215 research outputs found
Redefinición del género Propolydesmus Verhoeff, 1895 y revisión del género en las islas Canarias (Diplopoda, Polydesmida, Polydesmidae)
The genus Propolydesmus Verhoeff, 1895 is redefined, with Hormobrachium Attems, 1940 considered as its subjective junior synonym (syn. n.!); it currently encompasses at least a dozen valid species ranging from Macaronesia in the west to Central Europe in the east. Two species of Propolydesmus are known from the Canary Islands: P. laevidentatus (Loksa, 1967) (=Polydesmus brincki Demange, 1970, syn. n.!), comb. n. ex Polydesmus, occurring in Madeira, the Azores and Tenerife, Canary Islands, and P. dismilus (Berlese, 1891), comb. n. ex Polydesmus, which is newly recorded from Macaronesia (Canary Islands, Tenerife). Gonopods of both these species are illustrated, and the range of variation in P. laevidentatus is shown to be considerable.Se redefine el género Propolydesmus Verhoeff, 1895 —considerando a Hormobrachium Attems, 1940 como un sinónimo junior subjetivo (syn. n.)— el cual comprende una docena de especies extendidas desde Macaronesia, al oeste, hasta Centroeuropa, al este. En las islas Canarias se conocen dos especies de Propolydesmus: P. laevidentatus (Loksa, 1967) (= Polydesmus brincki Demange, 1970, syn. n.), comb. n. ex Polydesmus, que vive en Madeira, Azores y Tenerife, y P. dismilus (Berlese, 1891), comb. n. ex Polydesmus, que se cita por primera vez en Macaronesia (islas Canarias: Tenerife). Se ilustran los gonopodos de ambas especies y se demuestra el considerable grado de variación de P. laevidentatus
Evidence for the Nucleon Resonance from Combined Studies of CLAS Photo- and Electroproduction Data
The analysis of the nine 1-fold differential cross sections for the
photo- and electroproduction reactions
obtained with the CLAS detector at Jefferson Laboratory was carried out with
the goal to establish the contributing resonances in the mass range from
1.6~GeV to 1.8~GeV. In order to describe the photo- and electroproduction data
with -independent resonance masses and hadronic decay widths in the
range below 1.5~GeV, it was found that an state is required
in addition to the already well-established nucleon resonances. This work
demonstrates that the combined studies of photo- and
electroproduction data are vital for the observation of this resonance. The
contributions from the state and the already established
state with a mass of 1.745~GeV are well separated by their
different hadronic decays to the and final states and the
different -evolution of their photo-/electroexcitation amplitudes. The
state is the first recently established baryon resonance for
which the results on the -evolution of the photo-/electrocouplings have
become available. These results are important for the exploration of the nature
of the ``missing'' baryon resonances.Comment: accepted for publication in Phys. Lett.
Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1GeV2 . I. ep→eπ+n
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive
π
+
electroproduction reaction
γ
∗
p
→
n
π
+
. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic range covered is
1.1
<
W
<
3
GeV and
1
<
Q
2
<
6
GeV
2
. Results were obtained for about 6000 bins in
W
,
Q
2
,
cos
(
θ
∗
)
, and
ϕ
∗
. Except at forward angles, very large target-spin asymmetries are observed over the entire
W
region. Reasonable agreement is found with phenomenological fits to previous data for
W
<
1.6
GeV, but very large differences are seen at higher values of
W
. A generalized parton distributions (GPD)-based model is in poor agreement with the data. When combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of
Q
2
, for resonances with masses as high as 2.4 GeV
Transverse Polarization of in Photoproduction on a Hydrogen Target in CLAS
Experimental results on the hyperon transverse polarization
in photoproduction on a hydrogen target using the CLAS detector at Jefferson
laboratory are presented. The was reconstructed in the
exclusive reaction via the
decay mode. The was reconstructed in the
invariant mass of two oppositely charged pions with the identified in
the missing mass of the detected final state. Experimental data
were collected in the photon energy range = 1.0-3.5 GeV
( range 1.66-2.73 GeV). We observe a large negative polarization of
up to 95%. As the mechanism of transverse polarization of hyperons produced in
unpolarized photoproduction experiments is still not well understood, these
results will help to distinguish between different theoretical models on
hyperon production and provide valuable information for the searches of missing
baryon resonances.Comment: pages 1
Comment on the narrow structure reported by Amaryan et al
The CLAS Collaboration provides a comment on the physics interpretation of
the results presented in a paper published by M. Amaryan et al. regarding the
possible observation of a narrow structure in the mass spectrum of a
photoproduction experiment.Comment: to be published in Physical Review
Induced polarization of {\Lambda}(1116) in kaon electroproduction
We have measured the induced polarization of the in the
reaction , detecting the scattered and
in the final state along with the proton from the decay .The present study used the CEBAF Large Acceptance Spectrometer (CLAS),
which allowed for a large kinematic acceptance in invariant energy
( GeV) and covered the full range of the kaon production
angle at an average momentum transfer GeV.In this experiment a
5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target.
We have mapped out the and kaon production angle dependencies of the
induced polarization and found striking differences from photoproduction data
over most of the kinematic range studied. However, we also found that the
induced polarization is essentially independent in our kinematic domain,
suggesting that somewhere below the covered here there must be a strong
dependence. Along with previously published photo- and electroproduction
cross sections and polarization observables, these data are needed for the
development of models, such as effective field theories, and as input to
coupled-channel analyses that can provide evidence of previously unobserved
-channel resonances.Comment: 13 figure
Cross sections for the γp→K*+Λ and γp→K*+Σ0 reactions measured at CLAS
The first high-statistics cross sections for the reactions γp→K*+Λ and γp→K*+Σ0 were measured using the CLAS detector at photon energies between threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. Differential cross sections are presented over the full range of the center-of-mass angles, and then fitted to Legendre polynomials to extract the total cross section. Results for the K*+Λ final state are compared with two different calculations in an isobar and a Regge model, respectively. Theoretical calculations significantly underestimate the K*+Λ total cross sections between 2.1 and 2.6 GeV, but are in better agreement with present data at higher photon energies
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