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EXPERIMENT GEMMA: SEARCH FOR THE NEUTRINO MAGNETIC MOMENT
A.G. Beda a, V.B. Brudanin b, V.G. Egorov b, D.V. Medvedev b, M.V. Shirchenko b, A.S. Starostin a,
a

- ITEP (State Science Center, Institute for Theoretical and Experimental Physics, Moscow, Russia) b - JINR (Joint Institute for Nuclear Research, Dubna, Russia)


Science motivation of the searching for



· minimally-extended Standard Model:

~ 10

­19

B (m / 1eV)

= e h / 2 m e B

Bohr magneton


Science motivation of the searching for



· number of extensions beyond the MSM:

10

­14

B (m / 1eV)

= e h / 2 m e B

Bohr magneton

~ 10

­10

- 10

­11



B

· Observation of (~10­12) => M/D preference


Limits for the NMM from astrophysics
B · · Nonstandard neutrino losses would delay the

1011 White dwarfs, luminosity function:

·

ignition of helium in the degenerate cores of 3 *1012 B low-mass red giants: SN1987A - neutrinos which are trapped in a SN core flip their helicity in electromagnetic interactions, taking them into nearly sterile righthanded states which escape directly from the inner SN core: 3 *1012 B


The history of the 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 2.2в10 13 / cm 2 / s 1989 ­ A revised analysis by P. Vogel and J. Engel [P.R.,D39,3378(1989)]:

( 2 ­ 4) 10 2.4 10

­10

B

1992 ­ Krasnoyarsk.. G.S. Vidykin et al. [Pis'ma v ZhETPh, 55,206(1992)] ~ 100 kg liquid scintillator C6F6, 254 days "on" / 78 days "off "
­10

B (90% CL)

1993 ­ Rovno. A.V. Derbin, L.A. Popeko et al. [JETP Letters, 57,768(1993)] 75 kg silicon multi-detector, 600 Si(Li) cells, -flux of ~ 2в10 13 / cm 2 / s , 30 days "on"/17 days "off "

1 .9 10

­10

B (95% CL)


The history of the reactor experiments
2001-2005 ­ Bugey. The MUNU experiment. Z. Darakchieva et al. [P.L.B. 615 (2005)]. ~ 11.4 kg CF4 TPC, 66.6 days "on" / 16.7 days "off "

9 10

­11

B

1989 ­ Moscow. Proposed to detect (­ e ) scattering with low-background HPGe. A.Vasenko et al. [P.T.E.(rus), 2,56(1989)] 2001- ... ­ Taiwan.. The TEXONO experiment H.T.Wong et al. [P.R. D75 (2007)] 1 kg HPGe detector, -flux of ~ 6.4в10 570 days "on" / 127 days "off "

12

/ cm 2 / s

7.4 10

­11

B (90% CL)

2005- ... ­ Udomlya. The GEMMA experiment A.Beda et al. [P.A.N. (rus), 70(2007)] 1.5 kg HPGe detector, -flux of ~ 2.7в10 216 days "on"/ 77 days "off "

13

/ cm 2 / s ,

5 .8 10

­11

B (90% CL)


Measurement of the NMM at reactor
· The effects of the NMM can be searched for
in the recoil electron spectrum (T) from the - e scattering.

· The total cross-section d/dT is a sum of

two: (d/dT)W + (d/dT)EM which depend on the recoil electron energy T in a very different way


d



/ d T [10

45

c m / M e V / f is s io n / e le c t r o n ]

2

00 0

d

E

M

/ dT ( )
-1 1

2 1 10
10 0
-1 1

6 10 45 3

dW / dT

10

1

10

10 0

T [ke V ]


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.

·


Reactor unit #2 of the "Kalinin" Nuclear Power Plant (400 km North from Moscow)

Power: 3 GW ON: 315 days/y OFF: 50 days/y

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

~70 m of W.E. Technological room just under reactor 14 m only! 2.71013 /cm2/s


Phase-1: 13 months (08.2005-09.2006) = 216 days ON + 77 days OFF

Phase-2: 19 months (09.2006-05.2008) = 283 days ON + 42 days OFF
Phase-3: 18 months (05.2008-11.2009) data analysis is in progress...


·

GEMMA background conditions

-rays 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.




1

A D C -1

E1

High freq. noise: E1 > E2
Ge d etec tor
Am p. A al: Real signDC

E1 = Energy E2

Low freq. noise:

E1 < E2



2

A D C -2

E2

13


25

A D C -3 [k e V ]

20

15

10

5

0 0 5 10 15 20 25

A D C -1 [k e V ]
30


0 00 0 00

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

true events

10 0 00 0

dT [ms]
1 0 00 0 0 100 20 0 3 00 400



1000
C o un ts / 0 .1 k e V / 1 0 0 0 h r

10 0 10

Of f
E n e rg y [k e V ] 65 70

1

0

5

10

15

20

25

30

35

40

45

50

55

60

1000 C o un ts / 0.1 k eV / 1 00 0 hr 10 0 10 E n e rg y 1 0 5 10 15 20 25 30 35 40 45 50 55 60 [k e V ] 65 70

On

10 0 50 0 -50 -10 0 0

( O n - O ff - W e a k ) E l e c tr o M a g n e tic

P ha s e - I I

E n e rg y 5 10 15 20 25 30 35 40 45 50 55 60

[k e V ] 65 70


CL
0 .9

Nonphysical region (X<0)

0 .8 0 .7 0 .6 0 .5 0 .4 0 .3 0 .2 0 .1

X<0.34 (90%CL)

S=1

- 0 .8

- 0.6

-0.4

- 0 .2

0.0

0 .2

0 .4

0 .6

0 .8

X


Experimental sensitivity

N

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

~ ( ~ Power / r 2 ) ~ log ( Tmax / Tmin )

t B m Tth

~ ~ ~ ~ ~

2.7 в1013 / cm2 / s 4 years 2.5 keV-1 kg-1 day 1.5 kg 2.5 keV

GEMMA I 2005 ­ 2009
-1

3.2 10

­11



B

hep-ex:1005.2736

19