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Nuclear Physics at Jefferson Lab Part II

Nuclear Physics at Jefferson Lab Part II. R. D. McKeown Jefferson Lab College of William and Mary. Taiwan Summer School June 29, 2011. Outline. Strange Quarks Standard Model Tests Dark Matter?. Strange Quarks in the Nucleon. Strange quarks- antiquarks virtual pairs

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Nuclear Physics at Jefferson Lab Part II

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  1. Nuclear Physics at Jefferson Lab Part II R. D. McKeown Jefferson Lab College of William and Mary Taiwan Summer School June 29, 2011

  2. Outline • Strange Quarks • Standard Model Tests • Dark Matter?

  3. Strange Quarks in the Nucleon • Strange quarks-antiquarks virtual pairs • produced by gluons • Contribution to proton’s magnetism • - (Stern’s discovery)? • - QCD analog of Lamb shift in atoms • Study using small (few parts • per million) left-right difference • in electron-proton force •  challenging experiments!

  4. Strange Quarks in the Nucleon valence u u sea s s p-N scattering • Polarized deep-inelastic scattering n-p elastic scattering HERMES semi-inclusive u proton u d Mass: Spin:

  5. Electroweak charged fermion couplings

  6. Weak Charges • QWp = 1 – 4 sin2qW~ 0.071 • QWn = -1

  7. Neutral weak form factors • Neutral weak • interaction • Electromagnetic • interaction g Z0 GEZ,p, GMZ,p GAZ,p GEg,p, GMg,p p p

  8. Use Isospin Symmetry (p  n) = (u  d) For vector form factors theoretical CSB estimates indicate < 1% violations (unobservable with currently anticipated uncertainties) (Miller PRC 57, 1492 (1998) Lewis and Mobed, PRD 59, 073002(1999)

  9. Parity-violating electron scattering Z0 g g Polarized electrons on unpolarizedtarget 2 For a proton: (Cahn & Gilman 1978) Forward angles Backward angles

  10. Theoretical Approaches • Soliton, NJL, … • Dispersion Integrals • Lattice QCD (VMD)

  11. Theoretical predictions for ms

  12. SAMPLE Experiment Polarized Injector Beam position feedback Beam current feedback Lumi Wien Filter Position, Angle, Charge Halo SAMPLE Detector Beam Current K11 Moller Polarimeter Accelerator E = 125 MeV 600 pulses/s Ipk = 3 mA Iave = 44 A PB = 36% Energy Fast phase shift (energy) feedback

  13. Experimental procedure • Asymmetry between pulses separated by 1/60 sremove effects due to 60 Hz • Rapid helicity reversal  reduce effects of long-term drifts • Slow helicity reversal  remove helicity-correlated electronics effects

  14. SAMPLE result GMs(Q2=0.1) = 0.37 +- 0.20 +- 0.26 +- 0.07

  15. sTheory and Experiment

  16. Other Experiments HAPPEX @ JLAB A4 @ Mainz G0 @ JLAB

  17. Global Analysis

  18. Theory Update • Nucleon models continue to struggle, with some • indication that higher mass poles are important • Precise lattice QCD - motivated prediction: • (Leinweber, et al., PRL 97, 022001 (2006) • New unquenched lattice • QCD result: • Doi, et al., arXiv:0903.3232

  19. HAPPEX-III Results preliminary APV = -23.742 ± 0.776 (stat)± 0.353 (syst)ppm preliminary A(Gs=0) = -24.158 ppm± 0.663 ppm GsE + 0.52 GsM = 0.005 ± 0.010(stat) ± 0.004(syst)± 0.008(FF)

  20. Measuring the Neutron “Skin” in the PbNucleus Neutron Star Lead Nucleus 10 km 10 fm crust skin • Parity violating electron scattering • Sensitive to neutron distribution • First clean measurement • Relevant to neutron star physics • Currently running in Hall A

  21. Lead (208Pb) Radius Experiment : PREX Elastic Scattering Parity-Violating Asymmetry Z0 : Clean Probe Couples Mainly to Neutrons Applications : Nuclear Physics, Neutron Stars, Atomic Parity, Heavy Ion Collisions PREX PREX data Rel. mean field A neutron skin of 0.2 fm or more has implications for our understanding of neutron stars and their ultimate fate Nonrel. skyrme • The Lead (208Pb) Radius Experiment (PREX) determines the neutron radius to be larger than the proton radius by +0.35 fm (+0.15, -0.17). • This result represents model-independent confirmation of the existence of a neutron skin, with relevance for neutron star calculations. • Plans for follow-up experiment to reduce uncertainties by factor of 3. This can quantitatively pin down the symmetry energy, an important contribution to the nuclear equation of state.

  22. Running of the Weak Coupling

  23. Global Fits

  24. PV electron-quark couplings General Form: Standard model:

  25. Qweak Precise determination of the weak charge of the proton Qw= -2(2C1u+C1d) =(1 – 4 sin2qW) Luminosity monitors Luminosity monitors scanner

  26. Qweak Overview

  27. Qweak LH2Cryotarget • 35 cm target cell, designed with CFD • Target tested and stable up to 160 A. Sufficient reserve cooling power to easily reach 180 A. Highest power LH2 target. • When using 960Hz spin flip rate, the target density fluctuations (an unknown before commissioning) appear to be small compared to expected counting statistical uncertainty (per quartet) of ~220 ppm. Target cell

  28. Accelerator Performance for Qweak CEBAF delivered a record 170 mA at 89% polarization !

  29. Qweak Projection

  30. Radiative Correction Uncertainty (Ramsey-Musolf)

  31. Constraints on Couplings HAPPEx: H, He G0 (forward): H, PVA4: H SAMPLE: H, D projection

  32. PV Deep Inelastic Scattering e- e- * Z* X N a(x) and b(x) contain quark distribution functions fi(x) For an isoscalar target like 2H, structure functions largely cancel in the ratio at high x at high x At high x, APV becomes independent of x, W, with well-defined SM prediction for Q2 and y 0 New combination of: Vector quark couplings C1q Also axial quark couplings C2q 1 Sensitive to new physics at the TeV scale PVDIS: Only way to measure C2q

  33. SoLID Spectrometer Babar Solenoid Shashlyk Calorimeter Gas Cerenkov Baffles ANL design International Collaborators: China (Gem’s) Italy (Gem’s) Germany (Moller pol.) GEM’s JLab/UVA prototype

  34. Statistical Errors (%) Strategy: sub-1% precision over broad kinematic range for sensitive Standard Model test and detailed study of hadronic structure contributions Error bar σA/A (%) shown at center of bins in Q2, x 4 months at 11 GeV 2 months at 6.6 GeV

  35. Sensitivity: C1 and C2 Plots 6 GeV World’s data PVDIS Precision Data PVDIS Qweak Cs

  36. SoLID: Comprehensive PVDIS Study Strategy: requires precise kinematics and broad range Fit data to: C(x)=βHT/(1-x)3 • Measure AD in NARROW bins of x, Q2 with 0.5% precision • Cover broad Q2 range for x in [0.3,0.6] to constrain HT • Search for CSV with x dependence of AD at high x • Use x>0.4, high Q2, and to measure a combination of the Ciq’s

  37. PV Møller Scattering SLAC E158 result: APV= (-131 ± 14 ± 10) x 10-9

  38. E158 Result

  39. New JLab Experiment Polarized Beam • Unprecedented polarized luminosity • unprecedented beam stability Liquid Hydrogen Target • 5 kW dissipated power (2 X Qweak) • computational fluid dynamics Toroidal Spectrometer • Novel 7 “hybrid coil” design • warm magnets, aggressive cooling Integrating Detectors • build on Qweak and PREX • intricate support & shielding • radiation hardness and low noise

  40. Toroidal Spectrometer Separate Moller events from background Mollers e-p elastic

  41. Projected MOLLER Results Projected systematic error: dA/A = 1%

  42. Systematic Error Estimate

  43. INT EIC Workshop, Nov. 2010 Future PV Program at Jlab • PV Moller Scattering: • Custom Toroidal Spectrometer • 5kw LH Target • SOLID (PVDIS): • High Luminosity on LD2 and LH2 • Better than 1% errors for small bins • Large Q2 coverage • x-range 0.25-0.75 • W2> 4 GeV2

  44. INT EIC Workshop, Nov. 2010 Weak Mixing in the Standard Model JLab Future

  45. INT EIC Workshop, Nov. 2010 Beyond the Standard Model Kurylov, et al.

  46. INT EIC Workshop, Nov. 2010 Muon g-2 e Momentum Spin SUSY?

  47. INT EIC Workshop, Nov. 2010 On the horizon: A New Muon g-2 Experiment at Fermilab Goal: 0.14 ppm Future Goals Expected Improvement Update: Oct 2010: Dam(Expt – Thy) =297 ± 81 x 10-113.6 s x10-11 BNL E821 3.6 s 2010 e+e- Thy D. Hertzog

  48. R. D. McKeown June 15, 2010 Cosmology and Dark Matter • Dark sector is new physics, beyond the standard model • Many direct searches for dark matter interacting with • sensitive detectors (hints, no established signal yet…) • Controversial evidence for • excess astrophysical positrons… → many predictions for new physics

  49. Va. Tech. Physics Colloquium, Dec. 3, 2010 PAMELA Data on Cosmic Radiation Surprising rise in e+ fraction But not p • Could indicate low mass A’ (MA’ < 1 GeV ) • Or local astrophysical origin??

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