Precision Measurement of a and b in Neutron β Decay The Nab/abBA Experimental Program L. Peter Alonzi III, for the Nab Collaboration University of Virginia April APS Meeting, Denver, 03 May 2009
Motivation Spectrometer Outline Neutron Decay Theory and Measurement Principles The Nab Spectrometer L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 2 / 11
Motivation Spectrometer World Neutron Experimental Results and Nab goal Electron-neutrino parameter a : − 0 . 1054 (55) Byrne et al, [2002] − 0 . 1017 (51) Stratowa et al, [1978] Experimental results − 0 . 091 (39) Grigorev et al, [1968] − 0 . 103 (4) PDG, [2008] ∆ a ≃ 1 × 10 − 3 Nab goal: a Fierz interference term b : � Experimental results none ∆ b ≃ 3 × 10 − 3 Nab goal: L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 3 / 11
Motivation Spectrometer World Neutron Experimental Results and Nab goal Electron-neutrino parameter a : − 0 . 1054 (55) Byrne et al, [2002] − 0 . 1017 (51) Stratowa et al, [1978] Experimental results − 0 . 091 (39) Grigorev et al, [1968] − 0 . 103 (4) PDG, [2008] ∆ a ≃ 1 × 10 − 3 Nab goal: a Fierz interference term b : � Experimental results none ∆ b ≃ 3 × 10 − 3 Nab goal: L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 3 / 11
Motivation Spectrometer Neutron Decay Rate p ν e W dw ≃ k e E e (E 0 − E e ) 2 n dE e dΩ e dΩ ν � � �� � k e · � � � k ν + bm e k ν k e × 1 + a + � � σ n � · B + A E e E ν E e E ν E e 1 −| λ | 2 A = − 2 | λ | 2 +Re( λ ) B = 2 | λ | 2 − Re( λ ) a = 1+3 | λ | 2 1+3 | λ | 2 1+3 | λ | 2 λ = G A (0) (with τ n ⇒ CKM V ud ) G V (0) L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 4 / 11
Motivation Spectrometer Neutron Decay Rate p ν e W dw ≃ k e E e (E 0 − E e ) 2 n dE e dΩ e dΩ ν � � �� � k e · � � � k ν + bm e k ν k e × 1 + a + � � σ n � · B + A E e E ν E e E ν E e 1 −| λ | 2 A = − 2 | λ | 2 +Re( λ ) B = 2 | λ | 2 − Re( λ ) a = 1+3 | λ | 2 1+3 | λ | 2 1+3 | λ | 2 λ = G A (0) (with τ n ⇒ CKM V ud ) G V (0) L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 4 / 11
Motivation Spectrometer Decay Kinematics p p2 (MeV 2 /c 2 ) Yield (arb. units) 0.5 proton phase space 1.4 E e = 0.075 MeV cos θ e ν = 1 1.2 0.4 0.236 MeV 1 0.3 0.450 MeV 0.8 cos θ e ν = 0 0.6 0.2 0.4 0.700 MeV 0.1 0.2 cos θ e ν = -1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.2 0.4 0.6 0.8 1 1.2 1.4 p p2 (MeV 2 /c 2 ) E e (MeV) • E p ∼ eV and E e ∼ 0-800 keV • For a given E e • cos θ e ν is a function of p 2 p only ( p 2 p = p 2 e + p 2 ν + 2 p e p ν cos θ e ν ) dw ≃ Constant + a p 2 • dE e d Ω e d Ω ν p L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 5 / 11
Motivation Spectrometer Decay Kinematics p p2 (MeV 2 /c 2 ) Yield (arb. units) 0.5 proton phase space 1.4 E e = 0.075 MeV cos θ e ν = 1 1.2 0.4 0.236 MeV 1 0.3 0.450 MeV 0.8 cos θ e ν = 0 0.6 0.2 0.4 0.700 MeV 0.1 0.2 cos θ e ν = -1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.2 0.4 0.6 0.8 1 1.2 1.4 p p2 (MeV 2 /c 2 ) E e (MeV) • E p ∼ eV and E e ∼ 0-800 keV • For a given E e • cos θ e ν is a function of p 2 p only ( p 2 p = p 2 e + p 2 ν + 2 p e p ν cos θ e ν ) dw ≃ Constant + a p 2 • dE e d Ω e d Ω ν p L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 5 / 11
Motivation Spectrometer Beamline 13: Spallation Neutron Source, Oak Ridge, TN L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 6 / 11
Motivation Spectrometer The Nab Symmetric Configuration B 0 Nab Spectrometer Field Profiles 4 U (10 4 V) 3 2 1 B (T) B TOF 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 z (m) L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 7 / 11
Motivation Spectrometer Geant4 Simulation P = 0.949 MeV/c p a120 P = 1.140 MeV/c p -2 10 ← a147 β a120 → -3 10 2.4 r 1.3 r 1.0 10 -4 3.4 2.0 1.0 2.0 11.0 5.0 2.0 + 1.5 + 7.0 0 0.01 0.02 0.03 0.04 0.05 - 6.2 -2 400 TOF µ s -2 11.8 3.9 100 1.0 + + 8.4 1.3 9.0 4.6 - 50 - 10 -1 11.0 25 3.0 P = 0.949 MeV/c p a147 β 2.4 P = 1.140 MeV/c 1.3 p z z -2 10 0.014 0.039 dimensions�in�cm dimensions�in�cm Current�density:��3500 A/cm 2 Current�density:��3500 A/cm 2 10 -3 a120 → ← a147 β -4 10 -5 10 0 0.01 0.02 0.03 0.04 0.05 -2 TOF µ s -2 L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 8 / 11
Motivation Spectrometer Geant4 Simulation Ideal Spectrometer Practicable Spectrometer -3 -3 × 10 × 10 0.35 0.3 E = 300 keV E = 300 keV e 0.3 e 0.25 0.25 0.2 500 keV 500 keV 0.2 0.15 0.15 0.1 0.1 0.05 0.05 700 keV 700 keV 0 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 0.01 0.02 0.03 0.04 0.05 2 2 P [(MeV/c) ] TOF -2 [ µ s -2 ] p Measured a E e Seed -0.10500 300 keV -0.10526(10) 500 keV -0.10509(10) 700 keV -0.10529(10) L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 9 / 11
Motivation Spectrometer Basic design and features of asymmetric Nab Features: Segmented • U tolerance ∼ µ V → ∼ mV Si detector 0-31 kV • magnetic cos θ filter • no count rate penalty vs. TOF region (field r B · B 0 ) symmetric Nab magnetic filter region (field B 0 ) 2 (z)= (1-( )�) B B z detector α 0 4 Magnetic field B [T] decay volume (z)�~ B r B linear�field�decay (field r B,DV · B 0 ) B,DV 0 3 (small�gradient, detector 30 kV -3 ~10 /cm) Neutron filter�region 2 beam expansion�region 1 0-30 kV B (z)�= r B B 0 decay�volume 0 -z 2 -z 1 z 1 z 2 z 3 Stefan Baeßler, March 2009 Height z [m] L.P. Alonzi (UVa) The Nab Experiment 03 May ’09 10 / 11
The Nab collaboration R. Alarcon 1 , L.P. Alonzi 2 , S. Baeßler 2 ∗ , S. Balascuta 1 , J.D. Bowman 3 † , M.A. Bychkov 2 , J. Byrne 4 , J.R. Calarco 5 , V. Cianciolo 3 , C. Crawford 6 , z 2 , M.T. Gericke 7 , F. Gl¨ uck 8 , G.L. Greene 9 , R.K. Grzywacz 9 , E. Frleˇ V. Gudkov 10 , F.W. Hersman 5 , A. Klein 11 , J. Martin 12 , S.A. Page 6 , A. Palladino 2 , S.I. Penttil¨ a 3 , D. Poˇ c 2 † , K.P. Rykaczewski 3 , cani´ W.S. Wilburn 11 , A.R. Young 13 , G.R. Young 3 . 1 Arizona State University 2 University of Virginia 3 Oak Ridge National Lab 4 University of Sussex 5 Univ. of New Hampshire 6 University of Kentucky 7 University of Manitoba 8 Uni. Karlsruhe/RMKI Budapest 9 University of Tennessee 10 University of South Carolina 11 Los Alamos National Lab 12 University of Winnipeg 13 North Carlolina State Univ. ∗ Experiment Manager † Co-spokesmen Home page: http://nab.phys.virginia.edu/
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