1. 1/30Peter Fierlinger FERMILAB 13.10.05 Diamond-like Carbon for Ultra-cold Neutrons Peter Fierlinger

2. 2/30Peter Fierlinger FERMILAB 13.10.05 W E p-Accelerator Synchrotron SLS neutron source SINQ Paul Scherrer Institut, Switzerland

3. 3/30Peter Fierlinger FERMILAB 13.10.05 Contents Ultra-cold neutrons (UCN) Motivation: Electric dipole moment of the neutron (nEDM) Life time of the free neutron The new UCN source at the PSI accelerator UCN related R&D: DLC DLC test experiment @ ILL

4. 4/30Peter Fierlinger FERMILAB 13.10.05 E 50 nm - Gravity ~ 100 neV / m - Magnetic field ~ 60 neV / T - Strong interaction: „Fermi potential“ Ultra-cold neutrons UCN can be stored in traps for ~ 1000 s V┴V┴

5. 5/30Peter Fierlinger FERMILAB 13.10.05 spin 1/2 nEDM Magnetic moment µ AXIAL VECTOR Electric dipole moment d POLAR VECTOR T transformation P transformation Purcell and Ramsey, PR78(1950)807, Lee and Yang, Landau A nonzero particle EDM violates P, T and, assuming CPT conservation, also CP Predicted: d ~ 10 -26 - 10 -28 e. cm (MSSM) d < 10 -31 e. cm (SM) Experimental Limit: ILL-Sussex-RAL (1999): ( -1.0 ± 3.6 ) ·10 -26 e·cm STATISTICAL LIMIT

6. 6/30Peter Fierlinger FERMILAB 13.10.05  n & CKM matrix PERKEO II without PERKEO II Universality: (885.7±1 s) STATISTICAL LIMIT

7. 7/30Peter Fierlinger FERMILAB 13.10.05 Pulsed operation: 8 sec on 800 sec off nEDM Cockroft-Walton: 800keV, 40mA Injector II: 72MeV, 2mA Ring cyclotron: 600MeV, 2mA, p-accelerator @ PSI UCN Source

8. 8/30Peter Fierlinger FERMILAB 13.10.05 Spallation target Shutter n-Guide Cold sD 2 moderator UCN storage volume, 2m 3 UCN tank system (~6m high) D 2 O moderator Coated walls To experiments p beam 4000 UCN/cm3

9. 9/30Peter Fierlinger FERMILAB 13.10.05 Storage materials low loss probability per wall collision µ long storage time µ(E) ~  high Fermi potential more UCN low spin flip probability per wall collision  polarized UCN (e.g. in nEDM) E Intensity typical UCN spectrum

10. 10/30Peter Fierlinger FERMILAB 13.10.05 Storage materials Al Pb Ni C Diamond BeO Be 300 K Be 70 K 58 Ni 65 Cu CuFe DLC

11. 11/30Peter Fierlinger FERMILAB 13.10.05 Diamond-like Carbon „sp 2 “ „sp 3 “ Production: e.g. pulsed laser deposition (PLD) Laser Target Substrate Layer DENSITY

12. 12/30Peter Fierlinger FERMILAB 13.10.05 Reflectometry φφ v┴v┴ Detector V ┴ ~ < 7 m/s ~ UCN Ohter methods used: XPS, NEXAFS, Raman, LaWAVE

13. 13/30Peter Fierlinger FERMILAB 13.10.05 Adiabatic condition Gravity: 1 m = 100 neV Magnetic field: 60 neV/T DLC test experiment No mechanical slits Depolarization probability  Loss probability µ measured simultaneously: Most common storage material: Beryllium μ(E, ,T) ~ 4. 10 -5 (at 70 K) β ~ 5. 10 -6 μ, β of DLC = ? Monte Carlo program (E) Experimental setup Samples Method I: µ(T,E) and  (T,E) Method II:  (T,E)

14. 14/30Peter Fierlinger FERMILAB 13.10.05 Monte Carlo program Geant4 : CERN particle tracking simulation toolkit Fermi potential, wall reflections Wall losses & spin flips Absorption, scattering Gravity & magnetic fields (space-, time-dependent) Spin tracking Adapted for UCN:

15. 15/30Peter Fierlinger FERMILAB 13.10.05 Setup: n+ 3 He  t+p+780keV

16. 16/30Peter Fierlinger FERMILAB 13.10.05 Substrates: Al tubes Quartz tubes Al foils PET foils Coatings: DLC, laser arc, Dresden DLC, PLD, VT Be, sputtered, PNPI & TUM Film thickness > 100 nm ( ~ 10 x penetration depth) Samples 70 mm

17. 17/30Peter Fierlinger FERMILAB 13.10.05 Method I Detector count rate: B Sample Magnet UCN from ILL-turbine Detector B 10 5 1 100 % 0 0 100 200 300 400 time [s]

18. 18/30Peter Fierlinger FERMILAB 13.10.05 Method I: cleaning 100 Lost neutrons magnet spin- flipped B field 90% 100 % time (s) Magnetic field 60 Losses from the storage volume Simulated ! wall loss decay top 100 Lost neutrons Fall through magnet spin- flipped B field 90% 100 % Storagetime (s) Magnetic field 60 Losses from the storage volume Simulated ! simulated measured Count rate

19. 19/30Peter Fierlinger FERMILAB 13.10.05 Method I: storage Potential energy Wall collisions (E) 1 / (s.cm_height) [neV ] 1000 800 600 400 200 0 1000 800 600 400 200 0

20. 20/30Peter Fierlinger FERMILAB 13.10.05 Method I: spectrum 120 s storage 320 s storage simulated measured Typical # of UCN stored ~ 600

21. 21/30Peter Fierlinger FERMILAB 13.10.05 Method I: analysis 1. 2. Detector count rate log 10 100 % 0 100 % 0 Magnetic field  up to 450 s

22. 22/30Peter Fierlinger FERMILAB 13.10.05 Method I: loss probability  tot * Measurement: with Compare to simulation )E()E( 11 nst    

23. 23/30Peter Fierlinger FERMILAB 13.10.05 Method I: results Wall loss coefficient  [1 / wall collision] x 10 -4 DLC is a good choice

24. 24/30Peter Fierlinger FERMILAB 13.10.05 Method I: analysis 1. 2. log 10 1. 2. Detector count rate 100 % 0 100 % 0 Magnetic field

25. 25/30Peter Fierlinger FERMILAB 13.10.05 Method I: depolarization ~ 1 in 200 s: Poisson Statistics

26. 26/30Peter Fierlinger FERMILAB 13.10.05 Method II Detector Count rate: time [s] Sample Magnet 0 100 200 300 400 100 % 0 B 10 5 1 UCN Detector

27. 27/30Peter Fierlinger FERMILAB 13.10.05 Method II: analysis 1 / (s.cm_height) Wall collision distribution par Accumulating neutrons ProductionLoss Energy [neV] Height [mm]

28. 28/30Peter Fierlinger FERMILAB 13.10.05 Method I & II: results Spin flip probability  [1 / wall collision] …Method I …Method II

29. 29/30Peter Fierlinger FERMILAB 13.10.05 Interpretation So-called „anomalous losses“:  (0 K) ~ 2. 10 -7 theor. but: ~ 10 -5 exp. Hydrogen:  =  C +  H N H ~ 0.3 N C Explains also spin flips

30. 30/30Peter Fierlinger FERMILAB 13.10.05 Conclusions - Monte Carlo package for UCN included in GEANT4 - Loss and depolarization measured simultaneously for the first time - Hydrogen is a good candidate for the explanation of the losses - DLC is top candidate for the UCN source at PSI

31. 31/30Peter Fierlinger FERMILAB 13.10.05 BACKUP

32. 32/30Peter Fierlinger FERMILAB 13.10.05 Motivation: nEDM ILL-Sussex-RAL (1999): ( -1.0 ± 3.6 ) ·10 -26 e·cm Theoretical predictions: SUSY : 10 -25 -10 -28 e·cm Imagine the neutron were the size of the Earth...  x  1  m

33. 33/30Peter Fierlinger FERMILAB 13.10.05 nEDM measurement B0B0 B0B0 B0B0 B1B1 B0B0 B1B1 Free Precession  /2 Pulse Polarized UCN in a trap  /2 Pulse 100 s + + ±E±E

34. 34/30Peter Fierlinger FERMILAB 13.10.05 UCN Transmission EDM-UCN beam at ILL: TOF Foil coated with -Be (black) -DLC (red) UCN Chopper Sample Detector 2 m

35. 35/30Peter Fierlinger FERMILAB 13.10.05 UCN Physics in Geant4 Fermi potential, wall reflections Wall losses & spin-flips Absorption, scattering gravitational & magnetic fields (space-, time-dependent) Numerical solution of the Bloch equation L/L/ from NIM A 457 (2001), 338-346 components of P after  /2 flip at |B| = 1g

36. 36/30Peter Fierlinger FERMILAB 13.10.05 Filling Simulated spectrum shift (1 spin component) Energy [neV] 90300 Rel. Intensity

37. 37/30Peter Fierlinger FERMILAB 13.10.05 RK4

38. 38/30Peter Fierlinger FERMILAB 13.10.05 Low field transitions B0B0 B earth

39. 39/30Peter Fierlinger FERMILAB 13.10.05 Spin tracking Coupled equations : „Bloch“-equation Treated classically

40. 40/30Peter Fierlinger FERMILAB 13.10.05 Penetration depth …. „Penetration depth“ Energy inside the barrier

41. 41/30Peter Fierlinger FERMILAB 13.10.05 The Magnet

42. 42/30Peter Fierlinger FERMILAB 13.10.05 Neutron life time CKM (quark mixing) matrix is unitary: V ud (neutr)= 0.9725±0.0013 PDG 2004 V ud (nucl)= 0.9740±0.0005 Coupling for Leptons = Coupling for Quarks (885.7±1 s) PDG 2004 STATISTICAL LIMIT

43. 43/30Peter Fierlinger FERMILAB 13.10.05 Superthermal converters Superfluid He – zero absorption cross section but needs very low temperatures ( ~ 0.5 K) (NIST, ILL, SNS) Solid D 2 – absorption lifetime 150 ms, 2 orders of magnitude higher production rate as compared with He, temperature of ~ 8K sufficient (Munich, Los Alamos, PSI) Solid CD 4 – compared with D 2 more low lying rotational states – investigations at the very beginning Solid O 2 – phonons and magnons excitation but temperatures below 2K needed

44. 44/30Peter Fierlinger FERMILAB 13.10.05 Deuterium D2 nuclear spin : S = 0,2 (ortho) and S = 1(para) Ortho-D2 : J = 0,2,4 …(rotational quantum number) Para-D2 : J = 1,3,5… Energy of the lowest rotational state: –Para-D2 J =1 E = 7.5 meV –Ortho-D2 J = 0 E = 0 meV Importance of high ortho-D2 concentration Additional up-scattering channel !

45. 45/30Peter Fierlinger FERMILAB 13.10.05 Maxwell spectrum v v UCN < 7m/s v th ~ 2 km/s v c ~ 1 km/s

46. 46/30Peter Fierlinger FERMILAB 13.10.05 4 He

47. 47/30Peter Fierlinger FERMILAB 13.10.05 Maxwell Distribution Neutron density between v and v+dv at thermal equilibrium (average velocity)

48. 48/30Peter Fierlinger FERMILAB 13.10.05 Raman spectra

49. 49/30Peter Fierlinger FERMILAB 13.10.05 A oder und B A mit den elektronen B mit neutrino

50. 50/30Peter Fierlinger FERMILAB 13.10.05 Maxwell Distribution Neutron density between v and v+dv at thermal equilibrium (average velocity)

51. 51/30Peter Fierlinger FERMILAB 13.10.05  - decay Correlation coefficients: A – parity violation, coupling constant ratio  G A /G V D – time-reversal violation R – parity and time-reversal violation

52. 52/30Peter Fierlinger FERMILAB 13.10.05 Superallowed β-decays Ft = ft(1 + δ R )(1 – δ C ) = K/[2G V 2 (1 + Δ R )] Universality: G V = G μ cosθ = G μ V ud V ud 2 = K/[2G μ 2 (1 + Δ R ) Ft] V ud = 0.9740  0.0005(10) (unitarity value: ~0.9756) Courtesy H.K. Walter New measurements?

53. 53/30Peter Fierlinger FERMILAB 13.10.05 UCN turbine Maxwellian distribution 2000 UCN/cm 3 extracted UCN 40 UCN/cm 3 1~10 UCN/cm 3 at experiment

54. 54/30Peter Fierlinger FERMILAB 13.10.05

55. 55/30Peter Fierlinger FERMILAB 13.10.05 Inelastic scattering

56. 56/30Peter Fierlinger FERMILAB 13.10.05 Fermipot  …range must be small for f(  )  f Many scatterers:

57. 57/30Peter Fierlinger FERMILAB 13.10.05 Reflectivity At boundary: Outside Inside