BEPCII/BESIII: one billion J/Psi events collected in 40 days



 the accumulated J/Psi events in the latest run
The Institute of High Energy Physics announced that till 4: 00 PM, May 22, 2012, BEPCII/BESIII has accumulated one billion J/Psi events during the past run, which is a significant and new milestone for BEPCII/BESIII.

This past run lasted about 40 days from April 9 to May 22, a total of 1.3 billion J/Psi events were collected. Over the past few days, the number of collected J/Psi events has reached a new high to about 40 million daily. It is estimated that the data acquisition efficiency of BEPCII is 120 times higher than that of the BEPC. In this run, the peak luminosity of BEPCII reached 2.93 X 1032cm-2 s-1, 59 times higher than that of the BEPC.

In the 1999-2001 run, BEPC/BESII collected a total of 58 million J/Psi events, which was quite an unbelievable number to many people at that time. It is obvious that how greatly the performance of BEPCII/BESIII has been improved.

"This is a remarkable milestone, which demonstrates that the accelerator and the detector work perfectly well. It also provides great opportunities for physics." commented Yifang WANG, director of IHEP and spokesperson of the BESIII collaboration until 2011. . CHEN Hesheng, former IHEP director and project manager of BEPCII congratulated the achievements and said that these be attributed to the collective efforts of all the project staff and the departments concerned.

J/ψ is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Prof. Samuel C.C. Ting from MIT was credited for finding what he called the "J" particle, the same particle as the "psi" found at nearly the same time at the Stanford Linear Accelerator Center by a group led by Prof. Burton Richter.

By analyzing the 58 million J/Psi events collected at BESII and the 220 million events at BESIII, the BES Experiment has achieved a series of important physics results, such as the discovery of X(1835).

The Upgraded Beijing Electron Positron Collider (BEPC II) is a two-ring e+e- collider running in the tau-charm energy region (Ecm = 2.0-4.2 GeV), which, with a designed luminosity of 1 × 10^33 cm-2 s-1 at the beam energy of 1.89 GeV, is an improvement of a factor of 100 over its successful predecessor, BEPC. The 202 m long linac of the new machine can accelerate electrons and positrons up to 1.89 GeV at a positron injection rate of 50 mA/min.

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