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New light vector particles—hidden photons—are present in many extensions of the standard model of particle physics. They can be produced in nuclear reactors and registered by neutrino detectors. We obtain new limits on the models with the hidden photons from an analysis of published results of the TEXONO neutrino experiment. Accounting for oscillations between the visible and hidden photons, we find that the neutrino experiments are generally insensitive to the hidden photons lighter than

A number of extensions of the standard model of particle physics (SM) introduce massive vectors, singlet with respect to the SM gauge group. These hypothetical particles are called hidden photons, dark photons, or paraphotons

The hidden photon can couple to the SM via vector portal interaction. The corresponding coupling constant is dimensionless, and hence low- and high-energy experiments exhibit similar sensitivity to this type of new physics, if the hidden photon is sufficiently light. In particular, the hidden photon

The mixing term in Eq.

For sufficiently small

The oscillations between the states

The oscillation is terminated by absorption of the photon in the reactor material. The photon absorption length in a nuclear reactor,

In the nonresonance case, the condition [Eq.

The hidden photon production rate is obtained by convolution of the probability [Eq.

However, the neutrino detectors are made of dense material, so the effective photon mass is certainly not smaller than that in water. For the numerical estimates below, we chose

In the resonance case,

Therefore, in the two very narrow mass ranges, the number of signal events in the detector gets amplified a hundred thousand times with respect to the Compton-based result,

A side remark concerns the recent letter

Now we turn to the analysis of the experimental data of the TEXONO neutrino experiment

In Fig.

95% C.L. exclusion upper limit in the parameter plane

A side remark concerns Ref.

Even more important is that the estimation of the upper limit ignores possible systematic errors. The upper limit corresponds to

Indeed, signatures of the hidden photon interactions in the NEOS detector are practically indistinguishable from signatures of positrons in the electron antineutrino induced inverse beta decay (IBD) reactions. The NEOS experiment detected 339.1 thousand IBD events whose signature includes a part from a prompt positron signal as well as a delayed event resulting from

To conclude, we present theoretical description of the expected dark photon signal in reactor neutrino experiments and obtain corrected upper limits on the hidden photon mass

We thank S. Gninenko, S. Troitsky, and I. Tkachev for valuable discussions. The theoretical analysis of hidden photon production and detection within the oscillation approximation was supported by the RSF Grant No. 17-12-01547. The analysis of the experimental data adopted to limit the model parameters was supported by the Grant of the Russian Federation Government, Agreement No. 14.W03.31.0026.