Charmonium Exotic States

Abstract

In this thesis, the QCD sum rules approach has been used to study the nature of the following charmonium resonances: Y(3930), Y(4140), X(4350), Y(4260), Y(4360) and Y(4660). There is a strong evidence that these states have non-conventional (or exotic) hadronic structures since their respective masses and decay channels observed experimentally are inconsistent with expected for a conventional charmonium state. The same phenomenon occurs on the bottomonium sector, where new states like Yb(10890) and Yb(11020) observed recently could indicate the existence of new bottomonium exotic states. In this way, one verifies that the Y(4140) state could be described as a D*sD*s (0++) molecular state or even as a mixture of D*sD*s (0++) and D*D* (0++) molecular states. For the Y(3930) and X(4350) states, both cannot be described as a D*D* (0++) and D*sD*s0 (1-+), respectively. From the sum rule point of view, the Y(4660) state could be described as a \psi' f0(980) molecular state. The extension to the bottomonium sector is done in a straightforward way to demonstrate that the \Upsilon' f0(980) molecular state is a good candidate for describing the structure of the Yb(10890) state. In the following, one estimates the mass of the exotic Bc-like molecular states using the sum rule approach, where these new exotic states would correspond to bound states of D(*) and B(*) mesons. All of these mass predictions could (or not) be checked in a near future experiments at LHC. A large study using the Double Ratio of Sum Rules approach has been evaluated for studying the heavy baryon masses in QCD. The obtained results for the unobserved heavy baryons, with one (Qqq) and two (QQq) heavy quarks will be an excellent test for the capability of the sum rule approach in predicting their masses.