High Energy Hadron-hadron Collisions Research Articles

How far can we see back in time in high-energy collisions using charm hadrons?

We use open charm production to estimate how far we can see back in time in high-energy hadron-hadron collisions. We analyze the transverse momentum distributions of the identified D mesons from pp, p–Pb and A–A collisions at the ALICE and STAR experiments covering the energy range from sNN=200GeV up to 7 TeV. Within a non-extensive statistical framework, the common Tsallis parameters for D mesons represent higher temperature and more degrees of freedom than that of light-flavour hadrons. Assuming Bjorken-expansion, the production of D mesons corresponds to a significantly earlier proper time, τ D = (0.18 ± 0.06)τ LF.

Multiplicity dependence of the freezeout parameters in high energy hadron-hadron collisions* *Supported by Princess Nourah bint Abdulrahman University, Researchers Supporting Project Number PNURSP2024R106, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. We would like to express our gratitude for the support received from Abdul Wali Khan University Mardan, Pakistan; Hubei University of Automotive Technology, Doctoral Research Fund number BK202313; University

We examined the transverse momentum ( ) spectra of various identified particles, encompassing both light-flavored and strange hadrons ( , , , ϕ, , , , and ), across different multiplicity classes in proton-proton collisions (p-p) at a center-of-mass energy of TeV. Utilizing the Tsallis and Hagedorn models, parameters relevant to the bulk properties of nuclear matter were extracted. Both models exhibit good agreement with experimental data. In our analyses, we observed a consistent decrease in the effective temperature (T) for the Tsallis model and the kinetic or thermal freeze-out temperature ( ) for the Hagedorn model, as we transitioned from higher multiplicity (class-I) to lower multiplicity (class-X). This trend is attributed to the diminished energy transfer in higher multiplicity classes. Additionally, we observed that the transverse flow velocity ( ) experiences a decline from class-I to class-X. The normalization constant, which represents the multiplicity of produced particles, was observed to decrease as we moved toward higher multiplicity classes. While the effective and kinetic freeze-out temperatures, as well as the transverse flow velocity, show a mild dependency on multiplicity for lighter particles, this dependency becomes more pronounced for heavier particles. The multiplicity parameter for heavier particles was observed to be smaller than that of lighter particles, indicating a greater abundance of lighter hadrons compared to heavier ones. Various particle species were observed to undergo decoupling from the fireball at distinct temperatures: lighter particles exhibit lower temperatures, while heavier ones show higher temperatures, thereby supporting the concept of multiple freeze-out scenarios. Moreover, we identified a positive correlation between the kinetic freeze-out temperature and transverse flow velocity, a scenario where particles experience stronger collective motion at a higher freeze-out temperature. The reason for this positive correlation is that, as the multiplicity increases, more energy is transferred into the system. This increased energy causes greater excitation and pressure within the system, leading to a quick expansion.

Anisotropic flow and the valence quark skeleton of hadrons

We study transverse momentum anisotropies, in particular, the elliptic flow v2 due to the interference effect sourced by valence quarks in high-energy hadron-hadron collisions. Our main formula is derived as the high-energy (eikonal) limit of the impact-parameter dependent cross section in quantum field theory, which agrees with that in terms of the impact parameter in the classical picture. As a quantitative assessment of the interference effect, we calculate v2 in the azimuthal distribution of gluons at a comprehensive coverage of the impact parameter and the transverse momentum in high-energy pion-pion collisions. In a broad range of the impact parameter, a sizable amount of v2, comparable with that produced due to saturated dense gluons or final-state interactions, is found to develop. This is in contrast with similar studies in heavy-ion collisions using classical color charge distributions in which such a contribution from geometric correlations was found to be small and has, hence, been ignored in recent studies. In our calculations, the valence sector of the pion wave function is obtained numerically from the Basis Light-Front Quantization, a non-perturbative light-front Hamiltonian approach. And our formalism is generic and can be applied to other small collision systems like proton-proton collisions.

Charmed meson production based on dipole transverse momentum representation in high energy hadron-hadron collisions available at the LHC

The production of D-mesons in high-energy pp collisions at the LHC kinematic regime is analyzed with the color dipole approach in the momentum representation. We present predictions for the D-meson differential cross section in terms of the transverse momentum and rapidity distributions taking into account the nonlinear behavior of the QCD dynamics. Comparison between our results and the corresponding experimental measurements reported by the ALICE and LHCb Collaborations in different rapidity bins is performed. We show that the D-meson production in the high energy limit can be properly addressed by using the QCD dipole transverse momentum distributions.

Multisource Thermal Model Describing Transverse Momentum Spectra of Final-State Particles in High-Energy Collisions

In this minireview article, the transverse momentum spectra of final-state particles produced in high-energy hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions described by the multisource thermal model at the quark or parton level are summarized. In the model, the participant or contributor quarks or partons are considered to contribute together to the transverse momentum distribution of final-state particles with different modes of contributions. The concrete mode of contribution is generally determined by the difference of azimuthal angles of contributor partons in their emissions.

Study of inclusive single-jet production in the framework of kt -factorization unintegrated parton distributions

The present work is intended to study the double-differential cross section of the inclusive single-jet production as the functions of the transverse momentum and the rapidity of the jet in the high-energy hadron-hadron collisions. The angular-ordering-constraint ${k}_{t}$-factorization framework is used to calculate the above cross section that is available experimentally. The conditions are taken in accordance with the LHC experiments. The results are compared and analyzed using the existing CMS LHC data. The scheme-dependent unintegrated parton distribution functions (UPDF) of Kimber-Martin-Ryskin (KMR) and Martin-Ryskin-Watt (MRW) in the leading-order and the next-to-leading order (NLO) are used to predict the input partonic UPDF. The utilized phenomenological frameworks prove to be relatively successful in generating satisfactory results compared to the different experiment data, such as CMS (8 and 13 TeV). Extensive discussions and comparisons are made regarding the behavior of the contributing partonic subprocesses. Finally, it is shown that the application of the KMR UPDF to the single-jet differential cross sections have better agreement with the CMS data; on the other hand, they are very similar to those of NLO-MRW.

Power corrections to TMD factorization for Z-boson production

A typical factorization formula for production of a particle with a small transverse momentum in hadron-hadron collisions is given by a convolution of two TMD parton densities with cross section of production of the final particle by the two partons. For practical applications at a given transverse momentum, though, one should estimate at what momenta the power corrections to the TMD factorization formula become essential. In this paper we calculate the first power corrections to TMD factorization formula for Z-boson production and Drell-Yan process in high-energy hadron-hadron collisions. At the leading order in Nc power corrections are expressed in terms of leading power TMDs by QCD equations of motion.

Latest LHCf physics results

The LHCf experiment is dedicated to the measurement of very forward particle production in the high energy hadron-hadron collisions at LHC, with the aim of improving the cosmic-ray air shower developments models. The detector has taken data in p-p collisions at different center of mass energies, from 900 GeV up to 7 TeV, and in p-Pb collisions at s=5.02 TeV. The results of forward production spectra of neutrons in p-p collisions and π0 in p-Pb collisions, compared with the models most widely used in the High Energy Cosmic Ray physics, are presented in this paper.

Sudakov resummations in Mueller-Navelet dijet production

In high energy hadron-hadron collisions, dijet production with large rapidity separation proposed by Mueller and Navelet, is one of the most interesting processes which can help us to directly access the well-known Balitsky-Fadin-Kuraev-Lipatov evolution dynamics. The objective of this work is to study the Sudakov resummation of Mueller-Navelet jets. Through the one-loop calculation, Sudakov type logarithms are obtained for this process when the produced dijets are almost back-to-back. These results could play an important role in the phenomenological study of dijet correlations with large rapidity separation at the LHC.

Double Parton Scattering and 3D Proton Structure: A Light-Front Analysis

Double parton scattering, occurring in high energy hadron-hadron collisions, e.g. at the LHC, is usually investigated through model dependent analyses of the so called effective cross section $\sigma_{eff}$. We present a dynamic approach to this fundamental quantity making use of a Light-Front model treatment. Within such a framework $\sigma_{eff}$ is initially evaluated at low energy scale using the model and then, through QCD evolution, at high energy scale to reach the experimental conditions. Our numerical outcomes are consistent with the present experimental analyses of data in kinematical region we investigate. An important result of the present work is the $x_i$ dependence of $\sigma_{eff}$, a feature directly connected to double parton correlations and which could unveil new information on the three dimensional structure of the proton.

First indication of LPM effect in LHCf, an LHC experiment

The Large Hadron Collider forward (LHCf) experiment is dedicated to the measurement of very forward neutral particle production in the high energy hadron-hadron collisions at LHC. The aim of the experiment is to improve the cosmic ray air shower development models and its setup gives an important opportunity to directly measure the Landau Pomeranchunk Migdal (LPM) effect in heavy absorber. This work presents the analysis for LPM effect on data taken in 2010 and 2013 at √ s = 7 TeV and √ s NN = 5.02 TeV respectively. We study the interactions of gamma, mainly produced by π 0 decay, in one of the calorimeter pairs of LHCf. This is composed by 16 Tungsten layers as absorbers and 16 plastic scintillators for energy measurements (Arm2). We use three parameters to describe the mean shower profile with respect the photon mean energy. The results are compared with Epics MonteCarlo simulation with LPM active and inactive models, shows a first evidence of LPM effect.

Double parton correlations in constituent quark models

Double parton correlations, having effects on the double parton scattering processes occurring in high-energy hadron-hadron collisions, for example at the LHC, are studied in the valence quark region, within constituent quark models. In this framework, two particle correlations are present without any additional prescription, at variance with what happens, for example, in independent particle models, such as the MIT bag model in its simplest version. From the present analysis, conclusions similar to the ones obtained recenty in a modified version of the bag model can be drawn: correlations in the longitudinal momenta of the active quarks are found to be sizable, while those in transverse momentum are much smaller. However, the used framework allows to understand clearly the dynamical origin of the correlations. In particular, it is shown that the small size of the correlations in transverse momentum is a model dependent result, which would not occur if models with sizable quark orbital angular momentum were used to describe the proton. Our analysis permits therefore to clarify the dynamical origin of the double parton correlations and to establish which, among the features of the results, are model independent. The possibility to test experimentally the studied effects is discussed.

The phenomenology of central exclusive production at hadron colliders

Central exclusive production (CEP) processes in high-energy hadron-hadron collisions provide an especially clean environment in which to measure the nature and quantum numbers (in particular, the spin and parity) of new resonance states. Encouraged by the broad agreement between experimental measurements and theoretical predictions based on the Durham approach, we perform a detailed phenomenological analysis of diphoton and meson pair CEP final states, paying particular attention to the theoretical uncertainties in the predictions, including those from parton distribution functions, higher-order perturbative corrections, and non-perturbative and proton dissociation contributions. We present quantitative cross-section predictions for these CEP final states at the RHIC, Tevatron and LHC colliders.

Near-integrability and confinement for high-energy hadron-hadron collisions

We investigate an effective Hamiltonian for QCD at large $s$, in which longitudinal gauge degrees of freedom are suppressed, but not eliminated. In an axial gauge the effective field theory is a set of coupled ($1+1$)-dimensional principal-chiral models, which are completely integrable. The confinement problem is solvable in this context, and we find the longitudinal and transverse string tensions with techniques already used for a similar Hamiltonian in ($2+1$) dimensions. We find some a posteriori justification for the effective Hamiltonian as an eikonal approximation. Hadrons in this approximation consist of partons, which are quarks and solitonlike excitations of the sigma models. Diffractive hadron-hadron scattering appears primarily due to exchange of longitudinal flux between partons.

ON THE RELATION BETWEEN THE WIDTH OF CHARGE BALANCE FUNCTION AND HADRONIZATION TIME IN RELATIVISTIC HEAVY ION COLLISION

A Monte Carlo study on the charge balance function in high energy hadron-hadron and relativistic heavy ion collisions are carried out using the Monte Carlo generators PYTHIA and AMPT, respectively. A strong dependence of the width of balance function on multiplicity is found in both cases. Using the mean parton-freeze-out time of a heavy-ion-collision event as the characteristic hadronization time for the event, it is found that for a fixed multiplicity interval the width of balance function is consistent with being independent of hadronization time.

Narrowing of the charge balance function and hadronization time in relativistic heavy-ion collisions

The width of charge balance function in high energy hadron-hadron and relativistic heavy-ion collisions are studied using the Monte Carlo generators PYTHIA and AMPT, respectively. The narrowing of balance function as the increase of multiplicity is found in both cases. The mean parton-freeze-out time of a heavy-ion collision event is used as the characteristic hadronization time for the event. It turns out that for a fixed multiplicity interval the width of balance function is consistent with being independent of hadronization time.

Spin physics in high-energy hardon interaction

Data on single-spin asymmetry (AN) in high-energy hadron-hadron collisions are discussed. The data are classified according to the beamand target types. The single-spin asymmetry AN is considered as a function of kinematical variables and the sort of participant particles. Data from the PROZA and FODS facilities operating in beams of the IHEP accelerator are presented. The origin of a large single-spin asymmetry is briefly considered.

Hyperon polarization in different inclusive production processes in unpolarized high energy hadron-hadron collisions

We apply the picture proposed in a previous Letter, which relates the hyperon polarization in unpolarized hadron-hadron collisions to the left-right asymmetry in singly polarized reactions, to the production of different hyperons in reactions using different projectiles and/or targets. We discuss the different ingredients of the proposed picture in detail and present the results for hyperon polarization in reactions such as pp, ${K}^{\ensuremath{-}}p,$ ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}p,$ and ${\ensuremath{\Sigma}}^{\ensuremath{-}}p$ collisions. We compare the results with the available data and make predictions for future experiments.

Minijets and transverse energy flow in high energy collisions

When studying the production of minijets and transverse energy flow in high energy hadron-hadron or nucleus-nucleus collisions, two essential points have to be taken into account. First, one has to account for the virtuality of the colliding partons and secondly, it is important to avoid double counting, when many links in a parton chain can be interpreted as the momentum transfer in a hard subcollision. The Linked Dipole Chain model, introduced for low-x DIS, is particularly suitable for a study of these problems. It describes (mini)jet production in a kT-factorizing formalism, which includes all links in a parton chain on an equal footing, avoiding double counting. In a ``naive'' calculation based on integrated structure functions, the cross section blows up for small pT, which makes it necessary to introduce a soft cutoff. In our approach we find a dynamical suppression at low pT, which makes it possible to extrapolate to higher energies and make more reliable predictions for RHIC and LHC.

Inelastic Diffraction and Color-Singlet Gluon Clusters in High-Energy Hadron-Hadron and Lepton-Hadron Collisions

It is proposed that the ``colorless'' objects which manifest themselves in large-rapidity-gap events are color-singlet gluon clusters due to self-organized criticality (SOC), and that optical-geometrical concepts and methods are useful in examining the space-time properties of such objects. A simple analytical expression for the $t$ dependence of the inelastic single diffractive cross section $d\ensuremath{\sigma}/dt$ ( $t$ is the four-momentum transfer squared) is derived. Comparison with existing data and predictions for future experiments are presented. The main differences and similarities between the SOC approach and the ``partons in the Pomeron (Pomeron and Reggeon)'' approach are discussed.