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Measuring Parity Violating Neutron Spin Rotation

n. Measuring Parity Violating Neutron Spin Rotation. Kangfei Gan The George Washington Unversity. NNPSS ’07 20 Jul 2007. n. Collaboration. C.D. Bass 1 , B.E. Crawford 2 , J.M. Dawkins 1 , T.D. Findley 1 , K. Gan 3 ,

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Measuring Parity Violating Neutron Spin Rotation

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  1. n Measuring Parity Violating Neutron Spin Rotation Kangfei Gan The George Washington Unversity NNPSS ’07 20 Jul 2007

  2. n Collaboration C.D. Bass1, B.E. Crawford2, J.M. Dawkins1, T.D. Findley1, K. Gan3, B.R. Heckel4, J.C. Horton1, C.R. Huffer1, P.R. Huffman5, D. Luo1, D.M. Markoff6, A.M. Micherdzinska1, H.P. Mumm7, J.S. Nico7, A.K. Opper3, E. Sharapov8, M.G. Sarsour1, W.M. Snow1, H.E. Swanson4, V. Zhumabekova9  Indiana University / IUCF 1 Gettysburg College 2 The George Washington University 3 University of Washington 4 North Carolina State University / TUNL 5 North Carolina Central University 6 National Institute of Standards and Technology (NIST) 7 Joint Institute for Nuclear Research, Dubna, Russia 8 Al-Farabi Khazakh National University 9 NSF PHY-0100348

  3. Motivations Compared to strong interaction, the magnitude of weak interaction is very small. Direct exchange of short ranged weak vector bosons (W, Z) suppressed by repulsive strong interaction. N N Mesons In Nucleon-Nucleon (NN) interactions, the weak interaction couplings are not well understood. DDH model (Desplanques et al, 1980) N N *Holstein. Weak Interactions in Nuclei

  4. n Theoretical description Historically the PV nuclear interaction has been described by the DDH quark model => 6 weak meson exchange coupling constants:fp , hr0 , hr1 , hr2 , hw0 , hw1 n-4He spin rotation in terms of weak couplings • *New “Hybrid” Effective Field Theory description is valid for ELab< 40MeV • 5 dimensionless Danilov parameters (related to the S-P scattering amplitudes: 1S0-3P0, 3S1-1P1, 3S1-3P1 transitions) • and a long-range one-pion exchange parameter (proportional to the PV pion-nucleon coupling constant h1p) • *Liu, C.P., 2006, Parity Violating Observables of Two-Nucleon Systems in Effective Field Theory, arXiv: nucl-th/0609078 v1 28 Sep 2006 • Low Energy, Few Body Interaction measurements are useful • Neutron Spin Rotation project

  5. n For 4He: = 0 For a neutron polarized in the +y direction: PV Neutron Spin Rotation Forward scattering amplitude for low-energy neutrons: Index of Refraction of a medium: Neutron’s phase as it passes through the medium:

  6. n y ASM z x PV Neutron Spin Rotation PSM detector • PV rotation angle / unit length (dfPV/dx) approaches a finite limit for zero neutron energy: dfPV/dx ~ 10-6 rad/m based on dimensional analysis 3x10-7 rad/m goal in n+4He • dfPC/dx (due to B field) can be much larger than dfPV/dx, and is vn dependent

  7. n Cross section of Spin Rotation Apparatus Side View

  8. n 3.1x 108 n/sec/cm2 1.2 x 109 n/sec/cm2 B Neutron flux Polarizing Super Mirror Polarized beam • spin-dependent scattering from magnetized mirrors • Alternating layers of magnetic surface (cobalt) and absorptive layer (titanium and gadolinium); 1mm separation; Placed in 300 G permanent box. • Typical polarization: 98%; transmission: 25% unpolarized beam 14 mrad

  9. Input Coil

  10. Beam Guide

  11. n Target Design thermometry (1 per target body) LHe level sensor (1 per chamber) fluxgate magnetometer (2 per target body control strings: drainpipes & magnetometers LHe centrifugal pump driveshaft pi-coil

  12. n y y jp- f f x x p-Coil y beam direction z • a rectangular coil that produces a vertical magnetic field in the path of the beam • wound to prevent field leakage beyond the coil • designed so that the spin of a typical cold neutron will precess a total ofpradians over the path of the coil p-coil x

  13. n PI-COIL Empty PV Material FRONT TARGET BACK TARGET FLIPPING COIL Polarimeter Design MAGNETIC SHIELDING • Moving LHe target about pi-coil isolates ϕPV from ϕPC signal that can be measured as an asymmetry in beam intensity between target states PV Material Empty PSM ASM TOP VIEW

  14. n L R Flight of the Neutron polarizer passes neutrons with “up” vertical spin state into target L R

  15. n PC PV +PC L R Flight of the Neutron L & R neutrons experience Larmor precession about residual B-fields R neutrons experience additional rotation due to NN weak interaction L R

  16. n - PC - (PC+ PV) L R Flight of the Neutron L R Pi-Coil precesses neutron spin 180o about vertical axis

  17. n -(PC + PV) + PC = - PV -PC + (PC+ PV) = + PV L R Flight of the Neutron L R L & R neutrons experience Larmor precession about residual B-fields L neutrons experience additional rotation due to NN weak interaction with LHe

  18. n PI-COIL FRONT TARGET BACK TARGET FLIPPING COIL Flight of the Neutron MAGNETIC SHIELDING Empty PV Material PV Material Empty PSM ASM • Neutron spins are either parallel or antiparallel to the ASM • Parallel spins pass through ASM and enter 3He Ion Chamber detector • Asymmetry of count rate for flipping coil states & target states yields spin rotation

  19. Looking from downstream End. Top view.

  20. Segmented Ion Chamber Detector • High flux n beam, current mode detector • Not sensitive to gammas • High efficiency, low noise • Separate PV rotation (v independent) from NPV rotation (v dependent)

  21. Layout (4 segmentations) Graph by: Chris S. Blessinger

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