Measurement of the Omega_c Lifetime

We present the measurement of the lifetime of the Omega_c we have performed using three independent data samples from two different decay modes. Using a Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts normally used in charm analysis. The short but measurable lifetime of the Omega_c is demonstrated by a clear enhancement of the signals at short but finite decay lengths. Using a continuous maximum likelihood method we determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs. This makes the Omega_c the shortest living weakly decaying particle observed so far. The short value of the lifetime confirms the predicted pattern of the charmed baryon lifetimes and demonstrates that the strong interaction plays a vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip

Search for the exotic Ξ−−(1860)\Xi^{--}(1860) Resonance in 340GeV/c Σ−\Sigma^--Nucleus Interactions

We report on a high statistics search for the $\Xi^{--}(1860)$ resonance in $\Sigma^-$-nucleus collisions at 340GeV/c. No evidence for this resonance is found in our data sample which contains 676000 $\Xi^-$ candidates above background. For the decay channel $\Xi^{--}(1860) \to \Xi^-\pi^-$ and the kinematic range 0.15$<x_F<$0.9 we find a 3$\sigma$ upper limit for the production cross section of 3.1 and 3.5 $\mu$b per nucleon for reactions with carbon and copper, respectively.Comment: 5 pages, 4 figures, modification of ref. 43 and 4

Charge Asymmetries for D, D_s and Lambda_c Production in Sigma- - Nucleus Interactions at 340 GeV/c

CERN experiment WA89 has studied charmed particles produced by a Sigma^- beam at 340 GeV/c on nuclear targets. Production of particles which have light quarks in common with the beam is compared to production of those which do not. Considerable production asymmetries between D^- and D^p, D_s^ and D_s^+ and Lambda_c and Antilambda_c are observed. The results are compared with pion beam data and with theoretical calculations.Comment: LaTeX ; 16 pages including 4 ps figure

Search for the pentaquark candidate Θ+\Theta^+(1540) in the hyperon beam experiment WA89

We report on a high-statistics search for the \t1540 resonance in $\Sigma^-$-nucleus collisions at 340 \gevc1 . No evidence for this resonance was found in our data sample which contains 13 millions $K^0_s \to \pi^+\pi^-$ decays above background. For the decay channel $\Theta^+ \to K^0_s p$ and the kinematic range $x_F>$ 0.05 we find the production cross section to be $BR(\Theta^+ \to K^0_s p)\cdot \sigma_0 <$ 1.8 $\mu$b per nucleon at 99% CL.Comment: 5 pages, 4 figure

Electrical Conductivity of the Thermal Dusty Plasma under the Conditions of a Hybrid Plasma Environment Simulation Facility

We discuss the inductively heated plasma generator (IPG) facility in application to the generation of the thermal dusty plasma formed by the positively charged dust particles and the electrons emitted by them. We develop a theoretical model for the calculation of plasma electrical conductivity under typical conditions of the IPG. We show that the electrical conductivity of dusty plasma is defined by collisions with the neutral gas molecules and by the electron number density. The latter is calculated in the approximations of an ideal and strongly coupled particle system and in the regime of weak and strong screening of the particle charge. The maximum attainable electron number density and corresponding maximum plasma electrical conductivity prove to be independent of the particle emissivity. Analysis of available experiments is performed, in particular, of our recent experiment with plasma formed by the combustion products of a propane–air mixture and the CeO2 particles injected into it. A good correlation between the theory and experimental data points to the adequacy of our approach. Our main conclusion is that a level of the electrical conductivity due to the thermal ionization of the dust particles is sufficiently high to compete with that of the potassium-doped plasmas

New Data On

Among the ground state charmed hadrons the\Omega 0 c is the least known particle. It has so far been observed in a few decay channels only and with low statistics. Using a data sample of 1993 from the CERN hyperon beam experiment WA89 the\Omega 0 c has been found in 7 decay modes which cover final states with\Omega \Gamma , \Xi \Gamma and . We present a measurement of the\Omega 0 c mass and its lifetime. 1 Introduction The \Omega 0 c (ssc) is the least well known weakly decaying charmed baryon. First found in the former hyperon beam experiment WA62 [1] it has been seen by Argus [2] and E687 [3]. These experiments found the\Omega 0 c in four different decay channels. In the following we present new data on the\Omega 0 c in seven decay modes obtained in the CERN hyperon beam experiment WA89. The measured lifetimes of the three charmed baryons + c (udc), \Xi + c (usc), \Xi 0 c (dsc) differ by almost a factor of 4. For the \Xi 0 c decay the direct decay and the deca..