Study of Tau Neutrinos Production using Nuclear Emulsions at CERN-SPS

Abstract

The DsTau (NA65) experiment aims to study $Ds\rightarrow\tau +\nu_{\tau}, \tau\rightarrow X +\nu_{\tau}$ differential production cross section using 400 GeV/c proton and tungsten target. The nuclear emulsion tracker is adopted to detect $Ds\rightarrow\tau +\nu_{\tau}$ small angle kinks and short flight lengths in the in mm scale. The analysis of 2.3 $\times$ 10$^{8}$ proton interactions in tungsten will produce about 1000 detected $Ds\rightarrow\tau +\nu_{\tau}, \tau\rightarrow X +\nu_{\tau}$ cascade decays and will reduce the uncertainty of $\nu_{\tau}$ flux to 10\%. In addition, about 10$^{5}$ charm pair associating events will be collected during the analysis. The charm production properties and correlations between two charm's angles or momenta or fragmentations will be analyzed. Not only interactions with tungsten but also interactions with plastic and emulsion are identified using the vertex position. Therefore, Z dependence analysis of target nucleus can be carried out for proton interactions. A pilot run was carried in 2018 and preliminary results on proton interactions and charm productions were obtained. About 22\% of the pilot run data was processed and the systematic small kink decay search is scheduled to start soon. Physics run is scheduled for 2021 and 2022. The beam exposure in 2021 was successful and all emulsion films were developed and are ready for scanning and analysis.