Speaker
Peter Stoffer
(HISKP, University of Bonn)
Description
K_{l4} decays have several features of interest: they allow an accurate measurement of ππ-scattering lengths; the decay is the best source for the determination of some low-energy constants of chiral perturbation theory (χPT); one form factor of the decay is connected to the chiral anomaly. We present the final results of our dispersive analysis of K_{l4} decays, which provides a resummation of ππ- and Kπ-rescattering effects [1,2]. The free parameters of the dispersion relation are fitted to the data of the high-statistics experiments E865 [3,4] and NA48/2 [5,6]. The data input is corrected for additional isospin-breaking effects, which were not taken into account in the experimental analyses [7]. By matching to χPT at NLO and NNLO, we determine the low-energy constants L1r, L2r, and L3r. Recently published data [6] from NA48/2 allow even a determination of L9r. In contrast to a pure chiral treatment, the dispersion relation describes the observed curvature of one of the K_{l4} form factors, which we understand as an effect of rescattering beyond NNLO.
References
1. G. Colangelo, E. Passemar, and P. Stoffer, arXiv:1501.05627 [hep-ph].
2. P. Stoffer, PhD thesis, University of Bern, 2014, arXiv:1412.5171 [hep-ph].
3. S. Pislak et al. (BNL-E865 Collaboration), Phys. Rev. Lett. 87, 221801 (2001),[Erratum-ibid. 105, 019901 (2010)], [arXiv:hep-ex/0106071].
4. S. Pislak et al. (BNL-E865 Collaboration), Phys. Rev. D67, 072004 (2003), [Erratum-ibid. D81, 119903 (2010)], [arXiv:hep-ex/0301040].
5. J. Batley et al. (NA48-2 Collaboration), Eur. Phys. J. C70, 635 (2010).
6. J. Batley et al. (NA48/2 Collaboration), Phys. Lett. B715, 105 (2012), [arXiv:1206.7065 [hep-ex]], [Addendum-ibid. B740, 364 (2015)].
7. P. Stoffer, Eur. Phys. J. C74, 2749 (2014), [arXiv:1312.2066 [hep-ph]].
Primary author
Peter Stoffer
(HISKP, University of Bonn)
Co-authors
Emilie Passemar
(Indiana University/JLab)
Prof.
Gilberto Colangelo
(Berna University)
