1. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 1/47 JLab Physics Overview The Standard Model of Particle Physics — What are the Challenges? Introduction to Electron Scattering Thomas Jefferson National Accelerator Facility (JLab) Recent Research Highlights from JLab Parity Violation in Deep Inelastic Scattering Summary and Outlook Xiaochao Zheng Univ. of Virginia April 17, 2009

2. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 2/47 What is the Visible World Made of?

3. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 3/47 And How Do They Interact with Each Other? SU(2) L X U(1) Y SU(3) C

4. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 4/47 Success of the Standard Model Electro-weak theory tested to very good precision QCD tested in the high energy (perturbative, = “weak”) region Major Challenges within the Standard Model Understand and test QCD in extreme conditions (RHIC, LHC) Understand and test QCD in “strong” interaction region (non- perturbative) Understand the nucleon structure, how quarks and gluons form the nucleon's mass, momentum, and spin Standard Model of Particle Physics energy (GeV) (~1/distance) aSaS

5. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 5/47 Standard Model of Particle Physics Success of the Standard Model Electro-weak theory tested to very good precision QCD tested in the high energy (perturbative, = “weak”) region Major Challenges within the Standard Model Understand and test QCD in extreme conditions (RHIC, LHC) Understand and test QCD in “strong” interaction region (non- perturbative) Understand the nucleon structure — how quarks and gluons form the nucleon's mass, momentum, and spin typically studied by lepton scattering on the nucleon/nucleus

6. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 6/47 Success of the Standard Model Electro-weak theory tested to very good precisions QCD tested in the high energy (perturbative, = “weak”) region Major Challenges within the Standard Model Understand and test QCD in extreme conditions (RHIC, LHC) Understand and test QCD in “strong” interaction region (non- perturbative) Understand the nucleon structure — how quarks and gluons form the nucleon's mass, momentum, and spin Studying Nucleon Structure Using Electron Scattering typically studied by lepton scattering on the nucleon/nucleus

7. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 7/47 Electrons (m's) interact with the target by exchanging a “virtual” photon; Two variables to describe how the target behaves: 1/Q 2 and n; Studying Nucleon Structure Using Electron Scattering

8. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 8/47 The cross section: For point-like target Exploring Nucleon Structure Using Electron Scattering

9. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 9/47  (Quasi-) elastic – the nucleus (nucleon) appears as a rigid body, x-section described by form factors  Resonance region – quarks inside the nucleon react coherently  Deep Inelastic Scattering (DIS): Quarks start to react incoherently (start to see constituents of the nucleon) Can test pQCD Exploring Nucleon Structure Using Electron Scattering Elastic, quasi-elastic, resonances, deep inelastic (highly non-pertubative, phenomenology models)

10. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 10/47 Exploring Nucleon Structure Using Electron Scattering Elastic, quasi-elastic, resonances, deep inelastic  (Quasi-) elastic – the nucleus (nucleon) appears as a rigid body  Resonance region – quarks inside the nucleon react coherently  Deep Inelastic Scattering (DIS): Quarks start to react incoherently (start to see constituents of the nucleon), x-section described by structure functions (Can test pQCD)

11. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 11/47 Phys. Rev. D 66, 010001 (2002) F 2 (x,Q 2 )+c(x) 0.1 1.0 10 10 2 10 3 10 4 10 5 10 6 0.1 1.0 10 10 2 Q 2 (GeV 2 ) F 2 (x,Q 2 )+c(x) Q 2 (GeV 2 ) 10 9 8 7 6 5 4 3 2 1 0 3.5 3 2.5 2 1.5 1 0.5 0 Current Knowledge of Nucleon Unpolarized Structure

12. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 12/47 Structure Functions in the Quark-Parton Model After 35 years of DIS experiments, the unpolarized structure of the nucleon is reasonably well understood (for moderate x Bj region). in the infinite momentum frame (IMF): x: fraction of nucleon's momentum carried by a particular quark (P  ∞)

13. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 13/47 Medium & High Energy Physics Facilities for Lepton Scattering High luminosity, yet “continuous” polarized beam makes JLab an unique facility. ~ns: “continuous” >>ns: “pulsed”

14. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 14/47 Scientific Mission How are hadrons constructed from quarks and gluons of QCD? What is the QCD basis for the nucleon-nucleon force? Where are the limits of our understanding of nuclear structure? To what precision can we describe nuclei? To what distance scale can we describe nuclei? Where does the transition from nucleon-meson to QCD quark-gluon description occur? To make progress toward these research goals we must address critical issues in “strong QCD”: What is the mechanism of confinement? Where does the dynamics of the q-q interation make a transition from the strong (confinement) to the perturbative QCD regime? How does Chiral symmetry breaking occur? Symmetry Tests in Nuclear Physics

15. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 15/47 How are hadrons constructed from quarks and gluons of QCD? What is the QCD basis for the nucleon-nucleon force? Where are the limits of our understanding of nuclear structure? To what precision can we describe nuclei? To what distance scale can we describe nuclei? Where does the transition from nucleon-meson to QCD quark-gluon description occur? To make progress toward these research goals we must address critical issues in “strong QCD”: What is the mechanism of confinement? Where does the dynamics of the q-q interation make a transition from the strong (confinement) to the perturbative QCD regime? How does Chiral symmetry breaking occur? Symmetry Tests in Nuclear Physics Scientific Mission

16. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 16/47 CEBAF @ JLab Today Main Physics Programs: nucleon electromagnetic form factors (including strange f.f.); N ->N* electromagnetic transition form factors; spin structure of the nucleon form factor and structure of light nuclei nuclear medium effects (“EMC” effects) Standard Model test (parity violation in electron scattering)...

17. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 17/47 Employment: ~650 User community: ~1200

18. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 18/47 JLab Accelerator 20 cryomodules End Stations Recirculation arcs Helium Refrigerator 0.4-GeV linac 45 MeV Injector

19. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 19/47 EXPERIMENT AL HALLS INJECT OR RECIRCULATIO N ARCs (Magnets) NORTH LINAC SOUTH LINAC C B A The Accelerator (CEBAF)

20. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 20/47 Three Experimental Halls Hall A: pair of high resolution spectrometers (HRS), E' up to 4 GeV/c, = 7 msr luminosity up to 10 39 cm -2 s -1 Hall C: High Momentum (HMS and Short-Orbit Spectrometers (SOS) luminosity up to 10 39 cm -2 s -1 Hall B: CEBAF Large Acceptance Spectrometer (CLAS) luminosity up to 10 34 cm -2 s -1

21. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 21/47 Recent Highlights of JLab Research (a very limit number of)

22. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 22/47 Nucleon Form Factors e-nucleon elastic cross section determined by the EM form factors: In the Breit (centre-of-mass) frame the Sachs FF can be written as the Fourier transforms of the charge and magnetization radial density distributions. Two different methods have been carried out so far: Rosenbluth separation Polarization transfer

23. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 23/47 JLab Data on the EM Form Factors Provide a Testing Ground for Theories Constructing Nucleons from Quarks and Glue Proton Neutron Electric Magnetic

24. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 24/47 JLab Polarization-Transfer Data Polarization transfer data from JLab Hall A: E93-027 PRL 84, 1398 (2000) E99-007 PRL 88, 092301 (2002) Investigate possible experimental sources for discrepancy:  optimized Rosenbluth experiment confirmed SLAC results Investigate possible theoretical sources for discrepancy  two-photon contributions

25. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 25/47 Nucleon Spin Structure Experiments Inclusive : Sum Rules: GDH, Bjorken..... Nucleon structure functions and asymmetries spin asymmetry A 1 at high x (valence quark structure); structure function g 2 at low Q2; test of the spin “duality”. Longitudinal Semi-inclusive. Exclusive: DVCS......

26. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 26/47 Virtual Photon Asymmetries Before JLab, the large x region remains poorly explored SU(6): A 1 n =0 SU(6): A 1 p =5/9

27. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 27/47 What Makes the Large x Region Interesting?

28. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 28/47 Pre-JLab Data on A 1 n (1) Bag Model (2) LSS(BBS) (3) BBS (4) Duality (5) CQM (6) LSS 2001 (7) Statistical Model (8) SU(6) (9) Chiral Soliton #1 (10) Chiral Soliton #2

29. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 29/47 A 1 n Results First time A 1 n turns positive Indicate the importance of quark orbital angular momentum to the nucleon spin X. Zheng et al., Phys. Rev. Lett. 92, 012004 (2004); Phys. Rev. C 70, 065207 (2004)

30. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 30/47 Data for Dq/q Before JLabWith JLab Data

31. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 31/47 Parity Violation Deep Inelastic Scattering (PVDIS)

32. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 32/47 Weak charged currents given by a SU(2) L group with weak isospin T; But the observed neutral current couples to right-handed fermions, while neutral current from SU(2) L does not. Electroweak Interaction – The Standard Model

33. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 33/47 Weak charged currents given by a SU(2) L group with weak isospin T; Combine neutral current from SU(2) L and QED [U EM (1) g ] to construct: completes SU(2) L U(1) Y, Y : weak hyper charge Electroweak Interaction – The Standard Model observable theory photon Z0Z0

34. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 34/47 Electroweak Interaction – The Standard Model Mixing of the SU(2) L and U EM (1) g is giving by:... the Weak Mixing angle q W In the Standard Model Lepton neutral currents are given by vector and axial couplings

35. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 35/47 Standard Model works well at present energy range; But, there are many conceptual reasons for new physics: Challenges of the Standard Model Data exist: cannot be explained by the SM ( m n, NuTeV anomaly...); (250 GeV ~ 5 x 10 14 GeV ~ 2.4 x 10 18 GeV)?

36. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 36/47 Standard Model works well at present energy range; But, there are many conceptual reasons for new physics: Challenges of the Standard Model Data exist: cannot be explained by the SM ( m n, NuTeV anomaly...); (250 GeV ~ 5 x 10 14 GeV ~ 2.4 x 10 18 GeV)? indirect searches: E158, NuTeV, Qweak, PVDIS High energy direct searches: LEP, LHC

37. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 37/47 Test of The Standard Model Direct searches (LHC) Indirect searches: Search for forbidden processes (bb-decay, EDM......); New physics modify: at low energies; (expected)

38. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 38/47 Neutral Weak Couplings from Charged Lepton Scattering Asymmetries (ratios) in charged lepton-N scattering can be used to measure products

39. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 39/47 Asymmetries (ratios) in charged lepton-N scattering can be used to measure products Neutral Weak Couplings from Charged Lepton Scattering parity-violating e L, e R cross sections lepton charge conjugate-violating e L, e + R cross sections

40. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 40/47 Deuterium: PVDIS Asymmetries A PV = +

41. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 41/47 Deuterium: PVDIS Asymmetries A PV = + + g: coupling constant, L: mass limit, h A q : effective coefficient New physics sensitivity: Sensitive to: Z' searches, compositeness, leptoquarks Mass limit:

42. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 42/47 PV DIS and Other SM Test Experiments E158/Moller (SLAC) NuTeV (FNAL)Atomic PV PVDIS (JLab) Qweak (JLab) 2 (2C 1u +C 1d ) Coherent quarks in the proton Purely leptonic Weak CC and NC difference Nuclear structure? Other hadronic effects? Coherent Quarks in the Nucleus - 376C 1u - 422C 1d Nuclear structure? (2C 1u -C 1d )+Y(2C 2u -C 2d ) Isoscalar quark scattering Cartoons borrowed from R. Arnold (UMass) Different Experiments Probe Different Parts of Lagrangian, PVDIS is the only one accessing C 2q

43. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 43/47 PVDIS asymmetry has the potential to explore New Electroweak Physics etc...... However, hasn't been done since 1978. (Re)start PVDIS at JLab 6 & 12 GeV 1970's, result from SLAC E122 consistent with sin 2 q W =1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) PVDIS Experiment – Past, Present and Future

44. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 44/47 JLab 6 GeV Experiment 08-011 Use 85mA, 6 GeV, 80% polarized beam on a 25-cm LD2 target; Two Hall A High Resolution Spectrometers detect scattered electrons; Measure PV asymmetry A d at Q 2 =1.10 and 1.90 GeV 2 to 2.7% (stat.); A d at Q 2 =1.10 will investigate the possible higher twist effects; If HT is small, can extract 2C 2u -C 2d from A d at Q 2 =1.90 to ±0.04 (or with reduced precision if higher twists are un-expectedly large) Schedule to run Nov-Dec. 2009. Co-spokesperson & contact: X. Zheng Co-spokesperson: P.E. Reimer, R. Michaels Grad. students: Xiaoyan Deng, Diancheng Wang, Huaibo Ding. (Hall-A Collaboration Experiment, approved by PAC27, re-approved by PAC33 for 32 days, rated A-)

45. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 45/47 World Data on C 1,2q MIT/ Bates SLAC/Prescott Qweak ( expected ) R. Young (PVES) R. Young (combined) PDG best fit Cs APV SAMPLE SLAC/ Prescott R. Young ( combined ) all are 1 s limit Expected: JLab 6 GeV PV-DIS E08-011 (assuming small hadronic effects) C 2u +C 2d 1.25 1.5 1.75 1.0 0.75 0.5 0.25 0 -0.5 -0.75 C 2u -C 2d - 0.20.40.20- 0.4 0.10 0.125 0.15 0.175 C 1u -C 1d - 0.4 - 0.6 - 0.8 C 1u +C 1d Tl APV

46. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 46/47 6 GeV (2010-2014): Hall A: Nuclear physics: “short-range correlations”, Deeply Virtual Compton Scattering (DVCS), measurements of Generalized Parton Distributions (GPD). Hall B: Analysis of nucleon resonance data Hall C: Qweak: test of the Standard Model Outlook: Research Opportunities at JLab 2010- 12 GeV (2015 - ) Hall A: PVDIS program using a large solenoid device Compton polarimeter (laser, detectors)

47. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 47/47 6 GeV: Hall A: Nuclear physics: “short-range correlations”, Deeply Virtual Compton Scattering (DVCS), measurements of Generalized Parton Distributions (GPD). Hall B: Analysis of nucleon resonance data Hall C: Qweak: test of the Standard Model Outlook: Research Opportunities at JLab 2010- 12 GeV Hall A: PVDIS program using a large solenoid device Compton polarimeter (laser, detectors) As a group, can pursue: detector development “Joint”-training students can participate in all these experiments

48. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 48/47 Existing Chinese Collaborations  Hall A Neutron spin structure experiments University of Science and Technology of China, Prof. Yunxiu Ye, Dr. Hai-jiang Lu, Ph.D. student: Yi Zhang (with Dr. Jian-ping Chen, JLab) China Atomic Energy Institute, Prof. Shuhua Zhou, Prof. Xiaomei Li (with Dr. Jian-ping Chen, JLab) Neutron transversity experiments Beijing University, Prof. Bo-qiang Ma, Prof. Yajun Mao (with Prof. Haiyan Gao, Duke Univ.)  Hall B (with Prof. Liping Gan, Univ. of North Carolina-Wilmington) PrimEx (Primakoff Experiment to measure  0 lifetime) CIAE, Prof. Xiaomei Li,  Hall C (with Dr. Li-guang Tang, Hampton Univ.) ”Hyper-nuclear” experiments Lanzhou University, Prof. Bitao Hu

49. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 49/47 PVDIS Asymmetries A PV = + Deuterium: Also sensitive to: quark-gluon correlations (higher-twist effects) Charge symmetry violation

50. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 50/47 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV...... However, hasn't been done since 1978. Do a first measurement at JLab 6 GeV: If observe a significant deviation from the SM value, it will definitely indicate something exciting; Indicate either electroweak new physics, or current understanding of strong interaction is worse than we thought. 1970's, result from SLAC E122 consistent with sin 2 q W =1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) PVDIS Experiment – Past, Present and Future  New electroweak Physics  Non-perturbative QCD (higher-twist) effects  Charge symmetry violation Likely to be small, but need exp confirmation Small from MRST fit (90% CL ~1%) At the 6 GeV precision:

51. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 51/47 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV...... However, hasn't been done since 1978. Do a first measurement at JLab 6 GeV: If observe a significant deviation from the SM value, it will definitely indicate something exciting; Indicate either electroweak new physics, or current understanding of strong interaction is worse than we thought. well-planned At 12 GeV, a larger, well-planned PVDIS program could separate all three: New Physics, HT, CSV, important information for both EW and Strong interaction study. 1970's, result from SLAC E122 consistent with sin 2 q W =1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) PVDIS Experiment – Past, Present and Future

52. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 52/47 Scorecard XNoYesNoNew Physics XNo Yesd/u XNo YesIsospin XYesNo YesHigher twist dpQ2Q2 yx

53. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 53/47 Apparatus Needed for PVDIS Large Acceptance and High Luminosity

54. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 54/47 Large Angle Large Acceptance: Concept CW 90 µA at 11 GeV 40-60 cm liquid H 2 and D 2 targets Luminosity > 10 38 /cm 2 /s JLab Upgrade Need high rates at high x For the first time: sufficient rates to make precision PV DIS measurements solid angle > 200 msr Resolution<2% Count at 100 kHz online pion rejection of 10 2 Need magnet to block γ’s and low energy π’s

55. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 55/47 Plan View of the Spectrometer BaBar Solenoid?

56. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 56/47 NIM A320, 144 (1992) pi/e rejection 10 (-2~-3) at E=0.4~4 GeV/c based on energy resolution dE/E≤ 1.4+6.7%/sqrt[E(GeV)] time resolution ≤1ns radiation hard can work in mag fields Shashlyk (Shashlik) Calorimeter can cut/isolate detector here to form a double-layer struct. for improved PID

57. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 57/47 Shashlyk (Shashlik) Calorimeter

58. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 58/47 Scaling Violation in QCD Bjorken limit:, x Bj fixed, (strict) one photon exchange no scale (Q 2 )dependence, scaling High, soft gluon emission, logQ 2 dependence Low, hard gluon emission 1/(Q 2 ) (t-2) dependence “higher-twist effects”

59. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 59/47 Current Knowledge on Weak Coupling Coeffecients J. Erler, M.J. Ramsey-Musolf, Prog. Part. Nucl. Phys. 54, 351 (2005) (R. Young, R. Carlini, A.W. Thomas, J. Roche, PRL 99, 122003 (2007) & priv. comm.) new

60. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 60/47 Current Knowledge on Weak Coupling Coeffecients J. Erler, M.J. Ramsey-Musolf, Prog. Part. Nucl. Phys. 54, 351 (2005) (R. Young, R. Carlini, A.W. Thomas, J. Roche, PRL 99, 122003 (2007) & priv. comm.) new PDG2002 (best): (2C 2u -C 2d )=±0.24

61. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 61/47 JLab Hall A

62. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 62/47 Hall B CLAS

63. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 63/47 Hall C View

64. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 64/47 Medium and High Energy Physics Facilities in Europe and U.S.

65. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 65/47 Jlab 6 GeV

66. Xiaochao Zheng, Seminar at TsingHua University, Beijing, China 66/47 Upgrade magnets and power supplies CHL-2 Jlab 6 GeV 1212 Add new hall Enhance equipment in existing halls