Article

# Precise tests of low energy QCD from decay properties

[more]
University of Birmingham, Edgbaston, Birmingham, B15 2TT UK
(Impact Factor: 5.44). 01/2010; 70(3):635-657. DOI: 10.1140/epjc/s10052-010-1480-6

ABSTRACT We report results from the analysis of the $\mbox {$\mbox { ($\mbox {$\mbox {) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003–2004.
The hadronic form factors in the S- and P-wave and their variation with energy are obtained. The phase difference between
the S- and P-wave states of the ππ system is accurately measured and allows a precise determination of $\mbox {$\mbox { and $\mbox {$\mbox {, the I = 0 and I = 2 S-wave ππ scattering lengths: $\mbox {$\mbox {. Combination of this result with the other NA48/2 measurement obtained in the study of $\mbox {$\mbox { decays brings an improved determination of $\mbox {$\mbox { and the first precise experimental measurement of $\mbox {$\mbox {, providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based
on analyticity and chiral symmetry, even more precise values are obtained: $\mbox {$\mbox { and $\mbox {$\mbox {.

### Full-text

Available from: Italo Mannelli, Jun 03, 2015
0 Followers
·
153 Views
• ##### Article: Radiative corrections to the charged pion-pair production process π − γ → π + π − π − at low energies
[Hide abstract]
ABSTRACT: We calculate the one-photon loop radiative corrections to the charged pion-pair production process π −γ → π +π −π −. In the low-energy region this reaction is governed by the chiral pion-pion interaction. The pertinent set of 42 irreducible photon-loop diagrams is calculated by using the package FeynCalc. Electromagnetic counterterms with two independent low-energy constants [TEX equation: \hat k_1] and [TEX equation: \hat k_2] are included in order to remove the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved by including soft photon radiation below an energy cut-off Λ. The purely electromagnetic interaction of the charged pions mediated by one-photon exchange is also taken into account. The radiative corrections to the total cross section (in the isospin limit) vary between +10% close to threshold and about −1% at a center-of-mass energy of 7m π . The largest contribution comes from the simple one-photon exchange. Radiative corrections to the π +π − and π −π − mass spectra are studied as well. The Coulomb singularity of the final-state interaction produces a kink in the dipion mass spectra. The virtual radiative corrections to elastic π −π − scattering are derived additionally.
European Physical Journal A 12/2013; 49(12). DOI:10.1140/epja/i2013-13159-7 · 2.42 Impact Factor
• ##### Article: Precise measurement of Ke4 form factors and branching ratios at the NA48/2 experiment
[Hide abstract]
ABSTRACT: The NA48/2 experiment at CERN [1] collected similar to 18.10(9) charged kaon decays during the years 2003/4. Along with the primary goals of the collaboration, i.e., the measurement of the CP-violating asymmetry in the K-+/- -> pi(+/-)pi(+)pi(-) and K-+/- -> pi(+/-)pi(0)pi(0) channels, the collected data allowed to perform many other interesting analyses. In this paper the measurement of the K-+/- -> e(+/-)nu pi(+)pi(-) and K-+/- -> e(+/-)nu pi(0)pi(0) decays' branching ratios (BR) and form factors will be reviewed.
Nuclear Physics B - Proceedings Supplements 10/2011; 219-220:149-152. DOI:10.1016/j.nuclphysbps.2011.10.086 · 0.88 Impact Factor
• Source
##### Article: Precise determination of resonance pole parameters through Pad\'e approximants
[Hide abstract]
ABSTRACT: In this work, we present a precise and model--independent method to extract resonance pole parameters from phase-shift scattering data. These parameters are defined from the associated poles in the second Riemann sheet, unfolded by the analytic continuation to the complex pole using Pad\'e approximants. Precise theoretical parameterizations of pion-pion scattering phase shifts based on once-- and twice-- subtracted dispersion relations are used as input, whose functional form allows us to show the benefit and accuracy of the method. In particular, we extract from these parametrization the pole positions of the $f_0(500)$ at $\sqrt{s}=(453\pm 15) - i(297 \pm 15)$ MeV, the $\rho(770)$ at $\sqrt{s}=(761.4\pm 1.2)-i(71.8 \pm 1.0)$ MeV, and the pole of the $f_2(1270)$, located at $\sqrt{s}=(1267.3\pm 1.7)-i(95.0\pm 2.3)$ MeV. The couplings of the resonances to two pions are also determined with high precision, obtaining respectively, $3.8\pm 0.4$ GeV, $5.92\pm 0.15$ and $4.41\pm 0.23$ GeV$^{-1}$. Special attention is dedicated to the systematic treatment of the theoretical and statistical uncertainties, together with their comparison with previous determinations.
Physical Review D 10/2014; 90(9). DOI:10.1103/PhysRevD.90.097901 · 4.86 Impact Factor