arXiv subjects

J. Haidenbauer

Publications and source records attributed to J. Haidenbauer.

At least 55 records · Page 3Linked to original sources

arXiv2015

On the near-threshold $\bar pp$ invariant mass spectrum measured in $J/ψ$ and $ψ'$ decays

A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/ψ\to x \bar pp$ and $ψ(3686) \to x \bar pp$ $(x = γ,\, ω,\, ρ,\, π,\, η)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered and, in addition, an older phenomenological model constructed by the Jülich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar pp$ FSI. It turns out that the interaction in the isospin-1 $^1S_0$ channel required for the description of the $J/ψ\to γ\bar pp$ decay predicts a $\bar NN$ bound state.

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arXiv2015

A study of hyperons in nuclear matter based on chiral effective field theory

The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field theory and fitted to Lambda-N and Sigma-N scattering data, are investigated. Results for the single-particle potentials of the Lambda and Sigma hyperons in nuclear matter are reported, based on a conventional first-order Brueckner calculation. The Sigma-nucleus potential is found to be repulsive, in agreement with phenomenological information. A weak Lambda-nucleus spin-orbit interaction can be achieved by an appropriate adjustment of a low-energy constant corresponding to an antisymmetric Lambda-N -- Sigma-N spin-orbit interaction that arises at next-to-leading order in the effective field theory approach.

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arXiv2014

Do $ΞΞ$ bound states exist?

The existence of baryon-baryon bound states in the strangeness sector is examined in the framework of SU(3) chiral effective field theory. Specifically, the role of SU(3) symmetry breaking contact terms that arise at next-to-leading order in the employed Weinberg power counting scheme is explored. We focus on the 1S0 partial wave and on baryon-baryon channels with maximal isospin since in this case there are only two independent SU(3) symmetry breaking contact terms. At the same time, those are the channels where most of the bound states have been predicted in the past. Utilizing $pp$ phase shifts and $Σ^+ p$ cross section data allows us to pin down one of the SU(3) symmetry breaking contact terms and a clear indication for the decrease of attraction when going from the NN system to strangeness S=-2 is found, which rules out a bound state for $ΣΣ$ with isospin I=2. Assuming that the trend observed for S=0 to S=-2 is not reversed when going to $ΞΣ$ and $ΞΞ$ makes also bound states in those systems rather unlikely.

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arXiv2014

Production of charmed pseudoscalar mesons in antiproton-proton annihilation

We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on pbarp to KbarK by connecting the processes via SU(4) flavor symmetry. Our predictions for the DDbar production cross section are in the order of 10^{-2} -- 10^{-1} mu b. They turned out to be comparable to those obtained in other studies. The cross section for a D_sD_s pair is found to be of the same order of magnitude despite the fact that its production in pbarp scattering requires a two-step process.

hep-ph↗

arXiv2014

The electromagnetic form factors of the proton in the timelike region

The reactions ppbar -> e+e- and e+e- -> ppbar are analyzed in the near-threshold region. Specific emphasis is put on the role played by the interaction in the initial- or final antinucleon-nucleon state which is taken into account rigorously. For that purpose a recently published NNbar potential derived within chiral effective field theory and fitted to results of a new partial-wave analysis of ppbar scattering data is employed. Our results provide strong support for the conjecture that the pronounced energy dependence of the e+e- <-> ppbar cross section, seen in pertinent experiments, is primarily due to the ppbar interaction. Predictions for the proton electromagnetic form factors G_E and G_M in the timelike region, close to the NNbar threshold, and for spin-dependent observables are presented. The steep rise of the effective form factor for energies close to the ppbar threshold is explained solely in terms of the ppbar interaction. The corresponding experimental information is quantitatively described by our calculation.

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arXiv2013

Final-State Interactions in the Process pp -> pKLambda

The possibility to determine the pLambda scattering length from the final-state interaction in the reaction pp->pKLambda is investigated experimentally. From a transversely polarized measurement, the K analyzing power (A_N) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A_N is found. The influence of N*-resonances on the pLambda invariant mass spectrum is investigated by exploiting the large acceptance for the process pp->pKLambda->pKppi and is found to be the main source of uncertainty for determining the pLambda scattering length.

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arXiv2013

Elastic pbar-d scattering and total pbar-d cross sections reexamined

We update our recent analysis of pbar-d scattering, performed within the Glauber theory including the single- and double pbar-N scattering mechanisms. Specifically, now we consider also Nbar-N amplitudes from a new partial-wave analysis of pbar-p scattering data. Predictions for differential cross sections and the spin observables A_y^d, A_y^pbar, A_xx, A_yy are presented for antiproton beam energies between 50 and 300 MeV. Total polarized cross sections are calculated utilizing the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated.

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arXiv2013

Elastic pbar-d scattering and total pbar-d cross sections

Elastic pbar-d scattering is studied within the Glauber theory based on the single- and double pbar-N scattering mechanisms. The full spin dependence of the elementary pbar-N scattering amplitudes is taken into account and both the S- and D-wave components of the deuteron are considered. The treatment of the spin dependence is done in a (properly modified) formalism developed recently by Platonova and Kukulin for the pd -> pd scattering process. Predictions for differential cross sections and the spin observables A_y^d, A_y^pbar, A_xx, A_yy are presented for antiproton beam energies between 50 and 300 MeV, using amplitudes generated from the Nbar-N interaction model developed by the Juelich group. Total polarized cross sections are calculated utilizing the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated.

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arXiv2013

Coupled-channel dynamics in the reactions piN --> piN, etaN, KLambda, KSigma

Elastic piN scattering and the world data of the family of reactions pi^- p --> eta n, K^0 Lambda$, K^0 Sigma^0, K^+ Sigma^-, and pi^+ p --> K^+ Sigma^+ are described simultaneously in an analytic, unitary, coupled-channel approach. SU(3) flavor symmetry is used to relate both the t- and the 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. Partial-wave amplitudes are determined and the resonance content is extracted from the analytic continuation, including resonance positions and branching ratios, and possible sources of uncertainties are discussed. The results provide the final-state interactions for the ongoing analysis of photo- and electroproduction data.

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arXiv2013

Hyperon-nucleon interaction at next-to-leading order in chiral effective field theory

Results for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models.

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arXiv2013

Study of the $Λp$ Interaction Close to the $Σ^+n$ and $Σ^0p$ Thresholds

The $Λp$ interaction close to the $ΣN$ threshold is considered. Specifically, the pronounced structure seen in production reactions like $K^-d \to π^- Λp$ and $pp\to K^+ Λp$ around the $ΣN$ threshold is analyzed. Modern interaction models of the coupled $ΛN - ΣN$ systems generate such a structure either due to the presence of a (deuteron-like) unstable bound state or of an inelastic virtual state. % A determination of the position of the prominent peak as observed in various experiments for the two aforementioned reactions leads to values that agree quite well with each other. Furthermore, the deduced mean value of $2128.7\pm 0.3$ MeV for the peak position coincides practically with the threshold energy of the $Σ^+ n$ channel. This supports the interpretation of the structure as a genuine cusp, signaling an inelastic virtual state in the $^3S_1-^3D_1$ partial wave of the $ΣN$ isospin 1/2 channel. % There is also evidence for a second peak (or shoulder) in the data sets considered which appears at roughly 10-15 MeV above the $ΣN$ threshold. However, its concrete position varies significantly from data set to data set and, thus, a theoretical interpretation is difficult.

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arXiv2013

Baryon-baryon interactions from chiral effective field theory

Results from an ongoing study of baryon-baryon systems with strangeness S=-1 and -2 within chiral effective field theory are reported. The investigations are based on the scheme proposed by Weinberg which has been applied rather successfully to the nucleon-nucleon interaction in the past. Results for the hyperon-nucleon and hyperon-hyperon interactions obtained to leading order are reviewed. Specifically, the issue of extrapolating the binding energy of the H-dibaryon, extracted from recent lattice QCD simulations, to the physical point is addressed. Furthermore, first results for the hyperon-nucleon interaction at next-to-leading order are presented and discussed.

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arXiv2012

Spin dependence of the pbar-d and pbar-3He interactions

Elastic scattering of antiprotons on deuteron and 3He targets is studied within the Glauber-Sitenko theory. In case of pbar-d scattering, the single- and double pbar-N scattering mechanisms and the full spin dependence of the elementary pbar-N scattering amplitudes are taken into account on the basis of an appropriately modified formalism developed for p-d scattering. Differential cross sections and analyzing powers are calculated for antiproton beam energies between 50 and 300 MeV, using the Nbar-N model of the Juelich group as input. Results for total polarized cross sections are obtained via the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is discussed.

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arXiv2012

The proton-antiproton mass threshold structure in psi(3686) radiative decay revisited

The near-threshold behavior of the ppbar invariant mass spectrum from the psi(3686) -> gamma ppbar decay reported recently by the BESIII Collaboration is analyzed. The enhancement in the ppbar invariant mass spectrum near threshold is nicely reproduced by the ppbar final-state interaction based on the isospin averaged 1S0 partial-wave amplitude as predicted by the Julich nucleon--antinucleon model. Contributions from the f_2(1910) or f_2(1950) mesons, as promoted in earlier works, are not needed.

hep-ph↗

arXiv2012

Precise calculation of the two-step process for K- d -> pi Sigma N in the Lambda (1405) resonance region

The reaction K- d -> pi Sigma N is investigated taking into account single scattering and the two-step process due to Kbar N -> pi Sigma rescattering. The influence of some common approximations are examined. It is found that the treatment of the kinematics in the Green's function that appears in the loop integral of the rescattering process has a rather strong impact on the resulting lineshape of the pi Sigma invariant mass spectrum. Specifically, a calculation with correct kinematics where the three-body unitarity cut due to the nK- p threshold occurs at the physical value yields a pronounced peak in the invariant mass spectrum at this threshold and, at the same time, suppresses the signal in the region of the Lambda(1405) resonance. On the other hand, an approximation applied in past calculations shifts that threshold down and, consequently, leads to an accidental and therefore erroneous enhancement of the signal of the Lambda(1405) in the pi Sigma invariant mass spectrum.

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arXiv2011

Dynamical coupled-channel approaches on a momentum lattice

Dynamical coupled-channel approaches are a widely used tool in hadronic physics that allow to analyze different reactions and partial waves in a consistent way. In such approaches the basic interactions are derived within an effective Lagrangian framework and the resulting pseudo-potentials are then unitarized in a coupled-channel scattering equation. We propose a scheme that allows for a solution of the arising integral equation in discretized momentum space for periodic as well as twisted boundary conditions. This permits to study finite size effects as they appear in lattice QCD simulations. The new formalism, at this stage with a restriction to S-waves, is applied to coupled-channel models for the sigma(600), f0(980), and a0(980) mesons, and also for the Lambda(1405) baryon. Lattice spectra are predicted.

hep-lat↗

arXiv2011

Exotic bound states of two baryons in light of chiral effective field theory

Baryon-baryon bound states in the strangeness S=-2, S=-3, and S=-4 sectors are considered. In particular, the dependence of the corresponding binding energies on the quark mass (or equivalently the pion mass) is explored in the framework of chiral effective field theory, in order to connect with current lattice QCD calculations. For a bound state in the Xi-Xi 1S0 channel, predicted by our leading-order effective field theory interaction, binding energies are inferred that are roughly in line with a recent lattice QCD result at meson and baryon masses that correspond to those in the lattice simulation. With regard to the so-called H-dibaryon it is shown that the SU(3) breaking effects induced by the differences of the pertinent two-baryon thresholds (Lambda-Lambda, Xi-N, Sigma-Sigma) have a very pronounced impact on its binding energy. A bound H-dibaryon as found in two lattice calculations could be shifted above the Lambda-Lambda or even above the Xi-N threshold for physical masses of the involved baryons.

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arXiv2011

Scattering lengths of strangeness S=-2 baryon-baryon interactions

We reconsider a method based on dispersion theory, that allows one to extract the scattering length of any two-baryon system from corresponding final-state interactions in production reactions. The application of the method to baryon-baryon systems with strangeness S=-2 and S=-3 systems is discussed. Theoretical uncertainties due to the presence of inelastic channels with near-by thresholds are examined for the specific situation of the reaction K^- d -> K^0 Lambda Lambda and the coupling of Lambda Lambda to the Xi N channel. The possibility to disentangle spin-triplet and spin-singlet scattering lengths by means of various polarization measurements is demonstrated for several production reactions in K^- d and gamma d scattering. Employing the method to available data on the Lambda Lambda invariant mass from the reaction ^{12}C(K^-,K^+ Lambda Lambda X), a 1S0 scattering length of a(Lambda Lambda)=-1.2\pm 0.6 fm is deduced.

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