We present and discuss the theory and phenomenology of the leading twist theory of nuclear shadowing which is based on the combination of the generalization of the Gribov–Glauber theory, QCD ...factorization theorems, and the HERA QCD analysis of diffraction in lepton–proton deep inelastic scattering (DIS). We apply this technique for the analysis of a wide range of hard processes with nuclei–inclusive DIS on deuterons, medium-range and heavy nuclei, coherent and incoherent diffractive DIS with nuclei, and hard diffraction in proton–nucleus scattering–and make predictions for the effect of nuclear shadowing in the corresponding sea quark and gluon parton distributions. We also analyze the role of the leading twist nuclear shadowing in generalized parton distributions in nuclei and in certain characteristics of final states in nuclear DIS. We discuss the limits of applicability of the leading twist approximation for small x scattering off nuclei and the onset of the black disk regime and methods of detecting it. It will be possible to check many of our predictions in the near future in the studies of the ultraperipheral collisions at the Large Hadron Collider (LHC). Further checks will be possible in pA collisions at the LHC and forward hadron production at the Relativistic Heavy Ion Collider (RHIC). Detailed tests will be possible at an Electron–Ion Collider (EIC) in the USA and at the Large Hadron–Electron Collider (LHeC) at CERN.
We examine the role played in double-parton interactions (DPI) by the parton–parton correlations originating from perturbative QCD parton splittings. Also presented are the results of the numerical ...analysis of the integrated DPI cross sections at Tevatron and LHC energies. To obtain the numerical results the knowledge of the single-parton GPDs gained by the HERA experiments was used to construct the non-perturbative input for
generalized double-parton distributions
. The perturbative two-parton correlations induced by three-parton interactions contribute significantly to a resolution of the longstanding puzzle of an excess of multi-jet production events in the back-to-back kinematics observed at the Tevatron.
We argue that with an increase of the collision energy, elastic photoproduction of ρ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction into large ...masses, which results in the sizable inelastic nuclear shadowing correction to σγA→ρA and the reduced effective ρ-nucleon cross section. We take these effects into account by combining the vector meson dominance model, which we upgrade to include the contribution of high-mass fluctuations of the photon according to QCD constraints, and the Gribov–Glauber approximation for nuclear shadowing, where the inelastic nuclear shadowing is included by means of cross section fluctuations. The resulting approach allows us to successfully describe the data on elastic ρ photoproduction on nuclei in heavy ion UPCs in the 7 GeV<Wγp<46 GeV energy range and to predict the value of the cross section of coherent ρ photoproduction in Pb–Pb UPCs at sNN=5.02 TeV in Run 2 at the LHC, dσPbPb→ρPbPb(y=0)/dy=560±25 mb.
pQCD physics of multiparton interactions Blok, B.; Dokshitzer, Yu; Frankfurt, L. ...
The European physical journal. C, Particles and fields,
04/2012, Volume:
72, Issue:
4
Journal Article
Peer reviewed
Open access
We study production of two pairs of jets in hadron–hadron collisions in view of extracting contribution of
double hard interactions
of three and four partons (3→4, 4→4). Such interactions, in spite ...of being power suppressed at the level of the total cross section, become comparable with the standard hard collisions of two partons, 2→4, in the
back-to-back kinematics
when the transverse momentum imbalances of two pairing jets are relatively small.
We express differential and total cross sections for two-dijet production in double parton collisions through the generalized two-parton distributions,
2
GPDs (Block et al., Phys. Rev. D 83, 071501,
2011
), and treat them in the leading logarithmic approximation of pQCD that resums collinear logarithms in all orders.
A special emphasis is given to 3→4 double hard interaction processes which, being of the same order in
as the 4→4 process, turn out to be
geometrically enhanced
compared to the latter and should contribute significantly to four-jet production.
The framework developed here takes into systematic consideration perturbative
Q
2
evolution of
2
GPDs. It can be used as a basis for future analysis of NLO corrections to multiparton interactions (MPI) at LHC and Tevatron colliders, in particular for improving evaluation of QCD backgrounds to new physics searches.
We test the hypothesis that configurations of a proton with a large-x parton, xp ≳ 0.1, have a smaller than average transverse size. The application of the QCD Q2 evolution equations shows that these ...small configurations also have a significantly smaller interaction strength, which has observable consequences in proton-nucleus collisions. We perform a global analysis of jet production data in proton- and deuteronnucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the xp dependence of the average interaction strength, σðxpÞ, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given σðxpÞ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-xp parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for largexp quarks in nuclei based on color screening.
We analyze recent data from high-momentum-transfer (p, pp) and (p, ppn) reactions on carbon. For this analysis, the two-nucleon short-range correlation (NN-SRC) model for backward nucleon emission is ...extended to include the motion of the NN pair in the mean field. The model is found to describe major characteristics of the data. Our analysis demonstrates that the removal of a proton from the nucleus with initial momentum 275-550 MeV/c is 92(+8/-18) % of the time accompanied by the emission of a correlated neutron that carries momentum roughly equal and opposite to the initial proton momentum. This indicates that the probabilities of pp or nn SRCs in the nucleus are at least a factor of 6 smaller than that of pn SRCs. Our result is the first estimate of the isospin structure of NN-SRCs in nuclei, and may have important implication for modeling the equation of state of asymmetric nuclear matter.
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 hard phenomena at small
x
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
/
ψ
and
Υ
production as well as in high
t
ρ
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 those 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 as 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.
We propose a new method to determine at what transverse momenta particle production in high-energy pp collisions is governed by hard parton-parton processes. Using information on the transverse ...spatial distribution of partons obtained from hard exclusive processes in ep/\gamma p scattering, we evaluate the impact parameter distribution of pp collisions with a hard parton-parton process as a function of p_T of the produced parton (jet). We find that the average pp impact parameters in such events depend very weakly on p_T in the range 2 < p_T < few 100 GeV, while they are much smaller than those in minimum-bias inelastic collisions. The impact parameters in turn govern the observable transverse multiplicity in such events (in the direction perpendicular to the trigger particle or jet). Measuring the transverse multiplicity as a function of p_T thus provides an effective tool for determining the minimum p_T for which a given trigger particle originates from a hard parton-parton process.
We model effects of color fluctuations (CFs) in the light-cone photon wave function and for the first time make predictions for the distribution over the number of wounded nucleons ν in the inelastic ...photon–nucleus scattering. We show that CFs lead to a dramatic enhancement of this distribution at ν=1 and large ν>10. We also study the implications of different scales and CFs in the photon wave function on the total transverse energy ΣET and other observables in inelastic γA scattering with different triggers. Our predictions can be tested in proton–nucleus and nucleus–nucleus ultraperipheral collisions at the LHC and will help to map CFs, whose first indications have already been observed at the LHC.
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