Abstract: | Neutrino neutral-current induced single photon production is a sub-leading
order process for accelerator-based neutrino beam experiments including T2K. It
is, however, an important process to understand because it is a background for
electron (anti)neutrino appearance oscillation experiments. Here, we performed
the first search of this process below 1 GeV using the fine-grained detector at
the T2K ND280 off-axis near detector. By reconstructing single photon
kinematics from electron-positron pairs, we achieved 95\% pure gamma ray sample
from 5.738$ imes 10^{20}$ protons-on-targets neutrino mode data. We do not
find positive evidence of neutral current induced single photon production in
this sample. We set the model-dependent upper limit on the cross-section for
this process, at 0.114$ imes 10^{-38}$ cm$^2$ (90\% C.L.) per nucleon, using
the J-PARC off-axis neutrino beam with an average energy of
$left<E_
u
ight>sim 0.6$ GeV. This is the first limit on this process below
1 GeV which is important for current and future oscillation experiments looking
for electron neutrino appearance oscillation signals. |