Fierz Interference in Neutron Decay Leah Broussard Oak Ridge National Laboratory Beta Decay as a Probe of New Physics November 1-3, 2018 University of Massachusetts Amherst
A probe for new physics • CKM unitarity • Competitive with LHC limits 1 • LQCD calc g A now 1% 2 𝑊 calc shifts from unitarity 3 • New Δ 𝑆 𝑾 𝒗𝒆 𝑊 𝑊 Hardy and Towner, CIPANP2018 𝑒 𝑒′ 𝑣𝑡 𝑣𝑐 𝑊 𝑊 𝑊 = 𝑡 𝑡′ 𝑑𝑒 𝑑𝑡 𝑑𝑐 𝑊 𝑊 𝑊 𝑐 𝑐′ 𝑢𝑒 𝑢𝑡 𝑢𝑐 10 -5 𝑣𝑐 | 2 = 0.9994(5) (PDG 18) |𝑾 𝒗𝒆 | 2 + |𝑊 𝑣𝑡 | 2 + |𝑊 0.9984(4) • Beyond Standard Model • Scalar, Tensor, Right-handed currents • Improved LQCD calcs of g A , g S , g T 4 1 Gonzalez-Alonso, Naviliat-Cuncic, and Severijns, arXiv:1803.08732 2 Chang et al , Nature 558 (2018) 91-94 3 Seng, Gorchtein, Patel, Ramsey-Musolf, arXiv:1807.10197 4 Gupta et al , PRD 98 (2018) 034503 Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 2
Neutron β -decay observables dW ∝ 1 + 𝒃 Ԧ 𝑞 𝑓 ∙ Ԧ 𝑞 𝜑 + 𝒄 𝑛 𝑓 𝜏 𝑜 ∙ 𝑩 Ԧ 𝑞 𝑓 + 𝑪 Ԧ 𝑞 𝜉 + 𝑬 Ԧ 𝑞 𝑓 × Ԧ 𝑞 𝜑 + Ԧ 𝐹 𝑓 𝐹 𝜑 𝐹 𝑓 𝐹 𝑓 𝐹 𝜉 𝐹 𝑓 𝐹 𝜑 𝝁 2 +𝝁 1−𝝁 2 𝒉 𝑩 𝑩 = −2 𝒃 = 𝝁 = 1+3𝝁 2 1+3𝝁 2 𝒉 𝑾 𝜷(𝐹 𝑓 ) Asymmetries: 𝜷 meas (𝐹 𝑓 ) = 1+𝒄𝑛 𝑓 /𝐹 𝑓 CKM unitarity: 𝝊 −1 = 𝑋 ∝ 𝑾 𝒗𝒆 2 1 + 3 𝝁 2 Goal: dA/A or da/a → 0.1% and d τ → 0.1 s B ( b ν ), b linear sensitivity to BSM S , T : 𝒄 𝑪𝑻𝑵 = 2 1+3 𝝁 2 𝒉 𝑻 𝝑 𝑻 − 12 𝝁 𝒉 𝑼 𝝑 𝑼 2 𝑪𝑻𝑵 = 𝒄 𝝃 1 + 3𝝁 2 𝝁𝒉 𝑻 𝝑 𝑻 − 4𝒉 𝑼 𝝑 𝑼 1 + 2𝝁 Not yet measured in neutron decay, until… Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 3
UCNA collaboration Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 4
UCNA experiment More from Andy Saunders, next 2010: 700 nm Mylar 2011-12: 500 nm Mylar 2012-13: 130/180 nm 6F6F 1 Brown et al, PRC 97 035505 (2018) Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 5
Fierz term from UCNA • UCNA: 4 π β acceptance, low neutron/ambient backgrounds, energy reconstruction → direct spectral extraction of b n • “Super - sum” removes distortion from A Σ = 1 − + 1 + 𝑂(𝐹) 2 − 𝑂(𝐹) 2 + 𝑂(𝐹) 1 𝑂(𝐹) 1 2 2 • 2010 data set dominant error: energy calibration +0.90 𝒄 𝒐 = 0.067 ± 0.005 𝑡𝑢𝑏𝑢 −0.061 𝑡𝑧𝑡 –0.041 < 𝒄 𝒐 < 0.225 (90% CL) 1 Hickerson et al , PRC 96 (2017) 042501 Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 6
Complementary approaches for b • 2 new datasets: 2011-12, 2012-13 • 2012 improved E reconstruction: b vs octet → 𝑩 • 2 techniques: spectrum 𝜯 vs asymmetry 1+𝒄 m E • 𝜯 limited by E calibration, 𝑩 𝒏 by statistics • Preliminary: 𝒄 𝒐 = 𝑦. 𝑦𝑦 ± 0.03 (blinded) blinded Thanks X. Sun (Caltech) for slide content Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 7
Fundamental Neutron Physics at the Spallation Neutron Source FNPB program: 𝒐𝒒 → 𝒆𝜹 n 3 He Nab nEDM Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 8
Nab Collaboration R. Alarcon a , S. Baessler b,c (Project Manager), S. Balascuta a , L. Barrón Palos n , T. Bailey m , K. Bass i , N. Birge i , A. Blose f , D. Borissenko b , J.D. Bowman c (Co-Spokesperson), L. J. Broussard c , A.T. Bryant b , J. Byrne d , J.R. Calarco c,i , J. Caylor i , K. Chang b , T. Chupp o , T.V. Cianciolo c , C. Crawford f , X. Ding b , W. Fan b , W. Farrar b , J. Farr, N. Fomin i , E. Frlež b , J. Fry b , M.T. Gericke g , M. Gervais f , F. Glück h , G.L. Greene c,i , R.K. Grzywacz i , V. Gudkov j , J. Hamblen e , C. Hayes m , C. Hendrus o , T. Ito k , A. Jezghani f , H. Li b , M. Makela k , N. Macsey g , R. Mammei g , J. Martin l , M. Martinez a , D.G. Matthews f , M. McCrea f , P. McGaughey k , C.D. McLaughlin b , P. Mueller c , D. Perryman i , D. van Petten b , S.I. Penttilä c (On-site Manager), D. Počanić c (Co-Spokesperson), Y. Qian b , G. Randall a , G. Riley i , C.A. Royse m , K.P. Rykaczewski c , A. Salas-Bacci b , S. Samiei b , E.M. Scott i , T. Shelton j , S.K. Sjue k , A. Smith b , E. Smith k , E. Stevens b , J. Wexler m , R. Whitehead i , W.S. Wilburn k , A.Young m , B.Zeck m Main project funding: Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 9
Nab measurement principles • Goal: Δa /a ~10 -3 and Δb ~3×10 -3 • 4π β acceptance : “tear - drop” 𝑞 𝑓 2 + 2𝑞 𝑓 𝑞 𝜑 cos 𝜄 𝑓𝜉 + 𝑞 𝜉 2 = 𝑞 𝑓 2 Yield: ∝ 1 + 𝒃 • 𝑞 𝑞 𝐹 𝑓 cos 𝜄 𝑓𝜉 Bowman, J Res NIST 110 40 (2005) Pocanic et al , NIMA 611 211 (2009) Baessler et al , J Phys G 41 114003 (2014) Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 10
Nab measurement principles • Asymmetric spectrometer with long TOF arm: proton TOF ⇒ momentum 𝑢 𝑞 = 𝑀 𝑛 𝑞 = 𝑔 cos 𝜄 𝑞 𝑞 𝑞 𝑞 • Adiabatic field expansion 𝑀 𝑢 𝑞 = 𝑛 𝑞 𝑒𝑨 න 𝑞 𝑞 1 − 𝐶 𝑨 𝐶 0 sin 2 𝜄 + 𝑟 𝑊 𝑨 − 𝑊 𝑨 0 0 7 m 𝐹 0 • Expand for small angles • For each E e fit central 75% to obtain a • Edges verify spectrometer response J. Phys: Conf Ser. 876 012005 (2017) W. Fan, UVA Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 11
Nab spectrometer installation gif credit: J. Fry, UVA Installation crew nominated for ORNL “Significant Event Award” Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 12
Expected statistical uncertainty • 1.4 MW routine at SNS • Expect 1600 decays/s = 200 p/s in top detector • Up to Δa /a ~2×10 -3 each run-cycle • Require 2 years SNS running for statistics goal • Including 50% duty factor, 10% background, several systematic runs Δa /a ~7×10 -4 D. Pocanic Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 13
Nab expected systematics for a Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 14
Systematics for Fierz term b • Full β energy collected, except: • Bounce history (deadlayer ), bremsstrahlung, detector response… • Also backgrounds, edge effects, timing cutoff, proton efficiency… • Statistical uncertainty ~3 × 10 −4 • if gain free parameter → 5 × 10 −4 • Initial (partial) parametric study of systematics: Systematic Requirement Gain Free parameter Offset ±0.06 keV Max. nonlinearity ±0.05 keV Resolution ±2 keV Energy tail ±10% H. Li, UVA Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 15
Magnetic field • Precise (relative) field mapping required for ∆𝑀 𝑀 ≤ 2 × 10 −5 • Locate electron/proton flux tubes 𝛿 ( < 2% ) B filter B TOF B filter ( 1% ) B DV B TOF B DV B filter ( 1% ) S. Penttila, ORNL J. Fry, UVA Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 16
Detector effects • Calibration (dE ~ 0.2 keV) • Linearity to ~10 -4 → radioactive sources; need high precision calibrated pulser • Temperature stability to 0.5 K → sensors, leakage current, pulser gain? • Detector response vs. event energy/hit location; uniformity → • Si detector: 2 mm thick, 11 collimated radioactive sources; cm diameter active area, 100 electron-gun studies nm deadlayer, 127 hex pixels • Cross-talk → radioactive sources, • 40-50 ns rise times proton beam (physical); pulsers • 3 keV @ 30 keV FWHM (electronic) Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 17
Detector effects • dE in tail (ratio ~ 4.4×10 -4 ) • Backscattering = sum both detectors but… • Bounce history of electrons → radioactive source studies to benchmark simulations • Detector deadlayer uniformity → measure with proton and electron gun • Bremsstrahlung needs ×10 improvement → characterize in situ with radioactive sources; electron-gun and gamma detector • Rate-dependent effects: backgrounds, accidentals, deadtime E. Frlez, UVA Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 18
Detector effects • Proton trigger efficiency < 100 ppm/keV (efficiency slope 50%) → proton gun • TOF bias <0.3 ns on average between electrons and protons (from detector response) → collimated fast S. Baessler timing source, electron-gun Weighting potential y position [mm] -300 V 0 V x position [mm] Graphic by A. Jezghani, UKY Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 19
45 Ca Fierz term • Learn high precision calibration • Also nice BSM target • Source on thin 6F6F foil • UCNA spectrometer with UCNB/Nab detectors • 10 8 events collected 207 Bi, 139 Ce, 113 Sn 45 Ca source source insert Goal |b|~10 -2 UCNB Si Energy [MeV} L. Hayen, KU Leuven detectors 1 Gonzalez-Alonso and Naviliat-Cuncic , PRC 94 (2016) 035503 2 Hayen et al , RMP 90 (2018) 015008 Leah Broussard Beta Decay as a Probe of New Physics, November 1-3, 2018 20
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