2,557 research outputs found
Implications of a DK Molecule at 2.32 GeV
We discuss the implications of a possible quasinuclear DK bound state at 2.32
GeV. Evidence for such a state was recently reported in D_s^+pi^o by the BaBar
Collaboration. We first note that a conventional quark model c-sbar assignment
is implausible, and then consider other options involving multiquark systems.
An I=0 c sbar n nbar baryonium assignment is one possibility. We instead favor
a DK meson molecule assignment, which can account for the mass and quantum
numbers of this state. The higher-mass scalar c-sbar state expected at 2.48 GeV
is predicted to have a very large DK coupling, which would encourage formation
of an I=0 DK molecule. Isospin mixing is expected in hadron molecules, and a
dominantly I=0 DK state with some I=1 admixture could explain both the narrow
total width of the 2.32 GeV state as well as the observed decay to D_s^+ pi^o.
Additional measurements that can be used to test this and related scenarios are
discussed.Comment: 6 pages, 1 figur
Dynamics of hadron strong production and decay
We generalize results of lattice QCD to determine the spin-dependent
symmetries and factorization properties of meson production in OZI allowed
processes. This explains some conjectures previously made in the literature
about axial meson decays and gives predictions for exclusive decays of vector
charmonia, including ways of establishing the structure of Y(4260) and Y(4325)
from their S-wave decays. Factorization gives a selection rule which forbids
near threshold with the tensor meson in helicity 2. The
relations among amplitudes for double charmonia production \e^+e^-\to
\psi\chi_{0,1,2} are expected to differ from the analagous relations among
light flavour production such as \e^+e^-\to \omega f_{0,1,2}.Comment: 13 pages; journal versio
Options for the SELEX state D_{s\J}^+(2632)
We consider possible assignments for the D_{s\J}^+(2632), which was
recently reported in D and DK final states by the SELEX
Collaboration at Fermilab. The most plausible quark model assignment for this
state is the first radial excitation () of the
D, although the predicted mass and strong decay branching fractions
for this assignment are not in agreement with the SELEX data. The reported
dominance of D over DK appears especially problematic. An intriguing
similarity to the K is noted. --^3\D_1 configuration
mixing is also considered, and we find that this effect is unlikely to resolve
the branching fraction discrepancy. Other interpretations as a -hybrid
or a two-meson molecule are also considered, but appear unlikely. Thus, if this
state is confirmed, it will require reconsideration of the systematics of
charmed meson spectroscopy and strong decays.Comment: 6 revtex4 pages, 2 eps figure
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
A chromomagnetic mechanism for the X(3872) resonance
The chromomagnetic interaction, with proper account for flavour-symmetry
breaking, is shown to explain the mass and coupling properties of the X(3872)
resonance as a = 1 state consisting of a heavy quark-antiquark
pair and a light one. It is crucial to introduce all the spin-colour
configurations compatible with these quantum numbers and diagonalise the
chromomagnetic interaction in this basis. This approach thus differs from the
molecular picture and from the diquark-antidiquark picture.Comment: 4 pages - revtex4 - Typos corrected, refs. added, to be published in
Phys. Rev.
Decisive Search for a Diquark-Antidiquark Meson with Hidden Strangeness
Diquark-antidiquark states are expected to exist as a natural complement of
mesons and baryons. Although they were predicted long ago, and some candidates
were found experimentally, none has, as yet, been reliably identified. We
suggest that the search for the so-called -meson in reactions such as
photoproduction and should provide a decisive way to settle this issue. Estimates of the
cross sections are given using present experimental information on the C-meson
and assuming its diquark-antidiquark structure. Sizable cross sections are
predicted (of the order of 0.1 b for photoproduction and of the order of
0.1 mb for at the maximum with an insignificant background). Failure to
find this kind of signal would imply that the C-meson is {\it not} a
diquark-antidiquark state.Comment: 9 pages in LATex + 6 figs. (available from authers upon request),
IUHET-269/9
Radiative decays: a new flavour filter
Radiative decays of the orbital excitations of the ,
and to the scalars , and are shown to
provide a flavour filter, clarifying the extent of glueball mixing in the
scalar states. A complementary approach to the latter is provided by the
radiative decays of the scalar mesons to the ground-state vectors ,
and . Discrimination among different mixing scenarios is strong.Comment: 12 pages, 1 table, 0 figure
Spin-dependent Parton Distributions from Polarized Structure Function Data
In the past year, polarized deep inelastic scattering experiments at CERN and
SLAC have obtained structure function measurements off proton, neutron and
deuteron targets at a level of precision never before achieved. The
measurements can be used to test the Bjorken and Ellis-Jaffe sum rules, and
also to obtain information on the parton distributions in polarized nucleons.
We perform a global leading-order QCD fit to the proton deep inelastic data in
order to extract the spin-dependent parton distributions. By using parametric
forms which are consistent with theoretical expectations at large and small
, we find that the quark distributions are now rather well constrained. We
assume that there is no significant intrinsic polarization of the strange quark
sea. The data are then consistent with a modest amount of the proton's spin
carried by the gluon, although the shape of the gluon distribution is not well
constrained, and several qualitatively different shapes are suggested. The
spin-dependent distributions we obtain can be used as input to phenomenological
studies for future polarized hadron-hadron and lepton-hadron colliders.Comment: 23 pages, DTP/94/3
Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis.
BACKGROUND: An open-label study indicated that selective depletion of B cells with the use of rituximab led to sustained clinical improvements for patients with rheumatoid arthritis. To confirm these observations, we conducted a randomized, double-blind, controlled study. METHODS: We randomly assigned 161 patients who had active rheumatoid arthritis despite treatment with methotrexate to receive one of four treatments: oral methotrexate (> or =10 mg per week) (control); rituximab (1000 mg on days 1 and 15); rituximab plus cyclophosphamide (750 mg on days 3 and 17); or rituximab plus methotrexate. Responses defined according to the criteria of the American College of Rheumatology (ACR) and the European League against Rheumatism (EULAR) were assessed at week 24 (primary analyses) and week 48 (exploratory analyses). RESULTS: At week 24, the proportion of patients with 50 percent improvement in disease symptoms according to the ACR criteria, the primary end point, was significantly greater with the rituximab-methotrexate combination (43 percent, P=0.005) and the rituximab-cyclophosphamide combination (41 percent, P=0.005) than with methotrexate alone (13 percent). In all groups treated with rituximab, a significantly higher proportion of patients had a 20 percent improvement in disease symptoms according to the ACR criteria (65 to 76 percent vs. 38 percent, P< or =0.025) or had EULAR responses (83 to 85 percent vs. 50 percent, P< or =0.004). All ACR responses were maintained at week 48 in the rituximab-methotrexate group. The majority of adverse events occurred with the first rituximab infusion: at 24 weeks, serious infections occurred in one patient (2.5 percent) in the control group and in four patients (3.3 percent) in the rituximab groups. Peripheral-blood immunoglobulin concentrations remained within normal ranges. CONCLUSIONS: In patients with active rheumatoid arthritis despite methotrexate treatment, a single course of two infusions of rituximab, alone or in combination with either cyclophosphamide or continued methotrexate, provided significant improvement in disease symptoms at both weeks 24 and 48
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