Hard probes in heavy ion collisions at the lhc: pdfs, shadowing and pa collisions
This manuscript is the outcome of the subgroup ``PDFs, shadowing and $pA$ collisions'' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at the LHC''. In addition to the experimental parameters for $pA$ collisions at the LHC, the issues discussed are factorization in nuclear collisions, nuclear parton distributions (nPDFs), hard probes as the benchmark tests of factorization in $pA$ collisions at the LHC, and semi-hard probes as observables with potentially large nuclear effects. Also, novel QCD phenomena in $pA$ collisions at the LHC are considered. The importance of the $pA$ program at the LHC is emphasized.
Electron Ion Collider: The Next QCD Frontier - Understanding the glue that binds us all
This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community. It was commissioned by the managements of Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (JLab) with the objective of presenting a summary of scientific opportunities and goals of the EIC as a follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a community-wide effort in nuclear science following a series of workshops on EIC physics and, in particular, the focused ten-week program on "Gluons and quark sea a…
Nuclear parton distribution functions with uncertainties in a general mass variable flavor number scheme
In this article we obtain a new set of nuclear parton distribution functions (nuclear PDFs) at next-to-leading order and next-to-next-to-leading order accuracy in perturbative QCD. The common nuclear deep-inelastic scattering (DIS) data analyzed in our study are complemented by the available charged-current neutrino DIS data with nuclear targets and data from Drell-Yan cross-section measurements for several nuclear targets. In addition, the most recent DIS data from the Jefferson Lab CLAS and Hall C experiments are also added to our data sample. For these specific datasets, we consider the impact of target mass corrections and higher twist effects which are expected to be important in the r…
A U.S.-based Electron-Ion Collider
Abstract An Electron-Ion Collider (EIC) in USA is currently discussed as a next-generation facility for high-energy nuclear physics. The main goal of the EIC is to study fundamental questions of Quantum Chromodynamics, which include the origin of the nucleon mass and spin and the three-dimensional structure of the nucleon in terms of quarks and gluons, the emergent properties of dense systems of gluons, and influence of nuclear matter on distributions of quarks and gluons and propagation of color charges through it. The EIC machine designs are aimed at achieving variable center of mass energies of 20 – 100 GeV, upgradable to 150 GeV, high degree of polarization ( 70%) of beams of electrons,…
Constraints on nuclear parton distributions from dijet photoproduction at the LHC
Using QCD calculations of the cross section of inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions in the LHC kinematics as pseudo-data, we study the effect of including these data using the Bayesian reweighting technique on nCTEQ15, nCTEQ15np, and EPPS16 nuclear parton distribution functions (nPDFs). We find that, depending on the assumed error of the pseudo-data, it leads to a significant reduction of the nPDF uncertainties at small values of the momentum fraction $x_A$. Taking the error to be 5\%, the uncertainty of nCTEQ15 and nCTEQ15np nPDFs reduces approximately by a factor of two at $x_A=10^{-3}$. At the same time, the reweighting effect on EPPS16 nPDFs is much smalle…
Nuclear-mass dependence of azimuthal beam-helicity and beam-charge asymmetries in deeply virtual Compton scattering
The nuclear-mass dependence of azimuthal cross section asymmetries with respect to charge and longitudinal polarization of the lepton beam is studiedfor hard exclusive electroproduction of real photons. The observed beam-charge and beam-helicity asymmetries are attributed to the interference between the Bethe-Heitler and deeply virtual Compton scattering processes. For various nuclei, the asymmetries are extracted for both coherent and incoherent-enriched regions, which involve different (combinations of) generalized parton distributions. For both regions, the asymmetries are compared to those for a free proton, and no nuclear-mass dependence is found.
Inclusive and diffractive dijet photoproduction in UPCs at the LHC in NLO QCD
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 u…
Nucleon dissociation and incoherent J/ψ photoproduction on nuclei in ion ultraperipheral collisions at the CERN Large Hadron Collider
Using the general notion of cross section fluctuations in hadron-nucleus scattering at high energies, we derive an expression for the cross section of incoherent J / ψ photoproduction on heavy nuclei d σ γ A → J / ψ Y / d t , which includes both elastic d σ γ p → J / ψ p / d t and proton-dissociation d σ γ p → J / ψ Y / d t photoproduction on target nucleons. We find that, with good accuracy, d σ γ A → J / ψ Y / d t can be expressed as a product of the sum of the d σ γ p → J / ψ p / d t and d σ γ p → J / ψ Y / d t cross sections, which have been measured at HERA, and the common nuclear shadowing factor, which is calculated using the leading twist nuclear shadowing model. Our prediction for …
Predictions for exclusive $\Upsilon$ photoproduction in ultraperipheral ${\rm Pb}+{\rm Pb}$ collisions at the LHC at next-to-leading order in perturbative QCD
We present predictions for the rapidity-differential cross sections of exclusive $\Upsilon$ photoproduction in ultraperipheral collisions (UPCs) of lead ions at the Large Hadron Collider (LHC). We work in the framework of collinear factorization at next-to-leading order (NLO) in perturbative QCD, modeling the generalized parton distributions (GPDs) through the Shuvaev transform of nuclear parton distribution functions (nPDFs). While the effects due to the GPD modeling turn out to be small, the direct NLO predictions still carry significant nPDF-originating uncertainties and depend strongly on the choices of the factorization and renormalization scales. To tame the scale dependence and to ac…