A combined study of $b \to s \gamma$ and the muon anomalous magnetic moment in gauge-mediated supersymmetry breaking models

Abstract

We study both the branching ratio for $b \to s \gamma$ decay and the muon anomalous magnetic moment, $a_{\mu} \equiv (g-2)_{\mu} /2$, in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Combining new experimental data on $a_{\mu}$ and the branching ratio for $b \to s \gamma$, useful limits on the parameter space of these models are derived. In particular, we explicitly show that, with the presently available experimental data, constraints from the decay $b \to s \gamma$ are more stringent than those from $a_{\mu}$ in broad region of the parameter space. We include the supersymmetric one-loop correction to the mass of $b$ quark, $m_b$, and find that in order to have a correct value of $m_b$, the region of large tan$\beta$ and $\mu <0$ (in our convention) is not allowed in these models (if there are no further assumptions like $b - \tau$ Yukawa coupling unification). The region of large tan$\beta$ and $\mu >0$ is also strongly constrained. We present bounds on supersymmetric particle masses as a function of $\tan \beta$.