Study of double charmonium production around √s = 10.58 GeV with the BaBar detector

In this thesis the analysis on double charmonium production at the energy of the $\Upsilon$(4S), with the \babar~data is documented. The aim of this analysis is to understand the mechanism of production of double charmonium states fro \ee annihilation, in particular after the discrepancies which at the beginning of these studies appeared. With successive studies, these discrepancies have been almost solved. This analysis was already performed by \babar~ collaboration \cite{shuwei}, and in this thesis we want to update that work, with a luminosity early four times higher (468 $fb^{1}$. In the mean time, also Belle collaboration published on this analysis \cite{bellecccc}, obtaining results compatible with \babar~ and finding out a new charmonium state, named X(3940). We aim here also to confirm this state. This thesis is composed by five chapters. Chapter I is an introduction to charmonium spectroscopy, with a description of the NRQCD, which the theorethical framework of this analysi, then the potential models that have been developed to describe the mass spectrum. The theories related to the double charmonium production mechanisms are presented in Chapter II: in particular the calculation of the cross section and the dicrepancies between theory and experiment. Then in Chapter III the \babar~detector is described. In Chapter IV there is a description on how has been performed the analysis: the analysis strategy, selection and cut optimization, and validation of the fit are documented, before the unblind of the interested region. In chapter V we give the final results, after unblind.