Speaker
Description
The initial motivation to study d+Au collisions was to use it as a control experiment to decouple the effects of cold nuclear matter effects in the nuclear modification factors (RAA) obtained from heavy ion collisions like Au+Au. Since the year 2013, there has been a growing evidence of the possibility of formation of Quark Gluon Plasma (QGP) in small systems. Suppression in the nuclear modification factor RAA of Pi0 and jets is observed in the central d+Au collisions, which could be attributed to formation of QGP droplets but, along with this, the results also indicate a counter-intuitive enhancement of RAA in peripheral events.
Direct photons are transparent to the QGP and thus RAA of direct photons at high pT should be unity for all classes of event activity. We observe that, in d+Au system, for central collisions the RAA of direct photons is close to unity but for peripheral collisions there is a significant enhancement which matches the degree of enhancement that is observed in RAA of Pi0s. This indicates a bias in centrality determination using Glauber model for small system collisions.
Furthermore, the direct photon measurement for d+Au can be used to experimentally determine the effective number of binary collisions Nexp for each event sample. By using this Nexp, the RAA of pi0 is re-obtained and this is close to unity for peripheral collisions but still show a significant suppression in central collisions which could be an indication of a formation of QGP droplets in central d+Au collisions.
In this talk, I will highlight preliminary approved results from d+Au collisions and the status of analysis in p+Au and 3He+Au system.
| Session | Heavy Ions and QCD |
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