Strangeness in the Nucleon Kent Paschke University of Massachusetts EINN ‘05 September 24, 2005

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Strange Quarks in the Nucleon Strange Sea   measured in  N scattering Spin polarized DIS Inclusive:  s = ± 0.06 uncertainties from SU(3), extrapolation Semi-inclusive:  s = 0.03 ± 0.03 fragmentation function Strange vector FF Strange mass  N scattering: ~30% Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Flavor Separation of Nucleon Form Factors Measuring cannot separate all three flavors (assumes heavy quarks are negligible) Adding in a measurement of and assuming charge symmetry then we can write

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Accessing Weak Neutral Current Amplitude Interference with EM amplitude makes NC amplitude accessible Longitudinal spin asymmetry violates parity (polarized e -, unpolarized p):

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Parity-violating electron scattering ~ few parts per million For a proton: For 4 He: G E s alone (but only available at low Q 2 ) Forward angle Backward angle For deuterium: enhanced G A e sensitivity

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Instrumentation for PVES Large -Acceptance Detectors (G 0, A4)  Large kinematic range  Large Detected Background Spectrometer (HAPPEx)  Good background rejection  Small solid angle Cumulative Beam Asymmetry Helicity-correlated asymmetry  x~10 nm,  I/I~1 ppm,  E/E~100 ppb Helicity flips Fast: Pockels cell Slow: half-wave plate flips Need Highest possible luminosity High rate capability High beam polarization DetectorsIntegrating (HAPPEx) vs. Counting (G 0, A4)

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005  Beam helicity is chosen pseudo-randomly at 30 Hz Helicity state, followed by its complement Data analyzed as “pulse-pairs” Polarized Electron Source Optical Pumping HV Extraction and Injection calculated at 15Hz

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Controlling Systematic Uncertainty HAPPEX: Polarization monitored continuously with a Compton polarimeter. (Average ~88% with superlattice photocathode.) False Asymmetries Beam Asymmetries – Source laser control, careful measurement and correction Electronics pickup Background Asymmetries Normalization Polarimetry – continuous measurement/monitoring. Control of systematic error Linearity/Deadtime Background Dilution Polarimetry is dominant systematic error in two recent experiments

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Experimental Overview G M s, (G A ) at Q 2 = 0.1 GeV 2 SAMPLE HAPPEX G E s G M s at Q 2 = 0.48 GeV 2 G E s G M s at Q 2 = 0.1 GeV 2 G E s at Q 2 = 0.1 GeV 2 ( 4 He) Precision spectrometer, integrating A4 open geometry, integrating G E s G M s at Q 2 = 0.23 GeV 2 G E s G M s at Q 2 = 0.1 GeV 2 Open geometry Fast counting calorimeter for background rejection G0 G E s +  G M s over Q 2 = [0.12,1.0] GeV 2 G M s, G A e at Q 2 = 0.3, 0.5, 0.8 GeV 2 Open geometry Fast counting with magnetic spectrometer + TOF for background rejection

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Measure G M s at Q 2 ~0.1 GeV 2 Backward angle, H and 2 H at low Q 2 Air Cerenkov detector covers 2 sr from 130°-170° Analog integrating electronics for asymmetry measurement Pulse-Counting for background studies SAMPLE at MIT-Bates Theory prediction for anapole moment radiative correction. Result of Zhu et al for G A commonly used to constrain G S M result. G s M (Q 2 =0.1) = 0.37  0.20  0.26  0.07

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 HAPPEx-I in Hall A G E s G M s at Q 2 =0.48 GeV 2 High Resolution Spectrometers eliminate background Analog integration of Cerenkov calorimeter for asymmetry measurement Tracking for background/kinematics studies

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 HAPPEX-II: 1 H and 4 He 3 GeV beam in Hall A  lab ~ 6  Q 2 ~ 0.1 GeV 2 Septum magnets (not shown) High Resolution Spectrometers detectors targetA PV G s = 0 (ppm) Stat. Error (ppm) Syst. Error (ppm) sensitivity (proposed) 1H1H  (G E s +0.08G M s ) = He  (G E s ) = Cherenkov cones PMT Elastic Rate: 1 H: 120 MHz 4 He: 12 MHz Background ≤ 3% Brass-Quartz integrating detector Hall A at Jlab

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, HAPPEX-II Data A raw = ppm ±.71 ppm (stat) Short run (~ 5 days) Beam Polarization ~ 86% Beam asymmetries small Background f <3% Dense gas target A raw correction < 0.2 ppm Perfect sign-flip with /2 plate Raw Asymmetry (after beam corrections) ppm Helicity Window Pair Asymmetry A raw = ppm ± 0.20 ppm (stat) Hydrogen 4 He ~1/2 proposed time Beam asymmetries small A raw correction ~ 0.06 ppm Background f ~1% Beam Polarization ~ 80%

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 PVA4 at Mainz Calorimeter: 1022 PbF 2 crystals 20 cm LH 2 target 20  A, 80% polarized beam LuMo MAMI Microtron, 2000-present G E s +  G M s at Q 2 = 0.23, 0.1 GeV 2 Calorimeter distinguishes elastic via energy resolution, 0.8 sr from 30° to 40° Elastic rate: 10 MHz, total rate 100 MHz

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 G 0 Experiment in Hall C Measure forward and backward asymmetries –recoil protons for forward measurement: G E s, G M s –electrons for backward measurements: G M s, G A e Fast Counting/Magnetic spectrometer Forward measurements complete (2004) Back-angle measurements scheduled E beam = 3.03 GeV, GeV I beam = 40  A, 80  A P beam = 75%, 80%  = 52 – 76 0,  = 0.9 sr, 0.5 sr l target = 20 cm L = 2.1, 4.2 x cm -2 s -1 A ~ -1 to -50 ppm, -12 to -70 ppm

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 G 0 Forward-angle Measurement lead collimators elastic protons detectors target beam TOF used to ID elastic recoil protons Measurement of yield and asymmetry of spectrum used to deduce background fraction and asymmetry Acceptance Q 2 =[0.12, 1.0] GeV 2 for 3 GeV incident beam Time-of-flight measured over 32 ns beam bunch spacing Detector 15 acceptance: Q 2 =[0.44,0.88] GeV 2 subdivided by TOF Hear more tomorrow from Benoit Guillon

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 G 0 Backward Angle Electron detection Turn magnet/detector package around Add Cryostat Exit Detectors (“CEDs”) to define electron trajectory Add aerogel Cerenkovs to reject pions Begin Backward Angle installation in 2005 Planned measurements of H, 2 H Q.E. Combine with forward angle to separate G s E, G s M, G A at 2 or 3 Q 2 points Likely to run in 2006 at Q 2 ~0.3 GeV 2, Q 2 ~0.8 GeV 2

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Results

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Extrapolated from G0 Q 2 =[0.12,0.16] GeV 2 95% c.l.  2 = 1 World Data at Q 2 ~ 0.1 GeV 2 G E s = ± 0.29 G M s = 0.62 ± 0.32 Would imply that 7% of nucleon magnetic moment is Strange Note: excellent agreement of world data set Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Perspective at Q 2 ~ 0.1 GeV 2 1.Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992). 2.Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996). 3.Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, (1999). 4.Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, (2001). 5.Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, (2002). 6.Lattice - R. Lewis et al., Phys. Rev. D 67, (2003). 7.Lattice + charge symmetry - Leinweber et al, Phys. Rev. Lett. 94, (2005).  -K oscillation of proton would produce a positive G E s

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Anticipated Results from HAPPEX-II 2-3X improvement for each HAPPEX measurement Q 2 ~ 0.1 GeV 2 Experiment Running NOW Results available (early?) 2006 Result matching current central value: would convincingly establish a non-zero result would find G M s ~3  from zero

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 G 0 Forward - Measured Asymmetries “no vector strange” asymmetry, A NVS, is A(G E s, G M s = 0) inside error bars: stat, outside: stat & pt-pt Global error accounts for large background corrections f ~5-20%  A/A NVS ~40-60%

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 World Forward-angle Hydrogen Data  ~ Q 2 ) G0 Results are big news: Amplifies interesting low Q 2 structure Strong constraint at Q 2 ~0.2 GeV 2 Significant non-zero result at higher Q 2 G0G0

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Possible interpretation of G 0 results Fit world data set with dipole form for G M s and G E n -like behavior for G E s If not a statistical fluctuation, data implies large value of  s and strong Q 2 -variation of G E s Will be addressed by future measurements

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Future HAPPEx run PAC28 last month conditionally approved a new HAPPEx proposal to run at ~0.6 GeV 2 to obtain an unprecedented precision (2007?) Requires 1% polarimetry

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Prospective JLab Q 2 = 0.6, 0.23 GeV 2 G0 Run in March ’06 at Q 2 = ~0.6 GeV 2 G0 Run in Summer of ‘06 at Q 2 = ~0.23 GeV 2 HAPPEX-III Run at Q 2 = ~0.6 GeV 2 (not before 2007) Also, A4 at 0.23 GeV 2 or 0.5 GeV 2 ? G 0 Backward HAPPEX-III GMsGMs GEsGEs 0.6 GeV 2

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Summary GEsGEs 0.6 GeV 2 G0 backward HAPPEX-III GMsGMs Suggested large values at Q 2 ~0.1 GeV 2 HAPPEX-II, H and He running now! Possible large values at Q 2 >0.4 GeV 2 G 0 backangle, approved for Spring ’06 HAPPEX-III, conditionally approved ? A4 backangle? Large possible cancellation at Q 2 ~0.2 GeV 2 G 0 backangle, conditionally approved for Summer ’06 A4 backangle?

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Transverse Asymmetry

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Interest in A T A T is T-odd, P-even As a radiative correction, it is similar to other T-odd QED FSI that obscure measurements of nuclear  -decay, neutron  -decay, or other searches for T-odd, P-even interactions. Probe of nucleon structure Doubly virtual Compton scattering (VVCS) constrains interpretation from DVCS Dominated by spectrum of hadronic intermediate states Provides a clear and accessible window on the treatment of hadronic intermediate states in box diagrams. G E /G M is influenced by the real part of 2-  amplitude. A T is generated from the imaginary part of the 2-  amplitude. “elastic” “inelastic”

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 A T Data from 0.2 GeV-3 GeV SAMPLE “elastic” “single pion” sum hep-ph/ Pasquini & Vanderhaeghen Resonance region treated in a model incorporating pion electroproduction amplitudes A4 P&VdH HAPPEX (prelim) Afanasev and Merenkov, hep-ph/ Optical theorem: relate to  tot (  (*) p) Low Q 2 and very forward angle At fixed Q 2, flat with energy

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 A T at E158  (Azimuthal angle) 46 GeV ep  ep Sign: A T <0 Magnitude: ~2.5 ppm Without enhancement by inelastic states, A T ep ~ Q 2 ~ 0.06 GeV 2 46 GeV ee  ee backward angle Sign: opposite A T ep ? Magnitude: ~3.5 ppm

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 A T from Nuclei Afanasev Without inelastic states, Predicted value, ~10 -5 at 6 degrees, 3 GeV

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Backup

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 World Data at Q 2 ~ 0.1 GeV 2 Extrapolated from G0 Q 2 =[0.12,0.16] GeV 2 95% c.l.  2 = 1 G E s = ± G M s = 0.72 ± 0.40

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 LQCD prediction for  s with Charge Symmetry Leinweber et al. PRL 94, (2005) Use charge symmetry to relate valence quark magnetic dipole moments and loop contributions Use Lattice QCD only to calculate ratios of valence quark magnet dipole moments LQCD results in excellent agreement with measured octet magnetic moments  s = -(0.046  0.019)  N Lattice calculation

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Strange Vector FF and Lattice QCD Lattice - Lewis, Wilcox & Woloshyn PRD 67, (2003) Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, (2001).

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Extraction of SVFF from A PV Electromagnetic FF Axial FF (G A Z ) Including radiative corrections, A PV from hydrogen is: Axial FF:  (A PV ) = 0.33 ppm EMFF: dominated by G n M,  (A PV ) = 0.53 ppm Total:  (A PV ) = 0.62 ppm, 2.8%

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 Axial Form Factor Axial Form Factor: Uncertainty dominated by “anapole moment” [Zhu et al, 2000] Assume dipole FF, with M A = GeV  (G A Z ) ~ 0.12, E G0 Backward Angle  (G A Z ) ~ 0.14 Compatible with Phys. Rev. C 69, (2004) [Maekawa et al, 2000]  (A PV ) = 0.33 ppm

Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 EM Form Factors uncertainty  (A PV )/A PV GpMGpM 2%negligible GpEGpE 1.5%0.24 ppm GnEGnE 8%0.26 ppm GnMGnM 2%0.44 ppm Total 0.53 ppm But: 2-photon effects can complicate this picture at 2-4% level Experimental constraint: E in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q 2