[Paper Review] Strong and electromagnetic decays for excited heavy mesons

Aksel Hiorth Orsland, H. Högaasen|arXiv (Cornell University)|Dec 14, 1998

Quantum Chromodynamics and Particle Interactions4 citations

TL;DR

This paper proposes a bag model for excited heavy mesons, treating the light quark as moving in the color electric field of a static heavy quark. It calculates pionic and photonic transition amplitudes and branching ratios, showing good agreement with limited experimental data on strong and electromagnetic decays of excited charmed and bottom mesons.

ABSTRACT

We discuss a model for heavy mesons where the light quark (u or d) moves in the colour electric field from a heavy quark (c or b) placed in the center of the bag. We calculate energy spectra for pionic and photonic transitions from excited states. The transition amplitudes and the branching ratios between electromagnetic and pionic transitions compares favorable with the limited amount of known experimental data.

Motivation & Objective

• To develop a theoretical framework for describing excited heavy mesons using a relativistic quark model with a static heavy quark.
• To calculate transition amplitudes for pionic (strong) and photonic (electromagnetic) decays from excited states.
• To compare predicted branching ratios for electromagnetic and strong decays with existing experimental measurements.
• To assess the validity of the model in describing the energy spectra and decay patterns of excited heavy mesons.
• To provide a phenomenological description of heavy meson decays consistent with known data from charmed and bottom meson states.

Proposed method

• The model treats the heavy quark (c or b) as fixed at the center of a spherical bag, creating a color electric potential.
• The light quark (u or d) is described as moving in the effective potential generated by the heavy quark’s color field.
• The energy spectra of excited states are obtained by solving the Dirac equation in the bag model framework with a static potential.
• Transition amplitudes for γ and π emission are computed using electromagnetic and strong transition operators derived from the model.
• Branching ratios for electromagnetic versus strong decays are calculated using the computed matrix elements.
• Results are compared with available experimental data on D*, B*, and other excited heavy meson states.

Experimental results

Research questions

• RQ1 How do the predicted transition amplitudes for pionic and photonic decays compare with experimental data for excited heavy mesons?
• RQ2 What is the predicted energy spectrum of excited states in the bag model with a static heavy quark?
• RQ3 How do the branching ratios between electromagnetic and strong decays depend on the quantum numbers of the initial and final states?
• RQ4 To what extent does the model reproduce known decay patterns of charmed and bottom mesons?
• RQ5 What is the role of the color electric field in determining the structure and decay properties of excited heavy mesons?

Key findings

• The model successfully reproduces the energy spectra of excited heavy mesons, including states like D* and B*.
• Calculated transition amplitudes for pionic and photonic decays show good agreement with limited experimental data on D* and B* decays.
• The branching ratios for electromagnetic versus strong decays are in favorable quantitative agreement with observed values for charmed mesons.
• The model predicts a clear hierarchy in decay widths, with dominant transitions to lower-lying states, consistent with experimental trends.
• The inclusion of the static heavy quark as a source of color electric field leads to a realistic description of the excitation spectrum and decay patterns.
• The results support the validity of the bag model approach for describing excited heavy mesons, particularly in the context of strong and electromagnetic decays.