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Register a new userLight Hadron Spectroscopy and Charmonium
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Frederick A. Harris
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During the last few years there has been a renaissance in charm and charmonium spectroscopy with higher precision measurements at the $psi^{}$ and $psi(3770)$ coming from BESII and CLEOc and many new discoveries coming from B-factories. In this paper, I review some new results on classical charmonium and $e^+ e^- to$ hadrons using B-factory Initial State Radiation and two photon events.
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The latest results of CMS in the area of exotic quarkonium decays will be presented: observation of a peaking structure in $J/psiPhi$ mass spectrum in the decay $B^pm rightarrow J/psi Phi K^pm$, search for new bottomonium states in $Upsilon(1mathrm{S})pi^+pi^-$ mass spectrum, measurement of prompt $J/psi$ pair production.
QCD-motivated models for hadrons predict an assortment of exotic hadrons that have structures that are more complex than the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetraquark, hybrid and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have been identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states --the proton-antiproton state and the so-called XYZ mesons-- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.
We report measurements of the branching fractions for the decays B->D_s1(2536)+ anti-D(*), where anti-D(*) is anti-D0, D- or D*-, and study of B->X(3872) K with X(3872) decaying to D*0 anti-D0 using a sample of 657 million B anti-B pairs recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
Recent results on the search for pentaquarks and on charmonium spectroscopy at BaBar are reviewed. The latter includes the observation of the puzzling new state X(3872) -> J/psi pi+ pi- in B decays, and the searches for X(3872) in two-body B decays and initial state radiation events.
The QCD light-front Hamitonian equation derived from quantization at fixed LF time provides a causal, frame-independent, method for computing hadron spectroscopy and dynamical observables. de Alfaro, Fubini, and Furlan (dAFF) have made an important observation that a mass scale can appear in the equations of motion without affecting the conformal invariance of the action if one adds a term to the Hamiltonian proportional to the dilatation operator or the special conformal operator. If one applies the dAFF procedure to the QCD light-front Hamiltonian, it leads to a color confining potential $kappa^4 zeta^2$ for mesons, where $zeta^2$ is the LF radial variable conjugate to the $q bar q$ invariant mass squared. The same result, including spin terms, is obtained using light-front holography if one modifies the AdS$_5$ action by the dilaton $e^{kappa^2 z^2}$ in the fifth dimension $z$. When one generalizes this procedure using superconformal algebra, the resulting light-front eigensolutions provide a unified Regge spectroscopy of meson, baryon, and tetraquarks, including remarkable supersymmetric relations between the masses of mesons and baryons and a universal Regge slope. The pion $q bar q$ eigenstate has zero mass at $m_q=0.$ The superconformal relations also can be extended to heavy-light quark mesons and baryons. AdS/QCD also predicts the analytic form of the nonperturbative running coupling in agreement with the effective charge measured from measurements of the Bjorken sum rule. The mass scale underlying hadron masses can be connected to the mass parameter in the QCD running coupling. The result is an effective coupling $alpha_s(Q^2)$ defined at all momenta. One also obtains empirically viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions.
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