Target Normal Single-Spin Asymmetry in Inclusive DIS n↑(e,e

with a Polarized 3He Target

Tim Holmstromwith Xiaodong Jiang, Todd Averett, Ron Gilman

Hall A Collaboration Meeting

January 5, 2007

N x

kk

N

x

kk

• 1-exchange AN=0 (Time-Reversal Invariance).• AN≠0 due to imaginary part of 1 2 interference• Connected to 3-current correlation function

• At quark level requires Chiral Symmetry Breaking to generate AN

• Clean probe to 2 response to DIS

TN SkkA

qq1 q2

AN: A Direct 2-exchange Measurement

Recent Surprises with 2-Exchange

• Rosenbluth vs. polarization transfer in nucleon FF's – Disagreement solved by two- exchange

– Elastic intermediate state (Blunden et al.)

– General Parton Distribution Functions (Afanasev et al.)

• ep ep with transversely polarized beam – Contribution of inelastic intermediate excitations exceeds

the elastic intermediate state by orders of magnitude – In agreement with two- calculation by Afanasev et al. – Interference of one- exchange and two- exchange

("Compton") at the amplitude level

Normal Beam Asymmetry from 2γ-exchange

• Data from HAPPEX on the proton and 4He targets• Measures absorptive part of Compton scattering amplitude,

integrated over photon virtualities and W • Calculations by Afanasev&Merenkov

New Theoretical Predictions• Metz et. al. pointed out that

a non-zero AN can be due to two-photon exchange in a parton picture using a mechanism similar to gT=g1+g2.

• Afanasev and Weiss calculate AN in a constituent quark picture.– Their predictions are shown

to the right for proton and neutrons.

Relation to Ay experiment

• The Ay experiment will run with the next group of 3He experiments.

• Ay will measure the target normal single spin asymmetry using inclusive quasi-elastic scattering.

• GPD parameterizations predict Ay = 1.5%.• Thus there is 2 order of magnitude fall off between

quasi-elastic parton prediction and the recent DIS prediction.

• This suggests that AN is very sensitive to the transition from hardronic to partonic degrees of freedom.

Previous Measurement• Only one previous measurement of the vertical

target single spin asymmetry by S. Rock et al. at SLAC in 1970.

• Vertically polarized butanol target, 18 GeV electron beam.

• The average for all DIS points gives the proton asymmetry is AN

p = ±%.

No new measurement has been published in 35 years.

Goals of this Proposal

• Use the 336 hours polarized target normal beam already approved for E06-010/06-011.

• Control systematic uncertainty to the 104 level.– Improved PID with d2n Gas Cherenkov– Luminosity monitoring with Hall A Lumis– Overall control of systematic bias– Advances in the 3He target allow fast target spin flips.

• Provide tight limits on target single spin asymmetries:

DIS Parity, Ay, and Transversity.• Test the predictions of the constituent quark model.

• Measure the target normal single-spin asymmetry on the neutron to 104 level.

Big Bite Spectrometer

The Transversity experiments plan to use the standard BigBite electron detector package:

Scintillator trigger plane Three wire chambersLead glass calorimeterNew d2n Gas Cherenkov

Big Bite Performance during GeN

• Big Bite was used successfully during the GeN experiment.• The wire chambers showed good momentum and z position resolution.

New BigBite Gas Cherenkov for d2n

• Designed to have a 500 to 1 pion rejection.• To be built and commissioned in July/August of 2007.

Trigger DAQ

Single arm trigger

Scintillator plane hit

Number of photons in the Cherenkov

Energy threshold in the calorimeter

DAQ rate of less then 2kHzDeadtime less then 5%.

Aggressive in setting the calorimeter threshold

Independent fromTransversity trigger!

Hall A Lumis

• The high rate HAPPEX parity experiments have built and installed luminosity monitors (Lumis) in the Hall A beam pipe.

• These detectors worked very well at 30 Hz for HAPPEX.

• With one Slug of HAPPEX data• Using 14 minute time windows• Systematic bias was 5105

Downstream of targetIn beam pipe

Transversity Kinematics Bite

Expected Results

• E= 6 GeV, target polarization = 42%.• f is the neutron dilution factor.• One Big Bite Setting gets all x bins at once.

<x> E

Gev

e

Deg.

Q2

GeV2

W

GeV

EGeV

d(e,e)

nb/GeV/sr

f Rate

Hz

NDIS

106

ANn

104

0.135 0.815 30.0 1.310 3.050 0.431 29.6 0.350 817.49 989.0 2.16

0.225 1.246 30.0 2.003 2.793 0.398 19.4 0.366 493.42 569.9 2.66

0.315 1.612 30.0 2.592 2.554 0.340 13.0 0.380 281.82 340.9 3.39

0.405 1.925 30.0 3.095 2.331 0.381 8.4 0.391 204.14 247.0 3.87

Results Compared to SLAC proton.

Two order of magnitude improvement!

Systematic UncertaintiesThis measurement will be dominated by systematic uncertainty.

1. Relative luminosity2 background3. Quasi-elastic background

½ of the E03-004 data will be taken with beam in the scattering plane

AN=0 Clear measurement of our total systematic bias

Random quad run structure of target polarization or

Better control of Systematic drifts

Blind the data analysis

Relative Luminosities

L

LNN

L

LNN

Ameas

meassysmeas A

L

LNN

L

LN

A

1

51052

1

L

L

L

L

A sysmeas

After neutron dilution (AN)sys= 3.4 104

for all four x bins.

The Hall A Lumis are accurate to 5105 in our time scale.

Luminosity enters directly

as an asymmetry systematic.

Backgrounds: Radaitive Corrections

• The modified Regge GPD model predicts for the lowest x bin a quasi-elastic signal spin asymmetry Ay=102, with a 30% uncertainty.

• The Ay experiment E05-015 will test this model giving us a better correction.

For the highest x bin radaitive background is less then 1%.

For the lowest x bin radaitive background of 10%.

Backgrounds: Pions

The p/e ratio:less then 10:1 for the two high x binsless then 100:1 for the lowest x.

Lead glass calorimeter rejection 100 to 1.

Gas Cherenkov will have pion rejection of 500 to 1 for all x

The pion asymmetry Awill be measured very accurately.

Beam Time Request

Density tests, position measurements, and linearity studies will be done in coordination with the Transversity experiments.

Time (Hours)

Production on Pol. 3He

672 (Shared with E06-010 and E06-011)

Reference Cell Runs Optics and Detector

Checks

16 (Shared with E06-010 and E06-011)

Target Overhead: Spin Rotation and Polarization

32 (Shared with E06-010 and E06-011)

Total 0 new Hours

(Time shared with E06-010 and E06-011)

SummaryExperimental goal: measure the target single-spin asymmetry An

N on the neutron during the Transversity experiments.

•AN is a clean probe to 2 response to DIS.•Test the constituent quark model prediction of An

N.

•Look for the transition from hardronic to partonic degrees of freedom.

Backup Slides

Theory Connection: Other Transverse Spin Experiments

• Great Interest in SSA in SIDIS with transversely polarized target – Collins and Sivers Effect– Recent results from HERMES, COMPASS, and JLAB

• For Sivers: the Brodsky-Hwang-Schmidt mechanism at quark-level, – Further theoretical development: Belitsky, Ji, and Yuan …– Similar mechanism may be at work in Inclusive scattering.

• Independent check of systematics of SSA from 2-exchange for SIDIS.•Complementary to the studies of dynamics of SSA in SIDIS.

Relation with other ExperimentsJefferson Lab is unique

High luminosity polarized 3He target

Large acceptance of the BigBite spectrometer

+

Unique Physics reach now=

HERMES has data with the target spin normal to the scattering angleBut few polarization flips a year leads to systematic challenges

Systematic Check for these experiments:

Transversity, Ay, and 12 GeV target single-spin PV

3He Polarized Target• E03-004 will use the new

potassium/ rubidium hybrid 3He target.

• These cells will be used for the first time in GeN, and preliminary studies suggest that PT>50%.

• The target will be flipped every 10~20 minutes.

Target densities will need to be monitored.

Spin Duality saw 8104 differences.

Improved because of rotating /4 plate

Overall Systematic Cancellation

• Half of the Transversity beam time will be spent with target spin left and right of the beamline. Since:

• A full analysis will be done of this data, which will give us a clean measure of our systematic bias.

• The quad run structure of target polarization, the random sequence of orruns will also to better cancel slow drifts in the spectrometer or beam.

• Periodic special runs will be done to understand the behavior of the Lumi and detectors such as:– Target density runs– Beam position off runs– Linearity studies.

0 TN SeeA

Pion Background Rejection• The SAID model estimates a 3% pion asymmetry near our

kinematics.• Aggressive PID cuts can make the correction smaller then the

statistical error.

Analysis of L-HRSPb-glass Calorimeter

rejection of6001850 can beachieved with aggressive cuts.

Monte Carlo Studies of AerogelCherenkov

rejection of15 for the lowestx bin can beachieved with aggressive cuts.

Electron efficiency 94%50% with aggressive cuts.

Expected Results with Cuts

• E= 6 GeV, target polarization = 42%.• f is the neutron dilution factor.• One Big Bite Setting gets all x bins at once.

<x> E

Gev

e

Deg.

Q2

GeV2

W

GeV

EGeV

d(e,e)

nb/GeV/sr

f Rate

Hz

NDIS

106

ANn

104

0.135 0.815 30.0 1.310 3.050 0.431 29.6 0.350 817.49 776.9 3.54

0.225 1.246 30.0 2.003 2.793 0.398 19.4 0.366 493.42 468.9 4.24

0.315 1.612 30.0 2.592 2.554 0.340 13.0 0.380 281.82 267.8 4.27

0.405 1.925 30.0 3.095 2.331 0.381 8.4 0.391 204.14 194.0 4.51

Target Polarization Differences

• Polarization differences do not cause asymmetries they only change the size of the asymmetry.

• NMR and EPR will be used to measure the polarization to a relative 4%.

10

10

P

P

0

1

2

PPAmeas

%4. measmeassysN AP

PAA

Two-Photon Effects in Inclusive DIS

mq≠0

uss

mQQ

QmQ

meeA q

q

qqN ˆˆˆ

4

/41

12

24

222

22

2

If ANn ≠0

Would require chiral symmetry breaking,due to strong interaction effects beyond the leading twist QCD picture of DIS.