| Physicists have found J/ψ,ψ(2S),ψ(3770) which are a series of charmonium state and they try their best to find new members of charmonium system. Charmonium system provide ideal places to study and search for new hadrons, and the study of theirs production and decays are regarded as great importance to test and develop Quantum Chromodynamics (QCD) theory which describes the strong interactions. It is of great importance to test and develop QCD theory for understanding the natures of strong interactions. Up to now, all established hadrons are consisted by two or three quarks, but QCD theory predicts the existence of new forms of hadrons (multi-quark states, hybrids, glueballs), and the multi-quark states are consisted by more than three quark states; the hybrids are consisted by the pair of quark-antiquark and gluons or three quarks and gluons (qqg, qqg); the glueballs are consisted by pure gluon(gg, ggg). But the new hadrons have not been found in experiment by now. So searching for the multi-quark states, hybrids and guleballs in experiments in order to testing and developing QCD theory is one of the goals for many high energy physics experiments in the world.There are many studies ofηc in all aspects. However, there are very many differ-ences on theηc resonance curve, mass and width for different experiments. Not only are precision measurements needed to validate our theoretical understanding, precise mea-surements of these M1 transitions are critical for normalizingηc branching fractions, a key input to extracting other properties such as (ηc). The measurements ofηc mass and width is the basement and ensure for precise measurementing ofηc branching fractions. Using 24.5 millionψ(2S) decays collected by the CLEO-c detector the CLEO-c collabo-ration measured magnetic dipole transitions in the charmonium system. They measured the branching fractions of J/ψandψ(2S) decaying toηc by magnetic dipole transitions. Then they gave the following branching fractions:B(ψ(2S)â†'γηc)=(4.32±0.16±0.60)×10-3, B(J/ψâ†'γηc)/B(ψ(2S)â†'γηc)=4.59±0.23±0.64, B(J/ψâ†'γηc)=(1.98±0.09±0.30)%. They found that the line shape ofηc has been distorted due to the energy of gamma dependence of the magnetic diploe transition rate. Using about 100 millionψ(2S) decay collected with the BESâ…¢detector at BECPâ…¡we have intensivly studied on the accurate measurement meth-ods forηc resonance parameters, signal fitting and error by the decay channelψ'â†'γηc, also we accurately measure the mass and width ofηc. Then we give the further physical explanation for the distortion ofηc that the asymmetrical reasons maybe the interference between the resonance and continuous amplitude. This reason and width (about 30MeV) ofηc maybe causing the interference between itself and the direct decay final state of non-ηc resonance state decay (background) fromψ(2S). So, we use the method that the interference between the signal and background to fit the mass spectrum ofηc. At the same time, we take into account the effect of efficiency and mass resolution.Ï€0 is always used as signal or background in many physics analyse and a main source of systematic error. We can accurately estimate the systematic error caused by it by measuring the precision for the reconstruction efficiency ofÏ€0, especially for low momentumÏ€0. In this article, I useψ(2S)â†'Ï€0Ï€0J/ψ, J/ψâ†'μ+μ-/e+e- decay channel to measure the reconstruction efficiency of low momentumÏ€0.This work is based on 106 millionψ(2S) events which were firstly collected with the upgraded BESâ…¢detector and BEPCâ…¡Collider on 2009. This data sample is about seven times of BESⅡψ(2S) data (14 million), is about four times of CLEOc experimental group collected samples (27 million) at Cornell University, is the world's largest collected data sample in theψ(2S) resonance peaks. |
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