Directed Flow of $\mathrm{\Lambda }$-Hyperons in 2-6 AGeV Au+Au Collisions

Directed flow measurements for $\mathrm{\Lambda }$-hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2, 4, and 6 AGeV; $b<5-6$ fm). The measurements indicate that $\mathrm{\Lambda }$-hyperons flow consistently in the same direction and with smaller magnitudes than those of protons. Such a strong positive flow [for $\mathrm{\Lambda }$s] has been predicted in calculations which include the influence of the $\mathrm{\Lambda }$-nucleon potential. The experimental flow ratio $\mathrm{\Lambda }$/p is in qualitative agreement with expectations ($\sim 2\mathrm{/}3$) from the quark counting rule at 2 AGeV but is found to decrease with increasing beam energy.