Upsilon decay widths in magnetized asymmetric nuclear matter

Abstract: The in-medium partial decay widths of $\Upsilon (4S) \rightarrow B\bar B$ in magnetized asymmetric nuclear matter are studied using a field theoretic model for composite hadrons with quark (and antiquark) constituents. The medium modifications of the decay widths of $\Upsilon (4S)$ to $B\bar B$ pair in magnetized matter arise due to the mass modifications of the decaying $\Upsilon (4S)$ as well as of the produced $B$ and $\bar B$ mesons. The in-medium masses of the open bottom meson in magnetized nuclear matter are computed from their interactions with the nucleons and the scalar mesons within a chiral effective model. The mass modification of the $\Upsilon(4S)$ arises due to the medium modification of a scalar dilaton field, which is introduced in the model to simulate the gluon condensates of QCD. The charged $B^{\pm}$ mesons have additional contributions from the Landau energy levels, leading to positive shifts in their masses in the presence of a magnetic field. In the presence of an external magnetic field, there are contributions to the masses of the $B$, $\bar B$ mesons and $\Upsilon(4S)$ state (longitudinal component) due to the pseudoscalar meson-vector meson (PV) mixing ($B-B^*$, $\bar B- \bar {B^*}$ and $\Upsilon(4S)-\eta_b(4S)$ mixings), which are also considered in the present study. The PV mixing effects are observed to be the dominant contributions to the mass shifts of these mesons, which lead to appreciable modifications in the decay widths of $\Upsilon (4S)$ to the neutral ($B^0 \bar {B^0}$) and the charged ($B^+ B^-$) pairs in the presence of a magnetic field. These should have observable consequence in the production of open bottom mesons and bottomonium states at LHC and RHIC, where huge magnetic fields are produced in ultra-relativistic peripheral heavy ion collisions.