1/30Peter FierlingerStanford, Diamond-like Carbon for Ultra-cold Neutrons Peter Fierlinger

2/30Peter FierlingerStanford, W E p-Accelerator Synchrotron SLS neutron source SINQ Paul Scherrer Institut, Switzerland

3/30Peter FierlingerStanford, 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 ILL

4/30Peter FierlingerStanford, 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┴

5/30Peter FierlingerStanford, 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 ~ e. cm (MSSM) d < e. cm (SM) Experimental Limit: ILL-Sussex-RAL (1999): ( -1.0 ± 3.6 ) · e·cm STATISTICAL LIMIT

6/30Peter FierlingerStanford,  n & CKM matrix PERKEO II without PERKEO II Universality: (885.7±1 s) STATISTICAL LIMIT

7/30Peter FierlingerStanford, Pulsed operation: 8 sec on 800 sec off nEDM Cockroft-Walton: 800keV, 40mA Injector II: 72MeV, 2mA Ring cyclotron: 600MeV, 2mA, PSI UCN Source

8/30Peter FierlingerStanford, 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

9/30Peter FierlingerStanford, 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

10/30Peter FierlingerStanford, Storage materials Al Pb Ni C Diamond BeO Be 300 K Be 70 K 58 Ni 65 Cu CuFe DLC

11/30Peter FierlingerStanford, Diamond-like Carbon „sp 2 “ „sp 3 “ DENSITY 1...igniting Laser with beam guides 2...cathode cylinder 3...anode 4...filtering electrode 5...plasma beam 6...opening to the coating chamber

12/30Peter FierlingerStanford, Reflectometry φφ v┴v┴ Detector V ┴ ~ < 7 m/s ~ UCN Other methods used: XPS, NEXAFS, Raman, LaWAVE

13/30Peter FierlingerStanford, 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) ~ (at 70 K) β ~ μ, β of DLC = ? Monte Carlo program (E) Experimental setup Samples Method I: µ(T,E) and  (T,E) Method II:  (T,E)

14/30Peter FierlingerStanford, 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:

15/30Peter FierlingerStanford, Setup: n+ 3 He  t+p+780keV

16/30Peter FierlingerStanford, 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

17/30Peter FierlingerStanford, Method I Detector count rate: B Sample Magnet UCN from ILL-turbine Detector B % time [s]

18/30Peter FierlingerStanford, 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

19/30Peter FierlingerStanford, Method I: storage Potential energy Wall collisions (E) 1 / (s.cm_height) [neV ]

20/30Peter FierlingerStanford, Method I: spectrum 120 s storage 320 s storage simulated measured Typical # of UCN stored ~ 600

21/30Peter FierlingerStanford, Method I: analysis Detector count rate log % % 0 Magnetic field  up to 450 s

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

23/30Peter FierlingerStanford, Method I: results Wall loss coefficient  [1 / wall collision] x DLC is a good choice

24/30Peter FierlingerStanford, Method I: analysis log Detector count rate 100 % % 0 Magnetic field

25/30Peter FierlingerStanford, Method I: depolarization ~ 1 in 200 s: Poisson Statistics

26/30Peter FierlingerStanford, Method II Detector Count rate: time [s] Sample Magnet % 0 B UCN Detector

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

28/30Peter FierlingerStanford, Method I & II: results Spin flip probability  [1 / wall collision] …Method I …Method II

29/30Peter FierlingerStanford, Interpretation So-called „anomalous losses“:  (0 K) ~ theor. but: ~ exp. Hydrogen:  =  C +  H N H ~ 0.3 N C Explains also spin flips

30/30Peter FierlingerStanford, 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

31/30Peter FierlingerStanford, BACKUP

32/30Peter FierlingerStanford, DLC Deposition on large foils Fraunhofer Institut Dresden, Coating facility in Dortmund

33/30Peter FierlingerStanford, Vacuum Arc Deposition 1...igniting Laser with beam guides 2...cathode cylinder 3...anode 4...filtering electrode 5...plasma beam 6...opening to the coating chamber

34/30Peter FierlingerStanford, Motivation: nEDM ILL-Sussex-RAL (1999): ( -1.0 ± 3.6 ) · e·cm Theoretical predictions: SUSY : e·cm Imagine the neutron were the size of the Earth...  x  1  m

35/30Peter FierlingerStanford, nEDM measurement B0B0 B0B0 B0B0 B1B1 B0B0 B1B1 Free Precession  /2 Pulse Polarized UCN in a trap  /2 Pulse 100 s + + ±E±E

36/30Peter FierlingerStanford, UCN Transmission EDM-UCN beam at ILL: TOF Foil coated with -Be (black) -DLC (red) UCN Chopper Sample Detector 2 m

37/30Peter FierlingerStanford, 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), components of P after  /2 flip at |B| = 1g

38/30Peter FierlingerStanford, Filling Simulated spectrum shift (1 spin component) Energy [neV] Rel. Intensity

39/30Peter FierlingerStanford, RK4

40/30Peter FierlingerStanford, Low field transitions B0B0 B earth

41/30Peter FierlingerStanford, Spin tracking Coupled equations : „Bloch“-equation Treated classically

42/30Peter FierlingerStanford, Penetration depth …. „Penetration depth“ Energy inside the barrier

43/30Peter FierlingerStanford, The Magnet

44/30Peter FierlingerStanford, Neutron life time CKM (quark mixing) matrix is unitary: V ud (neutr)= ± PDG 2004 V ud (nucl)= ± Coupling for Leptons = Coupling for Quarks (885.7±1 s) PDG 2004 STATISTICAL LIMIT

45/30Peter FierlingerStanford, Maxwell spectrum v v UCN < 7m/s v th ~ 2 km/s v c ~ 1 km/s

46/30Peter FierlingerStanford, He

47/30Peter FierlingerStanford, Maxwell Distribution Neutron density between v and v+dv at thermal equilibrium (average velocity)

48/30Peter FierlingerStanford, A oder und B A mit den elektronen B mit neutrino

49/30Peter FierlingerStanford, The spectrometer P ERKEO II (Heidelberg – ILL) [J. Reich, H. Abele, D. Dubbers et al., NIMA 440 (2000) 535] // [H. Abele, S. Baeßler. D. Dubbers et al., to appear in PRL]: [H. Abele, S. Baeßler, D. Dubbers et al., PLB 407 (1997) 212]:

50/30Peter FierlingerStanford, Maxwell Distribution Neutron density between v and v+dv at thermal equilibrium (average velocity)

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

52/30Peter FierlingerStanford, 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 =  (10) (unitarity value: ~0.9756) Courtesy H.K. Walter New measurements?

53/30Peter FierlingerStanford, Differential decay probability: p e-e- Angular correlations:

54/30Peter FierlingerStanford, UCN turbine Maxwellian distribution 2000 UCN/cm 3 extracted UCN 40 UCN/cm 3 1~10 UCN/cm 3 at experiment

55/30Peter FierlingerStanford,

56/30Peter FierlingerStanford, Inelastic scattering

57/30Peter FierlingerStanford, Strategy: –Magneto-gravitational trapping of UCN, avoiding wall collisions –No losses due to depolarisation (?), but: –Control of losses –In-situ measurement of N(t) using proton detectors [F.J. Hartmann, I. Altarev, S. Paul et al., TU München, E18] Setup of the trap with permanent magnets Magnetic storage (TU München, PNPI) TAKEN FROM O: ZIMMER [O. Zimmer, JP G 26 (2000) 67-77] UCN density at FRM II: 10 4 cm -3 (at ILL: 50 cm -3 )

58/30Peter FierlingerStanford, 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

59/30Peter FierlingerStanford, 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 !

60/30Peter FierlingerStanford, sD 2 Moderator liquidsolid Slow freezing around triple point

61/30Peter FierlingerStanford, UCN Extraction  = 30ms v = 5m/s Attenuation length = 150mm mono sD 2 crystal real sD 2 crystal

62/30Peter FierlingerStanford, Raman spectra

63/30Peter FierlingerStanford, Fermipot  …range must be small for f(  )  f Many scatterers:

64/30Peter FierlingerStanford, Reflectivity At boundary: Outside Inside