PR06-005

1
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

2
Parity Violating Asymmetry
Electron can scatter off of proton by exchanging
either a virtual photon or a Z0
e e
e e
g
Z0

P
P

• The cross section in terms of electromagnetic,
  weak and interference contribution
• Asymmetry due to interference between Z0 and g

3
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
ELASTIC Strangeness (GMs,GEs) Axial FF
RESONANCE Res. Isospin decomposition Axial
hadronic current
DIS PDFs (d/u, s/u), standard model xF3
PVES n-scattering
4
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
5
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
6
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
7
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
8

• 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

9
DUALITY for g-Z interference tensor?
Leading order criteria
Simple Model
Duality is satisfied if on average sn/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 lt3 globally

PROTON
DIS model
Resonance model
DATA NEEDED!
10
DUALITY for g-Z interference tensor?
Leading order criteria
Simple Model
Duality is satisfied if on average sn/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 lt3 globally

PROTON
DIS model
Resonance model
11
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

12
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
  (0.2ltxlt0.7).

13
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/A4 11 GeV
  goal is 2-3 total uncertainty
• Constraining radiative corrections and Higher
  Twist effects in current (E05-007) and future (11
  GeV) DIS-PV experiments

14
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

15
Neutrino Oscillation
neutrino
antineutrino

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

16
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 x0.25), we can
  provide factor of two improvement on HT limits.
  Measure from x0.2 to x0.7 for H, D, and C

17
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
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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

19
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
20
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 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, 5 locally Nuclear
  effects in F2 are gt10

PROTON
DEUTERON, CARBON
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BEAM REQUEST
Total request 30 days of 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)
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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
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Summary

• Measure Ap, Ad, and AC for M lt W lt 2.2 GeV and
  ltQ2gt 0.8 GeV2
• First weak current measurements in full resonance
  region. Surprises possible.
• New regime for study of duality, higher twist
  effects, and EMC effect

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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

25
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!

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BACKUP SLIDES
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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
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A Simple Model

• sin2qW 0.25 ? axial current suppressed
• Isospin symmetry
• Negligible strange and charm form factors

Assume
DEUTERON
PROTON

r(W) depends on (I0)/(I1)

• 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

29

• Why study duality?
• 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

30
Background in Moller Scattering

• SLAC E158 found (204) 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)

31
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 0.2ltxlt0.8 (E05-007 has x0.25)
• 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

32
Relation to E04-101

• Limited to Delta region (Wlt1.25 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

33
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.

34
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).

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FADC-based Fast Counting DAQ

36
Scaler Electronics-based Fast Counting DAQ
37
Pion Background

• 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

38
Kinematic Determination of Q2

• 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 lt0.9
• Will be checked using normal counting mode (with
  tracking) at low beam current. Elastic peak
  positions

39
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
  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 lt 1

40
HALL A vrs C
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