Hydrodynamical Model of Multiparticle Production at Large Transverse Momentum

Abstract

The large transverse momentum phenomena in the central region can be understood by considering the hydrodynamical expansion of a fireball which is formed in the collision of hadrons. The hydrodynamical equation of the hadronic flmd with large transverse velocity is solved analytically in the central region under the appropriate boundary condition. For the case of the relativistic three-dimensional ideal fluid, the resultant particle spectrum EdN/d'p at large transverse momentum has the form s'1'p'i' which is consistent with the ISR data. § l. Introduction Recent experiments of high energy hadron collisions accumulate a large amount of data and reveal many interesting features of multiple production phenomena. One of them is the phenomenon at large transverse momentum. It has been found in the measurements at CERN ISR and NAL that the differential cross section of produced pi-meson at large transverse momentum (Pr>2 Ge V /c) falls less steeply (say, fJr-) than what is expected from an extrapolation of the exponential behavior at low transverse momentum, and the cross section at large fixed tranverse momen­ tum increases strongly with the incident energy, which is also a contrast to the low transverse mom en tun1 results. D The charged particle nmltiplicity as a function of the transverse momentum of photons (rr 0) detected at a center-of-mass angle of 90° is measured. 2> It is reported that the total associated multiplicity increases with the transverse momen­ tum of detected 7r0 and this increase is found almost at a wide polar angle with respect to the beam direction (17c.m.~90') and is observed even in the direction of the detected 7Z0 as well as its opposite side. This fact that a particle with large transverse momentum is accompanied by many particles, is considered to be con­ sistent with the following picture. The particles with large transverse momentum are produced from a fireball which is formed by the collision of particles and is at rest in the center-of-mass frame. In what follovvs, this picture is employed only in the central region, since the largest transverse momentum particles are found m this region and the leading particle effect must be taken into account particularly in the non-central region. It is the purpose of this paper to understand the large transverse momentum phenomena by considering the hydrodynamical expansion