)/MC(parton) xγxγ

LISHEP Rio de Janeiro16 Integrated survival probabilities Compared to: 0.47 ± 0.16 for x γ < ± 0.14 for x γ > 0.9 H1 Coll., Eur.Phys.J C51,549(2007) Compared to: 0.6 – 0.9, depending on dPDF ZEUS coll.,Eur.Phys.J C55,177 (2008) Lower E t scenario Higher E t scenario S= σ (data) σ (theory)

LISHEP Rio de Janeiro17 Lower E t scenario Higher E t scenario x IP

LISHEP Rio de Janeiro18 H1 and ZEUS observe the data have harder E t slope than NLO W.Slomiński, ZEUS, DIS 2008 The suggestion of E t dependence is even stronger when looking at the double ratio NLO/data for photoproduction and DIS – some systematic uncertainties cancelled….. E t dependence of suppression?

LISHEP Rio de Janeiro19 Global and resolved only suppression… Global suppression 0.53 Data H1 preliminary, suppression of NLO resolved component by 0.3 H1 lower E t cut scenario Much worse agreement than for global suppression

LISHEP Rio de Janeiro20 Global and resolved only suppression… Global suppression 0.53 Data H1 preliminary, suppression of NLO resolved component by 0.3 H1 lower E t cut scenario No E t dependence but prize is worse agreement data & NLO for x γ and also for other distributions!!!

LISHEP Rio de Janeiro21 (Some) answers… Is factorization valid for diffractive dijets and D* production in DIS and photoproduction? Factorization seems to be valid for difractive DIS dijets and D* DIS and photoproduction. Factorization is broken for dijets in photoproduction. How large is the suppression in comparison to no breaking ? Suppression seems to be dependent on the E t cut of the leading jet, it is about 0.5 for lower E t cut of jets and is weaker for higher E t cut Does breaking of factorization occur in both PH direct and resolved dijet production? Yes, it was obtained by both H1 and ZEUS by three independent measurements. The global suppression gives better agreement data & NLO than resolved only suppression

LISHEP Rio de Janeiro22 Weak points…. The most weak points: data & NLO → without hadronization corrections (taken from LO Monte Carlo!) direct comparison with NLO not possible theory – huge scale uncertainties → NNLO? Outlook Very important for LHC predictions, measuring of Higgs in diffraction etc.