The role of strangeness in baryon and electric charge stoppings

RESUMO

Recently it has been proposed that comparing the net-baryon ($B$) stopping with net-electric charge ($Q$) stopping can help studies of the baryon stopping mechanism in nuclear collisions. Here we find the $B/Q\times Z/A$ ratio to be very sensitive to the difference between $s$ and $\bar s$ quark rapidity distributions. For mid-rapidity of isobar collisions at 200A GeV, a multi-phase transport (AMPT) model gives slightly more $\bar s$ than $s$, which leads to $B/Q\times Z/A<1$, while the model without the $s-\bar s$ asymmetry gives $B/Q\times Z/A \geq 1$. Comparing Ru+Ru and Zr+Zr isobar collisions, the AMPT (and UrQMD) model gives $B/\Delta Q\times \Delta Z/A<1$ at mid-rapidity at all centralities, which strongly contradicts the recent STAR data. We also find that the $B/\Delta Q\times \Delta Z/A$ ratio is very sensitive to the net-light quark ($u,d$) stoppings, but it is less sensitive to the $s-\bar s$ asymmetry than the $B/Q\times Z/A$ ratio by a factor of 3. These results are expected to help us resolve the stopping puzzle and better understand the baryon stopping mechanism in the future.