Observation of the $\phi(1680)$ and the Y(2175) in $e^+ e^- \to \phi\pi^+\pi^-$

TL;DR

This paper reports the first measurements of the resonance parameters of the $phi(1680)$ and observes the Y(2175) structure in $e^+ e^- o phi extpi^+ extpi^-$, using a large data sample collected at KEKB.

Contribution

It provides the first measurements of the $phi(1680)$ resonance parameters and reports the observation of the Y(2175) structure in $e^+ e^-$ annihilation.

Findings

Measured $phi(1680)$ mass and width: 1689 MeV/$c^2$ and 211 MeV/$c^2$

Observed Y(2175) with mass 2079 MeV/$c^2$ and width 192 MeV/$c^2$

Used 673 fb$^{-1}$ data sample at KEKB for analysis.

Abstract

The cross sections for $e^+ e^- \to \phi\pi^+\pi^-$ and $e^+ e^- \to \phi \fzero$ are measured from threshold to $\sqrt{s}=3.0$ $\hbox{GeV}$ using initial state radiation. The analysis is based on a data sample of 673 fb$^{-1}$ collected on and below the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. First measurements are reported for the resonance parameters of the $\phi(1680)$ in the $\phi\pi^+\pi^-$ mode: $m=(1689\pm 7\pm 10)$ MeV/$c^2$ and $\Gamma=(211\pm 14\pm 19)$ MeV/$c^2$. A structure at $\sqrt{s}=2.1 \hbox{GeV}/c^2$, corresponding to the so called Y(2175), is observed; its mass and width are determined to be $2079\pm13^{+79}_{-28}$ MeV/$c^2$ and $192\pm23^{+25}_{-61} \hbox{MeV}/c^2$, respectively.