HOPE a magnetic UCN trap to measure the

HOPE – a magnetic UCN trap to measure the neutron lifetime Felix Rosenaua, Florian Martina, Sergey Ivanova, Kent Leungb, Martin Simsona, Oliver Zimmera a. Institut Laue Langevin, b. North Carolina State University • Material bottle experiments State of the art Motivation - 888. 4 ± 3. 3 s • In beam experiments • Determination of - 886. 3 ± 1. 2 stat ± 3. 2 syst s Nico et al. Phys. Rev. C 71 (2005) 055502 Marciano & Sirlin PRL 96 (2006) 032002 • Magnetic bottle experiments - Permanent magnet 20 -pole bottle Ezhov et al. to be published • Uncertainty due to radiative corrections: - He-II filled 4 -pole trap: 833 +74 – 63 Dzhosyuk et al. J. Res. NIST 110 (2005) 339 s R E A N A L Y S I S • Accuracy needed to bring down the experimental error bar to the same level: t 12 s Nesvizhevsky et al. JETP 75 (1992) 405 - 885. 4 ± 0. 9 stat ± 0. 4 syst s t 100 s Arzumanov et al. Phys. Lett. B 483 (2000) 15 - 878. 5 ± 0. 8 s t 5 s Serebrov et al. Phys. Lett. B 605 (2005) 72 - 880. 7 ± 1. 8 s t 110 s Pichlmaier et al. Phys. Lett. B 693 (2010) 221 - 881. 6 ± 0. 8 stat ± 1. 9 syst s Arzumanov et al. JETP Lett. 95 (2012) 224 General characteristics Magneto-gravitational trapping Value - No wall interactions Accuracy needed 0. 34 s 3 10 -4 Current values 880 ± 1. 1 s (S=1. 8) -1. 2701 ± 0. 0025 (S=1. 9) (PDG 2012) Fast coil ramping - Allows “fill and empty” measurements Full diameter trap openings - Efficient electron detection - Manipulation of UCN gas by moveable piston and absorber - Efficient filling and emptying The magnet system Reflecting walls - Monitoring of depolarisation and marginally traped UCNs • Superconducting solenoids • Top coil (5 T) - Possibility to focus protons onto a detector LHe bath Charged particle detection • Bias coil (0. 5 T) - Avoid depolarisation - Decay particle extraction Absorber - A charged particle detector can be installed on top of the trap - Bias field guides the particles to the detector - e--simulations gave a 60% probability of reaching the top of the trap • Bottom coil (1. 7 T) - Magnetic UCN plug • Permanent magnet system provides radial confinement - 32 magnet slices form a Halbach type octupol Projections of a single electron track inside the trap UCN potential [ne. V] - Nd. Fe. B permanent magnets, BR = 1. 35 T - B(r) = BR(r/R)3 - 12 stacked modules: 1. 2 m total length Distribution of electrons at the top of the trap Spectrum cleaning • PET absorber - A movable absorber comes from the top - The absorber is shaped to let pass the decay products Preliminary tests § Teflon plug - A teflon plug comes from the bottom for symmetry breaking - permanent magnets have been tested on PF 2 using a material plug on the bottom - high storage times (>800 s) have achieved UCN guide Timeline Plug SUN 2 on H 172 B: new UCN source @ ILL, beam position for HOPE Year Quarter Installation on SUN 2 First systematic tests Construction and tests of electron detector Sketch and photo of the test setup at PF 2@ILL Result: Long storage time, limited by material plug “fill and empty” neutron lifetime experiment Lifetime measurement with electron detection I 2013 II IV I 2014 II IV I 2015 II IV I 2016 II IV