arXiv subjects

E. M. Henley

Publications and source records attributed to E. M. Henley.

30 records · Page 2Linked to original sources

arXiv1997

Isospin Splitting in the Pion-Nucleon Couplings from QCD Sum Rules

We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant coming from isospin violation in the strong interaction. The effect can be attributed primarily to the difference of the quark condensates and . Assuming that the pi0 is a pure isostate we obtain for the splitting between the coupling of proton and neutron to the neutral pion an interval of [0.008 ; 0.023], the uncertainties coming mainly from the input parameters. In order to obtain the coupling to a physical pi0 we have to take pi - eta mixing into account leading to an interval of [0.012 ; 0.037]. The charged pion nucleon coupling is found to be the average of the two neutral ones. Electromagnetic effects are not included.

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arXiv1997

Isospin Breaking in the Pion-Nucleon Coupling from QCD Sum Rules

We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant $g_{NNπ}$ coming from isospin violation in the strong interaction. The effect can be attributed primarily to the difference of the quark condensates $<{\bar u}u>$ and $<{\bar d}d>$. For the splitting $(g_{ppπ_0} - g_{nnπ_0}) / g_{NNπ}$ we obtain an interval of $1.2 * 10^{-2}$ to $3.7 * 10^{-2}$, the uncertainties coming mainly from the input parameters. The charged pion nucleon coupling is found to be the average of $g_{ppπ_0}$ and $g_{nnπ_0}$. Electromagnetic effects are not included.

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arXiv1995

The Weak Parity-Violating Pion-Nucleon Coupling (Revised)

We use QCD sum rules to obtain the weak parity-violating pion-nucleon coupling constant $f_{πNN}$. We find that $f_{πNN}\approx 2\times 10^{-8}$, about an order of magnitude smaller than the ``best estimates'' based on quark models. This result follows from the cancellation between perturbative and nonperturbative QCD processes not found in quark models, but explicit in the QCD sum rule method. Our result is consistent with the experimental upper limit found from $^{18}$F parity-violating measurements.

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arXiv1995

The Weak Parity-Violating Pion-Nucleon Coupling

We use QCD sum rules to obtain the weak parity-violating pion-nucleon coupling constant $f_{πNN}$. We find that $f_{πNN}\approx 3\times 10^{-8}$, up to an order of magnitude smaller than the ``best estimates" based on quark models. This result follows from the cancellation between perturbative and nonperturbative QCD processes not found in quark models, but explicit in the QCD sum rule method. Our result is consistent with the experimental upper limit found from $^{18}$F parity-violating measurements.

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arXiv1994

Time Reversal Invariance in the beta-Decays of A = 8 Nuclei

We examine time reversal invariance in the beta-decays of 8B(2+) and 8Li(2+) to 8Be(2+) in detail, with particular attention to final state interactions of the two alpha particles from the decay of 8Be, and of the electron (positron) with the daughter nucleus. A R-matrix formulation is used, with the initial state described by a shell model. The R-matrix parameters are obtained by fitting the alpha-αscattering phase shifts and allowed beta-decay rates. Because the nuclear final state interaction effects on the time reversal test come from second forbidden beta-decays, they are small and can be minimized by a suitable choice of kinematic conditions. The e(+/-)-nucleus Coulomb interaction induced T-violation effects depend on the first forbidden operators.

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arXiv1994

A Proposed Test of Charge Symmetry in $Σ$ Decay

The semi-leptonic decays of $Σ^\pm$ offer a vehicle for observing charge symmetry-breaking. The effect is expected to be about 6\%, enhanced due to the replacement of two u quarks by d quarks. We propose that present experimental data be improved to search for this effect.

hep-ph↗

arXiv1994

Pi- Eta Mixing from QCD Sum Rules

The $q^2$ dependence of the $π$-$η$ mixing amplitude is examined with the use of QCD sum rules. The linear slope of the mixing function $θ(q^2)$ is found to be much smaller than that for $ρ$-$ω$ mixing. Thus the mixing amplitude is approximately the same in the space-like region as in the time-like one, and one may neglect the $q^2$ dependence of the mixing. A comparison between a hadron-meson, an effective chiral model, and the QCD sum rules approaches is made.

hep-ph↗

arXiv1994

Mesons and the Structure of Nucleons

The role of mesons, particularly the pion, in the structure of nucleons is reviewed and investigated. Since quark-antiquark pairs are likely to ``transform" into mesons at large distances, mesons are expected to contribute to nucleon structure. Their effects on the Gottfried sum rule, on the strangeness content of the nucleon, and on the spin of the nucleon are discussed.

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arXiv1993

A Quark Model of Lambdabar-Lambda Production of Pbar-P Interactions

A quark model which includes both scalar and vector contributions to the reaction mechanism (SV quark model) is used in a DWBA calculation of $\bar ΛΛ$ production in $\bar p p$ interractions. Total and differential cross-sections, polarizations, depolarizations, and spin-correlattion coefficients are computed for laboratory momenta from threshold to 1695 MeV/c. The free parameters of the calculation are the scalar and vector strengths, a quark cluster size parameter,and the parameters of the unknown $\bar ΛΛ$ potentials. Good agreement with experiment is found for constructive interference of the scalar and vector terms, and for $\bar ΛΛ$ potentials which differ from those suggested by several authors on the basis of SU(3) arguments. The fit to the data is better than that obtained by other quark models, which use only scalar $or$ vector annihilation terms. The agreement with experiment is also better than that found in meson-exchange models. The recent suggestion[1] that measurement of the depolarization parameter $D_{nn}$ can be used to discriminatebetween meson-exchange and quark models is examined in detail. We conclude that a measurement of $D_{nn}$ will provide a test of which of these models, as presently constructed,is the more appropriate description of strangeness production in the $\bar p p \ rightarrow \bar ΛΛ$ reaction.

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arXiv1993

Electromagnetic Gauge Invariance of Chiral Hybrid Quark Models

In this work, we investigate the question, whether the conventional analysis of the electromagnetic form factors of the nucleon, evaluated in the framework of the cloudy bag model (CBM) or other chirally invariant hybrid quark models utilizing the same philosophy, is gauge invariant. In order to address that point, we first formulate the CBM in a style that resembles the technique of loop integrals. Evaluating the self energy and the electromagnetic form factors of the nucleon in that manner and comparing with the standard analysis where nonrelativistic perturbation theory is used, allows us to show that our approach is appropriate and to point out, what approximations are made in the standard derivation of the model. {}From the form of those loop integrals, we then show that additional diagrams are needed to preserve electromagnetic gauge invariance and we assess the corresponding corrections.

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arXiv1993

The Off Shell $ρ$-$ω$ Mixing in the QCD Sum Rules

The $q^2$ dependence of the $ρ-ω$ mixing amplitude is analyzed with the use of the QCD sum rules and the dispersion relation. Going off shell the mixing decreases, changes sign at $q^2 \simeq 0.4 m_ρ^2 > 0$ and is negative in the space like region. Implications of this result to the isospin breaking part of the nuclear force are discussed.

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arXiv1993

A Quark Model of Antilambda-Lambda Production in Pbar-P Interactions

A quark model which includes both scalar and vector contributions to the reaction mechanism is used in a DWBA calculation of total and differential cross-sections, polarizations, and spin correlation coefficients for the reaction $\bar p p \rightarrow \bar ΛΛ$ at laboratory momenta from threshold to 1.92 GeV/c. The free parameters of the calculation include the scalar and vector strengths, a quark cluster size parameter, and six parameters in the unknown $\bar ΛΛ$ interaction. Excellent agreement with experiment is found for a constructive interference of scalar and vector terms, and for a $\bar ΛΛ$ potential which differs from that suggested by several authors on the basis of SU(3) arguments. The fit to the data is better than that obtained by other quark models, which use only scalar or vector annihilation terms. The agreement with experiment is as good as that found in meson-exchange models, which use more parameters than the present calculation.

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