Status report of Hermes

1. Status report of Hermes Delia Hasch Physics Research Committee, DESY Oct 27/28 2004 • Spin physics: •  finalised and new results on: • inclusive, semi-inclusive and exclusive measurements • nuclear effects

2. 2004 • transversity and friends (see PRC56,57 reports) • nuclear effects • exclusive processes PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 data taking 2004 • very successful data taking with • transversely polarised H target • high statistic data sets on unpola- • rised D, Kr, Xe from end-of-fill runs

3.  final data set on g1(x) PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 polarised structure function g1(x) • reanalised g1p • finalised g1d • new, more rigorous bin to bin • unfolding procedure applied: •  accounts for radiative+acceptance • uncorrelates systematic uncertainties • (small) statistical correlation known world data: Q2< 100 GeV2 0.002 < x < 0.9 for Q2>1 GeV2

4. PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 quark polarisations from sidis first 5-flavour fit to Dq • flavour separation by flavour tagging Purities unpolarised pdfs and fragmentation funtions

5. PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 outlook: FF from multiplicities • from high statistic polarised and unpolarised proton data set: p+ ,p- , K+, K-multiplicities p+ K+ • extraction of Dq with Hermes set of fragmentation functions • towards NLO analysis of Dq

6. M Q2>>, t<< g*L asymptotically 4 GPDs @twist-2: H H conserve ~ E Eflip nucleon helicity F for fixed xB and t ~ ~ ~ ~ H,E,H,E N N’ vector mesons pseudoscalar mesons t ( H + E) x dx =Jq = 1/2 DS+ Lz 10-30%(DIS) PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 hunting for Lq factorisation theorem for hard exclusive processes: - Műller(1994) - Generalised Parton Distributions - Ji & Radyushkin(1996) - meson production: quantum number of final state selects different GPDs:  DVCS 

7. comparison with GPD based model: • Vanderhaeghen, Guichon & Guidal (1999) - L/T separation not possible … but: suppressed by1/Q2 Hermes kinematics: 0.80 < e < 0.96  at large Q2 dominates PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 ep  e’p+n cross section for exclusivity ensured by missing mass technique  Q2 dependence in general agreement with theoretical expectation  power correction (k┴ and soft overlap) calculation overestimate data

8. outlook: transverse target-spin asymmetry ~ ~ TSA linear dependence on E and H, E and H target spin asymmetry x PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 • quadratic combination of GPDs appears in unpolarised cross section pion pole contribution particulary sensitive to E

9. interference between S-wave and lower r0 tail mpp< 0.6 GeV indication of r0 –f2 interference mpp~ 1.3 GeV minimum interference between S-P waves mpp~ 0.77 GeV • GPD model predictions: w/o 2-gluon exchange with 2-gluon exchange PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 exclusive p+p-production sensitive to interference between different p+p- isospin states Legendre moments: @low x:sensitive to 3-gluon exchange Odderon

10. DVCS-BH interference leads to non-zero azimuthal asymmetry PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 Deeply Virtual Compton Scattering Bethe-Heitler @HERMES kinematics: DVCS << Bethe-Heitler

11. tiny e-p sample (L~10pb-1) …BUT… HERA: >2004 e- PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 latest news: BCA vs t GPD calculations: • Vanderhaeghen et al., (1999,2001) - • t-dependence of BCA: high sensitivity to model assumptions different parametrisations for H: • t-dependence factorised • Regge-motivated ansatz • with and w/o D-term

12. multiplicity|A multiplicity|D PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 what happens in a nuclear medium?  reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction  understanding of the space-time evolution of the hadron formation process  FF modification

13. p > p, p > p, p > K ¯ • statistics on Kr doubled • first data on Xe ! PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 hadron separation vs n Kr  first time hadron discrimination in g*N p+ = p- = p0 ~ K- , K+ > K- • Hermes energy well suited for study of nuclear effects He, N, Ne, Kr, Xe  study A-dependence

14. PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 FF modification(parton energy loss) [X.N.Wang et al., PRL89(2002)] • 1 free parameter tuned on 14N (quark-gluon correlation strength inside nuclei) • dE/dx from HERMES  dE/dx for (Au+Au) @RHIC

15. fixed by HERMES data PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 Gluon density [X.N.Wang et al., PRL89(2002)] • cold hot • nuclear matter correlation •  gluon density in Au+Au order of magnitude higher than in cold matter

16. new tool: double-hadron attenuation pure absorption model ruled out  Kr statistics doubled; first Xe ! PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004  disentangling between absorption and energy loss [T. Falter et al. 2004] leading hadron: z1 >0.5 subleading hadron: z2< z1

17. PRC58 Delia Hasch Status report of Hermes Desy Oct 27/28 2004 outlook shutdown finished  recoil on track …E-Hall… ready for taking DATA!