Min Huang Duke University, TUNL On behalf of the E (g2p) collaboration

Transcription

1 Min Huang Duke University, TUNL On behalf of the E (g2p) collaboration Hall A Collaboration Meeting, June 13th, 2013

2 E g 2p & the LT Spin Polarizability Spokespeople Alexandre Camsonne (JLab) Jian-Ping Chen (JLab) Don Crabb (UVA) Karl Slifer (UNH) Post Docs Kalyan Allada Elena Long James Maxwell Vince Sulkosky Jixie Zhang Graduate Students Toby Badman Melissa Cummings Chao Gu Min Huang Jie Liu Pengjia Zhu Ryan Zielinski Hall A Collaboration Meeting 2013 Min Huang 2

3 Electron Scattering Inclusive polarized differential cross section e(e,k) θ γ* * (ν,q) e (E,k ) P (M,0) W g1, g2: polarized nucleon spin structure functions Hall A Collaboration Meeting 2013 Min Huang 3

4 How to Obtain g 2 e e e e measured by g2p experiment, essential contribution to g2 in this kinematic region A t Will measure both asymmetry and cross section Hall B EG4 data will be combined, g2p has one measurement to cross check Hall A Collaboration Meeting 2013 Min Huang 4

5 Motivation Measure the proton spin structure function g 2 in the low 2 Q 2 region (0.02<Q 2 <0.2 GeV 2 ) for the first time Extract δ LT to provide a benchmark test of χpt calculations Opportunity to test the Burkhardt-Cottingham sum rule Crucial inputs for hydrogen hyperfine splitting and proton charge radius measurements Talk by Jixie Zhang: proton FF Hall A Collaboration Meeting 2013 Min Huang 5

6 Experimental Setup Large Scale Installation in Hall A Transverse polarized NH3 target (2.5/5T field) Low beam current (<100 na) -> >newbeamline diagnostics Rasters Septum magnets Septa BCM Rasters Chicane BPM Hall A High Resolution Spectrometer (HRS) Polarized NH3 Target Local Dump APS April Meeting 2013 Min Huang 6

7 kinematics Coverage run concurrently with G p e M p < W < 2 GeV 0.02 < Q 2 < 0.2 GeV 2 Beam Energy /GeV Target age Field /T APS April Meeting 2013 Min Huang 7

8 Projections Resonance MAID Hall A Collaboration Meeting 2013 Min Huang 8

9 Status of Analysis Hall A Collaboration Meeting 2013 Min Huang 9

10 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 Hall A Collaboration Meeting 2013 Min Huang courtesy Pengjia Zhu 10

11 Optics Determine center angle with high accuracy Pointing method Uncertainty of θ 1% contribution to cross section 4% d(δe )=100 KeV Preliminary results LHRS 5.77, RHRS 5.67 To determine uncertainty still in progress Beam position Data calibration: large beam offset from center, corrections Hall A Collaboration Meeting 2013 Min Huang 11

12 Optics with Target tfield 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 Sieve slit target: use field map to ray trace the electrons Used simulation to check this idea SNAKE to generate the forward transport functions Data calibration/snake to provide the reverse transport functions Q3 VDC Target Septum Q2 Sieve e slit Q1 Dipole Hall A Collaboration Meeting 2013 Min Huang 12

13 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 courtesy Chao Gu Hall A Collaboration Meeting 2013 Min Huang 13

14 Target Polarization Target polarization measured via NMR and recorded every 30s Offline calibration done using thermal equilibrium (TE) measurements Polarization averaged across each production run. Detailed systematic uncertainty study close to be finalized courtesy Toby Badman Hall A Collaboration Meeting 2013 Min Huang 14

15 Cut Efficiencies Detector eeco calibrations and defficiencies ce cesweedo were done to odee determine e cuts for PID Similar analysis for LHRS courtesy Melissa Cummings Hall A Collaboration Meeting 2013 Min Huang 15

16 Multi track track Study Motivation: VDC one track events probability gets as low as 70% around elastic region courtesy Jie Liu Hall A Collaboration Meeting 2013 Min Huang 16

17 Up Next Hall A Collaboration Meeting 2013 Min Huang 17

18 Summary The g2p experiment, ran in spring of 2012, took data covering M p < W < 2 GeV, 0.02 < Q 2 < 0.2 GeV 2 p Will provide a precision measurement of g 2p in the low Q 2 region for the first time Results will shed light on several physics puzzles Hall A Collaboration Meeting 2013 Min Huang 18

19 Backup Hall A Collaboration Meeting 2013 Min Huang 19

20 Spin LT Polarizability Can be calculated via χpt δ LT more suitable to test t the chiral dynamics of QCD (in comparison to the forward spin polarizability γ 0 ) Neutron data show large deviation from χpt calculations No proton data yet plot courtesy of V. Sulkosky Hall A Collaboration Meeting 2013 Min Huang 20

21 BC Sum Rule P N g2p projected H. Burkhardt and W. N. Cottingham, Annals. Phys., 56(1970)453 BC satisfied within errors for Neutron Inconsistency seen in proton data Mostly unmeasured for proton Hall A Collaboration Meeting 2013 Min Huang 21

22 Hydrogen Hyperfine Structuret Hydrogen hyperfine splitting in the ground state has been measured to a relative high accuracy of S is the proton structure correction and has the largest uncertainty Z can be determined from elastic scattering, -41.0± pol involves contributions of the inelastic part (excited state), and can be extracted to 2 terms corresponding to 2 different spin- dependent structure function of proton Hall A Collaboration Meeting 2013 Min Huang 22

23 Hydrogen Hyperfine Structuret g2 p Experiment Integrand of 2 B2 is dominated by low Q2 part g2p is unknown in this region, so there e may be huge error when calculating 2 This experiment will provide a constraint Hall A Collaboration Meeting 2013 Min Huang 23