The VII-th International Conference on the Initial Stages of High-Energy Nuclear Collisions : Initial Stages 2023

Disentangling centrality bias and final state effects in small system collisions

Not scheduled

2h

Københavns Universitetsbibliotek Nord

Poster Collective dynamics from small to large systems Reception and poster session

Speaker

Niveditha Ramasubramanian (Stony Brook University)

Description

Centrality dependence of nuclear modification factor of Pi0 in d+Au collision shows a suppression in most central events, which is expected if QGP droplets are formed in small systems, but also a strange enhancement in peripheral collisions. To disentangle possible biases in centrality determination from energy loss , PHENIX presents invariant yields of high pT Pi0 and direct photons as a function of event activity for d+Au collisions at 200GeV.
It is found that the ratio of directγ-to-π0 of d+Au for different centrality classes are consistent with minimum bias and with that of p+p except for most central events. In other words, any possible bias in centrality determination is also present in direct photon yields and thus they cancel in the ratio. Furthermore, a double ratio is defined by normalising Raa of Pi0 with Raa of direct photons. As initial state effects are expected to be similar for the production of Pi0 and direct photons, these also cancel in this double ratio. By doing this, a clean signal is obtained to study the final state effects. A suppression of 20% with a 4.5 sigma confidence is obtained for most central events with respect to minimum bias along with a strong agreement between peripheral events and minimum bias.