963 research outputs found
Measurement of the reaction \gamma p \TO K^ + \Lambda(1520) at photon energies up to 2.65 GeV
The reaction \gamma p \TO K^+\Lambda(1520) was measured in the energy range
from threshold to 2.65 GeV with the SAPHIR detector at the electron stretcher
facility ELSA in Bonn. The production cross section was
analyzed in the decay modes , , , and
as a function of the photon energy and the squared
four-momentum transfer . While the cross sections for the inclusive
reactions rise steadily with energy, the cross section of the process \gamma p
\TO K^+\Lambda(1520) peaks at a photon energy of about 2.0 GeV, falls off
exponentially with , and shows a slope flattening with increasing photon
energy. The angular distributions in the -channel helicity system indicate
neither a nor a exchange dominance. The interpretation of the
as a molecule is not supported.Comment: 11 pages, 16 figures, 4 table
Measurement of gamma p --> K+ Lambda and gamma p --> K+ Sigma0 at photon energies up to 2.6 GeV
The reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma0 were measured
in the energy range from threshold up to a photon energy of 2.6 GeV. The data
were taken with the SAPHIR detector at the electron stretcher facility, ELSA.
Results on cross sections and hyperon polarizations are presented as a function
of kaon production angle and photon energy. The total cross section for Lambda
production rises steeply with energy close to threshold, whereas the Sigma0
cross section rises slowly to a maximum at about E_gamma = 1.45 GeV. Cross
sections together with their angular decompositions into Legendre polynomials
suggest contributions from resonance production for both reactions. In general,
the induced polarization of Lambda has negative values in the kaon forward
direction and positive values in the backward direction. The magnitude varies
with energy. The polarization of Sigma0 follows a similar angular and energy
dependence as that of Lambda, but with opposite sign.Comment: 21 pages, 25 figures, submitted to Eur. Phys. J.
Hadrons in AdS/QCD models
We discuss applications of gauge/gravity duality to describe the spectrum of
light hadrons. We compare two particular 5-dimensional approaches: a model with
an infrared deformed Anti-de Sitter metric and another one based on a dynamical
AdS/QCD framework with back-reacted geometry in a dilaton/gravity background.
The models break softly the scale invariance in the infrared region and allow
mass gap for the field excitations in the gravity description, while keeping
the conformal property of the metric close to the four-dimensional boundary.
The models provide linear Regge trajectories for light mesons, associated with
specially designed infrared gravity properties. We also review the results for
the decay widths of the f0's into two pions, as overlap integrals between
mesonic string amplitudes, which are in qualitative agreement with data
Where is the pseudoscalar glueball ?
The pseudoscalar mesons with the masses higher than 1 GeV are assumed to
belong to the meson decuplet including the glueball as the basis state
supplementing the standard nonet of light states
. The decuplet is investigated by means of an algebraic approach based
on hypothesis of vanishing the exotic commutators of "charges" and
their time derivatives. These commutators result in a system of equations
determining contents of the isoscalar octet state in the physical isoscalar
mesons as well as the mass formula including all masses of the decuplet:
, K(1460), , and . The physical
isoscalar mesons , are expressed as superpositions of the "ideal"
states ( and ) and the glueball with the mixing
coefficient matrix following from the exotic commutator restrictions. Among
four one-parameter families of the calculated mixing matrix (numerous solutions
result from bad quality of data on the and K(1460) masses) there is
one family attributing the glueball-dominant composition to the
meson. Similarity between the pseudoscalar and scalar decuplets, analogy
between the whole spectra of the and mesons and affinity of
the glueball with excited states are also noticed.Comment: 18 pp., 2. figs., 2 tabs.; Published version. One of the authors
withdraws his nam
Evidence for the positive-strangeness pentaquark in photoproduction with the SAPHIR detector at ELSA
The positive--strangeness baryon resonance is observed in
photoproduction of the final state with the SAPHIR detector at
the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in the invariant mass distribution with a confidence level. We find
a mass MeV and an upper limit of the width
MeV at 90% c.l. From the absence of a signal in
the invariant mass distribution in at the
expected strength we conclude that the must be isoscalar.Comment: 9 pages, 4 figure
Coherent manipulation of atomic qubits in optical micropotentials
We experimentally demonstrate the coherent manipulation of atomic states in
far-detuned dipole traps and registers of dipole traps based on two-dimensional
arrays of microlenses. By applying Rabi, Ramsey, and spin-echo techniques, we
systematically investigate the dephasing mechanisms and determine the coherence
time. Simultaneous Ramsey measurements in up to 16 dipole traps are performed
and proves the scalability of our approach. This represents an important step
in the application of scalable registers of atomic qubits for quantum
information processing. In addition, this system can serve as the basis for
novel atomic clocks making use of the parallel operation of a large number of
individual clocks each remaining separately addressable.Comment: to be published in Appl. Phys.
Radiative decays with light scalar mesons and singlet-octet mixing in ChPT
We study different types of radiative decays involving f0(980) and a0(980)
mesons within a unified ChPT-based approach at one-loop level. Light scalar
resonances which are seen in pi pi, pi eta, K K-bar channels of phi(1020)
radiative decays and in J/psi decays are responsible for key questions of
low-energy dynamics in the strong interaction sector, and decays phi(1020) ->
gamma a0(980), phi(1020) -> gamma f0(980), a0(980) -> gamma gamma, f0(980) ->
gamma gamma are of interest for current experimental programs in Juelich,
Frascati and Novosibirsk. From theoretical point of view it is important to
verify whether light scalar mesons are members of some flavor octet or nonet.
We find a value of mixing angle dictated by consistency with experiment and
coupling structures of ChPT Lagrangian. Decay widths f0(980)/a0(980) -> gamma
rho(770)/omega(782), which are not studied experimentally yet, are predicted.
We also obtain several relations between widths, which hold independently of
coupling constants and represent a fingerprint of the model.Comment: 18 pages, 8 figures; misprints in text and tables corrected,
discussion extended, references added; version accepted for publication in
Eur.Phys.J.
K0-Sigma+ Photoproduction with SAPHIR
Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are
presented. We show the first measurement of the differential cross section and
much improved data for the total cross section than previous data. The data are
compared with model predictions from different isobar and quark models that
give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the
same energy range. Results of ChPT describe the data adequately at threshold
while isobar models that include hadronic form factors reproduce the data at
intermediate energies.Comment: 4 pages, Latex2e, 4 postscript figures. Talk given at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97), Brookhaven National Laboratory, USA, October 13-18, 1997. To be
published in Nucl. Phys. A. Revised version due to changes in experimental
dat
Radiative open charm decay of the Y(3940), Z(3930), X(4160) resonances
We determine the radiative decay amplitudes for decay into and , or and of some of the charmonium like
states classified as X,Y,Z resonances, plus some other hidden charm states
which are dynamically generated from the interaction of vector mesons with
charm. The mass distributions as a function of the or
invariant mass show a peculiar behavior as a consequence of
the nature of these states. The experimental search of these
magnitudes can shed light on the nature of these states.Comment: 18 pages, 9 figure
Towards resolution of the scalar meson nonet enigma
By the application of a linear mass spectrum to a composite system of both
the pseudoscalar and scalar meson nonets, we find three mass relations for the
masses of the scalar states which suggest the assignment for the
scalar meson nonet: Comment: 16 pages, LaTe
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