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

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

 final data set on g 1 (x) new, more rigorous bin to bin unfolding procedure applied:  accounts for radiative+acceptance  uncorrelates systematic uncertainties  (small) statistical correlation known  reanalised g 1 p  finalised g 1 d polarised structure function g 1 (x) Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 world data: Q 2  100 GeV  x  0.9 for Q 2 >1 GeV 2

quark polarisations from sidis  flavour separation by flavour tagging Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 Purities unpolarised pdfs and fragmentation funtions first 5-flavour fit to  q

outlook: FF from multiplicities Delia Hasch Status report of Hermes Desy Oct 27/ PRC58   from high statistic polarised and unpolarised proton data set:  ,  , K , K  multiplicities KK  extraction of  q with Hermes set of fragmentation functions  towards NLO analysis of  q

quantum number of final state selects different GPDs :  DVCS  vector mesonspseudoscalar mesons Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 N *L*L t N’   Q 2 >>, t<< H,E,H,E ~ ~ 4 H H conserve ~ E E flip nucleon helicity ~ asymptotically for fixed x B and t meson production: hunting for L q factorisation theorem for hard exclusive processes: Generalised Parton Distributions - Műller (1994) - - Ji & Radyushkin (1996) %(DIS) J q ( H + E) x dx = J q = 1/2  L z

cross section for cross section for ep  e ’   n ep  e ’   n  Q2 dependence in general agreement with theoretical expectation  power correction (k ┴ and soft overlap) calculation overestimate data Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 L/T separation not possible … but:  suppressed by 1/Q 2 Hermes kinematics:   at large Q 2  dominates -Vanderhaeghen, Guichon & Guidal (1999) - comparison with GPD based model: exclusivity ensured by missing mass technique

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

exclusive     production Legendre moments: interference between S-wave and lower  0 tail m   0.6 GeV minimum interference between S-P waves m   0.77 GeV indication of  0 –f 2 interference m   1.3 GeV  GPD model predictions: w/o 2-gluon exchange with 2-gluon exchange sensitive to interference between different     isospin x: sensitive to 3-gluon exchange  Odderon Delia Hasch Status report of Hermes Desy Oct 27/ PRC58

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

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

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 Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 multiplicity| A multiplicity| D

hadron separation vs hadron separation vs Delia Hasch Status report of Hermes Desy Oct 27/ PRC58         ~ K -, K   K  Kr  first time hadron discrimination in  * N p  p, p  , p  K ¯  Hermes energy well suited for study of nuclear effects  statistics on Kr doubled  first data on Xe ! He, N, Ne, Kr, Xe  study A-dependence

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

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 Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 fixed by HERMES data

Delia Hasch Status report of Hermes Desy Oct 27/ PRC58 new tool: double-hadron attenuation leading hadron: z 1  0.5 subleading hadron: z 2  z 1 [T. Falter et al. 2004] pure absorption model ruled out  Kr statistics doubled; first Xe !  disentangling between absorption and energy loss

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

  cross section: Q 2 dependence factorisation theorem: asymptotically for fixed x B and t fit: 1/Q p p=1.9±0.5 p=1.7±0.6 p=1.5±1.0  Q 2 dependence in agreement with theoretical expectation Delia Hasch Status report of Hermes Desy Oct 27/ PRC58

Power correction -Vanderhaeghen, Guichon & Guidal (1999) - intrinsic transverse momentum of the active quark (k perp ) (Q2>>) → 0 soft overlap contribution → no gluon exchange