Ultracold neutrons and neutron decay

1. 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

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

3. Ultracold neutron production at in Grenoble Neutron turbine A. Steyerl (TUM/ILL 1985) • Properties of UCN • 900 total reflection angle • storage in bottles possible • long observation time • high precision in experiments ~50 cm-3 Ekin < 250 neV,  > 80 nm, v < 7 m/s, “T”  2 mK Vertical guide cold source reactor core

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

5. „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 downscattering EUCN + D • detailed balance: •  for D >> kBT >> EUCNÞsup << sdown UCN cold neutron Phonon EUCN • two converter materials: • Solid deuterium (SD): abs  0   0.15 s  in-pile needed • superfluid4He (He-II): abs = 0   800 s (<n)  beam possible • but in-pile even better

6. Some projected UCN sources (SD) Mainz TRIGA: currently 2×105 UCN/pulse  20/cm3 in V = 10 l, (after upgrade 2×106 UCN per pulse)  student‘s training and UCN developments present UCN density at ILL: 30/cm3 PSI: > 1000/cm3 in V = 2000 liters Mini-D2 UCN source at Munich: 104/cm3 in transport tube with V = 30 liters D2&Cryo UCN Mini-D2 source

7. UCN production in superfluid helium R. Golub, J.M. Pendlebury, PL 53A (1975) 133  free neutron dispersion cold neutron beam 12 K converter „phonon-roton“ dispersion of superfluid 4He q 7 nm-1 • reaction cross section sreaction = 0 • 0.7 K:storage  500 s (due to phonon absorption) • 0.5 K: storage  800 s • PI = 14 cm-3s-1 at intense cold beam (for d/d(0.89 nm) = 3109 cm-2s-1nm-1) • UCN 104 cm-3possible at a cold-neutron guide

8. Experiments at FRM II with prototpye He-II UCN source O.Zimmer et al., Phys. Rev. Lett. 99 (2007) 104801 First successfull extraction of UCN accumulated in superfluid helium

9. At the beam (NL1 at FRM II)

10. International competition in UCN production + insitu He-II UCN sources at ILL (Cryo-EDM), NIST (n-lifetime), and SNS (EDM)

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

12. Big bang nucleosynthesis and the neutron lifetime 10-6 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)3He, d(d,p)3H, 3He(n,)4He ... after 30 min: primordial abundances of light elements: 1H 75% 4He 25% 2H 30ppm 3He 13ppm 7Li 410-10

13. G. Mathews et al., Phys. Rev D 71 (2005) 021302

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

15. H. Abele, Prog. Part. Nucl. Phys. 60 (2008) 1

16. cold neutron beam: Experiments • UCN storage: 885.7(8) s 878.5(8) s A. Serebrov et al., PLB 605 (2005) 72

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

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

19. Proposed large volume magnetic storage experiment no UCN collisions with material walls: S. Paul et al. • UCN = 103– 104 cm-3(PSI /FRM II): • Nstored = 107– 108 • Statistical accuracy: • n~ 0.1 s in 2-4 days • Systematics: • Spin flips negligible (simulation) • use different values Bmax to check expected EUCN independence of proton detectors focusing coils neutron absorber 1.2 m superconducting coils B  2 T (at wall) volume ~ 700 l R. Picker et al., J. Res. NIST 110 (2005) 357 slit for filling UCN UCN detector

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

21. D. Bowman, Int. Workshop UCN Sources and Experiments Sept. 13-14 2007 TRIUMF

22. we prepareNeutron lifetime experimentwith magneto-peristaltic UCN extraction from superfluid4He into a magnetic trap O. Zimmer, NIM A 554 (2005) 363 K. Leung, O.Z., arXiv:0811.1940 Bx proton detector cold neutron beam beam switched off Halbach magnetic octupole (1.3 T) with V = 5 liters and 106 neutrons per filling  statistical accuracy: 0.1 s in 50 days

23. The end ... or rather the beginning Merci!