HERA @ DESY

2. HERMES @ HERA HERA @ DESY HERA: e+/e- (27GeV) - proton (920 GeV) collider HERA-e self-polarizing due to Sokolov-Ternov effect

3. Internal Gas Target:He , H , D , H unpol: H2,D2,He,N2,Ne,Kr,Xe The HERMES Spectrometer Kinematic Range: 0.02 < x < 0.8 at Q2 > 1 GeV2 and W > 2 GeV Reconstruction:Dp/p < 2%,Dq< 1 mrad Particle ID:TRD, Preshower, Calorimeter a 1997: Cherenkov, 1998a: RICH + Muon-ID

4. Semi-Inclusive Deep Inelastic Scattering The cross section can be expressed as a convolution of a distribution function and a fragmentation function.

5. Virtual Photon Asymmetry - Path to Dq • Virtual photon can only couple to quarks of opposite helicity • Select quark helicity by changing target polarization direction • Different targets give sensitivity to different quark flavors

6. Linear System in Quark Polarizations Correlation between detected hadron and the struck quark allows flavor separation Inclusive DIS →DS Semi-inclusive→

7. Du(x), Dd(x) ~ 0 Polarized Quark Densities • First complete separation of pol. PDFs without assumption on sea polarization • good agreement with NLO-QCD • No indication forDs(x)<0 • In measured range (0.023 – 0.6) Du(x) > 0 Dd(x) < 0

8. dotted: CTEQ-6L & fit dashed: dashed-dotted: HERMES: polarized and unpolarized s-PDF Fit x-dependence of multiplicities to get S(x) PDF and Kaon FF • Need longitudinal polarized deuterium target • strange quark sea in proton and neutron identical • fragmentation simplifies • All needed information can be extracted from HERMES data alone • inclusive A1,d(x,Q2)and kaon AK1,d (x,Q2) double spin asym. • Kaon multiplicities  DQK and DSK • Only assumptions used: • isospin symmetry between proton and neutron • charge-conjugation invariance in fragmentation solid: S(x)= Q(x): CTEQ-6L & DSS s(x) + sbar(x)

9. HERMES: polarized and unpolarized s-PDF Inclusive Asymmetry Kaon Asymmetry

10. HERMES 1996-2000 HERMES 2002-05 Distribution Functions Leading Twist • 3 distribution functions survive the integration over transverse quark momentum unpolarized DF Helicity DF Transversity DF Transversity basis

11. Properties of the Transversity DFs • For non-relativistic quarks dq(x)=Dq(x) • dq(x) probes the relativistic nature of the quarks • Due to Angular Momentum Conservation • Different QCD evolution • No gluon component • Predominately sensitive to valence quarks • Bounds • Soffer Bound: • T-even • Chiral odd • Not measurable in inclusive DIS

12. Forbidden • Need chiral odd fragmentation function Measuring Transversity • Need a chiral odd fragmentation function: ‘Collins FF’ • Transverse quark polarization affects transverse hadron momentum • Observed asymmetry in azimuthal angle about lepton scattering plane

13. Sivers Function f^1T(x,pT2) • Distribution function • Chiral even BUT! • Naïve T-ODD • A remnant of the quark transverse momentum can survive the photo-absorption and the fragmentation process, thus the cross section depends on the angle between the target spin direction and the hadron production plane • Azimuthal distribution • The transverse momentum distribution is nucleon-spin dependent. • Non-vanishing Sivers function requires quark orbital angular momentum • Requires Lz

14. How to Measure Transversity Collins azimuthal moment Sivers azimuthal moment Assuming gaussian distributions for initial an final quark momentum

15. + large positive u+ u- - large negative Collins Amplitudes  All Pions 0 data lies nicely between the + and - data

16. Collins Amplitudes for Kaons • No significant K+ ampl. • K+ comparable to + • K- pos. trend?

17. Sivers Amplitudes  All Pions + large - ~zero

18. Large pos. K+ K+ larger than +? Significant sea quark contribution? K- consistent zero

19. Theoretical fits to Hermes-COMPASS data M. Anselmino,et al., arXiv:0805.2677v1

20. exclusive: all products of the reaction are detected missing energy (DE) and missing Mass (Mx) = 0 from DIS: ~0.3 The Hunt for Lq Study of hard exclusive processes leads to a new class of PDFs Generalized Parton Distributions possible access to orbital angular momentum

21. unpolarized polarized quantum numbers of final state select different GPD vector mesons pseudo-scaler mesons DVCS AUT,sr,F,w AUT,sp+ AC,ALU,AUT, AUL GPDs Introduction What does GPDs charaterize? conserve nucleon helicity flip nucleon helicity not accessible in DIS

22. ~ DsC~cosf∙Re{ H+ xH +… } polarization observables: ~ ~ H DsLU~sinf∙Im{H+ xH+ kE} DsUT ~ DsUL~sinf∙Im{H+ xH+ …} beam target H, E DVCS ASYMMETRIES  different charges: e+ e- (only @HERA!): H H DsUT~sinf∙Im{k(H- E) + … } kinematically suppressed x = xB/(2-xB ),k = t/4M2

23. Selection of the exclusive event sample Identification by the missing mass technique (~12%) Not possible to separate associated from elastic production. Possible with Recoil Detector for 2006/2007 data.

24. Extraction of Asymmetries Transverse Target and Beam Charge • Full transverse target data set analyzed 2002-2005 • Electron 100 pb-1 and positron 70 pb-1 arXiv:0802.2499 submitted to JHEP

25. Beam Charge Asymmetry Goeke et al., Prog. Part. Nucl. Phys. 47 (2001) 401 Code: VGG [Vanderhaegen et al., priv. comm] The factorized t dependence is disfavoured and the Regge ansatz with no D term best describes these BCA data NLO twist-2 gluon helicity flip

26. Sensitivity to Jq Hermes: Transverse Target Spin Asymmetry

27. Suppressed Asymmetries

28. Extraction of AsymmetriesLongitudinal Beam Spin and Beam Charge Preliminary results from 96-05 data sets

29. Beam Charge Asymmetry Changes in the new analysis • 2.5 times more statistics than previous publication • 6-bins in all kinematical variables • Systematical errors include new model-dependent studies Results agree with former publications

30. Beam Charge Asymmetry (higher twist) (higher twist) Bin-wise fractions of associated production. The factorized ansatz and the VGG variant with the D-term is dis-favored by the beam charge asymmetry.

31. Beam Spin Asymmetry (higher twist) Pure DVCS squared asymmetries are compatible with zero, in agreement with model assumptions.

32. Beam Spin Asymmetry (higher twist) Result agrees with Dual model predictions, but fractions of associated productions are not corrected for.

33. Hermes: Charge and Beam Spin Asymmetry Heavy Targets Beam Charge Asymmetry Beam Spin Asymmetry Why nuclear DVCS: • constrain nuclear GPDs • constrain models attempting to describe nuclear matter • neutron and proton matter distribution in nuclei

34. 1 Tesla Superconducting Solenoid Photon Detector • 3 layers of Tungsten/Scintillator • PID for higher momentum • detects Δ+pp0 Scintillating Fiber Detector (SFT) • 2 Barrels • 2 Parallel- and 2 Stereo-Layers in each barrel HERA BEAM Silicon Detector • 16 double-sides sensors • 2 layers • Inside HERA vacuum Target Cell Recoil Detector – Installed Jan 06

35. E-loss in outer SFT + p - Recoil Detector running PID proton-pion • Installed January 06 • e+ running till July 06 • Si not available for e+ data • Switched to e- July 06 • Detector fully functional • End of data taking July 07 • Total luminosity luminosity 06 and 07 1 fb-1 of data collected ! What's to come? • Analysis of full data set using only forward spectrometer • Analysis of recoil data to suppress associated background • Exclusive meson production

36. Summary • Isoscaler extraction of the strange sea polarization • Positive but consistent with zero • Strange quark distribution different than expected • The full data sets for the Sivers and Collins analyses are available as preliminary results. • Impressive fits are available • New major data sets are available for DVCS on the proton both for hydrogen and heavy nuclei. • Deuteron will come soon. • 2006 and 2007 data starting to be analyzed • 1 fb-1 of data on tape • Recoil detector to quantify associated production • Many other results not shown …Which Hadron (p,K,p) is Which