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The NPDGamma Experiment

The NPDGamma Experiment . A measurement of the parity violating directional γ - asymmetry in polarized cold neutron capture on hydrogen. Nadia Fomin University of Tennessee for the NPDGamma Collaboration Charlottesville, VA October 6 th , 2008. Outline. Introduction and Motivation

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The NPDGamma Experiment

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  1. The NPDGamma Experiment A measurement of the parity violating directional γ-asymmetry in polarized cold neutron capture on hydrogen. Nadia Fomin University of Tennessee for the NPDGamma Collaboration Charlottesville, VA October 6th, 2008

  2. Outline • Introduction and Motivation • First Run at LANSCE • Analysis and Preliminary Results • Next Phase at SNS

  3. N N PC PV M N N Introduction • Weak interaction at low momentum transfer between nucleons is accessible through measurements of small parity-odd amplitudes • Natural scale ~x10-7, set by relative size of meson vs boson exchange amplitudes • Weak NN couplings are largely unknown: non-perturbative regime makes calculations and experiments challenging • Why do we care? • Weak interaction is manifested in long range nuclear interactions • Inconsistent results from previous measurements (ex: fπ) • weak NN couplings => allows for a quantitative interpretation of PV phenomena at nuclear and atomic scales • probe of QCD – nuclear properties at short range

  4. Introduction - continued Corresponding to • DDH model – uses valence quarks to calculate effective PV meson-nucleon coupling directly from SM via 7 weak meson coupling constants • Observables can be written as their combinations • EFT – 5 low energy constants, connect to 5 parity-odd S-P NN amplitudes • Model-independent

  5. DDH predicted to be -5x10-8 Reaction of interest: isolates the ΔI=1 part of the weak interaction + Eγ=2.2MeV + We measure Aγ, the PV asymmetry in the distribution of emitted gammas.

  6. LANSCE at Los Alamos National Laboratory • 800MeV protons @ ~100μA, 20Hz • Tungsten Spallation Target -> Neutrons • H2 moderator • FP12 - 20m SM guide, straight beamline LINAC Spallation Source Guide Hall

  7. Experimental Setup

  8. NDPGamma on FP12 10G magnetic guide field coils to preserve neutron polarization

  9. TOF 1/λ 3He Spin Filter • 3He gas is polarized via spin exchange with laser-polarized Rb • σsinglet/σtriplet~104 – neutrons with spins || to 3He pass through (filter) • 3He Polarization ~ 55% • Relaxation time ~500hrs At the pulse source, a simple relationship exists between energy and arrival time of the neutrons

  10. Resonant RF Spin Flipper • A resonant RF magnetic field (B1coswt) is applied for a time t to precess the neutron spin by π. • B1(t) 1/TOF, for reversing neutron spin in wide energy range (~0.5-50 meV). • Rapid spin reversal minimizes systematic effects

  11. LH2 target and CsI detector array 30 cm 30 cm • 3π acceptance • Current-mode experiment • γ-rate ~100MHz (single detector) • Low noise solid-state amplifiers 16L vessel of liquid parahydrogen Ortho-hydrogen scatters the neutrons and leads to beam depolarization

  12. Data Summary from 2006 run Number of good runs (8.5min long) Neutron Polarization Spin Flip Efficiency Para fraction in LH2 target Al background Depolarization Stern-Gerlach steering Asym γ-ray circ.pol. Asym ~5000 53±2.5% 98.8±0.5% 99.98±0.2% ~25% (ave) 2% 10-10 10-10

  13. Analysis Procedure i i θ j γ energy deposition Neutron Polarization Neutron depolarization SF efficiency Detector geometry Capture Locus Raw asymmetry is formed between each pair of detectors {i,j} for each spin sequence, for each time bin via Raw asymmetry for a detector pair {ij}, time bin t, is related to physics asymmetry via:

  14. Analysis Procedure - continued • Time bins (40μs) are averaged over with neutrons polarization and other energy-dependent quantities as weights. • Asymmetry for a detector pair is then given by • AUD is extracted from a fit of Araw to θ, the angle of detector pair i i θ j Calibration Target: 35Cl -target with a large and well-known γ-asymmetry (26±7)x10-6

  15. Preliminary Hydrogen Result A γ,UD=(-1.9±2.0±0.2)x10-7 A γ,LR=(-1.1±2.1±0.2)x10-7

  16. Spallation Neutron Source at ORNL • 1.4 GeV protons, 60Hz • LHg Spallation target -> neutrons • H2 moderator • 17m SM guide, curved

  17. 7 - Engineering Diffractometer IDT CFI Funded Commission 2008 11A - Powder Diffractometer Commission 2007 9 – VISION 6 - SANS Commission 2007 12 - Single Crystal Diffractometer Commission 2009 5 - Cold Neutron Chopper Spectrometer Commission 2007 13 - Fundamental Physics Beamline Commission 2008 4B - Liquids Reflectometer Commission 2006 14B - Hybrid Spectrometer Commission 2011 4A - Magnetism Reflectometer Commission 2006 15 – Spin Echo 3 - High Pressure Diffractometer Commission 2008 17 - High Resolution Chopper Spectrometer Commission 2008 18 - Wide Angle Chopper Spectrometer Commission 2007 1B - Disordered Mat’ls Commission 2010 2 - Backscattering Spectrometer Commission 2006 Spallation Neutron Source at ORNL

  18. FNPB – commissioned on September 12th, 2008 • BL13(a/b) • cold beamline • UCN beamline - nEDM

  19. FNPB – cold beamline commissioned on Sep 12th, 2008

  20. Supermirror polarizer CsI Detector Array Liquid H2 Target H2 Vent Line H2 Manifold Enclosure Spin Flipper FNPB guide Magnetic Field Coils Beam Stop Conceptual design of Experiment

  21. What’s new for the SNS run • SuperMirror Polarizer replaces the 3He Polarizer (x4.1) • Higher moderator brightness (x12) => more cold/slow neutrons • New LH2 target – thinner windows, smaller background contribution Predicted size -5x10-8 - NPDGamma will make a 20% measurement, most precise so far • Installation begins in November 2008 • Production Hydrogen Data – summer 2009

  22. The NPDGamma collaboration P. Alonzi3, R.Alracon1, S. Balascuta1, L. Barron-Palos2, S. Baeßler3, J.D. Bowman4,J.R.Calarco9, R.D. Carlini5, W.C. Chen6, T.E. Chupp7, C. Crawford8, M. Dabaghyan9, J.Dadras12,A. Danagoulian10, M. Dawkins11, N. Fomin12, S.J. Freedman13, T.R. Gentile6, M.T. Gericke14R.C. Gillis11, G.F. Greene4,12, F. W. Hersman9, T. Ino15, G.L. Jones16, B. Lauss17, W. Lee18, M. Leuschner11, W. Losowski11, R. Mahurin12, Y. Masuda15, J. Mei11, G.S. Mitchell19, S. Muto15, H. Nann11, S. Page14, D.Počanic3,S.I. Penttila4, D. Ramsay14,20, A. Salas Bacci10, S. Santra21, P.-N. Seo22, E. Sharapov23, M. Sharma7, T. Smith24, W.M. Snow11, W.S. Wilburn10 V. Yuan10 1Arizona State University 2Universidad Nacional Autonoma de Mexico 3University of Virginia 4Oak Ridge National Laboratory 5Thomas Jefferson National Laboratory 6National Institute of Standards and Technology 7Univeristy of Michigan, Ann Arbor 8University of Kentucky 9University of New Hampshire 10Los Alamos National Laboratory 11Indiana University 12University of Tennessee 13University of California at Berkeley 14University of Manitoba, Canada 15High Energy Accelerator Research Organization (KEK), Japan 16Hamilton College 17Paul Scherrer Institute, Switzerland 18Spallation Neutron Source 19University of California at Davis 20TRIUMF, Canada 21Bhabha Atomic Research Center, India 22Duke University 23Joint Institute of Nuclear Research, Dubna, Russia 24University of Dayton

  23. Systematic Effects (#) see Ref. [30] sn is the neutron spin and k is momentum of particle. (*) size calculated (**) size measured

  24. E1 E1 E1 E1 is primarily sensitive to the ∆I = 1 component of the weak interaction What gives rise to parity violation in ? Low-energy continuum states M1 (PC) Bound states p exchange

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