Amplitude Analysis And Branching Fraction Measurement Of D_s~+?K~-K~+?~+?~0 At BES?

In the Standard Model,the strong interaction is described by quantum chromodynamics(QCD).QCD has been precisely verified in high-energy region,where perturbative calculations are applicable.In contrast,the non-perturbative behaviors of QCD in lowenergy region is still not fully understood.The mass of the charm quark lies in between the perturbative and non-perturbative regions,and charmed hadrons provide an ideal place to test relevant theoretical models.This thesis presents a first covariant-tensor-based amplitude analysis of the D_s⁺?K^-K⁺?⁺?⁰ decay using the electron-positron collision data samples collected by the BES? detector at the Beijing electron-positron collider.The center-of-mass energies of the collisions are between 4.178 and 4.226 GeU,and the integrated luminosity is 6.32 fb^-1.The intermediate processes of this decay is studied and their contributions are precisely measured,which provides experimental information for understanding the dynamics of the D_s⁺ four-body decay.In addition,the absolute branching fraction(BF)of D_s⁺?K^-K⁺?⁺?⁰ decay is measured with greatly improved precision.Candidates of D_s⁺?K^-K⁺?⁺?⁰ decays are reconstructed using the double-tag method for the amplitude analysis.The number of the reconstructed candidates is 3000 with a purity of 97.5%.The nominal model used in the amplitude analysis contains nine intermediate components with eighteen amplitudes.The results of the amplitude analysis show that double-vector decay channels,D_s⁺? VV,dominate the decay,where V denotes a vector meson.The processes D_s⁺???⁺ and D_s⁺?(?)^*(892)⁰K^*(892)⁺ account for the largest two fractions,(50.81±1.01±2.20)%and(23.15±0.89±0.74)%,respectively.Their absolute BFs are determined to be(5.59±0.15±0.30)%for D_s⁺???⁺and(5.64±0.23±0.27)%for D_s⁺? (?)^*(892)⁰K^*(892)⁺,which are consistent with those measured by other experiments,but discrepancies with predictions of low-energy effective theories are indicated.Using the results of the amplitude analysis,the relative BFB(K₁(1270)?K^*(892)?)/B(K₁(1270)?K? is determined to be 0.99±0.15±0.18,which is consistent with those from other experiments within three standard deviations.With the model determined from the amplitude analysis,the detection efficiency of the D_s⁺ four-body decay is estimated,and the absolute BF of this decay is determined to be B(D_s⁺?K^-K⁺?⁺?⁰)=(5.42±0.10±0.17)%.This result is in accord with the world-average result,while the uncertainty is reduced by a factor of 1/3.The absolute BF of each intermediate process is also measured in this thesis.For all the results shown above,the first are statistical and the second systematic.The results of the amplitude analysis of the D_s⁺?K^-K⁺?⁺?⁰ decay contribute to further understanding of non-perturbative QCD,and provide crucial information for optimizing the decay model of the D_s⁺ meson in the BES? Monte Carlo simulation.Using the covariant-tensor formulae of the S,P,and D waves in the D_s⁺?VV process,the relations of the coefficients in the covariant-tensor-based amplitude and in the helicity amplitude are derived in this thesis.The relations are used to calculate the transverse polarization fraction of D_s⁺?VV decays and provide a basis on the measurement of the CP asymmetry in D_s⁺? VV decays.