The Laboratory takes part in experiments with BES-III on an electron-positron collider BEPC-II (c-tau factory) currently run at the Institute of High Energy Physics (Academy of Science, China) in Bejing.

The following results have been obtained:

  •  tau-lepton mass has been measured with the best accuracy
  •  beam energy measurement system at BEPC-II has been modernized
The collider provides for the collision of electron and positron beams in the energy range from 2 to 4.4 GeV in the center-of-mass system. To register the products of collision a universal detector BES-III has been used capable of registering both charged and neutral particles, determine the impulse and particle type. A good resolution of the detectors’ registration systems combined with a high luminosity of the collider provide unique opportunities to study the charmonium and charmed particles physics (bound states of quarks, which include a c-quark) and tau-lepton.

Huge amount of statistical data obtained in this experiment exceeds the results of the previous experiments many times. Thanks to it it has become possible to study meson properties which incorporate c-quark and tau-lepton at a qualitatively new level. In experiments on BES-III it is possible to measure with a unique accuracy the mass of tau-lepton, one of the fundamental particles, which represents an important parameter in the Standard model.

An important methodological problem which is being solved during the experiments on BEPC-II is the measurement of the energy of electron and positron beams. A precise determination of the collider energy level is necessary for the solution of many physical problems, including the measurement of tau-lepton and D-meson mass. Almost the only method of energy measurement on the accelerators with high luminosity (e+e- factories) is the method of inverse Compton scattering (ICS) of laser radiation onto collider beams. Beam energy is determined by measuring the energy of scattered gamma rays. The study, application and development of this method on BEPC-II collider is important because it is planned to use it in the experiments on B-factory of SuperKEKB and the project of SuperC-Tau factory.

The Laboratory is a member of The Interdisciplinary Center for Elementary Particle Physics and Astrophysics.

Research area expert: Michail Nikolaevich Achasov (Ph. D., Physics and Mathematics), achasov@inp.nsk.su

Elementary particle physics section at NSU
Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Siences