119185139
Pion photoproduction in a dynamical coupled‐channel model
Pion photoproduction reactions are investigated in a dynamical coupled‐channel approach based on the Julich πN model, which presently includes the hadronic πN and ηN stable channels as well as the πΔ, σN and ρN effective channels. This model has been quite successful in the description of πN→πN scattering for center‐of‐mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward‐Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center‐of‐mass energy for the reactions γp→π+n, γp→π0p and γn→π−p are in good agreement with the experimental data.
119190125
Finite volume effects in pion-kaon scattering and reconstruction of the κ(800) resonance
A bstractSimulating the κ(800) on the lattice is a challenging task that starts to become feasible due to the rapid progress in recent-years lattice QCD calculations. As the reso- nance is broad, special attention to finite-volume effects has to be paid, because no sharp resonance signal as from avoided level crossing can be expected. In the present article, we investigate the finite volume effects in the framework of unitarized chiral perturbation theory using next-to-leading order terms. After a fit to meson-meson partial wave data, lattice levels for πK scattering are predicted. In addition, levels are shown for the quantum numbers in which the σ(600), f0(980), a0(980), φ(1020), K*(892), and ρ(770) appear, as well as the repulsive channels. Methods to extract the κ(800) signal from the lattice spec- trum are presented. Using pseudo-data, we estimate the precision that lattice data should have to allow for a clear-cut extraction of this resonance. To put the results into con- text, in particular the required high precision on the lattice data, the σ(600), the P -wave resonances K*(892) and ρ(770), and the repulsive πK, ππ phases are analyzed as well.
53708602
Scalar mesons moving in a finite volume and the role of partial wave mixing
Phase shifts and resonance parameters can be obtained from finite-volume lattice spectra for interacting pairs of particles, moving with non-zero total momentum. We present a simple derivation of the method that is subsequently applied to obtain the ππ and πK phase shifts in the sectors with total isospin I = 0 and I = 1/2 , respectively. Considering different total momenta, one obtains extra data points for a given volume that allow for a very efficient extraction of the resonance parameters in the infinite-volume limit. Corrections due to the mixing of partial waves are provided. We expect that our results will help to optimize the strategies in lattice simulations, which aim at an accurate determination of the scattering and resonance properties.
16407243
Kaon–nucleon scattering lengths from kaonic deuterium experiments revisited
Abstract We analyse the impact of the recent measurement of kaonic hydrogen X rays by the SIDDHARTA collaboration on the allowed ranges for the kaon–deuteron scattering length in the framework of non-relativistic effective field theory. Based on data from K ¯ N scattering only, we predict the kaon–deuteron scattering length A K d = ( − 1.46 + i 1.08 ) fm , with an estimated uncertainty of about 25% in both the real and the imaginary part.
46785821
Chiral dynamics and S-wave contributions in semileptonic B decays
A bstractThe flavor-changing neutral current process b → sl+l− is beneficial to testing the standard model and hunting for new physics scenarios. In exclusive decay modes like B → K*(892)l+l−, the S-wave effects may not be negligible and thus have to be reliably estimated. Using the scalar form factors derived from dispersion relations in two channels and matched to Chiral Perturbation Theory, we investigate the S-wave contributions in $ {{\overline{B}}^0}\to {K^{-}}{\pi^{+}}{l^{+}}{l^{-}} $, with the Kπ invariant mass lying in the vicinity of the mass of K*(892), and Bs → K−K+l+l− with mKK ~ mϕ. We find that the S-wave will modify differential decay widths by about 10% in the process of $ {{\overline{B}}^0}\to {K^{-}}{\pi^{+}}{l^{+}}{l^{-}} $ and about 5% in Bs → K−K+l+l−. A forward-backward asymmetry for the charged kaon in the final state arises from the interference between the S-wave and P-wave contributions. The measurement of this asymmetry offers a new way to determine the variation of the Kπ S-wave phase versus the invariant mass.
204016596
Meson baryon interaction in the hadron exchange picture
Elastic πN scattering and the reaction π+p→K+Σ+ are described simultaneously in a unitary coupled‐channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t‐ and u‐ channel exchanges that drive the meson‐baryon interaction in the different channels. Angular distributions, polarizations, and spin‐rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.
116702082
Radiative decay of the Delta*(1700)
Electromagnetic properties provide information about the structure of strongly interacting systems and allow for independent tests of hadronic models. The radiative decay of the Delta(1700) is studied, which appears dynamically generated in a coupled channel approach from the rescattering of the (3/2^+) decuplet of baryons with the (0^-) octet of pseudoscalar mesons. The radiative decay is predicted from the well-known couplings of the photon to the mesons and hadrons which constitute this resonance in the dynamical picture.
117511031
Chiral dynamics in gamma p ---> pi0 eta p and related reactions
Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ and $\Delta^*(1700)$ resonances are dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and the $N^*(1535)$. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $1/2^-$ and $3/2^-$ states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.
119447848
Clues to the nature of the Δ∗(1700) resonance from pion- and photon-induced reactions
Abstract We make a study of the π − p → K 0 π 0 Λ , π + p → K + π + Λ , K + K ¯ 0 p , K + π + Σ 0 , K + π 0 Σ + , and η π + p reactions, in which the basic dynamics is given by the excitation of the Δ ∗ ( 1700 ) resonance which subsequently decays into K Σ ∗ ( 1385 ) or Δ ( 1232 ) η . In a similar way we also study the γ p → K 0 π + Λ , K + π − Σ + , K + π + Σ − , K 0 π 0 Σ + , and η π 0 p related reactions. The cross sections are proportional to the square of the coupling of Δ ∗ ( 1700 ) to Σ ∗ K ( Δη ) for which there is no experimental information but which is provided in the context of coupled channels chiral unitary theory where the Δ ∗ ( 1700 ) is dynamically generated. Within present theoretical and experimental uncertainties one can claim a global qualitative agreement between theory and experiment. We provide a list of items which need to be improved in order to make further progress along these lines.
10765600
Photo- and Electron-Production of Mesons on Nucleons and Nuclei
In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of ηπ 0 p and K 0 π 0 � + , together with related reactions will be shown, having with common denominator the excitation of the �(1700) resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the e + e − → φf0(980) reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the N ∗ (1535) resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the ω in nuclei, showing that present experimental results claiming a shift of the ω mass in the medium are tied to a particular choice of background and are not conclusive. On the other hand, the same experimental results show unambiguously a huge increase of the ω width in the nuclear medium.
30722169
Charge fluctuations and electric mass in a hot meson gas
Net charge fluctuations in a hadron gas are studied using an effective hadronic interaction. The emphasis of this work is to investigate the corrections of hadronic interactions to the charge fluctuations of a noninteracting resonance gas. Several methods such as loop, density, and virial expansions are employed. The calculations are also extended to SU(3), and some resummation schemes are considered. Although the various corrections are sizable individually, they cancel to a large extent. As a consequence, we find that charge fluctuations are rather well described by the free resonance gas.