Nuclear responses for double-beta decays by hadron, photon, and neutrino probes and MOON experiment

Abstract

Neutrino-less double-beta decays (0νββ) with the mass sensitivities of the solar and atmospheric ν masses are of great interest for studying the Majorana nature of neutrinos and the absolute mass spectrum as suggested by recent ν oscillation experiments. Here nuclear responses (nuclear matrix elements) for 0νββ are crucial. They are well studied experimentally by using charge-exchange, photo-nuclear and neutrino reactions. MOON(Mo Observatory Of Neutrinos) is a high sensitivity 0νββ experiment with the mass sensitivity of an order of 30 meV. Experimental studies of the nuclear responses and the present status of MOON are briefly discussed. Neutrino-less ββ decays and Majorana neutrino massesDouble beta decays are of great interest from viewpoints of particle and astronuclear physics. They have been extensively discussed, as given in recent review papers and references therein [1, 2, 3]. Double beta decays with two ν's, which conserve the lepton number, are within the standard model(SM), while those without ν violate the lepton number conservation law by ∆L = 2 and thus are beyond SM. The transition rates for two-neutrino (2νββ) and neutrino-less (0νββ) decays are given aswhere G 2ν and M 2ν are the phase space factor and the nuclear matrix element for 2νββ, and G 0ν and M 0ν are those for 0νββ. m ν is the effective Majorana ν-mass term. The 0νββ is caused also by the right-handed weak current, the ν-Majoron coupling, the ν-SUSY coupling, and others. Here discussions are restricted on 0νββ due to the light ν-mass. The effective mass term is written aswhere m i , u ei , and φ i are the mass eigen value, the coefficient for the electron neutrino, and the Majorana phase, respectively, with i = 1, 2, 3. * ) Presented by the author at the Workshop on calculation of double-beta-decay matrix elements (MEDEX'05), Corfu, Greece, September 26-29, 2005.

Muon capture reaction on Mo100 to study the nuclear response for double- β decay and neutrinos of astrophysics origin

“…Thus one can derive the MCR response, i.e. the strength distribution, as a function of E, from the mass (A − x) distribution of the residual isotopes, as suggested in 1972 [6], and also in 2001's [2,7,8]. The MCER and the neutron emission schemes are illustrated in Fig.2.…”

“…Thus experimental studies of them are very valuable. Experimental studies of the neutrino nuclear responses for DBDs and astro neutrinos are described in review articles [1][2][3][4][5].…”

“…Astro-neutrino nucleo-syntheses and astro-neutrino nuclear reactions are studied by investigating astro neutrino nuclear interactions. Then one needs nuclear responses for astro neutrinos and astro anti-neutrinos [1,2]. So far, the single β − matrix element M (β − ) and the neutrino response have been extensively studied by charge exchange reactions [1,5].…”

“…Neutrino properties such as the Majorana nature, the absolute mass scale and others beyond the standard electroweak model are studied by investigating neutrino-less double beta decays (DBD) [1][2][3][4][5]. Here the ν responses for DBD (β − and β + responses) are necessary to get the neutrino properties beyond the standard model.…”

MOON for a next-generation neutrino-less double-beta decay experiment; present status and perspective

“…To search for 0νββ in QD∼IH mass ranges, one has to use ββ isotopes of the order of 0.1∼1 t (tonne) even in cases of such favorable ββ nuclides as 82 Se, 100 Mo and 150 Nd with large phase volumes. [2][3][4][5][6]. This is a brief report on the expected background and the neutrino mass sensitivity of MOON.…”