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VOLUME 87 (2008) | ISSUE 3 | PAGE 147
Di-pion emission in heavy quarkonia decays
PACS: 12.38.Lg, 13.25.Hw
Abstract
The di-pion spectrum for the Υ(nS) → Υ (n'S) transition with n\leq 4 has the form {dw}/{dq}\sim (phase space)  |η-x|2, with x=\frac{q^2-4m^2_\pi}{(\Delta M)^2 -4 m^2_\pi}< q^2 \equiv M^2_{\pi\pi}, and Δ M=M(nS) -M(n'S). The parameter η  is calculated and the spectrum is shown to reproduce the experimental data for all 3 types of decays: 3→ 1, 2→ 1 and 3→ 2 with \eta \approx 0.5; 0, and -3, respectively.