An experimental limit on neutron mirror-neutron oscillation
Ulrich SchmidtPhysikalisches Institut, Universität Heidelberg, Germany
Properties of mirror particles
For each particle exists a mirror particle which has exactly the same properties in the mirror world, as the particle in the world beside handedness.
Interaction between particles and mirror particles: gravity
Possible interaction between particles and mirror particles:
Oscillations/mixing between neutral particles and mirror particles
g g¢« n n¢« n n¢«
phenomenology of oscillationn n¢«
, ,n m V m
L M Mn m m V
22 2 2
2 2( ) (0) sin ( / )
mn t n m E t
m E
E V V with
free flying neutron: only magnetic field counts for E
osc m
2L
E B
2 22
1( ) (0) sin ( 1 ( ) )
1 ( ) L oscL osc osc
tn t n
2 22
1( ) (0) sin ( 1 ( ) )
1 ( ) L oscL osc osc
tn t n
2
( ) (0) , 1,L oscosc
tn t n t t
“field free” region
2
1( ) (0) , 1
( ) LL osc
n t n t
magnetic field strongly suppress oscillationn n¢«
n beam
beam dump
field free region
detector
field free region
2
( ) (0)osc
tn t n
2
( ) (0)dosc
tn t n
4
( ) (0)dosc
tn t n
Reappearance experiment
( )dn t
Problem: loss of neutrons due to -decay, scattering ...
R ± R is compatible with 1 => osc
t
R
2count rate without magnetic field
1count rate with magnetic field osc
tR
But !!
Only is suppressed by a moderate magnetic field (0.1 mT)n n¢«
Disappearance experiment
principle of our measurement:measuring loss of neutrons due to n n¢«
n beam
field free region2
( ) (0)osc
tn t n
detector
CASCADE: Multiple Boron Layers on GEMs
• GEMs can be operated to be transparent for charges!
they can be cascaded!
• Each one can carry two Boron layers.
• Last one operated as amplifier.
Accumulate single layer detection efficiency up to 50% for thermal neutrons (1.8Å) and up to 75% for cold neutrons (5Å).
10B + n 7Li + + 2.79 MeV ( 6%) 3838 b
7Li*+ + 2.31 MeV (94%)
Problem:n-counting at very high rates
Conventionel (3He-counters): < 10kHz/cm2
CASCADE: up to 10 MHz /cm2
The Gas Electron Multiplier (GEM)
Amplifier Mode• In hole high fields allow
Gas amplification 1 - 400
Transparent Mode• At gain 1, electric fields
transport charges through the holes
ElectronsIons
pict
ures
fro
m S
auli
The GEM inherently introduces high rates capability of 10 MHz/cm2 !
taken from Sauli et al.: http://www.cern.ch/GDD
0 1 2 3 4 5 6neutron flight path [m]
0
0.25
0.5
0.75
1
1.25
1.5
1.75re
sidu
al m
agne
tic f
ield
[µ
T]
´´´´´))(´)((
2sin
41)()( intint
0
´´
0
22
2´ dxdxxBxB
vl
ttP
l x
oscnn
length flight path
927.0
velocity of neutrons
B-field integralalong neutron flight path
gyromagnetic ratio
U. KinkelZ.Phys.C 54 ,573-575(1992)
2count rate without magnetic field
1count rate with magnetic field osc
tR
0
0 1
(90% confidence level)1.000020(27) 2.7s Bosc
B
N
N
measuring cycle:- 0.5s without magnetic field- switch magnetic field on, wait 0.1 s- 0.5s with magnetic field- switch magnetic field off, wait 0.1 s
length flight path: 6m , = 11Å => v = 360m/s => t = 17ms
2 day measurement, about 105 individual ratios R
scattering (standard deviation) of the individual ratios: 0.0082
1 2 5 10 20 50 100correlation time [s]
2
4
6
8
10
12
rela
tive
erro
r si
ngle
rat
io01
3error of the individual ratios calculated from number of count: 0.0039
=> sensitivity is limited by intensity fluctuations of the beam
figure of merit 4 Nt
VCN beam
50% monitor counter
detector
field free region
2
~
(without magnetic field)
1 (with magnetic field)
d
m
d osc
m
n
n tR
n
n
noise of R~ will be much less than noise of R
dn
mn
Thank youfor your attention
Experiment FRM II
Barbara Böhm 1
Wolfgang Häusler 2
Dominik Streibel 2
1 Physikalisches Institut Heidelberg2 FRM II (Forschungsreaktor München II)
CASCADE detector
Martin Klein 1
Gerd Mozel 1
Jörg Betz 1
Stefan Backfisch 1
n
The Assembled 2D-Detector
GEM-foils coated with 10B and 2D readout
structure
EMI shielding (500 µm Al)
Power supply and
thermal management
FPGA based
readout board ASIC
frontend-electronic
Detector entrance window (100 µm
Al)