Diffractive Structure Functions from the H1 and ZEUS Experiments at HERA

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1 Diffractive Structure Functions from the H and Experiments at HERA SINP MSU Irina A. Korhavina (Moscow State University) On Behalf of the H and Collaborations O U T L I N E : Diffraction σ D r from LRG and (V)FPS/LPS Diffractive Parton Densities F D L Test QCD Summary HERA Ee=7,5 GeV Ep=9 GeV p th International QCD Conference - QCD (5th anniversary) 8th June - 3rd July Montpellier (France)

2 Diffraction at HERA H and collected.5 fb data: good measurement accuracy new detailed results test QCD assumptions and predictions Hprelim--, Hprelim--, Hprelim--7, NPB 86() Diffractive dissociation: R DD = σ DD σ Incl 5%. t-channel exchange (IP ): vacuum quantum numbers colour singlet small momentum transfer t M Y = m p elastic diffraction M Y > m p proton dissociation (BG) η(lrg) I. Korhavina Diffraction at HERA, QCD

3 Signatures and Selection Methods Proton Spectrometer (PS) method no p diss background (BG) t, measured directly larger (<.) accessible low Acc ( %) Large Rapidity Gap (LRG) method p diss background ( 5 %) t not measured η max η max e FPC p smaller (<.3) accessible higher Acc ( %) I. Korhavina Diffraction at HERA, QCD 3

4 e p e ( x IP ) IP,IR } ( t ) ( Q) p } η Kinematics and Cross Sections X (M( M) X ) X W = invariant mass of γ p system M X = invariant mass of γ IP system M Y = invariant mass of proton (dissociative) system = fraction of proton momentum carried by IP β = x/ = fraction of IP momentum carried by struck parton t = (4-momentum exchanged at p vertex) typically: t < GeV [ ] d 4 σ ep exp dβdq d dt = πα Y βq 4 + F D(4) (β, Q,, t) y Y + F D(4) L (β, Q,, t) σ D(3) r = πα βq 4 Y + σ D(4) r (β, Q,, t) Y + = + ( y) (β, Q, ) = σr D(4) (β, Q,, t)dt in case t is not measured I. Korhavina Diffraction at HERA, QCD 4

5 H vs : Measurement Comparison σ r D(3) = β=.67 β=.8 β=.7 β=.8 β=.433 β=.3 β=.43 β=.3 β=.667 β=. β=.67 β=. β=.3 β=.7 β=.3 β=.5 β=.67 β=.5 β=.8 β=.67 β=.8 β=.433 β= LRG (M N <.6 GeV)x.87 6 pb - H H 6 FIT B Fit extrapolation β=.667 β=. β=.3 β=.5 β=.8 x= Q (GeV ) H and : (V)FPS/LPS or LRG - agree (within normalisation uncertainty) basis for the combination of H- inclusive diffractive data reduction of experimental uncertainties I. Korhavina Diffraction at HERA, QCD 5

6 σ D(3) r (V)FPS/LPS vs LRG: Measurement Comparison (LRG) = σ D(3) r Ratio σ D(3) r (elastic)+σr D(3) (p diss) (LRG)/σr D(3) independent of,β,q = ((V)FPS/LPS)= + σ D(3) r (p diss)/σr D(3) measure p diss contribution: (elastic): σ r D(3) (LPS)/ σ r D(3) (LRG) LPS/LRG Average fit β=. β=.65 β=.3 β=.98 β=.9 β=.55 β=.65 β=.7 β=.3 β= GeV 3.9 GeV.5 GeV LRG/LPS=.3 LPS/LRG by.76±.(stat.) +.3.(syst.) LRG/(V)FPS by H.±.(stat.)±.5(syst.) (V)FPS/LRG=.83 β=.37 β=.4 β=.8 β=.69 4 GeV β=. β=.48 β= β= Q =4 GeV σr D(3) (LRG)/σr D(3) ((V)FPS/LPS). = const in (, β, Q )) = p diss and elastic diffraction similar Methods & Measurements - different but agree (within normalisation uncertainty) I. Korhavina Diffraction at HERA, QCD 6

7 Factorisation of Diffractive Cross Sections The structure of the colour singlet is studied within QCD: QCD hard scattering factorisation theorem: (at fixed and t) σ D (γ p Xp) = parton i f D i (x, Q,, t) σ γ i (x, Q ) σ γ i : universal hard scattering cross section fi D : universal partonic distribution functions (PDFs), obey evolution equations Theorem s validity is proved for diffractive DIS by J.Collins Factorisation theorem relates: F D(4) /L (β, Q,, t) = i β d C /L,i( β f D i (,, Q, t) I. Korhavina Diffraction at HERA, QCD 7

8 σ D(3) r NLO QCD Fits DPDFs QCD fits to data sets of diffractive PDFs. To reach this goal - DPDFs were modelled using phenomenological parameterisations Proton vertex factorisation assumed and IP and IR contributions accounted for: f D i (β, Q,, t) = f IP,IR (, t) f i/ip (β, Q ) + f IR (, t) f i/ir (β, Q ) IP and IR fluxes: f IP,IR (, t) = A IP,IRe B IP,IR t x α IP,IR (t) IP α IP,IR (t) = α IP,IR ()+α IP,IR t Distributions at Q of QUARKs and GLUONs: f d,u,s (, Q ) = A q B q ( ) C q f g (, Q ) = A g B g ( ) C g Lots of parameters to fit some were fixed Fits to LRG data: Fit H 6 DPDF A Cg= Fit H 6 DPDF B Fits to LRG+LPS data: Fit DPDF S Fit DPDF C Bg=Cg= Fit to LRG DIS dijet data: Fit H 7 Jets DPDF Fit to LRG + LPS+ DIS dijet data: Fit DPDF SJ I. Korhavina Diffraction at HERA, QCD 8

9 Quark Distributions - from σ D r (Q ) f q Q DPDF SJ exp. uncertainty DPDF C light c = 6 GeV f q c Q = GeV light b H 7 Jets DPDF exp. uncertainty exp. + theo. uncertainty H 6 DPDF fit A H 6 DPDF fit B f q.4.3 Q = 6 GeV light f q.4.3 Q = GeV light singlet()..5 H singlet()..5 H.. b c.. b c..5 singlet µ f =5 GeV..5 singlet µ f =9 GeV f q () for all Fits - similar I. Korhavina Diffraction at HERA, QCD 9

10 Gluon Distributions f g.6.4 Q = 6 GeV DPDF S exp. uncertainty DPDF C f g.6.4 Q = GeV f g.6.4 Q DPDF SJ exp. uncertainty DPDF C = 6 GeV f g.6.4 Q = GeV Fit LRG+LPS+DIS dijet - fits well to dijet data - decreased uncertainties f g Q = 6 GeV f g Q = GeV f g Q = 6 GeV f g Q = GeV comparable precision for f g and f q different Fits - very different f g at large discrepansy - low sensitivity to f g H 7 Jets DPDF exp. uncertainty exp. + theo. uncertainty H 6 DPDF fit A H 6 DPDF fit B gluon() H gluon µ f =5 GeV gluon() H gluon µ f =9 GeV I. Korhavina Diffraction at HERA, QCD

11 First Measurement of F D L σ D r ( y Y + ) = F D y Y + F D L F D L α s g(x) direct measurement of g(x) Data at 3 proton energies used: 9, 46 and 575 GeV At fixed Q and, high y corresponds to low β ), β, Q IP.3.5 Q β = 4 GeV =.3 =.33 H Preliminary E p E p E p = 8 GeV = 575 GeV = 46 GeV ), β, Q IP.3. Q = 4 GeV =.3 H Preliminary F Q = 3.5 GeV =.3 D L (x. (x σ r D F L H 6 DPDF Fit A D F L H 6 DPDF Fit B D F L I. Korhavina Diffraction at HERA, QCD y / Y + β

12 Test QCD: diffractive dijet PhP (pb) obs dσ/dx γ 5 diff dijet γp 99- energy scale uncertainty (a) DPDF SJ 4 3 DPDF exp. uncertainty H Fit 7 Jets.8 (pb/gev) jet dσ/de T diff dijet γp 99- energy scale uncertainty DPDF SJ DPDF exp. uncertainty H Fit 7 Jets.8 (a) Fits LRG+LPS+DIS dijet H 7 Jets - fit well to difractive dijet PhP data.5 renorm. scale dependence.5 renorm. scale dependence ratio to DPDF SJ obs x γ.4 diff dijet γp 99- DPDF SJ (b) DPDF exp. uncertainty..8 H Fit 7 Jets.8 ratio to DPDF SJ jet E T diff dijet γp 99- DPDF SJ (b) DPDF exp. uncertainty H Fit 7 Jets.8 (GeV) Ratios of DATA/NLO QCD no suppression obs x γ 8 4 jet E T (GeV) I. Korhavina Diffraction at HERA, QCD

13 Test QCD: diffractive charm production F D(3)cc. Q =4 GeV =.4 F D(3)cc.5 Q =5 GeV =.4. F D(3)cc β Q =4 GeV =. diff D* 98- DPDF SJ DPDF SJ (extrapolated) DPDF exp. uncertainty F D(3)cc β Q =5 GeV =. Fit LRG+LPS+DIS dijet - fit well to charm difractive DIS data β β I. Korhavina Diffraction at HERA, QCD 3

14 SUMMARY 5 years of HERA operation detailed studies of diffractive reactions Consistency reached between different experiments, methods and data sets measured DPDFs, corresponding to elastic diffraction (single-diffractive reaction) DPDFs measured with higher accuracy, accounting for dijet data predictions for other processes possible predictions for diffractive charm production and diffractive dijet photoproduction agree with measured cross sections in agreement with DGLAP QCD predic- First measurement of FL D tions I. Korhavina Diffraction at HERA, QCD 4