1 / 27

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.

cachet
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related