Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

12 Biennial Report 2005-071.2.3.7 High energy diffuse neutrino background as a probe of Supernova - GammaRay Burst connectionDetection of supernova (SN) features in the afterglow spectra of several long duration (typically> 2 sec) Gamma Ray Bursts (GRBs) in the past one decade has provided strong support to thehypothesis that a significant fraction, if not all, of the long duration GRBs arise from collapseof massive stars and are thus associated with supernova explosions. In this work we explore thepossibility of using the experimental upper limit on the diffuse high energy (TeV – PeV) neutrinobackground to place an upper limit on the ratio of GRB rate to supernova rate in the universe.Pijushpani Bhattacharjee, Sovan Chakraborty, Srirupa Das Gupta, Kamales KarTheo1.3 Nuclear Theory1.3.1 Nuclear Reactions1.3.1.1 η meson production in nucleon-nucleon collisions within an effective LagrangianmodelWe investigate the pp → ppη and pn → pnη reactions within an effective Lagrangian model forlaboratory kinetic energies ranging from very close to η meson production threshold to about 10GeV. Production amplitudes include contributions from the mechanism of excitation, propagationand decay of N*(1535), N*(1650), and N*(1710) baryonic resonances. The initial interaction betweentwo incoming nucleons is modeled by the exchange of π, ρ, ω and σ mesons where the vertexparameters are taken to be the same as those used in the previous applications of this model.Parameters of the resonance vertices also have been taken from our earlier studies wherever applicable.Calculations have been done for total as well as differential η production cross sections. Todescribe the data for energies closer to the production threshold final state interactions among theout-going particles have been included by means of a generalized Watson-Migdal method. Termscorresponding to the excitation of N*(1535) resonance and pion exchange process dominate thecross sections. With a single set of vertex parameters our model is able to describe the availabledata well on total cross sections for beam energies ranging from close to threshold to upto 10 GeV.R ShyamTheo1.3.1.2 A fully relativistic description of Hypernuclear production in proton- andpion-Nucleus CollisionsExclusive A(p,K + ) Λ B and A(π,K + ) Λ B ′ reactions leading to two body final states, have beeninvestigated in a fully covariant model based on an effective Lagrangian picture. The explicitkaon production vertex is described via creation, propagation and decay into relevant channel ofN*(1650), N*(1710) and N*(1720) intermediate baryonic resonance states, in the initial collisionof the projectile with one of the target nucleons. The bound state wave functions are obtainedby solving the Dirac equation with appropriate scalar and vector potentials. The calculated crosssections show strong sensitivity to the final hypernuclear state excited in the reaction. Cross sections