Parity Violating Electron Scattering in Resonance region (Res-Parity)

1. Parity Violating Electron Scattering in Resonance region (Res-Parity) (P05-xxx) P. Bosted, Hall A meeting, June 2005 • Physics Overview • Motivation • Experiment • Count rates and Errors • Expected Results • Request • Summary: “Easy” experiment, never done before, relevant to wider community

2. PARITY VIOLATING ASYMMETRY Electron can scatter off of proton by exchanging either a virtual photon or a Z0 e’ e g e’ e Z0 + P P • The cross section in terms of electromagnetic, weak and interference contribution • Asymmetry due to interference between Z0 and g

3. Deep Inelastic asymmetry In the Standard Model and assuming quark degrees of freedom, at LO In the valence region, for a proton target: ≈1-0.75x

4. Resonance region asymmetry • For a resonance ARL can be written in terms of response functions • Isospin symmetry relates weak and EM vector current • Enchanced d,s quark contributions • Sensitive to axial hadronic current also Details have so far been worked out only for N→∆(1232) sensitive to axial vector transition form factor

5. A Simple Model • sin2qW = 0.25 ->axial current suppressed • Isospin symmetry • Negligible strange and charm form factors Assume DEUTERON PROTON r(W) depends on (I=0)/(I=1) r(W) • Different dependencies in the resonant and DIS cases • Resonant case the current is expressed through the square of the sum over parton charges • DIS case the sum of the square gives the current

6. QUARK-HADRON DUALITY • In QCD can be understood from an OPE of moments of structure functions Duality is described in OPE as higher twist (HT) effects being small or cancelling For spin-averaged structure function, duality works remarkably well to low values of Q2

7. DUALITY for the gamma-Z interference tensor ? •Leading order criteria Simple Model •Duality is satisfied if on averagesn/sp = 2/3 PROTON • Average of the D(1232) and the elastic peak tend to equal the DIS curve • Higher resonances oscillate around the DIS curve DIS model Resonance model DATA NEEDED!

8. PHYSICS MOTIVATION • Provide the first measurements of the parity violating asymmetries over the full resonance region for proton, deuteron, and carbon. • Explore both global and local quark-hadron duality with the previously un-studied combination of structure functions • Sensitive to down and strange quark currents • Sensitive to axial hadronic current

9. PHYSICS MOTIVATION • The results are of practical importance : • Modeling neutrino cross sections needed for neutrino oscillation experiments. • Understanding backgrounds and radiative corrections for other PV experiments (E05-007 in near future) • Understanding the role of higher twist effects • If duality is verified small higher • twist effects

10. NEUTRINO OSCILLATION • Major world-wide program to study neutrino mass, mixing • Interpretation needs neutrino cross sections in few GeV region on various nuclei (proton, oxygen, steel, …) • Neutrino beams not monochromatic, flux hard to measure: direct cross section measurements problematic • Rely on models. Res-Parity will constrain models (especially d,s quark currents, axial hadronic current, and nuclear dependence: is EMC effect same for u and d quarks?).

11. BACKGROUND IN E158 • SLAC E158 measured PV in Moller scattering, with large systematic error from low Q2 ep background • Res-PV will constrain models used to estimate the background • Result is improved confidence in the important E158 limits on physics beyond the Standard Model

12. Experimental Setup Target density fluctuation & other false asym monitored by the Luminosity Monitor C, 25-cm LD2, LH2 targets (highest cooling power) Pol e- beam, 4.8 GeV, 80 uA, 80%, DPb/Pb= 1.2% Electrons detected by the two HRS independently Beam intensity asymmetry controlled by parity DAQ Fast counting DAQ handle up to 1MHz rate with 103 pion rej.

13. KINEMATICS AND RATES for LD2 target x Y Q2 E’ W2p/e MHz dA/A 0.175 0.50 0.6 2.8 3.9 0.6 0.8 4.5 0.245 0.39 0.7 3.2 3.1 0.2 0.9 4.0 0.359 0.29 0.8 3.6 2.3 0.0 1.0 3.8 0.575 0.19 0.9 4.0 1.5 0.0 1.2 3.2 • Rates similar to E05-007. • Pion/electron ratio smaller • Run low E’ settings in one HRS, high E’ in other

14. New Instruments and/or Upgrades Compton polarimeter: will use green laser (in progress); expect to achieve DPb/Pb= 1.1% for electron analysis method; 25-cm long racetrack-shaped LH2/LD2 cell, 2.5 gm/cm2 C target (as used in Hall C) FADC-based and scaler-based fast counting DAQs, both being developed by the E05-007 (PVDIS) collaboration.

15. PROJECTED STATISTICAL ERRORS • Relative error of 5% to 10% per bin • Local duality (3 resonance regions) tested at 4% level • Global duality (whole region) tested at 2% level • Ratio of proton/deuteron (d/u) and C/deuteron (EMC effect) tested to 3% level

16. SYSTEMATIC ERRORS The ratio of asymmetries on hydrogen or C to deuterium is almost free of experimental systematic errors, allowing a very precise comparison with theory

17. REQUEST

18. REQUEST (continued) • Electronics same as E05-007 • Compton polarimeter as for E05-007 • High beam polarization, moderately good beam stability and charge asymmetry (less stringent than Happex or G0)

19. COLLABORATION • Experience in PV (E158, Happex, G0) • Augments E05-007 (DIS-PV: more people to develop needed equipment

20. SUMMARY • FIRST weak current measurements in full resonance region. Surprises possible. • Measure Ap, Ad, and AC for M < W < 2.2 GeV and <Q2> = 0.8 GeV2 • Relatively easy (for PV) experiment using same equipment as E05-007 • Emphasizes d-quark contributions, sensitive to strangeness and axial hadronic current • New regime for study of duality, higher twist effects, and EMC effect • Needed to constrain models, which in turn are used for neutrino oscillation studies, backgrounds to experiments like SLAC E158, radiative corrections for DIS-parity experiments.

21. BACKUP SLIDES

22. DAQ: Comparison of two options • FADC-based: • Is what we eventually need (12 GeV program) • Full event sampling for detailed off-line analysis; • If there is a highly-rated experiment, 2 years is possible. • Scaler-based: • Similar to previous SLAC, and current Hall C scalers; • Mostly work for the electronics group, easy to do; • Still, need extra man-power and cost; • Specialized; • Only scaler info is recorded (on-line PID critical).

23. FADC-based Fast Counting DAQ

24. Scaler Electronics-based Fast Counting DAQ

25. RELATION TO PR05-007 • Complementary: lower W and Q2 • Study HT lower Q2 near W=2 GeV, effects bigger • Both proton and deuteron used • Information needed for precision DIS-Parity to accurately calculate radiative corrections and constrain HT.

26. COLLABORATION W. Boeglin, P Markowitz Florida International University, Miami, FL C Keppel Hampton University, Hampton VA G. Niculescu, I Niculescu James Madison University, Harrionburg, VA P. E. Bosted (spokesperson), V. Dharmawardane (co-spokesperson), R. Ent, D. Gaskell, J. Gomez. M. Jones, D. Mack, R. Michaels, J. Roche, B. Wojtsekhowski Jefferson Lab, Newport News, VA T. Forest, N. Simicevic, S. Wells Louisiana Tech University, Ruston, LO K. Kumar, K. Paschke University of Massachusetts, Amherst, MA F. R. Wesselmann Norfolk state university, Norfolk, VA Yongguang Liang, A. Opper Ohio state university, Athens, OH P. Decowski Smith College, Northampton, MA R. Holmes, P. Souder University of Syracuse, Syracuse, NY S. Connell, M. Dalton University of Witwatersrand, Johannesburg, South Africa R. Asaturyan, H. Mkrtchyan (co-spokesperson), T. Navasardyan, V. Tadevosyan Yerevan Physics Institute, Yerven, Armenia

27. Pion Background • p/e ratio ranges 0.005 to 1.2 : average about 0.2 • p signal ~20x smaller than electron signal : net contamination average is 1% • Pion asymmetry measured in 4th layer lead glass (lead between 3rd and 4th layers to fill electron signal). Expect < 1ppm based on SLAC experiment

28. Kinematic Determination of Q2 • dA/A proportional to dQ2/Q2 • From standard HMS uncertainties of q and 0.1% in E’, central Q2 determined to 0.8% • Uncertainties in target, beam, collimater and quadrupole positions increase uncertainty in measured Q2 to 1% • Will be checked using normal counting mode at low beam current

29. RADIATIVE CORRECTIONS Un-radiated to radiated spin averaged cross section Determined by the x, Q2 dependence of F2 • The ratio of radiated to un-radiated ed parity violating asymmetry (Rp ) is close to unity → Shape and magnitude of Rp determined by the probablity for an electron to radiate a hard photon • Radiative corrections for Ap will be determined by an iterative fit to the data of this proposal •systematic error in Ap < 1%

30. SFs for the interference tensor ARL in terms of structure functions for the interference tensor of EM and weak currents Proportional to the weak interaction W1 W2 W3 Well measured • Can be use to study parity violating part of the weak neutral current • Depending on the isospin of the final excited state the interference cross section is expected to show a resonance structure ARL can be used to test duality for a linear combination of W1,2,3

31. OTHER PV EXPPERIMENTS • Most electron PV experiments have focused on elastic channels • •SAMPLE at BATES, HAPPEX and G0 at Jlab, A4 at Mainz • probe the strange quark form factors of the nucleon •Qweak at Jlab searching for physics beyond the standard Model • G0 plan to study N-D transition No approved experiment to study the full resonance region! •Essential in understanding the background in other PV experiments Largest systematic error of E158 •Understand the role of HT effects