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Abstract

Recently, evidence for the observation of about 2 keV and below nuclear
recoils from the coherent scattering of reactor anti-neutrinos off the
germanium nuclei has been reported. We analyze the observed data to estimate
the value of the weak mixing angle and constrain the neutrino millicharge,
magnetic moment, charge radius and anapole moment contributing to the coherent
scattering process. Currently, there is no definite model available for the
quenching factor at such low energies. To this end, we consider various models
of the quenching factor and show how it affects the interpretation of the
obtained results. We find that the bounds obtained are stronger in some cases
while comparable or weaker in other cases which show a strong dependence on the
choice and accuracy of a particular quenching factor model. The results are the
first at such low-energy nuclear recoils. We present an exhaustive list of
analytical functions for the different quenching factors corresponding to the
existing models and to the data from various experiments. Such functions will
be useful for any new physics study using the nuclear recoils due to the
reactor neutrinos.