LHC Energy Regions Research Articles

Reflective scattering and color conductivity in hadron collisions

The reflective scattering mode is supposed to play a significant role in hadron interactions at the LHC energy region and beyond. We discuss the connections of this mode to the color conducting medium formation in hadron collisions.

Energy loss of heavy and light quarks in holographic magnetized background

We systematically study holographic effects on the magnetic field dependence of the drag force, diffusion coefficient, jet quenching parameter of heavy quarks and the shooting string energy loss of light quarks in the RHIC and LHC energy regions by using the AdS/CFT correspondence in this paper. This study is motivated by the phenomena of strong magnetic field and jet quenching, which have been found in relativistic heavy ion collisions. The probe's direction of motion is perpendicular and parallel to the direction of magnetic field $B$. The effects of magnetic field on energy loss when moving perpendicular to the magnetic field direction are larger than moving parallel to the magnetic field direction, which implies that the magnetic field tends to suppress more quarks and jets when moving in the transverse direction than in the parallel direction. It is found that the diffusion coefficient decreases with the magnetic field in the transverse direction, but increases with the magnetic field in the parallel direction, which indicates that the quark may diffuse farther when moving parallel to the magnetic field direction. We also find that the magnetic field will enhance the energy loss of the light quarks when moving in the transverse direction than in the parallel direction.

Forward elastic scattering and Pomeron models

Recent data from LHC13 by the TOTEM Collaboration have indicated an unexpected decrease in the value of the $\rho$ parameter and a $\sigma_{tot}$ value in agreement with the trend of previous measurements at 7 and 8 TeV. These data at 13 TeV are not simultaneously described by the predictions from Pomeron models selected by the COMPETE Collaboration, but show agreement with the maximal Odderon dominance, as recently demonstrated by Martynov and Nicolescu. Here we present a detailed analysis on the applicability of Pomeron dominance by means of a general class of forward scattering amplitude, consisting of even-under-crossing leading contributions associated with single, double and triple poles in the complex angular momentum plane. We carry out fits to $pp$ and $\bar{p}p$ data in the interval 5 GeV - 13 TeV. The data set comprises all the accelerator data below 7 TeV and we consider two independent ensembles by adding either only the TOTEM data or TOTEM and ATLAS data at the LHC energy region. In the data reductions to each ensemble the uncertainty regions are evaluated with both one and two standard deviation ($\sim$ 68 \% and $\sim$ 95 \% CL, respectively). Besides the general analytic model, we investigate four particular cases of interest, three of them typical of outstanding models in the literature. We conclude that, within the experimental and theoretical uncertainties and both ensembles, the general model and three particular cases are not able to describe the $\sigma_{tot}$ and $\rho$ data at 13 TeV simultaneously. However, if the discrepancies between the TOTEM and ATLAS data are not resolved, one Pomeron model, associated with double and triple poles and with only 7 free parameters, seems not to be excluded by the complete set of experimental information presently available.

Chiral magnetic currents with QGP medium response in heavy-ion collisions at RHIC and LHC energies

We calculate the electromagnetic current with a more realistic approach in the RHIC and LHC energy regions in the article. We take the partons formation time as the initial time of the magnetic field response of QGP medium. The maximum electromagnetic current and the time-integrated current are two important characteristics of the chiral magnetic effect (CME), which can characterize the intensity and duration of fluctuations of CME. We consider the finite frequency response of CME to a time-varying magnetic field, find a significant impact from QGP medium feedback, and estimate the generated electromagnetic current as a function of time, beam energy and impact parameter.

Asymptotic regimes for hadron diffractive scatterings and Coulomb interaction: Arguments for the black disk mode

Comparative analysis of the interplay of hadron and Coulomb interactions in [Formula: see text] scattering amplitudes is performed in a broad energy interval, [Formula: see text], for two extreme cases: for the asymptotic interactions of hadrons in black disk and resonant disk modes. The interactions are discussed in terms of the [Formula: see text]-matrix function technique. In the asymptotic regime, the real part of the hadronic amplitude is concentrated in both cases on the boundary of the disks in the impact parameter space but the LHC energy region is not asymptotic for the resonant disk mode that lead to a specific interplay of hadronic and Coulombic amplitudes. For the [Formula: see text] scattering at [Formula: see text] an interplay of the hadron and Coulomb interactions in the resonant disk modes is realized in a shoulder in [Formula: see text] at [Formula: see text]. The absence of such a shoulder in the data at 8 TeV can be considered as an argument against the resonant disk mode.

Spatial distributions of magnetic field in the RHIC and LHC energy regions**Supported by National Natural Science Foundation of China (11375069, 11435054, 11075061, 11221504) and Key Laboratory foundation of Quark and Lepton Physics (Hua-Zhong Normal University) (QLPL2014P01)

Relativistic heavy-ion collisions can produce extremely strong magnetic fields in the collision regions. The spatial variation features of the magnetic fields are analyzed in detail for non-central Pb–Pb collisions at LHC at , 2760 and 7000 GeV and Au–Au collisions at RHIC at , 130 and 200 GeV. The dependencies of magnetic field on proper time, collision energies and impact parameters are investigated in this paper. It is shown that an enormous and highly inhomogeneous spatial distribution magnetic field can indeed be created in off-centre relativistic heavy-ion collisions in RHIC and LHC energy regions. The enormous magnetic field is produced just after the collision, and the magnitude of magnetic field of the LHC energy region is larger than that of the RHIC energy region at small proper time. It is found that the magnetic field in the LHC energy region decreases more quickly with the increase of proper time than that of the RHIC energy region.

High-energy scattering versus static QCD strings

We discuss the shape of the interaction region of the elastically scattered protons stipulated by the high-energy Pomeron exchange which turns out to be very similar with the shape of the static string representing the confining QCD flux tube. This similarity disappears when we enter the LHC energy region, which corresponds to many-Pomeron exchanges. Reversing the argument we conjecture a modified relationship between the width and the length of the confining string at very large lengths.

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au+Au collisions and in Pb+Pb collisions with the √sNN = 200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.

A Systematic Study of Magnetic Field in Relativistic Heavy-Ion Collisions in the RHIC and LHC Energy Regions

The features of magnetic field in relativistic heavy-ion collisions are systematically studied by using a modified magnetic field model in this paper. The features of magnetic field distributions in the central point are studied in the RHIC and LHC energy regions. We also predict the feature of magnetic fields at LHCsNN=900, 2760, and 7000 GeV based on the detailed study at RHICsNN=62.4, 130, and 200 GeV. The dependencies of the features of magnetic fields on the collision energies, centralities, and collision time are systematically investigated, respectively.

AN UPDATED ANALYSIS ON THE RISE OF THE HADRONIC TOTAL CROSS-SECTION AT THE LHC ENERGY REGION

A forward amplitude analysis on pp and [Formula: see text] elastic scattering above 5 GeV is presented. The dataset includes the recent high-precision TOTEM measurements of the pp total and elastic (integrated) cross-sections at 7 TeV and 8 TeV. Following previous works, the leading high-energy contribution for the total cross-section (σ tot ) is parametrized as ln γ(s/sh), where γ and sh are free real fit parameters. Singly-subtracted derivative dispersion relations are used to connect σ tot and the rho parameter (ρ) in an analytical way. Different fit procedures are considered, including individual fits to σ tot data, global fits to σ tot and ρ data, constrained and unconstrained data reductions. The results favor a rise of the σ tot faster than the log-squared bound by Froissart and Martin at the LHC energy region. The parametrization for σ tot is extended to fit the elastic cross-section (σ el ) data with satisfactory results. The analysis indicates an asymptotic ratio σ el /σ tot consistent with 1/3 (as already obtained in a previous work). A critical discussion on the correlation, practical role and physical implications of the parameters γ and sh is presented. The discussion confronts the 2002 prediction of σ tot by the COMPETE Collaboration and the recent result by the Particle Data Group (2012 edition of the Review of Particle Physics). Some conjectures on possible implications of a fast rise of the proton–proton total cross-section at the highest energies are also presented.

Gluon saturation and baryon stopping in the SPS, RHIC, and LHC energy regions

A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb+Pb collisions at the LHC are made in this paper.

THE POMERON AND ODDERON IN ELASTIC, INELASTIC AND TOTAL CROSS-SECTIONS AT THE LHC

A simple model for elastic diffractive hadron scattering, reproducing the dip-bump structure is used to analyze pp and [Formula: see text] scattering. The main emphasis is on the delicate and nontrivial dynamics in the dip-bump region, near t = -1 GeV 2. The simplicity of the model and the expected smallness of the absorption corrections enables one the control of various contributions to the scattering amplitude, in particular the interplay between the C-even and C-odd components of the amplitude, as well as their relative contribution, changing with s and t. The role of the nonlinearity of the Regge trajectories is scrutinized. The ratio of the real to imaginary parts of the forward amplitude, the ratio of elastic to total cross-sections and the inelastic cross-section are calculated. Predictions for the LHC energy region, where most of the existing models will be either confirmed or ruled out, are presented.