arXiv subjects

J. Haidenbauer

Publications and source records attributed to J. Haidenbauer.

At least 127 records · Page 7Linked to original sources

arXiv2005

The radiative decays $ϕ\toγa_0/f_0$ in the molecular model for the scalar mesons

We investigate the radiative decays of the $ϕ$ meson to the scalar mesons $a_0(980)$ and $f_0(980)$. We demonstrate that, contrary to earlier claims, these decays should be of the same order of magnitude for a molecular state and for a compact state and, therefore, the available experimental information is consistent with both, a molecular as well as a compact structure of the scalars. Thus, the radiative decays of the $ϕ$ meson into scalars establish a sizable $K\bar K$ component of the scalar mesons, but do not allow to discriminate between molecules and compact states.

hep-ph↗

arXiv2005

Precision calculation of $γd\to π^+ nn$ within chiral perturbation theory

The reaction $γd\to π^+ nn$ is calculated up to order $χ^{5/2}$ in chiral perturbation theory, where $χ$ denotes the ratio of the pion to the nucleon mass. Special emphasis is put on the role of nucleon--recoil corrections that are the source of contributions with fractional power in $χ$. Using the known near threshold production amplitude for $γp\to π^+ n$ as the only input, the total cross section for $γd\to π^+ nn$ is described very well. A conservative estimate suggests that the theoretical uncertainty for the transition operator amounts to 3 % for the computed amplitude near threshold.

nucl-th↗

arXiv2005

Partial-wave analysis of $\vec{p}\vec{p}\to ppπ^\circ$ data

We present a partial-wave analysis of the polarization data for the reaction $\vec{p}\vec{p}\to ppπ^\circ$, based solely on the recent measurements at IUCF for this channel. The fit leads to a $χ^2$ per degree of freedom of 1.7. Methods for an improved analysis are discussed. We compare the extracted values to those from a meson exchange model.

hep-ph↗

arXiv2004

Near threshold enhancement of the ppbar mass spectrum in J/Psi decay

We investigate the nature of the near-threshold enhancement in the ppbar invariant mass spectrum of the reaction J/Psi -> gamma ppbar reported recently by the BES Collaboration. Using the Juelich NNbar model we show that the mass dependence of the ppbar spectrum close to the threshold can be reproduced by the S-wave ppbar final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the NNbar interaction near threshold and of the J/Psi -> gamma ppbar reaction mechanism and in view of the controversal situation in the decay J/Psi -> pi0 ppbar, where no obvious signs of a ppbar final state interaction are seen, explanations other than final state interactions cannot be ruled out at the present stage.

hep-ph↗

arXiv2004

Parity nonconserving observables in thermal neutron capture on a proton

We calculate parity nonconserving observables in the processes where a neutron is captured on a proton at the threshold energy radiating a photon. Various potential models such as Paris, Bonn and Argonne $v18$ are used for the strong interactions, and the meson-exchange description is employed for the weak interactions between hadrons. The photon polarization $P_γ$ in the unpolarized neutron capture process and photon asymmetry $A_γ$ in the polarized neutron capture process are obtained in terms of the weak meson-nucleon coupling constants. $A_γ$ turns out to be basically insensitive to the employed strong interaction models and thus can be uniquely determined in terms of the weak coupling constants, but $P_γ$ depends significantly on the strong interaction models.

nucl-th↗

arXiv2004

Flatte-like distributions and the a_0(980)/f_0(980) mesons

We explore the features of Flatte-like parametrizations. In particular, we demonstrate that the large variation in the absolute values of the coupling constants to the pi-eta (or pi-pi) and KKbar channels for the a_0(980) and f_0(980) mesons that one can find in the literature can be explained by a specific scaling behaviour of the Flatte amplitude for energies near the KKbar threshold. We argue that the ratio of the coupling constants can be much better determined from a fit to experimental data.

nucl-th↗

arXiv2004

Remarks on the parity determination of narrow resonances

Recently several proposals were put forward to determine the parity of narrow baryonic resonances, in particular the $Θ^+$. In these proceedings we will briefly comment on the general problems in this task and then discuss in detail the potential of reactions of the type $\vec N\vec N\toΘ^+Y$, where $Y$ denotes a hyperon (either $Σ$ or $Λ$) and the arrows indicate that a polarized initial state is required. Besides reiterating the model--independent properties of this class of reactions we discuss the physics content of some model calculations.

hep-ph↗

arXiv2004

New results on the limit for the width of the exotic Theta^+ resonance

We investigate the impact of the Θ^+(1540) resonance on differential and integrated cross sections for the reaction K^+d{\to}K^0pp, where experimental information is available at kaon momenta below 640 MeV/c. The calculation utilizes the Jülich KN model and extensions of it that include contributions from a Θ^+(1540) state with different widths. The evaluation of the reaction K^+d{\to}K^0pp takes into account effects due to the Fermi motion of the nucleons within the deuteron and the final three-body kinematics. We conclude that the available data constrain the width of the Θ^+(1540) to be less than 1 MeV.

hep-ph↗

arXiv2004

Bounds on the bound η^3He system

We investigate the relation between the η^3He binding energy and width and the (complex) η^3He scattering length. Following our systematic analysis of the eta 3He scattering length we set limits on the η^3He binding. If bound states exist the binding energy (width) should not exceed 5 MeV (10 MeV). In addition, we comment on a recently claimed observation of an η-mesic ^3He quasi-bound state by the TAPS collaboration based on ηphotoproduction data. Although our limits are in reasonable agreement with the values reported by this collaboration, our analysis of these data does not lead to a solid conclusion concerning the existence of an η-mesic bound state. More dedicated experiments are necessary for further clarification.

nucl-th↗

arXiv2004

On the determination of the parity of the $Θ^+$

We critically examine the possibility of determining the parity of the $Θ^+(1540)$ from the reactions $NN\to Θ^+Y$ ($Y$ = $Λ$, $Σ$) recently discussed in the literature. Specifically, we study the energy dependence of those observables that were suggested to be the most promising ones to unravel the parity of the $Θ^+$, namely the spin correlation coefficient $A_{xx}$, and the spin transfer coefficient $D_{xx}$. We show that the energy dependence of $σ_0(1+A_{xx})$, corresponding to the spin-triplet production cross section, guarantees unambiguous information on the parity of the $Θ^+$. Here, $σ_0$ denotes the unpolarized cross section. Also, the possibility to determine the parity of the $Θ^+$ through the energy dependence of $σ_0D_{xx}$ is discussed.

hep-ph↗

arXiv2004

Analysis of Theta^+ production in K^+Xe collisions

The reaction K^+Xe->K^0pX is investigated in a meson-exchange model including rescattering of the secondary protons with the aim to analyze the evidence for the Theta^+(1540) resonance reported by the DIANA collaboration. We confirm that the kinematical cuts introduced by the DIANA collaboration efficiently suppress the background to the K^+n->K^0p reaction which may contribute to the Theta^+(1540) production. We find that these kinematical cuts do not produce a narrow structure in the K^0p effective mass spectra near 1540 MeV. We study the effect of a narrow Theta^+ resonance of both positive and negative parity in comparison with the DIANA data. We show that the K^+Xe->K^0pX calculations without Theta^+ contribution as well as the results obtained with a Theta^+ width of 1 MeV are in comparably good agreement with the DIANA results. More dedicated experiments are called for to establish this exotic baryon resonance.

nucl-th↗

arXiv2004

The $η{-}^3$He scattering length revisited

The possible existence of $η$-mesic nuclei poses an interesting and still open issue of research. Since the occurence of such $η$-nucleus bound states is reflected in the corresponding $η$-nucleus scattering length, we critically review the present knowledge for the $η$$^3$He system. Specifically, we scrutinize the available experimental information for the reaction $p{+}d \to η{+} ^3{\rm He}$ which is commonly used to extract the $η$$^3$He scattering length. We point out several striking discrepancies between the various measurements. Subject to those inconsistencies we deduce a value of $a{=}|4.3{\pm}0.3|{+}i(0.5{\pm}0.5)$ fm.

nucl-th↗

arXiv2004

Energy dependence of the Lambda/Sigma0 production cross section ratio in proton proton interactions

The production of the Lambda and Sigma0 hyperons has been measured via the pp->pK+Lambda / Sigma0 reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the Lambda/Sigma0 cross section ratio from about 28 at Q<=13 MeV to the high energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final state interactions in the p-Sigma0 channel seem to be much smaller compared to the p-Lambda one. Estimates of the effective range parameters are given for the N-Lambda and the N-Sigma systems.

nucl-ex↗

arXiv2003

An analysis of the reaction pp --> ppηnear threshold

It is shown that most of the available data on the $pp\to ppη$ reaction, including the invariant mass distributions in the $pp\to ppη$ reaction recently measured at COSY, can be understood in terms of the partial-wave amplitudes involving final $pp$ $S$ and $P$ states and the $η$ meson s-wave. This finding, together with the fact that results within a meson--exchange model are especially sensitive to the details of the excitation mechanism of the $S_{11}(1535)$ resonance, demonstrates the possibility of investigating the properties of this resonance in $NN$ collisions. The spin correlation function $C_{xx}$ is shown to disentangle the $S$- and $P$-wave contributions. It is also argued that spin correlations may be used to help constrain the contributions of the amplitudes corresponding to the final $pp$ $^3P_0$

nucl-th↗

arXiv2003

How to extract the $ΛN$ scattering length from production reactions

A dispersion integral is derived that allows one to relate directly (spin dependent) $ΛN$ invariant mass spectra, measured in a large-momentum transfer reaction such as $pp\to K^+pΛ$ or $γd\to K^+nΛ$, to the scattering length for elastic $ΛN$ scattering. The involved systematic uncertainties are estimated to be smaller than 0.3 fm. This estimate is confirmed by comparing results of the proposed formalism with those of microscopic model calculations. We also show, for the specific reaction $pp\to K^+Λp$, how polarization observables can be used to separate the two spin states of the $ΛN$ system.

hep-ph↗

arXiv2003

Influence of a Z+(1540) resonance on K+N scattering

The impact of a (I=0, J^P=1/2^+) Z^+(1540) resonance with a width of 5 MeV or more on the K+N (I=0) elastic cross section and on the P01 phase shift is examined within the KN meson-exchange model of the Juelich group. It is shown that the rather strong enhancement of the cross section caused by the presence of a Z^+ with the above properties is not compatible with the existing empirical information on KN scattering. Only a much narrower Z^+ state could be reconciled with the existing data -- or, alternatively, the Z^+ state must lie at an energy much closer to the KN threshold.

hep-ph↗

arXiv2003

NN($^1S_0$) pairs in $^3$He and in p$^3$He backward elastic scattering

It is shown that the shoulder observed in the cross section of $p^3He$ backward elastic scattering at proton beam energies of 0.4 -- 0.7 GeV can be explained by the mechanism of virtual $π$-meson production with a dominant contribution from the subprocesses $pd^*\to ^3$He$ π^0$ and $p(pp)\to^3$He$ π^+$, where $d^*$ denotes the singlet deuteron and the $pp$ pair is in the $^1S_0$ state. At high energies, 1-3 GeV, the mechanism of $np$-pair transfer dominates and probes high-momentum $NN(^1S_0$) correlations in $^3$He.

nucl-th↗

arXiv2003

Evidence that the a0(980) and f0(980) are not elementary particles

We study the interesting problem of whether it is possible to distinguish composite from elementary particles. In particular we generalize a model-independent approach of S. Weinberg to the case of unstable particles. This allows us to apply our formalism to the case of the a0(980) and f0(980) resonances and to address the question whether these particles are predominantly genuine, confined quark states (of $\bar q q$ or $qq\bar q\bar q$ structure) or governed by mesonic components.

hep-ph↗