International Journal of Modern Physics E

In the past four years we have witnessed the renaissance of the hadron spectroscopy. Many interesting new hadron states were discovered experimentally, some of which do not fit into the quark model easily. I will give a concise overview of these states and their possible interpretations. Topics covered in this review are: (1) candidates of new light hadrons including threshold enhancement, X(1835), X(1576), f₀(1810), recent candidates of the 1^-+ exotic mesons, Y(2175), threshold enhancement etc. (2) charmed mesons including p-wave non-strange charmed mesons, D_sj(2317) and D_sj(2460), recent candidates of higher excited charmed mesons, D_sj(2632) etc. (3) charmonium and charmonium-like states such as X(3872), Y(4260), X(3940), Y(3940), Z(3930) etc. The effect from the nearby S-wave open channels on the quark model spectrum above or near strong decay threshold is emphasized. Dynamical lattice simulations of DK and scattering and the extraction of their phase shifts may help resolve the underlying structure of D_sj(2317), D_sj(2460) and X(3872).

Ternary fission probabilities for thermal neutron induced fission of plutonium are analyzed within the framework of an evaporation-based model where the complexity of time-varying potentials, associated with the neck collapse, are included in a simplistic fashion. If the nuclear temperature at scission and the fission-neck-collapse time are assumed to be ~ 1.2 MeV and ~ 10^-22 s, respectively, then calculated relative probabilities of ternary-fission light-charged-particle emission follow the trends seen in the experimental data. The ability of this model to reproduce ternary fission probabilities spanning seven orders of magnitude for a wide range of light-particle charges and masses implies that ternary fission is caused by the coupling of an evaporation-like process with the rapid re-arrangement of the nuclear fluid following scission.

The oscillation parameters of an active light-neutrino and a sterile-neutrino scenario, extracted from LSND constraints, are confronted with WMAP and cosmological data. The value of the mixing angle θ is extracted from the primordial abundances of D, ⁴He and ⁷Li at constant WMAP baryonic density . It is found that the best value of sin²2θ, extracted from a θ² analysis of the combined set of data, depends strongly on the inclusion of the abundance of ⁷Li in the sample of primordial abundances.

We propose a model for the antihyperon polarization in high-energy proton-nucleus inclusive reactions, based on the final-state interactions between the antihyperons and other produced particles (predominantly pions). To formulate this idea, we use the previously obtained low-energy pion-(anti-)hyperon interaction using effective chiral Lagrangians, and a hydrodynamic parametrization of the background matter, which expands and decouples at a certain freezeout temperature.¹.

With the motivation of studying complete and incomplete fusion reactions in a ¹²C+⁵⁹Co projectile target system, the excitation functions for (C, p3n), (C, 2p2n), (C, αn), (C, α2n), (C, αp3n) and (C, 2α2n) reactions have been measured up to 80 MeV. The well-known activation technique followed by offline high purity Ge γ-ray spectroscopy was used. The measured experimental values were compared with the statistical model calculations by using the ALICE-91 and CASCADE codes. For the calculations obtained by CASCADE, the variation of parameter F_θ, which is the ratio of actual moment of inertia to the rigid body value have also been studied. Considerable enhancement of the measured excitation functions compared to theoretical predictions for some channels clearly indicates the presence of incomplete fusion with complete fusion in the present projectile energy range. The measurements of forward recoil range distribution of evaporation residues at 80 MeV projectile energy confirm these observations.

Excitation functions and differential recoil range distributions in the interaction of ¹⁶O with ⁷⁵As have been measured to investigate complete and incomplete fusion reactions. The measured cross sections were compared with theoretical calculations using the computer code ALICE-91. The results indicated predominant incomplete fusion processes in the production of near target products. This was further confirmed by recoil range distribution studies of the products at 104 MeV of beam energy. The relative contributions of complete and incomplete fusion channels are estimated from recoil range distribution measurements.

Angular distributions of fission fragments have been measured in ²⁴Mg + ¹⁹²Os and ²⁴Mg + ¹⁹⁷Au reactions at E_lab = 128 MeV which is close to entrance channel Coulomb barrier. Experimental angular anisotropies were in reasonably good agreement with those calculated using the statistical theory. Analysis of the angular distribution data of the present study and of our earlier measurement in ¹⁹F + ¹⁹⁷Au reaction has shown that contribution from non-compound nucleus fission in these systems is not significant.

Fission fragment angular anisotropies from ¹⁶O + ²³²Th, ¹²C + ²³⁶U, ¹¹B + ²³⁷Np, ¹⁴N + ²³²Th, ¹¹B + ²³⁵U and ¹²C + ²³²Th systems were calculated by means of the standard saddle point statistical model (SSPSM). The results were obtained with and without neutron emission correction in the reactions, and comparisons were made with the corresponding experimental data. The normal and anomalous behaviors of fission fragment anisotropies are extensively discussed.