Physics in Charm Energy Region

Abstract

Recent results on physics in the charm energy region are reviewed. (1) The new data and puzzles in exclusive hadronic decays of $J/ψ$ and $ψ'$ give new challenges to the theory of hadronic decays. (2) With the new observation for $ξ(2230)$ and $f_0(1500)$ in $J/ψ$ radiative decays and other experiments, the situation in searching for glueballs is encouraging, but theoretical uncertainties related to the properties of glueballs still remain and need to be further reduced. (3) For the prompt production of charmonium at large transverse momentum, gluon and quark fragmentations dominate over leading-order parton fusions. Color-singlet fragmentation is not the dominant mechanism for $J/ψ$ and $ψ'$ production. Color-octet fragmentation seems to be important to explain the $J/ψ$ and, in particular, the $ψ'$ excess, but further tests are required. The mechanism of charmonium production at fixed-target also needs studying. (4) Some theoretical and experimental results in charmonium and open charm hadrons are also reported.