We review the state-of-the-art of Glauber-inspired models for estimating the distribution of the number of participating nucleons in pA and AA collisions. We argue that there is room for improvement in these models when it comes to the treatment of diffractive excitation processes, and present a new simple Glauber-like model where these processes are better taken into account. We also suggest a new way of using the number of participating, or wounded, nucleons to extrapolate event characteristics from pp collisions, and hence get an estimate of basic hadronic final-state properties in pA collisions, which may be used to extract possible nuclear effects. The new method is inspired by the Fritiof model, but based on the full, semi-hard multiparton interaction model of Pythia 8.
Using the wounded nucleon, quark, and quark-diquark models, we extract the wounded source emission functions from the PHOBOS data for d+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. We apply these models to compute charged particle multiplicity distributions as functions of pseudorapidity for p+p, p+Al, p+Au, d+Au, $^3$He+Au, Cu+Cu, Cu+Au, Au+Au, and U+U collisions at the same energy and compare them with experimental data from the PHOBOS and PHENIX collaborations. In symmetric collisions of heavy nuclei, the obtained distributions differ among the tested models. On the other hand, in asymmetri…
The wounded nucleon and quark emission functions are extracted for different centralities in d+Au collisions at $\sqrt{s}=200\ \text{GeV}$ using Monte Carlo simulations and experimental data. The shape of the emission function depends on centrality in the wounded nucleon model, whereas it is practically universal (within uncertainties) in the wounded quark model. Predictions for $dN_{ch}/dη$ distributions in p+Au and $^3$He+Au collisions are presented.
We introduce TRENTO, a new parametric initial condition model for high-energy nuclear collisions based on eikonal entropy deposition via a "reduced thickness" function. The model simultaneously describes experimental proton-proton, proton-nucleus, and nucleus-nucleus multiplicity distributions, and generates nucleus-nucleus eccentricity harmonics consistent with experimental flow constraints. In addition, the model is compatible with ultra-central uranium-uranium data unlike existing models that include binary collision terms.
In the process of understanding nuclear collisions, reliable extrapolations from pp collisions, based on Glauber models, are highly desirable, though seldomly accurate. We review the inclusion of diffractive excitations and argue that they provide an important contribution to centrality observables in pA collisions. We present a method for distinguishing between diffractively and non-diffractively wounded nucleons, and a proof-of-principle for an extrapolation of multiparton interaction models built on this.
We discuss multiplicity fluctuations of charged particles produced in nuclear collisions measured event-by-event by the NA49 experiment at CERN SPS within the Glauber Monte Carlo approach. We use the concepts of wounded nucleons and wounded quarks in the mechanism of multiparticle production to characterize multiplicity fluctuations expressed by the scaled variance of multiplicity distribution. Although Wounded Nucleon Model correctly reproduce the centrality dependence of the average multiplicity in Pb+Pb collisions, it completely fails in description of corresponding centrality dependence of…
We formulate a baseline model for the net-proton number fluctuations in ultrarelativistic heavy-ion collisions. Our model includes total baryon number conservation, fluctuations of the participating nucleon number, limited acceptance, and a possibility that isospin is remembered by the participating wounded nucleons. Most importantly, we formulated the model as consisting of two components: wounded nucleons and the produced nucleon-antinucleon pairs. Those two components have different rapidity distributions. Owing to this feature we obtain also predictions for the rapidity dependence of the c…
Wounded parton scaling of multiplicities in ultra-relativistic light- and heavy-ion collisions
Institute of Nuclear Physics, Polish Academy of Sciences（波兰科学院核物理研究所）；AGH University of Kraków, Faculty of Physics and Applied Computer Science（克拉科夫AGH科技大学物理与应用计算机科学学院）
High-energy elastic diffraction of nucleons is considered in the framework of the simplest Regge-eikonal approximation. It is demonstrated explicitly that the effective transverse radius of nucleon in this nonperturbative regime is $\sim 0.2÷0.3$ fm and much less than the transverse size of the diffractive interaction region.
A simple Regge-eikonal model with the eikonal represented as a single-reggeon-exchange term is applied to description of the nucleon-nucleon elastic diffractive scattering at ultra-high energies. The range of validity of the proposed approximation is discussed. The model predictions for the proton-proton cross-sections at the collision energy 14 TeV are given.
The adequacy of the triple-Pomeron interaction approximation (the 3P-model) for description of the high-energy single diffractive dissociation of nucleons is analyzed via application to the available experimental data on nucleon-nucleon scattering, including the recent results produced by CMS Collaboration which allow to estimate reliably the triple-Pomeron coupling value. It is argued that the total contribution of secondary Reggeon exchanges is not negligible up to the Tevatron energy.
We analyze $pA$ interactions at ultra-high energies within the semiclassical approximation for high energy processes accounting for the diffractive processes and a rapid increase with the incident energy of the coherence length. The fluctuations of the strength of interaction expected in QCD and momentum conservation are taken into account also. We evaluate the number of wounded nucleons in soft and hard processes, the multiplicity of jets in the proton fragmentation region as a function of the variance of the distribution over the interaction strengths directly measured in forward diffractive…
Elastic diffractive scattering of nucleons is described in terms of Regge-eikonal approach. It is demonstrated that, in a wide kinematic region (starting from the U-70 energies), the eikonal of proton-proton scattering can be approximated by the sum of two Reggeon exchange terms (namely, the so-called soft Pomeron and $f$-Reggeon contributions). The range of applicability of the considered approximation is determined. The predictive value of the proposed phenomenological scheme is verified.
The charged particle multiplicity ($n_{ch}$) and pseudorapidity density $(dn_{ch}/dη)$ are key observables to characterize the properties of matter created in heavy ion collisions. The dependence of these observables on collision energy and the collision geometry are a key tool to understand the underlying particle production mechanism. Recently a lot of focus has been made on asymmetric and deformed nuclei collisions since these collisions can provide a deeper understanding about the nature of quantum chromodynamics (QCD). On phenomenological perspective a unified model which describes the ex…
We present a new model for building up complete exclusive hadronic final states in high energy nucleus collisions. It is a direct extrapolation of high energy pp collisions (as described by PYTHIA), and thus bridges a large part of the existing gap between heavy ion and high energy physics phenomenology. The model is inspired by the old Fritiof model and the notion of wounded nucleons. Two essential features are the treatment of multi-parton interactions and diffractive excitation in each NN sub-collision. Diffractive excitation is related to fluctuations in the nucleon partonic sub-structure,…
Initial state anisotropies in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model
在重离子碰撞的流体动力学模拟中，初始态的空间各向异性转化为末态粒子分布的动量各向异性。因此，理解初始各向异性的起源和量化它们的不确定性对于从实验数据中提取特定的QCD物质性质（如粘度）非常重要。在这项工作中，我们研究了受伤的核子的方法在Monte Carlo Glauber模型的框架，特别关注的不确定性所产生的碰撞核子对之间的核子-核子相互作用和碰撞核内的核子-核子关联的建模。我们比较了黑盘模型和概率轮廓函数方法的非弹性核子核子相互作用，并研究了初始状态的相关性，使用这些国家的最先进的建模的影响。
The diffractive electro- or photo-production of two mesons separated by a large rapidity gap gives access to generalized parton distributions (GPDs) in a very specific way. First, these reactions allow to easily access the chiral-odd transversity quark GPDs by selecting one of the produced vector meson to be transversely polarized. Second, they are only sensitive to the so-called ERBL region where GPDs are not much constrained by forward quark distributions. Third, the skewness parameter $ξ$ is not related to the Bjorken $x_\text{Bj}$ variable, but to the size of the rapidity gap. We analyze d…
We discuss two collider processes which combine a diffractively produced $ρ$ meson separated by a large rapidity gap from a hard exclusive scattering of a Pomeron on a nucleon, giving rise to a lepton pair or to a second meson. These two processes probe the nucleon quark content described by generalized parton distributions in a very specific way.
Initial state anisotropies and their uncertainties in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model
在重离子碰撞的流体动力学模拟中，初始态的空间各向异性被转化为末态粒子分布的动量各向异性。因此，在从实验数据中提取特定的QCD物质性质（如粘度）之前，理解初始态各向异性及其不确定性的起源是很重要的。在这项工作中，我们回顾了受伤的核子的方法的基础上的Monte Carlo Glauber模型，特别是图表的不确定性所产生的碰撞核子对和碰撞核内的核子-核子相关性之间的核子-核子相互作用的建模。我们讨论了非弹性核子-核子相互作用的黑盘模型和概率分布函数方法之间的差异，并研究了初始状态相关性的影响，使用国家的最先进的建模这些。
The CLAS collaboration at Jefferson Laboratory has compared nuclear parton distributions for a range of nuclear targets and found that the EMC effect measured in deep inelastic lepton-nucleus scattering has a strongly "isophobic" nature. This surprising observation suggests short-range correlations between neighboring $n$ and $p$ nucleons in nuclear wavefunctions that are much stronger compared to $p-p$ or $n-n$ correlations. In this paper we propose a definitive experimental test of the nucleon-nucleon explanation of the isophobic nature of the EMC effect: the diffractive dissociation on a nu…
We propose a new model for a homogeneous description of hadron-hadron and hadron-nucleus collisions, the Gluon Exchange Model, fundamentally based on color octet (gluon) exchange. In proton-proton collisions we provide an exact description of the final state proton and neutron spectrum including the proton diffractive peak. In proton-nucleus reactions we find that the projectile proton diquark cannot survive in more than about half of multiple proton-nucleon processes and consequently must be very frequently disintegrated, leading to long transfers of baryon number over rapidity space.
The role of the hard Pomeron (HP) exchanges in the high-energy diffractive interaction of nucleons is explored. It is demonstrated that the HP subdominance at available energies and low transferred momenta is due to the extremely low slope of its Regge trajectory.
We explore Glauber Monte Carlo predictions for the planned ultra-relativistic ${}^{16}{\rm O}$+${}^{16}{\rm O}$ and p+${}^{16}{\rm O}$ collisions, as well as for collisions of ${}^{16}{\rm O}$ on heavy targets. In particular, we present specific collective flow measures which are approximately independent on the hydrodynamic response of the system, such as the ratios of eccentricities obtained from cumulants with different numbers of particles, or correlations of ellipticity and triangularity described by the normalized symmetric cumulants. We use the state-of-the-art correlated nuclear distri…
Diffractive deeply virtual Compton scattering (DiDVCS) is the process $γ^*(- Q^2) + N \rightarrow ρ^0 + γ^* (Q'^2)+ N'$, where N is a nucleon or light nucleus, in the kinematical regime of large rapidity gap between the $ρ^0$ and the final photon-nucleus system, and in the generalized Bjorken regime where both photon virtualities $Q^2$ and $ Q'^2$ are large. We show that this process has the unique virtue of combining the large diffractive cross sections at high energy with the tomographic ability of deeply virtual Compton scattering to scrutinize the quark and gluon content of nucleons and li…
It is demonstrated that the elastic diffractive scattering of nucleons at collision energies higher than 540 GeV and transferred momenta lower than 2 GeV, including the Coulomb-nuclear interference region, can be described in the framework of a very simple Regge-eikonal model where the eikonal is just a sum of two supercritical Regge pole terms. The predictive value of the proposed approximation is verified.
Inspired by a recent study of Iancu, Mueller and Triantafyllopoulos [1] and earlier papers by Golec-Biernat and Wusthoff [2,3], we propose semi-inclusive diffractive deep inelastic scattering (SIDDIS) to investigate the gluon tomography in the nucleon and nuclei at small-$x$. The relevant diffractive quark and gluon parton distribution functions (DPDF) can be computed in terms of the color dipole S-matrices in the fundamental and adjoint representations, respectively. Novel correlations from the gluon tomography in the dipole S-matrix can be experimentally studied through the DPDFs in these pr…
We make predictions for the cross sections of diffractive dijet photoproduction in $pp$, $pA$ and $AA$ ultraperipheral collisions (UPCs) at the LHC during Runs 1 and 2 using next-to-leading perturbative QCD. We find that the resulting cross sections are sufficiently large and, compared to lepton-proton scattering at HERA, have an enhanced sensitivity to small observed momentum fractions in the diffractive exchange, commonly denoted $z_{P}^{\rm jets}$, and an unprecedented reach in the invariant mass of the photon-nucleon system $W$. We examine two competing schemes of diffractive QCD factoriza…
