Analysis of the Ammonia Target Polarization

Kangkang L. Kovacs, Physics Department, University of Virginia, Charlottesville, VA

Email: kangkangl@gmail.com

Contents:

Introduction

Target Setup in the Eg4 Experiment

Analysis of the Target Polarization

Conclusion

Introduction

The Eg4 experiment at the Jefferson Lab (E12-06-109) ran in Jlab Hall B in early 2006. The goal was to calculate the GDH Sum for at the lowest possible Jlab momentum transfer (0.015 < Q2 < 0.2 GeV2) in the resonance region ( W < 2 GeV ).

The experiment used a highly polarized electron beam and longitudinally polarized solid ammonia targets (ND3 and NH3). Various methods to

determine the deuteron target polarization will be discussed and their results will be compared.

Setup for the EG4 Experiment at the Jefferson Lab

Fig 1 is a diagram of the target inside the HallB detector.

The target system includes:

Superconducting magnet

Helium evaporation refrigerator

Microwave

NMR system

Insert housing the target material

The helium evaporation refrigerator can cool the target down to 1K (banjo temperature) with the superconducting magnet creating a magnetic field around 5T to keep the target sufficiently polarized.

The scattered particles then enter the drift chamber and are detected by the Cherenkov counter and other apparatus.

Diagram of the insert that houses the different target materials. The upper end of the insert is connected with NMR cables and microwave input. The lower end of the target insert has 4 cells that hold ND3 , NH3 and the carbon target respectively. The carbon target is used as a calibration to the ammonia target polarizations.

Target Preparation & Polarization Analysis:

Target Polarization: the target was polarized using the DNP method (Dynamic Nuclear Polarization) method. NH3: P ~ 80-90%, ND3: P ~ 20-40%

Target Preparation: the ND3/NH3 ammonia target was prepared by slowly freezing the ammonia gas at 77K and then crushing it into small pieces, approximately 1-2mm in diameter.

the Nuclear Magnetic Resonance System (NMR) was used to monitor the target polarization.

Photo of the target cell after the beam exposure. The beads in the center turned purple from the exposure while the beads at the edges did not receive much beam.

The target polarization during the experiment was monitored by a

Nuclear Magnetic Resonance (NMR) System. The method lies in inducing

and detecting nuclear magnetic transitions, where the rate of

transitions is proportional to the population difference between the

energy levels, therefore indicating the original polarization

value.

Area Method

P = PTE * (Aenhanced / ATE)

Ratio Method

April 5 – 19

Average CC = 193.25 +/- 9.65

April 20 – 30

Average CC = 219.87 +/- 10.78

Inclusive Scattering PbPt Analysis

PbPt = 0.152 +/- 0.035, Pb ~ 80%

run i t bpol tpol ratee- ratee+ A_al l err A_el a err f c1/ f c2 w=(0. 0, 3. 2) w=(0. 85, 1. 05) 51588 2 0. 85 0. 60 20. 25 0. 72 0. 0007 0. 0005 0. 0031 0. 0009 0. 99976 51589 2 0. 85 0. 60 20. 83 0. 74 0. 0013 0. 0005 0. 0035 0. 0009 0. 99988 51590 2 0. 85 0. 60 20. 69 0. 74 -0. 0008 0. 0004 0. 0013 0. 0008 1. 00042 51591 2 0. 85 0. 60 20. 27 0. 73 0. 0002 0. 0004 0. 0037 0. 0008 0. 99999 51594 2 -0. 85 0. 60 20. 75 0. 74 0. 0016 0. 0004 0. 0029 0. 0008 1. 00034 51595 2 -0. 85 0. 60 20. 69 0. 73 0. 0013 0. 0004 0. 0045 0. 0008 1. 00032 51610 2 -0. 85 0. 60 22. 53 0. 79 0. 0013 0. 0004 0. 0041 0. 0008 1. 00070 51611 2 -0. 85 0. 60 20. 84 0. 72 0. 0018 0. 0005 0. 0055 0. 0009 1. 00071 51618 2 -0. 85 0. 60 18. 75 0. 65 -0. 0003 0. 0004 0. 0033 0. 0008 0. 99931 51619 2 -0. 85 0. 60 18. 69 0. 64 -0. 0007 0. 0004 0. 0027 0. 0007 0. 99936 51570 4 0. 85 0. 60 14. 23 0. 47 -0. 0002 0. 0005 0. 0006 0. 0008 0. 99987 PbPt versus Q2 f or E0=1. 990 ND3 target Usi ng w=(0. 92, 0. 97) q2 Pbpt err A_pred di l Pbpt(c) err(c) 0. 042 0. 021 0. 142 0. 026 0. 208 -0. 019 0. 160 0. 050 0. 231 0. 071 0. 031 0. 188 -0. 031 0. 079 0. 059 0. 135 0. 056 0. 037 0. 202 -0. 082 0. 063 0. 071 0. 157 0. 046 0. 043 0. 238 0. 200 0. 052 0. 084 0. 133 0. 037 0. 051 0. 280 0. 209 0. 044 0. 101 0. 178 0. 033 0. 060 0. 291 0. 051 0. 040 0. 120 0. 203 0. 035 0. 071 0. 289 0. 262 0. 041 0. 144 0. 115 0. 035 0. 083 0. 281 0. 200 0. 042 0. 172 0. 179 0. 034 0. 098 0. 286 -0. 309 0. 040 0. 205 0. 163 0. 034 0. 115 0. 291 0. 061 0. 041 0. 245 0. 139 0. 034 0. 134 0. 293 -0. 176 0. 041 0. 292 0. 107 0. 035 0. 157 0. 291 0. 170 0. 042 0. 348 0. 160 0. 034 0. 183 0. 304 0. 035 0. 041 0. 416 0. 183 0. 038 0. 214 0. 290 -0. 061 0. 045 0. 496 0. 116 0. 041 0. 249 0. 292 -0. 099 0. 049 0. 593 0. 116 0. 048 0. 291 0. 320 0. 106 0. 058 0. 707 0. 084 0. 050 0. 339 0. 292 -0. 248 0. 059 0. 845 0. 286 0. 056 0. 394 0. 305 0. 072 0. 067 1. 010 0. 088 0. 079 0. 457 0. 320 0. 297 0. 096 1. 205 0. 000 0. 335 0. 530 0. 490 -1. 925 0. 469 average over q2=(0. 077, 0. 645) pbpt, err = 0. 152 0. 010 0. 035 0. 012

Conclusion

We were able to apply the ratio method on most of the NMR measurements during a run period and obtain stable ND3 polarization results.

Limits of the ratio method, especially at lower polarizations were discussed and compared to that of the area method.

Scattering Asymmetry method can be used to obtain the target polarization as well, thus offering us another source to check the reliability of the ratio method.