Heavy neutrino search in accelerator-based experiments

TL;DR

This paper investigates the potential to detect heavy neutrinos in the 1 MeV to 500 MeV mass range using existing neutrino experiment facilities, focusing on the T2K experiment's near detector to improve bounds on neutrino mixing parameters.

Contribution

It provides a feasibility study and sensitivity estimates for detecting heavy neutrinos in accelerator-based experiments, highlighting the potential to surpass previous experimental bounds.

Findings

T2K can improve sensitivity to heavy neutrino mixing parameters for 140 MeV < M < 500 MeV.

Heavy neutrinos are emitted predominantly in the forward direction, aiding detection.

Sensitivity at 10^{21} POT exceeds previous bounds from PS191.

Abstract

We explore the feasibility of detecting heavy neutrinos by the existing facilities of neutrino experiments. A heavy neutrino in the mass range 1 MeV < M < 500 MeV is produced by pion or kaon decay, and decays to charged particles which leave signals in neutrino detectors. Taking the T2K experiment as a typical example, we estimate the heavy neutrino flux produced in the neutrino beam line. Due to massive nature of the heavy neutrino, the spectrum of the heavy neutrino is significantly different from that of the ordinary neutrinos. While the ordinary neutrinos are emitted to various directions in the laboratory frame due to their tiny masses, the heavy neutrinos tend to be emitted to the forward directions and frequently hit the detector.The sensitivity for the mixing parameters is studied by evaluating the number of signal events in the near detector ND280. For the electron-type mixing, the sensitivity of T2K at 10^{21} POT is found to be better than that of the previous experiment PS191, which has placed the most stringent bounds on the mixing parameters of the heavy neutrinos for 140 MeV< M < 500 MeV.