arXiv subjects

W. M. Kloet

Publications and source records attributed to W. M. Kloet.

12 recordsLinked to original sources

arXiv2005

Lorentz contraction, geometry and range in antiproton-proton annihilation into two pions

We present a geometric interpretation of the so-called annihilation range in reactions of the type $\bar pp \to$ {\em two light mesons} based upon Lorentz effects in the highly relativistic final states ($γ=E_{\mathrm{cm}}/2mc^2\simeq 6.8-8.0$). Lorentz-boosted meson wave functions, within the framework of the constituent quark model, result in a richer angular dependence of the annihilation amplitudes and thus in higher partial wave contributions ($J>1$) than usually obtained. This approach sheds some light on what could be a "{\em short}" annihilation range and how it is influenced by the angular distribution of the final states.

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arXiv2004

Relativistic effects and angular dependence in the reaction antiproton-proton -> pi^- pi^+

We present a new fit to the LEAR data on antiproton-proton -> pi^- pi^+ differential cross sections and analyzing powers motivated by relativistic considerations. Within a quark model describing this annihilation we argue, since the pions are highly energetic, that relativistic effects cannot be neglected. The intrinsic pion wave functions are Lorentz transformed to the center of mass frame. This change in quark geometry gives rise to additional angular dependence in the transition operators and results in a relative enhancement of higher J \ge 2 partial wave amplitudes. The fit to the data is improved significantly.

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arXiv2004

A relativistic treatment of pion wave functions in the annihilation antiproton-proton -> pi^-pi^+

Quark model intrinsic wave functions of highly energetic pions in the reaction \bar pp->π^-π^+ are subjected to a relativistic treatment. The annihilation is described in a constituent quark model with A2 and R2 flavor-flux topology and the annihilated quark-antiquark pairs are in 3P_0 and 3S_1 states. We study the effects of pure Lorentz transformations on the antiquark and quark spatial wave functions and their respective spinors in the pion. The modified quark geometry of the pion has considerable impact on the angular dependence of the annihilation mechanisms.

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arXiv2003

The reaction antirproton-proton into pi+pi-: relativistic aspects and final-state interaction in the pion wave functions

We use a distorted wave approximation approach which includes $^3P_0$ and $^3S_1$ quark-antiquark annihilation mechanisms to reproduce the data set from LEAR on $\bar p p\to π^+π^-$ in the range from 360 to 1550 MeV/c. Improvements of the model are sought by implementing final-state interactions of the pions and by observing that the annihilation is too short-ranged in earlier attempts to describe the data. While the former improvement is due to to the final-state $ππ$ wave functions solely, the latter one originates from quark wave functions for proton, antiproton, and pions with radii slightly larger than the respective measured charge radii. This increase in hadron radius, as compared with typically much smaller radii used before in the quark model, increases the annihilation range and thereby the amplitudes for $J\ge2$ are much higher. Finally, given the very high kinetic energy of the final pions, we investigate the role of relativistic corrections in the pion wave functions when boosted into the center-of-mass frame.

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arXiv1999

Constraints on vector meson photoproduction spin observables

Extraction of spin observables from vector meson photoproduction on a nucleon target is described. Starting from density matrix elements in the vector meson's rest frame, we transform to spin observables in the photon-nucleon c.m. frame. Several constraints on the transformed density matrix and on the spin observables follow from requiring that the angular distribution and the density matrix be positive definite. A set of constraints that are required in order to extract meaningful spin observables from forthcoming data are enunciated.

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arXiv1998

Spin Information from Vector-Meson Decay in Photoproduction

For the photoproduction of vector mesons, all single and double spin observables involving vector meson two-body decays are defined consistently in the $γN$ center of mass. These definitions yield a procedure for extracting physically meaningful single and double spin observables that are subject to known rules concerning their angle and energy evolution. As part of this analysis, we show that measuring the two-meson decay of a photoproduced $ρ$ or $ϕ$ does not determine the vector meson's vector polarization, but only its tensor polarization. The vector meson decay into lepton pairs is also insensitive to the vector meson's vector polarization, unless one measures the spin of one of the leptons. Similar results are found for all double spin observables which involve observation of vector meson decay. To access the vector meson's vector polarization, one therefore needs to either measure the spin of the decay leptons, make an analysis of the background interference effects or relate the vector meson's vector polarization to other accessible spin observables.

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arXiv1997

pi-pi Scattering and the Meson Resonance Spectrum

A pi-pi, Kbar-K, and rho-rho(omega-omega) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities for elastic pi-pi scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the meson resonance table of the Particle Data Group. As expected, the pi-pi inelasticity is very strongly related to the opening of the Kbar-K channel near 1 GeV, and the opening of rho-rho(4pi) and omega-omega(6pi) channels in the 1.5 GeV region. The predictions of this model are compared to the various elastic pi-pi to pi-pi amplitudes, that were obtained from analyses of pi(-) p to pi(-) pi(+) n data. The role of the various resonances, in particular the glueball candidate f_0(1500) and the f_J(1710) is investigated.

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arXiv1996

Amplitude analysis of the $\overline{N}N \to K^-K^+$ reaction

A simple partial wave amplitude analysis of $\overline{p}p \rightarrow K^-K^+$ has been performed for data in the range $p_{\rm lab}$ = 360 -- 1000 MeV/$c$. In this low momentum interval only partial wave amplitudes with $J$ equal to 0, 1 and 2 are needed to obtain a good fit to the experimental data. This maximal $J$ = 2 value is smaller than what is required for the data of the reaction $\overline{p}p \rightarrow π^-π^+$ in the same momentum interval.

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arXiv1995

An amplitude analysis of the $\overline{N}N \to π^- π^+$ reaction

A simple partial wave amplitude analysis of $\overline{p}p \rightarrow π^- π^+$ has been performed for data in the range p$_{\sl lab}$ = 360 -- 1000 MeV/c. Remarkably few partial waves are required to fit the data, while the number of required $J$ values barely changes over this energy range. However, the resulting set of partial wave amplitudes is not unique. We discuss possible measurements with polarized beam and target which will severely restrict and help resolve the present analysis ambiguities. New data from the reaction $\overline{p}p \rightarrow π^0 π^0$ alone, are insufficient for that purpose.

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arXiv1994

The $ππ$ S-Wave in the 1 to 2 GeV Region from a $ππ$, $\bar{K}K$ and $ρρ$($ωω$) Coupled Channel Model

A simple $ππ$, $\bar{K}K$, and $ρρ$($ωω$) fully coupled channel model is proposed to predict the isoscalar S-wave phase shifts and inelasticities for $ππ$ scattering in the 1.0 to 2.0 GeV region. The S-matrix is required to exhibit poles corresponding to the established isoscalar J$^π$ = 0$^+$ resonances f$_0$(975), f$_0$(1400), and f$_0$(1710). A dominant feature of the experimental $ππ$ inelasticity is the clear opening of the $\bar{K}K$ channel near 1 GeV, and the opening of another channel in the 1.4 - 1.5 GeV region. The success of our model in predicting this observed dramatic energy dependence indicates that the effect of multi-pion channels is adequately described by the $ππ$ coupling to the $\bar{K}K$ channel, the $ρρ$(4$π$) and $ωω$(6$π$) channels.

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arXiv1993

Left-Right Asymmetry in $\bar{p}p \rightarrow π^- π^+$

Results for d$σ$/d$Ω$ and $A_N$ in the reaction $\bar{p}p \rightarrow π^- π^+$ are predicted by a simple quark model. They are compared to recent experimental data from LEAR, as well as to previous predictions from nucleon-exchange models. At low energy the quark model does better than the nucleon-exchange models, but the overall comparison to experiment remains poor. In particular, the double-dip structure of the experimental $A_N$ data is only partly represented. This shortcoming of the simple quark model is traced back to a too small J=2 amplitude. This has interesting implications for the range of this specific annihilation process.

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arXiv1993

Generalized $^3P_0$ and $^3S_1$ Annihilation Potentials for $\bar{p}p$ Decay into Two Mesons based on a Simple Quark Model

Within the quark model a generalization is proposed of the commonly used annihilation potential to describe antiproton-proton annihilation into two mesons, the so-called $^3P_0$ and $^3S_1$ mechanisms. This generalized potential treats the two mechanisms in a more symmetric way, has additional angular dependence, and results in an expanded set of selection rules.

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