高能重离子碰撞中心快度区鉴别粒子的平均横动量

末态粒子的平均横动量T>是高能重离子碰撞实验中的一个重要观测量.它反映了软质强子的特性和热核物质的性质,对其研究有助于获取碰撞系统的演化信息与规律.基于相对论重离子对撞机(RHIC)上的STAR、PHENIX实验组和大型强子对撞机(LHC)的ALICE实验组提供的金核-金核(Au+Au)和铅核-铅核(Pb+Pb)碰撞中心快度区实验数据,唯象公式能很好地描述不同碰撞能量下,鉴别粒子平均横动量T>随碰撞中心度、每核子对的平均碰撞次数、每核子对平均产生的带电粒子多重数赝快度密度及每次碰撞平均产生的带电粒子多重数赝快度密度的依赖关系.结果表明,鉴别粒子平均横动量T>与碰撞中心度呈线性关系,而与每核子对的平均碰撞次数2N_(coll)/N_(part)、每核子对平均产生的带电粒子多重数赝快度密度2/N_(part)dN_(ch)/dη及每次碰撞平均产生的带电粒子多重数赝快度密度1/N_(coll)dN_(ch)/dη呈幂律关系.同时,发现鉴别粒子平均横动量T>与碰撞中心度以及每核子对的平均碰撞次数唯象公式中的拟合参数与碰撞能量呈现非常好的幂律函数关系.因此,碰撞中心度及每核子对的平均碰撞次数是研究鉴别粒子平均横动量的优选物理量.本文结果可用于对实验上在其他碰撞能量下鉴别粒子平均横动量的预测.

Controlling the Worldwide Chaotic Spreading of COVID-19 through Vaccinations

The striking differences and similarities between the “Spanish-flu” of 1918 and the Coronavirus disease of 2019 (COVID-19) are analyzed. Progress in medicine and technology and in particular the availability of vaccines has decreased the death probability from about 2% for the Spanish-flu, to about 10-4 in the UK and 10-3 in Italy, USA, Canada, San Marino and other countries for COVID-19. The logistic map reproduces most features of the disease and may be of guidance for predictions and future steps to be taken in order to contrast the virus. We estimate 6.4 × 107 deceases worldwide without the vaccines, this value decreases to 1.6 × 107 with the current vaccination rate. In November 2021, the number of deceased worldwide was 5.1 × 106. To reduce the fatalities further, it is imperative to increase the vaccination rate worldwide to at least 120 millions/day and the AstraZeneca vaccine due to its efficacity and cost is a possible route to accomplish this.

Triple α-particle resonances in the decay of hot nuclear systems

The Efimov(Thomas) trimers in excited 12 C nuclei, for which no observation exists yet, are discussed by means of analyzing the experimental data of 70(64)Zn(64 Ni)+ 70(64)Zn(64 Ni) reactions at the beam energy of E/A = 35 MeV/nucleon. In heavy ion collisions, a-particles interact with each other and can form complex systems such as 8 Be and 12 C. For the 3 a-particle systems,multi-resonance processes give rise to excited levels of 12 C. The interaction between any two of the 3 a-particles provides events with one, two or three 8 Be. Their interfering levels are clearly seen in the minimum relative energy distributions. Events with the three a-particle relative energies consistent with the ground state of 8 Be are observed with the decrease of the instrumental error for the reconstructed 7.458 MeV excitation level in 12 C, which was suggested as the Efimov(Thomas) state.

The spin-isospin decomposition of the nuclear symmetry energy from low to high density

The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter.

Four α correlations in nuclear fragmentation: a game of resonances

Heavy ion collisions near the Fermi energy produce a‘freezout’region where fragments appear and later decay,emitting mainly neutrons,protons,alpha particles,and gamma rays.These decay products carry information about the decaying nuclei.Fragmentation events may result in high yields of boson particles,especially alpha particles,and may carry important information about the nuclear Bose Einstein condensate(BEC).We study‘in medium’fourαcorrelations and link them to the‘fission’of 16O in two 8Be in the ground state or 12C*(Hoyle state)+α.Using novel techniques for the correlation functions,we confirm the resonance of 16O at 15.2 MeV excitation energy,and the possibility of a lower resonance,close to 14.72 MeV.The latter resonance is the result of allαparticles having 92 keV relative kinetic energies.