UCN a measurement of the neutron lifetime using

UCN : a measurement of the neutron lifetime using ultracold neutrons stored in an asymmetric magnetic trap UCN Collaboration: N. Callahan, W. Fox, F. Gonzalez, E. Adamek, C. -Y. Liu, D. J. Salvat, and J. Vanderwerp, Center for Exploration of Energy and Matter; Physics Department, Indiana University, Bloomington, IN 47408, USA; Leah Broussard, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; S. M. Clayton, S. Currie, D. Fellers, M. A. Hoffbauer, S. W. T. Mac. Donald, M. Makela, C. L. Morris, J. D. Ortiz, J. Ramsey, A. Saunders, S. K. L. Sjue, Z. Tang, P. L. Walstrom, Z. Wang and H. Weaver, Los Alamos National Laboratory, Los Alamos, NM 87545, USA C. Cude-Woods Department of Physics, North Carolina State University, Raleigh, NC 27695, USA; Los Alamos National Laboratory, Los Alamos, NM 87545, USA and Department of Physics, North Carolina State University, Raleigh, NC 27695, USA; E. M. Egnel, West Point Military Academy, West Point, NY 10996, USA P. Geltenbort, Institut Laue-Langevin, 38000 Grenoble, France; Eric Fries, K. P. Hickerson and W. Wei California Institute of Technology, Pasadena, CA 91125, USA; A. T. Holley, Department of Physics, Tennessee Technological University, Cookeville, TN 38505, USA; A. Komives; Department of Physics and Astronomy, De. Pauw University, Greencastle, IN 46135, USA; R. W. Pattie, Jr, Department of Physics and Astronomy, East Tennessee State University, TN 37614, USA; S. J. Seestrom Sandia National Laboratory, Albuquerque, NM 87123, USA; E. I. Sharapov, Joint Institute for Nuclear Research, Dubna, Moscow 141980, Russia; J. Choi, J. Wexler and A. R. Young, Department of Physics, North Carolina State University, Raleigh, NC 27695, USA D. J. Salvat, DJ, ER Adamek, D Barlow, James D Bowman, LJ Broussard, NB Callahan, SM Clayton, et al. "Storage of Ultracold Neutrons in the Magneto-Gravitational Trap of the Ucn Τ Experiment. " Physical Review C 89, no. 5 (2014): 052501. C. L. Morris, E. R. Adamek, L. J. Broussard, N. B. Callahan, S. M. Clayton, C Cude-Woods, S. A. Currie, et al. "A New Method for Measuring the Neutron Lifetime Using an in Situ Neutron Detector. " Review of Scientific Instruments 88, no. 5 (2017): 053508. R. Pattie, N. Callahan, C. Cude-Woods, E. Adamek, L. J. Broussard, S. Clayton, et al. Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection. Science. 2018; 360(6389): 627 -32. N. Callahan, C-Y Liu, F. Gonzalez, E. Adamek, J. D. Bowman, L. Broussard, S. M. Clayton, et al. "Monte Carlo Simulations of Trapped Ultracold Neutrons in the Ucn Τ Experiment. " Physical Review C 100, no. 1 (2019): 015501. Student Postdoc Spokesperson emeritus 1

The two techniques used to measure n Cold Neutron Beam Number Observed Ultracold Neutron (UCN) Bottle Fill Store Count Time 2

UCN technique used to measure n Cold Neutron Beam Dagger Magnetic bottle Ultracold Neutron (UCN) Bottle In situ counting Number Observed Fill Store Count Time 3

History and status of n in 2019 Most precise Beam: n = 887. 7 ± 2. 2 s Most precise Bottle: n = 877. 7 ± 0. 8 s 4

Measuring the lifetime with UCN stored in a material bottle is challenging • Beam measurements require precise determination of the neutron beam fluence, decay volume, and absolute proton detector efficiency – • Bottle measurements must correct for UCN losses other than neutron beta decay – • Have involved multiple systematic corrections of order 5 sec These corrections are often of the same order as the quoted uncertainty We have designed a bottle that has negligible intrinsic losses using the magnetic interaction Dubbers & Schmidt, Reviews of Modern Physics 83 (1111) 2011 A. Serebrov, et al. (2008) 5

UCN Magneto-gravitational trap • Large Halbach array of permanent magnets – large neutron statistics • Intrinsically long lifetime - no material interactions during storage period • Asymmetric trap for rapid evolution and mixing of the phase space – fast removal of quasi-bound neutrons • In situ active detector – neutron unloading observed in real time 6

Illustration of cleaning and unloading • Load trap for 150 sec • Clean for a variable time (100 -400 sec) • Cleaners in trap for loading and cleaning • Dagger can also be lowered during loading and cleaning – “dagger cleaning” • Cleaners and dagger raised during storage time (10 – 1510 sec) • Dagger lowered to count remaining UCN – either in 1 single step, or multiple steps 7

Detector • The signals were discriminated with a 0. 5 photo-electron threshold. • Logic pluses with a width of 10 ns were digitized using a multi scalar with a clock period of 0. 8 ns. • Coincidences in software WSF/PM tube cover 20 nm of 10 B on Zn. S screen Light Output Efficiency Pulse shape 8

Cleaning The giant cleaner eliminates the need for a cleaning correction Dagger signal Active cleaner signal Neutron pulse due to heating from the trap door closing 9

FY 2017 results with giant cleaner and new source. -4 o t ed 10 n a e l c ap Tr • No cleaning correction needed • New “current mode” counting method • Agreement with last years data 10

Systematic uncertainties for “current mode” counting Upper bound Directio Effect (s) n Depolarization 0. 07 + Microphonic heating 0. 24 + Insufficient cleaning 0. 07 + Dead time/pileup 0. 04 ± Phase space evolution 0. 10 ± Residual gas interactions 0. 03 ± Background shifts Total Heating Limit established by long holding time excess <0. 01 0. 28 ± Method of evaluation Varied external holding field Detector for heated neutrons Detector for uncleaned neutrons Known hardware dead time Measured neutron arrival time Measured gas cross sections and pressure Measured background as function of detector position (uncorrelated sum) Insufficient Cleaning Limit established by short holding time excess Ttrap>40 days Steyerl et al. 2016 11

UCN unblinded results 12

bl blo oc c k( k co 20 rr) 18 RH RH (b ut RH te rf RH ly) ( Av AC) er ag e 894 892 890 888 886 884 882 880 Zn. S/10 B Active cleaner Zn. S/10 B Monitor no t(s) Blinded 2017 -2019 Data Added a preconditioning volume (Round House) • Filters beam fluctuations • Allows momentum filtering • Reduces loaded UCN by x 0. 6 (depol+time)

What do our new blinded data look like? 14

Where do things stand? UCNtn beam tn best l 0+→ 0+decays vud Pattie, RW, Nathan B Callahan, Chris Cude-Woods, Edith R Adamek, Leah J Broussard, SM Clayton, SA Currie, et al. "Measurement of the Neutron Lifetime Using a Magneto-Gravitational Trap and in Situ Detection. " 360, no. 6389 (2018): 627 -32. A. T. Yue, M. S. Dewey, D. M. Gilliam, G. L. Greene, A. B. Laptev, J. S. Nico, W. M. Snow, and F. E. Wietfeldt, Phys. Rev. Lett. 111, 222501 (2013). Märkisch, Bastian, Holger Mest, Heiko Saul, Xiangzun Wang, Hartmut Abele, Dirk Dubbers, Michael Klopf, et al. "Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam. " 122, no. 24 (2019): 242501. Seng, Chien-Yeah, Mikhail Gorchtein, Hiren H Patel, and Michael J %J Physical review letters Ramsey-Musolf. "Reduced Hadronic Uncertainty in the Determination of V U D. " 121, no. 24 (2018): 241804. Czzarnecki, Andrzej, William J Marciano, and Alberto %J ar. Xiv preprint ar. Xiv: . 06737 Sirlin. "Radiative Corrections to Neutron and Nuclear Beta Decays Revisited. " (2019). 15

Where are we heading? UCNtn beam tn best l 0+→ 0+decays vud Parallel Analysis Cal Tech IU LANL Unblind before Spring APS meeting Pattie, RW, Nathan B Callahan, Chris Cude-Woods, Edith R Adamek, Leah J Broussard, SM Clayton, SA Currie, et al. "Measurement of the Neutron Lifetime Using a Magneto-Gravitational Trap and in Situ Detection. " 360, no. 6389 (2018): 627 -32. A. T. Yue, M. S. Dewey, D. M. Gilliam, G. L. Greene, A. B. Laptev, J. S. Nico, W. M. Snow, and F. E. Wietfeldt, Phys. Rev. Lett. 111, 222501 (2013). Märkisch, Bastian, Holger Mest, Heiko Saul, Xiangzun Wang, Hartmut Abele, Dirk Dubbers, Michael Klopf, et al. "Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam. " 122, no. 24 (2019): 242501. Seng, Chien-Yeah, Mikhail Gorchtein, Hiren H Patel, and Michael J %J Physical review letters Ramsey-Musolf. "Reduced Hadronic Uncertainty in the Determination of V U D. " 121, no. 24 (2018): 241804. Czzarnecki, Andrzej, William J Marciano, and Alberto %J ar. Xiv preprint ar. Xiv: . 06737 Sirlin. "Radiative Corrections to Neutron and Nuclear Beta Decays Revisited. " (2019). 16

We have developed a new method for measuring the neutron lifetime • We have demonstrated an in situ active neutron detector that allows for many systematic tests and enables the measurement of corrections for cleaning effectiveness and phase space evolution • We have made a measurement of n for the first time with no extrapolation: 877. 7 ± 0. 7 (stat) +0. 3/-0. 1 (sys) s • All systematic uncertainties have been quantified by measurements • During 2017/2019 running we have achieved a statistical uncertainty of ± 0. 25 s (stat) ± 0. 15 s – Active Giant cleaner – Improved roundhouse Beam and bottle lifetime discrepancy remains 0+→ 0+ 4 std from unitarity Neutron decay consistent with unitarity 17