1. Ralf W. Gothe 1  Basic Tools: Experiment and Theory  Goals: Unveil the dynamics of the strong interaction  Connections: Not everything is difficult that sounds difficult Ralf W. Gothe Users Group Workshop and Annual Meeting June 8-10, 2009 Jefferson Lab, Newport News, VA Roadmap to the CLAS12 Physics Program

2. Ralf W. Gothe 2 A B C Jefferson Lab Today Two high-resolution 4 GeV spectrometers Large acceptance spectrometer electron/photon beams 7 GeV spectrometer 1.8 GeV spectrometer Hall A Hall B Hall C

3. Ralf W. Gothe 3 6 GeV CEBAF 11CHL-2 12 Upgrade magnets and power supplies Two 0.6 GeV linacs 1.1 Enhanced capabilities in existing Halls 1.1

4. Ralf W. Gothe 4 Overview of Upgrade Technical Performance Requirements Hall DHall BHall CHall A 4  hermetic detector GlueEx luminosity 10 35 CLAS12 High Momentum Spectrometer SHRS High Resolution Spectrometer HRS polarized photonshermeticityprecisionspace E  ~ 8.5-9.0  GeV 11 GeV beamline 10 8 photons/starget flexibility good momentum/angle resolutionexcellent momentum resolution high multiplicity reconstructionluminosity up to 10 38.

5. Ralf W. Gothe 5 CLAS12  Luminosity > 10 35 cm -2 s -1  Baryon Spectroscopy  N and N* Form Factors  GPDs and TMDs  DIS and SIDIS  Nucleon Spin Structure  Color Transpareny  … Central Detector Forward Detector 1m CLAS12

6. Ralf W. Gothe 6 CLAS12 Approved Experiments ProposalContact PersonPhysicsEnergy (GeV) PAC daysParallel Running Run Group daysComment E12-09-103Gothe, MokeevN* at high Q 2 1160 80 20 120 E12-06-119(a)SabatieDVCS pol. beam1180 E12-06-112Avakian ep→eπ +/-/0 X1160 E12-06-108StolerDVMP in π 0,η prod L/T separation 1180 8.8 6.6 20 E12-06-119(b)SabatieDVCS pol. target11120 50 5 175 Assume polarized experiments run 50% of time w/ reversed field E12-06- 109KuhnLong. Spin Str.1182 E12-07-107AvakianTMD SSA11103 E12-09-007(b)HafidiPartonic SIDIS11103 E12-09-009AvakianSpin-Orbit Corr.11103 E12-06-106HafidiColor Trans. ρ 0 1140 E12-06-117BrooksQuark Hadronizat.1160 E12-06-113BültmanNeutron Str. Fn.1140 cond. appr. E12-07-104GilfoyleNeutron mag. FF1156 26 82 007/008 need 26d reversed field E12-09-007(a)HafidiPartonic SIDIS1156 E12-09-008ContalbrigoBoer-Mulders w/ Kaons1156 Total1139517

7. Ralf W. Gothe 7 quark mass (GeV) Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asqtad action.  … resolution low high q e.m. probe LQCD (Bowman et al.) Physics Goals N,N *,  * … 3q-core+MB-cloud 3q-core pQCD LQCD, DSE and …  Study the structure of the nucleon spectrum in the domain where dressed quarks are the major active degree of freedom.  Explore the formation of excited nucleon states in interactions of dressed quarks and their emergence from QCD.

8. Ralf W. Gothe 8 Hadron Structure with Electromagnetic Probes vv N  p   p 

9. Ralf W. Gothe 9 Hadron Structure with Electromagnetic Probes

10. Ralf W. Gothe 10 Cross Section Decomposition

11. Ralf W. Gothe 11 Multipole Expansion of the CGLN Amplitudes

12. Ralf W. Gothe 12

13. Ralf W. Gothe 13 What do we really know? Spectroscopy

14. Ralf W. Gothe 14 Quark Model Classification of N*  (1232) D 13 (1520) S 11 (1535) Roper P 11 (1440) + q³g + q³qq + N-Meson + …

15. Ralf W. Gothe 15 N and  Excited States …  Orbital excitations (two distinct kinds)  Radial excitations (also two kinds)

16. Ralf W. Gothe 16 “Missing” Resonances? fewer degrees-of-freedom open question: mechanism for q 2 formation? Problem: symmetric CQM predicts many more states than observed (in  N scattering) Possible solutions: 1. di-quark model 2. not all states have been found possible reason: decouple from  N-channel model calculations: missing states couple to N , N , N , KY 3. coupled channel dynamics all baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only  (1405),  (1520), S 11 (1535) or f 0 (980)) old but always young new

17. Ralf W. Gothe 17  Process described by 4 complex, parity conserving amplitudes  7 well-chosen measurements are needed to determine amplitude.  For hyperon finals state 16 observables will be measured in CLAS ➠ huge redundancy in determining the photo- production amplitudes ➠ allows many cross checks.  7 observables measured in reactions without recoil polarization.  weak decay has large analyzing power γp→K + Λ FROST/HD  N  N’,  N, K , K , N 

18. Ralf W. Gothe 18

19. Ralf W. Gothe 19 Quasi-Real Electroproduction Meson spectroscopy: exotic, high t, coherent, J/  Baryon spectroscopy: heavy mass N*, hyperons Time-like Compton scattering: GPDs, …

20. Ralf W. Gothe 20 Quasi-Real Electroproduction Meson spectroscopy: exotic, high t, coherent, J/  Baryon spectroscopy: heavy mass N*, hyperons Time-like Compton scattering: GPDs, … DDVCS? Missing momentum analysis of all final state particles Double Deep Virtual Compton scattering

21. Ralf W. Gothe 21 Photoproduction of Lepton Pairs    ’e+e-’e+e- M ee > 1.2 GeV for TCS analysis CLAS/E1-6 CLAS/G7

22. Ralf W. Gothe 22 Color Transparency  Color Transparency is a spectacular prediction of QCD: under the right conditions, nuclear matter will allow the transmission of hadrons with reduced attenuation.  Unexpected in a hadronic picture of strongly interacting matter, but straightforward in quark gluon basis.  Small effects observed at lower energy. Expect significant effects at higher energy. CLAS12 projected A e+e+ e-e-

23. Ralf W. Gothe 23 Dynamical Mass of Light Dressed Quarks DSE and LQCD predict the dynamical generation of the momentum dependent dressed quark mass that comes from the gluon dressing of the current quark propagator. These dynamical contributions account for more than 98% of the dressed light quark mass. The data on N* electrocouplings at 0<Q 2 <12 GeV 2 will allow us to chart the momentum evolution of dressed quark mass, and in particular, to explore the transition from dressed to almost bare current quarks as shown above. Q 2 = 12 GeV 2 = (p times number of quarks) 2 = 12 GeV 2 p = 1.15 GeV per dressed quark DSE: lines and LQCD: triangles

24. Ralf W. Gothe 24 S 11 Q 3 A 1/2 F 15 Q 5 A 3/2 P 11 Q 3 A 1/2 D 13 Q 5 A 3/2 F 15 Q 3 A 1/2 D 13 Q 3 A 1/2 Constituent Counting Rule  A 1/2  1/Q 3  A 3/2  1/Q 5  G M  1/Q 4 *

25. Ralf W. Gothe 25 N →  Multipole Ratios R EM, R SM  New trend towards pQCD behavior does not show up.  CLAS12 can measure R EM and R SM up to Q² ~ 12 GeV².  R EM +1 M. Ungaro  G M 1/Q 4 * G D = 1 (1+Q 2 /0.71) 2

26. Ralf W. Gothe 26 Electrocouplings of N(1440)P 11 from CLAS Data N  (UIM, DR) PDG estimation N , N  combined analysis N  (JM) The good agreement on extracting the N* electrocouplings between the two exclusive channels (1  /2  ) – having fundamentally different mechanisms for the nonresonant background – provides evidence for the reliable extraction of N* electrocouplings.

27. Ralf W. Gothe 27 Electrocouplings of N(1520)D 13 from the CLAS 1  /2  data world data 10 -3 GeV -1/2 N  (UIM, DR) PDG estimation N , N  combined analysis N  (JM) A hel = A 1/2 2 – A 3/2 2 A 1/2 2 + A 3/2 2 A 1/2 A 3/2 L. Tiator

28. Ralf W. Gothe 28  CLAS N  world N  world Q 2 =0  (1700)D 33 N(1720)P 13 Higher Lying Resonances form the 2  JM Analysis of CLAS Data preliminary The A 1/2 electrocoupling of P 13 (1720) decreases rapidly with Q 2. At Q 2 >0.9 GeV 2 |A 3/2 |>|A 1/2 |. Will we able to access the Q 2 region where the A 1/2 amplitude of P 13 (1720) dominates?

29. Ralf W. Gothe 29 Kinematic Coverage of CLAS12 60 days L= 10 35 cm -2 sec -1,  W = 0.025 GeV,  Q 2 = 0.5 GeV 2 Genova-EG (e ’, p     ) detected W GeV Q 2 GeV 2 2  limit >1  limit > 2  limit >1  limit > 1  limit >

30. Ralf W. Gothe 30 Proton Electromagnetic Form Factors green : Rosenbluth data (SLAC, JLab) Pun05 Gay02 JLab/HallA recoil polarization data

31. Ralf W. Gothe 31 Quark Transverse Charge Densities in Nucleons longitudinally polarized nucleon q + = q 0 + q 3 = 0 photon only couples to forward moving quarks quark charge density operator p’p z Light-Front Formalism Miller (2007)

32. Ralf W. Gothe 32 transversely polarized nucleon transverse spin e.g. along x-axis : dipole field pattern Carlson, Vanderhaegen (2007) Quark Transverse Charge Densities in Nucleons

33. Ralf W. Gothe 33 data : Arrington, Melnitchouk, Tjon (2007) densities : Miller (2007); Carlson, Vdh (2007) induced EDM : d y = F 2p (0). e / (2 M N ) ρ0ρ0 ρTρT Quark Transverse Charge Densities in the Proton

34. Ralf W. Gothe 34 p n p ->  + (1232) p -> N * (1440) quadrupole pattern Tiator, Vdh (2008) Carlson, Vdh (2007) Transverse Transition Densities

35. Ralf W. Gothe 35 p -> D 13 (1520) Tiator, Vdh (2009) ρ0ρ0 ρTρT Transverse Transition Densities

36. Ralf W. Gothe 36 Elastic Scattering transverse quark distribution in coordinate space DIS longitudinal quark distribution in momentum space DES (GPDs) fully-correlated quark distribution in both coordinate and momentum space 3-dim quark structure of nucleon Burkardt (2000,2003) Belitsky,Ji,Yuan (2004) Generalized Parton Distributions

37. Ralf W. Gothe 37 Fourier transform of GPDs gives simultaneous distributions of quarks w.r.t. longitudinal momentum x P and transverse position b P + Δ /2 * Q 2 >> x + ξ x - ξ P - Δ /2 t = Δ 2 ξ = 0 Generalized Parton Distributions H,H,E,E (x, ξ,t) ~ ~ GPDs

38. Ralf W. Gothe 38 DVCS Kinematics Coverage of the 12 GeV Upgrade H1, ZEUS JLab Upgrade 11 GeV H1, ZEUS JLab @ 12 GeV 11 GeV 27 GeV 200 GeV W = 2 GeV Study of high x B domain requires high luminosity HERMES COMPASS

39. Ralf W. Gothe 39 Unpolarized beam, longitudinal target:  UL  ~ sin  {F 1 H + ξ (F 1 +F 2 )( H + ξ /(1+ ξ ) E) -… }d  ~ Kinematically suppressed H(ξ,t) ~ A =           =  ~ x B /(2-x B ) k = t/4M 2 Unpolarized beam, transverse target:  UT  ~ cos sin( s -) {k(F 2 H – F 1 E) + … }d  Kinematically suppressed E(ξ,t) How to Extract GPDs ? H(ξ,t) Polarized beam, unpolarized target:  LU  ~ sin  {F 1 H + ξ (F 1 +F 2 ) H + kF E) }d   LU  ~ sin  {F 1 H + ξ (F 1 +F 2 ) H + kF 2 E) }d  ~ Kinematically suppressed

40. Ralf W. Gothe 40 DVCS Polarized Beam Asymmetry2/25/0940 Volker Burkert, CLAS12 Workshop, Genoa e p ep  A =           =  LU ~sin  {F 1 H +…}d  Extract H(ξ,t)

41. Ralf W. Gothe 41 DVCS Longitudinal Target Asymmetry e p ep   UL ~sin  Im{F 1 H +  (F 1 +F 2 ) H... }d  ~ Extract H(ξ,t) ~ 2/25/0941 Volker Burkert, CLAS12 Workshop, Genoa e p ep  A =           =

42. Ralf W. Gothe 42 Transverse Momentum Distributions  TMDs are complementary to GPDs in that they allow to construct of the nucleon in space  TMDs are complementary to GPDs in that they allow to construct 3-D images of the nucleon in momentum space  TMDs can be studied in SIDIS experiments measuring azimuthal asymmetries or moments. Semi Inclusive Deep Inelastic Scattering

43. Ralf W. Gothe 43 TMDs in SIDIS Land Many spin asymmetries

44. Ralf W. Gothe 44 TMDs in SIDIS Land

45. Ralf W. Gothe 45 The cos2  moment of the azimuthal asymmetry gives access to the Boer-Mulders function, which measures the momentum distribution of transversely polarized quarks in unpolarized nucleons.. 4 <Q 2 < 5 GeV 2 TMDs in SIDIS Land

46. Ralf W. Gothe 46 The sin2  moment gives access to the Kotzinian- Mulders function, which measures the momentum distribution of transversely polarized quarks in the longitudinally polarized nucleon. TMDs in SIDIS Land

47. Ralf W. Gothe 47 per dressed quark Summary and Outlook