arXiv subjects

A. Nehme

Publications and source records attributed to A. Nehme.

11 recordsLinked to original sources

arXiv2011

The Eta decay into three neutral pions is mainly electromagnetic

In the framework of Chiral Perturbation Theory including photons, we found that the contribution of the photon exchange between two intermediate charged Kaons to the slope parameter of the decay (η\rightarrow 3π^{0}) amounts to (-0.0221\pm 0.0034). When compared with the experimental value, (α=-0.0317\pm 0.0016), on the one hand, and with the contribution of the up and down quark mass difference, (+0.013\pm 0.032), on the other hand, our result leads to the direct conclusion: \textit{The} (η\rightarrow 3π^{0}) \textit{decay \uline{cannot} be used to determine} (m_{d}-m_{u}).

hep-ph↗

arXiv2011

Electromagnetic Corrections to the (η\rightarrow 3π) Neutral Decay

Sutherland's theorem dictates that the contribution of the electromagnetic interaction to the decay process (η\rightarrow 3π^{0}) is neglected with respect to the one coming from the difference between the up and down quark masses. In the framework of chiral perturbation theory including virtual photons, we calculated the main diagram concerning the exchange of a virtual photon between two intermediate charged pions. The correction induced by this diagram on the slope parameter amounts to (17%) of the correction induced by the pure strong interaction at one-loop level. If this result is maintained when considering all the diagrams at the chiral order we are working, we can say without any doubt that Sutherland's theorem is strongly violated. As a direct consequence, any determination of light quark masses from the present decay \textit{should} take into account the electromagnetic interaction.

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arXiv2008

A note on the determination of light quark masses

We provide a model-independent determination of the quantity B_0(m_d-m_u). Our approach rests only on chiral symmetry and data from the decay of the eta into three neutral pions. Since the low-energy prediction at next-to-leading order fails to reproduce the experimental results, we keep the strong interaction correction as an unknown parameter. As a first step, we relate this parameter to the quark mass difference using data from the Dalitz plot. A similar relation is obtained using data from the decay width. Combining both relations we obtain B_0(m_d-m_u)=(4495+/-440) MeV^2. The preceding value, combined with lattice determinations, leads to the values m_u(2 GeV)=(2.9+/-0.8) MeV and m_d(2 GeV)=(4.7+/-0.8) MeV.

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arXiv2004

Size of Isospin Breaking in Charged K(L4) Decay

We evaluate the size of isospin breaking corrections to form factors $f$ and $g$ of the $K_{\ell 4}$ decay process $K^+\toπ^+π^-\ell^+ν_{\ell}$ which is actually measured by the extended NA48 setup at CERN. We found that, keeping apart the effect of Coulomb interaction, isospin breaking does not affect modules. This is due to the cancelation between corrections of electromagnetic origin and those generated by the difference between up and down quark masses. On the other hand, electromagnetism affects considerably phases if the infrared divergence is dropped out using a minimal subtraction scheme. Consequently, the greatest care must be taken in the extraction of $ππ$ phase shifts from experiment.

hep-ph↗

arXiv2004

Virtual Photon Correction to the $K^+\toπ^+π^0π^0$ Decay

We consider electromagnetic corrections to the non-leptonic kaon decay, $K^+\toπ^+π^0π^0$, due to explicit virtual photons only. The decay amplitude is calculated at one-loop level in the framework of Chiral Perturbation Theory. The interest in this process is twofold: It is actually measured by the NA48 collaboration from one side, and, the value of the amplitude at the $ππ$ threshold gives access to $ππ$ scattering lengths from the other side. We found that the present correction is about 5 to 6% the value of the Born amplitude squared. Combined with another piece published recently, this fixes the size of isospin breaking correction to the amplitude squared to 7% its one-loop level value in the absence of isospin breaking and at the center of Dalitz plot.

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arXiv2004

Splitting Strong and Electromagnetic Interactions in K(L4) Decays

We recently considered $K_{\ell 4}$ decays in the framework of chiral perturbation theory based on the effective Lagrangian including mesons, photons, and leptons. There, we published analytic one-loop-level expressions for form factors $f$ and $g$ corresponding to the mixed process, $K^0\toπ^0π^-\ell^+ν_{\ell}$. We propose here a possible splitting between strong and electromagnetic parts allowing analytic (and numerical) evaluation of Isospin breaking corrections. The latter are sensitive to the infrared divergence subtraction scheme and are sizeable near the $ππ$ production threshold. Our results should be used for the extraction of the $P$-wave iso-vector $ππ$ phase shift from the outgoing data of the currently running KTeV experiment at FNAL.

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arXiv2003

Isospin Breaking in $K_{\ell 4}$ Decays of the Charged Kaon

The charged $K_{\ell 4}$ decay, $K^+\toπ^+π^-\ell^+ν_{\ell}$ is studied in the framework of chiral perturbation theory based on the effective Lagrangian including mesons, photons, and leptons. We give analytic expressions for the two vectorial form factors, $f$ and $g$, calculated at one-loop level in the presence of Isospin breaking effects. These expressions may then be used to disentangle the Isospin breaking part from the measured form factors and hence improve the accuracy in the determination of $ππ$ scattering parameters from $K_{\ell 4}$ experiments.

hep-ph↗

arXiv2003

Isospin Breaking in $K_{\ell 4}$ Decays of the Neutral Kaon

In the presence of photons, the neutral $K_{\ell 4}$ decay, $K^0\toπ^0π^-\ell^+ν_\ell$, can be parameterized in terms of three vectorial, one anomalous, and one tensorial form factors. We present here analytic expressions of two vectorial form factors, $f$ and $g$, calculated at one-loop level in the framework of chiral perturbation theory based on the effective Lagrangian including mesons, photons, and leptons. These expressions may then be used to disentangle the Isospin breaking part from the measured form factors and hence improve the accuracy in the determination of $ππ$ scattering parameters from $K_{\ell 4}$ experiments.

hep-ph↗

arXiv2002

Electromagnetic Corrections to Charged Pion Scattering at Low Energies

The electromagnetic corrections to the low energy scattering amplitude involving charged pions only are investigated at leading and next-to-leading orders in the two-flavour chiral expansion. As an application, the corresponding variation in the strong $2S-2P$ level shift is evaluated. The relative variation is of the order of 5%.

hep-ph↗

arXiv2001

Isospin Breaking in Low-Energy Charged Pion and Kaon Elastic Scattering

We use chiral perturbation theory to evaluate the scattering amplitude for the process Pi^+ K^- to Pi^+ K^- at leading and next-to-leading orders in the chiral counting and in the presence of isospin breaking effects. We also discuss the influence of the latter on the combination of the S-wave Pi K scattering lengths which is relevant for the 2S - 2P energy levels shift of K Pi atoms.

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arXiv2001

Isospin breaking corrections to low-energy pi-K scattering

We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and next-to-leading order. As a direct application the releveant combination of the S-wave scattering lengths involved in the pion-kaon atom lifetime is determined. We discuss the sensitivity of the results with respect to the input parameters.

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