1,336 research outputs found

### Meson-like Baryons and the Spin-Orbit Puzzle

I describe a special class of meson-like \Lambda_Q excited states and present
evidence supporting the similarity of their spin-independent spectra to those
of mesons. I then examine spin-dependent forces in these baryons, showing that
predicted effects of spin-orbit forces are small for them for the same reason
they are small for the analogous mesons: a fortuitous cancellation between
large spin-orbit forces due to one-gluon-exchange and equally large inverted
spin-orbit forces due to Thomas precession in the confining potential. In
addition to eliminating the baryon spin-orbit puzzle in these states, this
solution provides a new perspective on spin-orbit forces in all baryons.Comment: 24 pages, 4 figure

### Flux Tube Zero-Point Motion, Hadronic Charge Radii, and Hybrid Meson Production Cross Sections

Flux tube zero-point motion produces quark displacements transverse to the
flux tube which make significant contributions to hadronic charge radii. In
heavy quark systems, these contributions can be related by Bjorken's sum rule
to the rates for semileptonic decay to hybrid mesons. This connection can be
generalized to other leptoproduction processes, where transverse contributions
to elastic form factor slopes are related to the cross sections for the
production of the associated hybrid states. I identify the flux tube overlap
integral responsible for these effects as the strong QCD analogue of the
Sudakov form factor of perturbative QCD.Comment: 16 pages, revised to clarify some points and to improve and correct
the notation for the flux tube wave function

### Rare $B$-Decays and Heavy to Light Semileptonic Transitions in the Isgur and Wise Limit

From the experimental branching ratios for $B^- --> \rho^0 l^-\bar\nu_l$ and
D^+ --> {\overl K}^{*0}({\overl K}^0) e^+ \nu_e one finds, in the Heavy Quark
Limit of $HQET$, $|V_{bu}|=(8.1\pm 1.7) x 10^{-3}$, larger but consistent with
the actual quoted range $(2 - 7) x 10^{-3}$. In the same framework one predicts
for $R(B --> K^*\gamma)=( 2 \pm 2 ) 10^{-2}$.Comment: 9 pages, 1 Figure avalaible on request from [email protected]

### Comment on "Valence QCD: Connecting QCD to the Quark Model"

I criticize certain conclusions about the physics of hadrons drawn from a
"valence QCD" approximation to QCD.Comment: 12 pages, 8 figures; some minor improvements made to the tex

### Exotic baryons from a heavy meson and a nucleon

We evaluate a hadronic molecule formed by a heavy meson and a nucleon
respecting heavy quark symmetry. The tensor force of pion exchange potential
plays a dominate role to produce an strong attraction in this system. Solving
coupled channel Schr\"odinger equations for PN and P* N, we find many bound and
resonant states with isospin I=0 while there are few resonances in I=1 state.
The rich structures with I=0 indicate that the spectrum of heavy baryons near
the threshold is influenced by the contributions from such hadron composite
structures.Comment: To appear in the proceedings of The 5th International Workshop on
Charm Physics (Charm 2012

### Remark on Charm Quark Fragmentation to $D^{**}$ Mesons

The observed $D^{**}$ mesons have $c\bar q$ flavor quantum numbers and
spin-parity of the light degrees of freedom $s_\ell^{\pi_{\ell}} = 3/2^+$. In
the $m_c \rightarrow \infty$ limit the spin of the charm quark is conserved and
the $c \rightarrow D^{**}$ fragmentation process is characterized by the
probability for the charm quark to fragment to a $D^{**}$ meson with a given
helicity for the light degrees of freedom. We consider the calculated $b
\rightarrow B_c^{**}$ fragmentation functions in the limit $m_c/m_b \rightarrow
0$ as a qualitative model for the $c \rightarrow D^{**}$ fragmentation
functions. We find that in this model charm quark fragmentation to
$s_\ell^{\pi_{\ell}} = 3/2^+$ light degrees of freedom with helicities $\pm
1/2$ is favored over fragmentation to $s_\ell^{\pi_{\ell}} = 3/2^+$ light
degrees of freedom with helicities $\pm 3/2$.Comment: 6 pages, CALT-68-192

### Test of OPE and OGE through mixing angles of negative parity N* resonances in electromagnetic transitions

In this report, by using the mixing angles of one-gluon-exchange model(OGE)
and one-pion-exchange model(OPE), and by using the electromagnetic Hamiltonian
of Close and Li, we calculate the amplitudes of L=1 N* resonances for
photoproduction and electroproduction. The results are compared to experimental
data. It's found that the data support OGE, not OPE.Comment: 5 pages, Latex, 1 figure, accepted by Phys.Rev.

### A Bjorken sum rule for semileptonic $\Omega_b$ decays to ground and excited charmed baryon states

We derive a Bjorken sum rule for semileptonic $\Omega_b$ decays to ground and
low-lying negative-parity excited charmed baryon states, in the heavy quark
limit. We discuss the restriction from this sum rule on form factors and
compare it with some models.Comment: 10 pages, RevTex, no figure, Alberta Thy--26--9

### On the nature of the X(3872)

We present recent studies of charmonium multiquark states. We use different
interacting models and numerical methods to study deeply bound four-quark
states and meson-meson molecules. No deeply bound four-quark states are found
in our analysis. A nice description of the X(3872) is obtained as a
$D\bar{D}^*-J/\Psi\omega$ coupled channel state.Comment: 3 pages. Talk presented at the Conference MESON 2010, 10-15 june
2010, Krakow, Poland. To be published in International Journal of Modern
Physics

### Form factors of heavy-light systems in point-form relativistic quantum mechanics: the Isgur-Wise function

We investigate electromagnetic and weak form factors of heavy-light mesons in
the context of point-form relativistic quantum mechanics. To this aim we treat
the physical processes from which such electroweak form factors are extracted
by means of a coupled channel approach which accounts for the dynamics of the
intermediate gauge bosons. It is shown that heavy-quark symmetry is respected
by this formulation. A simple analytical expression is obtained for the
Isgur-Wise function in the heavy-quark limit. Breaking of heavy-quark symmetry
due to realistic values of the heavy-quark mass are studied numerically.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201

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