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