Beam-Energy Dependence of the Directed Flow of Deuterons in Au+Au Collisions

We present a measurement of the first-order azimuthal anisotropy, v_1(y), of deuterons from Au+Au collisions at sqrt{s_NN} = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the v_1(y) slope, dv_{1}/dy|_{y=0}, for deuterons, where y is the rapidity, is extracted for semi-central collisions (10-40\% centrality) and compared to that of protons. While the v_1(y) slopes of protons are generally negative for sqrt{s_NN} > 10 GeV, those for deuterons are consistent with zero, a strong enhancement of the v_1(y) slope of deuterons is seen at the lowest collision energy (the largest baryon density) at sqrt{s_NN} =$ 7.7 GeV. In addition, we report the transverse momentum dependence of v_1 for protons and deuterons. The experimental results are compared with transport and coalescence models