parity violating electron scattering in resonance region (res-parity)
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Parity Violating Electron Scattering in Resonance region (Res-Parity)
(P05-xxx) P. Bosted, Hall A meeting, June 2005 Physics OverviewMotivationExperimentCount rates and ErrorsExpected ResultsRequestSummary: “Easy” experiment, never done before, relevant to wider community
PARITY VIOLATING ASYMMETRY
The cross section in terms of electromagnetic, weak and interference contribution
Asymmetry due to interference between Z0 and
Iweakã ódódódód ++=
LR
LRRL ódód
ódódA
+−
=
Electron can scatter off of proton by exchanging either a virtual photon or a Z0
e’
e P
e’
e P
Z0+
Deep Inelastic asymmetryIn the Standard Model and assuming quark degrees of freedom, at LO
( )[ ]( )∑
∑ +−=
22
22ãii
iA
eV
iV
eA
ãii
Z
DISRL
Q)x(f
gYggge/Q)x(f
M
QA
In the valence region, for a proton target:
)x(u
)x(d.
)x(u
)x(dY.
)x(u
)x(d..
QAp
2501
1100450510
10 24
+
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛+++
−= −
≈1-0.75x
Resonance region asymmetryFor a resonance ARL can be written in terms of response functions
)I(R â)I(R âR
)ù,q(Rv)ù,q(Rv
)ù,q(Rv)ù,q(Rv)ù,q(RvAA
T,LIT,LIT,LAV
TT
LL
'TVA'T
TAVT
LAVLsRe
RL
10 10
0
=+==
+++
=
==
•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
( )A 1.04 0.27F(Q ,E,E', ) 10 QRLN 2
e4 2→ −= − + ×Δ θ
A Simple Modelsin2W = 0.25 ->axial current suppressedIsospin symmetryNegligible strange and charm form factors
PROTON DEUTERON
Different dependencies in the resonant and DIS casesResonant case the current is expressed through the square of the sum over parton chargesDIS case the sum of the square gives the current
Assume
5
121090
1090
24
24
)óó(Q.A
óóQ.A
pnp,DISRL
pnp,sRe
RL
+×−=
×−=
−
−
24
24
1070
1090
Q.A
Q.A
d,DISRL
d,sReRL
−
−
×−=
×−=
r(W)
r(W) depends on (I=0)/(I=1)
QUARK-HADRON DUALITY
In QCD can be understood from an OPE of moments of structure functionsDuality 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
DUALITY for the gamma-Z interference tensor ?
•Leading order criteria
DATA NEEDED!
( ) ( )( )DIS
avepnres
avepn óóóó += 15
2
•Duality is satisfied if on average n/p = 2/3
PROTON
SimpleModel
Average of the (1232) and the elastic peak tend to equal the DIS curve
Higher resonances oscillate around the DIS curve
DIS model
Resonance model
PHYSICS MOTIVATIONProvide 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
PHYSICS MOTIVATIONThe 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
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?).
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
Experimental Setup
Electrons detected by thetwo HRS independently
Fast counting DAQ handle up to 1MHz rate with 103 pion rej.
C, 25-cm LD2, LH2 targets(highest cooling power)
Pol e- beam, 4.8 GeV, 80 uA,80%, P
b/P
b = 1.2%
Beam intensity asymmetrycontrolled by parity DAQ
Target density fluctuation& other false asym monitored
by the Luminosity Monitor
KINEMATICS AND RATES
Rates similar to E05-007. Pion/electron ratio smallerRun low E’ settings in one HRS, high E’ in other
x Y Q2 E’ W2 /e MHz A/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
for LD2 target
New Instruments and/or Upgrades
Compton polarimeter: will use green laser (in progress); expect to achieve Pb/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.
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
SYSTEMATIC ERRORSSource A/A
Beam Polarization
Kinematic determination of Q2
Detector and Electronic Linearity
Electromagnetic radiative corrections
Beam asymmetry
Pion contamination
Pair symmetric background
Target purity and density fluctuations
0.012
0.010
0.005
0.005
0.005
0.005
0.002
0.002
Total 0.020
The ratio of asymmetries on hydrogen or C to deuterium is almost free of experimental systematic errors, allowing a very precise comparison with theory
REQUEST
E Target P HRS-L/R time
4.8 GeV LH2 4.0, 3.2 GeV 2 days
4.8 GeV LH2 3.6, 2.8 GeV 2 days
4.8 GeV LD2 4.0, 3.2 GeV 2 days
4.8 GeV LD2 3.6, 3.8 GeV 2 days
4.8 GeV C 4.0, 3.2 GeV 2 days
4.8 GeV C 3.6, 2.8 GeV 2 dyas
Checkout 4 hours
Pass Change from E05-007 8 hours
Polarization measurements 8 hours
e+ asymmetry 4 hours
Total 13 days
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)
COLLABORATIONExperience in PV (E158, Happex, G0)
Augments E05-007 (DIS-PV: more people to develop needed equipment
SUMMARYFIRST 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 E05-007Emphasizes d-quark contributions, sensitive to strangeness and axial hadronic currentNew regime for study of duality, higher twist effects, and EMC effectNeeded to constrain models, which in turn are used for neutrino oscillation studies, backgrounds to experiments like SLAC E158, radiative corrections for DIS-parity experiments.
BACKUP SLIDES
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).
FADC-based Fast Counting DAQ
Scaler Electronics-based Fast Counting DAQ
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.
COLLABORATION
W. Boeglin, P MarkowitzFlorida International University, Miami, FL
C KeppelHampton University, Hampton VA
G. Niculescu, I NiculescuJames 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. WellsLouisiana Tech University, Ruston, LO
K. Kumar, K. PaschkeUniversity of Massachusetts, Amherst, MA
F. R. WesselmannNorfolk state university, Norfolk, VA
Yongguang Liang, A. OpperOhio state university, Athens, OH
P. DecowskiSmith College, Northampton, MA
R. Holmes, P. SouderUniversity of Syracuse, Syracuse, NY
S. Connell, M. DaltonUniversity of Witwatersrand, Johannesburg,
South Africa
R. Asaturyan, H. Mkrtchyan (co-spokesperson), T. Navasardyan, V. Tadevosyan
Yerevan Physics Institute, Yerven, Armenia
Pion Background/e ratio ranges 0.005 to 1.2 : average about 0.2
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
Kinematic Determination of Q2
dA/A proportional to dQ2/Q2
From standard HMS uncertainties of 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
RADIATIVE CORRECTIONSUn-radiated to radiated spin averaged cross section
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 photonRadiative corrections for Ap will be determined by an iterative fit to the data of this proposal
•systematic error in Ap < 1%
Determined by the x, Q2 dependence of F2
SFs for the interference tensor
ARL in terms of structure functions for the interference tensor of EM and weak currents
( ))Q'EE(WQW
M/)'EE(Q g)Q'EE( Q g
MQ
QA
EMEMvA
ZRL 2
22
1
222
22
2
42
42
−+
+−−+
+=
W1 W2 W3
Well measured
Proportional to the weak interaction
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
OTHER PV EXPPERIMENTSMost 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- 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
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