491 research outputs found
Multichannel calculation of excited vector resonances and the
A multichannel calculation of excited states is
carried out within a generalization of the Resonance-Spectrum Expansion, which
may shed light on the classification of the resonance, discovered
by BABAR and originally denoted X(2175). In this framework, a complete spectrum
of bare states is coupled to those OZI-allowed decay channels that
should be most relevant for the considered energy range. The included - and
-wave two-meson channels comprise the lowest pseudoscalar, vector, scalar,
and axial-vector mesons, while in the sector both the and
states are coupled. The only two free parameters are tuned so as to
reproduce mass and width of the , but come out reasonably close to
previously used values. Among the model's -matrix poles, there are good
candidates for observed resonances, as well other ones that should exist
according to the quark model. Besides the expected resonances as unitarized
confinement states, a dynamical resonance pole is found at MeV.
The huge width makes its interpretation as the somewhat dubious,
but further improvements of the model may change this conclusion.Comment: 6 pages, 5 figures, RevTex4; v2: very recent experimental result,
some extra discussion, and 2 references added; v3: 3 new figures, 2 new
equations, and some rephrasing; version accepted for publication in Phys.
Rev.
Comment on Intrinsic and dynamically generated scalar meson states
The scalar-meson assignments of Shakin and Wang in a generalized
Nambu--Jona-Lasinio model are contradicted by recent experimental information.
Also the strict distinction made by these authors between ``intrinsic'' and
``dynamically generated'' states is contested, as well as a number of other
statements.Comment: 7 pages, (v2 cosmetics, v3 corrections in one reference), to be
published in Phys.Rev.
A chiral model for bar{q}q and bar{q}bar{q}qq$ mesons
We point out that the spectrum of pseudoscalar and scalar mesons exhibits a
cuasi-degenerate chiral nonet in the energy region around 1.4 GeV whose scalar
component has a slightly inverted spectrum. Based on the empirical linear
rising of the mass of a hadron with the number of constituent quarks which
yields a mass around GeV for tetraquarks, we conjecture that this
cuasi-chiral nonet arises from the mixing of a chiral nonet composed of
tetraquarks with conventional bar{q}q states. We explore this possibility in
the framework of a chiral model assuming a tetraquark chiral nonet around 1.4
GeV with chiral symmetry realized directly. We stress that U_{A}(1)
transformations can distinguish bar{q}q from tetraquark states, although it
cannot distinguish specific dynamics in the later case. We find that the
measured spectrum is consistent with this picture. In general, pseudoscalar
states arise as mainly bar{q}q states but scalar states turn out to be strong
admixtures of bar{q}q and tetraquark states. We work out also the model
predictions for the most relevant couplings and calculate explicitly the strong
decays of the a_{0}(1450) and K_{0}^*(1430) mesons. From the comparison of some
of the predicted couplings with the experimental ones we conclude that
observable for the isovector and isospinor sectors are consistently described
within the model. The proper description of couplings in the isoscalar sectors
would require the introduction of glueball fields which is an important missing
piece in the present model.Comment: 20 pages, 3 figure
Real-time detection of single electron tunneling using a quantum point contact
We observe individual tunnel events of a single electron between a quantum
dot and a reservoir, using a nearby quantum point contact (QPC) as a charge
meter. The QPC is capacitively coupled to the dot, and the QPC conductance
changes by about 1% if the number of electrons on the dot changes by one. The
QPC is voltage biased and the current is monitored with an IV-convertor at room
temperature. We can resolve tunnel events separated by only 8 s, limited
by noise from the IV-convertor. Shot noise in the QPC sets a 25 ns lower bound
on the accessible timescales.Comment: 3 pages, 3 figures, submitte
Two photon decay of neutral scalars below 1.5 GeV in a chiral model for bar{q}q and bar{q}bar{q}qq states
We study the two photon decay of neutral scalars below 1.5 GeV in the context
of a recently proposed chiral model for bar{q}q and bar{q}bar{q}qq states. We
find good agreement with experimental results for the a_{0}(980)->gamma gamma.
Our calculations for f_{0}(980)->gamma gamma shows that further work is
necessary in order to understand the structure of this meson. The model
predicts Gamma(a_{0}(1450)->gamma gamma)=0.16+/-0.10KeV, Gamma(sigma->gamma
gamma)=0.47+/-0.66 KeV, Gamma(f(1370)->gamma gamma)=0.07+/-0.15 KeV,
Gamma(f(1500)->gamma gamma)=0.74+/-0.78 KeV.Comment: 6 pages, 1 figur
Effects of S-wave thresholds
The opening of a new S-wave threshold is frequently accompanied by an abrupt
dip in the magnitude of an amplitude for an already-open channel. One familiar
example is the behavior of the I=0 S-wave scattering amplitude at threshold. Numerous other examples of this phenomenon in recent data
are noted, and a unified description of the underlying dynamics is sought.Comment: 17 pages, 2 figures. Two additional references; typographic
correction. To be published in Phys. Rev.
Semiconductor few-electron quantum dot operated as a bipolar spin filter
We study the spin states of a few-electron quantum dot defined in a
two-dimensional electron gas, by applying a large in-plane magnetic field. We
observe the Zeeman splitting of the two-electron spin triplet states. Also, the
one-electron Zeeman splitting is clearly resolved at both the zero-to-one and
the one-to-two electron transition. Since the spin of the electrons transmitted
through the dot is opposite at these two transitions, this device can be
employed as an electrically tunable, bipolar spin filter. Calculations and
measurements show that higher-order tunnel processes and spin-orbit interaction
have a negligible effect on the polarization.Comment: 4 pages, 3 figure
Mixing among light scalar mesons and L=1 q\bar{q} scalar mesons
Following the re-establishment of the \sigma(600) and the \kappa(900), the
light scalar mesons a_0(980) and f_0(980) together with the \sigma(600) and the
\kappa(900) are considered as the chiral scalar partner of pseudoscalar nonet
in SU(3) chiral symmetry, and the high mass scalar mesons a_0(1450),
K^*_0(1430), f_0(1370) and f_0(1710) turned out to be considered as the L=1
q\bar{q} scalar mesons. We assume that the high mass of the L=1 q\bar{q} scalar
mesons is caused by the mixing with the light scalar mesons. For the structure
of the light scalar mesons, we adopted the qq\bar{q}\bar{q} model in order to
explain the "scalar meson puzzle". The inter-mixing between the light scalar
nonet and the high mass L=1 q\bar{q} nonet and the intra-mixing among each
nonet are analyzed by including the glueball into the high mass scalar nonet.Comment: 16 pages, 5 figure
Strong and radiative decays of the scalars f0(980) and a0(980) in a hadronic molecule approach
We analyze the electromagnetic and strong decay properties of the light
scalars a0(980) and f0(980) within a hadronic molecule interpretation. Both
scalars are discussed within a covariant and gauge invariant model which also
allows for finite size effects due to their spatially extended structure in the
K Kbar-bound state picture. Allowing for f0-a0 mixing we also study its
influence on the radiative decays f0/a0 to gamma gamma, f0/a0 to gamma omega,
and f0/a0 to gamma rho as well as the phi production of the f0 and a0.
Furthermore, we apply our formalism to describe the strong f0 to pi pi and a0
to pi eta decay properties.Comment: 16 pages, 6 figures, typos corrected, accepted for publication in
Phys. Rev.
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