Drell-Yan process in pApA collisions: the exact treatment of coherence effects

In this work, we investigate production of Drell-Yan (DY) pairs in proton-nucleus collisions in kinematic regions where the corresponding coherence length does not exceed the nuclear radius, $R_A$, and the quantum coherence effects should be treated with a special care. The results for the nucleus-to-nucleon production ratio available in the literature so far are usually based on the assumption of a very long coherence length (LCL) $l_c\gg R_A$. Since the onset of coherence effects is controlled by the coherence length $l_c$, we estimated its magnitude in various kinematic regions of the DY process and found that the LCL approximation should not be used at small and medium c.m. collision energies ($\sqrt{s} \lesssim 200$ GeV) as well as at large dilepton invariant masses. In order to obtain realistic predictions, we computed for the first time the DY cross section using the generalised color dipole approach based on the rigorous Green function formalism, which naturally incorporates the color transparency and quantum coherence effects and hence allows to estimate the nuclear shadowing with no restrictions on the CL. In addition to the shadowing effect, we studied a complementary effect of initial state interactions (ISI) that causes an additional suppression at large values of the Feynman variable. Numerical results for the nuclear modification factor accounting for the ISI effect and the finite $l_c$ are compared to the data available from the fixed-target FNAL measurements and a good agreement has been found. Besides, we present new predictions for the nuclear suppression as a function of dilepton rapidity and invariant mass in the kinematic regions that can be probed by the RHIC collider as well as by the planned AFTER@LHC and LHCb fixed-target experiments.Comment: 14 pages, 10 figure

Isolated photon production and pion-photon correlations in high-energy pppp and pApA collisions

A phenomenological study of the isolated photon production in high energy $pp$ and $pA$ collisions at RHIC and LHC energies is performed. Using the color dipole approach we investigate the production cross section differential in the transverse momentum of the photon considering three different phenomenological models for the universal dipole cross section. We also present the predictions for the rapidity dependence of the ratio of $pA$ to $pp$ cross sections. As a further test of the formalism, for different energies and photon rapidites we analyse the correlation function in azimuthal angle $\Delta\phi$ between the photon and a forward pion. The characteristic double-peak structure of the correlation function around $\Delta \phi\simeq \pi$ observed previously for Drell-Yan pair production is found for isolated photon emitted into the forward rapidity region which can be tested by future experiments.Comment: 11 pages, 9 figures. Improved version to be published in Physical Review

Mapping the dominant regions of the phase space associated with ccˉc \bar c production relevant for the Prompt Atmospheric Neutrino Flux

We present a detailed mapping of the dominant kinematical domains contributing to the prompt atmospheric neutrino flux at high neutrino energies by studying its sensitivity to the cuts on several kinematical variables crucial for charm production in cosmic ray scattering in the atmosphere. This includes the maximal center-of-mass energy for proton-proton scattering, the longitudinal momentum fractions of partons in the projectile (cosmic ray) and target (nucleus of the atmosphere), the Feynman $x_F$ variable and the transverse momentum of charm quark/antiquark. We find that the production of neutrinos with energies larger than $E_{\nu} >$ 10$^7$ GeV is particularly sensitive to the center-of-mass energies larger than the ones at the LHC and to the longitudinal momentum fractions in the projectile 10$^{-8}$ $< x <$ 10$^{-5}$. Clearly, these are regions where we do not control the parton, in particular gluon, densities. We also analyse the characteristic theoretical uncertainties in the charm production cross section coming from its QCD modelling. The precision data on the prompt atmospheric neutrino flux can efficiently constrain the mechanism of heavy quark production and underlying QCD dynamics in kinematical ranges beyond the reach of the current collider measurements.Comment: 11 pages, 9 figure

Drell-Yan phenomenology in the color dipole picture revisited

An extensive phenomenological study of the Drell-Yan (DY) process in $pp$ collisions at various energies is performed in the color dipole framework. Besides previously studied $\gamma^*$ production we have also included the $Z^0$ contribution relevant at large dilepton invariant masses. We investigate the DY cross section differential in invariant mass, rapidity and transverse momentum of the dilepton pair in $pp$ collisions at RHIC and LHC. We consider three different phenomenological models for the dipole cross section and found a reasonable agreement with the available data. As a further test of the color dipole formalism, we also study the correlation function in azimuthal angle between the dilepton pair and a forward pion $\Delta\phi$ for different energies, dilepton rapidites and invariant masses. The characteristic double-peak structure of the correlation function around $\Delta \phi\simeq \pi$ found for very forward pions and low-mass dilepton pairs is sensitive to the saturation effects and can be tested by future DY measurements in $pp$ collisions.Comment: 16 pages, 12 figures; typos corrected, references added, conclusions unchange

Heavy flavor production in high-energy pppp collisions: color dipole description

We present a detailed study of open heavy flavor production in high-energy $pp$ collisions at the LHC in the color dipole framework. The transverse momentum distributions of produced $b$-jets, accounting for the jet energy loss, as well as produced open charm $D$ and bottom $B$ mesons in distinct rapidity intervals relevant for LHC measurements are computed. The dipole model results for the differential $b$-jet production cross section are compared to the recent ATLAS and CMS data while the results for $D$ and $B$ mesons production cross sections -- to the corresponding LHCb data. Several models for the phenomenological dipole cross section have been employed to estimate theoretical uncertainties of the dipole model predictions. We demonstrate that the primordial transverse momentum distribution of the projectile gluon significantly affects the meson spectra at low transverse momenta and contributes to the largest uncertainty of the dipole model predictions.Comment: 22 pages, 9 figure

Fully-heavy tetraquark production by γγ\gamma \gamma interactions in hadronic collisions at the LHC

We investigate the production of the fully - heavy tetraquark states $T_{4Q}$ in the $\gamma \gamma$ interactions present in proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC). We focus on the $\gamma \gamma \rightarrow {\cal{Q}}{\cal{Q}}$ (${\cal{Q}} = J/\psi,\, \Upsilon$) subprocess, mediated by the $T_{4Q}$ resonance in the $s$ - channel, and present predictions for the hadronic cross sections considering the kinematical ranges probed by the ALICE and LHCb Collaborations. Our results demonstrate that the experimental study of this process is feasible and can be used to investigate the existence and properties of the $T_{4c}(6900)$ and $T_{4b}(19000)$ states.Comment: 5 pages, 2 figures, 2 tables. arXiv admin note: substantial text overlap with arXiv:1809.0812

Illuminating the charged leptons in the proton

The description of the structure of proton is fundamental in order to describe the standard model processes at the LHC as well as for the searching of New Physics. Quantum fluctuations imply the presence of photons and leptons inside the proton, which admit a parton distribution function (PDF). Although the lepton PDFs are expected to be small, its presence opens new production mechanisms. In order to explore the lepton - induced processes at the LHC, a precise determination of the leptonic content of the proton is needed. In this paper we propose to constrain the content of charged leptons inside the proton through the study of the QED Compton scattering in ultraperipheral proton - nucleus collisions at the LHC. We estimate the total cross sections and associated distributions considering different models for the lepton PDFs and distinct lepton flavours. We demonstrate that a future experimental analysis of this process is feasible and that it can be used to constrain the content of electrons, muons and taus inside the proton.Comment: 10 pages, 3 figures, 1 table. Improved version to be published in PR

Near threshold heavy vector meson photoproduction at LHC and EicC

The exclusive $J/\Psi$ and $\Upsilon$ photoproduction in fixed - target collisions at the LHC and $ep(A)$ collisions at the Electron ion collider in China (EicC) is investigated considering different models for the treatment of the vector meson production at low energies, close to the threshold. Results for the total cross sections and associated distributions are presented. We predict a large number of $J/\Psi$ events at the LHC in the rapidity range covered by the LHCb detector. For the EicC, our predictions point out that a detailed analysis of the near threshold $J/\Psi$ and $\Upsilon$ photoproduction is feasible. Moreover, our results indicate that the modeling of the near threshold vector meson production can be constrained by future experimental analyzes at the LHC and EicC.Comment: 14 pages, 4 figures, 2 table