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H. Haberzettl

Publications and source records attributed to H. Haberzettl.

At least 37 records · Page 2Linked to original sources
arXiv2010

Gauge-invariant formulation of $N N \to N N γ$

A complete, rigorous relativistic field-theory formulation of the nucleon-nucleon (NN) bremsstrahlung reaction is presented. The resulting amplitude is unitary as a matter of course and it is gauge invariant, i.e., it satisfies a generalized Ward-Takahashi identity. The novel feature of this approach is the consistent microscopic implementation of local gauge invariance across all interaction mechanisms of the hadronic systems, thus serving as a constraint for all subprocesses. The formalism is quite readily adapted to approximations and thus can be applied even in cases where the microscopic dynamical structure of the underlying interacting hadronic systems is either not known in detail or too complex to be treated in detail. We point out how the interaction currents resulting from the photon being attached to nucleon-nucleon-meson vertices can be treated by phenomenological four-point contact currents that preserve gauge invariance. In an advance application of the present formalism [K. Nakayama and H. Haberzettl, PRC 80, 051001(R) (2009)], such interaction currents were found to contribute significantly in explaining experimental data. In addition, we provide a scheme that permits the approximate treatment of current contributions resulting from pieces of the NN interaction that cannot be incorporated exactly. In each case, the approximation procedure ensures gauge invariance of the entire bremsstrahlung amplitude. We also discuss the necessary modifications when taking into account baryonic states other than the nucleon N; in detail, we consider the $Delta(1232)$ resonance by incorporating the couplings of the $NN$ to the $NΔ$ and $ΔΔ$ systems, and the $γN \to Δ$ transitions. We apply the formalism to the 280-MeV bremsstrahlung data from TRIUMF [PRD 41, 2689 (1990)] incorporating $γNΔ$ transition currents and find good agreement with the data.

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arXiv2010

Pion photoproduction in a dynamical coupled-channel model

Pion photoproduction reactions are investigated in a dynamical coupled-channel approach based on the Juelich pi-N model, which presently includes the hadronic pi-N and eta-N stable channels as well as the pi-Delta, sigma-N and rho-N effective channels. This model has been quite successful in the description of pi-N to pi-N 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 gamma p to pi+ n, gamma p to pi0 p and gamma n to pi- p are in good agreement with the experimental data.

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arXiv2009

Interaction current in $p p \to p p γ$

The nucleon-nucleon bremsstrahlung reaction is investigated based on a fully gauge-invariant relativistic meson-exchange model approach. In order to account consistently for the complicated part of the interaction current (which at present is too demanding to be calculated explicitly), a generalized contact current is introduced following the approach of Haberzettl, Nakayama, and Krewald [Phys. Rev. C74, 045202 (2006)]. The contact interaction current is constructed phenomenologically such that the resulting full bremsstrahlung amplitude satisfies the generalized Ward-Takahashi identity. The formalism is applied to describe the high-precision proton-proton bremsstrahlung data at 190 MeV obtained at KVI [H. Huisman et al., Phys. Rev. C65, 031001(R) (2002)]. The present results show good agreement with the data, thus removing the longstanding discrepancy between the theoretical predictions and experimental data. The present investigation, therefore, points to the importance of properly taking into account the interaction current for this reaction.

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arXiv2008

J/psi production at the Tevatron and RHIC from s-channel cut

We report on our recent evaluation of the s-channel cut contribution to J/psi hadroproduction. We show that it is likely significantly larger than the usual cut contribution of the colour-singlet model (CSM), which is known to underestimate the experimental measurements. Here the s-channel cut develops for configurations with off-shell quarks in the bound state. A correct treatment of its contribution requires the introduction of a four point function, partially constrained by gauge invariance and limiting behaviours at small and large momenta. When the unconstrained degrees of freedom are fixed to reproduce the Tevatron data, we show that RHIC data are remarkably well reproduced down to very low transverse momenta P_T without need of resummation of initial-state gluon effects. This unique feature might be typical of s-channel cut contribution.

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arXiv2008

Possible solution of the J/psi production puzzle

We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $c\bar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.

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arXiv2007

Time-delay in a multi-channel formalism

We reexamine the time-delay formalism of Wigner, Eisenbud and Smith, which was developed to analyze both elastic and inelastic resonances. An error in the paper of Smith has propagated through the literature. We correct this error and show how the results of Eisenbud and Smith are related. We also comment on some recent time-delay studies, based on Smith's erroneous interpretation of the Eisenbud result.

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arXiv2006

Gauge-invariant approach to meson photoproduction including the final-state interaction

A fully gauge-invariant (pseudoscalar) meson photoproduction amplitude off a nucleon including the final-state interaction is derived. The approach based on a comprehensive field-theoretical formalism developed earlier by one of the authors replaces certain dynamical features of the full interaction current by phenomenological auxiliary contact currents. A procedure is outlined that allows for a systematic improvement of this approximation. The feasibility of the approach is illustrated by applying it to both the neutral and charged pion photoproductions.

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arXiv2006

Photoproduction of Xi off nucleons

The photoproduction reaction $γN \to K K Ξ$ is investigated based on a relativistic meson-exchange model of hadronic interactions. The production amplitude is calculated in the tree-level approximation from relevant effective Lagrangians, whose (coupling constant) parameters are mostly fixed from the empirical data and/or quark models together with SU(3) symmetry considerations. Gauge invariance of the resulting amplitude is maintained by introducing the contact currents by extending the gauge-invariant approach of Haberzettl for one-meson photoproduction to two-meson photoproduction. The role of the intermediate low-lying hyperons and of the intermediate higher-mass hyperon resonances are analyzed in detail. In particular, the basic features of the production of $Ξ^-(1318)$ in $γp \to K^+ K^+ Ξ^-$ and their possible manifestations in the forthcoming experimental data are discussed.

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arXiv2005

Gauge-Invariant Approach to Meson Photoproduction Including the Final-State Interaction

A gauge-invariant formalism is presented for the practical treatment of photo- and electroproduction of pseudoscalar mesons off nucleons that allows an explicit incorporation of hadronic final-state interactions. The semi-phenomenological approach is based on a field theory developed by one of the authors. It generalizes an earlier approach by allowing for systematic improvement of approximations in a controlled manner. The practical feasibility is illustrated by applying the lowest-order result to the photoproduction of both neutral and charged pions.

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arXiv2005

Analyzing eta' photoproduction data on the proton at energies of 1.5--2.3 GeV

The recent high-precision data for the reaction $γp\to pη'$ at photon energies in the range 1.5--2.3 GeV obtained by the CLAS collaboration at the Jefferson Laboratory have been analyzed within an extended version of the photoproduction model developed previously by the authors based on a relativistic meson-exchange model of hadronic interactions [Phys. Rev. C \textbf{69}, 065212 (2004)]. The $η'$ photoproduction can be described quite well over the entire energy range of available data by considering $S_{11}$, $P_{11}$, $P_{13}$, and $D_{13}$ resonances, in addition to the $t$-channel mesonic currents. The observed angular distribution is due to the interference between the $t$-channel and the nucleon $s$- and $u$-channel resonance contributions. The $j=3/2$ resonances are required to reproduce some of the details of the measured angular distribution. For the resonances considered, our analysis yields mass values compatible with those advocated by the Particle Data Group. We emphasize, however, that cross-section data alone are unable to pin down the resonance parameters and it is shown that the beam and/or target asymmetries impose more stringent constraints on these parameter values. It is found that the nucleonic current is relatively small and that the $NNη^\prime$ coupling constant is not expected to be much larger than 2.

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arXiv2004

Some aspects of $Θ^+$ parity determination in the reaction $γN\to Θ^+ \bar{K}\to N K \bar{K}$

We analyze the problem of how to determine the parity of the $Θ^+$ pentaquark in the reaction $γN\to KΘ\to NK\bar{K}$, where $N=n,p$. Our model calculations indicate that the contribution of the non-resonant background of the reaction $γN\to NK\bar{K}$ cannot be neglected, and that suggestions to determine the parity based solely on the initial-stage process $γN\to KΘ$ cannot be implemented cleanly. We discuss the various mechanisms that contribute to the background, and we identify some spin observables which are sensitive.

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arXiv2004

Consistent analysis of the reaction $γp \to p η^\prime$ and $pp \to ppη^\prime$

The production of $η'$ mesons in the reactions $γp\to pη'$ and $pp\to ppη'$ is described consistently within a relativistic meson exchange model of hadronic interactions. The photoproduction can be described quite well over the entire energy range of available data by considering an $S_{11}$ and a $P_{11}$ resonance, in addition to the $t$-channel mesonic current. The observed angular distribution is due to the interference between the $t$-channel and the nucleon resonance $s$- and $u$-channel contributions. Our analysis yields positions close to 1650 MeV and 1870 MeV for the $S_{11}$ and $P_{11}$ resonances, respectively. We argue that, at present, identifying these states with the known $S_{11}(1650)$ resonance and the missing $P_{11}$ resonance predicted at 1880 MeV, respectively, would be premature. It is found that the nucleonic current is relatively small and that the $NNη^\prime$ coupling constant cannot be much larger than $g_{NNη^\prime}=3$. As for the $p p \to p p η^\prime$ reaction, different current contributions are constrained by a combined analysis of this and the photoproduction reaction. Difficulties to simultaneously account for the 47-MeV and 144-MeV angular distributions measured by the COSY-11 and DISTO collaborations, respectively, are addressed.

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arXiv2001

Reply to "Comment about pion electroproduction and the axial form factors"

It is shown that comments by Guichon [hep-ph/0012126], and also by Bernard, Kaiser, and Meißner [hep-ph/0101062], regarding my recent criticism [Phys. Rev. Lett. 85, 3576 (2000)] of how the axial form factor is supposed to enter pion electroproduction do not address the main point of my argument and therefore are irrelevant.

hep-ph↗
arXiv2000

Electromagnetic K+ production on the deuteron with hyperon recoil polarization

Photo- and electroproduction processes of K+ on the deuteron are investigated theoretically. Modern hyperon-nucleon forces as well as an updated kaon production operator on the nucleon are used. Sizable effects of the hyperon-nucleon final state interaction are seen in various observables. Especially the photoproduction double polarization observable C_z is shown to provide a handle to distinguish different hyperon-nucleon force models.

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arXiv2000

Hypernuclear Physics with Photons

We review the opportunities and challenges in the field of hypernuclear physics with electromagnetic probes. An overview is presented regarding our current understanding of the elementary production process on the nucleon. This amplitude is then used in the nuclear environment to study the hyperon-nucleon (YN) interaction. We discuss two scenarios: hypernuclear excitation that allows the investigation of hypernuclear structure and the bound Lambda in the nucleus, and quasifree kaon production on the deuteron and on nuclei, which permits a more direct access to the YN force. Specific examples are given for few-body systems and shell-model nuclei.

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arXiv2000

Nucleon Resonances in Meson Nucleon Scattering with Strangeness Production

An effective Lagrangian model in a coupled channels framework is applied to extract nucleon resonance parameters. In the K-matrix approximation, we simultaneously analyze all the available data for the transitions from pi N to five possible meson-baryon final states, pi N, pipi N, eta N, K Lambda, and KSigma, in the energy range from pi N threshold up to W = 2 GeV. In this work, we focus our efforts on the K Sigma channel. In particular, we include a set of Delta resonances around 1900 MeV: the S31(1900), P31(1910), and P33(1920) states. In most cases the parameters of nucleon resonances determined by the fits are consistent with the commonly accepted values in the literature. We find that in the low-energy region, the S11(1650), P11(1710), and P13(1720) states are important for the p(pi-,K0)Sigma0 and p(pi-,K+)Sigma- processes while the P33(1600) and D33(1700) states are significant for the pure I=3/2 reaction p(pi+,K+)Sigma+. In the high energy region, we find a D13 state at 1945 MeV which is important for the p(pi-,K0)Sigma0 reaction while the Delta resonances around 1900 MeV show up significantly in the p(pi-,K+)Sigma- and p(pi+,K+)Sigma+ processes.

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