We study the influence and interplay of initial state and final state effects in the dynamics of small systems, focusing on azimuthal correlations at different multiplicities. To this end we introduce a new model, matching the classical Yang-Mills dynamics of pre-equilibrium gluon fields (IP-GLASMA) to a perturbative QCD based parton cascade for the final state evolution (BAMPS) on an event-by-event basis. Depending on multiplicity of the event, we see transverse momentum dependent signatures of the initial, but also the final state in azimuthal correlation observables, such as $v_2leftlbrace 2PCrightrbrace(p_T)$. In low-multiplicity events, initial state correlations dominate for transverse momenta $p_T>2~mathrm{GeV}$, whereas in high-multiplicity events and at low momenta final state interactions dominate and initial state correlations strongly affect $v_2leftlbrace 2PCrightrbrace(p_T)$ for $p_T>2~mathrm{GeV}$ as well as the $p_T$ integrated $v_2leftlbrace 2PCrightrbrace$. Nearly half of the final pT integrated $v_2leftlbrace 2PCrightrbrace$ is contributed by the initial state in low-multiplicity events, whereas in high-multiplicity the share is much less. Based on Ref. [1], we are now able to carry out a systematic multiplicity scan, probing the dynamics on the border of initial state dominated to final state dominated - but not yet hydrodynamic regime.
تحميل البحث