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GEMMA: experimental searches for neutrino magnetic moment JINR: V. Brudanin, V. Egorov, D. Medvedev, M. Shirchenko , E. Shevchik, I. Zhitnikov, V. Belov ITEP: A. Beda, A. Starostin. Scientific motivation. Minimally extended Standard Model ( MSM) : ~ 10 – 19 B (m / 1eV). W.
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GEMMA:experimental searches for neutrino magnetic moment JINR:V. Brudanin, V.Egorov, D. Medvedev, M. Shirchenko, E. Shevchik, I. Zhitnikov, V. BelovITEP:A. Beda, A.Starostin
Scientific motivation Minimally extended Standard Model (MSM): ~ 10–19B (m / 1eV) W νL νR νL l νR l W γ γ
Scientific motivation Beyond the MSM: ≤10–14B (m / 1eV) ~ 10–10 - 10–11B
Calculation ofΛparameter • [] 4*10-9B ([m]/1eV)* (1TeV/)2 *m2/(m2-m2) Bell N. F. How magnetic is the neutrino? // WSPC Proceedings; hep-ph/0707.1556. • For =10-11Bandm=0.3 eV Λ<100 TeV
Scientific motivation (summary) Observation of~10-11-10-12Bwill: • give a hint of neutrino nature • allow to feel the scale ofΛ • set the restrictions on the number of astrophysical models
Direct searches for • Reactor neutrinos: • MUNU, TEXONO, GEMMA • <(2.9 – 9)*10-11 B (e) • Solar neutrinos: • SK+KamLand, Borexino • <(5.4 – 11)*10-11B (all) • Accelerator neutrinos: • LSND, DONUT • <1.1*10-9B (e) • <6.8*10-10B () • <3.7*10-7B (τ)
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 2.2×1013 / cm 2 / s 1989 –A revised analysis by P. Vogel and J. Engel [P.R.,D39,3378(1989)] gave a limit ( 2 – 4) 10 –10B 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 “ 2.4 10 –10B (90% C.L.) 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 ~ 2×1013 / cm 2 / s , 30 days “on”/17 days “off “ 1.9 10 –10B (95% C.L.)
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: ( d/dT )weak + ( d/dT )EM depending on the recoil energy T in different ways
Reactor unit #2 of the “Kalinin” Nuclear Power Plant (400 km North from Moscow) Power: 3 GW ON:315days/y OFF:50days/y Total mass above (reactor, building, shielding, etc.): ~70 mof W.E. Technological room just under reactor 14 monly! 2.71013 /cm2/s
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.
GEMMA background conditions -rayswere measu- red with Ge detector. The main sources are:137Cs ,60Co,134Cs. Neutronbackground was measured with 3He counters, i.e., thermal neutrons were counted.Their flux at the facility site turned out to be30 times lowerthan in the outside laboratory room. Charged component of the cosmic radiation (muons) was measu-red to be5 times lowerthan outside.
High freq. noise: E1 > E2 Real signal: E1 = E2 Low freq. noise: E1 < E2 E.Garcia e.a. NPB28A(1992)286
Spectrum before “matrix applying” Spectrum after “matrix applying” keV
microphonics true events mains freq. (50 Hz) Time selection of consecutive events:
Experimental sensitivity N: number of signal events expected B: background level in the ROI m: target (=detector) mass t: measurement time • N~ ( ~ Power/r2 ) • ~(Tmax- Tmin / Tmax*Tmin)1/2 • GEMMA I • ~2.7 ×1013 / cm2 / s • t ~4 years • B~ 2.5 keV-1 kg-1 day-1 • m~ 1.5 kg • Tth~2.8keV 2.9 10 –11B
Data Set • I phase – 5184 h ON, 1853 hOFF • II phase– 6798 h ON, 1021 hOFF • I+II – 11982hON, 2874 hOFF • III phase – 6152 h ON, 1613 hOFF • I+II+III – 18134hON, 4487hOFF 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. 139–143.
#2: 14 m #3: 10 m KNPP Udomlya Russia
GEMMA II ~5×1013 / cm2 / s t ~2 years B~ 0.5–1.0 keV -1kg -1day-1 m~ 6 kg (two detectors) Tth ~ 1.5 keV 1.0 10 -11B
GEMMA-II Lifting mechanism
Calibration spectrum in Dubna with (Fe-55, Al) source Achieved energy threshold is ~350 eV
Sensitivity of future experiments B =0.2 1/keV/kg/day