Observation of the Singly Cabibbo Suppressed Decay Λ_{c}^{+}→nπ^{+}

Area of Science:

• Particle Physics
• High Energy Physics
• Hadron Spectroscopy

Background:

• The Lambda_c+ is the lightest charmed baryon.
• Understanding its decays is crucial for testing the Standard Model and exploring new physics.
• Singly Cabibbo-suppressed decays offer unique insights into quark dynamics.

Purpose of the Study:

• To report the first observation of the Lambda_c+ -> n pi+ decay.
• To measure its branching fraction and compare it with theoretical predictions.
• To measure branching fractions of Cabibbo-favored decays for consistency.

Main Methods:

• Analysis of e+e- collision data collected at BESIII.
• Data collected at center-of-mass energies between 4.612 and 4.699 GeV.
• Statistical analysis to determine significance and measure branching fractions.

Main Results:

• Observed Lambda_c+ -> n pi+ decay with 7.3 sigma significance.
• Measured branching fraction of Lambda_c+ -> n pi+ as (6.6 +/- 1.2_stat +/- 0.4_syst) x 10^-4.
• Ratio of branching fractions Lambda_c+ -> n pi+ / Lambda_c+ -> p pi0 > 7.2 (90% CL), contradicting models.

Conclusions:

• The observed decay and its branching fraction provide crucial experimental data.
• The significant deviation from theoretical predictions highlights limitations in current models.
• Further theoretical and experimental work is needed to resolve discrepancies.