HOPE – a magnetic UCN trap to measure the neutron lifetime Felix Rosenaua, Florian Martina, Sergey Ivanova, Kent Leungb, Martin Simsona, Oliver Zimmera aInstitut Laue Langevin, bNorth Carolina State University Motivation Determination of Uncertainty due to radiative corrections: Accuracy needed to bring down the experimental error bar to the same level: State of the art In beam experiments 886.3 ± 1.2stat ± 3.2syst s Nico et al. Phys. Rev. C 71 (2005) 055502 Magnetic bottle experiments Permanent magnet 20-pole bottle Ezhov et al. to be published He-II filled 4-pole trap: 833 +74 –63 s Material bottle experiments 888.4 ± 3.3 s t  12 s Nesvizhevsky et al. JETP 75 (1992) 405 885.4 ± 0.9stat ± 0.4syst 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 ± 0.8stat ± 1.9syst s Arzumanov et al. JETP Lett. 95 (2012) 224 R E A N L Y S I Marciano & Sirlin PRL 96 (2006) 032002 Dzhosyuk et al. J. Res. NIST 110 (2005) 339 General characteristics Magneto-gravitational trapping No wall interactions 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 Reflecting walls Monitoring of depolarisation and marginally traped UCNs Value Accuracy needed 0.34 s 310-4 Current values (PDG 2012) 880 ± 1.1 s (S=1.8) -1.2701 ± 0.0025 (S=1.9) The magnet system Superconducting solenoids Top coil (5 T) Possibility to focus protons onto a detector Bias coil (0.5 T) Avoid depolarisation Decay particle extraction Bottom coil (1.7 T) Magnetic UCN plug LHe bath Charged particle detection 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 Absorber Permanent magnet system provides radial confinement 32 magnet slices form a Halbach type octupol NdFeB permanent magnets, BR = 1.35 T B(r) = BR(r/R)3 12 stacked modules: 1.2 m total length Projections of a single electron track inside the trap Distribution of electrons at the top of the trap UCN potential [neV] Spectrum cleaning PET absorber A movable absorber comes from the top The absorber is shaped to let pass the decay products Teflon plug A teflon plug comes from the bottom for symmetry breaking Preliminary tests permanent magnets have been tested on PF2 using a material plug on the bottom high storage times (>800s) have achieved Timeline UCN guide Plug SUN2 on H172B: new UCN source @ ILL, beam position for HOPE Year 2013 2014 2015 2016 Quarter I II III IV Installation on SUN2 First systematic tests Construction and tests of electron detector “fill and empty” neutron lifetime experiment Lifetime measurement with electron detection Sketch and photo of the test setup at PF2@ILL Result: Long storage time, limited by material plug