Search for invisible dark photon at NA62

T Spadaro

doi:10.1088/1742-6596/1526/1/012030

Abstract

Very weakly coupled new-physics particles in the MeV-GeV range appear as mediators in various “portals” to a hidden sector. Their interaction with Standard Model particles is feeble and these states are usually long-lived, so that the experimental search fully profits of a high-intensity setup, such as that of fixed-target experiments. Within the vector portal hidden-sector model a dark photon might exist which predominantly decays to dark matter particles. A search for such an invisible particle has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62 detector at CERN. The signal stems from the chain K + → π + π 0 followed by the π 0 decay to a photon-dark-photon pair. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set.

Highlights

Firm cosmological indications exist of a gravitationally-active abundant dark matter (DM)
Kaon decays taking place in a ∼ 60 m long sensitive volume, kept in a 10−6 mbar vacuum, can be reconstructed: the momentum of daughter particles is measured by a spectrometer made of a 270 MeV-PT -kick bending magnet and 4 straw-based chambers; photons are detected by a hermetic system made of two small angle calorimeters in the very-forward region (IRC and SAC), an electromagnetic calorimeter based on liquid krypton (LKr) in the forward region, and lead-glass annular calorimeters (LAV) at large angle
A different phenomenology is predicted for dark photons coupled to the baryonic current: the NA64, Belle-II, and Babar results would be suppressed by α2/4π relative to NA62, while the implication of K → π + invisible searches at E949 [12] and KTeV [13] and the limits put on Z → γ + invisible from the L3 [14]

Summary

Introduction

Firm cosmological indications exist of a gravitationally-active abundant dark matter (DM). Kaon decays taking place in a ∼ 60 m long sensitive volume, kept in a 10−6 mbar vacuum, can be reconstructed: the momentum of daughter particles is measured by a spectrometer made of a 270 MeV-PT -kick bending magnet and 4 straw-based chambers; photons are detected by a hermetic system made of two small angle calorimeters in the very-forward region (IRC and SAC), an electromagnetic calorimeter based on liquid krypton (LKr) in the forward region, and lead-glass annular calorimeters (LAV) at large angle.

Results

Conclusion