A3F-CNS Summer School 2023

Large-scale shell-model study of two-neutrino double beta decay in 82Se

7 Aug 2023, 17:25

15m

Theoretical Nuclear Physics Young Scientist Session II

Speaker

Mr Deepak Patel (IIT Roorkee)

Description

Double-beta ($\beta \beta$) decay is one of the rarest second-order weak interaction processes with two major decay modes: two-neutrino ($2\nu$) and neutrinoless ($0\nu$). Mayer [1] first introduced the $2\nu \beta \beta$ decay process as a nuclear disintegration with the simultaneous emission of two electrons and two antineutrinos. This process is allowed by lepton number conservation. The study of $2\nu \beta \beta$ decay provides an important test for the standard model and insights into the properties of neutrinos, which are currently a subject of intense research in nuclear and particle physics.

The half-life for the $2\nu \beta \beta$ decay can be given as, $t_{1/2}^{2\nu }=\frac{1}{G^{2\nu }{g}_A^4|M_{2\nu }{|}^2}$. Here, $G^{2\nu }$ denotes the phase-space factor [2]; $g_A$ is the axial-vector coupling strength [3]; $M_{2\nu }$ is the nuclear matrix element (NME) for $2\nu \beta \beta$ decay. There are several candidates for $2\nu \beta \beta$ decay in the nuclear chart, and among them, ${}^{82}$Se is an important candidate for this process. We have performed systematic shell-model calculations for studying the $2\nu \beta \beta$ decay process in ${}^{82}$Se. The jun45 effective interaction [4] is used to calculate the nuclear matrix element (NME) for $2\nu \beta \beta$ decay, having the $0f_{5/2}1p0g_{9/2}$ proton and neutron orbitals. For the calculation of NME, we have calculated 1000 intermediate $1^{+}$ states in ${}^{82}$Br up to the excitation energy of 7.427 MeV. Here, the experimental value for the energy of the lowest $1^{+}$ state in ${}^{82}$Br is taken at 0.075 MeV. Using the shell-model calculated value of NME, we have extracted the half-life of ${}^{82}$Se for $2\nu \beta \beta$ decay as $0.68\times {10}^{20}$ yr. This value is very close to the average value ${0.87}_{-0.01}^{+0.02}\times {10}^{20}$ yr given in Ref. [5].

References:
[1] M. Goeppert-Mayer, Phys. Rev. 48, 512 (1935).
[2] A. Neacsu, and M. Horoi, Adv. High Energy Phys. 2016, 7486712 (2016).
[3] J. T. Suhonen, Front. Phys. 5 55 (2017).
[4] M. Honma $et$ $al.$, Phys. Rev. C 80, 064323 (2009).
[5] A. S. Barabash, Universe 6, 159 (2020).

Presentation materials

Deepak_PPT.pdf