An experimental limit on neutron mirror-neutron oscillation Ulrich Schmidt
description
Transcript of An experimental limit on neutron mirror-neutron oscillation Ulrich Schmidt
An experimental limit on neutron mirror-neutron oscillation
Ulrich SchmidtPhysikalisches Institut, Universität Heidelberg, Germany
What are mirror particles ???
P
World is not P symmetric
P
R R
World is PR symmetric
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
RESEDA am FRM II
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)
20 40 60 80 100 120
20
40
60
80
100
120
0,070
0,095
0,13
0,18
0,24
0,32
0,44
0,59
0,81
1,1
1,5
2,0
2,7
3,5
Neutron-Pictures with the 2D-200 CASCADE Detector System
Tesa-Tape
old PC-MouseWater
Flow-
Controller
measured at instrument EKN at FZ
Jülich
Pixel (1.56mm)
Pix
el
(1.5
6m
m)