Session Q12: Baryons and B Lifetime Studies

Production of Charm Baryons in CDF II

Using the data collected with the CDF Run II detector preliminary results on ground state charm baryon $\Lambda_{c}^{+}$ and $\Sigma_{c}^{++,0}$ will be presented. The results are based on a large data sample made available by the displaced track trigger. The results on $\Sigma_{c}^{++,0}$ are the measurements made at Tevatron hadron collisions for the first time.   

BaBar Searches for Double Charm Baryons

We present the results of searches for $\Xi_{cc}^+\rightarrow \Lambda_c^+ K^- \pi^+$ and $\Xi_{cc}^{++}\rightarrow \Lambda_c^+ K^- \pi^+ \pi^+$. The decay $\Lambda_c(2880)\rightarrow \Lambda_c^+ \pi^- \pi^+$ is used as a control and reference mode. We search wide mass regions for the $\Xi_{cc} ^+$ and \Xi_{cc}^{++}$ baryons that include several previously reported signals and theoretical predictions. Experimentally observing double charm baryons is a major step in scrutinizing predictions involving diquarks in theoretical QCD. Our data set was collected with the BaBar detector at the PEP-II $e^+e^-$ storage rings and consists of 210 fb$^{-1}$ collected on the $\Upsilon(4S)$ resonance, and 22 fb$^{-1}$ collected approximately 40 MeV below this resonance.   

Studies in heavy baryon chiral perturbation theory

We investigate heavy baryon chiral perturbation theory (HBChPT) and its convergence properties by considering different power counting schemes and higher order terms. We apply these modifications to strong decays of the decuplet baryons and to axial currents of the octet baryons. Then we turn to weak decays of the octet and decuplet. We hope to improve the extraction of low energy constants of the theory with the goal of providing improved predictions for octet and decuplet baryon observables, including those involved in hypernuclear decay.   

Numerical calculations of electromagnetic contributions to baryon masses

We calculate numerically the electromagnetic contributions to the baryon masses which we analyzed recently using the heavy-baryon approximation in chiral effective field theory and methods developed in our earlier analyses of the baryon masses and magnetic moments. We find that the effects of the quark masses, the Coulomb and moment-moment interactions, and the mesonic corrections account fairly well for a pattern of coefficients in a mass-difference Hamiltonian that describes well the accurately known baryon mass splittings.   

$B^+$, $B^0$, $B^0_s$, $\Lambda_B$ lifetimes and lifetime ratios.

We present new, high-statistics measurements of b hadron lifetimes from exclusive decays containing a $J/\psi$ selected using a dimuon trigger in CDF. The analysis uses about 800 pb$^{-1}$ of data from Run II of the Tevatron collider. In addition to the channels $B^+ \rightarrow J/\psi K^+$, $B^0 \rightarrow J/\psi K^{0*}$, $B^0\rightarrow J/\psi K^0_s$, which are well measured at B factories, we measure lifetimes of $\Lambda_b$ and $B_s^0$, (unique to the Tevatron) in the channels $B^0_s\rightarrow J/\psi\phi$ and $\Lambda_b \rightarrow J/\psi\Lambda^0$. Systematic errors in the ratios of lifetimes are minimized by the consistent use of the $J/\psi$ vertex across all decay channels, to estimate proper decay time.   

Monte Carlo Free Estimation of the $B^+$ Meson Lifetime Using a Hadronic Decay Mode

We present a new measurement of the $B^{+}$ meson lifetime from exclusive decays ($B^{+} \rightarrow \bar{D^0}\pi^{+}$), selected using CDF's hadronic B trigger from about 800 pb$^{-1}$ of data from Run II of the Tevatron collider. The bias induced by this trigger is corrected on an event-per-event basis, using observed kinematic event variables, with no dependence on Monte Carlo simulation. The analysis is complementary to CDF's previously published analyses, which uses an efficiency curve obtained from simulation, and has independent systematic uncertainties.   

Measurement of the $\Lambda_b$ lifetime in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV

The lifetime of the $\Lambda_b$ baryon is presently the most interesting of all $b$-hadron lifetimes, and at the same time the least well known experimentally. We study the lifetime of the $\Lambda_b$ baryon using $\Lambda_b \to \Lamdbda_c^+\pi^+$ decay mode in 360~pb$^{-1}$ of CDF data. Our $\Lambda_b \to \Lamdbda_c^+\pi^+$ sample has in excess of $1400$ events and is the largest sample of $\Lambda_b$ decays in existence. We study the effects of the trigger bias and the presence of physics backgrounds on the measurement of the lifetime of $\Lambda_b$.   

$\Lambda_b$ lifetime measurement using semileptonic decays at D\O

Using approximately 1 fb$^{-1}$ of data collected by the D\O detector in Run II, a sample of over 2000 $\Lambda_b \rightarrow \Lambda_c \mu X (\Lambda_c \rightarrow K_s p)$ decays has been reconstructed. We present preliminary results of a measurement of the $\Lambda_b$ lifetime using this sample.   

Study of the form factor in semileptonic $\Lambda_b$ decays

We measure the $\Lambda_b$ baryon form factor using the exclusive decay ${\Lambda^0_b \rightarrow \Lambda^+_c \mu^- \bar{\nu}}$ followed by $\Lambda^+_c \rightarrow p^+ K^0_S$ and $K^0_S \rightarrow \pi^+ \pi^-$. The data sample corresponds to an integrated luminosity of approximately 1~fb$^{-1}$, recorded with the D\O\ detector in $p\bar{p}$ collisions at $\sqrt{s} =1.96$~TeV. We present a preliminary result on the Isgur-Wise slope.