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Title: Partonic structure of neutral pseudoscalars via two photon transition form factors

Abstract

Here, the γγ* → η c,b transition form factors are computed using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory, and thereby unified with equivalent calculations of electromagnetic pion elastic and transition form factors. The resulting γγ* → η c form factor, G ηc(Q 2), is consistent with available data; significantly, at accessible momentum transfers, Q 2G ηc(Q 2) lies well below its conformal limit. These observations confirm that the leading-twist parton distribution amplitudes of heavy-heavy bound states are compressed relative to the conformal limit. A clear understanding of the distribution of valence quarks within mesons thus emerges, a picture which connects Goldstone modes, built from the lightest quarks in nature, with systems containing the heaviest valence quarks that can now be studied experimentally, and highlights basic facts about manifestations of mass within the Standard Model.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1374604
Alternate Identifier(s):
OSTI ID: 1351044
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review D
Additional Journal Information:
Journal Volume: 95; Journal Issue: 7; Journal ID: ISSN 2470-0010
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Raya, Khepani, Ding, Minghui, Bashir, Adnan, Chang, Lei, and Roberts, Craig D. Partonic structure of neutral pseudoscalars via two photon transition form factors. United States: N. p., 2017. Web. doi:10.1103/PhysRevD.95.074014.
Raya, Khepani, Ding, Minghui, Bashir, Adnan, Chang, Lei, & Roberts, Craig D. Partonic structure of neutral pseudoscalars via two photon transition form factors. United States. doi:10.1103/PhysRevD.95.074014.
Raya, Khepani, Ding, Minghui, Bashir, Adnan, Chang, Lei, and Roberts, Craig D. Mon . "Partonic structure of neutral pseudoscalars via two photon transition form factors". United States. doi:10.1103/PhysRevD.95.074014. https://www.osti.gov/servlets/purl/1374604.
@article{osti_1374604,
title = {Partonic structure of neutral pseudoscalars via two photon transition form factors},
author = {Raya, Khepani and Ding, Minghui and Bashir, Adnan and Chang, Lei and Roberts, Craig D.},
abstractNote = {Here, the γγ* → ηc,b transition form factors are computed using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory, and thereby unified with equivalent calculations of electromagnetic pion elastic and transition form factors. The resulting γγ* → ηc form factor, Gηc(Q2), is consistent with available data; significantly, at accessible momentum transfers, Q2Gηc(Q2) lies well below its conformal limit. These observations confirm that the leading-twist parton distribution amplitudes of heavy-heavy bound states are compressed relative to the conformal limit. A clear understanding of the distribution of valence quarks within mesons thus emerges, a picture which connects Goldstone modes, built from the lightest quarks in nature, with systems containing the heaviest valence quarks that can now be studied experimentally, and highlights basic facts about manifestations of mass within the Standard Model.},
doi = {10.1103/PhysRevD.95.074014},
journal = {Physical Review D},
number = 7,
volume = 95,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}

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  • Cited by 3
  • We perform a perturbative QCD analysis of the quark transverse momentum effect on the pion-photon transition form factors {ital F}{sub {pi}{gamma}} and {ital F}{sub {pi}{gamma}{sup {asterisk}}} in the standard light-cone formalism, with two phenomenological models of the wave function as the input of the nonperturbative aspect of the pion. We point out that the transverse momentum dependence in both the numerator and the denominator of the hard scattering amplitude is of the same importance and should be considered consistently. It is shown that after taking into account the quark transverse momentum corrections, the results obtained from different model wave functionsmore » are consistent with the available experimental data at finite {ital Q}{sup 2}. {copyright} {ital 1996 The American Physical Society.}« less
  • We study photon-meson transition form factors {gamma}{sup {asterisk}}(Q{sup 2}){gamma}{r_arrow}{pi}{sup 0},{eta},{eta}{sup {prime}} at low and moderately high Q{sup 2} assuming a nontrivial hadronlike q{bar q} structure of the photon in the soft region. In the hard region, the q{bar q} photon wave function contains both a perturbative tail of the soft wave function such as the wave function of an ordinary hadron and a standard QED pointlike q{bar q} component. The latter provides the 1/Q{sup 2} asymptotical behavior of the transition form factor in accordance with QCD. The data on the {gamma}{pi}{sup 0} form factor are used for fixing the softmore » photon wave function which is found to have the same structure as the soft wave function of the pion reconstructed from the elastic pion form factor. Assuming universality of the ground-state pseudoscalar meson wave functions we calculate the {gamma}{eta}, {gamma}{eta}{sup {prime}} transition form factors and {eta}{r_arrow}{gamma}{gamma}, {eta}{sup {prime}}{r_arrow}{gamma}{gamma} partial widths and found them to be in perfect agreement with the data. {copyright} {ital 1997} {ital The American Physical Society}« less
  • Using the CLEO II detector, we have measured the differential cross sections for exclusive two-photon production of light pseudoscalar mesons {pi}{sup 0}, {eta}, and {eta}{sup {prime}}. From our measurements we have obtained the form factors associated with the electromagnetic transitions {gamma}{sup {asterisk}}{gamma}{r_arrow}meson. We have measured these form factors in the momentum transfer ranges from 1.5 to 9, 20, and 30GeV{sup 2} for {pi}{sup 0}, {eta}, and {eta}{sup {prime}}, respectively, and have made comparisons to various theoretical predictions. {copyright} {ital 1997} {ital The American Physical Society}
  • The QCD evolution of the pion distribution amplitude (DA) {phi}{sub {pi}} (x, Q{sup 2}) is computed for several commonly used models. Our analysis includes the nonperturbative form predicted by lightfront holographic QCD, thus combining the nonperturbative bound state dynamics of the pion with the perturbative ERBL evolution of the pion distribution amplitude. We calculate the meson-photon transition form factors for the {pi}{sup 0}, {eta} and {eta}' using the hard-scattering formalism. We point out that a widely-used approximation of replacing {phi} (x; (1 - x)Q) with {phi} (x;Q) in the calculations will unjustifiably reduce the predictions for the meson-photon transition formmore » factors. It is found that the four models of the pion DA discussed give very different predictions for the Q{sup 2} dependence of the meson-photon transition form factors in the region of Q{sup 2} > 30 GeV{sup 2}. More accurate measurements of these transition form factors at the large Q{sup 2} region will be able to distinguish the four models of the pion DA. The rapid growth of the large Q{sup 2} data for the pion-photon transition form factor reported by the BABAR Collaboration is difficult to explain within the current framework of QCD. If the BABAR data for the meson-photon transition form factor for the {pi}{sup 0} is confirmed, it could indicate physics beyond-the-standard model, such as a weakly-coupled elementary C = + axial vector or pseudoscalar z{sup 0} in the few GeV domain, an elementary field which would provide the coupling {gamma}{sup *}{gamma} {yields} z{sup 0} {yields} {pi}{sup 0} at leading twist. Our analysis thus indicates the importance of additional measurements of the pion-photon transition form factor at large Q{sup 2}.« less