Precise Measurement of the Neutron Beta Decay Parameters a and b Dinko Poˇ cani´ c, for the Nab Collaboration University of Virginia DoE Review of the FnPB/SNS, Oak Ridge, 23 April 2009 D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 1 / 24
Outline Outline Motivation and Goals Measurement principles Proton TOF and e- ν correlation Spectrometer design Detection function Overview of uncertainties Event statistics, rates, running time Systematic uncertainties Asymmetric design Spectrometer basics Summary D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 2 / 24
Basic facts Goals of the Experiment ◮ Measure the electron-neutrino parameter a in neutron decay ∆a ≃ 10 − 3 with accuracy of a − 0 . 1054 ± 0 . 0055 Byrne et al ’02 current results: − 0 . 1017 ± 0 . 0051 Stratowa et al ’78 − 0 . 091 ± 0 . 039 Grigorev et al ’68 ◮ Measure the Fierz interference term b in neutron decay ∆b ≃ 3 × 10 − 3 with accuracy of current results: none D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 3 / 24
Basic facts Goals of the Experiment ◮ Measure the electron-neutrino parameter a in neutron decay ∆a ≃ 10 − 3 with accuracy of a − 0 . 1054 ± 0 . 0055 Byrne et al ’02 current results: − 0 . 1017 ± 0 . 0051 Stratowa et al ’78 − 0 . 091 ± 0 . 039 Grigorev et al ’68 ◮ Measure the Fierz interference term b in neutron decay ∆b ≃ 3 × 10 − 3 with accuracy of current results: none D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 3 / 24
Basic facts Goals of the Experiment ◮ Measure the electron-neutrino parameter a in neutron decay ∆a ≃ 10 − 3 with accuracy of a − 0 . 1054 ± 0 . 0055 Byrne et al ’02 current results: − 0 . 1017 ± 0 . 0051 Stratowa et al ’78 − 0 . 091 ± 0 . 039 Grigorev et al ’68 ◮ Measure the Fierz interference term b in neutron decay ∆b ≃ 3 × 10 − 3 with accuracy of current results: none D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 3 / 24
Basic facts Goals of the Experiment ◮ Measure the electron-neutrino parameter a in neutron decay ∆a ≃ 10 − 3 with accuracy of a − 0 . 1054 ± 0 . 0055 Byrne et al ’02 current results: − 0 . 1017 ± 0 . 0051 Stratowa et al ’78 − 0 . 091 ± 0 . 039 Grigorev et al ’68 ◮ Measure the Fierz interference term b in neutron decay ∆b ≃ 3 × 10 − 3 with accuracy of current results: none D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 3 / 24
Basic facts Neutron Decay Parameters (SM) dw ≃ k e E e (E 0 − E e ) 2 dE e dΩ e dΩ ν � k e · � � � � � k e × � � � k ν + b m k e k ν k ν � × 1 + a + � � σ n � · A + B + D E e E ν E e E e E ν E e E ν with: A = − 2 | λ | 2 + Re( λ ) a = 1 − | λ | 2 1 + 3 | λ | 2 1 + 3 | λ | 2 B = 2 | λ | 2 − Re( λ ) Im( λ ) D = 2 1 + 3 | λ | 2 1 + 3 | λ | 2 λ = G A (with τ n ⇒ CKM V ud ) ( D � = 0 ⇔ T inv. violation) G V D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 4 / 24
Basic facts Neutron Decay Parameters (SM) dw ≃ k e E e (E 0 − E e ) 2 dE e dΩ e dΩ ν � k e · � � � � � k e × � � � k ν + b m k e k ν k ν � × 1 + a + � � σ n � · A + B + D E e E ν E e E e E ν E e E ν with: A = − 2 | λ | 2 + Re( λ ) a = 1 − | λ | 2 1 + 3 | λ | 2 1 + 3 | λ | 2 B = 2 | λ | 2 − Re( λ ) Im( λ ) D = 2 1 + 3 | λ | 2 1 + 3 | λ | 2 λ = G A (with τ n ⇒ CKM V ud ) ( D � = 0 ⇔ T inv. violation) G V D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 4 / 24
Basic facts Neutron Decay Parameters (SM) dw ≃ k e E e (E 0 − E e ) 2 dE e dΩ e dΩ ν � k e · � � � � � k e × � � � k ν + b m k e k ν k ν � × 1 + a + � � σ n � · A + B + D E e E ν E e E e E ν E e E ν with: A = − 2 | λ | 2 + Re( λ ) a = 1 − | λ | 2 1 + 3 | λ | 2 1 + 3 | λ | 2 B = 2 | λ | 2 − Re( λ ) Im( λ ) D = 2 1 + 3 | λ | 2 1 + 3 | λ | 2 λ = G A (with τ n ⇒ CKM V ud ) ( D � = 0 ⇔ T inv. violation) G V D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 4 / 24
Basic facts n-decay Correlation Parameters Beyond V ud ◮ Beta decay parameters constrain L-R symmetric, SUSY extensions to the SM. [ Reviews: Herczeg, Prog. Part. Nucl. Phys. 46 , 413 (2001), N. Severijns, M. Beck, O. Naviliat-ˇ Cunˇ ci´ c, Rev. Mod. Phys. 78 , 991 (2006), Ramsey-Musolf, Su, Phys. Rep. 456 , 1 (2008)] ◮ Fierz interference term, never measured for the neutron, offers a sensitive test of non-( V − A ) terms in the weak Lagrangian ( S , T ). [ S. Profumo, M. J. Ramsey-Musolf, S. Tulin, PRD 75 , 075017 (2007)] ◮ Measurement of the electron-energy dependence of a and A can separately confirm CVC and absence of SCC. [ Gardner, Zhang, PRL 86 , 5666 (2001), Gardner, hep-ph/0312124] ◮ A general connections exists between non-SM (e.g., S , T ) terms in d → ue ¯ ν and limits on ν masses. [ Ito + Pr´ ezaeu, PRL 94 (2005)] D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 5 / 24
Measurement principles Proton TOF and e- ν correlation Nab Measurement principles: Proton phase space p p2 (MeV 2 /c 2 ) proton phase space 1.4 cos θ e ν = 1 1.2 1 0.8 cos θ e ν = 0 0.6 0.4 0.2 cos θ e ν = -1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 E e (MeV) Note: For a given E e , cos θ e ν is a function of p 2 p only. D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 6 / 24
Measurement principles Proton TOF and e- ν correlation Measurement principles: Proton momentum response Yield (arb. units) 0.5 E e = 0.075 MeV 0.4 0.236 MeV 0.3 0.450 MeV 0.2 0.700 MeV 0.1 Slope = a 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 p p2 (MeV 2 /c 2 ) D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 7 / 24
Measurement principles Spectrometer design Measurement principles: Symmetric pectrometer Neutron Segmented Beam Si�detector TOF�region Decay transition Volume region acceleration region Elements of spectrometer to be shared with other planned n decay experiments, e.g., abBA . D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 8 / 24
Measurement principles Spectrometer design Measurement principles: Spectrometer field profiles B 0 Nab Spectrometer Field Profiles 4 U (10 4 V) 3 2 B (T) 1 B TOF 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 z (m) r B = B TOF B 0 D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 9 / 24
Measurement principles Detection function Measurement principles: Detection function (I) Proton time of flight in B field: � p p0 · � t p = f (cos θ p,0 ) cos θ p,0 = � B � where . � p p p p0 B � � decay pt. For an adiabatically expanding field prior to acceleration, � l � l m p dz m p dz f (cos θ p,0 ) = cos θ p ( z ) = . � B 0 sin 2 θ p,0 1 − B ( z ) z 0 z 0 To this we add effects of magnetic reflections and, later, of electric field acceleration. D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 10 / 24
Measurement principles Detection function Measurement principles: Detection function (II) The proton momentum distribution within the phase space bounds is given by P p ( p 2 [recall: cos θ e ν = f ( p 2 p ) = 1 + a β e cos θ e ν , p )] while � 1 � 1 � � � P p ( p 2 , p 2 dp 2 P t = p ) Φ p . p t 2 t 2 p p Detection function Φ relates the proton momentum and time-of-flight distributions! To extract a reliably: ◮ Φ must be as narrow as possible, ◮ Φ must be understood very precisely. Two methods (“A” and “B”) pursued to specify Φ. D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 11 / 24
Measurement principles Detection function Measurement principles: Detection function (II) The proton momentum distribution within the phase space bounds is given by P p ( p 2 [recall: cos θ e ν = f ( p 2 p ) = 1 + a β e cos θ e ν , p )] while � 1 � 1 � � � P p ( p 2 , p 2 dp 2 P t = p ) Φ p . p t 2 t 2 p p Detection function Φ relates the proton momentum and time-of-flight distributions! To extract a reliably: ◮ Φ must be as narrow as possible, ◮ Φ must be understood very precisely. Two methods (“A” and “B”) pursued to specify Φ. D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 11 / 24
Measurement principles Detection function Measurement principles: Detection function (II) The proton momentum distribution within the phase space bounds is given by P p ( p 2 [recall: cos θ e ν = f ( p 2 p ) = 1 + a β e cos θ e ν , p )] while � 1 � 1 � � � P p ( p 2 , p 2 dp 2 P t = p ) Φ p . p t 2 t 2 p p Detection function Φ relates the proton momentum and time-of-flight distributions! To extract a reliably: ◮ Φ must be as narrow as possible, ◮ Φ must be understood very precisely. Two methods (“A” and “B”) pursued to specify Φ. D. Poˇ cani´ c (UVa) The Nab Experiment/FnPB/SNS 23 Apr ’09 11 / 24
Recommend
More recommend
