402 research outputs found
Status and commissioning of the Helium Supply Plant (HeSu) and the Series Test Facility (STF)
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
Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu
We measure the magnetic susceptibility of ultrathin Co films with an in-plane
uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie
temperature the influence of the magnetic anisotropy can be investigated by
means of the parallel and transverse susceptibilities along the easy and hard
axes. By comparison with a theoretical analysis of the susceptibilities we
determine the isotropic exchange interaction and the magnetic anisotropy. These
calculations are performed in the framework of a Heisenberg model by means of a
many-body Green's function method, since collective magnetic excitations are
very important in two-dimensional magnets.Comment: 7 pages, 3 figure
Search for the exotic Resonance in 340GeV/c -Nucleus Interactions
We report on a high statistics search for the resonance in
-nucleus collisions at 340GeV/c. No evidence for this resonance is
found in our data sample which contains 676000 candidates above
background. For the decay channel and the
kinematic range 0.150.9 we find a 3 upper limit for the
production cross section of 3.1 and 3.5 b per nucleon for reactions with
carbon and copper, respectively.Comment: 5 pages, 4 figures, modification of ref. 43 and 4
A study of the centrally produced phiphi system in pp interactions at 450 GeV/c
The reaction pp to pfps(K+K-K+K-) in which the K+K-K+K- system is centrally
produced has been studied at 450 GeV/c. Phi phi production has been found to
dominate this reaction and is compatible with being produced by double Pomeron
exchange. An angular analysis of the phi phi system favours JPC = 2++ and its
dPT dependence is similar to that observed for glueball candidates.Comment: 11 pages, Latex, 4 Figure
Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c
Two-particle correlation functions of negatively charged hadrons from Pb-Pb
collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment
at the CERN SPS. A Coulomb correction procedure that assumes an expanding
source has been implemented. Within the framework of an expanding thermalized
source model the size and dynamical state of the collision fireball at
freeze-out have been reconstructed as a function of the centrality of the
collision. Less central collisions exhibit a different dynamics than central
ones: both transverse and longitudinal expansion velocities are slower, the
expansion duration is shorter and the system freezes out showing smaller
dimensions and higher temperature.Comment: 22 pages, 11 figures, Te
Measurement of the beauty production cross-section in 350 GeV/c -Cu interactions
Using a sample of triggered events, produced in --Cu interactions at 350~GeV, we have identified 26 beauty events. The estimated background in this sample is events. From these data, assuming a linear A-dependence, we measure a beauty production cross-section integrated over all of nb/N
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
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