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Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid- 4 He

n. Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid- 4 He. Anna Micherdzinska I ndiana U niversity C yclotron F acility. PANIC 27 Oct 2005. n. Collaboration. C.D. Bass 2 , B.E. Crawford 1 , J.M. Dawkins 2 , B.R. Heckel 5 , P.R. Huffman 4 ,

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Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid- 4 He

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  1. n Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid-4He Anna Micherdzinska Indiana University Cyclotron Facility PANIC 27 Oct 2005

  2. n Collaboration C.D. Bass2, B.E. Crawford1, J.M. Dawkins2, B.R. Heckel5, P.R. Huffman4, D. Luo2, D.M. Markoff4, A.M. Micherdzinska2, H.P. Mumm3, J.S. Nico3, M.G. Sarsour2, W.M. Snow2, H.E. Swanson5 Gettysburg College1 Indiana University / IUCF2 National Institute of Standards and Technology (NIST)3 North Carolina State University / TUNL4 University of Washington5 NSF PHY-0100348

  3. n Seminar overview • Motivation • Why study parity violation (PV) in neutron spin rotation • What is spin rotation? • Experiment • Experimental challenges • Design of apparatus • Summary/Goals

  4. n ~1/100 fm range ~1 fm Weak NN force Strong NN force Motivation • Parity Violation (PV) neutron spin rotation is a probe of theNN weak interaction after ~ 40 years of study hadronic weak interaction is not understood ( data + theory is inconsistent) • Why this is important to understend NN weak interactions ? • needed to interpret PV in atomic, nuclear and hadron physics • sensitive to q-q correlation in nucleon Relative weak/strong amplitudes: ~[e2/mW2]/[g2/m2]~10-7

  5. n N N ~1/100 fm range p, r, w ~1 fm PC PV Weak NN force N N Strong NN force The NN weak interaction: Theoretical description DDH meson exchange model assumes p, r, and w exchange dominate the low-energy PV NN potential as they do for strong NN Weak meson exchange coupling constants fp , hr0, hr1 , hr2 , hw0 , hw1

  6. Current knowledge about weak NN amplitudes n-4He orthogonal to 133Cs, p-4He n-4He spin rotation in terms of weak couplings (f=10-7rad/m, Dmitriev) DDH “best values”f=-(0.97fp+0.32hr0-0.11hr1+0.22hr0-0.22hr1) rad/mn+p->D+ asymmetry determinesf fDesplanques)plot:=310-7 rad/m,=510-9

  7. transversely polarized neutrons corkscrew due to weak NN interaction [opposite helicity components of |>z=1/2(|>x+ |>x) accumulate different phases fromsnpnterm in forward scattering amplitude] PV rotation angle per unit lengthd/dxrelated to PV amplitude[=(n-1)px, n-1=2f/p2] d/dx ~1x10-7 rad/m (DDH), 3x10-7 rad/m goal at NIST 06 in n+4He Parity Violating d/dx independent on vn Parity Conserving d/dx (due to B field) dependent of vn n Parity Violation in Neutron Spin Rotation z x analyzer polarizer

  8. n Suppression of B in target • All possible systematic effects have to be reduced… Magnetic field is responsiblefor all of these ! • (Earth field ~50mT cause rotation of 5A neutrons ~ 10rad/m) We have to reduce B field: • Magnetic shields fluxgates, trim coils 2nT in target region still not good enough (rotation 100 times bigger than fpv) • Target design – to extract tiny PV signal from much bigger due to magnetic field

  9. n qmag+fPV (qB-qF)+fPV -qF qF Cold Neutron Beam Cold Neutron Beam Target design to further suppress B rotation A B 3He n-detector Analyzer Target Chamber – back position p – Coil Target Chamber – front position Polarizer qmag-fPV (qB-qF)-fPV -qF -fPV qF+fPV z B – A = 2fPV y x

  10. n Target design B – A = 2fPV A B 3He n-detector Analyzer Target Chamber – back position p – Coil Target Chamber – front position Polarizer p – Coil Cold Neutron Beam

  11. n Cross section of Spin Rotation Apparatus

  12. n Systematic Effects in PV Spin Rotation Associated with residual longitudinal B (B< 10 nT) effect estimate of size • He diamagnetism(BHe ≠ Bvac) ~10-8 rad/m • He optical potential (VHe≠ Vvac) ~10-8 rad/m • small angle scattering in He ~10-8 rad/m LHe superfluid LHe:decrease small angle scattering by ~(5) PV spin rotation independent of neutron energy, B rotation depends on neutron energy. At NIST we will amplify effects by increasing B in separate measurements. However, no TOF… (future SNS !) previous version (1996): upper bound on systematic effects < 210-7 rad/m our goal: systematic effects < 110-7rad/m We will amplify systematic effects using ~ 100mT field

  13. n Summary and plans • We will perform challenging search for neutron spin rotation in LHe at NIST at the beginning of 2006 • Experimental apparatus was updated since 1996 measurement (receiving fPV(n,a) = ( 8.0 ±14 (stat) ± 2.2 (syst) ) 10-7rad/m) • New target, additional CRYOPERM magnetic shield, monitoring magnetic field outside and in the target region, active trim coils, all nonmagnetic materials, use of superfluid LHe. • NIST: increase the detected beam flux by a factor of 1.5, monitoring magnetic field outside of our apparatus. • Successful measurement (sensitivity goalfPV=310-7rad/min 3 months of data taking + ~1 month of systematic study) will broaden our knowledge about NN weak interaction • letter of intent approved to perform PV neutron spin rotation in LHe at SNS

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