POLARIZED 3 He in FUNDAMENTAL PHYSICS with COLD NEUTRONS. Tom Gentile National Institute of Standards and Technology (NIST)

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1 POLARIZED 3 He in FUNDAMENTAL PHYSICS with COLD NEUTRONS Tom Gentile National Institute of Standards and Technology (NIST)

2 NEUTRON SPIN FILTERS for FUNDAMENTAL PHYSICS EXPERIMENTS Decay correlation coefficients A (spin-electron) and B (spin-neutrino) asymmetry coefficients (measure neutron polarization produced by crossed supermirrors) D (time-reversal) coefficient Parity violating gamma asymmetry (NPDGamma) (discovery of effects on neutron beams on in-situ SEOP) Neutron spin rotation Few body physics: spin-dependence of n- 3 He scattering length

3 PRECISION NEUTRON POLARIMETRY for a MEASUREMENT of the n- 3 He INCOHERENT SCATTERING LENGTH of 3 He T.R. Gentile 1, M. Arif 1, W.C. Chen 1,2, D.S. Hussey 1, D.A. Pushin 1, L. Yang 1, M.G. Huber 3, F.E. Wietfeldt 3 and T.C. Black 4 1. National Institute of Standards and Technology 2. Indiana University 3. Tulane University 4. University of North Carolina at Wilmington Acknowledgements to NSF and DoE

4 Experimental Overview Spin We measure the n- 3 He spin-dependent scattering length using polarized 3 He gas trapped in a glass cell. The phase shift f between the two flipper states (off or on) is related to the spin-dependent scattering length (b i ) by

5 PHASE SHIFT MEASUREMENT (b) φ 0, [rad] R ξ (proportional to 3 He polarization) M.G. Huber et al, Phys. Rev. C 90, (2014).

6 PRECISION NEUTRON POLARIMETRY with POLARIZED 3 He P n = tanh[t P He ] T n = T 0 cosh[t P He ] t = opacity = cross section * 3 He density * cell length # P = 1 T 0 n % $ T n & ( ' 2 P n = neutron polarization T n = transmission of polarized cell T 0 = T E exp(-t) = transmission of unpolarized cell T E = transmission of empty cell NEUTRON POLARIZATION determined from transmission cross section proportional to l - time of flight analysis ideal PHYSICS ASYMMETRY proportional to P n

7 PRECISION NEUTRON POLARIMETRY with POLARIZED 3 He Unpolarized neutrons: T n = transmission of polarized cell T 0 = transmission of unpolarized cell T n = T 0 cosh[t P He ] t = opacity = cross section * 3 He density * cell length Perfectly polarized neutrons: T + = neutrons and 3 He polarization parallel T - = neutrons and 3 He polarization antiparallel P A = analyzing power # P A = tanh[t P He ] = 1 T 0 % $ T n ANALYZING POWER determined from relative transmission P A = T + T - T + +T - & ( ' 2

8 Skylight (polarimetry cell) Pistachio (interferometer cell) Three polarimetry cells used: Haystack, Skylight, Whiteface pressures = bar, yielding t = and P A = for P He = Relaxation times ~ 150 h intrinsic, 35 h at interferometer due to 2x10-3 cm -1 field gradient

9 Neutron polarization P n and spin flip efficiency s from 93 asymmetry and NT antiparallel methods 99.6 Pn s P n 92.9 NT antiparallel 99.5 s NT antiparallel asymmetry combined asymmetry combined

10 ILL MEOP compression apparatus used to polarize a silicon-windowed 10 cm long cylindrical cell then installed in a neutron spin-echo apparatus O. Zimmer et al, EPJ Direct 1-28 (2002). A precise measurement of the spin-dependent neutron scattering length of 3 He

11 NEUTRON POLARIMETRY WITH SPIN FILTERS G.L. Greene, A.K. Thompson, M.S. Dewey, Nucl. Instrum. Meth. A 356, 177 (1995). A method for the accurate determination of the polarization of a neutron beam using a polarized 3He spin filter O. Zimmer, Phys. Lett. B 461, (1999). A method for precise neutron beam polarisation analysis using an opaque spin filter O. Zimmer et al, Phys. Lett. B 455, (1999). High-precision neutron polarization analysis using opaque spin filters O.Zimmer et al., Nucl. Instrum. Meth. A 440, (2000). Spin filters and supermirrors: a comparison study of two methods of high-precision neutron polarisation analysis D.R. Rich et al, Nucl. Instrum. Meth. A 481, (2002). A measurement of the absolute neutron beam polarization produced by an optically pumped 3He neutron spin filter 0.3% in the neutron energy range from 40 mev to 10 ev M. Kreuz et al, Nucl. Instrum. Meth. A 547, (2005). The crossed geometry of two super mirror polarisers - a new method for neutron beam polarisation and polarisation analysis F.E. Wietfeldt and T.R. Gentile, J. Res. Natl. Inst. Stand. Technol. 110, (2005). A new method for precision cold neutron polarimetry using a 3He spin filter S.I. Penttila and J.D. Bowman, J. Res. Natl. Inst. Stand. Technol. 110, 1-5 (2005). Precision neutron polarimetry for neutron beta decay T.E. Chupp et al, Nucl. Instrum. Meth. A 574, (2007). "A large area polarized 3He neutron spin filter 0.1% with TOF analysis for the LANSCE FP12 cold neutron beam S. Masalovich, Nucl. Instrum. Meth. A 581, (2007). Method to measure neutron beam polarization with 2 1 neutron spin filter T. Ino et al, Physica B 406, (2011). Measurement of the neutron beam polarization of BL05/NOP beam line at J-PARC 0.03% in the neutron wavelength range from 0.1 nm (81 mev) to 0.7 nm (1.7 mev)

12 OPAQUE SPIN FILTERS 1 (50% 3 He polarization assumed) analyzing power A (15 bar-cm) A (25 bar-cm) T (15 bar-cm) transmission of desired spin state A (40 bar-cm) T (25 bar-cm) T (40 bar-cm) neutron wavelength [nm]

13 A, B, and C at the Institut Laue-Langevin Neutron polarization measured to be /- 0.1 % M. Schumann et al, Phys. Rev. Lett. 99, (2007) Measurement of the neutrino asymmetry parameter B in neutron decay M. Schumann et al, Phys. Rev. Lett. 100, (2008). Measurement of the proton asymmetry parameter in neutron beta decay D. Mund et al, Phys. Rev. Lett. 110, (2013). "Determination of the weak axial vector coupling l = g A /g V from a measurement of the b-asymmetry parameter A in neutron beta decay "

14 POLARIZING HIGH-FLUX NEUTRON BEAMS with POLARIZED 3 He SPIN FILTERS

15 PARITY VIOLATION in NUCLEON-NUCLEON INTERACTIONS g n + p n p Parity operator: r r PNC asymmetry: A γ ( σ ˆ n k ) γ g A γ = 0.11 f π 1 ~ 5 x 10 8 (meson exchange model)

16 3 He polarizer for NPDg experiment at LANSCE one year of nearly continuous use in 2005 for study of solid targets M.T. Gericke et al, Phys. Rev. C 74, (2006) NPDg result M. Gericke et al, Phys. Rev. C 83, (2011) A g = /- 2.1 (stat) +/- 0.2 (sys) x 10-7 Continuous operation in a high flux beam revealed decrease in 3 He polarization short term effect (alkali polarization) and long term effect (opacity to laser light) Effects studied on PF1b and tomography beam line at the ILL (Babcock et al) Polarizer: T.E. Chupp et al, Nucl. Instrum. Meth. A 574, (2007) Beam effects: M. Sharma et al, Phys. Rev. Lett. 101, (2008) E. Babcock et al, Phys. Rev. A 80, (2009)

17 POLARIZATION vs TIME for BooBoo, 2005 run on LANSCE Pebbles, 2006 NPDGamma run

18 BooBoo after 1 year in LANSCE beam ~10 8 n/(cm 2 -s) BooBoo pumped with two 50 W QPC lasers 1 narrowed or unnarrowed P Rb narrowed laser broad laser temperature [deg C]

19 BEAM EFFECTS STUDIES on PF1B at the ILL, 2007 Earl Babcock et al

20 Alkali polarization vs neutron flux Alkali relaxation vs time

21 Alkali relaxation vs neutron flux

22 BEAM EXPOSURE TESTS Orvieto (Rb/K hybrid) Lottie (pure Rb)

23 NEUTRON BEAM EFFECTS ON IN-SITU SEOP CELLS High flux neutron beams induce alkali-metal spin relaxation Neutron absorption by 3 He produces energetic triton and proton Relaxation rate proportional to square root of neutron flux: Minor at 10 8 n/s (LANSCE) Substantial at 10 9 n/s (NIST NG6, SNS FNPB) Dominates at n/s (ILL, new NIST NG-C) Long term effects: reduced transparency of cell, perhaps due to RbH?

24 Roadrunner DOUBLE CELL TEST

25 JLAB polarized 3 He target

26 REINCARNATION of SAREK

27

28 TESTS with SAREK - Oct 2016 D = [K]/[Rb] = 7 MAX POL (neutron-based) - 58% 30 expect 66% for T1=70 h and X= NMR signal [mv] pumping timc constant [h] pumping timc constant [h] NMR signal [mv] temp [C}

29 SUMMARY 3 He SPIN FILTERS PROVIDE A MEANS FOR HIGHLY ACCURATE DETERMINATION of NEUTRON POLARIZATION (and accurate 3 He polarization measurements) FUTURE EXPERIMENTS THAT WOULD USE IN-SITU SEOP 3 He SPIN FILTERS in HIGH FLUX NEUTRON BEAMS WOULD NEED TO ADDRESS BEAM-INDUCED RELAXATION, PROBABLY WITH LARGE DOUBLE CELLS POLARIZED 3 He HAS BEEN EMPLOYED TO DETERMINE THE SPIN-DEPENDENCE OF THE n- 3 He SCATTERING LENGTH BY BOTH NEUTRON SPIN-ECHO AND INTERFEROMETRY METHODS