Quark Matter 2018

Corona effect in AA collisions at LHC and RHIC

15 May 2018, 17:00

2h 40m

First floor and third floor (Palazzo del Casinò)

Poster Jet modifications and high-pT hadrons Poster Session

Speaker

Dr Vladislav Pantuev (INR, RAS)

Description

Following our earlier finding based on RHIC data about the dominant jet production from nucleus corona region, we reconsider this effect in nucleus-nucleus collisions at LHC energy. Our hypothesis was based on the experimental data, which raised the idea of a finite formation time for the produced medium. At RHIC energy and in low density corona region this time reaches about 2~fm/c. In the center of interaction region it's about 0.7 fm/c. All observed high $p_t$ particles are produced in the corona region and have a chance to escape during this 2~fm/c. After that, the formed high density matter absorbs all jets. Following this hypothesis, the nuclear modification factor $R_{AA}$ should be independent on particle momentum and be flat versus $p_t$. At the same time, we can describe at RHIC the finite azimuthal anisotropy of high $p_t$ particles, $v_2$. A separate prediction held that, at LHC energy, the formation time in the corona region should be two times smaller, about 1~fm/c. New data at LHC show that $R_{AA}$ is not flat and is rising with $p_t$. We add to our original hypothesis an assumption that a fast parton traversing the produced medium loses the fixed portion of its energy. A shift of about 7~GeV from the original power law $p^{-6}$ production cross section in $pp$ explains well all the observed $R_{AA}$ dependencies at all centrality. The shift of about 7~GeV is also valid at RHIC energy, where the cross section follows a power law with about $p^{-8}$ and this shift explains a very slow rise of $R_{AA}$ seen for neutral pions with $p_t$ above 15~GeV/c. We also show that the observed at LHC dependence of $v_2$ at high $p_t$ and our previous predictions agree. It is very attractive to call this value of 7 GeV as a parton binding energy.

Presentation materials

Corona_RHIC_LHC.pdf