Collective flow in 2.76 A TeV and 5.02 A TeV Pb+Pb collisions

In this paper, we study and predict flow observables in 2.76 A TeV and 5.02 A TeV Pb +Pb collisions, using the iEBE-VISHNU hybrid model with TRENto and AMPT initial conditions and with different forms of the QGP transport coefficients. With properly chosen and tuned parameter sets, our model calculations can nicely describe various flow observables in 2.76 A TeV Pb +Pb collisions, as well as the measured flow harmonics of all charged hadrons in 5.02 A TeV Pb +Pb collisions. We also predict other flow observables, including $v_n(p_T)$ of identified particles, event-by-event $v_n$ distributions, event-plane correlations, (Normalized) Symmetric Cumulants, non-linear response coefficients and $p_T$-dependent factorization ratios, in 5.02 A TeV Pb+Pb collisions. We find many of these observables remain approximately the same values as the ones in 2.76 A TeV Pb+Pb collisions. Our theoretical studies and predictions could shed light to the experimental investigations in the near future.Comment: 17 pages, 11 figure

THE EFFECTS OF FUNDAMENTAL MIXTURE PARAMETERS ON HOT-MIX ASPHALT PERFORMANCE PROPERTIES

Asphalt pavements are composed of three components: aggregate, asphalt binder, and air. In the process of plant production and on-site construction, the construction quality can vary in the three component and the variability can further affect a pavement\u27s future performance.. This research identifies aggregate gradation, binder content, and air voids content as the fundamental parameters. Understanding the fundamental parameters\u27 influence on the HMA mixture\u27s performance properties can provide valuable information on how to improve the current quality insurance practice. The objective of this study is to conduct well-controlled experiments to investigate how mix gradation, air voids and small range binder content deviation from design binder content can affect the performance properties of asphalt concrete. In this study, three aggregate sources were utilized, and two gradations (fine-graded and coarse-graded) were tested from each aggregate source. Two levels of binder content and air voids content were used to represent the construction variability levels of binder content and density, respectively. The three aspects of mixture performance that were evaluated include rutting, tensile cracking and moisture susceptibility. It is found that aggregate gradation is significant to rutting and IDT performance. In rutting, the gradation effect is aggregate specific. The effect of gradation on ITS can be reflected by the design binder content, which is closely related to the VMA value of the aggregate gradation. Therefore, the rutting performance seems more sensitive to gradation variation than the tensile strength of a mixture. Binder content variation in a permissible range can statistically affect the rutting and IDT strength performance. A \u27binder content window\u27 is determined from a fracture energy point of view; however, the rutting performance should not be compromised. On pavement density variation, the study showed that reducing air voids content can increase the mixtures\u27 engineering properties, both rutting and ITS. Several statistical regression models were developed using the fundamental parameters. The equations can effectively summarize the experimental data set, creating quantitative relationships that can be used to predict the response variables

One fluid might not rule them all

In this proceeding, we present our recent investigations on hydrodynamic collectivity in high-multiplicity proton--proton collisions at $\sqrt{s}=$ 13 TeV using the VISHNU hybrid model with different initial condition models, called HIJING, super-MC and TRENTo. We find that with carefully tuned parameters, hydrodynamic simulations can give reasonable descriptions of the measured two-particle correlations. However, multi-particle single and mixed harmonics cumulants can not be described by hydrodynamics with these three initial conditions, even for the signs in a few cases. Further studies show that the non-linear response plays an important role in the hydrodynamic expansion of the p--p systems. Such an effect can change $c_2\{4\}$ from a negative value in the initial state to a positive value in the final state. The failure of the hydrodynamic description of multi-particle cumulant triggers the questions on whether the hydrodynamics can rule all collision systems, including p--p collisions at the LHC.Comment: 4 pages, 4 figures, Quark Matter 2020 conference proceedings (accepted

The effects of pseudorapidity-dependent observables on (3+1)D Bayesian Inference of relativistic heavy-ion collisions

This proceeding highlights the effects of pseudorapidity-dependent charged hadron observables $dN^\mathrm{ch}/d\eta$ and $v_2^{\rm ch}(\eta)$ in Au+Au collisions at 200 GeV on constraining the initial-state nuclear stopping for the beam remnants and the effective QGP specific shear viscosity in a recent Bayesian inference analysis using an event-by-event (3+1)D hydrodynamics + hadronic transport theoretical framework.Comment: 4 pages; 1 figure; Conference proceedings for Quark Matter 2023, Sept 2023, Houston, Texas, US

Exploring the partonic collectivity in small systems at the LHC

Using the Hydro-Coal-Frag model that combines hydrodynamics at low $p_{\rm T}$, quark coalescence at intermediate $p_{\rm T}$, and the LBT transport model at high $p_{\rm T}$, we study the spectra and elliptic flow of identified hadrons in high multiplicity p--Pb and p--p collisions at the Large Hadron Collider (LHC). In p--Pb collisions, the Hydro-Coal-Frag model gives a good description of the differential elliptic flow over the $p_{\rm T}$ range from 0 to 6 GeV and the approximate number of constituent quark (NCQ) scaling at intermediate $p_{\rm T}$. Although Hydro-Coal-Frag model can also roughly describe the elliptic flow in high multiplicity p--p collisions with the quark coalescence process, the larger contribution from the string fragmentations leads to a notable violation of the NCQ scaling of $v_2$ at intermediate $p_{\rm T}$ as observed in the experiment. Comparison runs of the Hydro-Frag model without the coalescence process demonstrate that regardless the parameter adjustments, the Hydro-Frag model cannot simultaneously describe the $p_{\rm T}$ spectra and the elliptic flow of identified hadrons in either p--Pb collisions or p--p collisions. The calculations in this paper thus provide support for the existence of partonic degrees of freedom and the possible formation of the QGP in the small systems created at the LHC.Comment: 9 pages, 3 figure

An Investigation of the Significance of Residual Confounding Effect

Background: Observational studies are commonly conducted in health research. However, due to their lack of randomization, the estimated associations between the outcome and the exposure can be affected by unmeasured confounding factors. It is important to determine how likely a significant association observed between an outcome variable and a noncausally related exposure may be introduced by residual confounding factors. Methods: A simulation approach is developed based on the sufficient cause model to test the likelihood of significant associations observed between a noncausally related exposure and the outcome. Results: Based on the estimates from all 500 replicates, the association between the exposure and the outcome is found to be significant in 386 (77%) replicates when all confounders (component causes) are controlled for in the model. However, when a subset of real component causes and some noncausal factors are controlled for in the model, the association between exposure and the outcome becomes significant in 487 (97%) replicates. Conclusion: Even when all confounding factors are known and controlled for using conventional multivariate analysis, the observed association between exposure and outcome can still be dominated by residual confounding effects. Therefore, an observed significant association apparently provides limited evidence for a causal relationship