Diamond-like Carbon for Ultra-cold Neutrons

1/30Peter Fierlinger FERMILAB 13.10.05

Diamond-like Carbon for Ultra-cold Neutrons

Peter Fierlinger


W E

p-Accelerator

Synchrotron SLS

neutron source SINQ

Paul Scherrer Institut, Switzerland


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


E < 300 neV, T < 3 mK, v < 7 ms-1, > 50 nm

- Gravity ~ 100 neV / m

- Magnetic field ~ 60 neV / T

- Strong interaction:

„Fermi potential“

Ultra-cold neutrons

cF bNU

UCN can be stored in traps for ~ 1000 s

V┴

m/U2vv Fcrit


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


n & CKM matrix

V

A

G

G

PERKEO II

without PERKEO II

Universality:

udV VGG

C)1(G1 2

Vn

(885.7±1 s)

STATISTICAL LIMIT


Pulsed operation:8 sec on

800 sec off

nEDM

Cockroft-Walton: 800keV, 40mAInjector II: 72MeV, 2mARing cyclotron: 600MeV, 2mA,

p-accelerator @ PSI

UCN Source


Spallation target

Shutter

n-Guide

Cold sD2 moderator

UCN storage volume, 2m3

UCN tank system (~6m high)

D2O moderator

Coated walls To experiments

p beam

4000 UCN/cm3


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

Inte

nsity

typical UCN spectrum


Storage materials

50 100 150 200 250 300 35010-8

10-7

10-6

10-5

10-4

10-3

L

oss

Co

eff

icie

nt

Fermi potential [neV]

Al

Pb

Ni

C

Diamond

BeOBe 300 K

Be 70 K

58Ni

65Cu

Cu Fe

DLC


Diamond-like Carbon„sp2“

„sp3“

Production: e.g. pulsed laser deposition (PLD)

Laser

Target

SubstrateLayer

DENSITY


Reflectometry

φφv┴

Detector

V┴ ~ < 7 m/s ~ UCN

cF bNU

Ohter methods used: XPS, NEXAFS, Raman, LaWAVE


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)


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:


Setup:

n+3Het+p+780keV


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 m

m


Method I

Detector count rate:

B

Sample

Magnet

UCN from ILL-turbine

Detector

B

105

1100 %

00 100 200 300 400 time [s]


Method I: cleaning

100

Lo

st n

eutr

on

s

magnet

spin- flipped

B f

ield 90%

100 %time (s)

Magnetic field

60

Losses from the storage volume

Simulated !

wall loss

decay

top

100

Lo

st n

eutr

on

s

Fall through magnet

spin- flipped

B f

ield

90%100 %

Storagetime (s)

Magnetic field

60

Losses from the storage volume

Simulated !

0 20 40 60 80 100

1x100

1x101

1x102

1x103

1x104

1x105

C

ou

nts

Time [s]

simulated

measured

Co

unt

ra

te


Method I: storage

-35 0 350

200

400

600

800

1000

r [mm]

He

igh

t [m

m]

10.00

30.00

50.00

70.00

90.00

110.0

Potential energy Wall collisions (E)

1 / (

s.cm

_hei

ght)

[neV]

1000

800

600

400

200

0

1000

800

600

400

200

0


Method I: spectrum

20 30 40 50 60 70 80 9020

40

60

80

100

120

140

160

180

C

ou

nts

Energy [neV]

120 s storage

320 s storage

simulated

measured

Typical # of UCN stored ~ 600


Method I: analysis

1.

2.

Detector count rate

log10

100 %

0

100 %

0

Magnetic field

up to 450 s


Method I: loss probability

i

)tt(

spi2

*2

tot

i2

eNNN

111

)N/Nln(

tt1

n21

12

tot

01

tot*

Measurement:

with

Compare to simulation )E()E(11

nst


2

4

6

8

DLC -VT300 K

Be -TUM300 KBe -

PNPIQuartz300 K

Be - PNPI380 K

Be - PNPI300 K

DLCPET 2300 K

DLCPET 270 K

DLCPET 1may

DLCAl-Foil300 K

DLCPET 1juneDLC

Al-Foil70 K

Method I: results

Wall loss coefficient [1 / wall collision]

x 10-4

DLC is a good choice


Method I: analysis

1.

2.

log10

1.

2.

Detector count rate

100 %

0

100 %

0

Magnetic field


Method I: depolarization

<Nbg> ~ 1 in 200 s:

Poisson Statistics

1.68 x 10-51.7 x 10-5

Level 4Level 3

DLC PET-foil 70 K


Method II

Detector Count rate:

time [s]

Sample

Magnet

0 100 200 300 400

100 %

0

B

105

1

UCN

Detector


Method II: analysis

1 /

(s.c

m_h

eigh

t)

Wall collision distribution par

Accumulating neutrons

Production Loss

Energy [neV]

Hei

ght [

mm

]


0.0

0.5

1.0

1.5

2.0

2.5

x 10-5

DLCAl VT

BeTUM

BePNPI Quartz

BePNPI 380 K

BePNPI 300 K

DLC PET 2300 K

DLC PET 270 K

DLC PET 1May

DLC PET 1JuneDLC

Al foil300 K

DLC Al foil70 K

Method I & II: results

Spin flip probability [1 / wall collision]

…Method I

…Method II


Interpretation

So-called „anomalous losses“:

(0 K) ~ 2.10-7 theor.

but: ~ 10-5 exp.

Hydrogen: = C + H

NH ~ 0.3 NC

Explains also spin flips


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


BACKUP


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 1m


nEDM measurement

B0

B0

B0 B1

B0 B1

Free Precession

/2 Pulse

Polarized UCNin a trap

/2 Pulse

BdE

L

100 s

+

+

±E


UCN Transmission

0 2 4 6 8 10 12 14 16 180.0

0.2

0.4

0.6

0.8

1.0

Tra

nsm

issi

on

Velocity [ms-1]

EDM-UCN beam at ILL:• TOF• Foil coated with- Be (black)- DLC (red)

UCN

Chopper Sample

Detector

2 m


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/

from NIM A 457 (2001), 338-346

components of P after /2 flip at |B| = 1g


Filling

B

UCN v

Simulated spectrum shift (1 spin component)

Energy [neV]90300

Rel

. In

ten

sity


RK4


Low field transitions

B0Bearth


Spin trackingCoupled equations:

„Bloch“-equation

Treated classically


Penetration depth

VEm2

k22

k

1…. „Penetration depth“

Energy inside the barrier


The Magnet


Neutron life time

CKM (quark mixing) matrix is unitary:

1|V||V||V| 2ub

2us

2ud

Vud (neutr) = 0.9725±0.0013 PDG 2004 Vud (nucl) = 0.9740±0.0005

C)1(G1 2

Vn

Coupling for Leptons = Coupling for Quarks

udV VGG

V

A

G

G

(885.7±1 s) PDG 2004

STATISTICAL LIMIT


Superthermal converters• Superfluid He – zero absorption cross section but needs very low

temperatures ( ~ 0.5 K) (NIST, ILL, SNS)

• Solid D2 – absorption lifetime 150 ms, 2 orders of magnitude higher production rate as compared with He, temperature of ~ 8K sufficient (Munich, Los Alamos, PSI)

• Solid CD4 – compared with D2 more low lying rotational states – investigations at the very beginning

• Solid O2 – phonons and magnons excitation but temperatures below 2K needed


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 !


Maxwell spectrum

vvUCN < 7m/s

vth ~ 2 km/s

vc ~ 1 km/s


4He


Maxwell Distribution

Neutron density between v and v+dv at thermal equilibrium

(average velocity)


Raman spectra


A oder und B A mit den elektronen

B mit neutrino


Maxwell Distribution

Neutron density between v and v+dv at thermal equilibrium

(average velocity)


- decay

1 ...e eee

e e e e

e en

e

a A B Dm

dWE E E E

p p ppE E

ppE

RPp

b PE

Correlation coefficients:A – parity violation, coupling constant ratio GA/GV

D – time-reversal violationR – parity and time-reversal violation


Superallowed β-decays

Ft = ft(1 + δR)(1 – δC) = K/[2GV

2(1 + ΔR)]

Universality: GV = Gμ•cosθ = Gμ• Vud

Vud2 = K/[2Gμ

2 (1 + ΔR) Ft]

Vud = 0.9740 0.0005(10) (unitarity value: ~0.9756)

Courtesy H.K. Walter

New measurements?


UCN turbine

Maxwellian distribution2000 UCN/cm3

extracted UCN40 UCN/cm3

1~10UCN/cm3

at experiment



Inelastic scattering


Fermipot

i

ir'ik

i

)rr('ik

ir'ik e

rr

eae

i

)rr('ik

iiir'ik

rr

ea)r(e

i

…range

must be small for f()f

r

e)(fe

r'ikr'ik 0)VE(

m22

2

302if2

U3

2k|U|k

2)(f

)rr(4|rr|

e)k( i

i

)rr(ik

22i

Many scatterers:

)r()r( iii

dr)r(narr

e)r(e

i

)rr('ikr'ik

i


Reflectivity

ikxikx Ree x'ikTe

'ikR1

)R1(ikcontinuous

dx

d1

At boundary:

Outside Inside

Documents

Diamond-like Carbon for Ultra-cold Neutrons