Polarized Proton Target for the g 2. Experiment. Melissa Cummings The College of William and Mary On Behalf of the E Collaboration

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1 Polarized Proton Target for the g 2 p Experiment Melissa Cummings The College of William and Mary On Behalf of the E Collaboration APS April Meeting, April 16 th 2013

2 g 2 p Collaboration Spokespeople Alexandre Camsonne Jian- Ping Chen Don Crabb Karl Slifer Post Docs Kalyan Allada Dustin Keller James Maxwell Johnathan Mullholland Vince Sulkosky Jixie Zhang Graduate Students Toby Badman Melissa Cummings Chao Gu Min Huang Jie Liu Pengjia Zhu Ryan Zielinski JLab Target Group Chris Keith James Brock Chris Carlin Dave Meekins Josh Pierce 2

3 Introduction The g 2 p experiment will provide the Virst measurement of the proton spin structure function g 2 in the resonance region: 0.02 < Q 2 < 0.2 GeV 2 Ran concurrently with the GEp experiment, which measures the proton form factor ratio (G E /G M ) Data will shed light on outstanding physics puzzles The solid NH 3 target used for the experiment had never before been used in JLab s Hall A Data at 2.5T magnetic Vield is of particular interest 3

4 Thermal Equilibrium Polarization Material placed in a high magnetic Vield and cooled to low temperatures will polarize according to Boltzmann Statistics: P TE = e µb KT e µb KT e KT µb + e µb KT = tanh µb kt At 1K in 2.5T Vield: P TE = 0.25% for protons P TE = 92% for electrons 4

5 Dynamic Nuclear Polarization (DNP) Takes advantage of e- p spin coupling Use microwaves to induce forbidden transitions H = µ e B + µ p B + H ss e p e p ν µ = ν EPR ν NMR Both positive and negative proton polarizations can be achieved with the same magnetic Vield e p e p ν µ = ν EPR + ν NMR Relaxation Time: Proton: tens of minutes Electron: milliseconds 5

6 Target Setup - Improvements Polarized Target & Ins Refrigerator was constructed using improved techniques improved performance: 1.1K with 3W microwave power Last minute failure of original (UVa/JLab) magnet Hall B magnet was able to be modivied as a replacement Redesigned target insert Less cumbersome More reliable Overall easier to maintain! 6

7 Target Setup M. Cummings APS April Meeting April 16th

8 Magnetic Field Polarized Target & Ins Superconducting NbTi split- pair Capable of 10-4 uniformity over cylindrical volume 2 cm in diameter and 2 cm long Open geometry allows for beam to pass through or to the Vield 8

9 Target Insert Several advantages to using NH3 as a proton target: Can reach high polarizations Polarizes quickly Good resistance to radiation damage Material was irradiated at the NIST 10MeV linac prior to the run to produce extra radicals for use in DNP warm dose irradiations produce NH2 cold dose irradiations produce atomic hydrogen Material must be annealed during the run to recover high polarization M. Cummings APS April Meeting April 16th

10 Target Insert Microwaves are provided by the EIO tube and carried via wave guides to the horn positioned near the ammonia cups 5T: ~140 GHz 2.5T: ~70 GHz As radiation damage accumulates, optimal frequency changes M. Cummings APS April Meeting April 16th

11 NMR Used to measure proton polarization Observes the spin Vlip of the proton at its Larmor frequency Inductor of an LCR circuit is imbedded in the target material Can detect the energy lost or gained in the circuit as a function of the circuit s frequency RF Generator Q- Meter LCR Circuit TE 10, Event Polarization is recorded every 30s Raw Sweep Data Raw Baseline Data Index 11

12 NMR Signal Analysis Raw TE signal 10, Event with baseline Raw Sweep Data Raw Baseline Data Index Courtesy T. Badman 12

13 NMR Signal Analysis Baseline subtracted signal with TE 10, Event rd order polynomial Ait to wings Base Subtracted Data 0 3rd Order Polynomail Fit Index Courtesy T. Badman 13

14 NMR Signal Analysis Fit-subtracted TE 10, Event signal 0 Fit Subtracted Data Index Courtesy T. Badman 14

15 OfVline Polarization Results Calibration constants determined ofvline using thermal equilibrium measurements for each material (18 different NH 3 samples were used) P Enh P TE = (A G) Enh (A G) TE Polarization Offline Polarization Results for E=1.7 GeV, 2.5T, Transverse Polarization Offline Polarization Results for E=2.2 GeV, 5T, Longitudinal Run # Average polarization: for 2.5T running: ~30% for 5T running: ~70% Run # 15

16 Systematic Uncertainty Study Analysis is underway to determine polarization uncertainties Possible contributions to the uncertainty include: Magnetic Vield power supply precision Magnetic Vield uniformity He 4 manometer precision Baseline Vit Fit integration Magnetic Vield drift NMR drift Gain voltage 16

17 Summary Solid NH3 target was installed and used for the Virst time in Hall A to great success High polarizations were achieved during the run 2.5T running polarization much higher then expected! In extraction of g2p, target polarization goes directly into the cross section difference Target polarization will be one of the leading systematic contributions to cross section M. Cummings APS April Meeting April 16th