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Hard Exclusive Processes at COMPASS and COMPASS II DVCS: golden channel for GPD

Hard Exclusive Processes at COMPASS and COMPASS II DVCS: golden channel for GPD HEMP:  0 ,(+,,,…) or  0 ,… Nicole d’ Hose (CEA-Saclay) On behalf of the COMPASS Collaboration. What makes COMPASS unique for GPD?. CERN High energy muon beam 100 - 190 GeV.

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Hard Exclusive Processes at COMPASS and COMPASS II DVCS: golden channel for GPD

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  1. Hard Exclusive Processes at COMPASS and COMPASS II DVCS: golden channel for GPD HEMP: 0,(+,,,…) or 0,… Nicole d’Hose (CEA-Saclay) On behalf of the COMPASS Collaboration

  2. Whatmakes COMPASS unique for GPD? • CERN High energymuonbeam • 100 - 190 GeV • Explorethe intermediatexBjregion • Uncoveredregionbetween • ZEUS+H1 & HERMES + Jlab • beforenew collidersmaybeavailable • Transverse structure atx~10-2 • essential input for phenemenology • of high-energypp collision (LHC) With 2.5m LH2 target Lumi= 1032 cm-2 s-1 Limit for DVCS study Proton1 x1 Higgs? x2 Proton2 x1,2 = M Higgs / s  10-2 B M Higgs = 140 GeV and s =14 TeV

  3. Whatmakes COMPASS unique for GPD? • CERN High energymuonbeam • 100 - 190 GeV • μ+andμ-available • 80% Polarisation • with opposite polarization With 2.5m LH2 target Lumi= 1032 cm-2 s-1 Limit for DVCS study • 4.6 108+ • for 2.7 1013 protons /SPS spill • (9.6s each 48 s) • Lumi= 1032 cm-2 s-1 • with2.5m LH2 target B 3

  4. Experimental requirement for exclusive measurement DVCS :μp  μ’ p  Tests in 2008-09 (COMPASS) 40cm LH2 target + 1m RPD Phase 1: 2012-16 (COMPASS-II) 2.5 m LH2 target + 4m RPD Phase 2: > 2016 (in future) Polarised Transverse Target integrating RPD  μ’ SM2 ECAL2 SM1  ECAL1 upgraded ECAL1 p’ μ + ECAL0 before SM1 4

  5. Experimental requirement for exclusive measurement DVCS :μp  μ’ p   4m long ToF barrel + 1 GHz digitization of the PMT signal to cope for high rate (GANDALF boards) μ’ SM2 ECAL2 SM1 ECAL1 p’ ECAL0 made of 248 modules (12  12 cm2) of 9 cellsread by 9 MAPDs μ Prototype of the 2.5m long LH2 target + test of the cryostat 4

  6. Contributions of DVCS and BH atE=160 GeV  μ’ * θ μ p  Deep VCS Bethe-Heitler d  |TDVCS|2 + |TBH|2 + InterferenceTerm Monte-Carlo Simulation for COMPASS set-upwith only ECAL1+2 • Missing • DVCS acceptance • without ECAL0 BH dominatesstudy of InterferenceDVCS dominates excellent  Re TDVCSstudyof dDVCS/dt referenceyieldor Im TDVCS Transverse Imaging 6

  7. 2009 DVCS test run (10 days, short RPD+target) 251 evts 135 evts 54 evts |BH|2 |BH|2 |BH|2 PRELIMINARY PRELIMINARY PRELIMINARY BH 0.005 < xB < 0.01 0.01 < xB < 0.03 0.03 < xB • Є p  ’ p 35%  (0.8)4 for SPS + COMPASS avail. + trigger eff + dead time εglobal 0.14 confirmedεglobal = 0.1 as assumed for COMPASS II predictions 54evts 20 BH + 22DVCS + about 12  from 0

  8. Projections for Phase 1 in COMPASS-II • (test in autumn 2012 and 2 years 2015-16) • withrecoil proton detection and hydrogentarget • Transverse Imaging : d/dt • Constrains on the GPD H 8

  9. μ’ * θ μ p  Deeply Virtual Compton Scattering dσ(μpμp) = dσBH + dσDVCSunpol+ PμdσDVCSpol + eμaBHReADVCS +eμ PμaBHImADVCS Phase 1: DVCSexperiment with+, - beam+ unpolarized2.5m long LH2 (proton) target to studythe transverse imaging SCS,U  d( +) +d( -)  Using SCS,U and BH subtraction d DVCS/dt~exp(-B|t|) and integration over  9

  10. Transverse imaging at COMPASS d DVCS/dt~exp(-B|t|) mainlydominated byH(x, =x, t) • B(xB) = ½ < r2 (xB) >related to ½ < b2 (xB) > • distance between the active quark distance between the active quark • and the center of momentum of spectators and the center of momentum of the nucleon Transverse size of the nucleon • Impact ParameterRepresentation • q(x, b ) <-> H(x, =0, t) ? 1. 0.5 0.65 0.02 fm H1 PLB659(2008) COMPASS xB 10

  11. Transverse imaging at COMPASS d DVCS/dt~exp(-B|t|) 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% ansatzatsmallxB inspired by ReggePhenomenology: B(xB) = b0 + 2 α’ln(x0/xB) α’slope of Reggetraject withoutany model wecanextract B(xB) • B(xB) = ½ < r2 (xB) > r is the transverse size of the nucleon Accuracy > 2.5  if α’ = 0.125 and full ECALS 11

  12. Transverse imaging at COMPASS d DVCS/dt~exp(-B|t|) DVCS test in 2012 With1 week Using the 4m long RPD + the 2.5m long LH2 target 1/40 of the complete statistics 2012: wecandetermine one mean value of B in the COMPASS kinematic range 12

  13. Transverse imaging at COMPASS d excl./dt~exp(-B|t|) 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% Exclusive  model developed by Sandacz renormalisedaccording Goloskokov and Kroll prediction 13

  14. Transverse imaging at COMPASS d excl./dt~exp(-B|t|) 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% Exclusive  B~8 @ Q2=2 • B~5.5 after Q2=10 We are sensitive to the nucleontransverse size + to the meson transverse size

  15. Deeply Virtual Compton Scattering dσ(μpμp) = dσBH + dσDVCSunpol+ PμdσDVCSpol +eμaBHRe ADVCS +eμ PμaBHImADVCS Phase 1: DVCSexperimentto constrainGPD H with+, - beam+ unpolarized2.5m long LH2 (proton) target  d( +) -d( -) andRe(F1 H) DCS,U andIm(F1 H) SCS,U  d( +) +d( -) Angulardecomposition of sum and diffof the DVCS cross section willprovideumambiguousway to separate the Reand Imof the Compton FormFactors fromhigher twist contributions

  16. Deeply Virtual Compton Scattering dσ(μpμp) = dσBH + dσDVCSunpol+ PμdσDVCSpol +eμaBHRe ADVCS +eμ PμaBHImADVCS Phase 1: DVCSexperimentto constrainGPD H with+, - beam+ unpolarized2.5m long LH2 (proton) target  d( +) -d( -) and Re(F1 H) DCS,U andIm(F1 H) SCS,U  d( +) +d( -) • ImH(,t)=H(x= ,,t) • ReH(,t)= PdxH(x,,t) /(x-) dominance of Hat COMPASS kinematics   xB / (2-xB)

  17. μ’ * θ μ p  Beam Charge and Spin Difference (usingDCS ,U) Comparison to different models 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% ’=0.8 ’=0.05 (asymmetries +cross section) (onlyasymmetries) High precisionbeam flux and acceptancedetermination Systematicerror bands assuming a 3% charge-dependenteffect between+ and - (control with inclusive evts, BH…) 16

  18. Beam Charge and Spin Difference over the kinematic domain Statistics and Systematics Diff = (NBH+NDVCS)+ /a+ - ( NBH+NDVCS)-/a- a= lumiacceptance DiffSyst = a/achargedependent  Sum 3% (hypothesis) DiffStat= 1/(NBH+NDVCS)  Sum

  19. d( +) - d( -)  andRe(F1 H ) DCS,U Re(F1 H ) > 0at H1 < 0at HERMES/JLab Value of xB for the node? Predictionswith VGG andD.Mueller 2 years of data With ECAL2 + ECAL1 + ECAL0

  20. Constrains on the GPD E on transverselypolarized protons (NH3 target) 1) withoutrecoildetection (2007 & 2010) 2) withrecoildetectionPhase 2 (in a future addendum) q q E p p t the GPDEallowsnucleonhelicity flip soitisrelated to the angularmomentum Ji sum rule: 2Jq =  x (Hq(x,ξ,0)+Eq(x,ξ,0)) dx The GPD E is the ‘Holy-Grail’ of the GPD quest 19

  21. Hard Exclusive VectorMeson Production AUT(0L)  |-t’| Im( E* H ) / |H|2  sin( - S) 20

  22. Hard Exclusive VectorMeson Production AUT(0L)  |-t’| Im( E* H ) / |H|2 Eρ02/3 Eu + 1/3 Ed + 3/8 Eg • Eω2/3 Eu – 1/3 Ed + 1/8 Eg • Eρ+Eu – Ed - 3/8 Hg 0 q =  eq(x)dx Eu ~ -Ed • Goloskokov-Kroll: the mostcomplete model (Q2>3GeV2 x<0.2) • with H and E for quarks and gluons and with quark transverse degrees of freedom the asymptotically dominant (longitudinal) amplitude for L* p  L p but also the one for transversely polarized photons and vector mesons T* p  Tp

  23. 2007 results for the Transverse Target Asymmetry AUT(0L)  |-t’| Im( E* H ) / |H|2 Hermes Compass 2007 W=5 GeV Q2=3 GeV2 AUT() and AUT(+) shouldbe more promising To becompletedwith the analysis of 2010 data

  24. μ’ * θ μ p  Deeply Virtual Compton Scattering Phase 2 (in future): DVCSexperimentto constrainGPD E with+, - beamand transverselypolarized NH3 (proton) target Im(F2H– F1E)sin(- S) cos  DCS,T  dT ( +) –dT ( -) 23

  25. DCS,T and Transverse Target Asymmetry • Prediction for phase 2 (in future) • With a transverselypolarized NH3 (proton) target: 2 years of data 160 GeV muon beam 1.2 m polarised NH3 target global = 10% related to H and E CS,T With ECAL2 + ECAL1 24

  26. Summary for GPD @ COMPASS • GPDsinvestigatedwith Hard Exclusive Photon and Meson Production • +, - 160 GeV • COMPASS-II 2012-16: withLH2target + RPD (phase 1) • the t-slope of the DVCS and HEMP cross section •  transverse distribution of partons • the Beam Charge and Spin Sum and Difference • Re TDVCS and Im TDVCS for the GPD H determination • Longitudinal contribution of VectorMeson0,+,  GPD H • Total contribution of 0 GPDsEtilde and ET • Using the 2007-10 data: transv. polarized NH3targetwithout RPD • In a future addendum > 2016: transv.polarised NH3targetwith RPD (phase 2) • the Transverse Target Spin Asymm •  GPD E and angularmomentum of partons

  27. A very long and beautiful trip • « This desserves the detour…. » HERA HERMES Jlab COMPASS And future colliders

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