Charm lifetime

A review of the charmed meson and baryon lifetimes is presented. Our knowledge of charmed particle lifetimes has greatly improved over the past two years, a crucial r\^ole having been played by the E687 experiment at Fermilab, which has almost quadrupled the samples of $D$ mesons. The lifetime ratios $\tau(D^+)/\tau(D^0)$ and $\tau(D_s^+)/\tau(D^0)$ are now known with an accuracy of 1.7\% and 3.7\% respectively. In the baryon sector the statistics is still limited, but the experimental results on $\Lambda_c^+$, $\Xi_c^0$ and $\Xi_c^+$ exhibit a clear pattern of lifetime hierarchy, as expected from simple theoretical arguments. The first measurement of $\tau(\Omega_c^0)$ from E687 is also presented to complete the charmed baryon lifetime picture. The more accurate experimental scenario can provide information on non-perturbative QCD effects and the hadronic matrix elements.Comment: 10 pages, latex, 3 figures. Talk presented at the 6th. International Symposium on Heavy Flavour Physics (Pisa, June 1995

Effect of CH4_{4} addition on excess electron mobility in liquid Kr

The excess electrons mobility $\mu$ has been measured recently in liquid mixtures of Kr and CH$_{4}$ as a function of the electric field up to $E\approx 10^{4} V/cm$ and of the CH$_{4}$ concentration $x$ up to $x \approx 10$ at temperatures $T\approx 130 K,$ fairly close to the normal boiling point of Kr $(T_{b}\approx 120 K)$(folegani). We present here new data which extend the previous set in the region of low electric field. The experimental results are interpreted in terms of a kinetic model previously proposed to explain the concentration dependent behavior of $\mu$ in liquid Ar--Kr and Ar--Xe mixtures. The main result is that CH$_{4}$ is more effective in enhancing energy--transfer rather than momentum--transfer in comparison with mixtures of liquified noble gases. The field dependence of $\mu$ is quite complicate. In particular, at intermediate values of the field, there appears to be a crossover between two different electric--field dependent behaviors of $\mu.$ The electric field strength at crossover is well correlated with the concentration of CH$_{4}.$ This fact suggests that different excitations of the molecular solute might be involved in the momentum-- and energy--transfer processes for different values of the mean electron energy.Comment: 17, pages,7 figures, RevTeX4, submitted to J.Chem.Phy

Scalar meson properties from D-meson decays

Decay amplitudes of D(D_s)->f0(980)X, X=pi, K, are compared to experimental branching ratios with the aim of singling out the poorly known D->f0(980) transition form factor in these amplitudes. Since the other elements of the amplitudes are either calculable in an effective QCD theory using operator product expansion or are known from experiment (e.g. the pion and kaon decay constants), we can take advantage of these reactions to constrain the transition form factors obtained in relativistic quark models. In these models, the f0(980) wavefunction requires an unknown size parameter for both its non-strange ubar u(dbar d) and strange sbar s components, which we fit to the D(D_s) decay data.Comment: Talk given at the Few Body 18 conference in Santos, Brazil. 4 pages, to be published in Nuclear Physics

Charmed Baryons with J=3/2J = 3/2

The width of a recently discovered excited charmed-strange baryon, a candidate for a state $\Xi_c^*$ with spin 3/2, is calculated. In the absence of configuration mixing between the ground-state (spin-1/2) charmed-strange baryon $\Xi_c^{(a)}$ and the spin-1/2 state $\Xi_c^{(s)}$ lying about 95 MeV above it, one finds $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = (3/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$ and $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(s)} \pi) = (1/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$, where the tilde denotes the partial width with kinematic factors removed. Assuming a kinematic factor for P-wave decay of $p_{\rm cm}^3$, one predicts $\Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = 2.3$ MeV, while the $\Xi^*_c \to \Xi_c^{(s)} \pi$ channel is closed. Some suggestions are given for detecting the $\Sigma_c^*$, the spin-3/2 charmed nonstrange baryon, and the $\Omega_c^*$, the spin-3/2 charmed doubly-strange baryon.Comment: 11 pages, latex, 2 uuencoded figures sent separatel

Electron drift velocity measurements in liquid krypton–methane mixtures

Abstract Electron drift velocities have been measured in liquid krypton, pure and mixed with methane at different concentrations (1–10% in volume) versus electric field strength, and a possible effect of methane on electron lifetime has been investigated. While no effect on lifetime could be detected, since lifetimes were in all cases longer than what measurable, a very large increase in drift velocity (up to a factor 6) has been measured

One-pion transitions between heavy baryons in the constituent quark model

Single pion transitions of S wave to S wave, P wave to S wave and P wave to P wave heavy baryons are analyzed in the framework of the Heavy Quark Symmetry limit (HQS). We use a constituent quark model picture for the light diquark system with an underlying SU(2N_{f}) X O(3) symmetry to reduce the number of the HQS coupling factors required to describe these transitions. We also use the quantum theory of angular momentum to rewrite the one-pion transitions constituent quark model results in a more general form using the 6j- and 9j-symbols. We finally estimate the decay rates of some single pion transitions between charm baryon states.Comment: Latex, 33 pages including 2 figures (Postscript). Some typos are corrected with minor changes. Two references were added to the final version which will appear in Phy. Rev.

Ds+→ϕρ+D_s^+ \to \phi \rho^+ Decay

Motivated by the experimental measurement of the decay rate, $\Gamma$, and the longitudinal polarization, $P_L$, in the Cabibbo favored decay $D_s^+\to \phi {\rho}^{+}$, we have studied theoretical prediction within the context of factorization approximation invoking several form factors models. We were able to obtain agreement with experiment for both $\Gamma$ and $P_L$ by using experimentally measured values of the form factors $A_1^{D_s\phi}(0)$, $A_2^{D_s\phi}(0)$ and $V^{D_s\phi}(0)$ in the semi-leptonic decay $D_s^+\to \phi l^{+}\nu_{l}$. We have also included in our calculation the effect of the final state interaction ($fsi$) by working with the partial waves amplitudes $S$, $P$ and $D$. Numerical calculation shows that the decay amplitude is dominated by $S$ wave, and that the polarization is sensitive to the interference between $S$ and $D$ waves. The range of the phase difference $\delta_{SD} = \delta_S - \delta_D$ accommodated by experimental error in $P_L$ is large.Comment: 7 pages, LaTe

Nonresonant Three-body Decays of D and B Mesons

Nonresonant three-body decays of D and B mesons are studied. It is pointed out that if heavy meson chiral perturbation theory (HMChPT) is applied to the heavy-light strong and weak vertices and assumed to be valid over the whole kinematic region, then the predicted decay rates for nonresonant charmless 3-body B decays will be too large and especially B^- --> pi^- K^+ K^- greatly exceeds the current experimental limit. This can be understood as chiral symmetry has been applied there twice beyond its region of validity. If HMChPT is applied only to the strong vertex and the weak transition is accounted for by the form factors, the dominant B^* pole contribution to the tree-dominated direct three-body B decays will become small and the branching ratio will be of order 10^{-6}. The decay modes B^- --> (K^- h^+ h^-)_{NR} and bar{B}^0 --> (bar{K}^0 h^+h^-)_{NR} for h = pi, K are penguin dominated. We apply HMChPT in two different cases to study the direct 3-body D decays and compare the results with experiment. Theoretical uncertainties are discussed.Comment: 24 pages, 2 figures. New experimental results of direct 3-body D decays as Reported at ICHEP2002 are included. To appear in Phys. Re

Strong Decays of Strange Charmed P-Wave Mesons

Goldstone boson decays of P-wave $D_s^{**}$ mesons are studied within the framework of Heavy Hadron Chiral Perturbation Theory. We first analyze the simplest single kaon decays of these strange charmed mesons. We derive a model independent prediction for the width of $D_{s2}$ and use experimental information on $D_{s1}$ to constrain the S-wave contribution to $D_1^0$ decay. Single and double pion decay modes are then discussed and shown to be significantly restricted by isospin conservation. We conclude that the pion channels may offer the best hope for detecting one strange member of an otherwise invisible P-wave flavor multiplet.Comment: 16 pages, 2 updated figures not included but available upon request, CALT-68-1902. (Revised estimates for error on $D_{s2}$ width and for isospin violating neutral pion decay of $D'_{s1}$.