Xiaochao Zheng, International Workshop on Positrons at JLab 1/64 C 3q Measurement Using Polarized e + /e - Beams at JLab – Introduction — Standard Model of Electroweak Interaction – Neutral Weak Coupling Constants – C 3q Measurements – Summary Xiaochao Zheng Univ. of Virginia March 27, 2009

Xiaochao Zheng, International Workshop on Positrons at JLab 2/64 Four Interactions of Our Nature Electron scattering has been widely used to study Structure of the nucleon — strong interactions, pQCD; (Recently) parity violation electron scattering: strange-quark content of the nucleon (elastic) Electroweak interactions (DIS)

Xiaochao Zheng, International Workshop on Positrons at JLab 3/64 Electroweak Interaction – Charged Currents 1932, charged pion and muon decay indicate a fourth type of interaction: Much longer than strong ( s) or electromagnetic ( s) decays 1932, based on QED, Fermi proposed: 1956, when Parity violation was first proposed (and test by experiments), the only modification needed is:

Xiaochao Zheng, International Workshop on Positrons at JLab 4/64 If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then if q 2 <<M W 2 then

Xiaochao Zheng, International Workshop on Positrons at JLab 5/ , with developement of n beams, found: cannot be explained by CC; magnitude of strength indicate Neutral Currents. Electroweak Interaction – Neutral Currents If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then

Xiaochao Zheng, International Workshop on Positrons at JLab 6/ , construct a SU(2) L group using charged currents, quantum number: Weak isospin T. Linear combination of the two is a neutral current, but it couples only to Left- handed fermions, while experimentally observed NC couples to both R- and L-handed, On the other hand, EM [U(1) g ] also couple to both R- and L-H fermions. Can combine NC from SU(2) L and U EM (1) g to construct: completes SU(2) L U(1) Y, Y: weak hyper charge

Xiaochao Zheng, International Workshop on Positrons at JLab 7/64

Xiaochao Zheng, International Workshop on Positrons at JLab 8/64 SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? ElectroWeak Standard Model Data exist: cannot be explained by the SM ( m n, NuTeV anomaly...); (250 GeV ~ 5 x GeV ~ 2.4 x GeV)?

Xiaochao Zheng, International Workshop on Positrons at JLab 9/64 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) (Can test pQCD)

Xiaochao Zheng, International Workshop on Positrons at JLab 10/64 Weak Interaction in DIS (Parity Violating DIS)

Xiaochao Zheng, International Workshop on Positrons at JLab 11/64 study hadron structure elastic scattering: strange form factors A4(MAINZ), G0, HAPPEX (JLab), SAMPLE (MIT/Bates) DIS: higher twist effects, charge symmetry violation... PVDIS test the electroweak standard model E158(SLAC), Qweak(JLab) Electromagnetic observables — , A... Weak observables — parity violating asymmetries ( A PV ) (polarized beam + unpolarized target) A PV = + Parity Violating Electron Scattering

Xiaochao Zheng, International Workshop on Positrons at JLab 12/64 SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? ElectroWeak Standard Model Data exist: cannot be explained by the SM ( m n, NuTeV anomaly...); (250 GeV ~ 5 x GeV ~ 2.4 x GeV)?

Xiaochao Zheng, International Workshop on Positrons at JLab 13/64 SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? indirect searches: E158, NuTeV, Qweak, PVDIS High energy direct searches: LEP, LHC Search for Physics beyond the Standard Model ElectroWeak Standard Model (250 GeV ~ 5 x GeV ~ 2.4 x GeV)?

Xiaochao Zheng, International Workshop on Positrons at JLab 14/64 Testing the EW Standard Model – Running of sin 2 q W and the NuTeV Anomaly (expected)

Xiaochao Zheng, International Workshop on Positrons at JLab 15/64 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, (2007) & priv. comm. new PDG2002 (best): (2C 2u -C 2d )=±0.24 Some New Physics can affect C 2q, but not C 1q

Xiaochao Zheng, International Workshop on Positrons at JLab 16/64 Current Knowledge on C 1,2q MIT/ Bates SLAC/Prescott Qweak ( expected ) R. Young (PVES) R. Young (combined) PDG best fit Cs APV PDG 2006 fit SAMPLE SLAC/ Prescott R. Young ( combined ) all are 1 s limit Best: PDG2002 D(2C 2u -C 2d ) = 0.24 C 2u +C 2d C 2u -C 2d C 1u -C 1d C 1u +C 1d Tl APV

Xiaochao Zheng, International Workshop on Positrons at JLab 17/64 Neutral Weak Couplings in Electron DIS A PV = + axial electron * vector quark : vector electron * axial quark :

Xiaochao Zheng, International Workshop on Positrons at JLab 18/64 Deuterium: PVDIS Asymmetries A PV = +

Xiaochao Zheng, International Workshop on Positrons at JLab 19/64 Deuterium: PVDIS Asymmetries A PV = + + g: coupling constant, L: mass limit, h A q : effective coefficient New physics sensitivity:

Xiaochao Zheng, International Workshop on Positrons at JLab 20/64 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:

Xiaochao Zheng, International Workshop on Positrons at JLab 21/64 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

Xiaochao Zheng, International Workshop on Positrons at JLab 22/64 PVDIS Asymmetries A PV = + Deuterium: Also sensitive to: quark-gluon correlations (higher-twist effects) Charge symmetry violation

Xiaochao Zheng, International Workshop on Positrons at JLab 23/64 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV However, hasn't been done since '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

Xiaochao Zheng, International Workshop on Positrons at JLab 24/64 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV However, hasn't been done since (Re)start PVDIS at JLab 6 & 12 GeV Difficulty: separate New Physics and hadronic effects 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

Xiaochao Zheng, International Workshop on Positrons at JLab 25/64 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV However, hasn't been done since 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 interation 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:

Xiaochao Zheng, International Workshop on Positrons at JLab 26/64 PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV However, hasn't been done since 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 interation 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

Xiaochao Zheng, International Workshop on Positrons at JLab 27/64 JLab 6 GeV Experiment 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 limit the 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) Co-spokesperson & contact: X. Zheng Co-spokesperson: P.E. Reimer, R. Michaels (Hall-A Collaboration Experiment, approved by PAC27, re-approved by PAC33 for 32 days, rated A-)

Xiaochao Zheng, International Workshop on Positrons at JLab 28/64 Current Knowledge on C 1,2q MIT/ Bates SLAC/Prescott Qweak ( expected ) R. Young (PVES) R. Young (combined) PDG best fit Cs APV PDG 2006 fit SAMPLE SLAC/ Prescott R. Young ( combined ) all are 1 s limit Best: D(2C 2u -C 2d ) = 0.24 C 2u +C 2d C 2u -C 2d C 1u -C 1d C 1u +C 1d Tl APV

Xiaochao Zheng, International Workshop on Positrons at JLab 29/64 C 2q from JLab E MIT/ Bates SLAC/Prescott Qweak ( expected ) R. Young (PVES) R. Young (combined) PDG best fit Cs APV PDG 2006 fit SAMPLE SLAC/ Prescott R. Young ( combined ) all are 1 s limit Best: D(2C 2u -C 2d ) = (factor of six improvement); New physics mass limit: C 2u +C 2d C 2u -C 2d C 1u -C 1d C 1u +C 1d Tl APV JLab E (PDG fit) JLab E (R. Young's fit)

Xiaochao Zheng, International Workshop on Positrons at JLab 30/64 Higher precision, possibly sensitive to 1) New Physics beyond the SM; 2) Charge Symmetry Violation (CSV) Two approaches (conditionally approved): Hall C “baseline” SHMS+HMS: PR (P.E. Reimer, X-C. Z, K. Paschke) 1% on A d, extraction of C 2q, sin 2 q W (if higher-twist and CSV are negligible); PVDIS Program at JLab 12 GeV Hall A large acceptance “solenoid” device: PR 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 q W ), HT and CSV possible; Extract d/u at large x from PVDIS on a proton target, free of nuclear effects; Other hadronic physics study possible: A 1 n at large x, Semi-inclusive DIS.

Xiaochao Zheng, International Workshop on Positrons at JLab 31/64 Hall A large acceptance “solenoid” device: PR 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 q W ), HT and CSV possible; Extract d/u at large x from PVDIS on a proton target, free of nuclear effects; Other hadronic physics study possible: A 1 n at large x, Semi-inclusive DIS. Higher precision, possibly sensitive to 1) New Physics beyond the SM; 2) Charge Symmetry Violation (CSV) Two approaches (conditionally approved): Hall C “baseline” SHMS+HMS: PR (P.E. Reimer, X-C. Z, K. Paschke) 1% on A d, extraction of C 2q, sin 2 q W (if higher-twist and CSV are negligible); PVDIS Program at JLab 12 GeV

Xiaochao Zheng, International Workshop on Positrons at JLab 32/64 Hall A large acceptance “solenoid” device: PR 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 q W ), HT and CSV possible; Extract d/u at large x from PVDIS on a proton target, free of nuclear effects; Other hadronic physics study possible: A 1 n at large x, Semi-inclusive DIS. Higher precision, possibly sensitive to 1) New Physics beyond the SM; 2) Charge Symmetry Violation (CSV) Two approaches (conditionally approved): Hall C “baseline” SHMS+HMS: PR (P.E. Reimer, X-C. Z, K. Paschke) 1% on A d, extraction of C 2q, sin 2 q W (if higher-twist and CSV are negligible); PVDIS Program at JLab 12 GeV

Xiaochao Zheng, International Workshop on Positrons at JLab 33/64 Measurement of neutron asymmetry A 1 n in the valence quark region at JLab 12 GeV Flagship experiment Will be one of the first experiments to run (~2014?) PVDIS at 12 GeV Ultimate goal: clean separation of New Physics and CSV (2015 or later?) Summary ( )