Wen-Sheng Huo | Searcharxiv

arXiv2016

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

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 $40\%$.

hep-ph↗

arXiv2015

How to identify the structure of near-threshold states from the line shape

We revisit the compositeness theorem proposed by Weinberg in an effective field theory (EFT) and explore criteria which are sensitive to the structure of $S$-wave threshold states. On a general basis, we show that the wave function renormalization constant $Z$, which is the probability of finding an elementary component in the wave function of a threshold state, can be explicitly introduced in the description of the threshold state. As an application of this EFT method, we describe the near-threshold line shape of the $D^{\ast 0}\bar D^0$ invariant mass spectrum in $B\rightarrow D^{\ast 0}\bar D^0 K$ and determine a nonvanishing value of $Z$. It suggests that the $X(3872)$ as a candidate of the $D^{\ast 0}\bar D^0$ molecule may still contain a small $c\bar{c}$ core. This elementary component, on the one hand, explains its production in the $B$ meson decay via a short-distance mechanism, and on the other hand, is correlated with the $D^{\ast 0}\bar D^0$ threshold enhancement observed in the $D^{\ast 0}\bar D^0$ invariant mass distributions. Meanwhile, we also show that if $Z$ is non-zero, the near-threshold enhancement of the $D^{\ast 0}\bar D^0$ mass spectrum in the $B$ decay will be driven by the short-distance production mechanism. This conclusion is still true even if the long-distance production is enhanced by some unexpected mechanism.

hep-ph↗