Abstract
We present a first direct Q-value measurement of the Ga71(ν,e−)Ge71 reaction using the TITAN mass-measurement facility at ISAC/TRIUMF. The measurements were performed in a Penning trap on neon-like 71Ga21+ and 71Ge22+ using isobar separation of the on-line produced mother and daughter nuclei through threshold charge breeding in an electron-beam ion trap. In addition, isoionic samples of 71Ga21+ and 71Ge21+ were stored concurrently in the Penning trap and provided a separate Q-value measurement. Both independent measurements result in a combined Q-value of 233.5±1.2 keV, which is in agreement with the previously accepted Q-value for the ν cross-section calculations. Together with a recent measurement of the ν-response from the excited states in 71Ge, we conclude that there are no further uncertainties in the nuclear structure, which could remove the persistent discrepancy between the SAGE and GALLEX calibration measurements performed with neutrinos from reactor-produced 51Cr and 37Ar sources and the theoretical expectation.
Highlights
As neutrino physics experiments advance to increased precision, there has been a renewed interest in scrutinizing the discrepancy observed in the SAGE and GALLEX neutrino calibration measurements
Based on neutrino cross-section calculations performed by Bahcall [7], the ratio of measured to predicted 71Ge event rates, turned out to be consistently below expectation with an average deficit of 13% and ≈ 2.5 σ significance according to Ref. [4]
highly charged ions (HCIs), whereby on-line co-produced isobars have been separated through threshold charge breeding for the first time
Summary
As neutrino physics experiments advance to increased precision, there has been a renewed interest in scrutinizing the discrepancy observed in the SAGE and GALLEX neutrino calibration measurements. While arguments are made to explain the deficit with new physics and possible extensions to presently known neutrino properties [8,9,10], one obvious check is to verify the underlying nuclear physics assumptions as suggested by Haxton [11] and Bahcall [7] In this context the contributions from the two lowest lying states in 71Ge at 175.0 keV (5/2−) and 499.9 keV (3/2−), which can be reached by the CC reaction from the 51Cr and 37Ar neutrino sources, were recently re-evaluated from a high-precision 71Ga(3He, t) charge–exchange experiment to be 7.2 ± 2.0% [12] for the 51Cr source. This separation is based on threshold charge breeding using an electron-beam ion trap charge breeder (EBIT) [37]
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