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Measurement of G n E at Low Momentum Transfer

Exploring vital reasons for measuring GnE at low Q2, methodology using BLAST experiment, preliminary results, and future outlook. Highlights neutron charge-density distribution and relevance for parity violation experiments.

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Measurement of G n E at Low Momentum Transfer

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  1. Measurement of GnE at Low Momentum Transfer Scientific motivation (why GnEat low Q2) Methodology (how we measure GnE) BLAST experiment Preliminary results Discussion and a look ahead Vitaliy Ziskin MIT

  2. Why Measure GnE at Low Q2 • GE(Q2=0)=0, rms charge radius <r2>=-0.11fm2 • GnEat lowQ2is essential for parity violation experiments Neutron charge density distribution is poorly known as compared to a proton Vitaliy Ziskin MIT

  3. Why Measure GnE at Low Q2 (contd.) • Not enough high precision data at low Q2 Vitaliy Ziskin MIT

  4. How to Measure GnE • No free neutron targets, 2H or 3He targets are used • Cross section is dominated by GnM not sensitive GnE • Asymmetry measurements used instead Vitaliy Ziskin MIT

  5. p (n) 200% q CM w ( , q ) pq 100% d 0% (p) n n n V A ( e , e ' ) µ G G q CM = p n ed E M pq p p V A ( e , e ' ) µ G G q CM = 0 p ed E M pq ( e , e ' p ) ( e , e ' n ) Neutron Vector Asymmetry, AVed(p/2,0) Vitaliy Ziskin MIT

  6. South Hall e- Ring • 850 MeV polarized e- • Stored or extracted modes • 120 mA average current • Compton polarimeter Vitaliy Ziskin MIT

  7. Polarized Deuterium Target • Cell geometry: circular 15 mm x 600 mm • Cell coating: Drifilm • Cell temperature: T = 90K • Target density: dt=6.0x1013 nucl cm-2 (D) • Polarization Pz = ~0.72 (D) • Magnet holding field: B= 500mT (D) I n t e r n a l T a r g e t T e c h n i q u e • H2 and D2 target gases • Beam sees no foils • Low target density  Low-energy recoils • High beam currents • High polarization • Rapid reversal • Easy to orient Vitaliy Ziskin MIT

  8. BLAST Detector • Toroidal spectrometer • Dpe/pe= 3% • 32o target angle Wire Chambers Target Cerenkov Detectors Neutron Counters Scintillators Vitaliy Ziskin MIT

  9. Neutron Detectors • Six walls of plastic scintillator bars (Bicron-408) • Each scintillator is equipped with a flasher for timing • Total estimated neutron efficiency from effective material thickness: ~30% (right), ~10% (left) • Distance from target is 3.5 to 5.5 m • Double charged particle veto: TOF + Wire Chamber Vitaliy Ziskin MIT

  10. Neutron Reconstruction g counts neutron • Time of flight gamma-neutron separation • Use gamma to measure time resolution of ~2 ns • Neutron momentum resolution: ~5% (estimated) Vitaliy Ziskin MIT

  11. Missing Mass and Momentum Spectrum PRELIMINARY • High signal to noise ratio • 140k total neutrons after cuts • <2% empty target contribution • Some background from hydrogen not yet understood PRELIMINARY Vitaliy Ziskin MIT

  12. Extracting GnE • BLASTMC calculation for different GnEfrom H. Arenhovel (BONN+MEC+IC+FSI) • Calculatec2for eachGnEby comparing experimental AVed(90o,0)to BLASTMC • c2(GnE) = c2min • c2(GnE + DGnE) = c2min+1 Vitaliy Ziskin MIT

  13. Preliminary Results • 60 % of data has been analyzed for this conference • 252 kC • hPz = 0.475 +/- 0.010 • Assume dipole GnM=GD *statistical only Vitaliy Ziskin MIT

  14. Preliminary GnE World Plot PRELIMINARY Vitaliy Ziskin MIT

  15. Conclusion • Reconstruction is still work in progress, will affect experimental asymmetry at large Pm • Correction for radiative effects needs to be applied • Better value of GnM will be determined from a global fit and simultaneous measurement at BLAST • A study of model dependence is still needed • More data still to be analyzed • Final results to be a available next year Vitaliy Ziskin MIT

  16. BLAST COLLABORATION R. Alarcon, E. Geis, J. Prince, B. Tonguc, A. Young Arizona State University, Tempe, AZ 85287 J. Althouse, C. D’Andrea, A. Goodhue, J. Pavel, T. Smith, Dartmouth College, Dartmouth, NH D. Dutta, H. Gao, W. Xu Duke UniversityDurham, NC 27708-0305 H. Arenhövel, Johannes Gutenberg-Universität, Mainz, Germany T. Akdogan, W. Bertozzi, T. Botto, M. Chtangeev, B. Clasie, C. Crawford, A. Degrush, K. Dow, M. Farkhondeh, W. Franklin, S. Gilad, D. Hasell, E. Ilhoff, J. Kelsey, H. Kolster, M.Kohl, A. Maschinot, J. Matthews, N. Meitanis, R. Milner, R. Redwine, J. Seely, S. Sobczynski, C. Tschalaer, E. Tsentalovich, W. Turchinetz, Y. Xiao, C. Zhang, V. Ziskin, T. Zwart Massachusetts Institute of Technology, Cambridge, MA 02139 andBates Linear Accelerator Center, Middleton, MA 01949 J. Calarco, W. Hersman, M. Holtrop, O. Filoti, P. Karpius, A. Sindile, T. Lee University of New Hampshire, Durham, NH 03824 J. Rapaport Ohio University, Athens, OH 45701 K. McIlhany, A. Mosser United States Naval Academy, Annapolis, MD 21402 J. F. J. van den Brand, H. J. Bulten, H. R. Poolman Vrije Universitaet and NIKHEF, Amsterdam, The Netherlands W. Haeberli, T. Wise University of Wisconsin, Madison, WI 53706 Vitaliy Ziskin MIT

  17. Extracting Gen (Q2=0.14 GeV2/c2) Vitaliy Ziskin MIT

  18. Extracting Gen (Q2=0.20 GeV2/c2) Vitaliy Ziskin MIT

  19. Extracting Gen (Q2=0.29 GeV2/c2) Vitaliy Ziskin MIT

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