Hadron correlations in jets, ridges and opposite dijets at all $p_T$ above 2 GeV/c are discussed. Since abundant data are available from RHIC at intermediate $p_T$, a reliable hadronization scheme at that $p_T$ range is necessary in order to relate the semihard partonic processes to the observables. The recombination model is therefore first reviewed for that purpose. Final-state interaction is shown to be important for the Cronin effect, large B/M ratio and forward production. The effect of semihard partons on the medium is then discussed with particular emphasis on the formation of ridge with or without trigger. Azimuthal anisotropy can result from ridges without early thermalization. Dynamical path length distribution is derived for any centrality. Dihadron correlations in jets on the same or opposite side are shown to reveal detail properties of trigger and antitrigger biases with the inference that tangential jets dominate the dijets accessible to observation.
Azimuthal anisotropy is studied by taking into account the ridges created by semi-hard scattering, which is sensitive to the initial spatial configuration in non-central heavy-ion collisions. No rapid thermalization is required. Although hydrodynamics is not used in this study, the validity of hydrodynamical expansion is not excluded at later time after equilibration is achieved. Phenomenological properties of the bulk and ridge behaviors are used as inputs to determine the elliptic flow of pion and proton at low p_T. At intermediate p_T the recombination of shower partons with thermal partons…
This thesis discusses the phenomenological parton recombination approach to describe hadronization in heavy ion collisions. The very good agreement to RHIC data for the flow coefficients v_2 and v_4 is shown and extrapolations are used to make predictions for the LHC.
Parton recombination has been found to be an extremely useful model to understand hadron production at the Relativistic Heavy Ion Collider. It is particularly important to explore its connections with hard processes. This article reviews some of the aspects of the quark recombination model and places particular emphasis on hadron correlations.
The evolution of shower parton distributions in a jet is investigated in the framework of quark recombination model. The distributions are parameterized and the $Q^2$ dependence of the parameters is given by polynomials of $\ln Q^2$ for a wide range of $Q^2$.
We relate the fragmentation functions of partons into mesons and baryons in the framework of recombination of shower partons. The results are in reasonable agreement with the data. The implication is that the meson and baryon fragmentation functions are not independent when hadronization of the shower partons are taken into account. The conclusion therefore closes a conceptual gap in the system of fragmentation functions whose $Q^2$ evolution has been more extensively studied than their interrelationship.
A formalism for hadron production at high \pt in heavy-ion collisions has been developed such that all partons hadronize by recombination. The fragmentation of a hard parton is accounted for by the recombination of shower partons that it creates. Such shower partons can also recombine with the thermal partons to form particles that dominate over all other possible modes of hadronization in the $3<p_T<8$ GeV range. The results for the high \pt spectra of pion, kaon, and proton agree well with experiments. Energy loss of partons in the dense medium is taken into account on the average by an effe…
Hadron production at all $p_T$ in heavy-ion collisions in the framework of parton recombination is reviewed. It is shown that the recombination of thermal and shower partons dominates the hadron spectra in the intermediate $p_T$ region. In $d+Au$ collisions, the physics of particle production at any $η$ is basically the same as at $η=0$. The Cronin effect is described as a result of the final-state instead of the initial-state interaction. The suppression of $R_{CP}$ at high $η$ is due to the reduction of the soft parton density on the deuteron side, thus resulting in less pions produced by re…
We describe how parton recombination can address the recent measurement of dynamical jet-like two particle correlations. In addition we discuss the possible effect realistic light-cone wave-functions including higher Fock-states may have on the well-known elliptic flow valence-quark number scaling law.
We study hadron production in jets by applying quark recombination to jet shower partons. With the jet showers obtained from PYTHIA and augmented by additional non-perturbative effects, we compute hadron spectra in e+ + e-collisions at sqrt(s)=200 GeV. Including contributions from resonance decays, we find that the resulting transverse momentum spectra for pions, kaons, and protons reproduce reasonably those from the string fragmentation as implemented in PYTHIA.
Hadron production at forward rapidities in d+Au collisions is studied in the framework of parton recombination in the final state. Multiple scattering and gluon saturation in the initial state are not explicitly considered. The recombination of soft and shower partons is found to be important. The soft parton densities are determined by extrapolation from the parametrization fixed at η=0 with no unconstrained adjustments. The suppression of R_{CP} observed at high ηis understood as the simple consequence of the reduction of the soft parton density on the deuteron side compared to that on the g…
In a central nucleus-nucleus collision at high-energies, medium partons kicked by a near-side jet acquire a momentum along the jet direction and subsequently materialize as the observed ridge particles. They carry direct information on the early parton momentum distribution which can be extracted by using the ridge data for central AuAu collisions at \sqrt{s_{NN}}=200 GeV. The extracted parton momentum distribution has a thermal-like transverse momentum distribution but a non-Gaussian, relatively flat rapidity distribution at mid-rapidity with sharp kinematic boundaries at large rapidities tha…
Azimuthal anisotropy in heavy-ion collisions is studied by taking into account the ridges generated by semi-hard scattering of intermediate-momentum partons, which can be sensitive to the initial spatial configuration of the medium in non-central collisions. In a simple treatment of the problem where the recombination of only thermal partons is considered, analytical formulas can be derived that yield results in accord with the data on v_2 for p_T <1-2 GeV/c. Centrality dependence is described by a geometrical factor. Ridge phenomenology is used to determine the initial slopes of v_2 at low p_…
All hadronization processes, including fragmentation, are shown to proceed through recombination. The shower partons in a jet turn out to play an important role in describing the p_T spectra of hadrons produced in heavy-ion collisions. Due to the recombination of the shower partons with the soft thermal partons, the structure of jets produced in AA collisions is not the same as that of jets produced in pp collisions.
We analyze PHENIX near-side ridge data for central Au+Au collisions at \sqrt{s_{NN}}=200 GeV with the momentum kick model, in which a near-side jet emerges near the surface, kicks medium partons, loses energy, and fragments into the trigger particle and fragmentation products. The kicked medium partons subsequently materialize as the observed ridge particles, which carry direct information on the early parton momentum distribution and the magnitude of the momentum kick. We find that the PHENIX ridge data can be described well by the momentum kick model and the extracted early partons momentum …
Recombination is a hadronization process that converts partons to hadrons at late time, but the description has no quantitative significance without some meaningful input on the parton distributions at earlier time. Thus observations of particle spectra and correlations have definitive implications on the partonic processes at all transverse momenta. After presenting a general review of the subject at the Workshop, I selected two topics in nuclear collisions for more detailed discussion, which are summarized here. One is on the azimuthal anisotropy at low $p_T$ due to hard or semihard scatteri…
We investigate the role of jet and shower parton broadening by the strong colour field in the $Δη$-$Δϕ$ correlation of high $p_T$ particles. When anisotropic momentum broadening ($Δp_z > Δp_T$) is given to jet and shower partons in the initial stage, a ridge-like structure is found to appear in the two hadron correlation. The ratio of the peak to the pedestal yield is overestimated.
We apply the parton recombination approach to study the energy dependence of the elliptic flow, v_2 in heavy ion collisions from AGS to LHC energies. The relevant input quantities ($T, μ_B, η_T$) at the various center of mass energies are obtained from fits to the available data. The model yields a good description of the integrated v_2 data for charged particles at midrapidity from AGS to RHIC energies. In stark contrast to the current expectations, we observe a decrease of the integrated v_2 values above the highest RHIC energy. Thus, we predict a decrease of v_2 at LHC energies compared to …
We develop the notion of shower partons and determine their distributions in jets in the framework of the recombination model. The shower parton distributions obtained render a good fit of the fragmentation functions. We then illustrate the usefulness of the distributions in a problem where a jet is produced in the environment of thermal partons as in heavy-ion collisions. The recombination of shower and thermal partons is shown to be more important than fragmentation. Application to the study of two-particle correlation in a jet is also carried out.
In the momentum kick model, a near-side jet emerges near the surface, kicks medium partons, loses energy, and fragments into the trigger particle and fragmentation products. The kicked medium partons subsequently materialize as the observed ridge particles, which carry direct information on the magnitude of the momentum kick and the initial parton momentum distribution at the moment of jet-(medium parton) collisions. The initial parton momentum distribution extracted from the STAR ridge data for central AuAu collisions at \sqrt{s_{NN}}=200 GeV has a thermal-like transverse momentum distributio…
Ridge formation in near-side correlation in heavy-ion collisions is studied in the framework of a phenomenological model, called Correlated Emission Model (CEM). Successive soft emissions due to jet-medium interaction lead to the enhancement of thermal partons which follow the local flow directions. The correlation between the flow direction and the semihard parton direction is the major factor that causes the ridge formation to depend on the trigger direction relative to the reaction plane. With the use of a few parameters we have been able to reproduce the data on the ridge yields as functio…
In the (Delta phi)-(Delta eta) correlation associated with a near-side jet observed by the STAR Collaboration in heavy-ion collisions at RHIC [Ref. 1-6], the ridge structure can be explained by the momentum kick model in which the ridge particles are identified as medium partons which suffer a collision with the jet and acquire a momentum kick along the jet direction. If this is indeed the correct mechanism, the ridge structure associated with the near-side jet may be used to probe the parton momentum distribution at the moment of the jet-parton collision, leading to the result that at that in…
Q$^2$ variation of the nuclear-structure-function ratio $F_2^A(x,Q^2)/F_2^D(x,Q^2)$ is investigated in a parton model with Q$^2$-rescaling and parton-recombination effects. Calculated results are compared with the NMC (New Muon Collaboration) and the Fermilab-E665 experimental data. We find that our theoretical results show small Q$^2$ variations and that they are consistent with the data within present experimental accuracy.
Deep inelastic structure functions $F_2^A(x)$ are investigated in a $Q^2$ rescaling model with parton recombination effects. We find that the model can explain experimentally measured $F_2^A(x)$ structure functions reasonably well in the wide Bjorken$-x$ range ($0.005<x<0.8$). In the very small $x$ region ($x<0.02$), recombination results are very sensitive to input sea-quark and gluon distributions.
The parton recombination model has turned out to be a valuable tool to describe hadronization in high energy heavy ion collisions. I review the model and revisit recent progress in our understanding of hadron correlations. I also discuss higher Fock states in the hadrons, possible violations of the elliptic flow scaling and recombination effects in more dilute systems.
We propose to model hadronization of parton showers in QCD jets through a hybrid approach involving quark recombination and string fragmentation. This is achieved by allowing gluons at the end of the perturbative shower evolution to undergo a non-perturbative splitting into quark and antiquark pairs, then applying a Monte-Carlo version of instantaneous quark recombination, and finally subjecting remnant quarks (those which have not found a recombination partner) to Lund string fragmentation. When applied to parton showers from the PYTHIA Monte Carlo event generator, the final hadron spectra fr…
In an earlier paper we developed a Parton Bubble Model (PBM) for RHIC/LHC, based on a substructure of a ring of localized bubbles which initially contain 3-4 partons of almost entirely gluons. A Glasma Flux Tube Model (GFTM) which formed longitudinal flux tubes in the transverse plane of two colliding sheets of Color Glass Condensate (CGC) which pass through one another had been developed. These sheets create boost invariant flux tubes of longitudinal color electric and magnetic fields. A blast wave gives the tubes near the surface transverse flow in the same way it gave flow to the bubbles in…
We have studied the hadronization of jet parton showers based on the quark recombination model. This is achieved by letting gluons at the end of the perturbative shower evolution undergo a non-perturbative splitting into quark and antiquark pairs, then applying a Monte-Carlo version of instantaneous quark recombination, and finally subjecting remnant quarks (those which have not found a recombination partner) to Lund string fragmentation. When applied to parton showers from the PYTHIA Monte Carlo generator, the final hadron spectra from our calculation compare quite well to PYTHIA jets that ha…
We argue that the emission of hadrons with transverse momentum up to about 5 GeV/c in central relativistic heavy ion collisions is dominated by recombination, rather than fragmentation of partons. This mechanism provides a natural explanation for the observed constant baryon-to-meson ratio of about one and the apparent lack of a nuclear suppression of the baryon yield in this momentum range. Fragmentation becomes dominant at higher transverse momentum, but the transition point is delayed by the energy loss of fast partons in dense matter.
Mechanisms proposed to explain the jet-related correlation of long range in rapidity (the ridge) observed in high-energy heavy-ion collisions are reviewed. Limitations of a model using the combined effect of transverse flow and a direction bias of partons suffering energy loss are discussed. The influence of the time scale of the correlation mechanism on the rapidity range is investigated.
We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasi-thermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few GeV/c momentum range observed in Au+Au collisions at RHIC.
We extract the early parton momentum distribution using the STAR Collaboration data of ridge particles associated with a near-side jet in central AuAu collisions at \sqrt{s_{NN}}=200 GeV. The ridge particles are identified as medium partons kicked by the jet near the surface and they carry direct information on the parton momentum distribution at the moment of jet-parton collisions. The extracted parton momentum distribution has a thermal-like transverse momentum distribution but a rapidity plateau structure with a relatively flat rapidity distribution at mid-rapidities with sharp kinematic bo…
Proton production in the intermediate p_T region in d+Au collisions is studied in the parton recombination model. The recombination of soft and shower partons is shown to be important in central collisions, but negligible in peripheral collisions. It is found that the large nuclear modification factor for proton production can be well reproduced by a calculation of the 3-quark recombination process.
$SU(N_c)$ colour-singlet restriction, along with flavour and spin symmetry, on thermal partonic ensemble is shown to recombine the partons with internal colour structure into colour-singlet multi-quark clusters which can be identified with various hadronic modes at a given temperature. This provides a possible basis for recombination model for hadronization of quark-gluon plasma. This also leads to a natural explanation for the ratio of (anti)protons to pions and the quark number scaling of the elliptic flow coefficient in relativistic heavy-ion collisions.
We discuss hadron production in heavy ion collisions at RHIC. We argue that hadrons at transverse momenta P_T < 5 GeV are formed by recombination of partons from the dense parton phase created in central collisions at RHIC. We provide a theoretical description of the recombination process for P_T > 2 GeV. Below P_T = 2 GeV our results smoothly match a purely statistical description. At high transverse momentum hadron production is well described in the language of perturbative QCD by the fragmentation of partons. We give numerical results for a variety of hadron spectra, ratios and nuclear sup…
The near-side ridge structure in the (Delta phi)-(Delta eta) correlation observed by the CMS Collaboration for pp collisions at 7 TeV at LHC can be explained by the momentum kick model in which the ridge particles are medium partons that suffer a collision with the jet and acquire a momentum kick along the jet direction. Similar to the early medium parton momentum distribution obtained in previous analysis for nucleus-nucleus collisions at 0.2 TeV, the early medium parton momentum distribution in pp collisions at 7 TeV exhibits a rapidity plateau as arising from particle production in a flux t…
We show that hadron production in relativistic heavy ion collisions at transverse momenta larger than 2 GeV/c can be explained by the competition of two different hadronization mechanisms. Above 5 GeV/c hadron production can be described by fragmentation of partons that are created perturbatively. Below 5 GeV/c recombination of partons from the dense and hot fireball dominates. This can explain some of the surprising features of RHIC data like the constant baryon-to-meson ratio of about one and the small nuclear suppression for baryons between 2 to 4 GeV/c.
A simple phenomenological relationship between the ridge distribution in $Δη$ and the single-particle distribution in $η$ can be established from the PHOBOS data on both distributions. The implication points to the possibility that there is no long-range longitudinal correlation. An interpretation of the relationship is then developed, based on the recognition that longitudinal uncertainty of the initial configuration allows for non-Hubble-like expansion at early time. It is shown that the main features of the ridge structure can be explained in a model where transverse correlation stimulated …
The implications of parton recombination processes on the dynamics of ultrarelativistic heavy-ion reactions are investigated. To do so, the quark-gluon string transport model has been extended for partonic recombination and fusion processes. Parton recombination leads to short equilibration times and improves significantly on the theoretical description of measured directed and elliptic flow, i.e., v_1 and v_2, distributions in Au+Au collisions at sqrt(s) = 200 GeV, in particular what concerns their pseudorapidity dependence. The shape of v_2(eta) is found to be closely related to fast thermal…
We study the characteristics of correlation between particles in jets produced in heavy-ion collisions. In the framework of parton recombination we calculate the $η$ and $ϕ$ distributions of a pion associated with a trigger particle. The origin of the pedestal in $Δη$ is related to the longitudinal expansion of the thermal partons that are enhanced by the energy loss of hard partons traversing the bulk medium. The peaks in $Δη$ and $Δϕ$ are related to the same angular spread of the shower partons in a jet cone. No artificial short- or long-range correlations are put in by hand. A large part of…
The creation of partons with transverse momenta around 10 GeV/c in Pb-Pb collisions at LHC is expected to be so copious that the parton density may be high enough for neighboring jet cones to overlap. If the shower partons in adjacent jets can recombine to form trigger particles, the distribution of hadrons on the away side should be distinguishable from that due to the recoil of a single harder parton that can produce a similar trigger particle by fragmentation. The two-particle azimuthal correlation on the away side is generated by simulation of the two trigger types. Moments of the correlat…
A review is given on the subject of hadron production at intermediate $p_T$ in heavy-ion collisions. The underlying dynamical processes are inferred from interpreting the data in the framework of recombination. Ridge formation with or without triggers is found to play an important role in nearly all observables in that $p_T$ region. Correlation data would be hard to interpret without taking ridges into account. The semi-hard partons that create the ridges may even be able to drive elliptic flow without fast thermalization.
In heavy-ion collisions at very high energy the density of produced jets can be so high that the possibility of hadrons produced by recombination of shower partons in overlapping minijets may become important. We study such multi-minijet contribution to the hadron spectra and to dihadron correlation in Pb-Pb collisions at 2.76 TeV at LHC. We adjust the parameter controlling the momentum degradation of semihard partons by fitting the charged-particle distribution up to $p_T\sim 16$ GeV/c. The relative magnitudes of different identified hadrons and of various partonic components are fixed by the…
We review the formalism of quark recombination applied to the hadronization of a quark gluon plasma. Evidence in favor of the quark recombination model is outlined. Recent work on parton correlations, leading to detectable correlations between hadrons, is discussed. Hot spots from completely quenched jets are a likely source of such correlations which appear to be jet-like. It will be discussed how such a picture compares with measurement of associated hadron yields at RHIC.
We get the distributions of shower partons initiated by heavy quarks $c$ and $b$ by studying the fragmentation functions in the framework of the recombination model. The transverse momentum spectra of heavy flavored mesons are predicted with these distributions. We find that the contribution from the recombination of thermal-shower partons is an important part in the total spectrum for the mesons. We predict the heavy flavored meson productions for different centralities with the heavy quark fugacities fitted by the experimental data of $J/ψ$ transverse momentum spectra in Au+Au collisions.
The difference between the structures of jets produced in heavy-ion and hadronic collisions can best be exhibited in the correlations between particles within those jets. We study the dihadron correlations in jets in the framework of parton recombination. Two types of triggers, $π^+$ and proton, are considered. It is shown that the recombination of thermal and shower partons makes the most important contribution to the spectra of the associated particles at intermediate $p_T$. In $pp$ collisions the only significant contribution arises from shower-shower recombination, which is negligible in h…
Within the framework of the constituent quark model, it is shown that the single hadron fragmentation function of a parton can be expressed as a convolution of shower diquark or triquark distribution function and quark recombination probability, if the interference between amplitudes of quark recombination with different momenta is neglected. The recombination probability is determined by the hadron's wavefunction in the constituent quark model. The shower diquark or triquark distribution functions of a fragmenting jet are defined in terms of overlapping matrices of constituent quarks and part…
The production of pions and protons in the $p_T$ range between 10 and 20 GeV/c for Pb+Pb collisions at LHC is studied in the recombination model. It is shown that the dominant mechanism for hadronization is the recombination of shower partons from neighboring jets when the jet density is high. Protons are more copiously produced than pions in that $p_T$ range because the coalescing partons can have lower momentum fractions, but no thermal partons are involved. The proton-to-pion ratio can rise beyond 20. When such a high $p_T$ hadron is used as a trigger particle, there will not be any associa…
In hadronization models with color recombination, partons are allowed to regroup into color singlet structures that are different from those determined by the perturbative parton shower. This aims at modeling the possibility that soft interactions of partons with the underlying event can change color connections. If such an effect is at play in proton-proton collisions, it may be expected to be enhanced in proton-nucleus collisions due to the higher color charge density in the underlying event. Here, we provide a qualitative argument that color recombination effects could lead to a multiplicit…
The production of hadrons in heavy-ion collisions at RHIC in the low transverse-momentum ($p_T$) region is investigated in the recombination model with emphasis on the effects of minijets on the azimuthal anisotropy. Since the study is mainly on the hadronization of partons at late time, the fluid picture is not used to trace the evolution of the system. The inclusive distributions at low $p_T$ are determined as the recombination products of thermal partons. The $p_T$ dependencies of both pion and proton have a common exponential factor apart from other dissimilar kinematic and resonance facto…
Gluon distributions in the carbon and tin nuclei are investigated by using a $Q^2$ rescaling model with parton recombination effects. We obtain strong shadowings in the small $x$ region due to the recombinations. The ratio $G_A(x)/G_N(x)$ in the medium $x$ region is typically 0.9 for medium size nuclei. At large $x$, the ratio becomes large due to gluon fusions from different nucleons. Comparisons with recent New Muon Collaboration data for $G_{Sn} (x)/ G_C (x)$ indicate that more accurate experimental data are needed for testing the model.
Correlation between shower partons is first studied in high $p_T$ jets. Then in the framework of parton recombination the correlation between pions in heavy-ion collisions is investigated. Since thermal partons play very different roles in central and peripheral collisions, it is found that the correlation functions of the produced hadrons behave very differently at different centralities, especially at intermediate $p_T$. The correlation function that can best exhibit the distinctive features is suggested. There is not a great deal of overlap between what we can calculate and what has been me…
An interpretation of the ridge phenomenon found in pp collisions at 7 TeV is given in terms of enhancement of soft partons due to energy loss of semihard jets. A description of ridge formation in nuclear collisions can directly be extended to pp collisions, since hydrodynamics is not used, and azimuthal anisotropy is generated by semihard scattering. Both the p_T and multiplicity dependencies are well reproduced. Some suggestions are made about other observables.
Correlations among hadrons in jets produced in heavy-ion collisions are discussed in the framework of the recombination model. The basic correlation at the parton level is among the shower partons arising from kinematical constraint. The resultant correlation between hadrons at intermediate $p_T$ is amazingly rich in characteristics.
Within the AMPT Monte Carlo model, hot spots in the initial transverse parton density are shown to lead to harmonic flows which all contribute to dihadron azimuthal correlation. The net back-to-back dihadron correlation after subtraction of harmonic flows still has a double-peak that is independent of the initial geometric triangularity at a fixed impact-parameter and unique to the structure of jet-induced Mach cone and expanding hot spots dragged by radial flow. The longitudinal structure of hot spots also leads to a near-side ridge in dihadron correlation with a large rapidity gap. By succes…
Autocorrelation of two pions produced in heavy-ion collisions at intermediate $p_T$ is calculated in the framework of the recombination model. The differences of the pseudo-rapidities and azimuthal angles of the two pions are related to the angle between two shower partons in a jet. It is shown how the autocorrelation distribution reveals the properties of jet cone of the shower partons created by high-$p_T$ partons in hard collisions.
Several puzzles about the data at high $p_T$ in heavy-ion collisions are listed. The resolution of them all is given in the framework of parton recombination. More specifically, it is the recombination of the soft and semi-hard shower partons that enhances the region $3<p_T<9$ GeV/c, and gives rise to the large $p/π$ ratio in AuAu collisions. The Cronin effect can be explained in terms of final-state interaction for both $π$ and $p$. The structure of jets produced in AuAu is different from that in $pp$ collisions. The suppression of $R_{CP}$ in forward production can also be understood by exte…
Here I review the transverse momentum distributions of identified hadrons produced in Au-Au collisions at RHIC and Pb-Pb collisions at LHC in the framework of recombination model. Minijets play an important role in generating shower partons in the intermediate $p_T$ region. At LHC, the resultant soft shower partons are even found to dominate over the thermal partons in the non-strange sector. The azimuthal anisotropy of the produced hadrons could also be explained as the consequence of the effects of minijets. Harmonic analysis of the $ϕ$ dependence leads to $v_n(p_T, b)$ that can be well prod…
We show that the long-range rapidity correlations between the produced charged-hadron pairs from two BFKL parton showers generate considerable azimuthal angle correlations. These correlations have no 1/N_c suppression. The effect of gluon saturation on these correlations are discussed and we show that it is important. We show that a pronounced ridge-like structure emerges by going from the BFKL to the saturation region. We show that the ridge structure at high-energy proton-proton and nucleus-nucleus collisions has the same origin and its main feature can be understood due to initial-state eff…
