Measurement Of E⁺e^-→D_s^*+D_s^*- Cross Sections At BESⅢ

The meson composed of a charm quark and an anti-charm quark,known as the char-monium state（J/ψ,ψ（3686）,ψ（3770）,ψ（4040）,ψ（4160）andψ（4415））,lies in the tran-sition region between the perturbation and nonperturbation of quantum chromodynamic-s.The existence of many charmonium states in this energy region has been successful-ly predicted based on the phenomenological model of quantum chromodynamics.Their production and decay properties have been well explained theoretically,and they are in good agreement with experimental results.With the development of high-energy physic-s experiments,many new particles（XYZ particles）have been unexpectedly discovered above the open-charm threshold,which were not predicted theoretically.These particles,which is also known as charmonium-like mesons.The peculiar composition suggests that they are likely to be the exotic states predicted by quantum chromodynamics.They could be candidates of charmonium hybrids,hadronic molecules,multiquark states.The first charmonium-like state X（3872）through the final statesπ⁺π^-J/ψwas discovered by Belle experiment in the process of B^±→K^±π⁺π^-J/ψ,and was later verified by CDF and BABAR collaboration group.The properties of this state are completely inconsistent with those predicted by the potential model in this mass range.Many theoretical models are proposed to provide explanations but no unanimous conclusion can be drawn.Since then,the charmonium-like state has been widely sought as a research hotspot,Y（4260）,Y（4360）,Z_c（3900）^±and so on were discovered in succession by BABAR,Belle and BE-SIII experiments.Vector-charmonium-like states,which can be directly produced by electron-positron annihilation,have different distributions to the cross section of a certain hadronic final states.Therefore,it is common to measure the cross section to investigate whether there is any new states.The cross section of e⁺e^-→D_s^*+D_s^*-has been measured by CLEO-c,BABAR and Belle,but due to the limitation of statistics and energy range,the res-onance distribution cannot be clearly revealed.With the world’s largest e⁺e^-scan da-ta sample between the threshold and 4.95 Ge V accumulated by BESⅢ,the Born cross section of e⁺e^-→D_s^*+D_s^*-are measured precisely.Two enhancements in the E_CMdependent cross sections are observed around 4.2 and 4.45 Ge V.Fitting the cross sec-tions with a coherent sum of three Breit-Wigner amplitudes and one phase-space ampli-tude.The fitted mass and width for the first resonance are（4186.8±8.7±30）Me V/c²and（55±15±53）Me V,respectively.The fitted mass and width for the second resonance are（4414.6±3.4±6.1）Me V/c²and（122.5±7.5±8.1）Me V,respectively.An additional third BW amplitude describes the E_CMdependent cross sections around 4.79 Ge V better than just using two BW functions,with statistical significance greater than 5.9σ.The results provide important experimental data support for the study of charmonium-like states.In cross section measurement,the iterative method of initial state radiation correction is in-novated.To improve the measurement efficiency,the weight of the event is substituted for the generation of MC samples.At the same time,the measurement of the luminosity of XYZ Data in 2019 at BESⅢ also laid an important foundation for the cross section measurement.