42 research outputs found
Model-independent Study of Magnetic Dipole Transitions in Quarkonium
We study magnetic dipole (M1) transitions between two quarkonia in the
framework of non-relativistic effective field theories of QCD. Relativistic
corrections of relative order v^2 are investigated in a systematic fashion.
Non-perturbative corrections due to color-octet effects are considered for the
first time and shown to vanish at leading order. Exact, all order expressions
for the relevant 1/m and 1/m^2 operators are derived. The results allow us to
scrutinize several potential model claims. In particular, we show that QCD
excludes both contributions to the anomalous magnetic moment of the quarkonium
induced by low-energy fluctuations and contributions to the magnetic dipole
operators of the type induced by a scalar potential. Finally, we apply our
results to the transitions J/psi -> eta_c gamma, Upsilon(1S) -> eta_b gamma,
Upsilon(2S) -> eta_b(2S) gamma, Upsilon(2S) -> eta_b gamma, eta_b(2S) ->
Upsilon(1S) gamma, h_b(1P) -> chi_{b0,1}(1P) gamma and chi_{b2}(1P) -> h_b(1P)
gamma by assuming these quarkonium states in the weak-coupling regime. Our
analysis shows that the J/psi -> eta_c gamma width is consistent with a
weak-coupling treatment of the charmonium ground state, while such a treatment
for the hindered transition Upsilon(2S) -> eta_b gamma appears difficult to
accommodate within the CLEO III upper limit.Comment: 44 pages, 8 figures; typos corrected, one reference added; to appear
in Physical Review
The static force in background perturbation theory
The static force and the strong coupling , which
defines the gluon-exchange part of , are studied in QCD background
perturbation theory (BPT). In the region r\la 0.6 fm turns out
to be essentially smaller than the coupling in the static
potential. For the dimensionless function the
characteristic values and are shown to be
reached at the following separations: in quenched approximation and for . The numbers obtained appear to be by only
8% smaller than those calculated in lattice QCD while the values of the
couplings and in BPT are by
and larger than corresponding lattice couplings. With the use of
the BPT potential good description of the bottomonium spectrum is obtained.Comment: 21 pages, 1 figure. To be publised in Phys. Atom. Nucl. dedicated to
the 70-th birthday of Yu.A. Simono
Effects of perturbative exchanges in a QCD-string model
The QCD-string model for baryons derived by Simonov and used for the
calculation of baryon magnetic moments in a previous paper is extended to
include also perturbative gluon and meson exchanges. The mass spectrum of the
baryon multiplet is studied. For the meson interaction either the pseudoscalar
or pseudovector coupling is used. Predictions are compared with the
experimental data. Besides these exchanges the influence of excited quark
orbitals on the baryon ground state are considered by performing a multichannel
calculation. The nucleon-Delta splitting increases due to the mixing of higher
quark states while the baryon magnetic momenta decrease. The multichannel
calculation with perturbative exchanges is shown to yield reasonable magnetic
moments while the mass spectrum is close to experiment.Comment: 37 pages Revtex with 2 figures, to be published in Phys. Atom. Nucl.
dedicated to the 70th Birthday of Yu. A. Simono
Excited Charmed Mesons: Observations, Analyses and Puzzles
We review the status of recently observed positive parity charmed resonances,
both in the non-strange and in the strange sector. We describe the experimental
findings, the main theoretical analyses and the open problems deserving further
investigations.Comment: LaTeX, 25 pages, 5 figures. Invited revie
NRQCD Analysis of Bottomonium Production at the Tevatron
Recent data from the CDF collaboration on the production of spin-triplet
bottomonium states at the Tevatron p \bar p collider are analyzed within the
NRQCD factorization formalism. The color-singlet matrix elements are determined
from electromagnetic decays and from potential models. The color-octet matrix
elements are determined by fitting the CDF data on the cross sections for
Upsilon(1S), Upsilon(2S), and Upsilon(3S) at large p_T and the fractions of
Upsilon(1S) coming from chi_b(1P) and chi_b(2P). We use the resulting matrix
elements to predict the cross sections at the Tevatron for the spin-singlet
states eta_b(nS) and h_b(nP). We argue that eta_b(1S) should be observable in
Run II through the decay eta_b -> J/psi + J/psi.Comment: 20 pages, 3 figure
Study of the , , and in the radiative decays
In this paper we present an approach to study the radiative decay modes of
the into a photon and one of the tensor mesons ,
, as well as the scalar ones and .
Especially we compare predictions that emerge from a scheme where the states
appear dynamically in the solution of vector meson--vector meson scattering
amplitudes to those from a (admittedly naive) quark model. We provide evidence
that it might be possible to distinguish amongst the two scenarios, once
improved data are available.Comment: The large Nc argument improved; version published in EPJA
The newly observed open-charm states in quark model
Comparing the measured properties of the newly observed open-charm states
D(2550), D(2600), D(2750), D(2760), D_{s1}(2710), D_{sJ}(2860), and
D_{sJ}(3040) with our predicted spectroscopy and strong decays in a constituent
quark model, we find that: (1) the D(2\,^1S_0) assignment to D(2550) remains
open for its too broad width determined by experiment; (2) the D(2600) and
can be identified as the 2\,^3S_1-1\,^3D_1 mixtures; (3) if
the D(2760) and D(2750) are indeed the same resonance, they would be the
D(1\,^3D_3); otherwise, they could be assigned as the D(1\,^3D_3) and
, respectively; (4) the could be either the
's partner or the D_s(1\,^3D_3); and (5) both the
and interpretations for the seem likely. The
and radiative decays of these sates are also studied. Further
experimental efforts are needed to test the present quarkonium assignments for
these new open-charm states.Comment: 26 pages,7 figures, journal versio