M. Procario

Nuclear Dependence of Charm Production

Using data taken by SELEX during the 1996–1997 fixed target run at Fermilab, we study the production of charmed hadrons on copper and carbon targets withxa0Σ−, p, π−, and π+ beams. Parametrizing the dependence of the inclusive production cross section on the atomic number A as Aα, we determine α forxa0D+, D0, Ds+, D+(2010), Λc+, and their respective anti-particles, as a function of their transverse momentum pt and scaled longitudinal momentumxa0xF. Within our statistics there is no dependence of α on xF for any charm species for the interval 0.1<xF<1.0. The average value of α for charm production by pion beams is αmeson=0.850±0.028. This is somewhat larger than the corresponding average αbaryon=0.755±0.016 for charm production by baryon beams (Σ−, p).

Physics goals and experimental status of SELEX: Fermilab E781

SELEX is a fixed target experiment at Fermilab designed to do a systematic study of charm baryons. Data taking began in February, 1997, and preliminary charmed hadron signals have been observed.

Measurement of the [ital [bar B]][r arrow][ital D][sup *][ital l][bar [nu]] branching fractions and [vert bar][ital V][sub [ital c][ital b]][vert bar]

We study the exclusive semileptonic B meson decays B- ->D*0 l- nu and B0 ->D*+ l- nu using data collected with the CLEO II detector at CESR. We present measurements of the branching fractions B(B0 ->D*+ l-nu) = 0.5/f00* [4.49+/-0.32+/-0.39]% and B(B- ->D*0 l-nu) = 0.5/f+-*[5.13+/-0.54+/-0.64]%, where f00 and f+- are the neutral and charged B meson production fractions at the Upsilon(4s) resonance. Assuming isospion invariance and taking the charged to neutral B meson lifetimes measured at higher energy machines, we determine the ratio f+-/f00=1.04+/-0.14+/-0.13+-/-0.10; further assuming f+- + f00 = 1 we also determine the partial width G(B->D* l nu) = 29.9+/-1.9+/-2.7+/-2.0 ns-1 (independent of f+-/f00). From this partial width we calculate B ->D* l nu branching fractions that do not depend on f+-/f00, nor the individual B lifetimes, but only on the charged to neutral lifetime ratio. The product of the CKM matrix element |Vcb| times the normalization of the decay form factor at the point of zero recoil of the D* meson, F(y=1), is determined from a linear fit to the combined differential decay rate of the exclusive B->D* l nu decays: |Vcb|F(y) = 0.0351 +/- 0.0019 +/- 0.0018 +/- 0.0008. Using theoretical calculations of the form factor normalization we extract a value for |Vcb|. LATEX (REVTEX style) file with uuencoded figures attached (uses PSBOX). Available on WWW http://w4.lns.cornell.edu/public/CLNS/