PROGRESS IN τ-CHARM PHYSICS ACHIEVED BY BEPC/BES

Particle physics is a basic science which studies the smallest elements of matter and the properties of their interactions, deepening mankind’s knowledge of the microcosmos.τ-Charm physics is an important branch of elementary-particle physics.Systematic studies on the radiative decay,strong decay and weak decay of elementary particles will resolve and clarify many problems in the discipline, testing and deveploping the Standard Model of elementary particles.For example,what is the

List of talks on BES-Belle-CLEO-BABAR 2007 joint workshop on charm physics

The Institute of High Energy Physics of Chinese Academy of Sciences organized a workshop to estab- lish closer contacts between experimentalists （theorists） involved in the studies of charm physics from both c and B communities. The workshop covers talks of physics analysis and its results from four electron-positron colliding experiments （BES, Belle, CLEO and BaBar）. Presentations at the workshop are organized in the following sessions ： （1） Hadron spectroscopy and new resonances; （2） D^0-D^0 mixing; （3） Charmonium decays; （4） Charm hadronic and （semi-）leptonic decays; （5） QCD at low energy and T physics; （6） Partial wave analysis and Dalitz analysis, MC generator and Tools; （7） Detector upgrade. The workshop was held during November 26 27, 2007 in the Institute of High Energy Physics （IHEP）. There are 90 registered participants in total, and 38 of them are from abroad （Japan, America, Russia, Italy, Germany, France, Slovenia, Switzerland and so on） and the others from China. All 35 talks were given in a plenary session.

Search for the doubly heavy baryon Ξ_(bc)^(+)→ decaying to J/ψΞ_(c)^(+)

A first search for the Ξ_(bc)^(+)J/ψΞ_(c)^(+) decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1 recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local (global) significance of 4.3(2.8) and 4.1(2.4) standard deviations at masses of 6571 and 6694 MeV/c2, respectively. Upper limits are set on the Ξ+bc baryon production cross-section times the branching fraction relative to that of the B+c→J/ψD+s decay at centre-of-mass energies of 8 and 13 TeV, in the Ξ+bc and in the B+c rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to 20GeV/c, respectively. Upper limits are presented as a function of the Ξ+bc mass and lifetime.

Measurement of the lifetimes of promptly produced Ω_(c)^(0) and Ξ_(c)^(0) baryons

A measurement of the lifetimes of theΩ_(c)^(0)andΞ_(c)^(0)baryons is reported using proton-proton collision data at a centre-of-mass energy of 13 TeV,corresponding to an integrated luminosity of 5.4 fb;collected by the LHCb experiment.TheΩ_(c)^(0)andΞ_(c)^(0)baryons are produced directly from proton interactions and reconstructed in the p K^(-)K^(+)π^(+)nal state.TheΩ_(c)^(0)lifetime is measured to be 276.5±13.4±4.4±0.7 fs,and theΞ_(c)^(0)lifetime is measured to be 148.0±2.3±2.2±0.2 fs,where the first uncertainty is statistical,the second systematic,and the third due to the uncertainty on the D^(0)lifetime.These results con firm previous LHCb measurements based on semileptonic beauty-hadron decays,which disagree with earlier results of a four times shorterΩ_(c)^(0)lifetime,and provide the single most precise measurement of theΩ_(c)^(0)lifetime.