587 research outputs found
First case of Chlamydia trachomatis L2b proctitis in a woman
AbstractSince 2003, outbreaks of lymphogranuloma venereum (LGV) have been reported in European countries, North America, and Australia. Current LGV cases have been caused by Chlamydia trachomatis serovar L2. This sexually transmitted infection is predominantly found among men who have sex with men, specifically men who are seropositive for human immunodeficiency virus and have clinical signs of proctitis. The current outbreak has been almost exclusively attributed to a new variant, designated L2b. Although urogenital cases of LGV have been described in the heterosexual population, we report the first case of C. trachomatis L2b proctitis in a woman
Z-boson as "the standard candle" for high precision W-boson physics at LHC
In this paper we propose a strategy for measuring the inclusive W-boson
production processes at LHC. This strategy exploits simultaneously the unique
flexibility of the LHC collider in running variable beam particle species at
variable beam energies, and the configuration flexibility of the LHC detectors.
We propose their concrete settings for a precision measurement of the Standard
Model parameters. These dedicated settings optimise the use of the Z boson and
Drell-Yan pair production processes as ``the standard reference candles''. The
presented strategy allows to factorise and to directly measure those of the QCD
effects which affect differently the W and Z production processes. It reduces
to a level of 10^{-4} the impact of uncertainties in the partonic distribution
functions (PDFs) and in the transverse momentum of the quarks on the
measurement precision. Last but not the least, it reduces by a factor of 10 an
impact of systematic measurement errors, such as the energy scale and the
measurement resolution, on the W-boson production observables.Comment: 20 pages, 4 figure
ANALYSE DES NUCLÉONS ÉJECTÉS DANS UNE RÉACTION QUASI ÉLASTIQUE (p, p?) A 400 MeV
Une expérience de coïncidences (p,pγ) a été réalisée avec des protons incidents de 400 MeV sur différentes cibles 24Mg, 27Al, 28Si, 60Ni auprès de 1'accélérateur Saturne
Principle of Balance and the Sea Content of the Proton
In this study, the proton is taken as an ensemble of quark-gluon Fock states.
Using the principle of balance that every Fock state should be balanced with
all of the nearby Fock states (denoted as the balance model), instead of the
principle of detailed balance that any two nearby Fock states should be
balanced with each other (denoted as the detailed balance model), the
probabilities of finding every Fock state of the proton are obtained. The
balance model can be taken as a revised version of the detailed balance model,
which can give an excellent description of the light flavor sea asymmetry
(i.e., ) without any parameter. In case of
sub-processes not considered, the balance model and the
detailed balance model give the same results. In case of
sub-processes considered, there is about 10 percent difference between the
results of these models. We also calculate the strange content of the proton
using the balance model under the equal probability assumption.Comment: 32 latex pages, 4 ps figures, to appear in PR
Étude expérimentale et théorique de la production de nuclides légers rapides dans les interactions proton-noyau à haute énergie
Nous donnons la description d'une expérience réalisée au CERN et concernant la production de 1H, 2H, 3H, 3He, 4He lors des interactions proton-noyau (12C, 27Al, 197Au) à des angles variés (30°, 45°, 75°, 105°). Nous présentons également une théorie thermodynamique permettant d'interpréter les résultats expérimentaux obtenus
Flavor and Charge Symmetry in the Parton Distributions of the Nucleon
Recent calculations of charge symmetry violation(CSV) in the valence quark
distributions of the nucleon have revealed that the dominant symmetry breaking
contribution comes from the mass associated with the spectator quark
system.Assuming that the change in the spectator mass can be treated
perturbatively, we derive a model independent expression for the shift in the
parton distributions of the nucleon. This result is used to derive a relation
between the charge and flavor asymmetric contributions to the valence quark
distributions in the proton, and to calculate CSV contributions to the nucleon
sea. The CSV contribution to the Gottfried sum rule is also estimated, and
found to be small
Flavor Structure of the Nucleon Sea
The recent progress on our understanding of the flavor structure of
unpolarized and polarized nucleon sea is reviewed. The large flavor asymmetry
between the up and down sea quark distributions is now well established. This
asymmetry strongly suggests the importance of the mesonic degrees of freedom in
the description of the nucleon sea. The strong connection between the flavor
structure and the spin structure of the nucleon sea is emphasized. Possible
future measurements for testing various theoretical models are also discussed.Comment: 5pages, 4 figures, Invited talk presented at the QNP2002 conference,
Julich, June 200
The content of the D-meson at infinite coupling
We calculate the condensate in the D - and B - mesons using the
unquenched hopping parameter expansion at infinite coupling for the Wilson
lattice action. We discuss the phenomenological relevance of our result.Comment: 9 pages Latex file plus 2 uuencoded postscript figure
Polarized light-flavor antiquarks from Drell-Yan processes of h+\vec{N}\to\vec{l^{+-}} + l^{-+} + X
We propose a formula to determine the first moment of difference between the
polarized - and -quarks in the nucleon, {\it i.e.} from the Drell-Yan processes in collisions of unpolarized
hadrons with longitudinally polarized nucleons by measuring outgoing lepton
helicities. As coefficients in the differential cross section depend on the
- and -quark numbers in the unpolarized hadron beam, the difference
can be independently tested by changing the hadron
beam. Moreover, a formula for estimating the -factor in Drell-Yan processes
is also suggested.Comment: 10 pages, 1 figur
Chiral Quark Model with Configuration Mixing
The implications of one gluon exchange generated configuration mixing in the
Chiral Quark Model (QM) with SU(3) and axial U(1) symmetry
breakings are discussed in the context of proton flavor and spin structure as
well as the hyperon -decay parameters. We find that QM
with SU(3) symmetry breaking is able to give a satisfactory unified fit for
spin and quark distribution functions, with the symmetry breaking parameters
, and the mixing angle , both for NMC and the
most recent E866 data. In particular, the agreement with data, in the case of
, F, D, and , is quite striking.Comment: 16 pages, LaTex, Table and Appendix adde
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