Res-Parity:Parity Violating Electron Scattering in the

Resonance Region

Paul E. Reimery

yWith much help from the talented Res-Parity spokespersons, J.

Arrington, V. Dharmawardane, H. Mkrtchyan, X. Zheng and especially Peter BostedPeter Bosted

Physics: Resonance Structure, Duality, Nuclear Effects in PV scattering

Experiment

Projected Results

Summary:

–“Easy” experiment–Never done before; –Relevant to wider community

2

Parity Violation—A Tool

The cross section can be expressed terms of electromagnetic, weak and interference contribution:

dTotal = d + dweak + dinterference

Asymmetry due to interference between Z0 and

e’

e P

e’

e P

Z0+

Probe using weak interaction instead of EM interaction

EM interaction weights as parton charge squared– Emphasizes up quark

contribution– Weak interaction sensitive to

down and strange quark content

Parity Violation in Resonance Region poorly understood Q2 < 1GeV2 Mproton < W < 2 GeV

3

What is duality and why study it?

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.

c.f. earlier talk by M. Ramsey-Musolf at PAVI06 and

review by Melnitchouk, Ent and Keppel, Phys. Rept. 406 127 (2005), hep-ph/05012017

Gra

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ic from

Me

lnitch

ou

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Will higher twist terms cancel similarly with the Z0 probe in parity violation

4

Why Study Duality?

Duality works extremely well for spin-averaged structure function to low values of Q2.

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

Duality also appears to work for spin dependent structure functions

for Q2 > 1 GeV2.

JLab Hall C

data as discussed in

Melnitchouk et al. P

hys. Rept. 406

127 (2005)

5

Resonance Region Asymmetry

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

– A0¼ 6.5 £ 10-4;

– L, T, T0 denote longitudinal, transverse and axial; and

– VL,T,T0 represent lepton kinematic factors.

Sensitive to axial vector transition form factor, GA

N

Details have so far been worked out only for N→∆(1232)– c.f. JLab E04-101 and Jones and Petcov Phys. Lett. 91B 137 (1980)

6

Resonance Region Asymmetry

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

Simple, “toy” model:

depends on sin2W ) Assume sin2W = 0.25 ) VA term disappears

Pure magnetic or electric scattering No strange, charm contributions

ARLRes ¼ -9£ 10-5 Q2 (n/p)

7

Duality for -Z interference?

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

Resonance model

PROTON

DIS model

DATA NEEDED!

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Resonance Region Asymmetry: (1232)—significant departure from duality

Sato and Lee predict significant departure from Duality for N! ALR = 9£ 10-5Q2(1.075+V+A)

A,V contain axial and vector contributions from neutral current

ALR 2£ larger than duality predictions!

Duality

Sato and LeeE=4 GeV E=6 GeV

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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)– W resolution limited by Fermi motion.

First look at EMC effect with Z-boson probe

Important input to other PVES and -scattering measurements on nuclear targets

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Nuclear dependence (EMC effect)

If photon and Z-exchange terms have – identical dependence on parton distributions 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

no sea quark EMC effect seen by Drell-Yan (Fermilab E772)

– Different effect for Z-exchange

If we observe no nuclear dependence important constraint for PVES, -scattering on heavy targets

Res-Parity covers x-region (0.2<x<0.7) where nuclear dependence predicted to be largest in most models

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Benefits to other experiments

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Neutrino Oscillation

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

neutrino antineutrino

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

13

Background in Standard Model tests

NuTeV:– Nuclear effects in the weak interaction

(as opposed to EM nuclear effects)– Higher twist effects could explain part of

observed anomaly Møller Scattering:

– SLAC E158 found (22§4)% background correction 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)

DIS-Parity:– Constraining radiative corrections and Higher Twist effects in current

(E05-007) and future (11 GeV) DIS-PV experiments

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Experimental setup and expected results

15

Experimental Setup:

Use Hall A HRS spectrometers to simultaneously collect data at two kinematic points

A B C

Graphics courtesy of www.jlab.org

Graphics courtesy of www.jlab.org

Jefferson Laboratory Hall A Plan to maximize overlap in

setup with PV-DIS (E05-007)– Essentially same

experimental setup with different kinematics

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Experimental Setup

Electrons detected intwo HRS independently

Fast counting DAQ can take 1 MHz rate with 103 pion rejection

C, LD2, LH2 targets(highest cooling power)

4.8 GeV 85% polarized e- beam,80 A, P

b/P

b = 1.2%

Beam intensity asymmetry controlled by parity DAQ

(demonstrated by HAPPEX)

Target density fluctuation, other false asymmetries measuredby the Luminosity Monitor

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Collaboration

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. WojtsekhowskiJefferson 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 MarkowitzFlorida International University, Miami, FL

C KeppelHampton University, Hampton VA

E. HungerfordUniversity of Houston, Houston, TX

G. Niculescu, I NiculescuJames Madison University, Harrisonburg, VA

T. Forest, N. Simicevic, S. WellsLouisiana Tech University, Ruston, LA

E. J. Beise, F. BenmokhtarUniversity of Maryland, College Park, MD

K. Kumar, K. PaschkeUniversity of Massachusetts, Amherst, MA

F. R. WesselmannNorfolk State University, Norfolk, VA

Y. Liang, A. OpperOhio University, Athens, OH

P. DecowskiSmith College, Northampton, MA

R. Holmes, P. SouderUniversity of Syracuse, Syracuse, NY

S. Connell, M. DaltonUniversity of Witwatersrand, Johannesburg,

South AfricaR. Asaturyan,

H. Mkrtchyan (co-spokesperson), T. Navasardyan, V. Tadevosyan

Yerevan Physics Institute, Yerven, Armenia

Experienced PV collaboration (SLAC E158, HAPPEX, G0)

And the Hall A Collaboration

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Kinematics and Rates

Rates similar to PV-DIS (E05-007)—see talk by Xiaochao Zheng Pion/electron ratio smaller Low E0 settings in HRS-R, high E0 in HRS-L

Deuterium Kinematics, Rates, etc.

x Y Q2 E0 W e MHz A/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%

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Systematic Uncertainties

Statistical uncertainty--Always statistics limited– 4-6% per W bin– ¼ 2.5% integrated

over full W range

EMC effect: Smaller systematic uncertainties on target ratios (about 1%)

Source A/A

Beam Polarization 0.012

Kinematic Determination of Q2 0.009

Electromagnetic radiative corrections 0.008

Beam asymmetry 0.005

Pion contamination 0.005

DAQ deadtime and pile-up effects 0.003

Pair symmetric background 0.002

Target purity and density Fluctuations

0.002

Pole-tip background 0.001

TotalTotal 0.0180.018

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Res-Parity Beam time requests

Strong synergy with PV-DIS E05-007 (see talk by Xiaochao Zheng) Non-standard equipment: fast DAQ, upgraded Compton.

Both required for E05-007 (PV-DIS)

E Target PHRS (L,R) time 4.8 GeV LH2 4.0, 3.2 GeV 5 days4.8 GeV LH2 3.6, 2.8 GeV 4 days4.8 GeV LD2 4.0, 3.2 GeV 4 days4.8 GeV LD2 3.6, 2.8 GeV 4 days4.8 GeV C 4.0, 3.2 GeV 6 days4.8 GeV C 3.6, 2.8 GeV 6 days

Pass Change from E05-007 8 hoursPolarization measurements 8 hourse+ asymmetry 8 hours

Total requirement:

30 days of 80 mA, 85% Polarization, parity quality beam

(mostly longitudinal, some transverse to measure 2-photon background)

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Relative error of 5-7% per bin for 12 W bins shown (8-10% for H)

Local duality (3 resonance 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, – ¼5% locally:

Nuclear effects in F2 are >10%

Projected Uncertainties (W Binning)

PROTON

DEUTERON,CARBON

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Projected Uncertainties ( Binning)

PROTON

DEUTERON,CARBON

Relative error of 5-7% per bin for 12 bins shown (8-10% for H)

Local duality (3 resonance 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, – ¼5% locally:

Nuclear effects in F2 are >10%

Sato and Lee1232)

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Res-Parity: Summary

Easy measurement– Follow lead of PV-DIS@6GeV (E05-

007) New probe of

– Resonance structure– Duality

EMC effect with weak probe– Z0 sensitive to different quark

distribution combination Measure Higher Twist constraints for

PV-DIS Constrain PV background to Møller

Scattering experiments Expt. currently proposed but deferred

24

Easy measurement– Follow lead of PV-DIS@6GeV (E05-

007) New probe of

– Resonance structure– Duality

EMC effect with weak probe– Z0 sensitive to different quark

distribution combination Measure Higher Twist constraints for

PV-DIS Constrain PV background to Møller

Scattering experiments

Res-Parity: Summary

Exploration of Exploration of

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