Сессия ЯФ ОФН РАН, 30.11.07

г., ИТЭФ

Статус экспериментальных работ по

измерению магнитного

момента нейтрино

Старостин А.С.

ИТЕФ

Science motivation of the searching for μ minimally-extended Standard Model:

μ ~ 10–19 B (m / 1eV)

(B = eh /2me Bohr magneton) number of extensions beyond the MSM independently of

neutrino mass:

μ ~ 10–10 - 10–12 B

limits for the NMM from astrophysics (0.4 – 0.05) 10–10 B

(model dependent !!!)

it is necessary to make laboratory measurements sensitive

enough to reach ~ 10 –11 B region and test hypotheses beyond the MSM .

Experimental measurements μ

The effects of the NMM can be searched for in the recoil electron spectrum from - e scattering.

For a non-zero NMM the differential over the kinetic energy T of the recoil electron cross section d/dT is given by

At small recoil energy in d/dT the weak part practically constant, while the EL one grows as 1/T towards low energies.

As a neutrino source in the experiments it’s used solar neutrino and reactor antineutrino. In future it’s planes to use artificial neutrino sources.

(d/dT)weak + (d/dT)EL

Солнечные нейтрино

p + p d + e+ +e (E 0,420 MeV)

p + e- + p d +e (E =1,442 MeV)

3He +p 4He+ e+ +e(18,77 MeV)

7Be + e- 7Li +e (E =0,862 MeV)

8B 7Be* + e+ +e (E 14,6 MeV)

Ф ~ 6 1010 см -2с -1

Limit for the NMM from solar data The spectrum distortion analysis of SK electron recoil spectrum can

allow to set limit of : [hep-ex/0402015]

3.6 10-10B at 90% CL – SK data alone

1.1 10-10B at 90% CL – SK + constrains from the other solar neutrino and KamLAND results (Δm2 = 6.6 10-5 eV2, tan2 θ = 0.48).

BOREXINO claim (2010)

3.0 10–11 B

The average figures for LWR:

Fuel composition→ 235U , 239Pu , 238U , 241Pu

Average energy per fission Ef = 205.3 Mev.

Number of the fiss. / sec Nf = W/ Ef = 9.14×10 19 f/s n per fiss. = 7.2 → 6.0 ( fiss. fragments) + 1.2 ( 238U n,γ 239U → 239Np → 239Pu)

0 2 4 6 81E-5

1E-4

1E-3

0,01

0,1

1

0 < E < 9 MeV

An

tin

eu

trin

o s

pe

ctr

um

, 1

/(M

eV

*fissio

n)

Energy, MeV

F = n W/E = 6.4 × 10 20 /3GWth/secAt R = 14 m f 3 × 10 13 /cm 2 sec

Reactor as a source of antineutrino

MUNU experiment

France, Switzerland, Italy NPP (2800MWth) Bugey, France CF4 TPC total mass 11.4 kg Measurements e - scattering angle

with respect to R core direction MUNU data (66.6 d ON/16.7 d OFF)

[PLB 564, 2003; hep-ex/0502037] Limits depends on energy range

taken : T > 900 keV [PLB 564, 2003]

< 1.0 10 -10 B (90% CL) T > 700 keV [ hep-ex/0502037]

< 9.0 10 -11 B (90% CL)

TEXONO experiment

Collaboration: Taiwan, China, Turkey

Kuo-Sheng PP in Taiwan. Reactor thermal power - 3 GW.

Distance from center of reactor core 28

-flux equal ~ 7×1012 / cm 2 / s

HPGe mass 1 kg enclosed by active NaI/CsI anti-Compton, further by passive shielding & cosmic veto

TEXONO result TEXONO data (197/52 days ON/OFF - 2003) [PRL 90, 2003] (571/128 days ON/OFF - 2006) [hep-ex, 0605006]

BG level at 10-20 keV : ~ 1 day-1 keV-1kg-1 (cpd)

analysis threshold 12 keV

No excess of counts ON/OFF comparison

Limit:

< 7.4 10 -11 B (90% CL)

Experiment GEMMA ((GGermanium ermanium EExperiment for measurement xperiment for measurement

of of MMagnetic agnetic MMoment of oment of AAntineutrino) ntineutrino)

ITEP – LNP JINR DubnaITEP – LNP JINR Dubna

[Phys. of At.Nucl.,70,№11(2007)1873]

Spectrometer includes a Spectrometer includes a HPGeHPGe detector of detector of 1.5 kg1.5 kg installed within installed within NaINaI active active shielding. shielding.

HPGe + NaI are surrounded with multi-HPGe + NaI are surrounded with multi-layer passive shielding layer passive shielding electrolytic electrolytic coppercopper, borated , borated polyethylenepolyethylene and and leadlead..

Circuit noises were discriminated by means method of frequency analysis of signals.

Reactor #2 of the

“Kalininskaya” Nuclear Power Plant

(400 km North from Moscow)

Technological roomjust under reactor

14.0 m14.0 m only!

Power: 3 GWON: 300300 days/yOFF: 6565 days/y

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

~70 m~70 m of W.E.

0 500 1000 1500 2000 2500

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

1E+4

1E+5

1E+6

1E+7

1E+8

êýÂ

Ñ÷åò / êý / êã / ä åí ü

Cs-137 Co-60

K-40

Cs-134

Tl-208

U-238+

Áåç çàù è òû

Óñòàí î â ë åí àï àññè â í àÿ çàù è òà

Âêë þ ÷åí ààêòè â í àÿ çàù è òà

Th-232+

EnergyADCAmp. Gedetector

ADC-1

ADC-2

E1

E2

1

2

High freq. noise: E1 > E2

Real signal: E1 = E2

Low freq. noise: E1 < E2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

E [keV]

3..4

2

5..8

9..16

17..32

33..64

65..128

1

129..256

257..512

513..1024

1025..2048

2049..

Color LOG-scale:

E (ADC-1)

E (ADC-2)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 êýÂ

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Pb-210

Ge-73 Pb-212Pb-214

Th-234

Xe-133

Ñ÷åò / 0.1 êý / êã / ä åí ü

Ge-68

ПослеФурье-фильтрации

4 6 8 10 12 14 16 18

1000

100

10

1

0.1

X[Ga] + 10.86% X[Zn]( Ge-68 )ðàñï àä

The sensitivity of the current experiment

4

1

1

mt

BN

NN : number of signal events expected

BB : background level in the ROI

mm : target (=detector) mass

t t : measurement time

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

GEMMA I 2005 – 2008

~~ 2.7 ×1013 / cm2 / s

t ~ 3 years

B ~ 2.5 keV-1 kg-1 day-1

m ~ 1.5 kg T-th ~ 3.0 keV

4 10 -11 B

Preliminary result for 2 years

(anti)neutrino magnetic moment:

µ ≤ 5.8∙10–11 µB (90% CL)

Available as (hep-ex/0705.4576, Yad. Phys.(2007) 70, p.1925)

Status : “on” 446.9 d / “off” 123.2 d – collected “on” 216 d / “off” 77.2 d - processed

GEMMA II 2009 – 2011

Distance: 14m → 10m ~ 5.4×1013 / cm2 / s t ~ 3 years B ~ 0.2 keV -1 kg -1 day-1 m ~ 6.5 kg (two detectors) T-th ~1.2 keV

GEMMA III

expected sensitivity in future experiments

1 10 –11 B

Summary

For last years general results were obtained in reactor experiments

Now best limit on NMM µ ≤ 5.8∙10–11 µB (90% CL)

The GEMMA II planes to reach sensitivity to 2011y.

µ ~ (1.0 ÷1.5) ∙10–11 µB