Measurement of the muon beam direction and muon flux for the T2K neutrino experiment

TL;DR

This paper reports on the measurement of muon beam direction, stability, and flux in the T2K neutrino experiment, demonstrating precise control and understanding of the muon and neutrino beams for oscillation studies.

Contribution

It presents the first detailed measurement of muon beam properties and flux at T2K, including systematic error estimation and validation against predictions using hadron production data.

Findings

Muon beam direction was controlled within 0.3 mrad.

Muon flux measurement agrees with corrected predictions.

Systematic error in beam direction measurement is 0.28 mrad.

Abstract

The Tokai-to-Kamioka (T2K) neutrino experiment measures neutrino oscillations by using an almost pure muon neutrino beam produced at the J-PARC accelerator facility. The T2K muon monitor was installed to measure the direction and stability of the muon beam which is produced together with the muon neutrino beam. The systematic error in the muon beam direction measurement was estimated, using data and MC simulation, to be 0.28 mrad. During beam operation, the proton beam has been controlled using measurements from the muon monitor and the direction of the neutrino beam has been tuned to within 0.3 mrad with respect to the designed beam-axis. In order to understand the muon beam properties,measurement of the absolute muon yield at the muon monitor was conducted with an emulsion detector. The number of muon tracks was measured to be $(4.06\pm0.05)\times10^4$ cm$^{-2}$ normalized with $4\times10^{11}$ protons on target with 250 kA horn operation. The result is in agreement with the prediction which is corrected based on hadron production data.