31 research outputs found
Measurement of the Ds lifetime
We report precise measurement of the Ds meson lifetime. The data were taken
by the SELEX experiment (E781) spectrometer using 600 GeV/c Sigma-, pi- and p
beams. The measurement has been done using 918 reconstructed Ds. The lifetime
of the Ds is measured to be 472.5 +- 17.2 +- 6.6 fs, using K*(892)0K+- and phi
pi+- decay modes. The lifetime ratio of Ds to D0 is 1.145+-0.049.Comment: 5 pages, 2 figures submitted to Phys. Lett.
Confirmation of the Double Charm Baryon Xi_cc+ via its Decay to p D+ K-
We observes a signal for the double charm baryon Xi_cc+ in the charged decay
mode Xi_cc+ -> p D+ K- to complement the previously reported decay Xi_cc+ ->
Lambda_c K- pi+ in data from SELEX, the charm hadro-production experiment
(E781) at Fermilab. In this new decay mode we observe an excess of 5.62 events
over an expected background estimated by event mixing to be 1.38+/-0.13 events.
The Poisson probability that a background fluctuation can produce the apparent
signal is less than 6.4E-4. The observed mass of this state is
(3518+/-3)MeV/c^2, consistent with the published result. Averaging the two
results gives a mass of (3518.7+/-1.7)MeV/c^2. The observation of this new weak
decay mode confirms the previous SELEX suggestion that this state is a double
charm baryon. The relative branching ratio Gamma(Xi_cc+ -> pD+K-)/Gamma(Xi_cc+
-> Lambda_c K- pi+) = 0.36+/-0.21.Comment: 11 pages, 6 included eps figures. v2 includes improved statistical
method to determine significance of observation. Submitted to PL
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
Evidence for -atoms with DIRAC
We present evidence for the first observation of electromagnetically bound
-pairs (-atoms) with the DIRAC experiment at the CERN-PS.
The -atoms are produced by the 24 GeV/c proton beam in a thin Pt-target
and the and -mesons from the atom dissociation are analyzed in
a two-arm magnetic spectrometer. The observed enhancement at low relative
momentum corresponds to the production of 173 54 -atoms. The mean
life of -atoms is related to the s-wave -scattering lengths, the
measurement of which is the goal of the experiment. From these first data we
derive a lower limit for the mean life of 0.8 fs at 90% confidence level.Comment: 15 pages, 9 figure
DIRAC: A High Resolution Spectrometer for Pionium Detection
The DIRAC spectrometer has been commissioned at CERN with the aim of
detecting atoms produced by a 24 GeV/ high intensity proton
beam in thin foil targets. A challenging apparatus is required to cope with the
high interaction rates involved, the triggering of pion pairs with very low
relative momentum, and the measurement of the latter with resolution around 0.6
MeV/. The general characteristics of the apparatus are explained and each
part is described in some detail. The main features of the trigger system,
data-acquisition, monitoring and setup performances are also given.Comment: 49 pages, 37 figures. Figures 1, 2, 5 and 28 are removed because of
size limitations imposed by hep-ex. They don't offer essential information.
Latex class file 'elsart.cls' also provide
Hadronic Production of Lambda_c from 600 GeV/c pion, sigma and proton beams
We present data from Fermilab experiment E781 (SELEX) on the hadroproduction
asymmetry for anti-Lambda_c compared to Lambda_c+ as a function of xF and pt2
distributions for Lambda_c+. These data were measured in the same apparatus
using incident pi-, sigma- beams at 600 GeV/c and proton beam at 540 GeV/c. The
asymmetry is studied as a function of xF. In the forward hemisphere with xF >=
0.2 both baryon beams exhibit very strong preference for producing charm
baryons rather than charm antibaryons, while the pion beam asymmetry is much
smaller. In this energy regime the results show that beam fragments play a
major role in the kinematics of Lambda_c formation, as suggested by the leading
quark picture.Comment: 6 pages, 5 figures (postscript), RevTeX, submitted to Phy. Rev. Let
First measurement of the atom lifetime
The goal of the DIRAC experiment at CERN (PS212) is to measure the
atom lifetime with 10% precision. Such a measurement would yield a
precision of 5% on the value of the -wave scattering lengths
combination . Based on part of the collected data we present a first
result on the lifetime, s, and
discuss the major systematic errors. This lifetime corresponds to
.Comment: 18 pages, 6 figure
First Observation of the Cabibbo-suppressed Decays Xi_c+ -> Sigma+ pi- pi+ and Xi_c+ -> Sigma- pi+ pi+ and Measurement of their Branching Ratios
We report the first observation of two Cabibbo-suppressed decay modes, Xi_c+
-> Sigma+ pi- pi+ and Xi_c+ -> Sigma- pi+ pi+. We observe 59+/-14 over a
background of 87, and 22+/-8 over a background of 13 events, respectively, for
the signals. The data were accumulated using the SELEX spectrometer during the
1996-1997 fixed target run at Fermilab, chiefly from a 600GeV/c Sigma- beam.
The branching ratios of the decays relative to the Cabibbo--favored Xi_c+ ->
Xi- pi+ pi+ are measured to be B(Xi_c+ -> Sigma+ pi- pi+)/B(Xi_c+ -> Xi- pi+
pi+) = 0.48+/-0.20, and B(Xi_c+ -> Sigma- pi+ pi+)/B(Xi_c+ -> Xi- pi+ pi+) =
0.18+/-0.09, respectively. We also report branching ratios for the same decay
modes of the Lambda_c+ relative to Lambda_c+ -> p K- pi+.Comment: 15 pages, 5 figures, version 2 as accepted in PL