Pion pair production in photon-photon collisions at DCI

We complete the recalculation of the available two-loop expressions for the reaction γγ → ππ in the framework of chiral perturbation theory. Here, we present the results for charged pions. The cross section and the values of the dipole polarizabilities agree very well with the earlier calculation, provided the same set of low-energy constants (LECs) is used. With updated values for the LECs at order p 4 , we find for the dipole polarizabilities (α 1 − β 1 ) π ± = (5.7 ± 1.0) × 10 −4 fm 3 , which is in conflict with the experimental result recently reported by the MAMI Collaboration.

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“…Babusci et al (1992) [29] γγ → π + π − PLUTO [37] 38.2 ± 9.6 ± 11.4 DM 1 [38] 34.4 ± 9.2 DM 2 [39] 52.6 ± 14.8 MARK II [25] 4.4 ± 3.2…”

Section: Values Of the Polarizabilitiesmentioning

confidence: 99%

Revisiting at low energies

2006

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“…Some of the earliest results, like that from DM2 [9,10], were merely event distributions, but with data from Mark II [11] at PEP twenty years ago followed by CELLO [12,13] at PETRA, normalised cross-sections for charged pion production became available. With the Crystal Ball detector first running at SLAC and then moving to DESY, normalised cross-sections for π 0 π 0 production in two photon collisions also resulted [14,15].…”

Section: Introductionmentioning

confidence: 99%

Amplitude analysis of high statistics results on γγ→π+π- and the two photon width of isoscalar states

et al. 2008

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Abstract. We perform an amplitude analysis of the world published data on γγ → π + π − and π 0 π 0 . These are dominated in statistics by the recently published results from Belle on the charged pion channel. Nevertheless, having only limited angular information, a range of solutions remain possible. We present two solutions with Γ (f 0 (980) → γγ) = 0.42 and 0.10 keV, and Γ (f 2 (1270) → γγ) = 3.14 ± 0.20 and 3.82 ± 0.30 keV, respectively: the former being the solution favoured by χ 2 , the latter at the edge of acceptability. Models of the structure of the f 0 (980) predict two photon widths to be between 0.2 and 0.6 keV, depending on its composition as mainly KK, ss or qqqq. Presently available data cannot yet distinguish unambiguously between these predictions. However, we show how forthcoming results on γγ → π 0 π 0 can not only discriminate between, but also refine, these classes of partial wave solutions.

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“…However, it substantially differs from the results obtained in the dispersion approach [37] and chiral perturbation theory [38], which claims to be a strong interaction theory at low energies. Also note that the result on the electric polar izability of charged pions is close to an average exper imental value and is far enough from a weighted aver age value, both of which are calculated in [39] by using the experimental data presented in [28][29][30][40][41][42][43].…”

Section: Introductionmentioning

confidence: 92%