Constraining non-standard neutrino interactions with neutral current events at long-baseline oscillation experiments

A bstract We explore, for the first time, neutral-current events at long-baseline experiments to constrain vector and axial-vector neutrino non-standard interactions (NSI) with quarks. We leverage the flavor dependence of NSIs to perform an oscillation analysis in the neutral- current channel. We first introduce a framework to parametrize the effect of NSI on the cross section. Then, as an example, we analyze NOvA neutral-current data which provides significantly improved constraints on the axial-vector NSI parameters $$ {\varepsilon}_{\mu \mu}^A $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>μμ</mml:mi> <mml:mi>A</mml:mi> </mml:msubsup> </mml:math> , $$ {\varepsilon}_{\tau \tau}^A $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>ττ</mml:mi> <mml:mi>A</mml:mi> </mml:msubsup> </mml:math> and $$ {\varepsilon}_{e\mu}^A $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>eμ</mml:mi> <mml:mi>A</mml:mi> </mml:msubsup> </mml:math> . This is highly complementary to constraints from SNO data, which, differently from long-baseline neutral current data, is not sensitive to isospin conserving NSIs $$ {\varepsilon}_u^A $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>u</mml:mi> <mml:mi>A</mml:mi> </mml:msubsup> </mml:math> = $$ {\varepsilon}_d^A $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>d</mml:mi> <mml:mi>A</mml:mi> </mml:msubsup> </mml:math> . Additionally, we disfavor large values of the diagonal vectorial NSI $$ {\varepsilon}_{\mu \mu}^{VV} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>μμ</mml:mi> <mml:mi>VV</mml:mi> </mml:msubsup> </mml:math> and $$ {\varepsilon}_{\tau \tau}^V $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>ε</mml:mi> <mml:mi>ττ</mml:mi> <mml:mi>V</mml:mi> </mml:msubsup> </mml:math> which originate from the LMA-Dark solution. We also highlight the complementarity between NSI searches at oscillation experiments using charged current and neutral current channels.