Study Of The Purely Leptonic Decay D_s⁺â†'l⁺v And Measurement Of The Decay Constant F_Ds⁺

Richter and Ting found the first charm particle J/Ψ in1974, thus opened the new chapter of the high energy physics, and the charm physics also became the research focus of high energy physicists. Studying the production and decay natures of charm-particle, which contains charm quark, this is of great significance for testing the standard model, especially the perturbative and non-perturbative quantum chromodynamics (QCD). Charm physics studies are mainly divided into charmonium physics, charm-meson physics and charm-baryon physics etc.. Among charmonium physics mainly study the bound states composed of a pair positive and negative charm quarks, and particle physicists have found many charmonium particles such as J/Ψ,Ψ(2S),Ψ/(3770) and Ψ(4040) etc.. At the same time, scientists make efforts to search for unknown charmonium particles and new physics, by studying the production and decay natures of the found charmonium particles; in addition studies of charm-meson and charm-baryon also are extremely important aspects for high energy physicists. Searching for the CP violation and D0-D0mixing, have important physics significance to verify the standard model and find new physics.D0, D+(D-) and Ds+(Ds-) are the lightest charm mesons. Charm meson decays by weakly interaction, and the decay width is relatively narrow; thus the measurement of their branching ratios, especially the purely leptonic decay branching ratios, are very difficult, experimental results on their decay constants are not in consistent. In short, the measurements of the decay constants fD+and fDs+are still one of main topics in charm-meson physics.BESIII built on BEPCII is a important high energy physics detector, which is the upgraded version of BESII. BESⅢ/BEPCⅡ completely cover tau-charm energy region, and is an ideal laboratory for studying charm physics. We accumulated to470pb-1Ψ(4040) data at4010MeV energy point at BESIII/BEPCII from May4,2011to June3. Because the point of4010MeV is just in the vicinity of the threshold DsDs at which can avoid to produce Ds*meson and reduce background, therefore this is a good opportunity for researching Ds+meson decay at BESⅢ. In this thesis, we study the purely leptonic decay of Ds+meson and the measure decay constant fD(?) using these data.