The transverse energy distribution in hadron-lead collisions

The transverse energy cross-sectiondσ/dE _T has been measured in the pseudorapidity region 0.6<η<2.4 for hadron-lead collisions at 200 GeV/c incident hadron momentum. TheE _T distribution extends to 40 GeV, which is twice the kinematic limit forp-p collisions at the same incident beam momentum. The distribution ofE _T is found to shift towards low pseudorapidities with increasing total transverse energy.     

The influence of flow on the jet quenching power in heavy-ion collisions

The flow pattern and evolution of the medium created in ultrarelativistic heavy ion collisions can have significant influence on the energy loss of hard partons traversing the medium. We demonstrate that within a range of assumptions for longitudinal and transverse flow which are all compatible with the measured hadronic single particle distributions, the quenching power of the medium can vary within a factor five. Thus, the choice of the medium evolution is one of the biggest uncertainties in jet quenching calculations and needs to be addressed with some care.     

Multiparton collisions and multiplicity distribution in high-energy collisions

We discuss the multiplicity distribution for the highest accessible energies of pp- and -interactions from the point of view of multiparton collisions. The inelastic cross sections for single, σ₁, and multiple (double and, presumably, triple), σ₂ parton collisions are calculated from the analysis of experimental data on the multiplicity distribution up to Tevatron energies. It is found that σ₁ becomes energy independent while σ₂ increases with for GeV. The observed growth of p with multiplicity is attributed to the increasing role of multiparton collisions for the high-energy -inelastic interactions. σ₂₊₃ reproduces quite well the cross-section for the mini-jet production.     

Dispersion of the multiplicity distribution in hadron-nucleus collisions

It is argued that the measurements of the dispersion of the multiplicity distribution in hadron-nucleus collisions favour the processes of particle production in a sequence of collisions of the incident hadron with target nucleons. On the other hand, generation of particles on groups of nucleons treated as single units leads to large discrepancies.     

Isospin effects on squeeze-out flow in heavy-ion collisions

The squeeze-out flow in reactions of ¹²⁴Sn + ¹²⁴Sn and ¹²⁴Ba + ¹²⁴Ba at different incident energies for different impact parameters is investigated by means of an isospin-dependent quantum molecular dynamics model. For the first time, it is found that the more neutron-rich system (¹²⁴Sn + ¹²⁴Sn) exhibits weaker squeeze-out flow. This isospin dependence of the squeeze-out flow is shown to mainly result from the isospin dependence of nucleon-nucleon cross-section and the symmetry energy. Received: 14 March 2000 / Accepted: 29 September 2000     

The distribution of grey particles in very high-energy hadron-nucleus collisions

On its passage through the nucleus a very high-energy hadron strikes several target nucleons. These recoil nucleons initiate an intranuclear cascade. “Grey particles”, mostly protons with energy between 40 and 400 MeV result from the cascade. We can describe the mean number and distribution of grey particles by truncating the intranuclear cascade after the second generation. The number N_g of grey particles is very simply related to the number ν of initial hadron-nucleon collisions: , where a is a numerical constant close to 1.     

Note on the impact parameter analysis of high-energy proton-proton collisions

Following a prior analysis of measured pp elastic differential cross-sections, the impact parameter representation in terms of profile functions is calculated from two different parametrizations of single diffractive dissociation data. The derivative of this quantity, with respect to the collision energy squared s, measures the growth rate of the reaction's blackness. Its distribution in impact parameter space allows detailed insight into the growth pattern of the total diffractive cross-section and the approaching unitarity limit. Comparing the results with the elastic case, the different mechanisms of unitarization of two parametrizations are discussed. Received: 19 January 2001 / Accepted: 11 July 2001     

Role of the cascade interactions on the multiplicity distribution in hadron-nucleus collisions

Multiplicity distribution in proton-nucleus (p-A) collisions are investigated by the use of the Monte Carlo event generator MCMHA which has been developed based on the multi-chain model. The comparisons between the calculational results of MCMHA and the data are made through the parameters of negative binomial distributions. We can find nice agreement between them. The interpretation for the difference in the behaviour of 1/k in the backward hemisphere between \(p(\bar p) - p\) andp-A collisions is presented. In this connection, we also discuss the multiplicity ration 〈N〉 _pA /〈N〉 _pN .     

Kaon flow in heavy ion collisions

Using transport models that include explicitly the kaon degree of freedom, we have studied kaon flow, i.e., the average kaon transverse momentum as a function of rapidity, and the associated flow parameter in heavy ion collisions at both SIS and AGS energies. It is found that the pattern of kaon flow in heavy ion collisions is sensitive to the kaon potential used in the model and thus provides a useful means for studying the kaon properties in nuclear medium.     

Nuclear flow in heavy ion collisions

Short overview of the flow phenomenon from the low upto relativistic heavy ion energies is given. Strict difference between spectator and participant flow is emphased. The latter is described by the modification of the nuclear blast model. Thermal source expanding in a plane perpendicular to the line connecting the centers of projectile and target is assumed. Observed dependences of squeeze-out, side-splash and of mean transverse-energy in relativistic heavy-ion collisions on the particle's mass are reproduced. Partioning of initial projectile energy into thermal and compressional parts in²⁰⁹Bi(1 GeV/u)+²⁰⁸Pb and¹⁹⁷Au(150–800 MeV/u)+¹⁹⁷Au collisions is discussed.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.Experimental data obtained at Bi+Pb collisions [6] are the result of the group effort. The contribution of V. Wagner, M. Pachr, Yu. G. Sobolev, R. Simon, S. Hlava, M. umbera as well as of my student R. Pleska, who carried out most of the fits, is gratefully acknowledged. This work was supported by the Granting Agency of the Czech Republic under contract No. 202/93/1144. A.K. gratefully acknowledges support from EC during his stay at KVI Groningen, where part of this work was done.     

A flow paradigm in heavy-ion collisions

The success of hydrodynamics in high energy heavy-ion collisions leads to a flow paradigm, to understand the observed features of harmonic flow in terms of the medium collective expansion with respect to initial state geometrical properties. In this review, we present some essential ingredients in the flow paradigm, including the hydrodynamic modeling, the characterization of initial state geometry and the medium response relations. The extension of the flow paradigm to small colliding systems is also discussed.     

Collective flow in relativistic heavy-ion collisions

A brief introduction is given to the field of collective flow, currently being investigated experimentally at the Relativistic Heavy-Ion Collider, Brookhaven National Laboratory. It is followed by an outline of the work that I have been doing in this field, in collaboration with Nicolas Borghini and Jean-Yves Ollitrault.     

Angular distribution of dileptons in hadronic collisions

The polar and azimuthal angular distributions of the lepton pair produced in hadron-hadron collisions are studied. For large Q_T these are calculated from lowest-order QCD diagrams. For low Q_T we present simple expressions which take into account the effect of primordial quark transverse momentum on the angular distributions.     

Systematics of elliptic flow in heavy-ion collisions

We analyze elliptic flow from SIS to RHIC energies systematically in a realistic dynamical cascade model. We compare our results with the recent data from STAR and PHOBOS collaborations on elliptic flow of charged particles at midrapidity in Au+ Au collisions at RHIC. In the analysis of elliptic flow at RHIC energy, we find a good fitting with data at 1.5 times a scaling factor to our model, which characterizes that the model is required to have extra pressure generated from the subsequent parton scattering after the initial minijet production. In energy dependence of elliptic flow, we notice re-hardening nature at RHIC energies. Both these two observations would probably imply the possible formation of quark-gluon plasma.     

微通道平行流换热器流量分配均匀性研究

微通道平行流换热器以其造价低、重量轻、结构紧凑、换热效果好等诸多优点,在化学工程、石油、制冷等领域均有广阔的应用前景,但是制冷剂流量分配不均匀等问题严重影响了平行流换热器的性能。通过在平行流换热器的基础上设计了一种新的分流板结构,以水为模拟工质,运用数值模拟比较增加分流板前后的各管道流量和总流量分布不均匀度。结果表明:增加分流板以后,各通道流量分布的均匀性能提高4%-20%,速度越大改善越明显,改善后其总流量分配不均匀度比改善前降低了36%～78%。     

Influence of metastable-metastable collisions on electron distribution function in afterglow

The time dependence of the electron distribution function in helium afterglow, for pressures of 60–260 Pa, is calculated for the case in which metastable-metastable reactions are present. The time variation of the shape of the distribution function shows that careful consideration must be made of the time derivative of the distribution function in the Boltzmann equation for the calculation of the rate constant of such reactions from experimentally determined distribution function.     

The flow velocity distribution from the doppler information on a plane in three-dimensional flow

In order to observe and estimate the flow of fluid in three-dimensional space, the pulsed Doppler method has been used widely. However, the velocity information acquired is only the velocity component in the beam direction of the wave even if an observation plane is formed by beam scanning. Accordingly, it is difficult to know the velocity distribution in the observation plane in tree-dimensional flow. In this paper, the new idea for processing the velocity distribution in the beam direction on an observation plane for transposing to flux distribution (flow function method) has been introduced. Further, the flow in an observation domain is divided into two kinds of flows, viz., the base flow which indicates the directivity of the flow in the observation domain and the vortex which is considered a two-dimensional flow. By applying the theory of a stream function to the two-dimensional flow, and by using the physical feature of a streamline to the base flow, the velocity component v which intersects perpendicularly to the beam direction is estimated. The flow velocity distribution in a scanning plane (observation plane) can be known from these two components of velocity, viz., beam direction componentu and perpendicular component to the beam directionv. The principle was explained by an example of the blood flow measurement in normal and abnormal heart chamber, by the ultrasonic Doppler method.