Nab, a new precise study of neutron beta decay at SNS Dinko Po cani - PowerPoint PPT Presentation

Nab, a new precise study of neutron beta decay at SNS Dinko Poˇ cani´ c University of Virginia Jefferson Lab Newport News, VA, 4 May 2012

Outline Goals and motivation CKM matrix: V ud (messy neutron results) Non- V − A interaction terms; Second class currents Measurement principles Electron-neutrino correlation a ; detection function Apparatus Spectrometer and its optimization Si Detectors; Electrode and vacuum systems Overview of uncertainties Event rates, statistical uncertainties Systematic uncertainties Polarized program: abBA/PANDA Measurement principle Rates and uncertainties Summary D. Poˇ cani´ c (UVa) Nab experiment : Outline 4 May ’12 2 / 43

Neutron Decay Parameters (SM) dw ≃ p e E e (E 0 − E e ) 2 dE e dΩ e dΩ ν 1 + a � p e · � A � + B � � p ν + b m � p e p ν � � × + � � σ n � · + . . . E e E ν E e E e E ν where: A = − 2 | λ | 2 + Re( λ ) a = 1 − | λ | 2 1 + 3 | λ | 2 1 + 3 | λ | 2 B = 2 | λ | 2 − Re( λ ) λ = G A ( with τ n ⇒ CKM V ud ) 1 + 3 | λ | 2 G V also: C = κ (A + B) where κ ≃ 0 . 275 . D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 3 / 43

Goals of the Nab 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 (in n decay) D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 4 / 43

Quark-lepton (Cabibbo) universality Basic weak-interaction V - A form (e.g., µ decay): M ∝ � e | l α | ν e � → ¯ u e γ α (1 − γ 5 )u ν is replicated in hadronic weak decays: M ∝ � p | h α | n � → ¯ u p γ α (G V − G A γ 5 )u n with G V , A ≃ 1 . Departure from G V = 1 ( CVC ) comes from weak quark (Cabibbo) mixing: G V = G µ cos θ C (= G µ V ud ) cos θ C ≃ 0 . 97  V ud V us V ub  3 q generations lead to the matrix (1973): V cd V cs V cb Cabibbo-Kobayashi-Maskawa (CKM)   V td V ts V tb CKM unitarity cond.: ∆V 2 = 1 − ( | V ud | 2 + | V us | 2 + | V ub | 2 ) ? = 0 , stringently tests the SM. D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 5 / 43

SM parameters determining V ud 0.980 Kaons +Unitarity [PDG 2010] 0.975 ft(0 + →0 + ) [Hardy09] ft(0 + →0 + ) [Liang09 – DD�ME2] PIBETA [Pocanic04] ft(0 + →0 + ) [Liang09 – PKO1] τ n [MAMBO II] V ud 0.970 τ n [Serebrov05] λ [PDG 2010] A [UCNA 2010] 0.965 τ n [PDG 2010] 0.960 �1.290 �1.280 �1.270 �1.260 λ = g A / g V A [PERKEO II, prel.] τ − 1 = | V ud | 2 | g V | 2 (1 + 3 | λ | 2 ) n D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 6 / 43

Status of A and λ in n decay Δ A/A = 0.1% (abBA goal) PERKEO II, prelim. Average: UCNA, 2010 -0.1187(8) Uncertainty of the average PERKEO II, 2002 scaled up by factor 2 . 3 × Global fit χ 2 / dof = 27 / 5 ! Liaud, 1997 Statistical probability for Yerozolimskii, 1997 this χ 2 is 6 × 10 − 5 . PERKEO,1986 -0.125 -0.120 -0.115 -0.110 Beta Asymmetry A D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 7 / 43

Status of A and λ in n decay (cont’d) Δ�λ/ = 0.03% λ (Nab/abBA goals) PERKEO II, prelim. UCNA, 2010 Average: -1.2733(20) Goals for ∆ a , ∆ A : PERKEO II, 2002 ⇒ ∆ λ ≃ 3 . 5 × 10 − 4 Mostovoi, 2001 i.e., an order of magn. improvement. Liaud, 1997 ∆ λ ≃ 0 . 27∆a ≃ 0 . 24∆A Yerozolimskii, 1997 λ a A PERKEO,1986 -1.28 -1.27 -1.26 -1.25 λ = / g g A V D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 8 / 43

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 int. term, never measured for the n , along with B , 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 connection 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) Nab experiment : Goals and motivation 4 May ’12 9 / 43

Updated limits for RH S and T currents n decay 0.15 0.15 2 2 Δχ C.L. Δχ C.L. 2.30 68.3% 2.30 68.3% 0.10 0.10 4.61 90% 4.61 90% 95.4% 6.17 6.17 95.4% 0.05 0.05 neutrino neutrino�mass mass (68%�C.L.) (68%�C.L.) R T / L A 0.00 R T / L A 0.00 -0.05 -0.05 muon�decay muon�decay “ 90%�C.L. ” “ 90%�C.L. ” -0.10 -0.10 neutron and nuclear�decays neutrino�mass neutron�and�nuclear�decays neutrino�mass (survey,�95%�C.L.) (68%�C.L.) (survey,�95%�C.L.) (68%�C.L.) -0.15 -0.15 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 R S / L V R / L S V Present limits ( n decay data) Projected limits with: τ n , a = − 0 . 10588(10), (SM values at origin of plot.) b ≡ 0, A = − 0 . 1186(1), B = 0 . 9807(30), [ τ n = 881 . 8(13) s ] C = − 0 . 23875(24). [After: G. Konrad, W. Heil, S. Baeßler, D. Poˇ cani´ c, F. Gl¨ uck, arXiv 1007.3027.] D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 10 / 43

Limits for LH S and T currents n decay 0.3 2 Δχ C.L. “present�limits” 0.04 muon�decay “ future�limits ” 2.30 68.3% “90%�C.L.” (68%�C.L.) 0.2 (68%�C.L.) 4.61 90% neutron�and 0.02 6.17 95.4% nuclear�decays 0.1 (survey,�68%�C.L.) 2 Δχ C.L. L T / L A 0.00 L T / L A 0.0 2.30 68.3% 4.61 90% neutron�and -0.1 -0.02 nuclear�decays 6.17 95.4% (survey,�68%�C.L.) -0.2 superallowed superallowed + + +������������+ nuclear�decays 0 →0 decays -0.04 nuclear�decays 0 → 0 decays 107 (68%�C.L.) 107 ( (���In),�90%�C.L.) P ( (���In),�90%�C.L.) P (68%�C.L.) -0.3 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 -0.04 -0.02 0.00 0.02 0.04 L S / L V L S / L V Present limits ( n decay data) Projected limits with: τ n , a = − 0 . 10588(10), (SM values at origin of plot.) b = 0 ± 0 . 003, A = − 0 . 1186(1), [ τ n = 881 . 8(13) s ] B = 0 . 9807(30), C = − 0 . 23875(24). [After: G. Konrad, W. Heil, S. Baeßler, D. Poˇ cani´ c, F. Gl¨ uck, arXiv 1007.3027.] D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 11 / 43

Correlation parameters with recoil correction [Gardner, Zhang, PRL 86 , 5666 (2001), Gardner, hep-ph/0312124] Most general form of hardonic weak current consistent with (V-A): � p(p p ) | J µ | n(p n , P) � = f 1 (q 2 ) γ µ − if 2 (q 2 ) q µ + f 3 (q 2 ) � q µ + g 1 (q 2 ) γ µ γ 5 ¯ u p (p p ) M n M n − ig 2 (q 2 ) σ µν γ 5 q ν + g 3 (q 2 ) � γ 5 q µ u n (p n , P) M n M n a , A , B ⇒ λ = g 1 τ n ∝ (f 1 ) 2 + 3(g 1 ) 2 while f 1 However, f 2 (weak magnetism) and SCC’s ( g 2 , g 3 ), remain unresolved in beta decays (best tested in A=12 system). With recoil corrections, Gardner and Zhang find: a(E e ) = func (f 2 ) while A(E e ) = func (f 2 , g 2 ) D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 12 / 43

Current and planned experiments aiming to measure a 1. Nab : goal is to measure ∆ a / a ≃ 10 − 3 • Discussed in this talk. 2. aCORN : goal is to measure ∆ a / a < 1 %; (with 0.5 % syst ) • Funded, under way at NIST, • Uses only part of neutron decay phase space. 3. aSPECT : aims to measure ∆ a / a ≃ 3 × 10 − 3 ( ∼ 1 % short-term) • Funded and running; • Singles measurement! • will become part of the PERC program with improvements. D. Poˇ cani´ c (UVa) Nab experiment : Goals and motivation 4 May ’12 13 / 43

How to accomplish the goals of Nab? Measure: ∆a ≃ 10 − 3 and ∆b ≃ 3 × 10 − 3 . a (n → p + e − + ¯ Basic approach: ν e ) ◮ Detect electrons directly, in Si detectors, ◮ Measure electron energy in Si detectors, ◮ Detect protons, after acceleration, in Si detectors, ◮ Determine proton momentum from TOF over a long flightpath (electron provides start pulse). A complex magneto-electrostatic apparatus is required to guide particles (nearly) adiabatically to detectors. Location: FnPB at SNS (backup NG-C at NIST). D. Poˇ cani´ c (UVa) Nab experiment : Measurement principles 4 May ’12 14 / 43

Electron–neutrino angle from E e and E p p Conservation of momentum in n beta decay, � p p + � p e + � p ν = 0 , yields p 2 p = p 2 e + 2 p e p ν cos θ e ν + p 2 ν . n Neglecting proton recoil energy, E e + E ν = E 0 , so that p ν = E 0 − E e . Therefore: e cos θ e ν is uniquely determined by mea- θ e ν suring E e and E p (or p p ⇒ TOF p ). − ν D. Poˇ cani´ c (UVa) Nab experiment : Measurement principles 4 May ’12 15 / 43