THE NEW RESULT OF THE NEUTRINO MAGNETIC MOMENT MEASUREMENT IN THE GEMMA EXPERIMENT

Abstract

The first result of the neutrino magnetic moment measurement at the Kalininskaya Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. An antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed 13.9 m away from the 3 GW reactor core is used in the spectrometer. The antineutrino flux is 2.73×10 13ν e /cm 2 /s. The differential method is used to extract the ν-e electromagnetic scattering events. The scattered electron spectra taken in 6200 and 2064 hours for the reactor on and off periods are compared. The upper limit for the neutrino magnetic moment µ ν <5.8×10 −11 µ B at 90% CL is derived from the data processing.

Experiment GEMMA: Search for the Neutrino Magnetic Moment

“…. 7) × 10 −11 µ B [3,4]. Similar limits were obtained for solar neutrinos [5,6], but due to oscillations at long distance (as well as matter-enhanced oscillations in the Sun) their flavor composition changes and therefore the solar NMM results could differ from the reactor ones.…”

“…In our previous work [4] we presented Phase-I (13 months' measurement including 5184 and 1853 hours of the reactor ON and OFF periods, respectively). Today we can add Phase-II -19 months from 09.2006 to 05.2008.…”

“…At a low recoil electron energy (T ≪ E ν ) the value of dσ W /dT becomes almost constant, while dσ EM /dT behaves as T −1 , so that the lowering of the detector threshold leads to a considerable increase in the NMM effect with respect to the weak unremovable contribution. 1 To realize this useful feature in our GEMMA spectrometer [4], we use a 1.5 kg HPGe detector with an energy threshold as low as 3 keV. The background is suppressed in several steps.…”

Spin flip of neutrinos with magnetic moment in core-collapse supernova

“…In the beginning of the year 1987 A. Dar proposed a scenario of supernova explosion based on the two-stage ν L → ν R → ν L transition of Dirac neutrinos, where the first stage could occur in the supernova core due to the electromagnetic scattering of neutrinos on charged particles, and the second one -in the supernova envelope due to the neutrino spin precession in the magnetic field of the star [13]. The detection of neutrinos from a nearby supernova SN1987A on February 23, Laboratory experiment GEMMA [28] µ ν < 5.8 · 10 −11 µ B 90% CL Cooling rates of white dwarfs [25] µ ν 10 −11 µ B Cooling rates of red giants (see e.g. [26]) µ ν 3 · 10 −12 µ B Supernova energy losses [30] µ ν (1.1 − 2.7) · 10 −12 µ B Absence of high-energy events µ ν 10 −12 µ B in the SN1987A neutrino signal [16] 1987 triggered a bunch of papers [14]- [17] (see also a related paper [18]), which idea was closely related to the Dar's one.…”

Electromagnetic properties of neutrinos

“…Upper bounds on the neutrino magnetic moment have been obtained in recent reactor experiments: µ ν ≤ 9.0 × 10 −11 µ B (MUNU collaboration [16]), µ ν ≤ 7.4 × 10 −11 µ B (TEXONO collaboration [17]. The best world limit µ ν ≤ 3.2 × 10 −11 µ B has been recently obtained by the GEMMA collaboration [18]. A stringent limit has also been obtained in the Borexino solar neutrino scattering experiments: µ ν ≤ 5.4 × 10 −11 µ B [19].…”