1/30peter fierlinger fermilab 13.10.05 diamond-like carbon for ultra-cold neutrons peter fierlinger
TRANSCRIPT
1/30Peter Fierlinger FERMILAB 13.10.05
Diamond-like Carbon for Ultra-cold Neutrons
Peter Fierlinger
2/30Peter Fierlinger FERMILAB 13.10.05
W E
p-Accelerator
Synchrotron SLS
neutron source SINQ
Paul Scherrer Institut, Switzerland
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
4/30Peter Fierlinger FERMILAB 13.10.05
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
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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
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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
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Pulsed operation:8 sec on
800 sec off
nEDM
Cockroft-Walton: 800keV, 40mAInjector II: 72MeV, 2mARing cyclotron: 600MeV, 2mA,
p-accelerator @ PSI
UCN Source
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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
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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
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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
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Diamond-like Carbon„sp2“
„sp3“
Production: e.g. pulsed laser deposition (PLD)
Laser
Target
SubstrateLayer
DENSITY
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Reflectometry
φφv┴
Detector
V┴ ~ < 7 m/s ~ UCN
cF bNU
Ohter methods used: XPS, NEXAFS, Raman, LaWAVE
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)
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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:
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Setup:
n+3Het+p+780keV
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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
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Method I
Detector count rate:
B
Sample
Magnet
UCN from ILL-turbine
Detector
B
105
1100 %
00 100 200 300 400 time [s]
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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
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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
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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
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Method I: analysis
1.
2.
Detector count rate
log10
100 %
0
100 %
0
Magnetic field
up to 450 s
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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
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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
24/30Peter Fierlinger FERMILAB 13.10.05
Method I: analysis
1.
2.
log10
1.
2.
Detector count rate
100 %
0
100 %
0
Magnetic field
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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
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Method II
Detector Count rate:
time [s]
Sample
Magnet
0 100 200 300 400
100 %
0
B
105
1
UCN
Detector
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Method II: analysis
1 /
(s.c
m_h
eigh
t)
Wall collision distribution par
Accumulating neutrons
Production Loss
Energy [neV]
Hei
ght [
mm
]
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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
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
NH ~ 0.3 NC
Explains also spin flips
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
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BACKUP
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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
33/30Peter Fierlinger FERMILAB 13.10.05
nEDM measurement
B0
B0
B0 B1
B0 B1
Free Precession
/2 Pulse
Polarized UCNin a trap
/2 Pulse
BdE
L
100 s
+
+
±E
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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
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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
36/30Peter Fierlinger FERMILAB 13.10.05
Filling
B
UCN v
Simulated spectrum shift (1 spin component)
Energy [neV]90300
Rel
. In
ten
sity
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RK4
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Low field transitions
B0Bearth
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Spin trackingCoupled equations:
„Bloch“-equation
Treated classically
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Penetration depth
VEm2
k22
k
1…. „Penetration depth“
Energy inside the barrier
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The Magnet
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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
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 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
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 !
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Maxwell spectrum
vvUCN < 7m/s
vth ~ 2 km/s
vc ~ 1 km/s
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4He
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Maxwell Distribution
Neutron density between v and v+dv at thermal equilibrium
(average velocity)
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Raman spectra
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A oder und B A mit den elektronen
B mit neutrino
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Maxwell Distribution
Neutron density between v and v+dv at thermal equilibrium
(average velocity)
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- 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
52/30Peter Fierlinger FERMILAB 13.10.05
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?
53/30Peter Fierlinger FERMILAB 13.10.05
UCN turbine
Maxwellian distribution2000 UCN/cm3
extracted UCN40 UCN/cm3
1~10UCN/cm3
at experiment
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Inelastic scattering
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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
57/30Peter Fierlinger FERMILAB 13.10.05
Reflectivity
ikxikx Ree x'ikTe
'ikR1
)R1(ikcontinuous
dx
d1
At boundary:
Outside Inside