J. P. Lansberg

Heavy-Quarkonium Production in High Energy Proton-Proton Collisions at RHIC

We update the study of the total {psi} and {Upsilon} production cross section in proton-proton collisions at RHIC energies using the QCD-based Color-Singlet (CS) Model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in {alpha}{sub s}, but which have so far been overlooked in such studies. Contrary to earlier claims, we show that the CS yield is consistent with measurements over a broad range of J/{psi} rapidities. We also find that charm-quark initiated processes, including both intrinsic and sea-like charm components, typically contribute at least 20 % of the direct J/{psi} yield, improving the agreement with data both for the integrated cross section and its rapidity dependence. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle {phi} to the detected J/{psi}. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.

Transition distribution amplitudes

We give a brief overview of the theoretical status of the Transition Distribution Amplitudes and discuss their experimental near future.

Backward DVCS and Proton to Photon Transition Distribution Amplitudes

We analyse deeply-virtual Compton scattering on a proton target, γ ∗ P → P ′ γ in the backward region and in the scaling regime. We define the transition distribution amplitudes which describe the proton to photon transition. Model-independent predictions are given to test this description, for current or planned experiments at JLab or by Hermes.

SINGLE TRANSVERSE-SPIN ASYMMETRY IN HARD EXCLUSIVE MESON ELECTROPRODUCTION IN THE BACKWARD REGION

We discuss the relevance of studying single transverse-spin asymmetry in hard-exclusive meson electroproduction in the backward region. Such an asymmetry could help us discriminate between contributions from a soft baryon exchange in the u-channel and a hard parton-induced scattering.

Transition Distribution Amplitudes for γ⋆γ collisions

We study the exclusive production of pi-pi and rho-pi in hard gamma* gamma scattering in the forward kinematical region where the virtuality of one photon provides us with a hard scale in the process. The newly introduced concept of Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation of these reactions thanks to two simple models for TDAs. The sizable cross sections for rho-pi and pi-pi production may be tested at intense electron-positron colliders such as CLEO and B factories (Belle and BaBar).

Exploring backward pion electroproduction in the scaling regime

We use general relations between the Transition Distribution Amplitudes (TDAs), entering the description of the p → π0 transition, and the proton Distribution Amplitudes (DAs) in the soft‐pion limit to estimate the size of the amplitude for backward electroproduction of π0 at large Q2.

Physics with ions at the Future Circular Collider

Abstract The unique physics opportunities accessible with nuclear collisions at the CERN Future Circular Collider (FCC) are summarized. Lead-lead (PbPb) and proton-lead (pPb) collisions at s NN = 39 and 63 TeV respectively with L int = 33 nb − 1 and 8 pb −1 monthly integrated luminosities, will provide unprecedented experimental conditions to study quark-gluon matter at temperatures O(1 GeV). The following topics are succinctly discussed: (i) charm-quark densities thrice larger than at the LHC, leading to direct heavy-quark impact in the bulk QGP properties, (ii) quarkonia, including ϒ ( 1 S ) , melting at temperatures up to five times above the QCD critical temperature, (iii) access to initial-state nuclear parton distributions (nPDF) at fractional momenta as low as x ≈ 10 − 7 , (iv) availability of about 5 ⋅ 10 5 top-quark pairs per run to study the high- x gluon nPDF and the energy loss properties of boosted colour-antennas, (v) study of possible Higgs boson suppression in the QGP, and (vi) high-luminosity γγ (ultraperipheral) collisions at c.m. energies up to 1 TeV.

Hard exclusive processes in the backward region

We review the potentialities offered by the study of backward exclusive processes in a new scaling regime, i.e. involving a large -timelike or spacelike- Q2 photon and a baryonic exchange in the t-channel. We recall the concept of Transition Distribution Amplitudes (TDAs) containing unique information on the hadron structure, then discuss how they enter the description of processes such as backward electroproduction of a pion, antiproton-proton annihilations into a dilepton + meson as well as into J/psi + meson. We then discuss first phenomenological studies for processes that are being analysed at JLAB and HERMES or that will be measured by Panda at GSI-FAIR. Finally we present outlooks for their theoretical studies based on approaches such as the pion-cloud model.