1. Dihadron production at JLab Sergio Anefalos Pereira (INFN - Frascati)

2. Physics Motivation Describe the complex nucleon structure in terms of partonic degrees of freedom of QCD ● measuring transverse momentum of final state hadrons in SIDIS gives access to the transverse momentum distributions (TMDs) of partons ● p T dependent spin asymmetries measurements give us access to different TMDs, providing information on how quarks are confined in hadrons ● azimuthal distributions of final-state particles in SIDIS, in particular, are sensitive to the orbital motion of quarks and play an important role in the study of TMD parton distribution functions of quarks in the nucleon. ● the goal of looking at dihadron SIDIS is have a full picture of the collinear structure of proton. 2

3. What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons + Higher Twist distribution functions 6 GeV  e(x) and h L (x) Leading Twist 3

4. + Higher Twist distribution functions 6 GeV  e(x) and h L (x) 12 GeV  h 1 (x), e(x) and h L (x) (since we will have higher Q 2 coverage ~ 10 GeV 2 ) Leading Twist 3 What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons

5. + Higher Twist distribution functions In addition to pions, at 12 GeV we'll be able to detect also kaons with  /k separation in the 3-8 GeV/c range. Leading Twist What we measure at 6 GeV and 12 GeV @ Jlab with dihadrons 4

6. The dihadron channel have some disadvantages (more complex kinematics, new angles, unknown but measurable DiFFs appear) but it also brings a very useful advantage: in single hadron production, the observables are convolution of TMDs in double hadron production, observables are product of TMDs Dihadron vs. single-hadron SIDIS 5

7. The dihadron channel have some disadvantages (more complex kinematics, new angles, unknown but measurable DiFFs appear) but it also brings a very useful advantage: in single hadron production, the observables are convolution of TMDs in double hadron production, observables are product of TMDs Dihadron vs. single-hadron SIDIS 5

8. SIDIS kinematical plane and observables longitudinal momentum fraction carried by the hadron the fraction of the virtual-photon energy carried by the two hadrons   X 6

9. SIDIS kinematical plane and observables longitudinal momentum fraction carried by the hadron the fraction of the virtual-photon energy carried by the two hadrons   X it selects the current fragmentation region (CFR) and target fragmentation region (TFR). The first comprise hadrons produced in the forward hemisphere (along the virtual photon) and the latest, in the backward hemisphere In these analysis we select events in the CFR 6

10. Dihadron angles definition the angle between the direction of P 1 in the  +  - center-of- mass frame, and the direction of P h in the photon-target rest frame. q k' k 7

11. Structure functions in terms of PDF and DiFF in the limit M 2 ≪ Q 2 8

12. Transversity extracted using the HERMES data for proton (red symbols) and COMPASS data for proton (blue ones) The dashed lines correspond to Torino’s transversity [arXiv:0812.4366] Dihadron with transversely polarized target Transversity using the COMPASS data for deuteron. model-independent extraction in collinear approximation [ arXiv:1206.1836v1] JLab will provide much precise data and also extend x up to 0.6. 9

13. Dihadron @ 6GeV 10

14. CLAS Continuous Electron Beam Energy 0.8-5.7 GeV 200  A, polarization 85% Simultaneous delivery to 3Halls JLab Accelerator CEBAF 11

15. Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers beam Drift chambers argon/CO 2 gas, 35,000 cells Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/  separation, 216 PMTs Liquid D 2 (H 2 )target +  start counter; e minitorus Broad angular coverage (8° - 140° in LAB frame) Charged particle momentum resolution ~0.5% forward dir CLAS is designed to measure exclusive reactions with multi-particle final states Hall B: Cebaf Large Acceptance Spectrometer 12

16. The e1f and eg1-dvcs experiments Hydrogen target (NH 3 ) Beam energy: 5.892 GeV 4.735 GeV Luminosity: 22.7 fb -1 Hydrogen target (NH 3 ) Beam energy: 5.967 GeV Luminosity: 50.7 fb -1 Deuterium target (ND 3 ) Beam energy: 5.764 GeV Luminosity: 25.3 fb -1 Beam polarization ~ 85% Proton polarization ~ 80% Beam polarization ~ 75 % Liquid Hydrogen target (unpolarized) Beam energy: 5.5 GeV Luminosity: 21 fb-1 13

17. Channel identification semi-inclusive channel two topologies have been analyzed:  e p  e’  +  - X  e p  e’  +  0 X  e’  +   X  0 is identified as M (   )   X 14

18. Channel identification semi-inclusive channel two topologies have been analyzed :  e p  e’  +  - X  e p  e’  +  0 X  e’  +   X  0 is identified as M (   )   X ++ -- dihadron sample defined by SIDIS cuts + CFR for both hadrons 14

19. ++ -- Channel identification semi-inclusive channel two topologies have been analyzed:  e p  e’  +  - X  e p  e’  +  0 X  e’  +   X  0 is identified as M (   )   X dihadron sample defined by SIDIS cuts + CFR for both hadrons Struck quark fragmenting in a hadron pair 14

20. MM > 1.5 GeV Semi-inclusive selection MM > 1.5 GeV 15

21. Monte Carlo study ClasDIS Monte Carlo (LUND) was used as event generator; Polarized proton and unpolarized deuteron MC were used to “simulate” NH 3 target; the full MC chain; same cuts used on data were applied. 16

22. Monte Carlo vs. Data + data - Monte Carlo p e p  p  Xb y W 2 Q 2 x F (   ) x F (   ) 17

23. + data - Monte Carlo Z  + Z  Z hh Pt  + Pt  - Pt hh M(     )  R  h Monte Carlo vs. Data 18

24. Beam-Spin Asymmetry (BSA) p 0 + p 1 sin  R + p 2 sin 2  R Monte Carlo generated x reconstructed asymmetries we have generated events with the following input parameters: p 0 = 0.0, p 1 = 0.03 and p 2 = 0.0 According to this function 19

25. Results Fitting function: integrated over all variables p 0 + p 1 sin  R + p 2 sin 2  R preliminary 20 Beam-Spin Asymmetry (BSA)

26. Results Beam-Spin Asymmetry (BSA) ▲ Sin  ▲ Sin  preliminary 21

27. Results Beam-Spin Asymmetry (BSA) ▲ Sin  (e1f) ▲ Sin  (eg1-dvcs) preliminary 22

28. Results Fitting function: integrated over all variables Target-Spin Asymmetry (TSA) p 0 + p 1 sin  R + p 2 sin 2  R preliminary 23

29. Results Target-Spin Asymmetry (TSA) ▲ Sin  ▲ Sin  preliminary 24

30. Dihadron @ 12GeV 25

31. End physics program @ 6 GeV in 2012 6 GeV CEBAF CHL- 2 Upgrade magnets and power supplies 12 GeV CEBAF add Hall D (and beam line) Beam Power: 1MW Beam Current: 90 µA Max Pass energy: 2.2 GeV Max Enery Hall A-C: 10.9 GeV Max Energy Hall D: 12 GeV May 2013 Accelerator Commissioning starts October 2013 Hall Commissioning starts 26

32. Q2 Kinematic coverage extending to higher x means lower cross sections need high luminosity: 10 35 cm -2 s -1 27

33. CLAS12 Configuration (Hall-B) DC R3 R2 R1 DC R3 R2 R1 EC Torus FTOF PCAL HTCC Solenoid RICH Wide acceptance and high resolution important in particular for hadron pair production Designed for luminosity 10 35 cm -2 sec -1 Highly polarized 11 GeV electron beam Transverse an Longitudinal polarized H and D targets RICH detector allows kaon detection 28

34. Layout of the RICH Constraints: the detector must fit in 1m low material budget large area for the photodetectors (several m 2 ) increasing azimuthal angle  decreasing momentum beam pipe particle’s trajectory target  DC1 DC2 DC3 ONE CLAS12 SECTOR Solutions: mirrors to focalize the light in small area variable aerogel thickness from 2 to 6/8 cm Different pattern: Cerenkov photons from small angle, high momentum particles directly detected photons from large angle and lower momentum particles are reflected toward the photodetectors and pass twice through the aerogel Requirements:  /k/p separation in the 3-8 GeV/c range  rejection >500 29

35. SoLID Configuration (Hall-A) Effective pol. neutron target Wide acceptance and high resolution High 10 36 luminosity8.8 and 11 GeV polarized beam Transverse and Longitudinal Polarized 3HeTarget > 60% polarization Large acceptance with full azimuthal- angle coverage 30

36. Flavor separation at JLab the asymmetry for a neutron target (for the specific case of the π+π− final state) can be written as: the equivalent equation for the proton is combining these two asymmetries (on neutron and proton targets) the u v and the d v flavors could be extracted separately. 31

37. Flavor separation with JLab 32

38. Dihadron production on neutron @ Jlab 11 GeV Projected statistical error for data on a neutron target. The yellow band represent the spread in predictions using different models for h1(x) (top plots) 33

39. Dihadron production on proton @ Jlab 11 GeV 34

40. Summary 6 Gev ●  the first measurements of dihadron A LU and A UL asymmetries have been presented; ●  preliminary results of a non-zero BSA and TSA for  +  - pair have been shown (will look at  +  0 as well); 12 GeV ● Jlab @ 12 GeV will measure transverse target SSA in hadron pair production in SIDIS and study the transversity distribution function and interference effects in hadronization using transverse polarized protons (CLAS12) and neutrons (SoLID); ● Flavor separation will also be possible combining both data (proton and neutron) to to extract the u v and the d v flavors separately. ●  Measurements with kaons in the final state will provide important information about strange quarks. 35

41. Backup slides 36

42. Generated and reconstructed asymmetries p1 = 0 p2 = 0 p1 = 0.03 p2 = 0 p1 = 0.03 p2 = 0.03 p1 = 0 p2 = 0.03 37

43. 38