Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1996-10-07
Phys.Lett. B392 (1997) 198-206
Physics
High Energy Physics
High Energy Physics - Phenomenology
12 pages Latex, 3 PS-files of figures, uses macros 'amstex' and 'psfig'; also available by anonymous ftp from ftp://wpts0.ph
Scientific paper
10.1016/S0370-2693(96)01515-8
We investigate the theoretical uncertainties of $P$-wave charmonium decays into two pions, $\chi_{\c J}\rightarrow \pi^+\pi^-$, $\pi^0\pi^0$. Constraining the pion distribution-amplitude from the recent precise data on $F_{\pi\gamma}(Q^2)$, we find an order-of-magnitude discrepancy between data and prediction. The disagreement persists even after inclusion of transverse degrees of freedom and Sudakov suppressions. We propose the colour-octet mechanism as the solution to the puzzle. The colour-octet decay contribution arising from the higher Fock component $|\c \cbar \g >$ of the $\chi_{\c J}$ wave function is actually not power suppressed with respect to the usual colour-singlet decay arising from the dominant $|\c \cbar >$ Fock state. An explicit calculation yields an agreement with the data for a very reasonable value for the single extra non-perturbative parameter.
Bolz Jan
Kroll Peter
Schuler Gerhard A.
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