Analysis of the Ammonia Target Polarization Kangkang L. Kovacs, Physics Department, University of Virginia, Charlottesville, VA

Contents:  Introduction  Target Setup in the Eg4 Experiment  Analysis of the Target Polarization  Conclusion

Introduction  The Eg4 experiment at the Jefferson Lab (E ) ran in Jlab Hall B in early The goal was to calculate the GDH Sum for at the lowest possible Jlab momentum transfer (0.015 < Q 2 < 0.2 GeV 2 ) in the resonance region ( W < 2 GeV ).  The experiment used a highly polarized electron beam and longitudinally polarized solid ammonia targets (ND 3 and NH 3 ). 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 ND 3, NH 3 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. NH 3 : P ~ 80-90%, ND 3 : P ~ 20-40%  Target Preparation: the ND 3 /NH 3 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 = P TE * (A enhanced / A TE )  Ratio Method

h2h2 h1h1

April 5 – 19 Average CC = / April 20 – 30 Average CC = /

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.