arXiv subjects

J. Haidenbauer

Publications and source records attributed to J. Haidenbauer.

At least 37 records · Page 2Linked to original sources

arXiv2018

Theoretical study of the $Δ^{++}-Δ^-$ configuration in the deuteron using antiproton beam

We study the manifestation of the $Δ^{++}-Δ^-$ component of the deuteron wave function in the exclusive reaction $\bar p d \to π^- π^- Δ^{++}$. Due to the large binding energy the internal motion in the $Δ-Δ$ system is relativistic. We take this into account within the light-cone (LC) wave function formalism and, indeed, found large differences between calculations based on the LC and non-relativistic (NR) wave functions. We demonstrate, that the consistent LC treatment of the $Δ-Δ$ system plays the key role in the separation of the signal and background. Within the LC approach, the characteristic shape of the momentum distribution of the $Δ-Δ$ bound system predicted by the meson-exchange model is well visible on the background of usual annihilations at beam momenta between 10 and 15 GeV/c.

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arXiv2018

In-medium properties of a $ΞN$ interaction derived from chiral effective field theory

The in-medium properties of a baryon-baryon interaction for the strangeness $S=-2$ sector derived within chiral effective field theory up to next-to-leading order are investigated. The considered $ΞN$ interaction is in line with available empirical constraints on the $ΛΛ$ $S$-wave scattering length and on $ΞN$ elastic and inelastic cross sections. In particular, there are no near-threshold bound states in the $ΞN$ system. A conventional $G$-matrix calculation for this interaction is performed and reveals that the single-particle potential of the $Ξ$-hyperon in nuclear matter is moderately attractive as suggested by recent experimental evidence for the existence of $Ξ$-hypernuclei.

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arXiv2018

Deuteron analysing powers in deuteron-proton elastic scattering at 1.2 and 2.27 GeV

The vector and tensor analysing powers in deuteron-proton elastic scattering have been measured in the forward hemisphere at deuteron kinetic energies of 1.2 GeV and 2.27 GeV using the ANKE spectrometer at the COSY storage ring. The results are compared with other experimental data and with predictions made within the framework of Glauber multiple scattering theory.

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arXiv2018

Faddeev approach to the reaction $K^- d \to πΣn$ at $p_{K} = 1$ GeV/c

The reaction $K^-d \to πΣn$ is studied within a Faddeev-type approach, with emphasis on the specific kinematics of the E31 experiment at J-PARC, i.e. $K^-$ beam momentum of $p_K = 1$ GeV/c and neutron angle of $θ_n=0^\circ$. The employed Faddeev approach requires as main input amplitudes for the two-body subsystems $\bar KN \to \bar KN$ and $\bar KN \to πΣ$. For the latter results from recently published chiral unitary models of the $\bar KN$ interaction are utilized. The $\bar KN \to \bar KN$ amplitude itself, however, is taken from a recent partial-wave analysis. Due to the large incoming momentum of the $K^-$, the $\bar KN$ interaction is probed in a kinematical regime where those chiral potentials are no longer applicable. A comparison of the predicted spectrum for various $πΣ$ charge channels with preliminary data is made and reveals a remarkable agreement as far as the magnitude and the line shape in general is concerned. Noticeable differences observed in the $πΣ$ spectrum around the $\bar KN$ threshold, i.e. in the region of the $Λ$(1405) resonance, indicate a sensitivity to the details of the employed $\bar KN \to πΣ$ amplitudes and suggest that pertinent high-precision data could indeed provide substantial constraints on the structure of the $Λ$(1405).

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arXiv2017

Scattering of decuplet baryons in chiral effective field theory

A formalism for treating the scattering of decuplet baryons in chiral effective field theory is developed. The minimal Lagrangian and potentials in leading-order SU(3) chiral effective field theory for the interactions of octet baryons ($B$) and decuplet baryons ($D$) for the transitions $BB\to BB$, $BB\leftrightarrow DB$, $DB\to DB$, $BB\leftrightarrow DD$, $DB\leftrightarrow DD$, and $DD\to DD$ are provided. As an application of the formalism we compare with results from lattice QCD simulations for $ΩΩ$ and $NΩ$ scattering. Implications of our results pertinent to the quest for dibaryons are discussed.

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arXiv2017

Lambda-nuclear interactions and hyperon puzzle in neutron stars

Brueckner theory is used to investigate the in-medium properties of a $Λ$-hyperon in nuclear and neutron matter, based on hyperon-nucleon interactions derived within SU(3) chiral effective field theory (EFT). It is shown that the resulting $Λ$ single-particle potential $U_Λ(p_Λ=0,ρ)$ becomes strongly repulsive for densities $ρ$ of two-to-three times that of normal nuclear matter. Adding a density-dependent effective $ΛN$-interaction constructed from chiral $ΛNN$ three-body forces increases the repulsion further. Consequences of these findings for neutron stars are discussed. It is argued that for hyperon-nuclear interactions with properties such as those deduced from the SU(3) EFT potentials, the onset for hyperon formation in the core of neutron stars is expected to be shifted to extremely high baryon density, thus potentially resolving the so-called hyperon puzzle.

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arXiv2017

SU(4) flavor symmetry breaking in D-meson couplings to light hadrons

The validity of SU(4)-flavor symmetry relations of couplings of charmed $D$ mesons to light mesons and baryons is examined with the use of $^3{\rm P}_0$ quark-pair creation model and nonrelativistic quark model wave functions. We focus on the three-meson couplings $ππρ$, $KKρ$ and $DDρ$ and baryon-baryon-meson couplings $NNπ$, $NΛK$ and $NΛ_c D$. It is found that SU(4)-flavor symmetry is broken at the level of 30% in the $DDρ$ tree-meson couplings and 20% in the baryon-baryon-meson couplings. Consequences of these findings for DN cross sections and existence of bound states D-mesons in nuclei are discussed.

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arXiv2017

First Model-Independent Measurement of the Spin Triplet $pΛ$ Scattering Length from Final State Interaction in the $\vec{p}p \rightarrow pK^{+}Λ$ Reaction

The $\vec{p}p \rightarrow pK^{+}Λ$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $pΛ$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm 0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.

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arXiv2016

Production of charmed baryons in $\bar p p$ collisions close to their thresholds

Cross sections for the charm-production reactions $\bar p p \to \bar Λ_c^- Σ_c^+$, $\bar Σ_cΣ_c$, $\bar Ξ_cΞ_c$, and $\bar Ξ_c'Ξ_c'$ are presented, for energies near their respective thresholds. The results are based on a calculation performed in the meson-exchange framework in close analogy to earlier studies of the Jülich group on the strangeness-production reactions $\bar p p \to \bar ΛΣ$, $\bar ΣΣ$, $\bar ΞΞ$ by connecting the two sectors via SU(4) flavor symmetry. The cross sections are found to be in the order of $0.1 - 1$ $μb$ at energies of $100$ MeV above the respective thresholds, for all considered channels. Complementary to meson-exchange, where the charmed baryons are produced by the exchange of $D$ and $D^*$ mesons, a charm-production potential derived in a quark model is employed for assessing uncertainties. The cross sections predicted within that picture turned out to be significantly smaller.

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arXiv2016

The electromagnetic form factors of the $Λ$ in the timelike region

The reaction $e^+e^- \to \bar ΛΛ$ is investigated for energies close to the threshold. Specific emphasis is put on the role played by the interaction in the final $\bar ΛΛ$ system which is taken into account rigorously. For that interaction a variety of $\bar ΛΛ$ potential models is employed that have been constructed for the analysis of the reaction $\bar p p \to \bar ΛΛ$ in the past. The enhancement of the effective form factor for energies close to the $\bar ΛΛ$ threshold, seen in pertinent experiments, is reproduced. Predictions for the $Λ$ electromagnetic form factors $G_M$ and $G_E$ in the timelike region and for spin-dependent observables such as spin-correlation parameters are presented.

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arXiv2016

Polarized proton-deuteron scattering as a test of time-reversal invariance

Scattering of protons with transversal polarization $p_y^p$ on deuterons with tensor polarization $P_{xz}$ provides a null-test signal for time-reversal (T) invariance violating but parity (P) conserving effects. We calculate the corresponding null-test observable at beam energies 100-1000 MeV within the spin-dependent Glauber theory considering T-violating P-conserving nucleon-nucleon interactions. The S-wave component of the deuteron wave function as well as the D-wave are taken into account and the latter is found to play an important role for the magnitude and the energy dependence of the observable in question. Specifically, with inclusion of the D wave the maximum of the obtained signal is shifted to higher beam energies, i.e. to 700-800 MeV.

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arXiv2016

Hyperons in nuclear matter from SU(3) chiral effective field theory

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force.

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arXiv2015

Strangeness S=-2 baryon-baryon interaction at next-to-leading order in chiral effective field theory

The strangeness $S=-2$ baryon-baryon interaction is studied in chiral effective field theory up to next-to-leading order. The potential at this order consists of 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 interaction in the $S=-2$ sector. Specifically, the couplings of the pseudoscalar mesons to the baryons are fixed by SU(3) symmetry and, in general, also the contact terms are related via SU(3) symmetry to those determined in a previous study of the $S=-1$ hyperon-nucleon interaction. The explicit SU(3) symmetry breaking due to the physical masses of the pseudoscalar mesons ($π$, $K$, $η$) is taken into account. It is argued that the $ΞN$ interaction has to be relatively weak to be in accordance with available experimental constraints. In particular, the published values and upper bounds for the $Ξ^- p$ elastic and inelastic cross sections apparently rule out a somewhat stronger attractive $ΞN$ force and, specifically, disfavor any near-threshold deuteron-like bound states in that system.

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arXiv2015

Exact calculations of a quasi-bound state in the $\bar{K} \bar{K} N$ system

Dynamically exact calculations of a quasi-bound state in the $\bar{K}\bar{K}N$ three-body system are performed using Faddeev-type AGS equations. As input two phenomenological and one chirally motivated $\bar{K}N$ potentials are used, which describe the experimental information on the $\bar{K}N$ system equally well and produce either a one- or two-pole structure of the $Λ(1405)$ resonance. For the $\bar{K}\bar{K}$ interaction separable potentials are employed that are fitted to phase shifts obtained from two theoretical models. The first one is a phenomenological $\bar{K}\bar{K}$ potential based on meson exchange, which is derived by SU(3) symmetry arguments from the Jülich $ππ- \bar{K} K$ coupled-channels model. The other interaction is a variant of the first one, which is adjusted to the $KK$ s-wave scattering length recently determined in lattice QCD simulations. The position and width of the $\bar{K}\bar{K}N$ quasi-bound state is evaluated in two ways: (i) by a direct pole search in the complex energy plane and (ii) using an "inverse determinant" method, where one needs to calculate the determinant of the AGS system of equations only for real energies. A quasi-bound state is found with binding energy $B_{\bar{K}\bar{K}N} = 12 - 26$ MeV and width $Γ_{\bar{K}\bar{K}N} = 61 - 102$ MeV, which could correspond to the experimentally observed $Ξ(1950)$ state.

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arXiv2015

Eta photoproduction in a combined analysis of pion- and photon-induced reactions

The $ηN$ final state is isospin-selective and thus provides access to the spectrum of excited nucleons without being affected by excited $Δ$ states. To this end, the world database on eta photoproduction off the proton up to a center-of-mass energy of $E\sim 2.3$ GeV is analyzed, including data on differential cross sections, and single and double polarization observables. The resonance spectrum and its properties are determined in a combined analysis of eta and pion photoproduction off the proton together with the reactions $πN\to πN$, $ηN$, $KΛ$ and $KΣ$. For the analysis, the so-called Jülich coupled-channel framework is used, incorporating unitarity, analyticity, and effective three-body channels. Parameters tied to photoproduction and hadronic interactions are varied simultaneously. The influence of recent MAMI $T$ and $F$ asymmetry data on the eta photoproduction amplitude is discussed in detail.

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arXiv2015

The $ψ$(3770) resonance and its production in $\bar pp \to D \bar D$

The production of a $D\bar D$ meson-pair in antiproton-proton ($\bar p p$) annihilation close to the production threshold is investigated, with special emphasis on the role played by the $ψ$(3770) resonance. The study is performed in a meson-baryon model where the elementary charm production process is described by baryon exchange. Effects of the interactions in the initial and final states are taken into account rigorously, where the latter involves also those due to the $ψ$(3770). The predictions for the $D\bar D$ production cross section are in the range of 30 -- 250 nb, the contribution from the $ψ$(3770) resonance itself amounts to roughly 20 -- 80 nb.

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arXiv2015

Photocouplings at the Pole from Pion Photoproduction

The reactions $γp\toπ^0 p$ and $γp\toπ^+ n$ are analyzed in a semi-phenomenological approach up to $E\sim2.3$ GeV. Fits to differential cross section and single and double polarization observables are performed. A good overall reproduction of the available photoproduction data is achieved. The Jülich2012 dynamical coupled-channel model -which describes elastic $πN$ scattering and the world data base of the reactions $πN\toηN$, $KΛ$, and $KΣ$ at the same time - is employed as the hadronic interaction in the final state. The framework guarantees analyticity and, thus, allows for a reliable extraction of resonance parameters in terms of poles and residues. In particular, the photocouplings at the pole can be extracted and are presented.

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arXiv2015

Polarized deuteron charge-exchange reaction $dp->{pp}_sNπ$ in the Delta-isobar region

Mechanisms of the charge exchange reaction $dp\to \{pp\}_{\!s} Nπ$, where $\{pp\}_{\!s}$ is a two-proton system at low excitation energy, are studied at beam energies 1 -- 2 GeV and for invariant masses $M_X$ of the final $Nπ$ system that correspond to the formation of the $Δ(1232)$ isobar. The direct mechanism, where the initial proton is excited into the $Δ(1232)$, dominates and explains the existing data on the unpolarized differential cross section and spherical tensor analyzing power $T_{22}$ for $M_X> 1.2$ GeV/$c^2$. However, this model fails to describe $T_{20}.

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