Observation of Λ_{c}^{+}→Λa_{0}(980)^{+} and Evidence for Σ(1380)^{+} in Λ_{c}^{+}→Λπ^{+}η

Area of Science:

• Particle Physics
• Hadron Spectroscopy

Background:

• The Lambda_c+ (car{u}d) is the lightest charmed baryon.
• Understanding its decay modes provides insights into the strong interaction and quark dynamics.

Purpose of the Study:

• To perform a partial wave analysis of Lambda_c+ -> Lambda pi+ eta.
• To determine branching fractions and decay asymmetry parameters.
• To investigate the intermediate processes and search for exotic states.

Main Methods:

• Analysis of 6.1 fb^-1 e+e- annihilation data at center-of-mass energies from 4.600 to 4.843 GeV.
• Utilizing the BESIII detector at the BEPCII collider.
• Partial wave analysis to disentangle decay amplitudes.

Main Results:

• First observation of the decay Lambda_c+ -> Lambda a0(980)+.
• Evidence for the pentaquark candidate Sigma(1380)+ decaying into Lambda pi+.
• Measured branching fraction product B[Lambda_c+ -> Lambda a0(980)+]B[a0(980)+ -> pi+ eta] = (1.05 +/- 0.16_stat +/- 0.05_syst +/- 0.07_ext)%.
• This measured value is 1-2 orders of magnitude larger than theoretical calculations.
• Precisely determined absolute branching fraction B(Lambda_c+ -> Lambda pi+ eta) = (1.94 +/- 0.07_stat +/- 0.11_syst)%.

Conclusions:

• The decay dynamics of Lambda_c+ are more complex than previously modeled.
• The significant discrepancy suggests a need for revised theoretical frameworks.
• The findings open new avenues for exploring exotic hadrons and their production mechanisms.