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

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

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

Perturbative and Non-perturbative Corrections to B→D(∗)lνB\to D^{(*)}l\nu

It is shown that certain double ratios introduced for computing semileptonic form factors are accurate to order $1/m_Q^2$, even when the action and current are accurate to order $1/m_Q$.Comment: Lattice99(heavyquarks); 3 + epsilon pp. LaTe

Rare BB-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]

Photocouplings of nucleon resonances with gluon and pion exchange currents

Photocouplings for the nucleon resonances most relevant to total photoabsorption are calculated in a constituent quark model including gluon and pion exchange. The sensitivity of the results to the different ingredients of the model is discussed.Comment: 23 pages including 9 tables, LaTe

Remark on Charm Quark Fragmentation to D∗∗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

A New Method for Selecting Exclusive Semileptonic Charmless B-Decays at e+e−e^+ e^- Colliders at the Υ(4S)\Upsilon(4S)

We introduce a new method for selecting exclusive semileptonic charmless B-decays in the presence of a large background. The method can be applied to charged and neutral B-mesons decaying into any exclusive neutral or charged hadronic final state. The method is designed for high luminosity \eplemi colliders operating at the $\Upsilon(4S)$. It employs an improved partial reconstruction technique for \Dstar-mesons and a novel 0-C event fit to both B-meson's decay products resulting in the kinematics of all particles (including neutrinos) in the event. The charged lepton energies are accessible from 1.0 \GeV to the kinematic limit.Comment: 10 pages with 7 figures in subdirectory fi

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.

Quark-Hadron Duality in Structure Functions

While quark-hadron duality is well-established experimentally, the current theoretical understanding of this important phenomenon is quite limited. To expose the essential features of the dynamics behind duality, we use a simple model in which the hadronic spectrum is dominated by narrow resonances made of valence quarks. We qualitatively reproduce the features of duality as seen in electron scattering data within our model. We show that in order to observe duality, it is essential to use the appropriate scaling variable and scaling function. In addition to its great intrinsic interest in connecting the quark-gluon and hadronic pictures, an understanding of quark-hadron duality could lead to important benefits in extending the applicability of scaling into previously inaccessible regions.Comment: 16 pages, 4 figures; minor typos correcte