The neutron beta decay correlation program at SNS Dinko Poˇ cani´ c University of Virginia NSAC Subcommittee Review Chicago, IL, 15 April 2011 D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 1 / 42
n-decay program at FnPB The FnPB neutron decay program at SNS ◮ Nab : a precise measurement of ◦ a , the electron-neutrino correlation in neutron decay, and ◦ b , the Fierz interference term (so far not measured in n decay). ◮ Polarized program (abBA/PANDA): precise measurements of ◦ A , the electron asymmetry in neutron decay, ◦ B , the neutrino asymmetry in neutron decay, ◦ C , the proton asymmetry in neutron decay; also δ a / a , δ A / A , δ B / B ≤ 10 − 3 , Goal uncertainties: and δ b ≤ 3 × 10 − 3 . D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 2 / 42
Motivation, goals Neutron Decay Parameters (SM) dw ≃ k e E e (E 0 − E e ) 2 dE e dΩ e dΩ ν � k e · � � � � � k ν + b m k e k ν � � × 1 + a + � � σ n � · A + B + . . . 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) n beta correlations at SNS 15 Apr ’11 3 / 42
Motivation, goals 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) n beta correlations at SNS 15 Apr ’11 4 / 42
CKM matrix: V ud 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) n beta correlations at SNS 15 Apr ’11 5 / 42
CKM matrix: V ud Status of A and λ in n decay (cont’d) Δ�λ/ = 0.03% λ (Nab/abBA goals) PERKEO II, prelim. UCNA, 2010 Average: Goals for ∆ a , ∆ A : -1.2733(20) 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) n beta correlations at SNS 15 Apr ’11 6 / 42
Beyond V ud 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) n beta correlations at SNS 15 Apr ’11 7 / 42
Beyond V ud non- V − A interaction terms 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% 6.17 95.4% 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 based on a = − 0 . 1030(1), (SM values at origin of plot.) b ≡ 0, and no improvement in A . [G. Konrad, W. Heil, S. Baeßler, D. Poˇ cani´ c, F. Gl¨ uck, arXiv 1007.3027.] D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 8 / 42
Beyond V ud non- V − A interaction terms 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% (68%�C.L.) “90%�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. 0.00 L T / L A 0.0 L T / L A 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 107 107 ( (���In),�90%�C.L.) P (68%�C.L.) ( (���In),�90%�C.L.) (68%�C.L.) P -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 assuming a = − 0 . 1030(1); (SM values at origin of plot.) b = 0 ± 0 . 003: no new A , B measurements. [G. Konrad, W. Heil, S. Baeßler, D. Poˇ cani´ c, F. Gl¨ uck, arXiv 1007.3027.] D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 9 / 42
Beyond V ud Second class currents 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) n beta correlations at SNS 15 Apr ’11 10 / 42
Comparison w/other experiments Little a Current experiments aiming to measure a 1. Nab : goal is to measure ∆a / a ∼ 10 − 3 ◮ Discussed in this presentation. 2. aCORN : goal is to measure ∆a / a ∼ 0 . 5 − 2 % ◮ Funded, under way at NIST, ◮ Uses only part of neutron decays. 3. aSPECT : aims to measure ∆a / a ∼ 10 − 3 ◮ Funded and running; recently overcame trapping problems, ◮ Stat. sensitivity not as good as Nab due to integration; presently ∼ 2 %/day—will likely improve on publ. results, not < 1 % this yr, ◮ Determination of detection function relies on theoretical model of spectrometer; if assumptions fulfilled, input param’s easy to measure. ◮ Singles measurement! ◮ will become part of the PERC program with improvements. D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 11 / 42
Comparison w/other experiments Polarized measurements Current state of the art in A : PERKEO II ◮ obtained A = − 0 . 1189(7) in 2002; − 0 . 1198(5) current prelim. ◮ data acquisition finished, ◮ data analysis of last (3rd) run completed; result not yet published, ◮ symmetric setup on cold n beam, similar to original abBA design, Electron�Detector�(Plastic�Scintillator) ◮ singles e detection ◮ benchmark design for all comparisons, Decay�Electrons ◮ major uncertainties: ◮ statistics, Polarized�Neutrons ◮ neutron beam polarization, ◮ background, Split�Pair�Magnet ◮ electron detection. Magnetic�Field PERKEO�II D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 12 / 42
Comparison w/other experiments Polarized measurements 1. abBA: aim δ A / A ≃ 1 × 10 − 3 ; (discussed in this talk) ◮ uses magnetic filter, ◮ expected improvements: background (coincidences), electron detection (Si detector), sensitivity to field inhomogeneities, ◮ measurements of C ( B ) planned 2. PERKEO III: aim δ A / A ≃ 2 × 10 − 3 in A ◮ data analysis of second run ongoing, aim to measure A and f 2 ◮ expected improvements: pulsed wide beam (statistics, background) 3. UCNA: aim δ A / A ≃ 2 × 10 − 3 (discussed at this meeting) ◮ achieved − 0 . 11966 +152 − 166 in 2010, ◮ uses (so far, dedicated) UCN source, ◮ major uncertainties: statistics, P n (so far: > 99 . 5% , viz. 99 . 7(1)% in PERKEO II), E loss in foil, muon veto bgd, ◮ further measurements of B , b planned, 4. PERC: aim δ A / A ≃ 3 × 10 − 4 ; (funded, being designed) ◮ uses magnetic filter behind a pulsed beam in a neutron guide, ◮ main expected improvements: counting statistics, background (singles det’n, but w/pulsed beam), sensitivity to field inhomogeneities; ◮ future measurements of a , C , et al., in planning. D. Poˇ cani´ c (UVa) n beta correlations at SNS 15 Apr ’11 13 / 42
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