%0 Generic
%A Zhang, Yapeng
%D 2013
%F heidok:14793
%K SIS18 energy, FOPI, strangeness physics
%R 10.11588/heidok.00014793
%T 3 lambda H and 4 lambda H production in Ni+Ni collisions at 1.91A GeV
%U https://archiv.ub.uni-heidelberg.de/volltextserver/14793/
%X $^3_{\Lambda}H$ and $^4_{\Lambda}H$ are identified from their two-body $\pi^-$-decay channel in Ni+Ni collisions at 1.91A GeV for the first time. The experiment was performed by the FOPI spectrometer at the SIS18 of GSI. The analyzed data sample consists of 56${\times}10^{6}$ events covering the most central 60\% of the total reaction cross section.  %  The reconstructed invariant mass of $^3_{\Lambda}H$ is $2.9926\pm0.0017$ GeV/c$^2$ with a width of $5.6\pm1.0$ MeV/c$^2$, and the one of $^4_{\Lambda}H$ is $3.9226{\pm}0.0010$ GeV/c$^2$ with a width of $4.0\pm1.6$ MeV/c$^2$. The significance of the $^3_{\Lambda}H$ and $^4_{\Lambda}H$ signal is 5.6 and 4.2, respectively. The $^3_{\Lambda}H$ and $^4_{\Lambda}H$ signal is observed in a certain phase space region in the $p_t/m-y_{lab}$ plane only.  %By applying the differential decay time efficiency obtained from MC simulation, the mean lifetime of $^3_{\Lambda}H$ and $^4_{\Lambda}H$ is found to be 263$\pm$64(sta)$\pm$44(sys) ps and 196$\pm$75(sta)$\pm$43(sys) ps, respectively. By taking reconstruction efficiency and the decay branching ratio into account, the yield of $^3_{\Lambda}H$ and $^4_{\Lambda}H$ for the analysed event sample is $7.5{\times}10^{-4}$ and $1.3{\times}10^{-4}$ per event, respectively.  %The $^3_{\Lambda}H$ and $^4_{\Lambda}H$ production in Ni+Ni at 1.91A GeV via coalescence process is naively discussed and it is shown that the observed results are not compatible with the expectations. The yield ratio of $^3_{\Lambda}H$e/$^3$He and $^4_{\Lambda}H$e/$^4$He is compared with the predictions of the thermal model for hadron chemistry.