Could saturation effects be visible in a future electron–ion collider?

We expect to observe parton saturation in a future electron–ion collider. In this Letter we discuss this expectation in more detail considering two different models which are in good agreement with the existing experimental data on nuclear structure functions. In particular, we study the predictions of saturation effects in electron–ion collisions at high energies, using a generalization for nuclear targets of the b-CGC model, which describes the ep HERA quite well. We estimate the total, longitudinal and charm structure functions in the dipole picture and compare them with the predictions obtained using collinear factorization and modern sets of nuclear parton distributions. Our results show that inclusive observables are not very useful in the search for saturation effects. In the small x region they are very difficult to disentangle from the predictions of the collinear approaches. This happens mainly because of the large uncertainties in the determination of the nuclear parton distribution functions. On the other hand, our results indicate that the contribution of diffractive processes to the total cross section is about 20% at large A   and small Q²$Q^2$, allowing for a detailed study of diffractive observables. The study of diffractive processes becomes essential to observe parton saturation.     

The single diffractive component in hadron-hadron collisions within the two-component Dual Parton model

The single diffractive component in hadronhadron interactions is studied in the two-component Dual Parton Model. We distinguish high mass single diffraction represented by a triple-Pomeron exchange and low mass single diffraction described via a two channel eikonal method. The calculated single diffractive cross sections, and the distributions agree quite well with data from collider and fixed target experiments. The fit of the model parameters to cross section data gives a extrapolation of the total, elastic, and single diffractive cross sections to supercollider energies which depends on the parton structure functions used for the minijet component.     

Shadowing effects on quark and gluon production in ultrarelativistic heavy ion collisions

A framework for including shadowing effects to quark and gluon production in very high energy nucleus-nucleus collisions is given. A formalism for impact parameter dependent nuclear structure functions of partons is introduced and, using two models to describe the average shadowing corrections to the parton number densities, the average numbers and the transverse energy spectrum of hard partons produced inU+U collisions at RHIC and LHC energies are computed. We conclude that shadowing and also the impact parameter dependence of structure functions should be taken into account at very high energies.     

A study of gluon scattering and gluon fragmentation in highp T interactions at the ISR

Gluon scattering processes are studied in hadronic highp _T events using data obtained with the Split Field Magnet detector (SFM) at the CERN ISR. The experimental set-up allowed the scanning of a wide range of parton energies and scattering angles. It is shown that for positive pions as trigger particles, the parton composition of the recoil jet is correlated with the polar angle and transverse momentum of the triggering pion. Over the kinematical region studied, the recoil jet originates predominantly from scatered gluons, with an increasing prevalence of the gluon component towards forward triggering angles. The variation of the momentum structure of the recoil jet with the trigger angle indicates that the fragmentation function of gluons is softer than that of quarks.     

Comparison of the k T-factorization approach and the QCD parton model for charm and beauty hadroproduction

We compare numerical predictions of the conventional QCD parton model and of the k _T-factorization approach (semihard theory) for heavy-quark production in high-energy hadron collisions. The total production cross sections and one-particle rapidity and p _T distributions, as well as two-particle correlations, are considered. The distinction between the predictions of the two approaches is not very large, while the shapes of the distributions are slightly different.     

How can we properly define the Q2 dependent parton distribution function in QCD?

We discuss how we can properly define the Q² dependent parton distribution functions in quantum chromodynamics within the framework of the operator product expansion and renormalization group techniques. It is proposed that the moments of the parton distribution functions at Q² should be defined as the hadronic expectation values of the twist-2 operators renormalized at Q². The integro-differential equations for the parton densities obtained by Altarelli and Parisi are reproduced in the leading logarithmic approximation. An application of our present formalism will be given in the case of a longitudinal structure function.     

Dual parton model of inelasticpp-interactions and cascade breaking of string

A new cascade model of string breaking with 6 free parameters is constructed. The dual parton model of inelasticpp-collisions, which uses the supposed model of breaking of string, agrees well with the wide set of the experimental data at ISR energies, including the multiplicity, rapidity and transverse momentum distributions, the different correlations and the production cross sections of baryons, antibaryons, strange particles and resonances. For the fitted values of the free parameters, the scaling functions of the model of string breaking are similar to the hadron structure functions. The inability of the dual parton model to explain the rise of the average transverse momentum with multiplicity at the SPS collider energies is discussed.     

Current and constituent quarks: Their implications for resonance excitations polarized and unpolarized inelastic structure functions

The transformation between constituent and current quarks is discussed and applied to the calculation of matrix elements for nucleon to resonance transitions induced by arbitrary currents belonging to an octet. In particular, previous results on πN and γN transitions are subsumed while weak interactions (ΔQ = 0 or 1) and longitudinal photon induced transitions are discussed for the first time. The implications of a non-trivial Melosh transformation upon previous calculations in quark parton models of the non-diffractive component of the deep inelastic structure functions are discussed. The magnitudes of the unpolarized structure functions are found to be unchanged but for the polarized structure functions significant corrections to previous calculations are discovered. In particular it is found that it is not necessary that the polarization asymmetry A^γP be positive in the deep inelastic region. Our approach is valid for all Q², even for photoproduction, and is not restricted to deep inelastic scattering in contrast to earlier parton model calculations. The saturation of various current algebra sum rules is discussed.     

QCD factorization for the DIS structure functions at small x

We suggest a new form of QCD factorization for inclusive processes at high energies and then reduce it to K _T -factorization. In turn, K _T -factorization can be reduced to collinear factorization when the unintegrated parton distributions have at least one maximum in k _⊥. This property of the parton distributions can be checked with studying data of experiment. The sharper the maximum is, the more accurate the transition to collinear factorization can be done. We apply our results to deduce theoretical restrictions requirements on fits for parton distributions in both K _T - and collinear factorizations contrary to the present situation where the fits are introduced from purely phenomenological consideration so that any formula for them is acceptable if it matches experimental data.     

Spin distributions in the quark parton model

Spin-dependent parton distributions are described in a broken SU(6) quark parton model. The model predicts definite forms for the spin-dependent structure functions in deep inelastic lepton-nucleon scattering and leads to several relations between Regge intercepts and couplings. Resonance electroproduction at large momentum transfer is explored via Bloom-Gilman duality.     

PDF and scale uncertainties of various DY distributions in ADD and RS models at hadron colliders

In the extra dimension models of ADD and RS we study the dependence of the various parton distribution functions on observables of Drell–Yan processes to NLO in QCD at LHC and Tevatron energies. Uncertainties at LHC due to factorisation scales in going from leading to next-to-leading order in QCD for the various distributions get reduced by about 2.75 times for a μ_F range 0.5Q<μ_F<1.5Q. Further uncertainties arising from the error on the experimental data are estimated using the MRST parton distribution functions.     

Low-pt jets and the rise with energy of the inelastic cross section

The contribution of QCD jets to the rise with energy of the inelastic cross section is discussed quantitatively and found to be large. It is seen that the inclusive jet yield is the fastest growing component of the total cross section. The dependence of this yield upon the rapidity cuts, the choice of parton densities, the QCD scale Q² and the transverse momentum cutoff p_cut are examined. At higher energies, multiple parton scattering processes are seen to be non-negligible. Extrapolations of the low-p_t jet yield to the Tevatron are presented also.     

A parton shower model for hadronic two-photon process in e+e− scattering

A new model of QCD parton shower is proposed which is dedicated to two-photon processes in e⁺e^? scattering. When hadron jets are produced, the photon may resolve into quark-antiquark pairs so that the structure functions of the photon should be introduced. Based on the Altarelli-Parisi equation for these functions, an algorithm is formulated that allows us to construct a model for parton showers for the photon. Our model consists of two parts, one of which describes the deep inelastic scattering of the photon and the other one the scattering of two quasi-real photons. Using the model some results are presented on parton distributions and jet production.     

The Strong Interaction at the Collider and Cosmic-Rays Frontiers

First data on inclusive particle production measured in proton–proton collisions at the Large Hadron Collider (LHC) are compared to predictions of various hadron-interaction Monte Carlos (qgsjet, epos and sibyll) used commonly in high-energy cosmic-ray physics. While reasonable overall agreement is found for some of the models, none of them reproduces consistently the ${\sqrt{s}}$ evolution of all the measured observables. We discuss the implications of the new LHC data for the modeling of the non-perturbative and semihard parton dynamics in hadron–hadron and cosmic-rays interactions at the highest energies studied today.     

Soft multihadron production from partonic structure and fragmentation functions

We describe a two-chain model for soft multiparticle production in hadronic collisions. The model is formulated in a parton framework and is consistent with the dual topological scheme for the Pomeron. The sole inputs are valence quark structure functions in the colliding hadrons and parton fragmentation functions, both of which are known from “hard” processes. Our model, which contains no adjustable parameters, reproduces the shape, the energy dependence, and the normalization of inclusive spectra both in the central region and in the fragmentation region. The model provides a natural explanation for the ratio of πp topp cross sections.     

Investigation of the parton structure of pomeron in b \bar b-pair double-Pomeron-exchange production on the CMS (LHC)

Production of b $\bar b$ -pairs in the process of hard double-Pomeron exchange (DPE) of protons has been studied on the CMS plant at the LHC accelerator energies of $\sqrt s = 7$ TeV. The method for estimation of valent parton contribution in the Pomeron structure is developed. On the basis of H1 (DESY) data for parton distributions in Pomeron the calculations were performed to predict the hard (valent) parton components in the Pomeron structure. The contribution of valent partons is estimated about 61%. Using program package CMSSW, the event reconstruction of studied process also was made. This method can be applied to the available experimental data from the CMS detector.     

High order moments of the\bar p p multiplicity distribution in the dual parton model

The first four moments of the \(\bar p\) p multiplicity distribution are computed in the framework of the dual parton model at ISR, SPS collider and Tevatron energies, and for different rapidity intervals. Our results exhibit a striking dependence of the various moments on the size of the rapidity interval which is characteristic of the nature of the rescattering chains in the dual parton model. They also show a violation of KNO scaling throughout the considered energy range. Our results indicate that only light clusters (consistent with known resonances) are produced at all energies.