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)