A silicon detector for neutrino physics

Abstract

In order to demonstrate the feasibility of conducting future νμ → ντ oscillation searches using a high-resolution, large-area silicon microstrip detector, the Silicon TARget (STAR) detector was built. STAR was installed in the NOMAD short baseline neutrino oscillation experiment at the CERN SPS neutrino beam, where it recorded approximately 10 000 neutrino interactions during the operation of the detector in the period 1997-98. It consists of five layers of silicon detectors interleaved with four layers of passive boron carbide as the target. The target mass is 45 kg, while the total silicon surface area is 1.14 m2 and contains 32 000 readout channels. The individual modules have a length of 72 cm, the longest built to date.

The detection of τ particles, produced in ντ charged-current interactions, would require a tracking detector with a precision of a few tens of microns in order to measure the position of the neutrino interaction vertex as well as the impact parameter of the τ decay products. The performance of STAR was studied by reconstructing the decays of K0S mesons produced in νμ charged-current interactions.

For both the primary and secondary vertices, the resolution in the y direction was found to be approximately 20 μm, while that in the z direction was found to be approximately 100 μm. The double vertex resolution, a measure of how accurately the distance between the vertices can be measured, was found to be approximately 20 μm in the y direction and 300 μm in the z direction. The impact parameter resolution of the muons resulting from νμ charged-current interactions, with respect to the primary vertex, was found to be 25 μm.

The vertex resolution and impact parameter results show that a microstrip silicon detector would be well-suited to measuring νμ → ντ oscillations. The high precision of silicon detectors has several other applications within neutrino physics, such as using a silicon detector as the near-detector in a future neutrino factory facility.