Ultracold neutrons and neutron decay Oliver Zimmer ILL Grenoble / TU München 19th Int. IUPAP Conf. On Few-Body Problems in Physics Bonn, 14 July 2008

Institut Laue-Langevin Forschungsreaktor FRM II W here do our neutrons come from? Reactor sources: Spallation sources: 58 MW 20 MW SNS Oak Ridge (ramping up) PSI Villigen

reactor core cold source Vertical guide Neutron turbine A. Steyerl (TUM/ILL 1985) Ultracold neutron production at in Grenoble Properties of UCN 90 0 total reflection angle  storage in bottles possible  long observation time  high precision in experiments ~50 cm -3 E kin 80 nm, v < 7 m/s, “T”  2 mK

The turbine for neutron decceleration… …a neutron phase space transformer VCN UCN A. Steyerl et al., Phys. Lett. A 116 (1986) 347 (50 cm -3 )

„Superthermal“ production of UCN no thermal equilibrium of neutron gas with scattering system Conversion of cold neutrons to UCN by a converter (dominantly by emission of single phonon) up-scattering suppressed by Boltzmann factor  “accumulation” of neutrons as UCN E UCN E UCN +  UCN cold neutron Phonon downscattering detailed balance:  for  >> k B T >> E UCN   up <<  down two converter materials: Solid deuterium (SD):  abs  0    0.15 s  in-pile needed superfluid 4 He (He-II):  abs = 0    800 s (<  n )  beam possible but in-pile even better

Some projected UCN sources (SD) Mainz TRIGA: currently 2×10 5 UCN/pulse  20/cm 3 in V = 10 l, (after upgrade 2×10 6 UCN per pulse)  student‘s training and UCN developments UCN D 2 &Cryo Mini-D 2 source Mini-D 2 UCN source at Munich:  10 4 /cm 3 in transport tube with V = 30 liters present UCN density at ILL : 30/cm 3 PSI: > 1000/cm 3 in V = 2000 liters

reaction cross section  reaction = K:  storage  500 s (due to phonon absorption) 0.5 K:  storage  800 s P I = 14 cm -3 s -1 at intense cold beam (for d  /d (0.89 nm) = 3  10 9 cm -2 s -1 nm -1 )  UCN  10 4 cm -3 possible at a 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 U CN production in superfluid helium

First successfull extraction of UCN accumulated in superfluid helium O.Zimmer et al., Phys. Rev. Lett. 99 (2007) Experiments at FRM II with prototpye He-II UCN source

At the beam (NL1 at FRM II)

Source locationSource typeUCN density [cm -3 ] commentwhen? ILL Grenoble, PF2LD 2 + turbine50still THE source> 1985 Los Alamos, 2.4 kW av proton SD in sourcenow Mainz TRIGA upgraded SD 2 20  200 in V = 10 lnow 2009 ILL Grenoble, H172 upgraded + magnetic trap He-II (0.5 K)> polarised in V = 6.4 l up to 40 l 2009 > 2011 PSI, 12 kW av protonSD 2 > 1000in V = 2000 l2010 North Carolina, 1 MW reactor SD in source2011 Munich, 20 MW reactorSD 2  in source2011 PNPI, 16 MW reactorHe-II (1.2 K) in 35 l exp. bottle in 350 l exp. bottle 2012 TRIUMF, 5 kW av protonHe-II (0.8 K)18000at exp. portproposal + insitu He-II UCN sources at ILL (Cryo-EDM), NIST (n-lifetime), and SNS (EDM) I nternational competition in UCN production

A world of matter nEDM neutron lifetime ??? nuclear few-body interactions

Big bang nucleosynthesis and the neutron lifetime s (100 MeV): quarks & gluons form nucleons n + e +  p +, n +  p + e, n  p + e + 1 s (1 MeV): neutrinos decouple  neutrons freely decay n  p + e +, p + n  d +  3 min (0.1 MeV): deuterons become stable p(n,  )d, d(d,n) 3 He, d(d,p) 3 H, 3 He(n,  ) 4 He... after 30 min: primordial abundances of light elements: 1 H 75% 4 He 25% 2 H 30ppm 3 He 13ppm 7 Li 4 

G. Mathews et al., Phys. Rev D 71 (2005)

N eutron  decay in Standard model: „V-A“ structure with known Fermi- and Gamow-Teller matrix elements precise determination of g A and g V from two independent n-decay observables  semileptonic weak cross sections  e.g. test of CKM unitarity: n + e +  p + e n + e  p + e p + p  d + e + + e... + various other tests of the standard model – listen next talk in this session! from  asymmetry (PERKEO) H. Abele, Prog. Part. Nucl. Phys. 60 (2008) 1

A. Serebrov et al., PLB 605 (2005) (8) s 878.5(8) s E xperiments cold neutron beam: UCN storage:

A. Serebrov et al., Phys. Lett. B 605 (2005) 72 UCN N eutron lifetime experiment with low-T Fomblin oil coated walls 878.5(8) s Frequency of wall collisions (/s)

UCN storage in a trap from permanent magnets (PNPI – ILL – TUM) V. Ezhov et al., J. Res. NIST 110 (2005) 345 Follow-up trap design (PNPI):

slit for filling 1.2 m superconducting coils B  2 T (at wall) focusing coils proton detectors volume ~ 700 l UCNUCN detector neutron absorber  UCN = 10 3 – 10 4 cm -3 (PSI /FRM II): N stored = 10 7 – 10 8 –Statistical accuracy:  n ~ 0.1 s in 2-4 days –Systematics: Spin flips negligible (simulation) use different values B max to check expected E UCN independence of  P roposed large volume magnetic storage experiment magnetic storage experiment R. Picker et al., J. Res. NIST 110 (2005) 357 no UCN collisions with material walls: S. Paul et al.

P. Huffman et al., Int. workshop Particle Physics with slow Neutrons, May 2008 ILL A superconducting Ioffe trap UCN production in He-II and in-situ detection (NIST)

D. Bowman, Int. Workshop UCN Sources and Experiments Sept TRIUMF

BxBx cold neutron beam beam switched off we prepare N eutron l ifetime experiment with magneto- peristaltic UCN extraction from superfluid 4 He into a magnetic trap Halbach magnetic octupole (1.3 T) with V = 5 liters and 10 6 neutrons per filling  statistical accuracy: 0.1 s in 50 days O. Zimmer, NIM A 554 (2005) 363 K. Leung, O.Z., arXiv: proton detector

Merci! The end... or rather the beginning