Study of tau neutrino production property with measuring open-Charms at 400 GeV proton beam dump

Abstract

The property of tau neutrino is not well known, due to difficulty of its production and detection. The comparison of the neutrino-nucleon cross-section of tau neutrinos and other neutrino flavours is one of the interesting topics. The tau neutrino cross-section has been measured by the DONUT experiment, but with a large statistical error of $\sim30\%$ and a systematical uncertainty of $\sim50\%$. The statistics of detected tau neutrinos will be improved by a planned experiment such as SHiP experiment at CERN in near future. The DsTau collaboration aims to reduce the systematic uncertainty to $10\%$ by measuring the mother particles($Ds$ mesons) of tau neutrinos at the beam source. $Ds$ mesons are generated by proton interactions with the beam dump target, which decay in sequence $Ds\rightarrow \tau + \nu_{\tau}$ and $\tau\rightarrow\nu_{\tau}+X$. DsTau will collect 1000 $Ds\rightarrow \tau$ associated events in $2.3 \times 10^{8}$ proton interactions with the tungsten target using the 400 GeV/c proton beam at CERN SPS. The rate and $x_{F}$ distribution of the $Ds$ production will be measured and the reduction of uncertainty on the tau neutrinos production will be achieved as the result. Since $Ds$ and tau mass difference is small, the kink angle$(\sim7mrad)$ in the $Ds$ to tau trajectory within a short distance of a few mm decay flight is difficult to detect. Emulsion Cloud Chambers, ECCs, dedicated structure with tungsten plates and nuclear emulsion plates are used to detect small angle kinks at $Ds$ to tau decays. Since large number, $10^{5}$ events, of associated charm production will be accumulated and analyzed in ECCs, physics of open-charm could be studied as a byproduct. The DsTau project introduction and results from small scale test exposure in 2016, 2017 are described.