LHCb上类粲夸克偶素强产生实验研究

In the Standard Model of particle physics, the strong interaction between quarks and gluons is described by the Quantum ChromoDynamics (QCD). However, due to the properties like “quark confinement” of QCD, theoretical calculations are difficult, and people still haven’t fully understood how the quarks and gluons form the hadrons like the proton and neutron. Since the observation of X(3872) by the Belle experiment in 2003, more and more charmonium-like states have been found. Understanding their structures and properties is the hot topic of both theoretical and experimental studies of QCD. .Here we propose to search for the charmonium-like states produced directly in the high energy proton-proton collisions, and measure their hadroproduction cross-section, with the largest J/ψ→μμ and ψ(2S)→μμ data samples collected by the LHCb experiment during the Run-I (2010-2013) and Run-II (2015-2018) periods. This will be the first systematic study of the hadroproduction of the charmonium-like states. It will provide more valuable information on how the quarks and gluons form the hadrons, and deepen our understanding of QCD.

在粒子物理标准模型中，夸克和胶子之间的强相互作用由量子色动力学来描述。由于量子色动力学的“夸克禁闭”等特性，使得理论计算困难，目前人们仍未完全理解夸克和胶子如何形成诸如质子和中子等强子。而随着2003年Belle实验发现X(3872)粒子以来，越来越多的类粲夸克偶素被发现。关于这些类粲夸克偶素的结构和性质的研究是目前量子色动力学理论和实验的热点课题。.本项目计划利用LHCb实验在运行一期（2010-2013）和运行二期（2015-2018）所取的目前世界上最大的J/ψ→μμ和ψ(2S)→μμ数据样本，来寻找类粲夸克偶素通过高能质子-质子对撞过程直接产生的证据，并测量类粲夸克偶素的强产生截面。这将是LHCb实验上首次对类粲夸克偶素的强产生进行系统的研究，将对我们理解夸克和强子如何形成强子态提供更多的非常有价值的信息，加深我们对于量子色动力学的理解。

本项目利用LHCb实验在运行一期（2010-2013）和运行二期（2015-2018）采集的质子-质子对撞数据，完成了重味夸克偶素ηc(1S), psi(2S)和Upsilon(nS)产生截面的测量，和类粲夸克偶素X(3872)双微分截面的首次测量；寻找了其它类粲夸克偶素通过高能质子-质子对撞过程直接产生的证据，并将测量其强产生截面。这是LHCb实验上首次对类粲夸克偶素的强产生进行系统的研究，对我们理解夸克和胶子如何形成强子态提供非常有价值的信息，加深了我们对于量子色动力学的理解。