Abstract
STAR’s measurements of directed flow () around midrapidity for , , , , and in collisions at are presented. A negative slope is observed for most of produced particles (, , , and ). In 5%–30% central collisions, a sizable difference is present between the slope of protons and antiprotons, with the former being consistent with zero within errors. The excitation function is presented. Comparisons to model calculations (RQMD, UrQMD, AMPT, QGSM with parton recombination, and a hydrodynamics model with a tilted source) are made. For those models which have calculations of for both pions and protons, none of them can describe for pions and protons simultaneously. The hydrodynamics model with a tilted source as currently implemented cannot explain the centrality dependence of the difference between the slopes of protons and antiprotons.
- Received 16 December 2011
DOI:https://doi.org/10.1103/PhysRevLett.108.202301
© 2012 American Physical Society