Search results for "Chiral perturbation Theory"

A new measurement of the K±→π±γγ decay at the NA48/2 experiment

2014

Abstract The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay K ± → π ± γ γ from these data sets based on 149 decay candidates with an estimated background of 15.5 ± 0.7 events is reported. The model-independent branching ratio in the kinematic range z = ( m γ γ / m K ) 2 > 0.2 is measured to be B MI ( z > 0.2 ) = ( 0.877 ± 0.089 ) × 10 − 6 , and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B ( K π γ γ ) = ( 0.910 ± 0.075 ) × 10 − 6 .

Kaon Physics at CERN – Recent Results from the NA48/2 and NA62 Experiments

2012

This letter presents recent results from the kaon experiments NA48/2 and its successor NA62 at CERN. With samples of 2.5 × 106 K µ 3 ± and 4.0 × 106 K e 3 ± events collected by NA48/2 in 2004, precise measurements of the form factors were performed. The Chiral Perturbation Theory was tested through a new study of K ± → π± γγ decays based on data taken with minimal trigger conditions. Using the beam line and detector of NA48/2 in the years 2007-2008, NA62 performed a precison measurement of the helicitysuppressed ratio of the charged kaon leptonic decay rates K ± → e+ ν and K ± → μ + ν Using the full data set, which is about ten times larger than the previous world data sample, the total unc…

Experiments on threshold pion electroproduction

2008

Experimental techniques to access the reactions p(e, e′ p)π0 and d(e, e′ d)π0 at low four momentum transfer and close to threshold are presented. For p(e, e′ p)π0 results at Q 2=0.1 GeV2/c 2 are given and compared to chiral perturbation theory. A new experimental program on d(e, e′ d)π0 is presented.

Sensitivity of EDM experiments in paramagnetic atoms and molecules to hadronic CP violation

2020

Experiments searching for the electric dipole moment (EDM) of the electron $d_e$ utilise atomic/molecular states with one or more uncompensated electron spins, and these paramagnetic systems have recently achieved remarkable sensitivity to $d_e$. If the source of $CP$ violation resides entirely in the hadronic sector, the two-photon exchange processes between electrons and the nucleus induce $CP$-odd semileptonic interactions, parametrised by the Wilson coefficient $C_{SP}$, and provide the dominant source of EDMs in paramagnetic systems instead of $d_e$. We evaluate the $C_{SP}$ coefficients induced by the leading hadronic sources of $CP$ violation, namely nucleon EDMs and $CP$-odd pion-nu…

Measurement of the Charged-Pion Polarizability

2015

The COMPASS collaboration at CERN has investigated pion Compton scattering, $\pi^-\gamma\rightarrow \pi^-\gamma$, at centre-of-mass energy below 3.5 pion masses. The process is embedded in the reaction $\pi^-\mathrm{Ni}\rightarrow\pi^-\gamma\;\mathrm{Ni}$, which is initiated by 190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, $Q^2<0.0015$\,(GeV/$c$)$^2$. From a sample of 63\,000 events the pion electric polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\ 0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times 10^{-4}\,\mbox{fm}^3$ under the …

Updated determination of chiral couplings and vacuum condensates from hadronic tau decay data

2016

We analyze the lowest spectral moments of the left-right two-point correlation function, using all known short-distance constraints and the recently updated ALEPH V-A spectral function from tau decays. This information is used to determine the low-energy couplings L10 and C87 of chiral perturbation theory and the lowest-dimensional contributions to the Operator Product Expansion of the left-right correlator. A detailed statistical analysis is implemented to assess the theoretical uncertainties, including violations of quark-hadron duality.

Erratum to: Some recent results in baryon chiral perturbation theory

2003

Chiral perturbation theory study of the axial N -> Delta(1232) transition

2008

We have performed a theoretical study of the axial Nucleon to Delta(1232) ($N\to\Delta$) transition form factors up to one-loop order in covariant baryon chiral perturbation theory within a formalism in which the unphysical spin-1/2 components of the $\Delta$ fields are decoupled.

Moments of nucleon structure functions at next-to-leading order in baryon chiral perturbation theory

2014

We obtain leading- and next-to-leading-order predictions of chiral perturbation theory for several prominent moments of nucleon structure functions. These parameter-free results turn out to be in overall agreement with the available empirical information on nearly all of the considered moments, in the region of low momentum transfer $({Q}^{2}l0.3\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2})$. Especially surprising is the situation for the spin polarizability ${\ensuremath{\delta}}_{LT}$, which thus far was not reproducible in chiral perturbation theory for proton and neutron simultaneously. This problem, known as the ``${\ensuremath{\delta}}_{LT}$ puzzle,'' is not seen in the present calcula…

The S01 − Λ(1405) and − Λ(1670) resonances in meson-baryon unitarized coupled channel chiral perturbation theory

2003

Abstract The s-wave meson-baryon system with strangeness S = −1 and isospin I = 0 is studied using the Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. The needed two particle irreducible potential is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. The K N, πΣ, νΛ , and KΞ two-body channels have been included. Off-shell behavior is parameterized in terms of low energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The masses, widths and branching ratios of the Λ(1405) and Λ(1670) resonances are determined. In our model, we find no one but two resonances in the Λ(1405) region.