Status of tension between NOvA and T2K after Neutrino 2024 and possible role of nonstandard neutrino interactions

In a previous work, we have shown that the data presented by the two long-baseline accelerator experiments NOvA and T2K at the Neutrino 2020 conference displayed a tension and that it could be alleviated by nonstandard neutrino interactions (NSI) of the flavor changing type involving the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>e</a:mi><a:mo>−</a:mo><a:mi>μ</a:mi></a:math> or the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>e</c:mi><c:mo>−</c:mo><c:mi>τ</c:mi></c:math> sectors with couplings <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo stretchy="false">|</e:mo><e:msub><e:mi>ϵ</e:mi><e:mrow><e:mi>e</e:mi><e:mi>μ</e:mi></e:mrow></e:msub><e:mo stretchy="false">|</e:mo><e:mo>∼</e:mo><e:mo stretchy="false">|</e:mo><e:msub><e:mi>ϵ</e:mi><e:mrow><e:mi>e</e:mi><e:mi>τ</e:mi></e:mrow></e:msub><e:mo stretchy="false">|</e:mo><e:mo>∼</e:mo><e:mn>0.1</e:mn></e:math>. As a consequence, a hint in favor of NSI emerged. In the present paper, we reassess the issue in light of the new data released by the two experiments at the Neutrino 2024 conference. We find that the tension in the determination of the standard <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:mi>C</k:mi><k:mi>P</k:mi></k:mrow></k:math>-phase <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mi>δ</m:mi><m:mi>CP</m:mi></m:msub></m:math> extracted by the two experiments in the normal neutrino mass ordering persists and has a statistical significance of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mo>∼</o:mo><o:mn>2</o:mn><o:mi>σ</o:mi></o:math>. Concerning the NSI, we find that including their effects in the fit, the two values of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>δ</q:mi><q:mi>CP</q:mi></q:msub></q:math> preferred by NOvA and T2K return in very good agreement. The current statistical significance of the hint of nonzero NSI is <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:mo>∼</s:mo><s:mn>1.8</s:mn><s:mi>σ</s:mi></s:math>. Further experimental data are needed in order to settle the issue.