A study of interference effects in photoproduced rho, omega and phi vector mesons decaying into the muon+ muon- final state and a measurement of the psi meson decaying to muon+ muon- branching fraction

This thesis is a study of the photoproduction of light and charmed-anticharmed mesons, using data collected by the FOCUS experiment. FOCUS is a fixed target photoproduction experiment at Fermi National Accelerator Laboratory (Fermi-lab), that collected data during 1996-1997. The experiment had a dimuon trigger which allowed us to obtain a very large sample of dimuon events.;The first analysis focuses on the study of the low mass vector mesons rho, o and &phis;, and provides the first high statistics measurement of the rho -- &phis; and rho -- o interference phases using muons. Attempts to determine such parameters, necessary for a better understanding of the production mechanisms of these vector mesons, date back to the end of the '60's, but a consistent analysis using leptonic final states ( e+e- or mu +mu-) is still missing. Our results are: frf=-31.2+/- 26.8&j0;a ndfrw= 184.5+/-3.5+/-3.1&j0; .;Our second analysis studies the psi' charmonium state and determines its branching fraction (BF) into the mu+mu- decay channel. The technique used to extract the BFpsi'→mu +mu- consists of measuring the yield of the psi' → mu+mu- decay (Y2b) relative to the yield of psi' → J/psipi+pi -, where the J/psi decays in mu +mu- (Y4 b). Fitting the psi' peak in the mu+mu - and mu+mu- pi +pi- mass plots, we report signal event yields of Y2b = 563 +/- 35 and Y4b = 1262 +/- 39. These measurements allow us to evaluate the psi' branching fraction as: BFy'→m+m-= 7.51+/-0.55stat+/- 0.55sys x10-3. This result significantly improves the precision of the world average value.