A proposal to construct SELEX - segmented large-x baryon spectrometer

Heavy flavor experiments currently in progress at e{sup +}e{sup -} colliders or in the fixed target programs at CERN and Fermilab are aimed at collecting large samples (> 10,000 reconstructed events) of charmed events. These experiments will provide a great deal of information about charmed meson systems, but the expected yield of charmed baryons is not large--10% or less of the sample size. The most detailed study of the charm strange baryon {Xi}{sub c}{sup +} comes not from a large-statistics central production experiment at high energy but rather from a 20-day run at modest beam flux in the CERN hyperon beam. This proposal exploits the advantages in triggering and particle identification of large-x production to make a systematic study of charm baryon production and decay systematics. For the dominant ({approx} 10% branching ratio) modes of these baryons, they expect to collect 10{sup 6} triggered events in each mode per running period. This will give adequate statistics to study even highly suppressed modes. The study of meson systematics by the Mark III spectrometer at SPEAR led to a revolution in the understanding of charmed meson decay mechanisms. No present experiment will supply a similar data set for the charmed baryons. A fixed target experiment cannot supply the absolute branching ratios that e{sup +}e{sup -} annihilation on the {Upsilon}(3770) resonance provides for the Mark III data. They can supply relative branching ratios for the non-leptonic and semileptonic decay modes of charmed baryons and establish the importance of two-body resonance modes in the decay mechanism. This information, along with lifetime measurements for {Lambda}{sub c}{sup +}, {Sigma}{sub c}{sup ++}, {Sigma}{sub c}{sup +}, {Sigma}{sub c}{sup 0}, {Xi}{sub c}{sup +} and {Omega}{sub c}{sup 0} baryons, will permit evaluation in the baryon sector of the role of color suppression, Pauli suppression, sextet enhancement and other varied mechanisms which influence decay rates of charmed hadrons. This information will be very difficult to obtain from existing spectrometers because of the wide range of particle identification methods needed to handle different decay modes. SELEX is designed specifically to do this job, as they said in the Letter of Intent.