Production of nuclei and hypernuclei in pion-induced reactions near threshold energies

Abstract

The Ultra-relativistic Quantum Molecular Dynamics model is employed to simulate ${\pi }^{-}+\mathrm{C}$ and ${\pi }^{-}+\mathrm{W}$ collisions at p${}_{\mathrm{lab}}=1.7$ GeV motivated by the recent HADES results. By comparing the proton and $\Lambda$ transverse momentum spectra, it was observed that the data and transport model calculation show a good agreement, if cluster formation is included to obtain the free proton spectra. Predictions of light cluster ($d$, $t$, ${}^3$He, ${}^4$He, as well as ${}_{\Lambda }^3$H and $\Xi$N) multiplicities and spectra are made using a coalescence mechanism. The resulting multiplicities suggest that the pion beam experiment can produce a substantial amount of ${}_{\Lambda }^3$H, especially in ${\pi }^{-}+\mathrm{W}$ collisions due to the stopping of the $\Lambda$ inside the large tungsten nucleus. The findings are supplemented by a statistical multi-fragmentation analysis suggesting that even larger hyper-fragments are produced copiously. It is suggested that even double strange hypernuclei are in reach and might be studied in more detail using a slightly higher pion beam momentum.

Comments: 9 pages, 10 figures