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Carl E. Carlson

Publications and source records attributed to Carl E. Carlson.

At least 91 records · Page 5Linked to original sources
arXiv2000

Predictions for the Decays of Radially-Excited Baryons

We consider decays of the lowest-lying radially excited baryons. Assuming a single-quark decay approximation, and negligible configuration mixing, we make model-independent predictions for the partial decay widths to final states with a single meson. Masses of unobserved states are predicted using an old mass formula rederived using large-$N_c$ QCD. The momentum dependence of the one-body decay amplitude is determined phenomenologically by fitting to observed decays. Comparison of these predictions to experiment may shed light on whether the Roper resonance can be interpreted as a three-quark state.

hep-ph↗
arXiv2000

Predictions for Decays of Radially Excited Baryons

We consider the strong decays of the lowest-lying radially excited baryons, in SU(6) language the states comprising the first excited 56-plet. Assuming a single-quark decay approximation, and negligible configuration mixing, we make model-independent predictions for the partial decay widths to final states with a single meson. Masses of unobserved states are predicted using results from large-N_c QCD, and the momentum dependence of the one-body decay amplitude is determined phenomenologically by fitting to observed decays, so that the baryon spatial wave functions are not assumed. We point out that comparison of these predictions to experiment may shed light on whether the Roper resonance can be consistently interpreted as a three-quark state.

hep-ph↗
arXiv2000

What we know about the Theoretical Foundation of Duality in Electron Scattering

We consider some of the things that we understand about the theoretical underpinnings of duality, including items such as why the resonance peak/background ratio is constant in general, why it falls for the $Δ(1232)$, what we might expect for scaling and duality with longitudinal or spin-dependent structure functions, and what kind of scaling or duality we might expect for semiexclusive processes.

hep-ph↗
arXiv2000

Scaling and Duality in Semi-exclusive Processes

We discuss extending scaling and duality studies to semi-exclusive processes. We show that semi-exclusive hard pion photoproduction should exhibit scaling behavior in kinematic regions where the photon and pion both interact directly with the same quark. We show that such kinematic regions exist. We also show that the constancy with changing momentum transfer of the resonance peak/scaling curve ratio, familiar for many resonances in deep inelastic scattering, is also expected in the semi-exclusive case.

hep-ph↗
arXiv1999

Semiexclusive Processes: A different way to probe hadron structure

Hard semiexclusive processes provide an opportunity to design effective currents to probe specific parton distributions and to probe in leading order parton distributions that fully inclusive reactions probe only via higher order corrections. High transverse momentum pion photoproduction is an example of a such a process. We discuss the perturbative and soft processes that contribute, and show how regions where perturbative processes dominate can give us the parton structure information. Polarized initial states are needed to get information on polarization distributions. Current polarization asymmetry data is mostly in the soft region. However, with somewhat higher energy, determining the polarized gluon distribution using hard pion photoproduction appears quite feasible.

hep-ph↗
arXiv1999

High Transverse Momentum Meson Production: A Different Way To Probe Hadron Structure

Hard, or high transverse momentum, pion photoproduction can be a tool for probing the parton structure of the beam and target. We discuss the perturbative and soft processes that contribute, and show how regions where perturbative processes dominate can give us the parton structure information. Polarized initial states are needed to get information on polarization distributions. Current polarization asymmetry data is mostly in the soft region. However, with the proposed EPIC machine parameters, determining the polarized gluon distribution using hard pion photoproduction appears quite feasible.

hep-ph↗
arXiv1999

Soft Contributions to Hard Pion Photoproduction

Hard, or high transverse momentum, pion photoproduction can be a tool for probing the parton structure of the beam and target. We estimate the soft contributions to this process, with an eye toward delineating the region where perturbatively calculable processes dominate. Our soft process estimate is based on vector meson dominance and data based parameterizations of semiexclusive hadronic cross sections. We find that soft processes dominate in single pion photoproduction somewhat past 2 GeV transverse momentum at a few times 10 GeV incoming energy. The recent polarization asymmetry data is consistent with the perturbative asymmetry being diluted by polarization insensitive soft processes. Determining the polarized gluon distribution using hard pion photoproduction appears feasible with a few hundred GeV incoming energy (in the target rest frame).

hep-ph↗
arXiv1998

Operator Analysis of L=1 Baryon Masses in Large N_c QCD

We consider in detail the mass operator analysis for the nonstrange L=1 excited baryons in large N_c QCD. We present a straightforward procedure for constructing the large N_c baryon wavefunctions, and provide complete analytic expressions for the matrix elements of all the independent isosinglet mass operators. We discuss the relationship between the old-fashioned operator analyses based on nonrelativistic SU(6) symmetry and the modern large N_c approach, which has a firmer theoretical foundation. We then suggest a possible dynamical interpretation for the subset of operators preferred strongly by the data.

hep-ph↗
arXiv1998

Perturbative QCD Applied to Baryons

We review standard applications of perturbative QCD to baryon production, and argue by examining data that it is generally relevant at high but experimentally feasible momentum transfers. Then we consider some new initiatives, particularly meson photoproduction off baryons and the seeming quagmire of Delta(1232) electroproduction.

hep-ph↗
arXiv1998

Decays of l=1 Baryons to Delta gamma

Recently we considered the electromagnetic decays of the orbitally-excited SU(6) 70-plet baryons in large-N_c QCD, fitting to the helicity amplitudes measured in photoproduction experiments. Using the results of this analysis, we predict the helicity amplitudes for the decays N^* \to Δγand Δ^* \to Δγ. These decays can be studied at a number of new experimental facilities, and thus provide another nontrivial test of the lowest order large-N_c predictions.

hep-ph↗
arXiv1998

Masses of Orbitally Excited Baryons in Large N_c QCD

We present the first phenomenological study of the masses of orbitally excited baryons in large N_c QCD. Restricting here to the nonstrange sector of the L=1 baryons, the 1/N_c expansion is used to order and select a basis of effective operators that spans the nine observables (seven masses and two mixing angles). Fits are performed using subsets of the complete set of nine operators, including corrections up to O(1/N_c) where leading order is N_c^1. This study shows that the 1/N_c expansion provides an excellent framework for analyzing the mass spectrum, and uncovers a new hierarchy of operator contributions.

hep-ph↗
arXiv1998

Approach to Perturbative Results in the N-Delta Transition

We show that constraints from perturbative QCD calculations play a role in the nucleon to Delta(1232) electromagnetic transition even at moderate momentum transfer scales. The pQCD constraints, tied to real photoproduction data and unseparated resonance response functions, lead to explicit forms for the helicity amplitudes wherein the E2/M1 ratio remains small at moderately large momentum transfer.

hep-ph↗
arXiv1998

Photoproduction of of l=1 Baryons: Quark Model versus Large N_c

We consider the electromagnetic decays of the orbitally-excited SU(6) 70-plet baryons, to compare the predictions of the naive quark model with those of large-N_c QCD. The helicity amplitudes measured in N^* photoproduction are computed in a large-N_c effective field theory, based on a Hartree approximation, and the amplitudes are fit to the current experimental data. Our results indicate that the success of the naive quark model predictions cannot be explained by large-N_c arguments alone. This is consistent with the conclusions of an earlier study of the N^*\to Nπdecays, that utilized the same approach.

hep-ph↗
arXiv1998

Measuring Polarized Gluon and Quark Distributions with Meson Photoproduction

We calculate polarization asymmetries in photoproduction of high transverse momentum mesons, focusing on charged pions, considering the direct, fragmentation, and resolved photon processes. The results at very high meson momentum measure the polarized quark distributions and are sensitive to differences among the existing models. The results at moderate meson momentum are sensitive to the polarized gluon distribution and can provide a good way to measure it. Suitable data may come as a by-product of deep inelastic experiments to measure $g_1$ or from dedicated experiments.

hep-ph↗
arXiv1998

Perturbative Duality in the Resonance Spin Structure Functions

We investigate the relations between the spin structure functions in the scaling and resonance regions. We examine the possible duality between the two, and draw inferences for the behavior of the asymmetry A_1 at large x. Finally, we point out the importance of additional polarized structure function data in the resonance region in terms of testing the hysteresis of perturbative physics.

hep-ph↗
arXiv1997

Probing Polarized Parton Distributions with Meson Photoproduction

Polarization asymmetries in photoproduction of high transverse momentum mesons are a flavor sensitive way to measure the polarized quark distributions. We calculate the expected asymmetries in several models, and find that the asymmetries are significant and also significantly different from model to model. Suitable data may come as a by-product of deep inelastic experiments to measure $g_1$ or from dedicated experiments.

hep-ph↗
arXiv1996

Schwinger's Dynamical Casimir Effect: Bulk Energy Contribution

Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence itself except to affirm that the Casimir effect is energetically adequate as a candidate explanation.

hep-th↗