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PR06-005

Parity Violating Electron Scattering in the Resonance Region (Res-Parity)

P. Bosted, J. Arrington, V. Dharmawardane, H. Mkrtchyan, X. Zheng

- Physics Overview:Resonance structure, Duality, Nuclear effects in PV scattering
- Experiment
- Projected Results
- Summary:“Easy” experiment

Never done before

Relevant to wider community

P. Bosted PAC29

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

P. Bosted PAC29

Physics Overview

Extraction of resonance structure in PVES

First test of local and global duality in PVES

Isospin and nuclear dependence

Physics input to future n and PV-DIS studies

PVES

n-scattering

ELASTIC

Strangeness (GMs,GEs)

Axial FF

DIS

PDFs (d/u, s/u), standard model

xF3

RESONANCE

Res. Isospin decomposition

Axial hadronic current

P. Bosted PAC29

Physics Goals - Proton

- First measurements of the parity violating asymmetry over the full resonance region*
- Sensitive to isospin decomposition of resonance region
- Explore both global and local quark-hadron duality with the previously un-studied combination of structure functions

*E04-101 will measure D region, but at large angle and only on a proton target

P. Bosted PAC29

Resonance Region asymmetry

For inelastic scattering, ARL can be written in terms of response functions

- Isospin symmetry relates weak and EM vector current
- Sensitive to axial hadronic current also

Details have so far been worked out only for N→∆(1232)

weakly sensitive to axial vector transition form factor

Resonance Region Asymmetry

For an isolated resonance, ARL can be written in terms of response functions

- Isospin symmetry relates weak and EM vector current
- Sensitive to axial hadronic current also

Details have so far been worked out only for N→∆(1232)

weakly sensitive to axial vector transition form factor

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

P. Bosted PAC29

Odd and even angular momentum states sum to equal strengths

- Explanation by Close and Isgur( Phys. Lett. B509, 81)
- DIS limit
- The magnitude of structure function is proportional to the sum of the squares of the constituent charges
- For a “resonant” state (made of two equal quarks)
- If duality holds:

P. Bosted PAC29

DUALITY for g-Z interference tensor?

•Leading order criteria

Simple

Model

•Duality is satisfied if on averagesn/sp = 2/3

- No reliable model for n/p ratio in res. region: use simple toy model
- Will data look anything like this?
- Duality good to ~5% in F2, our goal is to measure ALR to ~5% locally and <3% globally

PROTON

DIS model

Resonance model

DATA NEEDED!

DUALITY for g-Z interference tensor?

•Leading order criteria

Simple

Model

•Duality is satisfied if on averagesn/sp = 2/3

- No reliable model for n/p ratio in res. region: use simple toy model
- Will data look anything like this?
- Duality good to ~5% in F2, our goal is to measure ALR to ~5% locally and <3% globally

PROTON

DIS model

Resonance model

Physics Goals – Nuclear targets

- Parity violating asymmetries over the full resonance region for proton, deuteron, and carbon
- Global and local quark-hadron duality in nuclei. Better precision for global/local duality then proton data (higher luminosity targets), but W resolution limited by Fermi motion.
- First look at EMC effect with Z-boson probe
- Important input to other PVES and n-scattering measurements on nuclear targets

P. Bosted PAC29

Nuclear dependence (EMC effect)

If photon and Z-exchange terms have identical dependence on PDFs and EMC effect is flavor-independent, then we expect NO EMC effect in ARL

- If we see nuclear dependence Unexpected (?) physics
- Flavor dependence of EMC effect
- Different effect for Z-exchange
- If we observe no nuclear dependence important constraint for PVES, n-scattering on heavy targets
- We cover x-region where nuclear dependence predicted to be largest in most models (0.2<x<0.7).

P. Bosted PAC29

Impact on Future Experiments

- The results are of practical importance :

- Modeling n-A cross sections needed for oscillation experiments
- Understanding backgrounds in future PV experiments (e.g. 11 GeV Moller)
- SLAC E158: inelastic background dA/A=4% 11 GeV: goal is 2-3% totaluncertainty
- Constraining radiative corrections and Higher Twist effects in current (E05-007) and future (11 GeV) DIS-PV experiments

P. Bosted PAC29

Neutrino Oscillation

- Major world-wide program to study neutrino mass, mixing
- Interpretation requires neutrino cross sections in few GeV region on various nuclei: direct measurements difficult - rely in part on models
- Res-Parity will constrain these models, especially the isospin dependence and nuclear dependence

P. Bosted PAC29

Neutrino Oscillation

neutrino

antineutrino

- Resonance region probed by Res-Parity dominates total cross section for 1 < En < 5 GeV, important to MINERnA and MINOS

P. Bosted PAC29

Corrections to DIS-PV

- Significant fraction of measured events (Fres) come from Res. region for DIS at 6 and 11 GeV
- Effect of varying Res. asymmetry by 20% is significant: need data to provide constraints

- For the DIS-PV (deuterium at x=0.25), we can provide factor of two improvement on HT limits. Measure from x=0.2 to x=0.7 for H, D, and C

P. Bosted PAC29

Experimental Setup

Fast counting DAQ can take

1MHz rate with 103 pion rejection

Target density fluctuation, other false asymmetries measured

by the Luminosity Monitor

C, LD2, LH2 targets

(highest cooling power)

4.8 GeV 85% polarized e- beam,

80 mA, DPb/Pb= 1.2%

Electrons detected in

two HRS independently

Beam intensity asymmetry

controlled by parity DAQ

P. Bosted PAC29

KINEMATICS AND RATES

for LD2 target

x Y Q2 E’ W p/e MHz dA/A

0.17 0.50 0.6 2.8 2.0 0.6 0.8 4.9%

0.24 0.39 0.7 3.2 1.8 0.2 0.9 4.0%

0.35 0.29 0.8 3.6 1.5 0.1 1.0 3.8%

0.61 0.19 0.9 4.0 1.2 0.0 1.2 3.0%

- Rates similar to PV-DIS (E05-007)
- Pion/electron ratio smaller
- Low E’ settings in HRS-R, high E’ in HRS-L

P. Bosted PAC29

SYSTEMATIC ERRORS

Smaller systematic error on target ratios (about 1%)

Statistics 4-6% per W bin, ~2.5% when integrated over full W range – always statistics limited

P. Bosted PAC29

PROJECTED ERRORS

- Relative error of 5-7% per bin for 12 W bins shown (8-10% for H)
- Local duality (3 res.regions) tested to <4% (~5% for H): comparable to F2 and g1
- Global duality tested to <3%
- Ratio of H/D [“d/u”] and C/D [“EMC effect”] tested to 3-4% globally, ~5% locally: Nuclear effects in F2 are >10%

PROTON

DEUTERON,

CARBON

P. Bosted PAC29

BEAM REQUEST

Total request: 30 daysof 80 mA, 85% Polarization, parity quality beam (mostly longitudinal, some transverse to measure 2-photon background)

Non-standard equipment: fast DAQ, upgraded Compton. Both required for E05-007 (PV-DIS)

P. Bosted PAC29

Collaboration

- Experience in PV (E158, HAPPEX, G0)
- 3 young, enthusiastic co-spokespersons

P. E. Bosted (spokesperson), E. Chudakov,

V. Dharmawardane (co-spokesperson), A. Duer,

R. Ent, D. Gaskell, J. Gomez, X. Jiang, M. Jones,

R. Michaels, B. Reitz, J. Roche,

B. Wojtsekhowski

Jefferson Lab, Newport News, VA

J. Arrington (co-spokesperson), K. Hafidi, R. Holt,

H. Jackson, D. Potterveld, P. E. Reimer,

X. Zheng (co-spokesperson)

Argonne National Lab,Argonne, IL

W. Boeglin, P Markowitz

Florida International University, Miami, FL

C Keppel

Hampton University, Hampton VA

E. Hungerford

University of Houston, Houston, TX

G. Niculescu, I Niculescu

James Madison University, Harrisonburg, VA

T. Forest, N. Simicevic, S. Wells

Louisiana Tech University, Ruston, LA

E. J. Beise, F. Benmokhtar

University of Maryland, College Park, MD

K. Kumar, K. Paschke

University of Massachusetts, Amherst, MA

F. R. Wesselmann

Norfolk State University, Norfolk, VA

Y. Liang, A. Opper

Ohio 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

and the Hall A Collaboration

P. Bosted PAC29

Summary

- Measure Ap, Ad, and AC for M < W < 2.2 GeV and <Q2> = 0.8 GeV2
- First weak current measurements in fullresonance region. Surprises possible.
- New regime for study of duality, higher twist effects, and EMC effect

P. Bosted PAC29

Summary (continued)

- These data are imperative to constrain models needed for neutrino oscillation studies, backgrounds to other PV experiments (e.g. Moller scattering), radiative corrections and higher twist contributions to DIS PV measurements
- Relatively easy (for PV) experiment using same equipment as approved E05-007. Ready to run soon.
- Can only be done at JLab

P. Bosted PAC29

Perspective

- One of most cited results from Jlab: Gep using polarization transfer. Originally considered as relatively uninteresting engineering experiment, but relatively easy to do, so why not.
- One of the the most cited results from SLAC is the EMC effect: originally thought to be quite uninteresting. But, still not fully understood!
- A diverse and balanced program at Jlab really should include PVES in resonance region!

P. Bosted PAC29

BACKUP SLIDES

P. Bosted PAC29

Deep Inelastic asymmetry

In the Standard Model and assuming quark degrees of freedom, at LO

In the valence region, for a proton target:

≈ 1-x

P. Bosted PAC29

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)

- 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

P. Bosted PAC29

- Have a great impact on our ability to access kinematic regions that are difficult to access otherwise
- Duality in PV electron scattering will provide new constraints for models trying to understand duality and its QCD origins
- Would provide significant limits on the contributions of higher twists to 12 GeV DIS region

P. Bosted PAC29

Background in Moller Scattering

- SLAC E158 found (20§4)%background correction to Moller scattering from low Q2 ep inelastic scattering (mostly resonance region)
- Res-PV will constrain models of the background for future extension aiming at 2% to 3% precision using 11 GeV at JLab (with 1.5 m long target as in E158)

P. Bosted PAC29

Relation to E05-007 (DIS-Parity)

- Complementary: lower W and Q2
- Lower Q2 and better statistics factor of two greater sensitivity to HT
- Study HT for 0.2<x<0.8 (E05-007 has x=0.25)
- Extract HT for H, D, and C targets (E05-007 only measures deuterium)
- Res-Parity provides data to calculate radiative corrections and constrain HT for for high precision DIS-Parity measurement at 11 GeV

P. Bosted PAC29

Relation to E04-101

- Limited to Delta region (W<1.25 GeV)
- Lower Q2: 0.2-0.6 GeV2(parasitic measurement - depends on G0 energies)
- Only on proton target
- Backward angle to emphasize sensitivity to axial form factor

P. Bosted PAC29

New Instruments/Upgrades

Compton polarimeter: will use green laser (in progress); expect to achieve DPb/Pb= 1.1% for electron analysis method.

2.5 gm/cm2 C target (as used in Hall C); possibly an additional target cell.

FADC-based and scaler-based fast counting DAQs, both being developed by the PV-DIS collaboration.

P. Bosted PAC29

DAQ: Comparison of two methods

- FADC-based:
- Is what we eventually need (12 GeV program)
- Full event sampling at low rate for detailed off-line analysis;
- Being developed by Jlab electronics group.

- Scaler-based:
- Similar to previous SLAC, and current Hall C scalers;
- Straightforward to set up;
- Only scaler info is recorded (on-line PID critical).

P. Bosted PAC29

P. Bosted PAC29

Scaler Electronics-based Fast Counting DAQ

P. Bosted PAC29

- p/e ratio ranges 0.005 to 0.8 : average about 0.2
- p signal ~20x smaller than electron signal in lead glass, usually no Chrenkov signal: net contamination average is tiny

- Pion asymmetry will be measured with very high precision with both the scalar and FADC electronics

P. Bosted PAC29

- dA/A proportional to dQ2/Q2
- From standard HRS uncertainties of q and in E’, central Q2 determined to better than 0.5%
- Uncertainties in Q2 acceptance (plus beam, target, collimator, quadrupole positions) increase uncertainty in measured Q2 to <0.9%
- Will be checked using normal counting mode (with tracking) at low beam current. Elastic peak positions

P. Bosted PAC29

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 probability for an electron to radiate a hard photon. PV corrections under study (Zhu and Ramsey Musolf)
- Radiative corrections for Ap will be determined by an iterative fit to the data of this proposal

•systematic error in Ap < 1%

P. Bosted PAC29

Pro: better W resolution possible due to HRS optics (more momentum dispersion)

Pro: PV-DIS electronics allows clean electron PID, pion rejection

Pro: lower overhead due to common effort with approved PV-DIS

Con: need about 30% more running time due to lower acceptance and HRS maximum momenta limitations

P. Bosted PAC29

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