Res-Parity: Parity Violating Electron Scattering in the Resonance Region

1
Res-ParityParity Violating Electron Scattering
in the Resonance Region

• Paul E. Reimery

• Physics Resonance Structure, Duality, Nuclear
  Effects in PV scattering
• Experiment
• Projected Results
• Summary
• Easy experiment
• Never done before
• Relevant to wider community

yWith much help from the talented Res-Parity
spokespersons, J. Arrington, V. Dharmawardane, H.
Mkrtchyan, X. Zheng and especially Peter Bosted
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Parity ViolationA Tool

• The cross section can be expressed terms of
  electromagnetic, weak and interference
  contribution
• d?Total d?? d?weak d?interference
• Asymmetry due to interference between Z0 and ?

• 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 lt 1GeV2 Mproton lt W lt 2 GeV

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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.

Graphic from Melnitchouk et al. Phys. Rept. 406
127 (2005)

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

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
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

JLab Hall C data as discussed in Melnitchouk et
al. Phys. Rept. 406 127 (2005)
Duality also appears to work for spin dependent
structure functions for Q2 gt 1 GeV2.
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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.

• 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)

Sensitive to axial vector transition form factor,
GAN?
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Resonance Region Asymmetry

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

• Simple, toy model
• ? depends on sin2?W ) Assume sin2?W 0.25 ) VA
  term disappears
• Pure magnetic or electric scattering
• No strange, charm contributions
• ARLRes ¼ -9 10-5 Q2 (?n/?p)

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Duality for ?-Z interference?
PROTON

• 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 lt3 globally

DIS model
Resonance 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 Lee
E4 GeV
E6 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 (0.2ltxlt0.7) where
  nuclear dependence predicted to be largest in
  most models

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Benefits to other experiments
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Neutrino Oscillation

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

neutrino
antineutrino

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

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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 (224) 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
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Experimental Setup
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

C
A
B

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

Graphics courtesy of www.jlab.org
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Experimental Setup
Fast counting DAQ can take 1 MHz 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
(demonstrated by HAPPEX)
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Collaboration

• Experienced PV collaboration (SLAC E158, HAPPEX,
  G0)

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
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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. Deuterium Kinematics, Rates, etc. Deuterium Kinematics, Rates, etc. Deuterium Kinematics, Rates, etc. Deuterium Kinematics, Rates, etc. Deuterium Kinematics, Rates, etc. Deuterium Kinematics, Rates, etc. 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
Total 0.018
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Res-Parity Beam time requests
E Target PHRS (L,R) time
4.8 GeV LH2 4.0, 3.2 GeV 5 days 4.8 GeV LH2 3.6, 2.8 GeV 4 days 4.8 GeV LD2 4.0, 3.2 GeV 4 days 4.8 GeV LD2 3.6, 2.8 GeV 4 days 4.8 GeV C 4.0, 3.2 GeV 6 days 4.8 GeV C 3.6, 2.8 GeV 6 days
Pass Change from E05-007 8 hours Polarization measurements 8 hours e asymmetry 8 hours
Total requirement 30 days of 80 mA, 85
Polarization, parity quality beam (mostly
longitudinal, some transverse to measure 2-photon
background)

• 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)

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Projected Uncertainties (W Binning)

• Relative error of 5-7 per bin for 12 W bins
  shown (8-10 for H)
• Local duality (3 resonance regions) tested to lt4
  (5 for H) comparable to F2 and g1
• Global duality tested to lt3
• Ratio of H/D (d/u) and C/D (EMC effect) tested to
  
• 3-4 globally,
• ¼5 locally
• Nuclear effects in F2 are gt10

PROTON
DEUTERON, CARBON
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Projected Uncertainties (? Binning)

• Relative error of 5-7 per bin for 12 ? bins
  shown (8-10 for H)
• Local duality (3 resonance regions) tested to lt4
  (5 for H) comparable to F2 and g1
• Global duality tested to lt3
• Ratio of H/D (d/u) and C/D (EMC effect) tested to
  
• 3-4 globally,
• ¼5 locally
• Nuclear effects in F2 are gt10

PROTON
DEUTERON, CARBON
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Res-Parity Summary

• Easy measurement
• Follow lead of PV-DIS_at_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

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Res-Parity Summary

• Easy measurement
• Follow lead of PV-DIS_at_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

Exploration of Terra Incognita
Map from Library of Congress