Sensitivity of Pion versus Parton-Jet Nuclear Modification Factors to the Path-Length Dependence of Jet-Energy Loss at RHIC and LHC

We compare the jet-path length and beam-energy dependence of the pion nuclear modification factor and a patton-jet nuclear modification factor at RHIC and LHC, and contrast the predictions based on a linear pQCD and a highly non-linear hybrid AdS holographic model of jet-energy loss. It is found that both models require a reduction of the jet-medium coupling from RHIC to LHC to account for the measured pion nuclear modification factor. In the case of the parton-jet nuclear modification factor, however, which serves as a lower bound for the LO jet nuclear modification factor of reconstructed jets, the extracted data can be characterized without a reduced jet-medium coupling at LHC energies. It is concluded that when the reconstructed jets are sensitive to both quarks and gluons and thus provide more information than the pion nuclear modification factor, their information regarding the jet-medium coupling is limited due to the superposition with NLO and medium effects. Hence, a detailed description of the underlying physics requires both the leading hadron and the reconstructed jet nuclear modification factor. Unfortunately, the results for both the pion and the parton-jet nuclear modification factor are insensitive to the jet-path dependence of the models considered.

Developing crash modification factors for roundabouts using a cross-sectional method

The objective of the current study was to evaluate traffic and geometric features and their influences on the safety performance of roundabouts by developing suitable crash modification factors(CMFs).The cross-sectional method can be applied as an alternative method to estimate the CMFs when before-and-after studies are impractical to apply,e.g.,lack of data from the period after implementing treatments.To accomplish the study objective,CMFs were derived from generalised linear models(GLMs),i.e.,negative binomial(NB)regression,using data collected on regional roundabouts in Toowoomba City,Australia.Six years of crash data from 49 roundabouts included all recorded crashes as well as traffic and geometric features for the entire roundabouts.Several candidate models were developed using the GLMs.Five models were selected based on statistical significance,goodness-of-fit(GOF)measures,and cumulative residual(CURE)analysis.The results show that increasing the number of entry lanes,entry width,entry radius,traffic volume,circulatory roadway width,weaving width,and speed limit have positive effects on roundabout safety.On the other hand,increasing the number of legs,number of exit lanes,exit width,exit radius,weaving length,central island diameters,and presence of fixed object on a central island have negative effects on roundabout safety.The study shows that quantifying the risk factors can support road safety stakeholders to identify safety improvements at roundabouts more effectively and efficiently.

Bayesian spatial modeling to incorporate unmeasured information at road segment levels with the INLA approach:A methodological advancement of estimating crash modification factors

Estimating safety effectiveness of roadway improvements and countermeasures,using cross-sectional models,generally requires large amounts of data such as road geometric and traffic-related characteristics at road segment levels.These models do not consider all confounding crash contributory factors such as driving culture and environmental conditions at the segment level due to a lack of readily available data.This may result in inaccurate models representing actual conditions at road segment levels,followed by erroneous estimations of safety effectiveness.To minimize the effect of not including such variables,this study develops a new methodology to estimate safety effectiveness of roadway countermeasures,based on generalized linear mixed models,assuming zeroinflated Poisson distribution for the response,and adjusting for spatial autocorrelation using the spatial random effect.The Bayesian approach,with Integrated Nested Laplace Approximation,was used to make inference on this model with computational efficiency.Results showed that incorporating a spatial random effect into the models provided better model fit than non-spatial models;hence,estimated safety effectiveness based on such models is more accurate.The proposed approach is a methodological advancement in traffic safety,which allows evaluation of safety effectiveness or roadway improvements when data are not readily available.

Nuclear modification factor for J/ψ production in nucleus-nucleus collisions

The STAR Collaboration has offered an eminent nuclear modification factor of J/ψ at high p T and midrapidity produced in Cu-Cu collisions at sNN^（1/2） = 200 GeV. Recalling a prediction, we can understand that the feature of high-pT nuclear modification factor is related to cc produced by 2 → 1 and 2 → 2 partonic processes in deconfined matter, particularly in the prethermal stage and to the recombination of c and c. The nuclear modification factor at high p T is sensitive to the earliest form of deconfined matter that does not have a temperature.

Study on open charm hadron production and angular correlation in high-energy nuclear collisions

We study the production and angular correlationof charm hadrons in hot and dense matter produced in high-energy nuclear-nuclear collisions within a multiphasetransport model(AMPT).By triggering additional charm-anticharm quark pair production in the AMPT,the modeldescribes the D^0 nuclear modification factor in the low andintermediate pr regions in Au+Au collisions at√VSNN=200 GeV reasonably well.Further exploration of the D^0 pair azimuthal angular correlation for different centralitiesshows clear evolution from low-multiplicity to high-mul-tiplicity events,which is associated with the number ofcharm quark interactions with medium partons duringAMPT transport.

Safety effectiveness of roadway conversion with a two way left turn lane

In urban or suburban areas with a large number of access points, four-lane undivided highways are prone to crashes due to left-turning and through movements in a single lane. Many studies recommended expensive countermeasures like conversion from undivided to divided road with physical separation. One inexpensive alternative is reconfiguring the existing roadways by either increasing or decreasing the number of lanes. This study investigated the safety impact of converting four lane undivided roadways （4U） to five lane undivided roadways （ST） with a two way left turn lane （TIkrLTL）. This study used Empirical Bayes method to determine the safety impact of this inexpensive countermeasure. In this study, data from eight sites from Louisiana were collected for investigation, and site- specific crash modification factor （CMF） values were calculated. Although ST is usually not preferable due to its exposure of higher number of crashes in the existing literature, the findings of the current study indicated a positive safety impact. The benefit-cost ratio of this conversion ranges from 97 to 379. The current findings indicate that conversion of 4U to 5T is a feasible inexpensive solution for urban roadways with lower volume and a limited number of driveways.

Jet production at next-to-leading order in p+Au collisions at the RHIC

We calculate jet productions in p＋Au collisions at the RHIC at next-to-leading order with perturbative QCD. Inclusive jet transverse energy spectrum, dijet invariant mass spectrum, dijet angular distribution, and corresponding nuclear modification factors for the three observables in p＋Au collisions at √s=200 GeV are given, where the initial-state cold nuclear matter （CNM） effects are included by taking advantage of four parametrization sets of nuclear parton distribution functions （nPDFs） - EPS, nCTEQ, HKN and DS. We demonstrate that inclusive jet transverse energy （ET） spectrum, dijet invariant mass （MJJ） spectrum with all 4 nPDFs are increased at low ET or MJJ, whereas at high ET or MJJ large deviation of results with different nPDFs is observed. It is found that the dijet angular distributions in p＋Au collisions do not vary relative to those in p＋p collisions for all 4 nPDFs.

Centrality dependence of pT spectra for identified hadrons in Au+Au and Cu+Cu collisions at (~SNN)^(1/2)=200 GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidityin Au＋Au collisions at √sNN=200GeV is systematically studied in a quark combination model. The PTspectra of π^±, K^±, p（p） and A（A） in different centrality bins and the nuclear modification factors （Rcp） forthese hadrons are calculated. The centrality dependence of the average collective transverse velocity （β （r）） for the hot and dense quark matter is obtained in Au＋Au collisions, and it is applied to a relative smallerCu＋Cu collision system. The centrality dependence of PT spectra and the Rcp for π^0, Ks^0 and A in Cu-bCucollisions at √sNN = 200 GeV are well described. The results show that （β （r）〉is only a function of the numberof participants Npart and it is independent of the collision system.

Study of K^(*)(892)^(0)andФ(1020)meson production in proton–proton and Pb–Pb collisions at√S_(NN)=2.76 TeV

In this paper,we describe a study of charged particle yield as a function of pT for K^(*)(892)0 and phgr(1020)mesons in proton–proton(pp)and Pb–Pb collisions at√S_(NN)=2.76 TeV in the central rapidity region of|y|<0.5,in a pT range of 0<pT<15 GeV c^(−1)in pp collisions and in a pT range of 0<pT<20 GeV c−1 in Pb-Pb collisions.We also investigated a very important ratio,the nuclear modification factor,to study the effects of the medium in the most central region,i.e.0%–5%centrality.For data simulation,we used the EPOS-LHC and EPOS-1.99 models.To check the validity of these models'simulations,we compared the data obtained from these Monte Carlo simulation programs with ALICE experimental data for√S_(NN)=2.76 TeV.It was concluded that the models'predictions for the phgr-meson in pp and for the most central Pb-Pb collisions disagreed with the ALICE data,and that the difference increased with pT.This may be connected with the essential role of collective parton behaviors which could not have been taken into account by the models.For K^(*)0 mesons,both programs gave almost the same predictions,and with pT in the interval pT>3 GeV c^(−1),the predictions were very close to the experimental data.Both models gave higher predictions for the soft pT interval and lower predictions for the hard interactions.The values of the RAA distributions were lower than unity and both models were very close to the ALICE data.It is very interesting that the models were not able to describe the pT distributions,but they gave good predictions for their ratios.This may possibly be due to parton collective behaviors.We observed some additional suppression of K^(*)0 at low values of pT with respect to phgr-mesons,which may be related to the role of the masses of the particles in soft interactions.The rising trend for R_(AA)in the region from pT=10 GeV c^(−1)to 20 GeV c^(−1) observed by the ALICE experiment was absent for theФ-mesons.