Parton distribution functions are crucial to understand the internal kinematics of hadrons. There are currently a large number of distribution functions on the market, and thanks to today's technology, performing computational analysis of the differential cross-sections has become more accessible. Despite technological advances, accurately accessing to the internal structure of hadrons remains a difficult task from a theoretical point of view. In this work, we analyze the impact on the differential cross-sections when updating the sets of parton distribution and fragmentation functions, for the production of one hadron plus a direct photon at the energy scale of RHIC and LHC experiments.
We propose a formalism for calculating the event cross-section of parton interactions. In this formalism, we use the light-front bound-state wave function to expand scattering initial state. This leads to an expression of the cross-section in terms of square of wave functions which can be used to define the parton distribution functions. The probability interpretation of the partonic interactions among hadron-hadron scattering is naturally achieved. We apply this formalism to calculate the 4-particle final state cross-section for single parton, double parton and gluon splitting interactions. W…
The non-perturbative parton distributions in hadrons are derived from simple physical arguments resulting in an analytical expression for the valence parton distributions. The sea partons arise mainly from pions in hadronic fluctuations. The model gives new insights and a good description of structure function data.
A method is suggested to combine tree level QCD matrix for the production of multi jet final states and the parton shower in hadronic interactions. The method follows closely an algorithm developed recently for the case of $e^+e^-$ annihilations.
We briefly illustrate recent developments in the parton branching formulation of TMD evolution and their impact on precision measurements in high-energy hadronic collisions.
A simple model is presented for the parton distributions in hadrons. The parton momenta in the hadron rest frame are derived from a spherically symmetric, Gaussian, distribution having a width motivated by the Heisenberg uncertainty relation applied to the hadron size. Valence quarks and gluons originate from the `bare' hadron, while sea partons arise mainly from pions in hadronic fluctuations. Starting from a low Q^2 scale, the distributions are evolved with next-to-leading order DGLAP and give the proton structure function F2(x,Q^2) in good agreement with deep inelastic scattering data.
In the study of multiple scattering of partons in hadron-hadron collisions the possibility of a hard inelastic process at the parton level is included in its simplest possible way, $i.e.$ including the $2 \to 3$ transition. The specific physical process to which the treatment is applied is the inelastic collision of a nucleon with a heavy nucleus
The basic concepts and predictions of the `dynamical' GRV parton distributions for hadrons and photons are discussed. Comparisons of these predictions with recent experimental results, especially from HERA, are presented.
We suggest and explore two observables which may clarify the origin of the attenuation of semi-inclusive hadron production reported in DIS on nuclear targets.
The rates of multiparton collisions in high energy hadronic interactions provide information on the typical transverse distances between partons in the hadron structure. The different configurations of the hadron in transverse space are, on the other hand, at the origin of hadron diffraction. The relation between the two phenomena is exploted in an eikonal model of hadronic interactions.
An explicit model realizing parton-hadron duality and fitting the data is suggested. Complex nonlinear Regge trajectories are important ingredients of the model. The inclusion of $Δ$ and $N^*$ trajectories should account for all resonances in the direct channel. The exotic trajectory is responsible for the smooth background.
The fully unintegrated, off-diagonal quark-quark correlator for a spin-0 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects are of relevance for the phenomenology of certain hard exclusive reactions. In particular, they can be considered as {\it mother distributions} of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum depende…
The fully unintegrated, off-diagonal quark-quark correlator for a spin-1/2 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects, in particular, can be considered as mother distributions of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum dependent parton distributions. We find that none of these relations can be promoted to a m…
We propose a new procedure for parton-to-hadron fragmentation in proton-proton collisions. The hadronization is considered in the parton-parton center-of-mass system and hadrons are assumed to be emitted in the direction of outgoing partons in that frame and then their four-momenta are transformed to the overall center-of-mass system using relevant Lorentz transformations and appropriate distributions are constructed. For heavy hadron production the energy-momentum condition is imposed. In many cases our procedure disagrees with the commonly used rule that rapidity of produced hadron is the sa…
A physical model for parton densities in hadrons, based on Gaussian momentum fluctuations of partons and hadronic baryon-meson fluctuations, is presented. The model has previously been shown to describe proton structure function data, and is now applied to sea quark asymmetries and shown to describe the dbar-ubar asymmetry of the proton. By considering fluctuations involving strange quarks, the model gives an asymmetry between the momentum distributions of s and sbar, which would reduce the significance of the NuTeV anomaly.
Assuming so called global duality we argue that it is very likely that local duality needed to obtain results for the hadronic width of heavy meson decays within the $1/m_Q$ expansion holds. Hence, if the discrepancy between experiment and the theory concerning charm counting, the semileptonic branching fraction and the lifetimes of $b$ hadrons persist, it may be taken as a hint at some qualitatively new effect in (nonperturbative) QCD or even as a new physics.
I discuss the impact of the the coherent parton radiation on semi-inclusive production of hadrons in deep inelastic scattering at lepton-proton colliders. Such radiation can be consistently described in the $b$-space resummation formalism, which was originally developed to improve theoretical description of production of hadrons at $e^+e^-$ colliders and electroweak vector bosons at hadron-hadron colliders. I present the detailed derivation of the resummed cross section and the energy flow at the next-to-leading order of perturbative QCD. The theoretical results are compared to the experimenta…
Longitudinal and transverse parton distributions for pion and nucleon are calculated from hadron vertexes obtained by a study of form factors within relativistic quark models. The relevance of the one-gluon-exchange dominance at short range for the behavior of the form factors at large momentum transfer and of the parton distributions at the end points is stressed.
Significant colour interference effects are expected in V(=gamma,W,Z)+jet production at hadron colliders. These directly influence the hadronic antenna patterns and can provide a valuable diagnostic tool for probing the nature of the underlying parton subprocesses. Motivated by these ideas, we present quantitative predictions for the distributions of soft particles and jets in W+jet production at the Tevatron proton-antiproton collider.
CDF has recently measured a large number of double parton scatterings. The observed value of $σ_{eff}$, the non perturbative parameter which characterizes the process, is considerably smaller as compared with the naive expectation. The small value of $σ_{eff}$ is likely to be an indication of the importance of the two-body parton correlations in the many-body parton distributions of the proton.
It is shown that the contribution from double parton scattering to the inclusive double heavy meson yield is quite comparable with the usually considered mechanism of their production at the LHC energy. For some pairs of heavy flavored quarks in the final state the double parton scattering will be a dominant mode of their production.
Hadronic yields and yield ratios observed in Pb+Pb collisions at the SPS energy of 158 GeV per nucleon are known to resemble a thermal equilibrium population at T=180 +/- 10 MeV, also observed in elementary e+ + e- to hadron data at LEP. We argue that this is the universal consequence of the QCD parton to hadron phase transition populating the maximum entropy state. This state is shown to survive the hadronic rescattering and expansion phase, freezing in right after hadronization due to the very rapid longitudinal and transverse expansion that is inferred from Bose-Einstein pion correlation an…
We study how the components of hadronic wave functions in light-cone quantization depend on the ultraviolet cut-off by relating them in a systematic way to the matrix elements of a class of quark-gluon operators between the QCD vacuum and the hadrons. From this, we derive an infinite set of scale-evolution equations for the individual contributions to parton distributions from the Fock expansion. When summed over all the contributions, we recover the well-known DGLAP equation.
A model of independent pair parton interactions is proposed, according to which, hadron interactions are represented by a set of independent binary parton collisions. The final multiplicity distribution is described by a convolution of the negative binomial distributions in each of the partonic collisions. As a result, it is given by a weighted sum of negative binomial distributions with parameters multiplied by the number of active pairs. Its shape and moments are considered. Experimental data on multiplicity distributions in high energy $p\bar p$ processes are well fitted by these distributi…
The validity of local parton-hadron duality within the framework of HERWIG and JETSET event generators is investigated. We concentrate on ${\rm e}^{+}{\rm e}^{-}$ annihilations in LEP 2 energy range as these interactions provide theoretically the cleanest condition for the discussion of this concept.
A physical model is presented for the non-perturbative parton distributions in the nucleon. This is based on quantum fluctuations of the nucleon into baryon-meson pairs convoluted with Gaussian momentum distributions of partons in hadrons. The hadronic fluctuations, here developed in terms of hadronic chiral perturbation theory, occur with high probability and generate sea quarks as well as dynamical effects also for valence quarks and gluons. The resulting parton momentum distributions $f(x,Q_0^2)$ at low momentum transfers are evolved with conventional DGLAP equations from perturbative QCD t…
A selection of recent data referring to Pb+Pb collisions at the SPS CERN energy of 158 GeV per nucleon is presented which might describe the state of highly excited strongly interacting matter both above and below the deconfinement to hadronization (phase) transition predicted by lattice QCD. A tentative picture emerges in which a partonic state is indeed formed in central Pb+Pb collisions which hadronizes at about T = 185 MeV, and expands its volume more than tenfold, cooling to about 120 MeV before hadronic collisions cease. We suggest further that all SPS collisions, from central S+S onward…
We present a calculation of heavy-flavor production in hadronic collisions in association with one jet matched to parton shower Monte Carlo programs at next-to-leading order in perturbative QCD. Top-quark decays are included and spin correlations in the decay products are taken into account. The calculation builds on existing results for the radiative corrections to heavy-quark plus one jet production and uses the POWHEG BOX for the interface to the parton shower programs PYTHIA or HERWIG. A broad phenomenological study for the Large Hadron Collider and the Tevatron is presented. In particular…
Hadrons interaction at high energies is carried out by one color gluon exchange. All quarks and gluons contained in colliding hadrons take part in interaction and production of particles. The contribution of multiple parton interactions is negligible. Multiple hadrons production at high energies occurs only in three types of processes. The first process is hadrons production in gluon string, the second is hadrons production in two quark strings and the third is hadrons production in three quark strings. In proton-proton interaction production of only gluon string and two quark strings is possi…
The scale factor $σ_{eff}$, which characterizes double parton collisions in high energy hadron interactions, is a direct manifestation of the distribution of the interacting partons in transverse space, in such a way that different distributions give rise to different values of $σ_{eff}$ in different double parton collision processes. We work out the value of the scale factor in a few reactions of interest, in a correlated model of the multi-parton density of the proton recently proposed.
We summarize the current view on Parton-Hadron duality as it applies to B meson decays. It is emphasized that an OPE treatment is essential for properly formulating duality and its limitations. Duality violations are unlikely to become the limiting factor in describing semileptonic B width vis-a-vie higher order corrections. The consistent extraction of the b quark mass from B production and decays provides a striking example of the theoretical control achieved.
In this paper we provide a physical picture for the QCD phase transition in terms of qualitative changes in the spectral functions. Our approach takes into account the crossover nature of this transition and counts for the observed strong correlation seen in higher order susceptibilities. We demonstrate that the hadron resonance gas, which alone describes the thermodynamics at temperatures $T<T_c$, will appreciably contribute to the total pressure until $T\leq 3T_c$. In this intermediate regime the QCD matter consists of strongly correlated excitations, interpretable as either hadrons or parto…
Standard parton distribution function sets do not have rigorously quantified uncertainties. In recent years it has become apparent that these uncertainties play an important role in the interpretation of hadron collider data. In this paper, using the framework of statistical inference, we illustrate a technique that can be used to efficiently propagate the uncertainties to new observables, assess the compatibility of new data with an initial fit, and, in case the compatibility is good, include the new data in the fit.
We present an extensive study on generalized parton distributions of pions. In particular, we present the results for the pion-photon transition distribution amplitudes in the Nambu - Jona-Lasinio model. We discuss the phenomenology of such objects and give explicit estimates for cross sections. The spin structure of the proton is also studied: we discuss the results for the T-odd transverse momentum distributions in quark models.
If large-angle multigluon radiation gives significant contributions to parton showers in the LHC high-energy region, appropriate generalizations of parton branching methods are required for Monte Carlo simulations of exclusive high-multiplicity final states. We discuss the use in this context of transverse-momentum dependent kernels which factorize in the region of high energies. We give examples based on ep and p pbar multi-jet data, and point to possible developments for distributions associated with massive final states at the LHC.
Di-hadron correlations in proton-proton collisions at s^1/2 = 200 GeV are interpreted in terms of a fragmentation width and a momentum imbalance. A fragmentation width of 580 +- 50 GeV/c is obtained, and the momentum imbalance gives an `intrinsic' transverse momentum width of partons in the proton of 2.6 +- 0.2 GeV/c.
A parton-model description of high-energy hadronic interactions in the presence of Lorentz violation is presented. This approach is used to study lepton-hadron and hadron-hadron interactions at large momentum transfer. Cross sections for deep inelastic scattering and the Drell-Yan process are calculated at first order for minimal and nonminimal Lorentz violation. Estimated bounds are placed using existing LHC and future US-based Electron-Ion Collider data.
We present an analysis of the ψψproduction from double parton (DP) sacttering and single parton (SP) scattering in the large p_T region via color-octet gluon fragmentation. We find that at the Tevatron the DP ψψproduction is at the edge of the detectability at present, and at the LHC the DP cross section will dominate over the SP cross section in the lower p_T(min) region (i.e., p_T(min)<7GeV). We also conclude that the color-octet mechanism is of crucial importance to the double j/psi production at high energy hadron colliders.
We present an enumeration of all possible amplitudes that contribute to an n-jet process in QCD. We estimate the number of amplitudes for large number of jets and determine the actual number of amplitudes to be calculated, which is smaller due to relabelling among (massless) quark flavours.
Higgs boson production in association with bottom quarks, is one of the most important discovery channels for Higgs particles in the Standard Model (SM) and its supersymmetric extension at the LHC pp collider . The theoretical prediction of the corresponding cross section has been improved by including the complete next-to-leading order QCD corrections. We review the status results for the leading order to the partonic process and present calculations for the integrated cross-section in both single and double parton scattering collisions.
We present a model that realizes both resonance-Regge (Veneziano) and parton-hadron (Bloom-Gilman) duality. We first review the features of the Veneziano model and we discuss how parton-hadron duality appears in the Bloom-Gilman model. Then we review limitations of the Veneziano model, namely that the zero-width resonances in the Veneziano model violate unitarity and Mandelstam analyticity. We discuss how such problems are alleviated in models that construct dual amplitudes with Mandelstam analyticity (so-called DAMA models). We then introduce a modified DAMA model, and we discuss its properti…
We present a model for the structure of baryons in which the valence partons interact through a linear potential. This model can be derived from QCD in the approximation where transverse momenta are ignored. We compare the valence quark distribution function predicted by our model with that extracted from global fits to Deep Inelastic Scattering data. The only parameter we can adjust is the fraction of baryon momentum carried by valence partons. Our predictions agree well with data except for small values of the Bjorken scaling variable.
I review the linearized hydrodynamical treatment of a fast parton traversing a perturbative quark-gluon plasma. Using numerical solutions for the medium's response to the fast parton, I obtain the medium's distribution function which is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal particle spectrum. Two different freeze-out scenarios are considered which yield significantly different results. I conclude that any meaningful comparison of azimuthal hadron correlation functions to RHIC data requires implementing a realistic freeze-out scenario in an expanding medium.
We present heavy-flavor production in association with one jet in hadronic collisions matched to parton shower Monte Carlo predictions at next-to-leading order QCD with account of top-quark decays and spin correlations. We use the POWHEGBOX for the interface to the parton shower programs PYTHIA or HERWIG. Phenomenological studies for the LHC and the Tevatron are presented with particular emphasis on the inclusion of spin-correlation effects in top decay and the impact of the parton shower on the top-quark charge asymmetries. As a novel application of the present calculation the measurement of …
Detailed and precise background predictions are the backbone of large parts of high-energy collider phenomenology. This requires to embed precision QCD calculations into detailed event generators, to produce comprehensive software simulations. Only continued progress in this direction will allow us to exploit the full potential of measurements at the Large Hadron Collider, or at a future Electron-Ion Collider. This work presents a method to combine third-order QCD calculations for hadronic scattering processes with Monte-Carlo event generators, thus enabling a new generation of precision predi…
A next-to-leading order QCD analysis of spin asymmetries and structure functions in polarized deep inelastic lepton nucleon scattering is presented within the framework of the radiative parton model. The $Q^2$-dependence of the spin asymmetry $A_1^{p}(x,Q^2)$ is shown to be non-negligible for $x$-values relevant for the analysis of the present data. In the second part of the paper we present LO results for radiatively generated spin-dependent parton distributions of the photon and for its structure function $g_1^γ$.
A new model of QCD parton shower is proposed which is dedicated to two-photon process 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 r…
The angular structure of collisional and radiative energy losses of a hard parton jet propagating through the quark-gluon plasma is analyzed. The possibility to observe the energy losses of quark- and gluon-initiated jets in dense QCD-matter (jet quenching) measuring the characteristics of real hadronic jets in ultra-relativistic collisions of nuclei is investigated. In particular, using calorimetric studies of jet + jet, gamma + jet and Z + jet channels is discussed.
We explore the physics of the parton-hadron duality in the nucleon structure functions appearing in lepton-nucleon scattering. We stress that the duality allows one to extract the higher-twist matrix elements from data in the resonance region, and learn about the properties of resonances if these matrix elements are known. As an example, we construct the moments of $F_2(x, Q^2)$ for the low and medium $Q^2$ region, and from which we study the interplay between higher twists and the resonance contributions.
We present a new approach to combine multiple NLO parton-level calculations matched to parton showers into a single inclusive event sample. The method provides a description of hard multi-jet configurations at next-to leading order in the perturbative expansion of QCD, and it is supplemented with the all-orders resummed modelling of jet fragmentation provided by the parton shower. The formal accuracy of this technique is discussed in detail, invoking the example of electron-positron annihilation into hadrons. We focus on the effect of renormalisation scale variations in particular. Comparison …
The joint study of Double Parton Scatterings, in high energy proton-proton and proton-nucleus collisions, can provide a lot of information on multi-parton correlations. The multi-parton structure is in fact probed in a different way by DPS, in $p$-$p$ and in $p$-$A$ collisions. In $p$-$A$ collisions the interpretation of the experimental results may be however complicated by the presence of interference terms, which are missing in $p$-$p$. A suitable reaction channel, where interference terms are absent, is $WJJ$ production. By studying $WJJ$ production in $p$-$Pb$ collisions, we estimate that…
We calculate the spin density matrix of the hadron $h$ created via quark fragmentation in the process $e^-e^+ \to q\bar q \to h + X$. In the case of $h=Λ$ the experimental data could possibly elucidate the problem of $s$-quark contribution to the spin of the $Λ$-hyperon, to be compared with the case of the proton (``spin crisis''). Generally we find that for hadrons with spin 1/2 the parton description, using only probabilities, works much better than for vector particles, since in the former case the non diagonal matrix elements of the hadron spin density matrix are suppressed by a small fact…
We compare several recent theoretical studies of the single transverse spin asymmetry in dijet-correlations at hadron colliders. We show that the results of these studies are all consistent. To establish this, we investigate in particular the two-gluon exchange contributions to the relevant initial and final state interactions in the context of a simplifying model. Overall, the results confirm that the dijet imbalance obeys at best a non-standard or "generalized" transverse-momentum-dependent factorization.
We release an event generator package, GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown large contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the…
We recently proposed a new approach to high energy nuclear scattering, which treats hadronic collisions in a sophisticated way. Demanding theoretical consistency as a minimal requirement for a realistic model, we provide a solution for the energy conservation, screening problems and identical elementary interactions, the so-called "Parton-Based Gribov-Regge Theory" including enhanced diagrams. We can now present some of our results for SPS and RHIC energies.
We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.
