Near detector at a neutrino factory

A near detector at a neutrino factory is essential for the measurement of neutrino oscillations, by performing the ratio of neutrino interactions between the near and far detectors. The near detector needs to establish the neutrino flux, beam angle, divergence, and energy of the neutrino beam, as well as determining the polarization of the muons that produce the neutrinos. Cross-section measurements and other physics such as measurements of parton distribution functions and charm physics can also be carried out at a near detector.There are many technological choices for a near detector at a neutrino factory, but a detector comprising an active silicon target inside a magnetic field for precise vertex reconstruction, followed by muon and electron identification is capable of carrying out these goals. A prototype silicon detector consisting of four passive layers of boron carbide and five layers of silicon microstrip detectors (NOMAD-STAR) was implemented within the NOMAD neutrino oscillation experiment. Impact parameter and double vertex resolutions were measured for this detector and a sample of charm decays was reconstructed for the first time using silicon detectors inside a neutrino beam. Consequences and lessons learnt from this prototype shall be applied to the case of a near detector at a neutrino factory.