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Experimental overview on exclusive processes

Experimental overview on exclusive processes. Delia Hasch. 1 st Duality Workshop June 06-08, 2005; LNF-INFN, Frascati (Italy). Q 2. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm.

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Experimental overview on exclusive processes

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  1. Experimental overview on exclusive processes Delia Hasch 1st Duality Workshop June 06-08, 2005; LNF-INFN, Frascati (Italy)

  2. Q2 DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives Vector mesons (r, w, f): H E Pseudoscalar mesons (p, h): H E DVCS (g) depends on H, E, H, E Quantum number of final state selects different GPDs: ~ ~ ~ ~ t hard exclusive processes Q2>>, t<< • high luminosity  s~1/Q4, 1/Q6 • high Q2  hard regime • high resolution  exclusivity

  3. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm H1, ZEUS, HERMES: 27.5 GeV e+, e- prerequisities perspectives Compass: 100-190 GeV m+ Jlab: HallA,B up to 6 GeV e- CLAS H1, ZEUS: p (820 GeV) HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe HERMES Compass: d , p Hall A: p , n Hall B: p, d prerequisites H1, ZEUS  distinct signature in 4p det. HERMES, COMPASS, JLab:  missing mass/energy technique: CLAS: DMX ~ 30 MeV HERMES: DMX ~ 400 MeV

  4. ~  H H E DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives Deeply virtual Compton Scattering Bethe-Heitler HallA,B HERMES H1/ZEUS DVCS BH  NLO analysis of H1, ZEUS cross sections

  5. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives [A.Freund, M. McDermott EPJC23(2002)]  Hg Hq DVCS cross section • first measurement of t –slope: ds/dt = ds/dt|t=0∙exp(-bt) b= 6.02±0.35±0.39 GeV-2 absolute normalisation! • comparison to NLO QCD: band width given by b measurement

  6. ~  H H E DVCS sasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives ~ DsLU~sinf∙Im{F1H+ x(F1+F2)H+kF2E} ~ DsUL~sinf∙Im{F1H+ x(F1+F2)(H+ …} DsLU  separating GPDs through polarisation: DVCS-BH interference leads to non-zero azimuthal asymmetry beam target DVCS asymmetries ~ H, H, E ~ H, H DsUT~sinf∙Im{k(F2H- F1E) + … } H, E kinematically suppressed x = xB/(2-xB ),k = t/4M2

  7. ~  H H E DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives beam spin asymmetry CLAS [PRL87,2001] [PRL87,2001] PRELIMINARY (not for circulation) 0.15 < xB< 0.4 1.5 < Q2< 4.5 GeV2 -t< 0.5 GeV2 • Vanderhaeghen-

  8. ~  H H E DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives BSA on nuclear targets heavier targets : 4He, 14N, 20Ne, Kr, Xe … study dependence of coherent production on nuclei

  9. ~  H H DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives target spin asymmetry CLAS PRELIMINARY (not for circulation)

  10. ~  H H E DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives target spin asymmetry • Vanderhaeghen- transverse TSA: sensitivity to GPD E (Jq)

  11. ~  H H E DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives beam charge asymmetry (only @ HERA)

  12. ~  H H E DVCSsasymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives beam charge asymmetry (only @ HERA) GPD calculations: different parametrisations forH • Vanderhaeghen(1999/02)– AC: high sensitivity to GPD models (tiny e-psample ~10pb-1) HERA: 2004/05 e- beam (5x) … H1/ZEUS ?

  13. ~  H H E ~ ~  H E DVCS s asymm | VECTOR MESONSs asymm | PS MESONS s asymm prerequisities perspectives  H E DVCS  DVMS • DVCS theoretically cleanest process to study GPDs - azimuthal asymmetries from interference term relate directly to amplitude • hard exclusive meson production: flavour separation ! factorisation theorem for sL only!

  14. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives  H E s vs W in bins of Q2 J/Y r f • s~ Wdwith d=0.7 • no dependence on Q2  general transition to hard behaviour at high Q2+M2

  15. --- 2-gluon exchange --- quark exchange DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives 2002 [Vanderhaegen et.al. (1999)]  H E sL separation from angular distribution if SCHC holds (VM retains g* helicity):  r0 < 10% • CLAS: analysis of sL for r0(r+) from 6 GeV data (higher W !) going on …

  16. - Goeke, Polyakov & Vanderhaeghen(2001) - DVCS s asymm | VECTOR MESONSsasymm | PS MESONS s asymm prerequisities perspectives Erelated to Jq TSA sensitive to Jq  H E r0 transverse TSA interference of H and E: sS ~ |ST| sin (f-fS) E∙H  same x-dependence behaviour as GPD calculations

  17. ~ ~  H E DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives p+ cross section Comparison with GPD model for sL: [Vanderhaegen, Guichon, Guidal (1999)] • Q2 dependence: sT suppressed by 1/Q2 • Q2 dependence: in general agreement with the theoretical expectation • LO calculations too small • power corrections (k┴ ,soft overlap) overestimate data

  18. ~ ~  H E DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisities perspectives [Mankiewicz,Piller & Radyushkin (1999)] PRELIMINARY (not for circulation) x cross section ratios p0production: nop-pole  H dominates measure at  HERMES  Jlab: ~

  19. ~ ~  H E DVCS s asymm | VECTOR MESONS s asymm | PS MESONS sasymm prerequisities perspectives ~ ~  gives access to relative size of H and E p+ transverse TSA - Frankfurt, Pobylitsa, Polyakov & Strikman(1999) - - Frankfurt, Polyakov, Strikman & Vanderhaeghen(2000) - - Belitsky & Müller(2001) - ~ ~ interference of H and E: sS ~ |ST| sin (f-fS) E∙H g*L p → p+ n ~ ~ TARGET SPIN ASYMMETRY • soon from HERMES • Compass, Jlab …

  20. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisitiesperspectives dedicated experiments DVCS with recoil: 2006/07 • background “free” DVCS: • semi-inclusive bg: 5%  <<1% • associated bg: 10%  1%

  21. JLab dedicated DVCS experiments in 2004 - 2005 M. Garcon JLab/Hall A JLab/CLAS Inner Calorimetrer and supraconducting magnet within CLAS torus Dedicated, high statistics, DVCS experiments → Detection of 3 particles e, p and γ in final state → Firmly establish scaling laws (up to Q2 ~ 5 GeV2), if observed, or deviations thereof understood, first significant measurement of GPDs. → Large kinematical coverage in xB and t leads to femto-tomography of the nucleon → Opens the way for an ambitious program with JLab@12GeV (CLAS12 and other) p e’ e γ

  22. ~  H H E ~ ~  H E DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm prerequisitiesperspectives new facilities (high luminosity/energy/resolution) needed to map GPDs in an global analysis of all hard exclusive processes conclusions  H E • first exciting results on DVCS and DVMS available •  polarisation provides new observables sensitive • to different (combinations) GPDS • dedicated experiments for DVCS measurements going • on at JLab or starting soon at HERMES

  23. backup slides t – dependence of BSA for photon and pion production: PRELIMINARY (not for circulation)

  24. asymptotically for fixed xB and t factorisation theorem prediction fit: 1/Qp p=1.9±0.5 p=1.7±0.6 p=1.5±1.0

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