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Register a new userImportance of initial and final state effects for azimuthal correlations in p+Pb collisions
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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.
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In a framework of a semi-analytic model with longitudinally extended strings of fluctuating end-points, we demonstrate that the rapidity spectra and two-particle correlations in collisions of Pb-Pb, p-Pb, and p-p at the energies of the Large Hadron Collider can be universally reproduced. In our approach, the strings are pulled by wounded constituents appearing in the Glauber modeling at the partonic level. The obtained rapidity profile for the emission of hadrons from a string yields bounds for the distributions of the end-point fluctuations. Then, limits for the two-particle-correlations in pseudorapidity can be obtained. Our results are favorably compared to recent experimental data from the ATLAS Collaboration.
In high energy heavy ion collisions at RHIC there are important aspects of the medium induced dynamics, that are still not well understood. In particular, there is a broadening and even a double hump structure of the away-side peak appearing in azimuthal correlation studies in Au+Au collisions which is absent in p+p collisions at the same energies. These features are already present but suppressed in p+p collisions: 2 to 3 parton processes produce such structures but are suppressed with respect to 2 to 2 processes. We argue that in A+A collisions the different geometry for the trajectories of 3 as opposed to 2 particles in the final state, together with the medium induced energy loss effects on the different cross sections, create a scenario that enhances processes with 3 particles in the final state, which gives on average this double hump structure.
We study the correlations of D mesons produced in $p$+$p$ and $p$+Pb collisions. These are found to be sensitive to the effects of the cold nuclear medium and the transverse momentum ($p_T$) regions we are looking into. In order to put this on a quantitative footing, as a first step we analyse the azimuthal correlations of D meson-charged hadron(Dh), and then predict the same for D meson -anti D meson ($Doverline{D}$) pairs in $p$+$p$ and $p$+Pb collisions with strong coupling at leading order $cal{O}$($alpha_{s}^{2}$) and next to leading order $cal{O}$($alpha_{s}^{3}$) which includes space-time evolution (in both systems), as well cold nuclear matter effects (in $p$+Pb). This also sets the stage and baseline for the identification and study of medium modification of azimuthal correlations in relativistic collision of heavy nuclei at the Large Hadron Collider.
In this paper, production of ${rm W}^{pm}$ and ${rm Z}^{0}$ vector bosons in p-p, p-Pb (Pb-p), and Pb-Pb collisions at $sqrt{s_{rm NN}}=5.02$ TeV is dynamically simulated with a parton and hadron cascade model PACIAE. ALICE data of ${rm Z}^{0}$ production is found to be reproduced fairly well. A prediction for ${rm W}^{pm}$ production is given in the same collision systems, at the same energy and at the same energy. An interesting isospin-effect is observed in the sign-change of $mu^{pm}$ charge asymmetry in pp, pn, np, and nn collisions and in minimum bias p-Pb, Pb-p and Pb-Pb collisions at $sqrt{s_{rm NN}}=5.02$ TeV, respectively.
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