Search for invisible decay of the Upsilon(1S)

Area of Science:

• Particle Physics
• High-Energy Physics
• Experimental Physics

Background:

• The Upsilon(1S) is a bottomonium resonance, a bound state of a bottom and an anti-bottom quark.
• Invisible decays, where the final state particles are not detected, are predicted by some theoretical models.
• Understanding decay modes of heavy quarkonia provides insights into fundamental forces.

Purpose of the Study:

• To search for the invisible decay of the Upsilon(1S) meson.
• To constrain theoretical models predicting new physics phenomena.
• To establish an upper limit on the branching fraction of Upsilon(1S) invisible decay.

Main Methods:

• Utilized a data sample of 2.9 fb^-1 collected at the Upsilon(3S) resonance.
• Analyzed the Upsilon(3S) --> pi+ pi- Upsilon(1S) transition.
• Employed the Belle detector at the KEKB asymmetric-energy electron-positron collider.
• Searched for a signal consistent with invisible Upsilon(1S) decay products.

Main Results:

• No significant signal for the invisible decay of the Upsilon(1S) was observed.
• An upper limit on the branching fraction for Upsilon(1S) --> invisible was determined at the 90% confidence level.
• The upper limit was set at B(Upsilon(1S) --> invisible) < 2.5 x 10^-3.

Conclusions:

• The experimental search places stringent limits on the possibility of invisible Upsilon(1S) decays.
• This result disfavors certain theoretical scenarios that predict substantial invisible decay branching fractions.
• Further studies with larger datasets or different decay channels may be needed to probe these rare processes.