141 research outputs found
Analytical sun synchronous low-thrust manoeuvres
Article describes analytical sun synchronous low-thrust manoeuvres
Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector
Inclusive J/psi production in photon-photon collisions has been observed at
LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X
is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an
integrated luminosity of 617 pb^{-1}, yielding a cross-section of
sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the
event shapes of different types of gamma gamma processes in the PYTHIA program,
we conclude that (74 +/- 22)% of the observed J/psi events are due to
`resolved' photons, the dominant contribution of which is most probably due to
the gluon content of the photon.Comment: 13 pages, 8 figures, Accepted by Phys. Lett.
Energy dependence of Cronin momentum in saturation model for and collisions
We calculate dependence of Cronin momentum for and
collisions in saturation model. We show that this dependence is consistent with
expectation from formula which was obtained using simple dimentional
consideration. This can be used to test validity of saturation model (and
distinguish among its variants) and measure dependence of saturation
momentum from experimental data.Comment: LaTeX2e, 12 pages, 8 figure
Spallation reactions. A successful interplay between modeling and applications
The spallation reactions are a type of nuclear reaction which occur in space
by interaction of the cosmic rays with interstellar bodies. The first
spallation reactions induced with an accelerator took place in 1947 at the
Berkeley cyclotron (University of California) with 200 MeV deuterons and 400
MeV alpha beams. They highlighted the multiple emission of neutrons and charged
particles and the production of a large number of residual nuclei far different
from the target nuclei. The same year R. Serber describes the reaction in two
steps: a first and fast one with high-energy particle emission leading to an
excited remnant nucleus, and a second one, much slower, the de-excitation of
the remnant. In 2010 IAEA organized a worskhop to present the results of the
most widely used spallation codes within a benchmark of spallation models. If
one of the goals was to understand the deficiencies, if any, in each code, one
remarkable outcome points out the overall high-quality level of some models and
so the great improvements achieved since Serber. Particle transport codes can
then rely on such spallation models to treat the reactions between a light
particle and an atomic nucleus with energies spanning from few tens of MeV up
to some GeV. An overview of the spallation reactions modeling is presented in
order to point out the incomparable contribution of models based on basic
physics to numerous applications where such reactions occur. Validations or
benchmarks, which are necessary steps in the improvement process, are also
addressed, as well as the potential future domains of development. Spallation
reactions modeling is a representative case of continuous studies aiming at
understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie
Inclusive b decays to wrong sign charmed mesons
The production of wrong sign charmed mesons b → D (s)X, D (s) = (D 0, D +, D s), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z → bb events are exclusively reconstructed by searching for the decays D 0 → K -π +, D + → K -π +π + and D s + φπ + → K +K -π +. The wrong sign contribution is extracted by using two discriminant variables: the charge of the b-quark at decay time, estimated from the charges of identified particles, and the momentum of the charmed meson in the rest frame of the b-hadron. The inclusive branching fractions of b-hadrons into wrong sign charm mesons are measured to be: B(b → D 0X) + B(b → D -X) = (9.3 ± 1.7(stat) ± 1.3(syst) ± 0.4(B))%, B(b → D s -X) = (10.1 ± 0.4(B))%, B(b → D s -X) = (10.1 ± 1.0(stat) ± 0.6(syst) ± 2.8(B))% where the first error is statistical, the second and third errors are systematic. © 2003 Published by Elsevier Science B.V.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Production of Xi_c^0 and Xi_b in Z decays and lifetime measurement of Xi_b
The charmed strange baryon Xi_c^0 was searched for in the decay channel
Xi_c^0 -> Xi- pi+, and the beauty strange baryon Xi_b in the inclusive channel
Xi_b -> Xi- l- anti-nu X, using the 3.5 million hadronic Z events collected by
the DELPHI experiment in the years 1992--1995. The Xi- was reconstructed
through the decay Xi- -> Lambda pi-, using a constrained fit method for cascade
decays. An iterative discriminant analysis was used for the Xi_c^0 and Xi_b
selection. The production rates were measured to be f_{Xi_c^0} x BR(Xi_c^0 ->
Xi- pi+)= (4.7 +/- 1.4 (stat.) +/- 1.1 (syst.))10^{-4} per hadronic Z decay,
and BR(b -> Xi_b) x BR(Xi_b -> Xi- l- X)= (3.0 +/- 1.0 (stat.) +/- 0.3
(syst.))10^{-4} for each lepton species (electron or muon). The lifetime of the
Xi_b baryon was measured to be tau_{Xi_b} = 1.45{^{+0.55}_{-0.43}} (stat.) +/-
0.13 (syst.) ps. A combination with the previous DELPHI lifetime measurement
gives tau_{Xi_b} = 1.48{^{+0.40}_{-0.31}} (stat.) +/- 0.12 (syst.) ps.Comment: 21 pages, 9 figures, Accepted by Eur. Phys. J.
Study of double-tagged gamma gamma events at LEPII
Double-tagged interactions of photons with virtualities Q^2 between 10 GeV^2
and 200 GeV^2 are studied with the data collected by DELPHI at LEPII from 1998
to 2000, corresponding to an integrated luminosity of 550 pb^{-1}. The gam*
gam* -> mu+mu- data agree with QED predictions. The cross-section of the
reaction gam* gam* -> hadrons is measured and compared to the LO and NLO BFKL
calculations.Comment: 17 pages, 9 figures, Accepted by Eur. Phys. J.
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