Measurement of magnetic dipole strength in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>Ar</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>40</mml:mn> </mml:mmultiscripts> </mml:math> between 9.3 and 10.3 MeV

The magnetic dipole strength $B(M1\ensuremath{\uparrow})$ of $^{40}\mathrm{Ar}$ was measured in the excitation energy range between 9.3 and 10.3 MeV. The nuclear resonance fluorescence technique was used with monoenergetic, linearly polarized incident photon beams. The new data increase the known $B(M1\ensuremath{\uparrow})$ strength in this important excitation energy range by a factor of 2, resulting in an equivalent increase of the calculated neutral current neutrino cross section of $^{40}\mathrm{Ar}$. This observation is of special interest for liquid-argon (LAr)-based neutrino detectors. $B(M1\ensuremath{\uparrow})$ strength has not been found between 10.3 and 11.7 MeV excitation energy. With the new data, a more reliable detection capability of the large Deep Underground Neutrino Experiment LAr detectors can be derived for potential core-collapse supernova neutrinos via the neutral current interaction.