The nature of $Z_b$ states from a combined analysis of $Υ(5S)\rightarrow h_b(mP) π^+ π^-$ and $Υ(5S)\rightarrow B^{(\ast)}\bar B^{(\ast)}π$

Abstract

With a combined analysis of data on $Υ(5S)\rightarrow h_b(1P,2P)π^+π^-$ and $Υ(5S)\rightarrow B^{(\ast)}\bar B^{(\ast)}π$ in an effective field theory approach, we determine resonance parameters of $Z_b$ states in two scenarios. In one scenario we assume that $Z_b$ states are pure molecular states, while in the other one we assume that $Z_b$ states contain compact components. We find that the present data favor that there should be some compact components inside $Z_b^{(\prime)}$ associated with the molecular components. By fitting the invariant mass spectra of $Υ(5S)\rightarrow h_b(1P,2P)π^+π^-$ and $Υ(5S)\rightarrow B^{(\ast)}\bar B^{\ast}π$, we determine that the probability of finding the compact components in $Z_b$ states may be as large as about $40\%$.