ar X iv : h ep - p h / 06 05 07 2 v 4 1 5 Ju n 20 06 γγ → ππ , KK : leading term QCD vs handbag model
نویسنده
چکیده
The ”handbag” model was proposed as an alternative, at the present day energies, to the leading term QCD predictions for some hard exclusive processes. The recent precise data from the Belle Collaboration on the large angle cross sections γγ → ππ , KK allow a check of these two approaches to be performed. It is shown that the handbag model fails to describe the data from Belle, while the leading term QCD predictions are in reasonable agreement with these data. I. The leading term QCD predictions The leading contributions to the hard kernels for these amplitudes at large s = W 2 = (q1 + q2) 2 and fixed c.m.s. angle θ were first calculated in [1] for symmetric meson wave functions, φM(x) = φM(1 − x), and later in [2] (BC in what follows) for arbitrary wave functions. Two typical diagrams are shown in fig.1 . The main features of these cross sections are as follows (everywhere below we follow mainly the definite predictions from BC in [2]) . The helicity amplitudes look as : A (lead) λ1λ2 (s, θ) = 64π 9s ααs f 2 K ∫ 1 0 dxsφK(xs) ∫ 1 0 dysφK(ys)Tλ1λ2(xs, ys, θ). (1) The hard kernels Tλ1λ2(xs, ys, θ) are : T++ = T−− = (es − eu) 1 sin θ A D , (2) 1 E-mail: v.l.chernyak @ inp.nsk.su 1
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ar X iv : h ep - p h / 06 05 07 2 v 3 2 9 M ay 2 00 6 γγ → ππ , KK : leading term QCD vs handbag model
The ”handbag” model was proposed as an alternative, at the present day energies, to the leading term QCD predictions for some hard exclusive processes. The recent precise data from the Belle Collaboration on the large angle cross sections γγ → ππ , KK allow a check of these two approaches to be performed. It is shown that the handbag model fails to describe the data from Belle, while the leadin...
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تاریخ انتشار 2006