A Selection Rule for Multiquark Decays

By assuming SU(6)_cs symmetry for pentaquark decays one finds a selection rule, which strongly reduces the number of states able to decay into a baryon and a meson final state and allows an intriguing identification for the Theta^+ particle recently discovered with the prediction of a narrow width.Comment: 10 pages, no figure

Experimental Outlook for the Pentaquark

A critical look is taken at both positive and null evidence for the $\Theta^+$ pentaquark. Potential problems with experiments will be discussed and the question of what conclusion can be drawn from both the positive and the null results is examined. First the question of existence of the $\Theta^+$ pentaquark is considered, followed by a discussion of new experiments that are either planned or in progress to answer questions about its mass, width and isospin. Finally, indirect evidence for the parity of the $\Theta^+$ is examined, and suggestions for experiments to measure its parity directly are given.Comment: MESON2004 conference proceedings, 10 pages, 1 figur

QCD sum rules for the anti-charmed pentaquark

We present a QCD sum rule analysis for the anti-charmed pentaquark state with and without strangeness. While the sum rules for most of the currents are either non-convergent or dominated by the $DN$ continuum, the one for the non-strange pentaquark current composed of two diquarks and an antiquark, is convergent and has a structure consistent with a positive parity pentaquark state after subtracting out the $DN$ continuum contribution. Arguments are presented on the similarity between the result of the present analysis and that based on the constituent quark models, which predict a more stable pentaquark states when the antiquark is heavy.Comment: 19 pages, 8 figures, REVTex, revised version,new figures added and references update

Polarization Observables in γN→KKˉN\gamma N\to K\bar{K}N

We explore some of the rich structure of the polarization observables recently developed for processes like $\gamma N\to\pi\pi N$ and $\gamma N\to K \bar{K} N$ in the framework of a specific model for the latter process. Emphasis is placed on observables that may be accesible at existing facilities in the near future. The sensitivity of the observables to the details of the model indicate that they will be a very useful tool in differentiating between different models for reactions like these. In the framework of a model for $\gamma N\to K \bar{K} N$, we examine the sensitivity of the observables to coupling constants of the $\phi$, to the properties of the $\Lambda(1405)$, and to the existence of the $\Theta^+$.Comment: 21 pages, latex, 17 figures, 1 style file include

Prospects of accelerator and reactor neutrino oscillation experiments for the coming ten years

We analyze the physics potential of long baseline neutrino oscillation experiments planned for the coming ten years, where the main focus is the sensitivity limit to the small mixing angle $\theta_{13}$. The discussed experiments include the conventional beam experiments MINOS, ICARUS, and OPERA, which are under construction, the planned superbeam experiments J-PARC to Super-Kamiokande and NuMI off-axis, as well as new reactor experiments with near and far detectors, represented by the Double-Chooz project. We perform a complete numerical simulation including systematics, correlations, and degeneracies on an equal footing for all experiments using the GLoBES software. After discussing the improvement of our knowledge on the atmospheric parameters $\theta_{23}$ and $\Delta m^2_{31}$ by these experiments, we investigate the potential to determine $\theta_{13}$ within the next ten years in detail. Furthermore, we show that under optimistic assumptions and for $\theta_{13}$ close to the current bound, even the next generation of experiments might provide some information on the Dirac CP phase and the type of the neutrino mass hierarchy.Comment: 38 pages, 13 figures, Eqs. (1) and (5) corrected, small corrections in Figs. 8, 9, and Tab. 4, discussion improved, ref. added, version to appear in PRD, high resolution figures are available at http://www.sns.ias.edu/~winter/figs0403068.htm

Exotic and nonexotic magnetic transitions in the context of the SELEX and GRAAL experiments

We calculate magnetic transition moments in the chiral quark-soliton model, with explicit SU(3)-symmetry breaking taken into account. The dynamical model parameters are fixed by experimental data for the magnetic moments of the baryon octet and from the recent measurements of $\Theta^{+}$ mass. Known magnetic transition moments $\mu_{\Lambda\Sigma}$, $\mu_{N\Delta}$ are reproduced and predictions for other octet-decuplet and octet-antidecuplet transitions are given. In particular $\mu_{\Sigma\Sigma^{\ast}}$ recently constrained by SELEX is shown to be below $0.82 \mu_N$. The recent GRAAL data on $\eta$ photoproduction off the nucleon are explained in terms of a new narrow antidecuplet neutron-like resonance.Comment: 14 pages, 9 figures. Final version accepted for publication in Phys.Rev.

Octet, decuplet and antidecuplet magnetic moments in the chiral quark soliton model revisited

We reanalyse the magnetic moments of the baryon octet, decuplet, and antidecuplet within the framework of the chiral quark-soliton model, with SU(3) symmetry breaking taken into account. We consider the contributions of the mixing of higher representations to the magnetic moment operator arising from the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by experimental data for the magnetic moments of the baryon octet and from the masses of the octet, decuplet and of $\Theta^{+}$. The magnetic moment of $\Theta^{+}$ depends rather strongly on the pion-nucleon sigma term and reads $-1.19 {\rm n.m.}$ to $-0.33 {\rm n.m.}$ for $\Sigma_{\pi N} = 45$ and 75 MeV respectively. The recently reported mass of $\Xi^{--}_{\bar{10}}(1862)$ is compatible with $\Sigma_{\pi N} = 73$ MeV. As a byproduct the strange magnetic moment of the nucleon is obtained with a value of $\mu^{(s)}_N =+0.39$ n.m.Comment: RevTeX is used. 12 pages, 3 figures, final version for publication in Phys. Rev.

Observation of a narrow baryon resonance with positive strangeness formed in K+K^+Xe collisions

The charge-exchange reaction K^+ Xe --> K^0 p Xe' is investigated using the data of the DIANA experiment. The distribution of the pK^0 effective mass shows a prominent enhancement near 1538 MeV formed by \sim 80 events above the background, whose width is consistent with being entirely due to the experimental resolution. Under the selections based on a simulation of K^+Xe collisions, the statistical significance of the signal reaches 5.5\sigma. We interpret this observation as strong evidence for formation of a pentaquark baryon with positive strangeness, \Theta^+(uudd\bar{s}), in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron. The mass of the \Theta^+ baryon is measured as m(\Theta^+) = 1538+-2 MeV. Using the ratio between the numbers of resonant and non-resonant charge-exchange events in the peak region, the intrinsic width of this baryon resonance is determined as \Gamma(\Theta^+) = 0.34+-0.10 MeV.Comment: 19 pages, 8 figure