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1 Pierre Marage Univ. Libre de Bruxelles On behalf of the H1 and ZEUS collaborations Diffraction at HERA CIPANP 2006 Puerto-Rico 29/5-4/6/2006.

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Presentation on theme: "1 Pierre Marage Univ. Libre de Bruxelles On behalf of the H1 and ZEUS collaborations Diffraction at HERA CIPANP 2006 Puerto-Rico 29/5-4/6/2006."— Presentation transcript:

1 1 Pierre Marage Univ. Libre de Bruxelles On behalf of the H1 and ZEUS collaborations Diffraction at HERA CIPANP 2006 Puerto-Rico 29/5-4/6/2006

2 2 Content 1.Introduction : diffraction and QCD at HERA 2.Inclusive diffraction measurements 3.Diffractive parton distribution functions (dpdf) 4.Semi-inclusive diffraction and comparison with dpdf  jets  charm 5.Exclusive production  vector mesons: rho photoproduction - BFKL  DVCS -GPD

3 3 Hadronic interactions elastic scattering diffractive dissociation (differential absorption of hadronic components) high energy soft pomeron - unitarity ! Diffraction HERA some 10% of cross section in electroproduction !

4 4 Diffraction at HERA and QCD Hard scales : Q 2, large p t (jets), large quark mass (charm), large t  QCD analyses challenge : quark and gluon understanding of diffraction, unitarity mechanisms, etc. pomeron structure diffractive parton densities factorisation theorem colour dipole dipole – proton cross section lowest order = 2 gluon exchange small dipoles in presence of hard scale

5 5 xx Diffractive variables Inclusive cross section

6 6 Inclusive diffraction : 3 measurement methods 1. Proton spectrometers -> t measurement 2. Large rapidity gap NC and CC diffraction 3. Non-exponential fall off of ln M X 2 distribution : diffr. non-diffr.

7 7 MX MX  Q2 Q2     ZEUS H1 W Cross sections measurements

8 8 Factorisation and pdf’s Collinear factorisation cf. total ep cross section Vertex factorisation usefull hypothesis (Regge inspired)

9 9 Scaling violations large gluon content !

10 10 Parton distribution function parameterisations Fit A H1

11 11 Vertex factorisation :

12 12 ~1/Q² at large  => HigherTwist behaviour J. Bartels at al., Eur. Phys. J. C7, 443 (1999). 2-gluon exchange model Colour dipole

13 13

14 14 hard scales (Q 2, p T )  pdf evolution (perturbative QCD) sensitivity to gluon distr. fct. Dijets in diffractive DIS : factorisation ?

15 15 Joint (inclusive + jets) pdf fits Low sensitivity of fits to inclusive cross section to gluon pdf, especially at large z IP  use jets in combined fits H1 Fit AH1 Fit B Combined fit close to Fit B; dijets provide significant constraints on high  gluons !

16 16 x Diffractive charm production (photoprod.) ZEUS photoproduction hard scale pdf evolution (gluons)

17 17 x Diffractive charm production (DIS) H1 DIS Agreement with NLO calc. within the (large) errors.

18 18 Factorisation Factorisation tested with jets, charm But still large errors. NB low sensitivity of inclusive pdf’s to gluons at high   joint fits important Extrapolation from HERA CDF data Factorisation breaking by underlying interactions in hadron-hadron (Tevatron, LHC) and for resolved photons  gap survival probability

19 19 Vector meson production photoproduction soft diffraction (ex.  photoprod.) - low cross section increase with energy (soft pomeron) - fast fall of t distribution hard diffraction (J/ , large Q 2 ) - stronger energy dependence large gluon density at small x - flatter t distribution small dipole size hard soft

20 20 Large |t|  photoproduction and BFKL t helicity flips best described by BFKL-like approach

21 21 DVCS Generalised Parton Distributions rather ``hard´´ energy dependence rather ``soft´´ t dependence

22 22 Measurement precision of inclusive cross section Extraction of diffractive pdf’s Factorisation tests / joint fits with jets, charm (especially for gluon at large  ) Exclusive processes : vector mesons, DVCS, etc. QCD understanding of diffraction Conclusions

23 23 Extra slides

24 24

25 25 comparison with LO MC ZEUS

26 26 Diffractive jet prod.: sensitivity to pdf’s H1 Fit AH1 Fit B Low sensitivity of fits to inclusive cross section to gluon pdf, especially at large z IP  use jets in combined fits H1

27 27 comparison with LO MC

28 28 Combined fit of F 2 D and dijet data :  2 /ndf (total) = 196 / 217  2 /ndf (dijets) = 27 / 36  2 /ndf (F2D) = 169 / 190 Combined fit ~ close to Fit B; dijets provide important constraints on high z gluon ! Both datasets well described by the combined fit. Joint (inclusive + jets) pdf fits

29 29

30 30 Vector meson production

31 31 B values large for DVCS (compatible with a soft hypothesis)!  hard W dependence => Many ideas discussed

32 32 Leading neutron production

33 33

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