Search results for "Chiral perturbation Theory"
showing 10 items of 294 documents
Improved unitarized Heavy Baryon Chiral Perturbation Theory for π N scattering
2000
We show how the unitarized description of pion nucleon scattering within Heavy Baryon Chiral Perturbation Theory can be considerably improved, by a suitable reordering of the expansion over the nucleon mass. Within this framework, the $\Delta$ resonance and its associated pole can be recovered from the chiral parameters obtained from low-energy determinations. In addition, we can obtain a good description of the six $S$ and $P$ wave phase shifts in terms of chiral parameters with a natural size and compatible with the Resonance Saturation Hypothesis.
Radiative pion capture by a nucleon
2000
The differential cross sections for $\pi^- p \to \gamma n$ and $\pi^+ n \to \gamma p$ are computed up to $O(p^3)$ in heavy baryon chiral perturbation theory (HBChPT). The expressions at $O(p)$ and $O(p^2)$ have no free parameters. There are three unknown parameters at $O(p^3)$, low energy constants of the HBChPT Lagrangian, which are determined by fitting to experimental data. Two acceptable fits are obtained, which can be separated by comparing with earlier dispersion relation calculations of the inverse process. Expressions for the multipoles, with emphasis on the p-wave multipoles, are obtained and evaluated at threshold. Generally the results obtained from the best of the two fits are i…
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
2002
We study spin-dependent sum rules for forward virtual Compton scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at order $O(p^4)$. We show how these sum rules can be evaluated from low energy expansions (in the virtual photon energy) of the forward VVCS amplitudes. We study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher terms in the low energy expansion, which can be related to the generalized forward spin polarizabilities of the nucleon. The dependence of these observables on the photon virtuality $Q^2$ can be accessed, at small and intermediate $Q^2$ values, from existing and forthcoming data at Jefferson Lab.
Kaon Polarizabilities in Chiral Perturbation Theory
1997
We study the kaon polarizabilities in the framework of Chiral Perturbation Theory to order $p^4$. For the neutral kaon we find that them vanish and they have the first non-zero contribution to order $p^6$. We also emphasize the theoretical potential of an eventual measuremnet of the kaon polarizabilities, in particular of the neutral kaon ones.
Search for the decay K-s -> pi(0)e(+)e(-)
2001
Abstract A search for the decay K S →π 0 e + e − has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching fraction B (K S →π 0 e + e − ) −7 at 90% confidence level has been obtained.
Vector form factor of the pion : A model-independent approach
2003
4 páginas, 2 figuras, 3 tablas.-- Comunicación presentada a la 9ª High-Energy Physics International Conference on Quantum ChromoDynamics (QCD 02) celebrada del 2 al 9 de Julio de 2002 en Montpellier (Francia).-- arXiv:hep-ph/0209224v1
Generalized polarizabilities of the nucleon in chiral effective theories
1999
Using the techniques of chiral effective field theories we evaluate the so called generalized polarizabilities of the nucleon, which characterize the structure dependent components in virtual Compton scattering (VCS) as probed in the electron scattering reaction e N \to e' N gamma. Results are given for both spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale Expansion. Finally we compare our calculations with results from the pioneering VCS experiment on the proton from Mainz.
Clues for the existence of twoK1(1270)resonances
2007
The axial-vector meson ${K}_{1}(1270)$ was studied within the chiral unitary approach, where it was shown that it has a two-pole structure. We reanalyze the high-statistics WA3 experiment ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ at 63 GeV, which established the existence of both ${K}_{1}(1270)$ and ${K}_{1}(1400)$, and we show that it clearly favors our two-pole interpretation. We also reanalyze the traditional $K$-matrix interpretation of the WA3 data and find that the good fit of the data obtained there comes from large cancellations of terms of unclear physical interpretation.
A measurement of the decay KL→π0γγ
1992
Abstract The full data set of the experiment NA31 at CERN has been used to analyse the decay mode KL→π0γγ. A signal of 63 events has been observed with an estimated background of 6.0±1.7 events, corresponding to a branching ratio of (1.7±0.3)×10−6 consistent with our previous result based on partial statistics. The invariant mass spectrum of the two photons is found to be consistent with chiral perturbation theory, and the decay is dominated by the J = 0 two photon state.
Virtual Compton scattering and the generalized polarizabilities of the proton atQ2=0.92and 1.76 GeV2
2012
Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P{sub LL}-P{sub TT}/epsilon and P{sub LT}, and the electric and magnetic generalized polarizabilities (GPs) alpha{sub E}(Q{sup 2}) and beta{sub M}(Q{sup 2}) at values of the four-momentum transfer squared Q{sup 2} = 0.92 and 1.76 GeV{sup 2}. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q{sup 2}-…