Abstract
The cross section of the process $e^{+} e^{-} \rightarrow K^{+} K^{-}$ is measured at a number of center-of-mass energies $\sqrt{s}$ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of $M=2239.2 \pm 7.1 \pm 11.3$~and a width of $\Gamma=139.8\pm12.3\pm20.6$ MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
Highlights
The study of the hadron spectrum provides important input to understand the nonperturbative behavior of QCD
A typical example is Yð2175Þ observed by the BABAR Collaboration in 2006 in the process eþe− → γISRφf0ð980Þ [2], which was confirmed by the Belle, BESII, and BESIII experiments [3,4,5,6,7,8]
We have measured the Born cross section of eþe− → KþK− and the charged kaon form factor using data samples collected with the BESIII detector at 22 different c.m. energies from 2.00 to 3.08 GeV
Summary
The study of the hadron spectrum provides important input to understand the nonperturbative behavior of QCD. A further check of the experimental data on the light mesons listed in Particle Data Group (PDG) [1] reveals that many light mesons with a mass above 2 GeV are far from being firmly established. The BABAR collaboration measured the eþe− → KþK− cross section using the initial state radiation (ISR) technique. Their measurements range from the KþK− threshold up to 8 GeV, and some complicated structures between 1.8 and 2.4 GeV [20,21] are observed. Measuring the process eþe− → KþK− can provide important information on these higher excitations of the ρ and ω meson families around 2 GeV, which is crucial to construct the ρ and ω meson spectra. Perturbative QCD (pQCD) predicts the kaon form factor FKðQ2Þ asymptotically to be inversely proportional to the center-of-mass energy; this can be tested by a precise measurement of FK
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