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Upper Bound on Neutrino Magnetic Moment

D. Medvedev

1

Outline
Scientific motivation History Measurement under reactor GEMMA Perspectives

2

Scientific motivation
Minimally extended Standard Model (MSM):

~ 1019 B в (m / 1eV)
Bohr magneton B = eh / 2 me

3

Scientific motivation
Beyond the MSM:

1014 B в (m / 1eV) ~ 1010 - 1011 B

4

Scientific motivation
in case ~10-11-10-12 Neutrino nature parameter Astrophysical interest

B

:

5

First reactor experiments
1976 Savannah River. The first observation of the -e scattering F. Reines et al. [P.R.L.37,315(1976)]. ~ 16 kg plastic scintillator, flux of 2.2в1013 / cm 2 / s 1989 A revised analysis by P. Vogel and J. Engel [P.R.,D39,3378(1989)] gave a limit 1992 Krasnoyarsk. G.S. Vidykin et al. [Pis'ma v ZhETPh,
55,206(1992)]

( 2 4) в 10 2.4 в 10

10

B

~ 100 kg liquid scintillator C6F6, 254 days "on" / 78 days "off "
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1993 Rovno. A.V. Derbin, L.A. Popeko et al. [JETP Letters,
57,768(1993)]

B (90% CL)

75 kg silicon multi-detector, 600 Si(Li) cells, -flux of ~ 2в1013 / cm 2 / s , 30 days "on"/17 days "off "

1 .9 в 10

10

B (95% CL)

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upper bounds
upper limit Solar SK+KamLand White dwarfs Red giants Supernova 1987A "Cosmological" limit BOREXINO TEXONO MUNU <4*10 <10
-11 -12 -12 -11 -10 -10

Comments

<1.1*10 <3*10 <3*10

model dependent
should not be violated by more than two neutrino species

<1.5*10 <5.4*10 <7.2*10 <9*10

-11 -11

-11

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measurement under reactor
The effects can be searched in the recoil electron energy spectrum from the

-e

scattering

measured when the reactor is ON and OFF. The total cross-section d/dT is a sum of two: depending on the recoil energy T in different ways
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( d/dT )weak + ( d/dT )EM

d

/ dT [10

45

cm / MeV / fission / electron ]

2

1000

d

EM

/ dT ( )
-11

2 1 10
100
-11

5 6 10 34

dW / dT

10

1

10

100

T [keV]

GEMMA
Search for the Neutrino Magnetic Moment

A.G. Beda a, V.B. Brudanin b, V.G. Egorov b, D.V. Medvedev b, V.S. Pogosov b, c, E.A. Shevchik b, M.V. Shirchenko b, A.S. Starostin a, I.V.Zhitnikov b a - ITEP (State Science Center, Institute for Theoretical and Experimental Physics, Moscow, Russia); b - JINR (Joint Institute for Nuclear Research, Dubna, Russia); c - YerPhI (Yerevan Physics Institute, Yerevan, Armenia).
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Reactor unit #2 of the "Kalinin" Nuclear Power Plant (400 km North from Moscow)

Powe ON: OFF:

r: 3 GW 315 days/y 50 days/y

Total mass above
(reactor, building, shielding, etc.):

~70 m of W.E. Technological room just under reactor 14 m only! 2.7в1013 /cm2/s
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Experiment GEMMA
(Germanium Experiment
for measurement of Magnetic Moment of Antineutrino) [Phys. of At. Nucl.,67(2004)1948] Spectrometer includes a HPGe detector of 1.5 kg installed within NaI active shielding. HPGe + NaI are surrounded with multi-layer passive shielding : electrolytic copper, borated polyethylene and lead.

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GEMMA background conditions
were measured with Ge detector. The main sources are: 137Cs , 60Co, 134Cs. Neutron background was measured with 3He counters, i.e., thermal neutrons were counted. Their flux at the facility site turned out to be 30 times lower than in the outside laboratory room. Charged component of the cosmic radiation (muons) was measured to be 5 times lower than outside.
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-rays

Background suppresion

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1

ADC-1

E1

High freq. noise: E1 > E2
Ge detector

Amp.

Real signal: ADC Low freq. noise:

E1 = E2 Energy E1 < E2
E2

2

ADC-2

15 E.Garcia e.a. NPB28A(1992)286

25

ADC-3 [keV]

20

15

10

5

0 0 5 10 15 20 25

ADC-1 [keV]
16

30

1000000

Time selection of consecutive events: microphonics mains freq. (50 Hz)

true events

100000

10000 0 100 200 300

dT [ms]
400

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Final spectra

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Final distribution
Probability distribution [a.u.]

C.L.

100 90 80

X 0= -5.79

70 60 50 40
X = 8.37 (90% CL)

= 6.9
Re-normalized area

30 20

Non-physical region ( X< 0 )
-30.0 -20.0 -10.0 0 .0 10.0 20.0

X

10 0 30.0

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Experimental sensitivity

1 N

B mt

1 4

N B m t

: : : :

number of signal events expected background level in the ROI target (=detector) mass measurement time

N ~ ( ~ Power / r 2 ) ~ ( Tmax- Tmin / Tmax*Tmin )1/2
t B m Tth ~ ~ ~ ~ ~ 2.7 в1013 / cm2 / s 4 years 2.5 keV-1 kg-1 day-1 1.5 kg 2.8 keV

GEMMA I 2005 2009

2.9 в 10

11

B

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Data Set
I phase 5184 h ON, 1853 h OFF
-11

< 5.8 *10

B

II phase 6798 h ON, 1021 h OFF I+II 11982 h ON, 2874 h OFF
< 3.2 *10
-11

B

III phase I+II+III

6152 h 18134 h

ON, ON,

1613 4487
-11

h h

OFF OFF

< 2.9 *10

B

Beda A.G. et al. // Advances in High Energy Physics. 2012. V. 2012, Article ID 350150. Beda A.G. et al. // Physics of Particles and Nuclei Letters, 2013, V. 10, 2, pp. 139143.

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Perspectives
GEMMA II 2013
t B m Tth ~ ~ ~ ~ ~ 5в1013 / cm2 / s 2 years 0.5 keV -1 kg -1 day-1 6 kg (two detectors) 1.5 keV

1.0 в 10

-11

B

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GEMMA-II

Lifting mechanism

Future detectors
Ge detectors with very low threshold RFBR grant (~ 300 eV)

h = 25 mm d = 65 mm m = 460 g

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3,0 2,8 2,6
-11

Changing Background Constant Background

B

sensitivity to , 10

2,4 2,2 2,0 1,8 1,6 1,4 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0

E(threshold), keV
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Sensitivity of future experiments
B = 0.2 1/keV/kg/day
Mass, kg 4.5 10 20 4.5 10 20 Threshold, keV 0.4 0.4 0.4 0.3 0.3 0.3 Sensitivity, 10-12B 5.8 4.7 4.0 5.6 4.6 3.9

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