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Status report of Hermes

Explore the latest findings and future prospects in spin physics research by Hermes Delia Hasch presented at DESY in 2004, covering nuclear effects, transversity, quark polarizations, GPDs, and exclusive processes.

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Status report of Hermes

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  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!

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