Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar

TL;DR

This study analyzes the e+e- to J/psi pi+ pi- process using initial-state radiation at BaBar, identifying a new resonance at 4244 MeV/c^2 and examining the pi+ pi- system from Y(4260) decay.

Contribution

First measurement of the J/psi pi+ pi- mass distribution at BaBar with detailed resonance parameters and comparison to previous claims, notably not confirming a broad structure at 4.01 GeV/c^2.

Findings

Identified a resonance at 4244 MeV/c^2 with specified mass and width.

Observed the dominance of psi(2S) below 3.7 GeV/c^2.

Did not confirm the broad structure at 4.01 GeV/c^2 reported by Belle.

Abstract

We study the process $e^+e^-\to J/\psi\pi^{+}\pi^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BaBar detector at center-of-mass energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454 $\mathrm{fb^{-1}}$. We investigate the $J/\psi \pi^{+}\pi^{-}$ mass distribution in the region from 3.5 to 5.5 $\mathrm{GeV/c^{2}}$. Below 3.7 $\mathrm{GeV/c^{2}}$ the $\psi(2S)$ signal dominates, and above 4 $\mathrm{GeV/c^{2}}$ there is a significant peak due to the Y(4260). A fit to the data in the range 3.74 -- 5.50 $\mathrm{GeV/c^{2}}$ yields a mass value $4244 \pm 5$ (stat) $ \pm 4$ (syst)$\mathrm{MeV/c^{2}}$ and a width value $114 ^{+16}_{-15}$ (stat)$ \pm 7$(syst)$\mathrm{MeV}$ for this state. We do not confirm the report from the Belle collaboration of a broad structure at 4.01 $\mathrm{GeV/c^{2}}$. In addition, we investigate the $\pi^{+}\pi^{-}$ system which results from Y(4260) decay.