Min HuangDuke University, TUNL

On behalf of the E08-027 (g2p) collaboration

H ll A C ll b ti M ti J 13th 2013Hall A Collaboration Meeting, June 13th, 2013

E08‐027E08‐027 g2p & the LT Spin Polarizabilityg2 p y Spokespeople

Alexandre Camsonne Graduate Students

Toby Badman(JLab)

Jian-Ping Chen (JLab) Don Crabb (UVA)

Toby Badman Melissa Cummings Chao Gu

Don Crabb (UVA) Karl Slifer (UNH)

Post Docs Min Huang Jie Liu

P ji Zh Kalyan Allada Elena Long James Maxwell

Pengjia Zhu Ryan Zielinski

James Maxwell Vince Sulkosky Jixie Zhang

Hall A Collaboration Meeting 2013   Min Huang 2

Electron Scattering I l i l i d diff ti l ti Inclusive polarized differential cross section

e (E,k) e’ (E’,k’)θ

( , )

* ( )γ* (ν,q)

P (M 0)W g1, g2: polarized nucleon 

spin structure functionsP (M,0)

Hall A Collaboration Meeting 2013   Min Huang 3

How to Obtain gHow to Obtain g2e‐ e‐

e‐

e‐

measured by g2p experiment, essential contribution to g2 in this kinematic region

Hall B EG4 data will be combined, g2p has one measurement

A

Will measure both asymmetry and cross section

has one measurement to cross checktA

Hall A Collaboration Meeting 2013   Min Huang 4

Motivation Measure the proton spin structure function g2 in the low 2

Q2 region (0.02<Q2<0.2 GeV2) for the first time Extract δLT to provide a benchmark test of χPT LT p χ

calculations Opportunity to test the Burkhardt-Cottingham sum rulepp y g Crucial inputs for hydrogen hyperfine splitting and proton

charge radius measurementsgTalk by Jixie Zhang: proton FF

Hall A Collaboration Meeting 2013   Min Huang 5

Experimental SetupExperimental Setup Large Scale Installation in Hall A Large Scale Installation in Hall A

Transverse polarized NH3 target (2.5/5T field) Low beam current (<100 nA) > new beamline diagnostics

Septa

Low beam current (<100 nA) -> new beamline diagnostics Rasters

S t t

Hall A High Resolution

Septa Septum magnets

BCM Rasters Chicane BPM

L l

Hall A High Resolution Spectrometer (HRS)

LocalDump

Polarized NH3 Target

6APS April Meeting 2013   Min Huang

kinematics Coveragerun concurrently with G prun concurrently with Ge

p

Mp < W < 2 GeV0.02 < Q2 < 0.2 GeV2

Beam E Target Energy /GeV

a geField /T

2 254 2 52.254 2.51.706 2.51.158 2.52.254 5.03.352 5.0

7APS April Meeting 2013   Min Huang

ProjectionsProjections

• Resonance• Resonance— MAID

Hall A Collaboration Meeting 2013   Min Huang 8

Status of AnalysisStatus of Analysis

Hall A Collaboration Meeting 2013   Min Huang 9

Beam Position Calibration bpm resolution improved by adding a low pass filter

(software) More study still underway

raw ADC signal ADC signal after filter

time time

10courtesy Pengjia Zhu

Hall A Collaboration Meeting 2013   Min Huang

OpticsOptics Determine center angle with high accuracy Pointing method

Uncertainty of θ 1% contribution to cross section 4%d(ΔE’) 100 KeVd(ΔE’)=100 KeV

Preliminary resultsPreliminary results LHRS 5.77 °, RHRS 5.67°

To determine uncertainty still in progress Beam position Data calibration: large beam offset from center correctionsData calibration: large beam offset from center, corrections

Hall A Collaboration Meeting 2013   Min Huang 11

O ti ith T t Fi ldOptics with Target Field Electron path from target to sieve slit is not straight line now Electron path from target to sieve slit is not straight line now Current idea: separate reconstruction into 2 parts

VDC Sieve slit: no target field results VDC Sieve slit: no target field results Sieve slit target: use field map to ray trace the electrons

Used simulation to check this ideaUsed simulation to check this idea SNAKE to generate the forward transport functions Data calibration/SNAKE to provide the preverse transport functions

Q3

VDC

Target Septum

Sie e slit

Q2

Dipole

Hall A Collaboration Meeting 2013   Min Huang 12

Sieve slitQ1

Optics with Target Field Compared vertex variables between generated electrons

and reconstructed electrons A good consistency of mean value at 1% black: generated

red: reconstructed

Hall A Collaboration Meeting 2013   Min Huang 13

courtesy Chao Gu

lTarget Polarization Target polarization

measured via NMR and recorded every 30srecorded every 30s

Offline calibration done using thermal equilibrium (TE) t(TE) measurements

Polarization averaged across each production run.

Detailed systematic uncertainty study close to be finalizedbe finalized

Hall A Collaboration Meeting 2013   Min Huang 14

courtesy Toby Badman

ffCut Efficiencies Detector calibrations and efficiencies were done to determine e ec o c b o s d e c e c es we e do e o de e e

cuts for PID

courtesy Melissa CummingsHall A Collaboration Meeting 2013   Min Huang 15

Similar analysis for LHRS

Multi‐track StudyMulti track Study Motivation: VDC one track events probability gets as low

70% d l ti ias 70% around elastic region

courtesy Jie LiuHall A Collaboration Meeting 2013   Min Huang 16

Up NextUp Next

Hall A Collaboration Meeting 2013   Min Huang 17

Summary The g2p experiment, ran in spring of 2012, took data

covering Mp < W < 2 GeV, 0.02 < Q2 < 0.2 GeV2p

Will provide a precision measurement of g2p in the low Q2

region for the first time Results will shed light on several physics puzzles

Hall A Collaboration Meeting 2013   Min Huang 18

Backupp

Hall A Collaboration Meeting 2013   Min Huang 19

S i LT P l i bilitSpin LT Polarizability

Can be calculated via χPT δ it bl t t t th hi l δLT more suitable to test the chiral

dynamics of QCD (in comparison to the forward spin polarizabilityγ0)

Neutron data show large deviation Neutron data show large deviation from χPT calculations

No proton data yet

plot courtesy of V. SulkoskyHall A Collaboration Meeting 2013   Min Huang 20

lBC Sum Rule2 j t d

H. Burkhardt and W. N. Cottingham, Annals. Phys., 56(1970)453

P

g2p projected

BC satisfied within errors for Neutron

Inconsistency seen in proton data

Mostly unmeasured forN

Mostly unmeasured for proton

Hall A Collaboration Meeting 2013   Min Huang 21

H d H fi St tHydrogen Hyperfine Structure Hydrogen hyperfine splitting in the ground state has been measuredHydrogen hyperfine splitting in the ground state has been measured

to a relative high accuracy of 10-13

∆S is the proton structure correction and has the largest uncertainty

6 ∆Z can be determined from elastic scattering, -41.0±0.5×10-6

∆pol involves contributions of the inelastic part (excited state), and can be extracted to 2 terms corresponding to 2 different spin-can be extracted to 2 terms corresponding to 2 different spindependent structure function of proton

Hall A Collaboration Meeting 2013   Min Huang 22

H d H fi St tHydrogen Hyperfine Structure

Integrand of ∆2

g2p Experiment

B2 is dominated by low Q2 part

g2p is unknown in this region, so there may be huge eg o , so e e ay be ugeerror when calculating ∆2

This experiment will provide a constrainta constraint

Hall A Collaboration Meeting 2013   Min Huang 23