Observation of B+ --> plambdagamma

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• Radiative hyperonic B decays are rare processes predicted by the Standard Model.
• Understanding these decays can provide insights into fundamental particle interactions.
• Previous experimental searches for such decays have been limited.

Purpose of the Study:

• To report the first observation of the radiative hyperonic B decay B+ --> plambdagamma.
• To measure the branching fraction of this decay.
• To search for the decay B+ --> pepsilon0gamma and set an upper limit.

Main Methods:

• Analysis of a 140 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric energy e+e- collider.
• Reconstruction of B+ mesons decaying into plambdagamma final states.
• Examination of the invariant mass distribution of the plambda system.

Main Results:

• The first observation of the radiative hyperonic B decay B+ --> plambdagamma is reported.
• The measured branching fraction is (2.16(+0.58)(-0.53) +/- 0.20) x 10(-6).
• A peak near the threshold in the M(plambda) distribution is observed, consistent with theoretical expectations for the b --> sgamma transition.
• No significant signal was found for B+ --> pepsilon0gamma, with a 90% confidence-level upper limit on its branching fraction set at <4.6 x 10(-6).

Conclusions:

• The observation of B+ --> plambdagamma provides crucial experimental evidence for radiative hyperonic B decays.
• The observed features in the decay dynamics align with theoretical predictions for short-distance b --> sgamma processes.
• The results contribute to a more comprehensive understanding of B meson decays and the underlying fundamental interactions.