重新评估镓异常：显著性降至2.3σ

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"再探镓异常"这篇文章探讨的是一个在核物理学领域持续关注的现象，即镓异常。镓异常指的是由GALLEX和SAGE两个太阳中微子探测器观察到的，来自37Ar和51Cr两种元素电子捕获衰变过程中缺失的电子中微子流量。这个现象已经存在约二十年，它挑战了标准的中微子理论预测。研究者们利用了最新的核壳模型波函数，这些波函数是基于两核子相互作用得到的，来进行更为精确的中微子-原子核相互作用截面计算。通过这种方法，他们重新评估了GALLEX和SAGE实验中观察到的镓异常。相比于之前的评估，这个新计算将异常的显著性从3.0σ降低到了2.3σ，这表明其可能并不是一个无法用现有理论解释的强烈信号。这一结果与近期的科学研究相符，特别是对NEOS和DANSS反应堆实验数据的综合分析，它们暗示了一种名为短基线VE（Very Short Baseline Oscillation）消失的现象，这可能是由轻度活动且不带电的中微子——通常称为"无菌中微子"——引起的。这种混合现象进一步挑战了标准模型，可能揭示了中微子物理的未知特性或新的物理机制。文章的关键点包括：核壳模型在计算中微子截面中的应用、实验数据的新分析方法、以及对传统中微子理论的潜在修正。这篇研究对于理解太阳中微子行为、核物理的精细结构以及可能存在的新物理现象具有重要意义。同时，由于是开放获取资源，它也为学术界提供了广泛的研究和讨论空间，促进了对基础物理学问题的深入探索。

Physics Letters B 795 (2019) 542–547

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

The gallium anomaly revisited

J. Kostensalo

a,∗

, J. Suhonen

, C. Giunti

, P.C. Srivastava

University of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014, Finland

INFN, Sezione di Torino, Via P. Giuria 1, I-10125 Torino, Italy

Department of Physics, Indian Institute of Technology, Roorkee 247667, India

a r t i c l e i n f o a b s t r a c t

Article history:

Received

26 June 2019

Accepted

27 June 2019

Available

online 2 July 2019

Editor: W.

Haxton

Keywords:

Gallium

anomaly

Charged-current

cross-sections

Nuclear

shell model

Neutrino-nucleus

interactions

The gallium anomaly, i.e. the missing electron-neutrino ﬂux from

Ar and

Cr electron-capture decays

as measured by the GALLEX and SAGE solar-neutrino detectors, has been among us already for about

two decades. We present here a new estimate of the signiﬁcance of this anomaly based on cross-section

calculations using nuclear shell-model wave functions obtained by exploiting recently developed two-

nucleon

interactions. The gallium anomaly of the GALLEX and SAGE experiments is found to be smaller

than that obtained in previous evaluations, decreasing the signiﬁcance from 3.0σ to 2.3σ . This result is

compatible with the recent indication in favor of short-baseline

disappearance due to small active-

sterile

neutrino mixing obtained from the combined analysis of the data of the NEOS and DANSS reactor

experiments.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

Gallium-based solar-neutrino experiments, GALLEX [1–3] and

SAGE [4], were designed to detect pp neutrinos from the sun.

These two experiments are unique in having been tested for their

detection eﬃciency by

Ar and

Cr radioactive sources. These

sources emit discrete-energy electron neutrinos (E

< 1MeV)

based on their decay via nuclear electron capture (EC). Detection of

these neutrinos is achieved through the charged-current neutrino-

nucleus

scattering reaction

Ga(3/2

−

)

g.s.

→

Ge( J

) +e

−

(1)

to the lowest four (ﬂux from the

Cr source) or ﬁve (ﬂux from the

Ar source) nuclear states in

Ge. In this article we discuss also

the analogous reaction

Ga(3/2

−

)

g.s.

→

Ge( J

) +e

−

(2)

in order to test our calculated shell-model wave functions more

comprehensively.

The

scattering of

Ar and

Cr neutrinos off

Ga leads mainly

to the ground state and the excited states at 175 keV and 500

Corresponding author.

E-mail

address: joel.j.kostensalo@student.jyu.ﬁ (J. Kostensalo).

keV in

Ge. The scattering cross sections for the mentioned three

low-lying states can be estimated by using the data from charge-

exchange

reactions [5]or by using a microscopic nuclear model,

like the nuclear shell model [6]. In both cases it has been found

that the estimated cross sections are larger than the ones mea-

sured

by the GALLEX [1–3]and SAGE [4] experiments. The mea-

sured

neutrino capture rates (cross sections) are 0.87 ± 0.05 of

the rates based on the cross-section estimates by Bahcall [6]. The

related model calculations and analyses based on them have been

discussed in [7–9]. It should be noted that the response to the

ground state is known from the electron-capture ft value of

Ge.

The discrepancy between the measured and theoretical capture

rates constitutes the so-called “gallium anomaly”.

One

of the explanations to the gallium anomaly is associated

with the oscillation of the electron neutrinos to a sterile neutrino

in eV mass scale [7,9]. The same scheme could also explain the

so-called “reactor-antineutrino anomaly” [10–12], discussed, e.g. in

[9]. Searches for the sterile neutrinos are under progress in sev-

eral

laboratories. However, it should be remarked here that there

is no accepted sterile neutrino model to explain the experimen-

tal

anomalies consistently, and also alternative solutions to the

reactor-antineutrino anomaly have been proposed, like the proper

inclusion of ﬁrst-forbidden β-decay branches in the construction

of the cumulative antineutrino spectra [13].

https://doi.org/10.1016/j.physletb.2019.06.057

0370-2693/

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