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

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

The Omega-RICH

A large-aperture RICH for identification of secondary particles is in operation at the Omega spectrometer since 1984. Photons are detected in drift chambers with quartzwindows, using TMAE-loaded counting gases. The RICH was used by two experiments, WA69 and WA82, until 1988. It was then equipped with new drift chambers and mirrors and is in use since 1990 mainly for the hyperon beam experiment WA89. The present setup is described in more detail and efficiencies, resolutions and particle separation achieved are discussed. Work supported by the Bundesministerium fur Forschung und Technologie (codes 05 5HD15I, 06 HD524I, 06 MZ5265 TP2) 1) Physikalisches Institut, Univ. Heidelberg, Germany 2) CERN European Organization for Nuclear Research, Geneva, Switzerland 3) Max-Planck-Institut fur Kernphysik, Heidelberg, Germany 4) Institut fur Kernphysik, Univ. Mainz, Germany a) Now at Fermi Nat. Acc. Lab., Batavia, Ill., USA b) On leave from Lebedev Inst., Moscow, Russia 1 Introduction In 1984, ..

The Rich Counter in the CERN Hyperon Beam Experiment

The hyperon beam experiment WA89 at the CERN-SPS uses a ring-imaging Cherenkov counter (RICH) for identification of secondaries from \Sigma \Gamma N reactions. Cherenkov photons are generated in a 5 m long radiator volume filled with nitrogen at atmospheric pressure and detected in drift chambers. The drift chambers cover an active surface of 1:6 \Theta 0:75 m 2 , with a maximum drift path of 41 cm. Photo-electrons are counted on 1280 wires with a pitch of 2:54 mm, equipped with multihit-TDC&apos;s. The counting gas is ethane saturated with TMAE at 30 ffi C. The counter was operated in two beam periods in 1990 and 1991. The spatial resolution of the chambers is better than 2 mm and under normal running conditions 14 photo-electrons per ring have been detected on average. 1) CERN European Organization for Nuclear Research, Geneva, Switzerland 2) Physikalisches Institut, Univ. Heidelberg, Germany 3) Max-Planck-Institut fur Kernphysik, Heidelberg, Germany 4) Institut fur Kernphysik, Univ..

The Omega RICH in the CERN hyperon beam experiment

The Omega RICH, a large-aperture detector for identification of secondary pions, kaons, and (anti) protons was in operation at the CERN Omega spectrometer facility between 1984 and 1994. Cherenkov photons from a 5 m long radiator were detected in drift chambers with quartz windows, using TMAE-loaded counting gases. The RICH was used by experiments WA69 and WA82, until 1988. It was then equipped with new drift chambers and mirrors and was in use since 1990 in experiments WA89 and WA94. The setup in the WA89 hyperon beam experiment is described in more detail and efficiencies, resolutions, and physics results are discussed