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Register a new userDiffractive Vector Photoproduction using Holographic QCD
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We discuss diffractive photon-production of vector mesons in holographic QCD. At large $sqrt{s}$, the QCD scattering amplitudes are reduced to the scattering of pair of dipoles exchanging a closed string or a pomeron. We use the holographic construction in AdS$_5$ to describe both the intrinsic dipole distribution in each hadron, and the pomeron exchange. Our results for the heavy meson photon-production are made explicit and compared to some existing experiments.
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We present a holographic analysis of diffractive photoproducton of charmonium $J/psi$ and upsilonium $Upsilon$ on a proton, considered as a bulk Dirac fermion, for all ranges of $sqrt{s}$, i.e., from near threshold to very high energy. Using the bulk wave functions of the proton and vector mesons, within holographic QCD, and employing Witten diagrams in the bulk, we compute the diffractive photoproduction amplitude of $J/psi$ and $Upsilon$. The holographic amplitude shows elements of the strictures of vector meson dominance (VMD). It is dominated by the exchange of a massive graviton or $2^{++}$ glueball resonances near threshold, and its higher spin-j counterparts that reggeize at higher energies. Both the differential and total cross sections are controlled by the gravitational form factor $A(t)$, and compare well to the recent results reported by the GlueX collaboration near threshold and the world data at large $sqrt{s}$. The holographic gravitational form factors, including the D-term, which is due to the exchange of massive spin-0 glueballs, are in good agreement with lattice simulations. We use it to extract the holographic pressure and shear forces inside the proton. Finally, using a pertinent integral representation of the holographic gravitational form factor $A(t)$ near threshold, and its Pomeron counterpart way above threshold, we extract the generalized parton distribution (GPD) of gluons inside the proton at different resolutions.
Diffractive photoproduction of rho, phi and J/psi was studied in the BFKL approach to hard colour singlet exchange. Differential cross sections, the energy dependence and spin density matrix elements were calculated and compared to data from HERA. The overall description of data is reasonably good, except of the single flip amplitude which has the wrong sign. Importance of chiral odd components of the photon is stressed.
Diffractive photoproduction of $eta_c$ is an important process to study the effect of Odderon, whose existence is still not confirmed in experiment. A detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also unclear.Taking charm quarks as heavy quarks, we can use NRQCD and take $eta_c$ as a $cbar c$ bound state. Hence, in the production of $eta_c$a free $cbar c$ pair is first produced and this pair is transformed into $eta_c$ subsequently.In the forward region of the kinematics, the $cbar c$ pair interacts with initial hadron through exchanges of soft gluons. This interaction can be studied with HQET, which provides a systematic expansion in the inverse of the $c$-quark mass $m_c$. We find that the calculation of the $S$-matrix element in the forward region can be formulated as the problem of solving a wave function of a $c$-quark propagating in a background field of soft gluons. At leading order we find that the differential cross-section can be expressed with four functions, which are defined with a twist-3 operator of gluons. The effect of exchanging a Odderon can be identified with this operator in our case. We discuss our results in detail and compare them with those obtained in previous studies. Our results and those from other studies show that the differential cross-section is very small in the forward region. We also show that the production through photon exchange is dominant in the extremely forward region, hence the effect of Odderon exchange can not be identified in this region.For completeness we also give results for diffractive photoproduction of $J/Psi$.
We present a next-to-leading order QCD calculation of inclusive dijet photoproduction in ultraperipheral Pb-Pb collisions at the LHC and show that the results agree very well with various kinematic distributions measured by the ATLAS collaboration. The effect of including these data in nCTEQ or EPPS16 nuclear parton density functions (nPDFs) is then studied using the Bayesian reweighting technique. For an assumed total error of 5% on the final data, its inclusion would lead to a significant reduction of the nPDF uncertainties of up to a factor of two at small values of the parton momentum fraction. As an outlook, we discuss future analyes of diffractive nPDFs, which are so far completely unknown.
We present a first, detailed study of diffractive dijet photoproduction at the recently approved electron-ion collider (EIC) at BNL. Apart from establishing the kinematic reaches for various beam types, energies and kinematic cuts, we make precise predictions at next-to-leading order (NLO) of QCD in the most important kinematic variables. We show that the EIC will provide new and more precise information on the diffractive parton density functions (PDFs) in the pomeron than previously obtained at HERA, illuminate the still disputed mechanism of global vs. only resolved-photon factorization breaking, and provide access to a completely new quantity, i.e. nuclear diffractive PDFs.
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