Diquark-Antidiquark Interpretation of Mesons
  We study the spectroscopy of the states which defy conventional $c\bar{c}$ charmonium and $b\bar{b}$ bottomonium interpretation respectively, and are termed as exotic states. In August 2003 a state X(3872), was discovered [K. Abe\textit{\ et al.} (Belle Collaboration), Phys. Rev. Lett. \textbf{91}, 262001 (2003) [arXiv:hep-ex/0309032]] and in December 2007 a state Y(10890) was reported [K. F. Chen \textit{et. al.} [Belle Collaboration], Phys. Rev. Lett. \textbf{100}, 112001 (2008) [arXiv:0710.2577]. One possible interpretation of such exotic state is that they are tetraquark (diquark-antiquark) states. Applying knowledge of non-relativistic constituent quark model, we calculate the spectrum of hidden charm and bottom exotic mesons within diquark-antidiquark model. We investigate that X(3872) is $1^{++}$ state of the kind $X_{[cq]}=([cq]_{S=1}[ \bar{c}\bar{q}]_{S=0})_{S\mathrm{-wave}}$, and Y(10890) is $1^{--}$ state of the kind $Y_{[bq]}=([bq]_{S=0}[\bar{b}\bar{q}]_{S=0})_{\mathrm{P-wave}}$ and calculate the decay modes of these exotic states, further supporting X(3872) and Y(10890) as tetraquark (diquark-antidiquark) states and resolve the puzzling features of the data. We study the radiative decays of these states, using the idea of Vector Meson Dominance (VMD), which we hope will increase an insight about these tetraquark states. 
Abdur Rehman
hep-ph