With a multi-phase transport (AMPT) model,a γ-jet with known production point and momentum is triggered to search for the origin of double-peak structure in di-hadron azimuthal correlation in central Au+Au collisions at RHIC energy.The different configurations of triggered γ-jet produce different shapes of medium responses.The key of the double-peak structure is found to be a strong shadowing effect of dense core,which is related to transverse expansion and radial flow of partonic matter.
Multi-gap Resistive Plate Chamber (MRPC) is a new generation of gas detector with good tim-ing and spacial resolution, whose technique is widely applied in some recent high energy (nuclear) physics experiments. In this letter, we report a long-strip two-end readout MRPC and its test beam performance. The measurements show that the long-strip performs a transmission line characteristic and the impedance is independent of the length of strip. The MRPC module we developed is presented to gain a timing resolution of ～80 ps and a spacial resolution of ～6.4 mm. The possible application of the MRPC is also discussed.
The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α, γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12 C(α, γ)16 O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α, γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α, γ)16 O reaction rate at T9=0.2 is (8.78 ± 1.52) × 1015 cm3s-1mol-1. Some comparisons and discussions about our new 12 C(α, γ)16 O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α, γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α, γ)16O reaction rates.
In order to trace azimuthal angle dependence of the initial interaction in ultra-relativistic heavy ion collision, two azimuthal multiplicity-correlation patterns — neighboring and fixed-to-arbitrary angular- bin correlation patterns — are suggested. From the simulation of Au + Au collisions at SNN = 200 GeV by using the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without string melting, we observe that the correlation patterns change gradually from out-of-plane preferential one to in- plane preferential one when the centrality of collision shifts from the central collision to peripheral collision, meanwhile the anisotropic collective flow v2 keeps positive in all cases. This regularity is found to be collision energy independent. The physics behind the two opposite trends of correlation patterns, in particular, the presence of out-of-plane correlation patterns at RHIC energy, are discussed.
Production and properties of φ-meson under the extreme hot dense matter which is formed in Au + Au collisions at RHIC energy have been briefly reviewed.The issues are focused on transverse momentum (p T ) spectra of φ,elliptic flow of φ,nuclear modification factor of φ,the ratio of Ω(p T )/φ(p T ) versus p T,the ratio of Ω(p T /3)/φ(p T /2) versus p T /n q,spin alignment of φ and the enhancement of φ etc.These observables give the significant information of the strange quark dynamics in hot dense matter under the extreme condition.
The centrality, azimuthal and rapidity dependence of two-particle transverse-momentum correlations are studied for Au-Au collision at 200 GeV using RQMD (relativistic quantum molecular dynamics) with and without final hadron re-scattering models. The influences of the re-scattering effects on the measured correlations are discussed. The results are compared with those from current heavy ion experiments.
