Open Collections

Reconstructing ν̅ₑ energy spectrum and ground state branching fraction of laser trapped ⁹²Rb

University of British Columbia

The anti-electron neutrino ν̅ₑ energy spectra from the fission product ⁹²Rb is of interest for reactor neutrino physics and short baseline neutrino oscillation experiments. A study of the beta-neutrino correlation parameter a₁ was performed in laser trapped neutral ⁹²Rb, constraining the strong ground-state to ground-state (GS) first-forbidden 0⁻→ 0⁺ rank-0 nuclear matrix element ratio ξₒ/ω. The first-forbidden rank-0 correlation parameter depends non-linearly on beta energy W with a₁(ξₒ,ω,W) for a decay end-point of Wₒ. Two distinct analysis were performed via: 1) recoils coincident with atomic shake-off electrons (SOE); and 2) recoils coincident with the beta and atomic SOE. In the former case-1, no distinction can be made between transitions to the GS or excited states and we find the two possible solutions (ξ̅/ω})ᴿ^Sᴼᴱ^^⁺_R_S_O_E_^₋ = ⁺⁰^.⁴³⁷₋₀_.₅₁₂ ± (⁰^.⁰⁰⁵₀_.₀₀₈)ₛₜₐₜ ± (⁰^.⁰¹₀_.₀₁)ₛ_yₛ$ with a₁(W → Wₒ) → ⁰^.³⁰₀_.₃₆, respectively. In the later case-2, however, GS events are isolated through kinematic constraints on the reconstructed transition $Qₑₓₚ-value, with two possible solutions being (ξ̅/ω})ᴮᴿ^Sᴼᴱ^^⁺_B_R_S_O_E_^₋ = ⁺⁰^.⁵⁴¹₋₀_.₇₃₉ ± (⁰^.⁰⁰⁸₀_.₀₁₈)ₛₜₐₜ ± (⁰^.⁰¹₀_.₀₁)ₛ_yₛ with a₁(W → Wₒ) → ⁰^.⁵⁰₀_.₅₈, respectively. These are all significantly different from the naively expected |ξₒ/ω| ≫ 1, and a₁(W → Wₒ) = 1. From the beta-recoil 3-momenta, the ν̅ₑ energy spectra was also reconstructed for decays through the GS, and eventually compared with theory. We also present our future proposal to measure the GS branching ratio from the reconstructed Qₑₓₚ-value distribution.

Text

2019-10-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/72096

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/