Physics at Hermes Delia Hasch for the collaboration

Physics at Hermes Delia Hasch for the collaboration 16 th international spin physics symposium October 10 -16, 2004; Trieste (Italy) 2002 spin observables: new or final results since Spin 02 2004

nucleon quark structure unpolarised quarks and nucleons longitudinally polarised quarks and nucleons transversely polarised quarks and nucleons q(x): spin averaged Dq(x): helicity difference dq(x): helicity flip vector charge axial charge tensor charge well known unmeasured ! Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

nucleon quark structure Outline: Dq(x) dq(x) • the Hermes experiment • final result on g 1 for the proton and deuteron • first direct flavour decomposition of Dq • first measurement of transverse single-spin asymmetries • single beam-spin asymmetries Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

nucleon spin structure Outline: • the Hermes experiment • final result on g 1 for the proton and deuteron • first direct flavour decomposition of Dq • first measurement of transverse single-spin asymmetries • single beam-spin asymmetries • news on exclusive meson production and DVCS for further details: numerous Hermes talks in QCD spin session II Delia Hasch not covered: GDH SSA on AUL |hyperon Physics at|Hermes Trieste (Italy), 12 -10 -2004

Hermes @ DESY 27. 5 Ge. V (e+/e-) <Pb>~ self-polarised 53± 2. 5 % electrons: e <Pb>~ 53± 2. 5 % Stern-Gerlach separation H <|P t|> ~ 85 ± 3. 8 % • resolution: dp/p~2%, dq<1 mrad 1 → 2 H→ <|Pt|> ~ 84 ± 3. 5 % • particle ID: lepton ID with e~98%, hadron contamination <1% 1 H <|Pt|> ~ 74 ± 4. 2 % RICH: p, K, p ID within 2<E <15 Ge. V h pure nuclear-polarised atomic gas, flipped at 90 s time intervals Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

Hermes kinematics inclusive: Q 2 > 0. 1 Ge. V 2 : 0. 002 < x < 0. 9 with y<0. 91 W 2>3. 24 Ge. V 2 semi-inclusive: Q 2 > 1. 0 Ge. V 2 : 0. 02 < x < 0. 6 with y<0. 85, W 2>3. 24 Ge. V 2 0. 2<z<0. 8 Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

model-independent unfolding detector smearing QED radiative effects smearing within acceptance kinematic migration inside acceptance for each spin state j=0 bin: kinematic migration into the acceptance radiative effects detector smearing systematic correlations between bins fully unfolded resulting (small) statistical correlations known Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

quark helicity distributions Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

g 1/F 1 of the proton and deuteron proton Q 2 > 0. 1 Ge. V 2 0. 002 < x < 0. 9 Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

structure function g 1(x) Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

Dq from inclusive data • Duv and Ddv well determined: Duv >0, Ddv <0 • Dq and DG weakly constraint by data • Ds <0 expected from violation of Ellis-Jaffe SR more, direct probes needed Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

polarised quark distributions flavour separation by flavour tagging flavour content of final state hadrons related to flavour of struck quark via fragmentation functions Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

measured asymmetries Just like in short dq paper: pi, K for d all sea objects Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

purities @Hermes probability that g* hit a quark of flavour q when hadron of type h was detected Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

[PRL 92, 2004; hep-ex/0407032, submitted to PRD] quark polarisations first 5 -flavour fit to Dq • no significant polarisation results perfectly consistent with incl. fits: c 2/dof =0. 6… 1. 6 for BB(SU 3 -sym) and GRSV-valence • in measured range (0. 023 -0. 6): Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

light sea flavour asymmetry • no significant breaking of polarised SU(2)-flavour symmetry • c. QSM asymmetric sea disfavoured: c 2/dof=17. 6/7 Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

single-spin asymmetries f 1 g 1 transversity T-odd (Collins effect) (Sivers effect) Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

single target-spin asymmetry angle of hadron relative to final quark spin amplitudes fit simultaneously (prevents mixing effects due to acceptance) Delia Hasch Physics at Hermes angle of hadron relative to initial quark spin Trieste (Italy), 12 -10 -2004

transverse asymmetries [hep-ex/0408013, submitted to PRL] positive p+ and negative p- asym. significantly positive p+ asym. unexpected large p- first hint of T-odd DF from DIS Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

weighted transverse asymmetries see talk of G. Schnell I […] convolution integral over intrinsic quark transverse momenta Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

interference fragmentation [Jaffe etal, PRL 80, 1998] pp phase-shift analysis [Radici etal, PRD 65, 2002] spectator model in s-p channel ongoing analysis with transverse target polarisation Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

single beam-spin asymmetry Qd. Q-model prediction of z-dependence [Gamberg, Hwang, Oganessyan, PLB 584] Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

hunting for Lq factorisation theorem for hard exclusive processes: Generalised Parton Distributions - Műller (1994) - Ji & Radyushkin (1996) - ( H + E) x dx = Jq = 1/2 DS + Lz 10 -30%(DIS) Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

Generalised Parton Distributions 2>>, t<< Q 2 Q >>, t<< GPDs @twist-2: g, r 0 L, p+. . . H, E g*L x+x x-x N’ N ~ ~ H, E quantum number of final state selects different GPDs: DVCS t vector mesons Delia Hasch Physics at Hermes pseudoscalar mesons Trieste (Italy), 12 -10 -2004

exclusivity for ep e’p+(n) Missing Mass 2 = (g+p-p+)2 g, r 0 L, p+. . . use p- yield (ep e’p-n) to subtract non-exclusive background N Delia Hasch Physics at Hermes N’ Trieste (Italy), 12 -10 -2004

cross section for ep e’p+n no L/T separation but s. T suppressed by 1/Q 2 and e > 0. 8 [Vanderhaeghen, Guichon & Guidal (1999) ] p production: ~ H pseudovector contrib. ~ E pseudoscalar contrib. (pion pole related to Fp) asymptotically LO calculations underestimate the data for fixed x. B and evaluation of tthe power correction appears too large Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

exclusive meson production: AUT quadratic combination of GPDs appear in unpolarised crosss section target spin asymmetry polarisation provides new observables: ongoing analyses with transversely polarised target x particulary sensitive to E pion pole contribution Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

exclusive p+p- production [PLB 599, 2004] evidence for interference of pp in different wave states GPD model predictions: w/o 2 -gluon exchange with 2 -gluon exchange Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

deeply virtual Compton scattering Bethe-Heitler @HERMES kinematics: DVCS << Bethe-Heitler DVCS-BH interference leads to non-zero azimuthal asymmetry Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

DVCS asymmetries Beam Spin Asymmetry BSA ~ Delia Hasch Beam Charge Asymmetry BCA ~ Physics at Hermes Trieste (Italy), 12 -10 -2004

latest news: BCA vs t GPD calculations: - Vanderhaeghen (1999/02) – different parametrisations for H t-dependence of BCA: high sensitivity to model assumptions tiny e-p sample (L~10 pb-1) …BUT… HERA: >2004 e- Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

improvement of exclusivity > mid 2005: full reconstruction of exclusive events with recoiling proton • DVCS: HERA switches to e- ! Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

conclusion • longitudinally polarised protons and deuterons: final data on g 1 for proton and deuteron final data on Dq five flavour separation • transversely polarised protons: first results for Collins and Sivers effect ongoing analyses on transversity and friends (ALU, IFF, …) • exclusive processes: meson production: cross section, pp production ongoing analyses on transverse asym. Stay DVCS: single-spin andtuned charge… asymmetries New exiting results will come soon ! HERMES >mid 2005 : recoil detector Delia Hasch Physics at Hermes Trieste (Italy), 12 -10 -2004

Power correction -Vanderhaeghen, Guichon & Guidal (1999) - intrinsic transverse momentum of the active quark (kperp) (Q 2>>) → 0 soft overlap contribution → no gluon exchange