ΔVCS and Generalized Parton Distributions

1. ΔVCS and Generalized Parton Distributions CLAS@Jlab Students' seminar at Bosen Workshop

2. Outline Students' seminar at Bosen Workshop • Generalized Parton Distributions • Beam Spin asymmetry • The experiment at Jlab • First look at the Data

3. Generalized Parton Distributions(GPDs) Students' seminar at Bosen Workshop

4. General GPDs physics case Students' seminar at Bosen Workshop l’ l γ l’ γ or meson l GPDs γ* N’ N N N’ In the Bjorken limit: Large Low Fixed t standard notation GPDs appear in the amplitudes of exclusive reactions GPDs are a new way of describing the nucleon

5. y y z z x x x y z Nucleon form factor Partondistribution GPDs GPDs : combine information from form factors and parton distribution Students' seminar at Bosen Workshop

6. Beam Spin Asymmetry

7. Beam Spin Asymmetry (BSA)general case l = lepton, N= nucleon l’= scattered lepton, N’= recoil hadron, M= photon or meson P = polarization of incoming lepton k = number of independent variables Students' seminar at Bosen Workshop

8. Beam Spin Asymmetry (BSA) DVCS example BSA grants access to nucleon GPDs β,α are combinations of GPDs DVCS 2 BH BH + + Interference between DVCS and Bethe-Heitler processes Students' seminar at Bosen Workshop

9. Students' seminar at Bosen Workshop Beam spin asymmetry: ΔVCS case e’ e γ* γ л p L.L. Frankfurt, M. V. Polyakov,M. Strikman, M.Vanderhaeghen N Phys. Rev. Lett. 84: 2589-2592 (2000) P.A.M Guichon, L.Mossé, M.Vanderhaeghen Phys. Rev. D68 034018 (2003) • N-Δ transitions at a partonic level - large Nc approximation: ΔVCS can be described in terms of standard GPDs GPDs N-Δ

10. Students' seminar at Bosen Workshop 2 ΔVCS BH BH + + P.A.M Guichon, L.Mossé, M.Vanderhaeghen Phys. Rev. D68 034018 (2003) FIRST measurement

11. The experiment at Jefferson lab Students' seminar at Bosen Workshop

12. Students' seminar at Bosen Workshop Thomas Jefferson Laboratory (USA, Virginia) Hall B

13. CLAS detector Electromagnetic Calorimeter (EC, LAC) to detect showering particles Cherenkov Counters for e/л separation Torus magnet Drift chambers (DC) to determine trajectories of charged particles Inner calorimeter (IC) high energy resolution photon detector forseparation (DVCS) Time-of-flight counters (TOF) Students' seminar at Bosen Workshop

14. Chronology my arrival 2007 : ongoing analysis (DVCS , , , cross sections, , BSA ) 2005 data taking 35 days (from march to may 2005) beam energy 5.776 GeV 2005 calibrations December 2006 : first thesis published (DVCS BSA) 2008 : second data taking period

15. First look at the data Students' seminar at Bosen Workshop

16. Analysis plan Students' seminar at Bosen Workshop e’ e γ* γ л p N Basic event selection: 1 electron, 1 proton, 3 photons - reconstruct Δ particles via neutral pion reconstruction - develop exclusivity cuts - background and contamination studies - Beam Spin Asymmetry results

17. Delta reconstruction Which one to choose ? Before going further it would be wise to have a preview of the decay particles of Δ phase space Development of a kinematic filter different photon combinations

18. First look at the data Phase space generator Students' seminar at Bosen Workshop

19. Kinematic generator t e’ e γ* γ t max t min 0 t л p N ν: random number uniformly distributed Q2: random number uniformly distributed t random number uniformly distributed Students' seminar at Bosen Workshop

20. Prediction for ΔVCS DVCS photon = most energetic one 8% events under 0 GeV

21. First look at the data Selection cuts

22. Selection cuts Before cuts After cuts

23. Selection cuts: cut on

24. Selection cuts A = second resonance region (~1.5 GeV) B = third resonance region (~1.65 GeV)

25. Complementary slides Students' seminar at Bosen Workshop

26. Kinematic generator p Δ q 1 γ γ Students' seminar at Bosen Workshop

27. Kinematic generator uniformly distributed uniformly distributed Students' seminar at Bosen Workshop

28. Kinematic generator: validation generator result data

29. Selection cuts

30. Data analysis background and contamination Students' seminar at Bosen Workshop

31. Overview

32. Data first part of 01-113 experiment e1-dvcs experiment 35 days (from march to may 2005) approved for 60 days beam energy 5.776 GeV hydrogen target to be completed next year luminosity accumulated charge Students' seminar at Bosen Workshop

33. More about GPDs

34. Standard GPDs γ p’ 4 GPDs for each quark flavour e’ e t γ* x+ξ x-ξ p

35. Transition N-Δ GPDs 3 transition vector GPDs 4 transition pseudo-vector GPDs In the large Nc limit

36. Particle ID

37. Particle ID: electron Students' seminar at Bosen Workshop Scattered electron identification id = 11 cut on reconstructed vertex position Fiducial cuts (EC,DC) Cut on lost energy in inner part of EC: E_in>60 MeV Cut on E/p vs p Momentum threshold : p > 800 MeV Cut on number of p.e’s produced in CC: 10*N > 25

38. Particle ID: electron Students' seminar at Bosen Workshop Cut on lost energy in inner part of EC Fiducial cuts (EC)

39. Particle ID: electron Students' seminar at Bosen Workshop Cut on E/p vs p

40. Particle ID: proton Students' seminar at Bosen Workshop cut on reconstructed vertex position Fiducial cuts (θ,φ) Cut on recoil proton identification

41. Particle ID: photon Students' seminar at Bosen Workshop photon identification: E > 150 MeV Fiducial cuts (EC) cut on β = l/t detected in EC assume all particles detected in IC are photons detected in IC fiducial cuts to avoid photons with hit near IC edge

42. Fiducial cuts Students' seminar at Bosen Workshop proton photon electron