C3q Measurement Using Polarized e+/e- Beams at JLab Xiaochao Zheng Univ. of Virginia March 27, 2009 Introduction — Standard Model of Electroweak Interaction Neutral Weak Coupling Constants C3q Measurements Summary

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)

Electroweak Interaction – Charged Currents 1932, charged pion and muon decay indicate a fourth type of interaction: π −. → μ −. ν μ ˉ τ=2.6× 10 −8 𝑠 μ −. → 𝑒 −. ν 𝑒 ˉ ν μ τ=2.2× 10 −6 𝑠 Much longer than strong (10-23 s) or electromagnetic (10-16 s) decays 1932, based on QED, Fermi proposed: 𝑀= 𝑒 𝑢 𝑝 ˉ γ μ 𝑢 𝑝   −1 𝑞 2  −𝑒 𝑢 𝑒 ˉ γ μ 𝑢 𝑒  =− 𝑒 2 𝑞 2  𝑗 μ 𝑒𝑚  𝑝  𝑗 𝑒𝑚,μ  𝑒 𝑀=𝐺  𝑢 𝑛 ˉ γ μ 𝑢 𝑝   𝑢 ν 𝑒 ˉ γ μ 𝑢 𝑒   𝑢 ν 𝑒 ˉ γ μ 𝑢 𝑒  1956, when Parity violation was first proposed (and test by experiments), the only modification needed is: γ μ → γ μ 1− γ 5

𝑀 𝐶𝐶 = 4G 2 𝐽 μ 𝐽 μ +. If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then 𝑀=  𝑔 2 𝑢 ˉ ν μ γ μ 1 2 1− γ 5 𝑢 μ  1 𝑀 𝑊 2 − 𝑞 2  𝑔 2 𝑢 ˉ e γ μ 1 2 1− γ 5 𝑢 ν 𝑒   𝑔 2 𝑢 ˉ e γ μ 1 2 1− γ 5 𝑢 ν 𝑒  𝐺 2 = 𝑔 2 8 𝑀 𝑊 2 if q2<<MW2 then

Electroweak Interaction – Neutral Currents 1973, with developement of n beams, found: ν ˉ μ 𝑒 −. → ν ˉ μ 𝑒 −. ν μ 𝑁→ ν μ 𝑋 ν ˉ μ 𝑁→ ν ˉ μ 𝑋 cannot be explained by CC; magnitude of strength indicate Neutral Currents. 𝑀 𝑁𝐶 = 4𝐺 2 2ρ 𝐽 μ 𝑁𝐶 𝐽 𝑁𝐶,μ 𝐽 μ 𝑁𝐶 ν = 1 2  𝑢 ˉ ν γ μ 1 2 1− γ 5 𝑢 ν  𝐽 μ 𝑁𝐶 𝑞 =  𝑢 ˉ 𝑞 γ μ 1 2 𝑐 𝑉 𝑞 − 𝑐 𝐴 𝑞 γ 5 𝑢 𝑞  If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then 𝑀=  𝑔 2 𝑢 ˉ ν μ γ μ 1 2 1− γ 5 𝑢 μ  1 𝑀 𝑊 2 − 𝑞 2  𝑔 2 𝑢 ˉ e γ μ 1 2 1− γ 5 𝑢 ν 𝑒   𝑔 2 𝑢 ˉ e γ μ 1 2 1− γ 5 𝑢 ν 𝑒 

while experimentally observed NC couples to both R- and L-handed, 1961, 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 UEM(1)g to construct: 𝑗 μ 𝑒𝑚 𝐽 μ 𝑁𝐶 ⇔ 𝐽 μ 3 𝑗 μ 𝑌 completes SU(2)L U(1)Y, Y: weak hyper charge 𝑄= 𝑇 3 + 𝑌 2

𝑊 μ 1 𝑊 μ 2 𝑊 μ 3 𝐵 μ ⇔ 𝑊 μ +. 𝑊 μ −. 𝐴 μ 𝑍 μ 𝐴 μ = 𝐵 μ cos θ 𝑊 + 𝑊 μ 3 sin θ 𝑊 𝑚=0 𝑍 μ =− 𝐵 μ sin θ 𝑊 + 𝑊 μ 3 cos θ 𝑊 𝑚≠0

ElectroWeak Standard Model SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? (250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)? Data exist: cannot be explained by the SM ( mn, NuTeV anomaly...);

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) 𝑄 2 = 2M 𝑇 𝑁 ν

Weak Interaction in DIS (Parity Violating DIS)

Parity Violating Electron Scattering Electromagnetic observables — s, A... Weak observables — parity violating asymmetries (APV) (polarized beam + unpolarized target) APV = + 𝐴 𝐿𝑅 ≡  𝑟 −  𝑙  𝑟   𝑙 ≈ 𝑄 2 𝑀 𝑍 2 ≈120𝑝𝑝𝑚 𝑎𝑡 𝑄 2 =1  𝐺𝑒𝑉 𝑐  2 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)

ElectroWeak Standard Model SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? (250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)? Data exist: cannot be explained by the SM ( mn, NuTeV anomaly...);

ElectroWeak Standard Model SM works well at present energy range; Conceptual reasons for new physics: What happens in the “high-energy desert”? High energy direct searches: LEP, LHC indirect searches: E158, NuTeV, Qweak, PVDIS (250 GeV ~ 5 x 1014 GeV ~ 2.4 x 1018 GeV)? Search for Physics beyond the Standard Model

Testing the EW Standard Model – Running of sin2qW and the NuTeV Anomaly (expected)

Current Knowledge on Weak Coupling Coeffecients 𝐶 1q = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑞 𝐶 2q = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑞 new PDG2002 (best): (2C2u-C2d)=±0.24 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. Some New Physics can affect C2q, but not C1q

Current Knowledge on C1,2q all are 1 s limit R. Young (combined) PDG best fit SAMPLE PDG 2006 fit C2u+C2d 1.25 1.5 1.75 1.0 0.75 0.5 0.25 -0.5 -0.75 C2u-C2d - 0.2 0.4 0.2 - 0.4 0.10 0.125 0.15 0.175 C1u-C1d - 0.4 - 0.6 - 0.8 C1u+C1d SLAC/ Prescott Tl APV Cs APV R. Young (PVES) Qweak (expected) R. Young (combined) MIT/ Bates SLAC/Prescott Best: PDG2002 D(2C2u-C2d) = 0.24

Neutral Weak Couplings in Electron DIS APV = + 1 2  𝑒 ˉ γ μ 𝑔 𝑉 𝑒 − 𝑔 𝐴 𝑒 γ 5 𝑒  𝑒 ˉ γ μ 𝑔 𝑉 𝑒 − 𝑔 𝐴 𝑒 γ 5 𝑒 1 2  𝑞 ˉ γ μ 𝑔 𝑉 𝑞 − 𝑔 𝐴 𝑞 γ 5 𝑞  𝑞 ˉ γ μ 𝑔 𝑉 𝑞 − 𝑔 𝐴 𝑞 γ 5 𝑞 axial electron * vector quark : 𝐿 𝑆𝑀 𝑃𝑉 = − 𝐺 𝐹 2 𝑒 ˉ γ μ γ 5 𝑒 𝑞 𝐶 1q 𝑞 ˉ γ μ 𝑞 vector electron * axial quark : 𝐿 𝑆𝑀 𝑃𝑉 = − 𝐺 𝐹 2 𝑒 ˉ γ μ 𝑒 𝑞 𝐶 2q 𝑞 ˉ γ μ γ 5 𝑞 𝐶 1u = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑢 =− 1 2 + 4 3 sin 2 θ 𝑊 𝐶 2u = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑢 =− 1 2 +2 sin 2 θ 𝑊 𝐶 2d = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑑 = 1 2 −2 sin 2 θ 𝑊 𝐶 1d = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑑 = 1 2 − 2 3 sin 2 θ 𝑊

PVDIS Asymmetries + APV = Deuterium: 𝐴 𝑑 = 540𝑝𝑝𝑚 𝑄 2 2 𝐶 1u 1+ 𝑅 𝐶 𝑥 − 𝐶 1d 1+ 𝑅 𝑆 𝑥 +𝑌 2 𝐶 2u − 𝐶 2d 𝑅 𝑉 𝑥 5+ 𝑅 𝑆 𝑥 +4 𝑅 𝐶 𝑥

PVDIS Asymmetries APV = + + Deuterium: New physics sensitivity: 𝐴 𝑑 = 540𝑝𝑝𝑚 𝑄 2 2 𝐶 1u 1+ 𝑅 𝐶 𝑥 − 𝐶 1d 1+ 𝑅 𝑆 𝑥 +𝑌 2 𝐶 2u − 𝐶 2d 𝑅 𝑉 𝑥 5+ 𝑅 𝑆 𝑥 +4 𝑅 𝐶 𝑥 New physics sensitivity: 𝐿= 𝐿 𝑆𝑀 𝑃𝑉 + 𝐿 𝑁𝐸𝑊 𝑃𝑉 𝐿 𝑆𝑀 𝑃𝑉 = − 𝐺 𝐹 2 𝑒 ˉ γ μ 𝑒 𝑞 𝐶 2q 𝑞 ˉ γ μ γ 5 𝑞 𝐿 𝑁𝐸𝑊 𝑃𝑉 = 𝑔 2 4 Λ 2 𝑒 ˉ γ μ 𝑒 𝑓 ℎ 𝐴 𝑞 𝑞 ˉ γ μ γ 5 𝑞 g: coupling constant, L: mass limit, hAq: effective coefficient

PVDIS Asymmetries APV = + + Deuterium: New physics sensitivity: 𝐴 𝑑 = 540𝑝𝑝𝑚 𝑄 2 2 𝐶 1u 1+ 𝑅 𝐶 𝑥 − 𝐶 1d 1+ 𝑅 𝑆 𝑥 +𝑌 2 𝐶 2u − 𝐶 2d 𝑅 𝑉 𝑥 5+ 𝑅 𝑆 𝑥 +4 𝑅 𝐶 𝑥 New physics sensitivity: 𝐿= 𝐿 𝑆𝑀 𝑃𝑉 + 𝐿 𝑁𝐸𝑊 𝑃𝑉 𝐿 𝑆𝑀 𝑃𝑉 = − 𝐺 𝐹 2 𝑒 ˉ γ μ 𝑒 𝑞 𝐶 2q 𝑞 ˉ γ μ γ 5 𝑞 𝐿 𝑁𝐸𝑊 𝑃𝑉 = 𝑔 2 4 Λ 2 𝑒 ˉ γ μ 𝑒 𝑓 ℎ 𝐴 𝑞 𝑞 ˉ γ μ γ 5 𝑞 g: coupling constant, L: mass limit, hAq: effective coefficient Sensitive to: Z' searches, compositeness, leptoquarks Mass limit: ≈ 8 𝐺 𝐹 ∣Δ 2 𝐶 2u − 𝐶 2d ∣ −1 2

PV DIS and Other SM Test Experiments E158/Moller (SLAC) Atomic PV NuTeV (FNAL) Weak CC and NC difference Nuclear structure? Other hadronic effects? Purely leptonic Coherent Quarks in the Nucleus - 376C1u - 422C1d Nuclear structure? Qweak (JLab) PVDIS (JLab) Different Experiments Probe Different Parts of Lagrangian, PVDIS is the only one accessing C2q 2 (2C1u+C1d) Coherent quarks in the proton (2C1u-C1d)+Y(2C2u-C2d) Isoscalar quark scattering Cartoons borrowed from R. Arnold (UMass)

PVDIS Asymmetries APV = + Deuterium: Also sensitive to: 𝐴 𝑑 = 540𝑝𝑝𝑚 𝑄 2 2 𝐶 1u 1+ 𝑅 𝐶 𝑥 − 𝐶 1d 1+ 𝑅 𝑆 𝑥 +𝑌 2 𝐶 2u − 𝐶 2d 𝑅 𝑉 𝑥 5+ 𝑅 𝑆 𝑥 +4 𝑅 𝐶 𝑥 𝑅 𝑉 𝑥 = 𝑢 𝑉 𝑥 + 𝑑 𝑉 𝑥 𝑢 𝑥 + 𝑢 ˉ 𝑥 +𝑑 𝑥 + 𝑑 ˉ 𝑥 𝑅 𝑆 𝑥 = 2 𝑠 𝑥 + 𝑠 ˉ 𝑥 𝑢 𝑥 + 𝑢 ˉ 𝑥 +𝑑 𝑥 + 𝑑 ˉ 𝑥 𝑅 𝐶 𝑥 = 2 𝑐 𝑥 + 𝑐 ˉ 𝑥 𝑢 𝑥 + 𝑢 ˉ 𝑥 +𝑑 𝑥 + 𝑑 ˉ 𝑥 Also sensitive to: quark-gluon correlations (higher-twist effects) Charge symmetry violation 𝑢 𝑝 𝑥 ≠ 𝑑 𝑛 𝑥 𝑑 𝑝 𝑥 ≠ 𝑢 𝑛 𝑥

PVDIS Experiment – Past, Present and Future 1970's, result from SLAC E122 consistent with sin2qW=1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV ...... However, hasn't been done since 1978.

PVDIS Experiment – Past, Present and Future 1970's, result from SLAC E122 consistent with sin2qW=1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) PVDIS asymmetry has the potential to explore New Physics, study hadronic effects/CSV ...... However, hasn't been done since 1978. (Re)start PVDIS at JLab 6 & 12 GeV Difficulty: separate New Physics and hadronic effects

PVDIS Experiment – Past, Present and Future 1970's, result from SLAC E122 consistent with sin2qW=1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) 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 interation is worse than we thought. New electroweak Physics Non-perturbative QCD (higher-twist) effects Charge symmetry violation At the 6 GeV precision: Likely to be small, but need exp confirmation Small from MRST fit (90% CL ~1%)

PVDIS Experiment – Past, Present and Future 1970's, result from SLAC E122 consistent with sin2qW=1/4, established the Electroweak Standard Model; C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978) 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 interation is worse than we thought. 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.

JLab 6 GeV Experiment 08-011 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-) 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 Ad at Q2=1.10 and 1.90 GeV2 to 2.7% (stat.); Ad at Q2=1.10 will limit the higher twist effects; If HT is small, can extract 2C2u-C2d from Ad at Q2=1.90 to ±0.04 (or with reduced precision if higher twists are un-expectedly large)

Current Knowledge on C1,2q all are 1 s limit R. Young (combined) PDG best fit SAMPLE PDG 2006 fit C2u+C2d 1.25 1.5 1.75 1.0 0.75 0.5 0.25 -0.5 -0.75 C2u-C2d - 0.2 0.4 0.2 - 0.4 0.10 0.125 0.15 0.175 C1u-C1d - 0.4 - 0.6 - 0.8 C1u+C1d SLAC/ Prescott Tl APV Cs APV R. Young (PVES) Qweak (expected) R. Young (combined) MIT/ Bates SLAC/Prescott Best: D(2C2u-C2d) = 0.24

C2q from JLab E08-011 all are 1 s limit R. Young (combined) PDG best fit SAMPLE PDG 2006 fit C2u+C2d 1.25 1.5 1.75 1.0 0.75 0.5 0.25 -0.5 -0.75 C2u-C2d - 0.2 0.4 0.2 - 0.4 0.10 0.125 0.15 0.175 C1u-C1d - 0.4 - 0.6 - 0.8 C1u+C1d SLAC/ Prescott Tl APV Cs APV R. Young (PVES) JLab E08-011 (PDG fit) Qweak (expected) R. Young (combined) JLab E08-011 (R. Young's fit) MIT/ Bates SLAC/Prescott Best: D(2C2u-C2d) = 0.24 0.04 (factor of six improvement); New physics mass limit: → ≈ 8 𝐺 𝐹 ∣Δ 2 𝐶 2u − 𝐶 2d ∣ −1 2 ≈0.9TeV

PVDIS Program at JLab 12 GeV 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: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke) 1% on Ad, extraction of C2q, sin2qW (if higher-twist and CSV are negligible); Hall A large acceptance “solenoid” device: PR09-012 Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of New Physics (via C2q and sin2qW), 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: A1n at large x, Semi-inclusive DIS.

PVDIS Program at JLab 12 GeV 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: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke) 1% on Ad, extraction of C2q, sin2qW (if higher-twist and CSV are negligible); Hall A large acceptance “solenoid” device: PR09-012 Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of New Physics (via C2q and sin2qW), 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: A1n at large x, Semi-inclusive DIS.

PVDIS Program at JLab 12 GeV 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: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke) 1% on Ad, extraction of C2q, sin2qW (if higher-twist and CSV are negligible); Hall A large acceptance “solenoid” device: PR09-012 Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of New Physics (via C2q and sin2qW), 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: A1n at large x, Semi-inclusive DIS.

Summary (2013 - ) Measurement of neutron asymmetry A1n 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?)