Theoretical determination of ηb’s electromagnetic decay width
نویسنده
چکیده
First evidence of ηb was given in 2001 by ALEPH [1]. The search for ηb is done in the decay channel into two photons. One candidate event is found in the six–charged particle final state and none in the four–charged particle final state, giving the upper limits: Γ(ηb → γγ) × BR(ηb → 4 charged particles) < 48 eV , Γ(ηb → γγ) × BR(ηb → 6 charged particles) < 132 eV . This observation was the main motivation for a theoretical estimate of electromagnetic decay width for ηb [2]. More recently CDF has done a search for ηb in the process [3] ηb → J/ψJ/ψ with 7 events where 1.8 events are expected from background. This note is organised as follows: in Sect. 2 we shall compare the two photon decay width with the leptonic width of the Υ. Sect. 3 is devoted to the potential model predictions for ηb → γγ, with potential given by [5,6,7]. In Sect. 4 we show the predictions for ηb decay widths, using the procedure introduced in [8] for the description of mesons made out of two non relativistic heavy quarks, by means of the Non Relativistic Quantum Chromodynamics–NRQCD. In Sect. 5 we compare these different determinations of the ηb → γγ decay width together with a result based on a recent two-loop theoretical analysis of the charmonium decay [9].
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