Abstract
Neutrino neutral-current (NC) 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 protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of 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.
Highlights
Measurements of neutrino oscillation provide an emerging picture of the neutrino Standard Model
A series of high precision neutrino oscillation measurements by T2K [1,2,3,4,5] and others [6,7,8,9,10,11,12,13,14,15] are consistent with three massive neutrinos in the Standard Model (SM) [16]
This paper presents the result of the first search for NC1γ below 1 GeV in the T2K near detector data, which is relevant for current and future ne appearance oscillation experiments
Summary
T2K is a long-baseline neutrino oscillation experiment in Japan. Neutrinos are sent to the 50 kton Super-K detector with a baseline of 295 km. The neutrino beam simulation incorporates hadron production data from NA61/SHINE experiment at CERN [54] This analysis uses the ν-mode beam data from November 2010 to May 2013, resulting total statistics of 5.738 ́ 1020 protons-on-targets. The sub-detectors, going downstream in the neutrino flux are the P0D, followed by two FGDs and three TPCs which alternate to make the tracking region of ND280. The neutrino interaction is identified in the first FGD (FGD1), and subsequent TPC2 measures electron and positron tracks. Event selection The event selection of the photon sample has been developed for the νe charged current (νeCC) measurements in ND280 [65,66,67], where photons make a major background for ne (ne) analysis For these analyses the photon sample was made to study the background distribution. Particle identification based on energy loss measured in TPC is applied to select electron-like
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