BESIII上粲介子产生截面的测量

Study of the charmonium states is an important topic of high energy physics research. One of the most interesting topics in charmonium physics is the decay process. According to current experimental results, charmonia above the mass threshold of charmed meson pair have strong coupling to charmed mesons and mainly decay to final states including charmed mesons. All the existing measurements of open-charm cross section have large errors due to the limitation of statistics. BESIII experiment at the BEPCII e+e- collider is a unique experiment with the highest luminosity for charmonium physics study, which provides us an opportunity to make a precise measurement of charmed meson production cross section. BESIII has already accumulated three data samples at 4.01 GeV, 4.26 GeV, and 4.36 GeV with integrated luminosity about 500 pb-1 each. A scan at an energy range from 3.8 GeV to 5.0 GeV is proposed and will be carried out also with high statistics. With these data samples, e+e- annihilation cross section into open-charm final states can be measured in high precision. The resonance parameters of excited charmonium and some vector states, such as the Y(4260) and Y(4360), can be obtained. The decay mechanism of these states can also be studied. All these information will deepen our understanding of the physical phenomena, validate physical model, and promote the develepment of particle physics theory.

粲偶素物理是高能物理的一个重要研究领域，粲偶素衰变是这个领域中的一个重要研究课题。质量高于粲介子对阈值的粲偶素与粲介子有较强的耦合，产生含粲介子末态是它们的主要衰变模式。目前这些高质量粲偶素衰变到含粲介子末态截面的测量受限于数据的统计量还有较大的误差。北京正负电子对撞机BEPCII上的北京谱仪BESIII实验是目前在粲偶素能区运行的亮度最高的正负电子对撞实验。BESIII已经在4.01、4.26和4.36GeV能量点各采集了亮度约为500pb-1的数据，并计划在3.8至5.0GeV能量区域进行扫描。利用这些大统计量的数据可以精确测量正负电子对撞产生的含粲介子末态截面，确定粲偶素激发态和Y(4260)、Y(4360)等矢量态的共振参数，研究它们的产生衰变性质。这些研究工作将加深对物理现象的理解，检验模型，促进理论的完善和发展；同时还可能发现新的物理现象和物理规律。

粲偶素物理是高能物理的一个重要研究领域，粲偶素衰变是这个领域内的一个重要研究课题。质量大于粲介子对阈值的粲偶素与粲介子有较强的耦合，产生含粲介子末态是它们的主要衰变模式。在本项基金的支持下，基于BESIII探测器采集的正负电子对撞事例，我们主要研究了：e+e- -> D Dbar，gamma D Dbar，Ds*+ Ds*- 过程和eta_c -> phi phi，omega phi 过程。在正负电子对撞实验中进行含粲介子末态的研究可以检验现有的理论模型，特别是可以检验一些奇特态模型，这加深了我们对于质量大于粲介子对阈值的粲偶素和类粲偶素性质的理解。eta_c 的强衰变模式是研究量子色动力学的有效场所，因此eta_c 衰变的高精度测量可以帮助我们更好地理解eta_c 的性质，推动量子色动力学理论的发展。在本项基金的支持下，我们还在螺旋度坐标下唯象地研究了J/psi -> Lambda Lambdabar 和 Lambda -> Baryon pi- (Lambdabar -> anti-Baryon pi+)这两个过程中可能发生的CP破坏，给出了在BESIII上测量Lambda，Lambdabar衰变参数的精度。此外我们还参与了D*0分支比的测量，给出了目前世界上最高精度的测量。