Soft-collinear resummation in deeply virtual Compton scattering

We derive an all order resummation formula for the deeply virtual Compton scattering (DVCS) amplitude, which takes into account soft gluon exchanges in the non-singlet quark coefficient function. We identify the ladder diagrams responsible in light-like gauge for [alphaS log^2 (x +/- xi)]^n contributions. The resummed series results in a simple closed expression.Comment: 4 pages, 4 figure

Double logarithms resummation in exclusive processes : the surprising behavior of DVCS

Double logarithms resummation has been much studied in inclusive as well as exclusive processes. The Sudakov mechanism has often be the crucial tool to exponentiate potentially large contributions to amplitudes or cross-sections near phase-space boundaries. We report on a recent work where a very different pattern emerges : the DVCS quark coefficient function C(x,\xi) develops, near the particular point x=\xi, a non-alternate series in \alpha_s^n log^{2n}(x-\xi) which may be resummed in a cosh[K sqrt \alpha_s log(x-\xi)] factor. This result is at odds with the known result for the corresponding coefficient function for the pion transition form factor near the end point C(z) although they are much related through a z -> x/\xi correspondence.Comment: 9 pages, 1 figure, Presented at the Low x workshop, May 30 - June 4 2013, Rehovot and Eilat, Israe

Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions?

We point out that current calculations of inclusive two-particle correlations in p-A collisions based on the Color Glass Condensate approach exhibit a contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are quite distinct from the standard ones, in that they are apparent for particles widely separated in rapidity. The transverse size of the emitter which is reflected in these correlations is the gluonic size of the proton. This raises an interesting possibility of measuring the proton size directly by the HBT effect of particle pairs produced in p-A collisions.Comment: 11 pages, 3 eps figures; v2: comments, discussions, references and acknowledgements added, conclusions unchanged, final versio

Quark correlations in the Color Glass Condensate

The explanation of the ridge observed in p-p and p-A collisions at the Large Hadron Collider constitutes one of the open questions in our understanding of high-energy hadronic collisions. Apart from final-state hydrodynamic models, correlations between gluons in the wave function of the incoming hadrons, computed in the framework of the Color Glass Condensate, offer an alternative rationale to explain such phenomenon. A natural question is then what happens to quarks. Here we consider, for the first time, correlations between produced quarks in p-A collisions in the light-cone wave function approach to the CGC. We find a quark-quark ridge that shows a dip at $\Delta \eta\sim 2$ relative to the gluon-gluon ridge. The origin of this dip is the short range (in rapidity) Pauli blocking experienced by quarks in the wave function of the incoming projectile. We observe that these correlations, present in the initial state, survive the scattering process. We discuss possibilities for observing experimentally such correlations and future developments

QCD Reggeon Field Theory for every day: Pomeron loops included

We derive the evolution equation for hadronic scattering amplitude at high energy. Our derivation includes the nonlinear effects of finite partonic density in the hadronic wave function as well as the effect of multiple scatterings for scattering on dense hadronic target. It thus includes Pomeron loops. It is based on the evolution of the hadronic wave function derived in \cite{foam}. The kernel of the evolution equation defines the second quantized Hamiltonian of the QCD Reggeon Field Theory, $H_{RFT}$ beyond the limits considered so far. The two previously known limits of the evolution: dilute target (JIMWLK limit) and dilute projectile (KLWMIJ limit) are recovered directly from our final result. The Hamiltonian $H_{RFT}$ is applicable for the evolution of scattering amplitude for arbitrarily dense hadronic projectiles/targets - from "dipole-dipole" to "nucleus-nucleus" scattering processes.Comment: 35 pages, 5 figure