Isospin effect on elliptical flow for mass asymmetric nuclear collisions

Collective flow is the measure of the transverse motion imparted to the particles and fragments during the collision of two nuclei. Among the different kind of collective flow, elliptical flow enjoys the special status due to its sensitivity towards reaction dynamics. The azimuthal asymmetric emission pattern in which particles found to be preferentially emitted perpendicular to the reaction plane describes the elliptical flow. Elliptical flow has been studied extensively at BEVALAC, SIS and AGS energies [1]. In literature efforts have been made to understand the isospin effects on the elliptical flow. Isospin degree of freedom enter into the calculations via. Coulomb potential, symmetry potential and isospin dependent nucleon-nucleon cross-section. Recently, Zhang et al. [2] studied the elliptical flow in heavy-ion collisions for 2  Z particles at an incident energy ranging from several tens to hundred of MeV/nucleon. They showed that soft nuclear equation of state and energy dependent in-medium nucleonnucleon cross-section are required to describe the excitation function of the elliptical flow at intermediate energies. On the other hand, S. Kumar et al. [3] studied the elliptical flow for the whole mass range of symmetric reactions and they showed that transition energy for the whole mass range follow a power law behavior. K. S. Vinayak et al. [4] reported that the elliptical flow is highly sensitive towards the different forms of density dependent symmetry energy. Also in Ref. [5], an attempt has been made to study the effect of charge asymmetry and isospin dependent nucleon-nucleon cross-section on elliptical flow and they concluded that different aspects of elliptical flow strongly depend on the isospin dependence of the nucleon-nucleon cross-section and isotopic contents of the colliding nuclei. All these studies were silent about the isospin effects in mass asymmetric nuclear collisions. As noted by FOPI group [6], the reaction dynamics in asymmetric collisions is quite different as compared to symmetric collisions. This difference is due the different deposition of the excitation energy in symmetric and asymmetric collisions. The symmetric collisions generate high compression whereas asymmetric collisions lead to thermalization. Therefore, asymmetric collisions are helpful to investigate reaction dynamics. The mass asymmetric parameter is defined as,     P T P T A A A A    /  , where AP and AT are the masses of projectile and target respectively. The present work is carried out to study the effect of Coulomb potential on the transverse momentum dependence of elliptical flow by taking mass asymmetric collisions. The study is performed within the frame work of IQMD [7] model.