Measurement of the atmospheric $$\nu _{\mu }$$ flux with six detection units of KM3NeT/ORCA

Abstract

Abstract A measurement of the atmospheric $$\nu _{\mu }+\bar{\nu }_{\mu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>ν</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> <mml:mo>+</mml:mo> <mml:msub> <mml:mover> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:math> flux with energies between 1 and 100 GeV is presented. The measurement has been performed using data taken with the first six detection units of the KM3NeT/ORCA detector, referred to as ORCA6. The data were collected between January 2020 and November 2021 and correspond to 510 days of livetime, with a total exposure of 433 kton $$\cdot $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>·</mml:mo> </mml:math> years. Using machine learning classification, 3894 neutrino candidate events have been selected with an atmospheric muon contamination of less than 1 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> . The atmospheric $$\nu _{\mu }+\bar{\nu }_{\mu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>ν</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> <mml:mo>+</mml:mo> <mml:msub> <mml:mover> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:math> energy spectrum is derived using an unfolding procedure and the impact of systematic uncertainties is estimated. The atmospheric $$\nu _{\mu }+\bar{\nu }_{\mu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>ν</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> <mml:mo>+</mml:mo> <mml:msub> <mml:mover> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:math> flux measured using the ORCA6 configuration is in agreement with the values measured by other experiments.