My involvement in the Spin and Parity Programs at JLab, and beyond Xiaochao Zheng October 1, 2010 Introduction — nucleon structure and electron scattering Three types of Deep Inelastic Scattering (DIS) and some completed/future experiments at JLab Research opportunities What does it take to achieve a Ph.D.?
Exploring Nucleon Structure Using EM Probe k ' = E', k ' 2 = P' 2 W q = , q 2 =− q 2 Q k = E, k P = M, 0 The cross section: d 2 = Mott [ F 1 Q 2 , F 2 Q 2 , ] d dE' For point-like target
Exploring Nucleon Structure Using EM Probe (cont.) ➔ Elastic – the nucleus appears 2 = 2 M T as a rigid body Q ➔ Quasi-elastic – individual nucleon appears as a rigid body; nucleus = incoherent 2 = 2 M N Q sum of nucleons Nucleon form factors well measured (quasi-) elastic — rigid body
Exploring Nucleon Structure Using EM Probe (cont.) ➔ Resonance region – quarks inside the nucleon react coherently 1 W 2 GeV 1 W 2 GeV resonances — certain excitations of the internal structure For resonances, typically use phenomenological models to study N-N* transition amplitudes and polarizations.
Exploring Nucleon Structure Using EM Probe (cont.) Deep Inelastic Scattering (DIS): Quarks start to react incoherently Start to see constituents of the nucleon For DIS, perturbation theory starts to work, can test perturbative QCD.
Current Knowledge of Nucleon Unpolarized Structure (after 40 years of study) d 2 = Mott [ F 1 Q 2 , F 2 Q 2 , ] d dE' ● Phys. Rev. D 66, 010001 (2002)
Current Knowledge of Nucleon Unpolarized Structure (after 40 years of study) F 1 x = 1 e i 2 [ q i x ] 2 in the Quark-Parton Model and the infinite momentum frame (IMF) (P → ∞) After 39 years of DIS experiments, the unpolarized structure of the nucleon is reasonably well understood (for moderate x Bj region).
Polarized DIS (1980~present) Scattering cross section is spin-dependent (imaging throwing two small magnets together) N S N S N S S N vs. Longitudinal 2 2 d − d ∝ point − like [ ' g 1 x ,Q 2 ' g 2 x ,Q 2 ] d dE ' d dE' Transverse 2 2 d − d ∝ point − like [ ' ' g 1 x ,Q 2 ' ' g 2 x ,Q 2 ] d dE ' d dE'
Polarized Structure Function and the Nucleon Spin Structure in QPM and the infinite momentum frame: g 1 x = 1 x ] = 1 x − q i e i 2 [ q i e i 2 [ q i x ] 2 2 The integral of g 1 (x) over x describes how much of the nucleon's spin is carried by quarks' spin
But do we really understand strong interaction? To do this, we must understand the nucleon structure from the theory of strong interaction (QCD). 4 S Q 2 = 11 − 2 n f / 3 ln Q 2 / 2 Because strong interaction is highly non-perturbative, it is very difficult to predict the value of structure functions from QCD.
Data vs. Theory – How do we test QCD? For most cases, QCD cannot predict the value of structure functions because of their non-perturbative nature. However, the large x region provides a handful of exceptions: p /F 2 n and d/u At large x, valence quarks F 2 dominate, a relatively p , A 1 n , or ∆ u/u and ∆ d/d A 1 clean/easy region to study/model the nucleon Virtual photon 1 / 2 − 3 / 2 A 1 = asymmetry: 1 / 2 3 / 2 2 g 2 2 x g 1 − 2 g 1 2 2 = Q 2 = 4 M A 1 = ≈ .at large Q 2 2 F 1 F 1 Q
The 6 GeV Hall A Measurement (21 PAC days, 2001) (1) (2) (5) (6) (6) (3) (3) (4) (4) (1) SU(6) (2) (2) CQM CQM (2) (3) LSS(BBS) HHC not valid, (7) (4) BBS quark OAM? (5) Bag (8) Model (6) Duality (1) (7) LSS 2001 (2) (8) Statistical (9) Model (9) Chiral Soliton (4) (1) (Deutron data not shown: E143, E155, SMC) (3) (1)CQM (2)LSS(BBS):pQCD+HHC X. Zheng et al ., Phys. Rev. Lett. 92, 012004 (2004); (3)Statistical Model (4)LSS 2001 Phys. Rev. C 70, 065207 (2004)
Polarized DIS and Nucleon Spin Structure H. Avakian, S. Brodsky, A. Deur, F. Yuan, Phys. Rev. Lett.99:082001(2007) Figure credit: A. Deur
Future Experiments after the 11 GeV JLab Upgrade Fully approved in August 2010, rated A. There are in fact two experiments, one in Hall A, one in Hall C.
Expected Results Combined results from Hall C (neutron) and B (proton) 11 GeV experiments
Parity Violating DIS EM observables — σ , A ... (polarized beam + polarized target) hadron structure, strong interaction and its standard model (QCD); Weak observables — parity violating asymmetries ( A PV ) N S S N (polarized beam + unpolarized target) vs. A LR ≡ r − l 2 l ≈ Q 2 ≈ 120 ppm r M Z 2 = 1 GeV / c 2 at Q study hadron structure elastic scattering: strange form factors A4, G0, HAPPEX, SAMPLE DIS: non-perturbative effects, CSV etc... PVDIS test the standard model of electro-weak interaction Qweak
Test of EW Standard Model Using PVDIS For a deuterium target 2 2 C 1u [ 1 R C x ]− C 1d [ 1 R S x ] Y 2 C 2u − C 2d R V x A d = 540 ppm Q 5 R S x 4R C x u =− 1 u =− 1 4 e g V e g A C 1u = g A 2 W C 2u = g V 2sin 2 W sin 2 2 3 d = 1 e g A d = 1 − 2 e g V C 2d = g V − 2 sin 2 W C 1d = g A 2 W sin 2 2 3 From A d can extract C 1,2q and sin 2 θ W . In the SM, tree level 1970's, result from SLAC E122 consistent with sin 2 θ W = 1/4, confirmed the Standard Model prediction; Development in experimental technique allows to search for new physics
JLab 6 GeV Experiment 08-011 Co-spokesperson & contact: X. Zheng Co-spokesperson: P.E. Reimer, R. Michaels Students: Diancheng Wang, Xiaoyan Deng, Huaibo Ding, Kai Pan postdoc: Ramesh Subedi E08-011 ran Oct-Dec 2009 Used 105 µ A, 6 GeV, 85% polarized beam on a 20-cm LD2 target; Two Hall A High Resolution Spectrometers detect scattered electrons; Customerized DAQ built by UVa group Measure A d at Q 2 =1.10 and 1.90 GeV 2 to about 3-4 % (stat.); ● ANL, Calstate, FIU, Jlab, Kentucky, U. of Ljubljana (Slovenia), MIT, UMD, UMass, UNH, Universidad Nacional Autonoma de Mexico, Rutgers, Smith C., Syracuse, UVa, W&M
all are 1 σ limit Current Knowledge on C 1,2q R. Young PDG best fit SAMPLE (combined) 1.75 0.175 1.5 Tl APV 1.25 SLAC/ Prescott 1.0 0.15 R. Young Cs APV 0.75 (PVES) C 1d C 2u +C 2d 0.5 + C 1u 0.25 0.125 Qweak 0 ( expected ) 0.25 MIT/ Bates -0.5 PDG best fit 0.10 SLAC/Prescott -0.75 - 0.8 - 0.6 - 0.4 - 0.5 - 0.25 0 0.25 0.5 C 2u -C 2d C 1u -C 1d Best: ∆ (2C 2u -C 2d ) = 0.24
all are 1 σ limit The 6 GeV E08-011 R. Young PDG best fit SAMPLE (combined) 1.75 0.175 1.5 Tl APV 1.25 SLAC/ Prescott 1.0 0.15 R. Young Cs APV 0.75 C 1d (PVES) C 2u +C 2d 0.5 + C 1u 0.25 0.125 Qweak 0 ( expected ) 0.25 MIT/ Bates -0.5 PDG best fit 0.10 SLAC/Prescott -0.75 - 0.8 - 0.6 - 0.4 - 0.5 - 0.25 0 0.25 0.5 C 2u -C 2d C 1u -C 1d Best: ∆ (2C 2u -C 2d ) = 0.24 Expected: JLab 6 GeV PV-DIS E08-011 (assuming small hadronic effects and a 4% stat error on Ad)
PVDIS Program at JLab 12 GeV Two approaches: Hall C “baseline” SHMS+HMS: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke, 1% on A d , extraction of C 2q , sin 2 θ W (if higher-twists and CSV are negligible); Hall A large acceptance “solenoid” device: PR09-012 (conditionally approved) Measure A d to 1% for a wide range of (x,Q 2 ,y), clean separation of New Physics (via C 2q and sin 2 θ W ), HT and CSV possible; Extract d/u at large x from PVDIS on a proton target, free of nuclear effects; n at large x, Semi-inclusive DIS. Other hadronic physics study possible: A 1
PVDIS Program at JLab 11 GeV Two approaches: Hall C “baseline” SHMS+HMS: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke) 1% on A d , extraction of C 2q , sin 2 θ W (if higher-twist and CSV are negligible); Hall A large acceptance “solenoid” device: PR10-007 fully approved Measure A d to 1% for a wide range of (x,Q 2 ,y), clean separation of New Physics (via C 2q and sin 2 θ W ), HT and CSV possible; Extract d/u at large x from PVDIS on a proton target, free of nuclear effects; n at large x, Semi-inclusive DIS. Other hadronic physics study possible: A 1
Projected PVDIS Measurement with SOLID@11 GeV figure from K. Kumar, Seattle 2009 EIC Workshop EW talks
Projected PVDIS Measurement with SOLID@11 GeV figure from K. Kumar, Seattle 2009 EIC Workshop EW talks
Research Opportunities Ongoing 6 GeV Physics Program n in the valence quark Measurement of neutron asymmetry A 1 region at JLab 12 GeV Flagship experiment May be one of the first experiments to run (~2014?) SOLID program (2015 or later) PVDIS at 11 GeV — ultimate goal: clean separation of New Physics and CSV n , d/u measurements, SIDIS, etc. A 1
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