In a 40-day run ending on 22 May, the Institute of High-Energy Physics in China accumulated a total of 1.3 billion J/ψ events at the upgraded Beijing Electron Positron Collider (BEPCII) and Beijing Spectrometer (BESIII).
In a two-year run from 1999 until 2001, the earlier incarnations of BEPC and BESII had accumulated a highly impressive 58 million J/ψs. By analysing these and 220 million events at BESIII, important results such as the discovery of X(1835) have already been produced. Now, thanks to the upgrades, data-acquisition efficiency is 120 times higher, and as many as 40 million J/ψs were being collected daily towards the end of the latest run.
BEPCII is a two-ring electron–positron collider with beam energy of 1.89 GeV. With a design luminosity of 1 × 1033 cm–2s–1, it reached a peak of 2.93 × 1032 cm–2s–1 in the latest run, 59 times higher than that of its predecessor, BEPC.
