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Register a new userPerturbative QCD Analysis of Near Threshold Heavy Quarkonium Photoproduction at Large Momentum Transfer
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We apply perturbative QCD to investigate the near threshold heavy quarkonium photoproduction at large momentum transfer. From an explicit calculation, we show that the conventional power counting method will be modified and the three quark Fock state with nonzero orbital angular momentum dominates the near threshold production. It carries a power behavior of $1/(-t)^5$ for the differential cross section. We further comment on the impact of our results on the interpretation of the experiment measurement in terms of the gluonic gravitational form factors of the proton.
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The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $xi$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributions to the quantum anomalous energy, mass radius, spin and mechanical pressure in the proton. We use the recent GlueX data on the $J/psi$ photoproduction to illustrate the potential physics impact from the high-precision data from future JLab 12 GeV and EIC physics program.
The collinear factorization framework allows to describe the exclusive photoproduction of a $gamma,rho$ pair in the generalized Bjorken regime in terms of a perturbatively calculable coefficient function and universal generalized parton distributions. The kinematics are defined by a large invariant mass of the $gamma rho$ pair and a small transverse momentum of the final nucleon. We calculate the scattering amplitude at leading order in $alpha_s$ and the differential cross sections for the process where the $rho-$meson is either longitudinally or transversely polarized, in the kinematics of the near future Jlab experiments. Our estimate of the cross section demonstrates that this process is measurable at JLab 12-GeV.
We have studied the charmonium and bottomonium hybrid states with various $J^{PC}$ quantum numbers in QCD sum rules. At leading order in $alpha_s$, the two-point correlation functions have been calculated up to dimension six including the tri-gluon condensate and four-quark condensate. After performing the QCD sum rule analysis, we have confirmed that the dimension six condensates can stabilize the hybrid sum rules and allow the reliable mass predictions. We have updated the mass spectra of the charmonium and bottomonium hybrid states and identified that the negative-parity states with $J^{PC}=(0, 1, 2)^{-+}, 1^{--}$ form the lightest hybrid supermultiplet while the positive-parity states with $J^{PC}=(0, 1)^{+-}, (0, 1, 2)^{++}$ belong to a heavier hybrid supermultiplet.
High-accuracy $Upsilon$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $gamma ptoUpsilon p$, from which the absolute value of the $Upsilon p$ scattering length, $|alpha_{Upsilon p}|$, can be extracted using a Vector-Meson Dominance model. For this evaluation, we used $Upsilon$-meson photoproduction quasi-data from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|alpha_{Upsilon p}|$ with the recently determined scattering lengths for $omega p$, $phi p$, and $J/psi p$ using the A2, CLAS, and GlueX experimental data are performed. The role of the young vector-meson effect is evaluated.
We summarise the perspectives on heavy-quarkonium production at the LHC, both for proton-proton and heavy-ion runs, as emanating from the round table held at the HLPW 2008 Conference. The main topics are: present experimental and theoretical knowledge, experimental capabilities, open questions, recent theoretical advances and potentialities linked to some new observables.
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