QuickTime™ and a QuickTime™ and a TIFF (Uncompressed) decompressor TIFF (Uncompressed) decompressor are needed to see this picture. are needed to see this picture. Magnetic field for “PANDA*” * P roton A symmetry in N eutron D ec A y For the SNS-FnPB Magnet meeting Prepared by Tim Chupp QuickTime™ and a QuickTime™ and a TIFF (Uncompressed) decompressor TIFF (Uncompressed) decompressor are needed to see this picture. are needed to see this picture.
The proton Asymmetry e e p p ν ν N + N - N + - N - Asymmetry: __________ = C P n A F (1-f) + A false N + + N - background spin flip efficacy analyzing power neutron polarization g A | λ | λ = ____ C = k(A+B) = 4k ________ k=0.27484 g V 1+3| λ | 2 Standard Model dW p e . p n m e p e x p ν _____________ = S(E e ) [1 + a ______ + b ___ + ___ . ( A ____ + B ____ + D _______ )] J p e p ν dE e d Ω e d Ω ν E e E n E e J E e E ν E e E ν JTW-57
C and λ | λ | C = k(A+B) = 4k ________ 1+3| λ | 2 σ x σ λ PDG 2005 ___ ___ λ x λ -1.2695±0.0029 a -0.103±0.004 0.2688 A -0.1173±0.0013 0.2403 B +0.983 ±0.004 1.385 C +0.238 ±0.011* 1.430 D -0.0004±0.0006 φ 180.06±0.0029 * Abele, 2005 dW p e . p n m e p e x p ν _____________ = S(E e ) [1 + a ______ + b ___ + ___ . ( A ____ + B ____ + D _______ )] J p e p ν dE e d Ω e d Ω ν E e E n E e J E e E ν E e E ν JTW-57
Rudimentary Layout B y For adiabatic neutron spin transport B x M 1 M 2 Neutron spins tranported polarizer Spin analyzer Flipper Through detector N 0 (v) y X neutrons P(v) A(v) T P (v) R z T A (v) Detector L Detector 2 Detector 1 Neutron beam Into page +30 kV V 0 ~ ~ Allows proton ~ ~ Detailed design work needed. spectroscopy Uniform field B
General Design Issues Goal: σ x /x ~ 10 -3 or better • Neutron spin transported adiabatically from polarizer to analyzer (through detector) • Uniform B in decay region: mitigates proton reflections from magnetic traps • Proton orbit: d= 8 mm/B(T): 1-2T Needed (2 T for emiT proton segment • Electrostatic proton energy resolution desired: requirements on B in proton drift region TBA • Vacuum requirements: TBA
Neutron Polarization and Polarimetry M 1 M 2 polarizer Spin analyzer Flipper N 0 (v) X neutrons P(v) A(v) T P (v) R T A (v) Detector R Exp = Σ ( + ) + ∆ ( - ) =N 0 T 1 T 2 T P [ Γ 0 + ∆ PR] Γ ± = Σ ± ∆ M 1 = N 0 ε 1 +B 1 M 2 = N 0 T 1 T 2 T P T A ε 3 [ 1+PAR ] +B 2 P/A P n (5Å) T n P 2 T features fixed; limited λ bite PSM 99.x% 10% 0.1 3 He (60%) 80% 30% 0.2 flip P 3 ; P 3 varies Flipper: R u = 1 (unflipped); R f =F ≈ -1 (flipped) (-0.999 for AFP) (M 2 u - M 2 f ) _________ ~ PA(1-F) (1-f 2 ) (M 2 u + M 2 f ) BR (1% need to know to 0.1%)
Detector L Detector 2 Detector 1 Neutron beam Into page +30 kV V 0 ~ ~ Allows proton ~ ~ Detailed design work needed. spectroscopy Uniform field B Ideal: A 1 = A 2 =1, ε 1 = ε 2 =1, f 1 =f 2 =0 Proton detection: e.g. emiT2 • with adiabatic spin transport J||B • with adiabatic proton orbits, A =1 1000 (scattering: resid. gas, baffles, etc.) 100 Counts 10 1 0.1 20 40 60 80 Channel
Statistics 0.6 0.5 0.4 Probability 0.3 0.2 0.1 0.0 0 1 2 3 4 5 Decays per pulse ρ n ~ 10 3 /cm 3 We expect about 0.5 decays per pulse: about 2.5 million events per day. 0.1% precision requires < a few days NOT STATISTICS LIMITED Focus on systematics…
Systematics N + - N - __________ = C P n A F (1-f) + A false N + + N - background spin flip efficacy analyzing power neutron polarization Need to know: neutron polarization analyzing power spin flip efficiency backgrounds spin independent spin dependent (false asymmetry) e.g. False asymmetry from electrons emited from n-decay (BR) - study of proton energy dependence Noise, gain shifts, etc. - flip 3 He C is INDEPENDENT of P n , xy, L, tof, 3 He, B, BR, … statistical power
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