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In this work, we investigate the collective flow development in high energy proton proton (pp) collisions with a multiphase transport model (AMPT) based on PYTHIA8 initial conditions with a sub-nucleon structure. It is found that the PYTHIA8 based AMPT model can reasonably describe both the charged hadron productions and elliptic flow experimental data measured in pp collisions at $\sqrt{s}=13$ TeV. By turning on the parton and hadron rescatterings in AMPT separately, we find that the observed collective flow in pp collisions is largely developed during the parton evolutions, while no significant flow effect can be generated with the pure hadronic rescatterings. It is also shown that the parton escape mechanism is important for describing both the magnitude of the two-particle cumulant and the sign of the four-particle cumulants. We emphasize that the strong mass ordering of the elliptic flow results from the coalescence process in the transport model can thus be regarded as unique evidence related to the creation of deconfined parton matter in high energy pp collisions.

The impact of nuclear structure has garnered considerable attention in the high-energy nuclear physics community in recent years. This work focuses on studying the potential nuclear cluster structure in $^{16}\text{O}$ nuclei using anisotropic flow observables in $\rm O+O$ collisions at 200 GeV. Employing an improved AMPT model with various cluster structure configurations, we find that an extended effective parton formation time is necessary to align with the recent STAR experimental data. In addition, we reveal that the presented flow observables serve as sensitive probes for differentiating configurations of $\alpha$-clustering of $^{16}\text{O}$ nuclei. The systematic AMPT calculations presented in this paper, along with comprehensive comparisons to forthcoming experimental measurements at RHIC and the LHC, pave the way for a novel approach to investigate the $\alpha$-clustering structure of $^{16}\text{O}$ nuclei using $\rm O+O$ collisions at the ultra-relativistic energies., Comment: 10 pages, 11 figures

We study the production of $D^0$ meson in $p$+$p$ and $p-$Pb collisions using the improved AMPT model considering both coalescence and independent fragmentation of charm quarks after the Cronin broadening are included. After a detailed discussion of the improvements implemented in the AMPT model for heavy quark production, we show that the modified AMPT model can provide good description of $D^0$ meson spectra in $p-$Pb collisions, the $Q_{\rm pPb}$ data at different centrality and $R_{\rm pPb}$ data in both mid- and forward (backward) rapidities. We also studied the effects of nuclear shadowing and parton cascade on the rapidity dependence of $D^{0}$ meson production and $R_{\rm pPb}$. Our results indicate that having the same strength of the Cronin (i.e $\delta$ value) obtained from the mid-rapidity data leads to a considerable overestimation of the $D^0$ meson spectra and $R_{\rm pPb}$ data at high $p_{T}$ in the backward rapidity. As a result, the $\delta$ is determined via a $\chi^2$ fitting of the $R_{\rm pPb}$ data across various rapidities. This work lays the foundation for a better understanding of cold-nuclear-matter (CNM) effects in relativistic heavy-ion collisions.

Fluctuations of conserved charges, such as the net-baryon number fluctuations, are influenced by different dynamical evolution processes. In this paper, we investigate the influence of hadronic rescatterings on different orders of cumulants of the net-baryon number distribution. At the start of hadronic rescatterings, we introduce net-baryon number distributions reconstructed based on net-baryon cumulants of different orders obtained from computation in functional renormalization group (FRG), where the distributions were constructed using the maximum entropy method. This way we introduce the critical fluctuations of Quantum Chromodynamics (QCD) into the AMPT model. Firstly, we find that hadronic rescatterings have distinct effects on cumulant ratios of different orders for the net-baryon number. Secondly, we observe that the effect of hadronic rescatterings is more significant for critical fluctuations than dynamical fluctuations, because the two-, three- and four-particle correlation functions due to critical fluctuations are weakened more significantly by hadronic rescatterings., Comment: 10 pages, 8 figures

We present the first study of collectivity inside jets with high charged multiplicity $N^j_{\rm ch}$ in proton-proton collisions at the Large Hadron Collider. By incorporating final-state partonic and hadronic interactions through cascade models among jet shower partons and final hadrons, we investigate and compare to the CMS experimental data on multiplicity distribution, pseudorapidity distribution, and elliptic anisotropy coefficient $v^{j}_2$ of two-particle correlations within the jet. We show that final-state partonic interactions are essential for producing the flow-like long-range correlation, which leads to the enhanced tail in the $N^j_{\rm ch}$ dependence of $v^{j}_2$ above the non-flow correlation from jet parton showering at high multiplicities ($N^j_{\rm ch}\gtrsim70$) as observed in the CMS experimental data. In addition, we provide predictions for the pseudorapidity-gap dependence of $v^{j}_2$ that can be tested in future experimental measurements., Comment: 6 pages, 4 fiures