Search results for "partial wave"
showing 10 items of 74 documents
Observation of pseudoscalar and tensor resonances in J /ψ →γφφ
2016
Based on a sample of (1310.6 +/- 10.5) x 10(6) J/psi events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/psi -> gamma phi phi is performed in order to study the intermediate states. Results of the partial wave analysis show that the structures are predominantly 0(-+) states. The existence of the eta(2225) is confirmed, and its resonance parameters are measured. Two additional pseudoscalar states, the eta(2100) with a mass of 2050(-24-26)(+30+75) MeV/c(2) and a width of 250(-30-164)(+36+181) MeV/c(2) and the X(2500) with a mass of 2470(-19-23)(+15+101) MeV/c(2) and a width of 230(-35-33)(+64+56) MeV/c(2), are observed. In add…
Improved description of the -scattering phenomenology at low energies in covariant baryon chiral perturbation theory
2013
Abstract We present a novel analysis of the π N scattering amplitude in covariant baryon chiral perturbation theory up to O ( p 3 ) within the extended-on-mass-shell renormalization scheme and including the Δ ( 1232 ) explicitly in the δ -counting. We take the hadronic phase shifts provided by partial wave analyses as basic experimental information to fix the low-energy constants. Subsequently, we study in detail the various observables and low-energy theorems related to the π N scattering amplitude. In particular, we discuss the results and chiral expansion of the phase shifts, the threshold coefficients, the Goldberger–Treiman relation, the pion–nucleon sigma term and the extrapolation on…
Observation of a New Narrow Axial-Vector Mesona1(1420)
2015
The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV/c pions into the π(-)π(-)π(+) final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of 3π mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow peak is observed in the f0(980)π channel with spin, parity and C-parity quantum numbers J(PC)=1(++). We present a resonance-model study of a subset of the spin-density matrix selecting 3π states with J(PC)=2(++) and 4(++) decaying into ρ(770)π and with J(PC)=1(++) decaying into f0(980)π. We identify a new a1 meson with mass (1414(-13)(+15)) MeV/c2 and wid…
Helicity-coupling amplitudes in tensor formalism.
1993
The decay of a particle with spin to two other particles with spin is best described in the helicity formalism. It is the purpose of this paper to show that the helicity-coupling amplitudes, which appear in the angular distributions, can be expressed in terms of the covariant amplitudes in the tensor formalism. This allows for a systematic derivation for the energy dependence of the helicity-coupling amplitudes within the framework of the tensor formalism. The concept of pure intrinsic spin has been developed in the tensor formalism, for decays involving two spins in the final state, in order to bring the formalism to a form comparable to the standard $\ensuremath{\ell}S$-coupling scheme. A…
Inverse amplitude method in pi pi scattering in chiral perturbation theory to two loops
2002
The inverse amplitude method is used to unitarize the two loop $\pi\pi$ scattering amplitudes of SU(2) Chiral Perturbation Theory in the $I=0,J=0$, $I=1,J=1$ and $I=2,J=0$ channels. An error analysis in terms of the low energy one-loop parameters $\bar l_{1,2,3,4,}$ and existing experimental data is undertaken. A comparison to standard resonance saturation values for the two loop coefficients $\bar b_{1,2,3,4,5,6} $ is also carried out. Crossing violations are quantified and the convergence of the expansion is discussed.
σ→γγWidth from Nucleon Electromagnetic Polarizabilities
2008
The lightest QCD resonance, the $\ensuremath{\sigma}$, has been recently fixed in the $\ensuremath{\pi}\ensuremath{\pi}$ scattering amplitude. The nature of this state remains nowadays one of the most intriguing and difficult issues in particle physics. Its coupling to photons is crucial for discriminating its structure. We propose a new method that fixes this coupling using only available precise experimental data on the proton electromagnetic polarizabilities together with analyticity and unitarity. By taking into account the uncertainties in the analysis and in the parameter values, our result is ${\ensuremath{\Gamma}}_{\mathrm{pole}}(\ensuremath{\sigma}\ensuremath{\rightarrow}\ensuremat…
Role of a triangle singularity in the πN(1535) contribution to γp→pπ0η
2017
We have studied the $\ensuremath{\gamma}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}\ensuremath{\eta}$ reaction paying attention to the two main mechanisms at low energies, the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\mathrm{\ensuremath{\Delta}}(1700)\ensuremath{\rightarrow}\ensuremath{\eta}\mathrm{\ensuremath{\Delta}}(1232)$ and the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\mathrm{\ensuremath{\Delta}}(1700)\ensuremath{\rightarrow}\ensuremath{\pi}N(1535)$. Both are driven by the photoexcitation of the $\mathrm{\ensuremath{\Delta}}(1700)$ and the second one involves a mechanism that leads to a triangle singularity. We are able to evaluate quantitatively the cross section for thi…
N/Ddescription of two meson amplitudes and chiral symmetry
1998
The most general structure of an elastic partial wave amplitude when the unphysical cuts are neglected is deduced in terms of the N/D method. This result is then matched to lowest order, ${\mathcal{O}}(p^2)$, Chiral Perturbation Theory($\chi$PT) and to the exchange (consistent with chiral symmetry) of resonances in the s-channel. The extension of the method to coupled channels is also given. Making use of the former formalism, the $\pi\pi$ and $K\pi$(I=1/2) P-wave scattering amplitudes are described without free parameters when taking into account relations coming from the 1/$N_c$ expansion and unitarity. Next, the scalar sector is studied and good agreement with experiment up to $\sqrt{s}=…
Meson-baryon threshold effects in the light-quark baryon spectrum
2008
We argue that selected $S$ wave meson-baryon channels may play a key role to match poor baryon mass predictions from quark models with data. The identification of these channels with effective inelastic channels in data analysis allows to derive a prescription which could improve the extraction and identification of baryon resonances.
S=−1meson-baryon unitarized coupled channel chiral perturbation theory and theS01resonances Λ(1405) and -Λ(1670)
2003
The $s-$wave meson-baryon scattering is analyzed for the strangeness $S=-1$ and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four channels have been considered: $\pi \Sigma$, $\bar K N$, $\eta \Lambda$ and $K \Xi$. The required input to solve the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the $\pi\Sigma\to\pi\Sigma$ mass-spectrum, to the elastic $\bar K N \to \bar K N$ and $ \bar K N\to \pi \Sigma$ $t$--matrices and to the $ K^- p \to \eta \…