2,961 research outputs found
The role of secondary Reggeons in central meson production
We estimate the contribution of f_2 trajectory exchange to the central \eta
and \eta^\prime production. It is shown that secondary Reggeons may give a
large contribution to processes of double diffractive meson production at high
energy.Comment: 7 pages, Latex, 5 figure
Sea-quark effects in the pion charge form factor
It is shown that the data on the pion charge form factor admit the
possibility for a substantial sea-quark components in the pion wave function.
If the charge form factor is calculated with instant form kinematics in a
constituent quark model that is extended to include explicit
components in the pion wave function, that component will give the dominant
contribution to the calculated charge form factor at large values of
momentum transfer. The present experimental values can be described well
with component admixtures of up to 50%. The sensitivity of the
calculated charge form factor to whether one of the quarks or one of
the antiquarks is taken to be in the P-state is small.Comment: 14 page
Mixing of scalar tetraquark and quarkonia states in a chiral approach
A chiral invariant Lagrangian describing the tetraquark-quarkonia interaction
is considered at the leading and subleading order in the large-
expansion. Spontaneous chiral symmetry breaking generates mixing of scalar
tetraquark and quarkonia states and non-vanishing tetraquark condensates. In
particular, the mixing strength is related to the decay strengths of tetraquark
states into pseudoscalar mesons. The results show that scalar states below 1
GeV are mainly four-quark states and the scalars between 1 and 2 GeV
quark-antiquark states, probably mixed with the scalar glueball in the
isoscalar sector.Comment: 30 pages, 3 figures, 6 tables, to appear in Phys. Rev.
Five-quark components in decay
Five-quark components in the are shown to
contribute significantly to decay through
quark-antiquark annihilation transitions. These involve the overlap between the
and components and may be triggered by the confining
interaction between the quarks. With a 10% admixture of five-quark
components in the the decay width can be larger by factors 2 - 3
over that calculated in the quark model with 3 valence quarks, depending on the
details of the confining interaction. The effect of transitions between the
components themselves on the calculated decay width is however
small. The large contribution of the quark-antiquark annihilation transitions
thus may compensate the underprediction of the width of the by
the valence quark model, once the contains
components with 10% probability.Comment: accepted versio
The First Direct Distance and Luminosity Determination for a Self-Luminous Giant Exoplanet: The Trigonometric Parallax to 2MASS1207334-393254Ab
We present the first trigonometric parallax and distance for a young
planetary mass object. A likely TW Hya cluster member, 2MASSW J1207334-393254Ab
(hereafter 2M1207Ab) is an M8 brown dwarf with a mid to late L type planetary
mass companion. Recent observations of spectral variability have uncovered
clear signs of disk accretion and outflow, constraining the age of the system
to <10 Myr. Because of its late spectral type and the clearly youthful nature
of the system, 2M1207b is very likely a planetary mass object. We have measured
the first accurate distance and luminosity for a self-luminous planetary mass
object. Our parallax measurements are accurate to <2 mas (1sigma) for 2M1207Ab.
With 11 total epochs of data taken from January 2006 through April 2 007 (475
images for 2M1207Ab), we determine a distance of 58.8+-7.0 pc (17.0{+2.3}{-1.8}
mas, 1.28sigma) to 2M1207Ab and a calculated luminosity of 0.68-2.2x10^-5 Lsun
for 2M1207b. Hence 2M1207Ab is a clear member of the TW Hya cluster in terms of
its distance, proper motions, and youthful nature. However, as previously noted
by Mohanty and co-workers, 2M1207b's luminosity appears low compared to its
temperature according to evolutionary models.Comment: 12 pages, 3 figures, accepted to ApJ Letter
Pentaquark implications for exotic mesons
If the exotic baryon is a correlated with , then there should exist an exotic meson, GeV with width MeV. The
may be broad members of {\bf 10} \10bar in such a
picture. Vector mesons in the 1.4 - 1.7GeV mass range are also compared with
this picture
Spin of ground state baryons
We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page
Glueball enhancements in p(gamma,VV)p through vector meson dominance
Double vector meson photoproduction, p(gamma, G -> VV)p, mediated by a scalar
glueball G is investigated. Using vector meson dominance (VMD) and
Regge/pomeron phenomenology, a measureable glueball enhancement is predicted in
the invariant VV = rho rho and omega omega mass spectra. The scalar glueball is
assumed to be the lightest physical state on the daughter pomeron trajectory
governing diffractive vector meson photoproduction. In addition to cross
sections, calculations for hadronic and electromagnetic glueball decays, G -> V
V' (V,V'= rho, omega, phi, gamma), and gamma_v V -> G transition form factors
are presented based upon flavor universality, VMD and phenomenological
couplings from phi photoproduction analyses. The predicted glueball decay
widths are similar to an independent theoretical study. A novel signature for
glueball detection is also discussed
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