1. The NPDGamma Experiment Measurement of Parity-Violating Gamma-ray Asymmetry on Hydrogen with Polarized Cold Neutrons Serpil Kucuker Dogan University of Tennessee On behalf of the NPDGamma Collaboration

2. The NPDGamma Collaboration P. Alonzi 3, R.Alracon 1, S. Balascuta 1, L. Barron-Palos 2, S. Baeßler 3, J.D. Bowman 4,J.R.Calarco 9, R.D. Carlini 5, W.C. Chen 6, T.E. Chupp 7, C. Crawford 8, M. Dabaghyan 9, A. Danagoulian 10, M. Dawkins 11, N. Fomin 10, S.J. Freedman 13, T.R. Gentile 6, M.T. Gericke 14 R.C. Gillis 11, K. Grammer 12, G.L. Greene 4,12, F. W. Hersman 9, T. Ino 15, G.L. Jones 16, S. Kucuker 12, B. Lauss 17, W. Lee 18, M. Leuschner 11, W. Losowski 11, E. Martin 8, R. Mahurin 14, M. McCrea 14, Y. Masuda 15, J. Mei 11, G.S. Mitchell 19, S. Muto 15, M. Musgrave 12, H. Nann 11, S. Page 14, D.Počanic 3,S.I. Penttila 4, D. Ramsay 14,20, A. Salas Bacci 10, S. Santra 21, P.-N. Seo 3, E. Sharapov 23, M. Sharma 7, T. Smith 24, W.M. Snow 11, W.S. Wilburn 10 V. Yuan 10 1 Arizona State University 2 Universidad Nacional Autonoma de Mexico 3 University of Virginia 4 Oak Ridge National Laboratory 5 Thomas Jefferson National Laboratory 6 National Institute of Standards and Technology 7 Univeristy of Michigan, Ann Arbor 8 University of Kentucky 9 University of New Hampshire 10 Los Alamos National Laboratory 11 Indiana University 12 University of Tennessee 13 University of California at Berkeley 14 University of Manitoba, Canada 15 High Energy Accelerator Research Organization (KEK), Japan 16 Hamilton College 17 Paul Scherrer Institute, Switzerland 18 Spallation Neutron Source 19 University of California at Davis 20 TRIUMF, Canada 21 Bhabha Atomic Research Center, India 22 Duke University 23 Joint Institute of Nuclear Research, Dubna, Russia 24 University of Dayton

3. Outline Motivation and Theory Experimental Setup Targets Analysis Procedure Status

4. Motivation and Theory Measure the parity-violating (PV)  -ray asymmetry, A  in the reaction to a precision of 1  10 -8 in order to provide a sensitive test of hadronic weak interaction models In general, the PV asymmetry in a measurement can be expressed as an expansion in terms of the coupling constants

5. The asymmetry depends almost exclusively on the weak pion-nucleon coupling f  NPDGamma => Two-Body System- measures an asymmetry with a simple relation to f  - providing a theoretically clean interpretation of the experiment. Motivation and Theory Cont.

6. The main NPDGamma observable->up-down asymmetry in the angular distribution of gamma-rays with respect to the neutron spin direction. expected to be in the range of 0 to 10x10 -8 ILL and LANSCE provides A γ ≤2x10 -7 SNS–FOM(NP 2 ) x100 improved

7. Spallation Neutron Source at ORNL 1.4 GeV protons, 60Hz, 1 MW power Hg Spallation target neutrons H 2 moderator cold neutrons 17 m SM guide, curved

8. Experimental Setup

9. The NPDG Experiment at FnPB Liquid H 2 Target CsI Detector Array Beam Stop Spin Flipper

10. Components Super Mirror Polarizer Guide Field RF Spin Flipper (RFSF) Detector Array DAQ 16L LH 2 Target Ortho-Para Monitor Polarization Analyzer Ion-chamber Beam Intensity Monitors

11. Super Mirror Polarizer High Neutron Polarization~95% Stable Polarization

12. RF Spin Flipper Creates an oscillating magnetic field tuned to the Larmor frequency of the neutrons.

13. Detector Array 48 CsI(Tl) scintillator crystals coupled to 3 inch vacuum photodiodes 4 rings of 12 CsI (Tl) Detectors 15x15x15 cm 3 each Covers a solid angle of 3π High Count Rate Current mode gamma detection The gain is provided by low noise solid state preamplifiers

14. Commissioning Targets B 4 C For counting statistics limit 6 Li For background and shielding studies 35 Cl Commission the entire system -to demonstrate our ability to measure a large and well known PV asymmetry Al Largest source of background -measure the PV asymmetry for window subtraction for LH 2 target

15. LH 2 Target 16L liquid para-hydrogen vessel in a vacuum 30 cm diameter x30 cm long Target must be pure para- hydrogen to avoid Beam Depolarization and Reflection

16. Scattering from ortho-H 2 leads to depolarization. Target must be pure Para-Hydrogen. Distance (cm) Pure Ortho - H 2 Pure Para - H 2 MCNP calculation of neutron beam intensity in liquid hydrogen target

17. Analysis Procedure PV asymmetry Essentially seen in a difference of the number of gamma-rays going up and down Check for possible left-right asymmetry Asymmetry for a Detector Pair ii j θ

18. Analysis Procedure Cont. Dynamic Pedestal Subtraction - dilution from beta-delayed gammas Geometrical factors - cosine dependence of cross section Asymmetry from prompt Al gammas Beam polarization - ToF adjustment prior to asymmetry calculation

19. Status Beam profile measured Flux confirmed Detailed studies of new shielding material performed Polarization of beam established Precision measurements of detector locations completed Al and Chlorine data collection completed - Preliminary Data Analysis completed - Source of false asymmetry was found and corrected

20. Status Cont. LH 2 target set-up completed Target-cooled down and filled successfully Neutron Beam on LH 2 target Production Hydrogen Data

21. Talks Nadia Fomin-Measurement of the Parity-Violating directional Gamma-ray Asymmetry in Polarized Neutron Capture on 35Cl SESSION D11-EMBASSY F Elise Martin-Neutron Beam Characterization for the NPDGamma Experiment at SNS Matthew Musgrave-Neutron Polarization Measurements with a 3He Spin Filter for the NPDGamma Experiment Chad Gillis-A liquid parahydrogen target for the NPDGamma Experiment Kyle Grammer-Calculation of the Detector Solid Angles and Geometrical Factors for the NPDGamma Experiment