Diffractive vector meson production at HERA: From soft to hard QCD

Иванов, И. П.; Николаев, Н. Н.; Savin, A.

doi:10.1134/s1063779606010011

Cited by 160 publications

(296 citation statements)

References 289 publications

(667 reference statements)

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“…and hence for T (1) λ V λ γ , T (2) λ V λ γ , U (1) λ V λ γ , and U (2) λ V λ γ , follow from Eq. (23) and Eqs.…”

Section: Asymptotic Behavior Of Amplitudes At Small |T |mentioning

confidence: 99%

“…From the asymptotic behavior, the NPE amplitudes T (1) 00 , T (1) 11 , T (2) 01 , T (2) 10 and the UPE amplitudes…”

Section: Asymptotic Behavior Of Amplitudes At Small |T |mentioning

confidence: 99%

“…where 2 is the reconstructed invariant mass of the undetected hadronic system (missing mass), E V = ν +t/(2M) is the energy of the exclusively produced ρ 0 meson, and (E π + + E π − ) is the sum of the energies of the two detected pions in the target rest frame.…”

Section: Kinematicsmentioning

confidence: 99%

“…At HERMES kinematics Q is much smaller than ν, with Q/ν of the order of 0.1. The helicityamplitude ratios t (2) λ V λ γ and u (2) λ V λ γ can be extracted from data collected with a transversely polarized target, as they contribute linearly to the SDMEs n λ V λ V λ γ λ γ and s λ V λ V λ γ λ γ , respectively. Contributions of squares of moduli of the helicity-amplitude ratios u (1) 01 , u (1) 10 , u (1) 1−1 to u λ V λ V λ γ λ γ are much smaller than the contribution of |u (1) 11 | 2 according to the hierarchy of amplitudes established in Refs.…”

Section: Choice Of Free Parametersmentioning

confidence: 99%

“…[1,2]). Originally, the reaction mechanism was of primary interest, but now it has become apparent that this process also offers the possibility to study the structure of the nucleon and of the vector meson [1][2][3], especially at large virtuality Q 2 of the photon exchanged between electron and nucleon. In the one-photon-exchange approximation, all electroproduction observables can be expressed in terms of the virtual-photon spin-density matrix and the matrix elements of the electromagnetic current between quantum states of initial and final hadrons.…”

Section: Introductionmentioning

confidence: 99%

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Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

et al. 2017

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Exclusive ρ 0 -meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV 2 < Q 2 < 7.0 GeV 2 , 3.0 GeV < W < 6.3 GeV, and −t < 0.4 GeV 2 . Using an unbinned maximum-likelihood method, 25 parameters are extracted. These determine the real and imaginary parts of the ratios of several helicity amplitudes describing ρ 0 -meson production by a virtual photon. The denominator of those ratios is the dominant amplitude, the nucleon-helicity-non-flip amplitude F 0 1 2 0 1 2 , which describes the production of a longitudinal ρ 0 -meson by a longitudinal virtual photon. The ratios of nucleon-helicity-nonflip amplitudes are found to be in good agreement with those from the previous HERMES analysis. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to F 0 1 2 0 1 2 . Results obtained in a handbag approach based on generalized parton distributions taking into account the contribution from pion exchange are found to be in good agreement with these ratios. Within the model, the data favor a positive sign for the π − ρ transition form factor. By also exploiting the longitudinal beam polarization, a total of 71 ρ 0 spin-density matrix elements is determined from the extracted 25 parameters, in contrast to only 53 elements as directly determined in earlier analyses.

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“…and hence for T (1) λ V λ γ , T (2) λ V λ γ , U (1) λ V λ γ , and U (2) λ V λ γ , follow from Eq. (23) and Eqs.…”

Section: Asymptotic Behavior Of Amplitudes At Small |T |mentioning

confidence: 99%

“…From the asymptotic behavior, the NPE amplitudes T (1) 00 , T (1) 11 , T (2) 01 , T (2) 10 and the UPE amplitudes…”

Section: Asymptotic Behavior Of Amplitudes At Small |T |mentioning

confidence: 99%

Section: Kinematicsmentioning

confidence: 99%

Section: Choice Of Free Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

et al. 2017

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Heavy quarkonium: progress, puzzles, and opportunities

Brambilla¹,

Eidelman²,

Heltsley³

et al. 2011

Advances in the Physics of Particles and Nuclei

103

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A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly-found conventional states expanded to include hc(1P ), χc2(2P ), B + c , and η b (1S). In addition, the unexpected and still-fascinating X(3872) has been joined by * Editors † Section coordinators ‡ Corresponding author: bkh2@cornell.edu more than a dozen other charmonium-and bottomonium-like "XY Z" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of cc, bb, and bc bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrialstrength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hotand cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

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Direct quarkonium-plus-gluon production in DIS in the color glass condensate

Kang,

Li,

Salazar

2024

J. High Energ. Phys.

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We compute the differential cross-section for direct quarkonium production accompanied by a gluon in high-energy deep inelastic scattering (DIS) at small-x. We employ the Non-Relativistic QCD factorization framework, focusing on the S-wave contribution to the formation of the quarkonium, and including both color singlet and octet contributions. Our short distance coefficients for the production of the heavy quark pair are obtained within the Color Glass Condensate effective field theory. Our results pave the way towards the next-to-leading order computation of direct quarkonium in DIS, as well as the study of azimuthal correlations of direct quarkonium and jet.

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Diffractive vector meson production at HERA: From soft to hard QCD

Abstract: Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic QCD are reviewed with an emphasis on the BFKL color dipole and k T -factorization approaches.

Cited by 160 publications

References 289 publications

Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

Heavy quarkonium: progress, puzzles, and opportunities

Direct quarkonium-plus-gluon production in DIS in the color glass condensate

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