Ultracold neutrons from He-II for a neutron lifetime experiment Oliver Zimmer Institut Laue Langevin Grenoble PSI2013, Villigen, 12 September 2013

CKM unitarity test - goals for neutron decay? Marciano & Sirlin PRL 96 (2006)  n accuracy goal:0.34 s PDG: 880 ± 1.1 s (S=1.8) ± (S=1.9) Perkeo II: Mund et al. PRL 110 (2013) ± UCNA: Liu et al. PRL 105 (2010) ± Perkeo III: Maerkisch et al ??? ± uncertainty due to radiative corrections:

Material bottle experiments ± 3.3 s (  t  12 s) Nesvizhevsky et al. JETP 75 (1992) ± 0.9 stat ± 0.4 syst s (  t  100 s) Arzumanov et al. Phys. Lett. B 483 (2000) ± 0.8 s (  t  5 s) Serebrov et al. Phys. Lett. B 605 (2005) ± 1.8 s (  t  110 s) Pichlmaier et al. Phys. Lett. B 693 (2010) ± 0.8 stat ± 1.9 syst s Arzumanov et al. JETP Lett. 95 (2012) 224 In beam experiments  talk Scott Dewey ± 1.2 stat ± 3.2 syst s Nico et al. Phys. Rev. C 71 (2005) Magnetic bottle experiments permanent magnet 20-pole bottle Ezhov et al., still unpublished He-II filled 4-pole trap: –63 s Dzhosyuk et al. J. Res. NIST 110 (2005) 339 Projects: PENeLOPE, UCN , HOPE... all aiming at  n << 1 s Experimental situation  talk Peter Geltenbort  talk Alexey Fomin

perm. mag. trap (“fill and empty”) UCN  (electron detection) PENeLOPE (proton detection) PNPI / LPC / ILL TU Munich LANL R. Picker et al., J. Res. NIST 110 (2005) 357 V. Ezhov et al. J. Res. NIST 110 (2005) 345 Walstrom et al., Nucl. Instr. Meth. A 599 (2009) 82  talk Steven Clayton

HOPE – H albach O ctu P ole neutron lifetime E xperiment magneto-gravitational trap V eff  2 l trap depth 40 – 45 neV high-density UCN source counting the dead & survivors mgz  Poster Felix Rosenau

HOPE – H albach O ctu P ole neutron lifetime E xperiment magneto-gravitational trap V eff  2 l trap depth 40 – 45 neV high-density UCN source counting the dead & survivors mgz  Poster Felix Rosenau

94 mm B(r) = B R (r/R) 3 32 magnet slices NdFeB magnets: B R = 1.35 T Halbach octupole

12 octupoles + hands & forces = magnetic trap

 storage  800 s (teflon plug at trap bottom and a few mT bias field) PhD thesis Kent Leung UCN trapping tests at PF2  Peter Geltenbort

Shutter coil for vertical confinement for “fill and empty” method (5 T upper coil for later, optional proton focusing onto an aSPECT-type SDD) lower superconducting coil: A < 10 s ramping time

B ias coil to guide decay products to detector for “counting the deads” (later option) p/e - detector p and  gyrate about vertical bias field Simulation: 60 % probability to reach detector

Preparation of spectrum Diffusive piston for trajectory mixing Cut into spectrum with absorber  get rid of marginally trapped neutrons absorber diffusive piston 42 neV free access from top and bottom

Experiments? Start with well established “fill and empty” method Full access from top and bottom: insertion of diffusive paddle and absorber monitoring of depolarisation detection of marginally trapped neutrons Couple experiment to SUN-2 UCN source (pessimistic estimate: 3000 UCN/fill)  n ~ 0.5 s in 50 days (statistical) To be started in mid 2014

  800 s K and decay) P = 27 cm -3 s -1 in white cold beam at ILL (5 cm -3 s -1 in monochromatic beam)  UCN  10 4 cm -3 possible at cold-neutron guide „phonon-roton“ dispersion of superfluid 4 He free neutron dispersion q  7 nm K R. Golub, J.M. Pendlebury, PL 53A (1975) 133 converter cold neutron beam  UCN = P   -1 =  -1 decay +  -1 upscattering +  -1 capture +  -1 wall losses  capture ( 4 He) = 0 SUN-2 superfluid helium UCN source  talk Florian Martin

November 2012 SUN-2 assembly

Martin Simson

end of November 2012

 accumulated UCN from 4 liters He-II   120/cm 3

Double exponential fit, 0.64K: 50%  1 = 37 s 50%  2 = 165 s = W/V 0.64K 0.82K 1.05K Delay time Beryllium on supermirror on glass guide UCN loss per wall bounce: V = 233 neV

Project SuperSUN (3 m magnetic 12-pole UCN reflector) In-situ UCN polarizer Enhancement of UCN spectrum possible Weak dependence of  UCN on wall quality (values in source for E < 296 neV): Zimmer & Golub, arXiv: R = 5 cm numbers for monochromatic beam H172b (5 times more in direct beam) = W/V

Experimental team (HOPE and SUN-2 UCN source) Felix Rosenau Kent Leung Martin Simson Florian Martin Sergey Ivanov Oliver Zimmer Bastian Maerkisch (Uni Heidelberg):  -detector for HOPE Thorsten Lauer (TU Munich): coatings and TOF equipment Mikhail Lasakov (PNPI): Beryllium coatings Philipp Schmidt-Wellenburg, Martin Fertl, Florian Piegsa (SUN-1 UCN source) Thank you for your attention ! Special thanks to Paul Schurter and Ben van den Brandt