Narrow Results

Entropy production by a dilaton decay is studied in the model where the dilaton acquires potential via gaugino condensation in the hidden gauge group. Its effect on the Affleck-Dine baryogenesis is investigated. It is shown that the baryon asymmetry produced by this mechanism with the higher-dimensional terms is diluted by the dilaton decay and can be regulated to the observed value.

A narrow baryon state has been found in the channel of quasi-real photoproduction on a deuterium target at the HERMES experiment. Its mass is 1528±2.6±2.1 MeV and its width is somewhat larger than the experimental resolution of 4.3-6.2 MeV. This state may be interpreted as the predicted S=+1 exotic Θ⁺ pentaquark baryon. No signal for a hypothetical Θ⁺⁺ baryon was observed, indicating that the Θ⁺ is an isoscalar particle.

It has been ten years since the first report for a positive strangeness pentaquark-like baryon state. However, the existence of the pentaquark state is still controversial. Some contradictions between the experiments are unsolved. In this paper, we review the experimental search for the pentaquark candidates Θ⁺, Θ⁺⁺, Ξ^{- -}, and N* in detail. We review the experiments with positive results and compare the experiments with similar conditions but opposite results.

The search for undiscovered excited states of the nucleon continues to be a focus of experiments at Jefferson Lab. Recent LQCD calculations have confirmed long-standing quark-model predictions of many more states than have so far been identified.¹ A large effort for the N* program has been launched using the CLAS detector to provide the database that will allow nearly model-independent partial wave analyses to be carried out in the search for such states. Polarization observables play a crucial role in this effort, as they are essential in disentangling overlapping resonant and non-resonant amplitudes. In 2010, double-polarization data were taken at JLab using circularly polarized photons incident on a transversely polarized frozen-spin butanol target.² Our current analysis yields preliminary data of the T and F asymmetries of the K⁺Λ and K⁺Σ⁰ final states, which are compared to predictions of recent multipole analyses. This work is the first of its kind and will significantly broaden the world database for these reactions.

We investigate quark to $\mathrm{\Lambda }$ and $\bar{\mathrm{\Lambda }}$ longitudinal spin transfers in the light-cone SU(6) quark sepctator-diquark model and try to analyze the possible origins for the spin transfer difference between them measured by the COMPASS collaboration. The intermediate heavier hyperon decay processes are considered, while the final hadron transverse momentum is also included. We find that after taking into account the asymmetric nucleon $s/\bar{s}$ distribution effect, the results we get are qualitatively comparable with the difference of the COMPASS experimental data.