Nab and p Nab at SNS Stefan Baeler

Nab and p. Nab at SNS Stefan Baeβler Inst. Nucl. Part. Phys. 1

Idea of Nab experiment e- n p Nab @ Fundamental Neutron Physics Beamline (FNPB) @ Spallation Neutron Source (SNS) 8 meters Multipixel Si detectors for decay electrons and protons Cold Neutron Beam from left General Idea: J. D. Bowman, Journ. Res. NIST 110, 40 (2005) Original configuration: D. Počanić et al. , NIM A 611, 211 (2009) Asymmetric configuration: S. Baeßler et al. , J. Phys. G 41, 114003 2 (2014)

Ideogram of current experiments: PERKEO III (2019) UCNA (2018) (Nab goal) a. CORN (2017) PERKEO II (2013) UCNA (2013) ( ) UCNA (2010) ( ) Byrne (2002) ( ) PERKEO II (2002) Mostovoi (2001) PERKEO II (1997) ( ) Yerozolimskii (1997) Liaud (1997) PERKEO I (1986) Stratowa (1978) -1. 30 -1. 28 -1. 26 -1. 24 4

Motivation (2): CKM Unitarity 0. 98 PIBETA [Pocanic 04+S 18] 0. 975 Satula 12+S 18 DD-ME 2 PKO 1 PC-F 1 PC-PK 1 0. 97 [Li 11+S 18] [Liang 09+S 18] CKM unitarity [PDG 2019] 0. 965 0. 96 -1. 29 -1. 28 -1. 27 -1. 26 Seng-18 incorporates: C-Y Seng et al. , PRL 121, 241804 (2018) C-Y Seng et al. , PRD 100, 013001 (2019) M. Gorchtein, ar. Xiv: 1812. 04229 5

Motivation (3): Search for effective scalar (S) and tensor (T) interaction (from J. Hardy, I. Towner, PRC 91, 025501 (2015)) 6

Future search for effective scalar (S) and tensor (T) interaction Fig. from V. Cirigliano, M. Gonzales Alonso, after PPNP 104, 165 (2019) 7

Idea of the cos θeν spectrometer Nab @ SNS p e- n 1. 5 Proton phase space (Dalitz plot) pp 2 [Me. V 2/c 2] 1. 25 cos θeν = 1 Probability (arb. units) Ee = 700 ke. V 236 ke. V 1 0. 75 ke. V cos θeν = 0 0. 5 cos θeν = -1 0. 25 0 0 0. 2 0. 4 0. 6 0. 8 Ee [Me. V] 450 ke. V 8

Nab data analysis pp 2 distribution Full GEANT 4 spectrometer simulation: 12000 0. 0 Yield 0. 5 pp 1. 0 2 [Me. V 2/c 2] 1. 5 8000 4000 0 0 0. 002 0. 004 0. 006 Data analysis: Use edge to determine or verify the spectrometer TOF response function. Then, use central part to determine slope and 9 correlation coefficient a. Need agreement for all.

Nab spectrometer operation - 30 k. V Segmented Si detector TOF region (low field) 4 m flight path skipped Ø 81 mm magnetic filter region (field maximum) decay volume Neutron beam 1 m flight path skipped 0 k. V 0 -1 k. V 10

Nab spectrometer principle: measurement of Ee and tp - 30 k. V Adiabatic conversion TOF region (low field) 4 m flight path skipped magnetic filter region (field maximum) Neutron beam 1 m flight path skipped Proton Trajectory decay volume 0 k. V Magnetic Field 0 -1 k. V 11

Electron energy measurement with backscattering suppression TOF region (low field) 4 m flight path skipped Yield - 30 k. V magnetic filter region (field maximum) Neutron beam 1 m flight path skipped 5 10 4 10 3 10 2 10 1 detected Ee for e- in lower detector detected Ee with only lower detector Detector response for incoming Ee = 300 ke. V 1 0 decay volume 0 k. V 10 50 100 150 200 250 300 detected Ee [ke. V] 0 -1 k. V 12

Measurement idea - 30 k. V TOF region (low field) Setup to measure Fierz term (Nab-b) • Lower detector detects all protons. • Upward-going protons are reflected by a 1 k. V field above decay volume 0 k. V 4 m flight path skipped magnetic filter region (field maximum) TOF region (low field) decay volume 4 m flight path skipped magnetic filter region (field maximum) 0 k. V Neutron beam 1 m flight path skipped decay volume 0 -1 k. V +1 k. V Neutron beam Setup to measure proton asymmetry (Nab-a) • Only upper detector detects protons. • Downward-going protons are lost. 1 m flight path skipped -30 k. V 13

Nab goal for SNS run Experimental parameter none 100 ke. V none 40 μs 4. 4/√N 4. 7/√N Magnetic field Electrical potential inhomogeneity: Neutron Beam: … position … profile (including edge effect) … Doppler effect … Unwanted beam polarization Adiabaticity of proton motion Detector effects: … Electron energy calibration … Shape of electron energy response … Proton trigger efficiency … TOF shift due to detector/electronics Electron TOF correction Residual gas Background / Accidental coincidences Sum Systematic uncertainty Δa/a 5. 5· 10 -4 1. 7· 10 -4 2. 5· 10 -4 small can be small 1· 10 -4 2· 10 -4 4. 4· 10 -4 3· 10 -4 small 3. 8· 10 -4 small 14 1. 2· 10 -3

Status of Nab experiment: Magnetic field mapping Magnetic field on axis in filter and TOF region 4 4 3. 5 Run 484 Analytic Calculation 3 2. 5 2 Bz [T] 3 2. 5 2 1. 5 0. 5 1 0 0 5 0 15 20 25 30 35 z (arb) [cm] 0. 5 0 UPDATE 10 100 200 300 400 500 z (arb) [cm] 15

Status of Nab experiment: Detector development Detector subsystem is primarily responsibility of LANL (M. Makela, E. Smith et al. ): • Energy resolution a few ke. V • Lower (proton) detection threshold 10 ke. V • Detector transit time bias sub-ns Silicon detector in mount From UCNB @ LANL Yield Bi-207 source protons 200 400 Energy [ke. V] 1000 Signal: Electron, ~> 100 ke. V, followed by proton, ~18 ke. V, in neighboring pixel. Shown is the energy 16 of the second signal, and its delay after the first.

p. Nab: Measurement of correlation coefficients with polarized neutrons New addition: Neutron beam polarizer 17

p. Nab: Measurement idea Setup to measure electron asymmetry (as Nab-b): • Lower detector detects all protons. • Upward-going protons are reflected by a 1 k. V field above decay volume - 30 k. V TOF region (low field) 4 m flight path skipped magnetic filter region (field maximum) decay volume polarizer +1 k. V Neutron beam Spin flipper 1 m flight path skipped -30 k. V 4 m flight path skipped magnetic filter region (field maximum) decay volume polarizer 0 k. V Neutron beam Spin flipper 1 m flight path skipped 0 -1 k. V Setup to measure proton asymmetry (as Nab-a): • Only upper detector detects protons. • Downward-going protons are lost. 18

Features of measurement of beta asymmetry with p. Nab See S. Baessler et al. , JPG 41, 114003 (2014) 19

Statistical uncertainty for A and b from beta asymmetry Statistical uncertainty budget: none 100 ke. V 200 ke. V 20

Beta spectroscopy in neutron decay (unpolarized) beta spectrum: 0 200 SM SM Yield ] 400 Ee, kin (ke. V) 600 800 0 200 400 Ee, kin (ke. V) 600 800 21

Detector systematics 207 Bi 109 Cd 139 Ce 113 Sn 207 Bi Yield Residual Reconstructed energy Electron energy calibration Pulse height 10 5 10 4 10 3 10 2 10 1 detected Ee for e- in lower detector detected Ee with only lower detector width (mostly)backscattering (mostly) bremsstrahlung 1 0 50 100 150 200 250 300 detected Ee [ke. V] Pulse height Specification peak width fit parameter 0. 3 ke. V 1. 5 ke. V 1 ke. V 0. 01% 0. 0018 0. 2 ke. V 0. 3 ke. V 10 ke. V 2. 40% Requirements in p. Nab equal or less than what Nab requires! fit parameter 0. 03 ke. V 0. 1% 0. 0008 0. 05 ke. V 0. 1 ke. V 8 ke. V 0. 9% (numbers for Si detector, H. Li) 22

Neutron beam polarization If p. Nab is operated at NIST, we would use a He 3 polarizer, due to the feature to obtain an in-situ measurement of the polarization. No correction for Stern-Gerlach effects, no depolarization error, no time dependence. This is at the cost of some stat. sensitivity (see before). Unpolarized neutron beam 3 He cell Polarized neutron beam 23 See S. Penntila, D. Bowman, J Res. NIST 110, 309 (2005)

Nab schedule and potential p. Nab schedule Calendar Year 2019 2020 2021 2022 2023 2024 Nab installation Nab commissioning Change-over to polarized program At FNPB, or at new NG-C beamline at NIST Somewhere, we may have a 8 months shutdown Problem: Schedule for p. Nab@FTS conflicts with EDM installation. Scenarios: • With an additional 12 weeks, we could do a measurement with accuracy like PERKEO III, statistically limited • n. EDM moves elsewhere (e. g. , STS) 24 • p. Nab moves elsewhere

The Nab collaboration Active and recent collaborators: R. Alarcona, A. Atenciok, S. Baeßlerb, c (Project Manager), S. Balascutaa, L. Barrón Palosn, T. L. Baileym, K. Bassi, N. Birgei, A. Blosef, D. Borissenkob, J. D. Bowmanc (Co-Spokesperson), L. Broussardc, A. T. Bryantb, J. Byrned, J. R. Calarcoc, i, J. Caylori, K. Changb, T. Chuppo, T. V. Ciancioloc, C. Crawfordf, M. Cruzi, X. Dingb, W. Fanb, W. Farrarb, N. Fomini, E. Frležb, J. Fryb, M. T. Gerickeg, M. Gervaisf, F. Glückh, G. L. Greenec, i, R. K. Grzywaczi, V. Gudkovj, J. Hamblene, C. Hayesm, C. Hendruso, T. Itok, A. Jezghanif, H. Lib, M. Makelak, N. Macsaig, J. Mammeig, R. Mammeil, M. Martineza, D. G. Matthewsf, M. Mc. Creaf, P. Mc. Gaugheyk, C. D. Mc. Laughlinb, P. Muellerc, D. van Pettenb, S. I. Penttiläc (On-site Manager), D. E. Perrymani, R. Pickerp, J. Piercec, D. Počanićb (Co-Spokesperson), H. Presleyi , Yu Qianb, G. Randalla, G. Rileyi, K. P. Rykaczewskic, A. Salas-Baccib, S. Samieib, E. M. Scotti, T. Sheltonf, S. K. Sjuek, A. Smithb, E. Smithk, E. Stevensb, J. W. Wexlerm, R. Whiteheadi, W. S. Wilburnk, A. R. Youngm, B. Zeckm, M. Zemkei a Department of Physics, Arizona State University, Tempe, AZ 85287 -1504 i Department of Physics and Astronomy, University of Tennessee, b Department of Physics, University of Virginia, Charlottesville, VA 22904 - Knoxville, TN 37996 j Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208 k Los Alamos National Laboratory, Los Alamos, NM 87545 l Department of Physics, University of Winnipeg, Manitoba R 3 B 2 E 9, Canada m Department of Physics, North Carolina State University, Raleigh, NC 27695 -8202 n Universidad Nacional Autónoma de México, D. F. 04510, México o University of Michigan, Ann Arbor, MI 48109 p TRIUMF, Vancouver, Canada, V 6 T 2 A 3 4714 c Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 d Department of Physics and Astronomy, University of Sussex, Brighton BN 19 RH, UK e Department of Chemistry and Physics, University of Tennessee at Chattanooga, TN 37403 f Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 g Department of Physics, University of Manitoba, Winnipeg, Manitoba, R 3 T 2 N 2, Canada h KIT, Universität Karlsruhe (TH), Kaiserstraße 12, 76131 Karlsruhe, Germany Main project funding: 25

Summary 26

Parallel plate polarizer Goal: Achieve >99. 5% polarization at maximum transmission Proposed solution: Build short stack of thin substrates (quartz or sapphire) with doublesided SM coating. Neutrons go through substrate! Use perfect parallel plate polarizer, and select dimensions such that neutrons undergo two reflections. (A. K. Petukhov et al. , ar. Xi. V: 1906. 04690) SM is stack from sapphire plates: Sapphire 180 um Two stacks are needed for incoming beam with divergence, otherwise there would be neutrons parallel to the plates. Both stacks need to be in strong and uniform static 28 magnetic field to avoid depolarization (see C. Klauser et al. , NIM A 840, 181 (2016) )

Parallel plate polarizer (2) 2. Polarized beam at output of polarizer is not bent, and has very little displacement. One can interchange between polarized and unpolarized beam. 3. We do not have to move the magnet to change from Nab to p. Nab. 4. Largest loss mechanism in conventional SM or XSM setup is that neutrons that hit the substrate are lost. Here, they are not, except for the manageable effect of absorption. 5. Status: ILL team verified properties with small stack and small beam. I have not seen the data. Full polarizer @ILL in production. FNPB beam has larger divergence than PF 1 B, and therefore our problem is a bit less favorable. We are in the design optimization stage. Expected costs: ~$100 k, mostly for SM coatings. 29