Production asymmetry of ${\nu }_{\tau }$ neutrinos and ${\overline{\nu }}_{\tau }$ antineutrinos from a fixed target experiment SHiP

Abstract

We discuss how to calculate cross sections as well as rapidity, transverse momentum and energy distributions of ${\nu }_{\tau }$ and ${\overline{\nu }}_{\tau }$ produced from the direct $D_s^{\pm }\to {\nu }_{\tau }/{\overline{\nu }}_{\tau }$ and chain $D_s^{\pm }\to {\tau }^{+}/{\tau }^{-}\to {\nu }_{\tau }/{\overline{\nu }}_{\tau }$ decays in $p{+}^{96}\mathrm{Mo}$ scattering with proton beam $E_{\mathrm{lab}}$ = 400 GeV \textit{i.e.} at ${\sqrt{s}}_{NN}$ = 27.4 GeV. The $\tau$ decays are simulated with the help of the \textsc{Tauola} code and include multiple decay channels of $\tau$ in amounts proportional to their branching ratios. In our calculations we include $D_s^{\pm }$ from charm fragmentation $c\to D_s^{+}$ and $\bar{c}\to D_s^{-}$ as well as those from subleading fragmentation of strange quarks/antiquarks $s\to D_s^{-}$ and $\bar{s}\to D_s^{+}$. The $s\ne \bar{s}$ asymmetry of the strange quark content of proton is included. The different contributions to $D_s^{\pm }$ and ${\nu }_{\tau }/{\overline{\nu }}_{\tau }$ are shown explicitly. We discuss and quantify a not discussed so far effect of asymmetries for production of ${\nu }_{\tau }$ and ${\overline{\nu }}_{\tau }$ caused by subleading fragmentation mechanism and discuss related uncertainties. A potential measurement of the asymmetry is discussed. Estimates of a number of observed ${\nu }_{\tau }/{\overline{\nu }}_{\tau }$ in the ${\nu }_{\tau }/{\overline{\nu }}_{\tau }{+}^{208}\mathrm{Pb}$ reaction, with 2m long target are given with the help of the NuWro program. We refer also to the production of the high-energy (anti)neutrinos in the atmosphere.

29 pages, 15 figures, 3 tables, second version contains important modifications with respect to the first one

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