D meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution

When nonlinear effects on the gluon evolution are included with constraints from HERA, the gluon distribution in the free proton is enhanced at low momentum fractions, x < 0.01, and low scales, Q^2 < 10 GeV^2, relative to standard, DGLAP-evolved, gluon distributions. Consequently, such gluon distributions can enhance charm production in pp collisions at center of mass energy 14 TeV by up to a factor of five at midrapidity, y \sim 0, and transverse momentum p_T -> 0 in the most optimistic case. We show that most of this enhancement survives hadronization into D mesons. Assuming the same enhancement at leading and next-to-leading order, we show that the D enhancement may be measured by D^0 reconstruction in the K^-\pi^+ decay channel with the ALICE detector.Comment: 15 pages, 4 figures, final version accepted by J. Phys.

Charm and beauty of the Large Hadron Collider

With the acceleration of lead nuclei in the LHC, heavy-ion physics will enter a new energy domain. One of the main novelties introduced by the 30-fold energy-jump from RHIC to the LHC is the abundant heavy-quark production. After discussing a few examples of physics issues that can be addressed using heavy quarks, we present a selection of results on the expected experimental capability of ALICE, the dedicated heavy-ion experiment at the LHC, in the open-heavy-flavour sector.Comment: 10 pages, 5 figures. Invited talk at Strangeness in Quark Matter (SQM) 2004, Cape Town, South Africa, 15-20 September 2004. Submitted to J. Phys.

Future Small x Physics with ep and eA Colliders

The interaction of spatially small dipoles with nucleons, nuclei is calculated in the DGLAP approximation at the top of HERA energies and found to be close to the $S$-channel unitarity limit in the case of the color octet dipoles. The DGLAP analyses of the current diffractive data appear to support this conclusion as they indicate a $\sim 30-40$ probability of the gluon induced diffraction for $Q^2\sim 4$GeV$^2$. The need for the high-precision measurements of the $t$-dependence of inclusive and exclusive diffraction for pinpointing higher twist effects in the gluon sector is emphasized.The $eA$ collisions at HERA would provide a strong amplification of the gluon densities allowing to reach deep into the regime of nonlinear QCD evolution. Connection between the leading twist nuclear shadowing and leading twist diffraction in $ep$ scattering is explained. The presented model independent results for the nuclear shadowing for light nuclei indicate much larger shadowing for the gluon sector than for the sea quark sector.It is argued that HERA in $eA$ mode would be able to discover a number of new phenomena including large gluon shadowing, large nonlinearities in parton evolution, small $x$ color transparency in the vector meson production followed by color opacity at $x\le .005$, large probability of inclusive diffraction. Implications for the nucleus-nucleus collisions at LHC are discussed as well.Comment: 17 pp, 12 fig. Plenary talk to be published in the proceedings of 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 1999. Submitted to Nucl.Phys.Proc.Supp

Physics opportunities at RHIC and LHC

Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models - although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) -- all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Psi meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data. The role of future experiments with the STAR and ALICE detectors is pointed out

Coherent photon-hadron interactions in pA collisions: Small-x physics after HERA

In this letter we study the photoproduction of heavy quarks and vector mesons in the coherent proton-nucleus (pA) interactions for RHIC and LHC energies and analyze if these processes can be used to determine the QCD dynamics at high energies. The integrated cross section and rapidity distribution are estimated using the Color Glass Condensate (CGC) formalism. A comparison with the linear dynamics predictions is also presented. Our results indicate that the nonlinear dynamics can be proven in those reactions, which are well suited for studing saturation effects.Comment: 5 pages, 3 figures. Version to be published in Physical Review

On relevance of triple gluon fusion in J/ψJ/\psi hadroproduction

A contribution to $J/\psi$ hadroproduction is analyzed in which the meson production is mediated by three-gluon partonic state, with two gluons coming from the target and one gluon from the projectile. This mechanism involves double gluon density in one of the protons, hence this contribution enters at a non-leading twist. It is, however, relevant due to an enhancement factor coming from large double gluon density at small~$x$. We calculate the three-gluon contribution to $J/\psi$ hadroproduction within perturbative QCD in the $k_T$-factorization framework. Results are obtained for differential $p_T$-dependent cross-sections for all $J/\psi$ polarizations and for the sum over the polarization components. The rescattering contribution is found to provide a significant correction to the standard leading twist cross-section at the energies of the Tevatron or the LHC at moderate $p_T$. We suggest $J/\psi$ production in proton-nucleus collision as a possible probe of the triple gluon mechanism.Comment: 20 pp, 9 figure

The Physics of Ultraperipheral Collisions at the LHC

We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon-nucleon (nucleus) interactions. The current LHC detector configurations can explore small $x$ hard phenomena with nuclei and nucleons at photon-nucleon center-of-mass energies above 1 TeV, extending the $x$ range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic $J/\psi$ and $\Upsilon$ production as well as in high $t$ $\rho^0$ production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.Comment: 229 Pages, 121 figure

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, $k_T$ factorization including low-$x$ resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at $7$ TeV and at $13$ TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from $10\%$ to $50 \%$ at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.Comment: 61 pages, 25 figures, 11 table