On the Nature of the Rapidity-Spectra at RHIC and Some Other Energies
Goutam Sau, S. K. Biswas, A. C. Das Ghosh, A. Bhattacharya, S. Bhattacharyya
备注：
23 pages, 24 figures. Results updated, One reference added, Discussion and Conclusions updated, A few new figures introduced, Section 2 updated, Some figure caption have been changed. Accepted for publication in IL Nuovo Cimento B.
On the basis of the Grand Combinational Model (GCM) outlined and somewhat detailed in the text, we have attempted to capture here the several interesting assorted characteristics of the rapidity-spectra of the major varieties of secondaries produced in diverse nuclear reactions at various energies, though the main thrust of our work lies on addressing the data-trends from RHIC-BNL experiments. Obviously the core of the present approach is purely phenomenological. Still, the method and the model address the features of the data modestly well. And the method appears to have the rich potentiality, if the systematic sets of data for rapidity-studies at gradually increasing energies were available.
We utilize the ALCOR model for mid-rapidity hadron number predictions at AGS, SPS and RHIC energies. We present simple fits for the energy dependence of stopping and quark production.
The rapidity dependence of the chemical freeze-out thermal parameters $T$ and $μ_B$ are determined at the highest RHIC and SPS energies. These show a systematic behavior towards an increase in $μ_B$ away from mid-rapidity and a corresponding decrease in the temperature $T$.
Final state average transverse energy and charged particle multiplicity at the central rapidity unit of central Au-Au collisions at RHIC are studied within a framework of lowest order perturbative QCD and Bjorken's hydrodynamical picture. In particular, effects of initial minijet production and the $pdV$ work during the subsequent evolution of the QGP are investigated. Nuclear shadowing effects are included in a consistent manner, and the dependence of the results on the minijet transverse momentum cut-off parameter $p_0$ is shown.
We investigate the scaling properties in inclusive hadron production and the associated single transverse spin asymmetry in the forward rapidity region at RHIC. We find that the spin-averaged experimental data in both $pp$ and $dAu$ collisions demonstrates a transverse-momentum-dependent geometric scaling. We introduce the transverse momentum dependent Collins fragmentation function to study the scaling of the single transverse spin asymmetries. The general feature of the scaling analysis is consistent with the experimental observations, in particular, for the transverse momentum dependence of…
Predictions on central rapidity densities of charged particles at energies of the Relativistic Heavy Ion Collider and the Large Hadron Collider, for central collisions between the largest nuclei that will be available at these accelerators, are reviewed. Differences among the results of the existing models are discussed in relation with their underlying physical basis and with the possibilities to discriminate them.
Quark coalescence predictions for various multi-strange baryon to anti-baryon ratios for central Au+Au collisions at RHIC energies are compared to preliminary data of the STAR collaboration. The formation of Quark Matter and the sudden recombination of its constituent quarks into hadrons is found to be in agreement with these preliminary data. It seems that strange hadron and antihadron production in Au+Au collisions at RHIC is similar to that in Pb+Pb collisions at CERN SPS.
The evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy relativistic systems is proposed as an indicator for local equilibration and longitudinal expansion. In a Relativistic Diffusion Model, bell-shaped distributions in central collisions at AGS energies and double-humped nonequilibrium spectra at SPS show pronounced longitudinal collective expansion when compared to the available data. The broad midrapidity valley recently discovered at RHIC in central Au+Au collisions at sqrt(s_NN) = 200 GeV indicates rapid local equilibration which is most likely due to deconfinement, and fas…
A new geometrical scaling method with 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 the net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distribution…
We present a phenomenological approach (EPOS), based on the parton model, but going much beyond, and try to understand proton-proton and deuteron-gold collisions, in particular the transverse momentum results from all the four RHIC experiments. It turns out that elastic and inelastic parton ladder splitting is the key issue. Elastic splitting is in fact related to screening and saturation, but much more important is the inelastic contribution, being crucial to understand the data. We investigate in detail the rapidity dependence of nuclear effects, which is actually relatively weak in the mode…
The rapidity distribution of well-defined particles pions, Kaons, protons and their antiparticles measured in the BRAHMS experiment (Au+Au collisions), at $\sqrt{s_{NN}}$ = $62.4$ and $200$ GeV, are compared with huge statistical ensembles of 100, 000 events deduced from the Cosmic Ray MonteCarlo (CRMC) EPOS event-generator. All these data are then compared to the Landau hydrodynamical model. We conclude that the Landau hydrodynamical model is capable of describing both experimental data and EPOS $1.99$ event-generator results, and that they are in good agreement.
On the basis of universal scaling properties, we claim that in Au+Au collisions at RHIC, the QCD critical point is within reach. The signal turns out to be an extended plateau of net baryons in rapidity with approximate height of the net-baryon rapidity density approximately 15 and a strong intermittency pattern with index s_2=1/6 in rapidity fluctuations. A window also exists, to reach the critical point at the SPS, especially in Si+Si collisions at maximal energy.
In the framework of the recently proposed saturation picture, we examine in a systematic way whether the nuclear modification factor measured for d-Au collisions at RHIC may be simply explained. The Cronin peak which is obtained at mid-rapidity around $k_{\bot}\simeq 3$ GeV may be reproduced at the proper height only by boosting the saturation momentum by an additional nuclear component as already shown in the literature. In this respect, mid-rapidity RHIC data cannot necessarily be seen as a probe of the saturation picture. The large rapidity ($η\simeq 3$) region allows us to test the shape o…
We study the dependence of parton energy loss (quenching) on rapidity in ultra-relativistic nuclear collisions at RHIC. This can provides invaluable information on the density of the medium, which should be more dilute going away from mid-rapidity, thereby reducing the effect of quenching. We predict a clear effect at moderate transverse momenta $\sim$ 3 GeV.
We modified the gluon saturation model by rescaling the momentum fraction according to saturation momentum and introduced the Cooper-Frye hydrodynamic evolution to systematically study the pseudo-rapidity distributions of final charged hadrons at different energies and different centralities for Au-Au collisions in relativistic heavy-ion collisions at BNL Relativistic Heavy Ion Collider (RHIC). The features of both gluon saturation and hydrodynamic evolution at different energies and different centralities for Au-Au collisions are investigated in this paper.
Net-baryon rapidity distributions in central Au+Au collisions at 200 GeV per nucleon are shown to consist of three components. The nonequilibrium contributions are accounted for in a Relativistic Diffusion Model. Near midrapidity, a third fraction containing approximately 22 protons reaches local statistical equilibrium in a discontinuous transition. It may be associated with a deconfinement of the participant partons and thus, serve as a signature for Quark-Gluon Matter formation.
Using a multiphase transport model (AMPT), which includes both initial partonic and final hadronic interactions, we study the rapidity distributions of charged particles such as protons, antiprotons, pions, and kaons in heavy ion collisions at RHIC. The theoretical results for the total charged particle multiplicity at midrapidity are consistent with those measured by the PHOBOS collaboration in central Au+Au collisions at $\sqrt s$ = 56 and 130 AGeV. We find that these hadronic observables are much more sensitive to the hadronic interactions than the partonic interactions.
Recently Beccattini and Cleymamns have proposed a model to understand the p-pbar data obtained at RHIC and SPS. We have shown that this model has a much greater applicability and can very well be used to describe the rapidity spectra of protons and antiprotons separately measured at the highest energy of Relativistic Heavy Ion Collider i.e., 200 GeV/A by BRAHMS Collaboration. We have also determined that the contribution of the decay products of the heavier resonances like delta, lambda etc. actually dominate over the protons (antiprotons) of pure thermal origin. We have also imposed the crite…
We calculate azimuthal correlations in dAu collisions at different rapidities and centralities and argue that experimentally observed depletion of the back-to-back pick can be quantitatively explained by gluon saturation in the Color Glass Condensate of the Gold nucleus.
In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy systems is proposed as an indicator for local equilibration and longitudinal expansion. The broad midrapidity valley recently discovered at RHIC in central Au + Au collisions at sqrt(s_NN)= 200 GeV suggests rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion. Rapidity spectra of produced charged hadrons in d + Au and Au + Au systems at RHIC energies and their centrality dependence are well described in a three-sources RDM. In central co…
We use a Modified DKLMT model (called M-DKLMT model) to study the cold nuclear matter (CNM) effects on the color singlet J/psi production in dAu collisions at RHIC. The cold nuclear effect of dipole-nucleus interactions has been investigated by introducing a nuclear geometric effect function f(ξ) to study the nuclear geometry distribution effect in relativistic heavy-ion collisions. The dependencies of nuclear modification factors (RdA) on rapidity and centrality are studied and compared to experimental data. It is found that the M-DKLMT model can well describe the experimental results at both…
The charged-particle's final state spectrum is derived from an analytic perturbative solution for the relativistic viscous hydrodynamics. By taking into account the longitudinal acceleration effect in relativistic viscous hydrodynamics, the pseudorapidity spectrum describes well the nucleus-nucleus colliding systems at RHIC and LHC. Based on both the extracted longitudinal acceleration parameters $λ^{*}$ and a phenomenological description of the $λ^{*}$, the charged-particle's pseudorapidity distributions for $\sqrt{s_{NN}}$ = 5.44 TeV Xe+Xe collisions are computed from the final state express…
We have addressed the question of whether saturation (CGC) has been observed in deuteron-gold collisions at RHIC. We have made a detailed analysis of the Cronin peak characteristic of the nuclear modification factor measured for d-Au collisions at mid-rapidity. The Cronin peak which is obtained around $p_t\simeq 3$ GeV may be reproduced at the proper height only by boosting the saturation momentum by a huge non-perturbative additional component. At forward rapidity, we get a quantitative agreement with data, reproducing hadron production spectra and the $R_{CP}$ ratio using a recently develope…
We show that geometric scaling is satisfied to good accuracy in the forward region of d+Au collisions at RHIC. Scaling violations do show up, however, at mid-rapidity, and the anomalous dimension of the small-x gluon distribution evolves to near its DGLAP limit for transverse momenta of a few GeV. This represents a first consistency check of RHIC deuteron-nucleus and HERA DIS phenomenology, and of the universality of the underlying Color Glass Condensate (CGC) theory, which describes both phenomena. It also reconciles successful leading-twist LO and NLO perturbative QCD computations of mid-rap…
We investigate the photoproduction of $ρ$ mesons in ultraperipheral heavy ion collisions at RHIC and LHC energies in the dipole approach and within two phenomenological models based on the the Color Glass Condensate (CGC) formalism. We estimate the integrated cross section and rapidity distribution for meson production and compare our predictions with the data from the STAR collaboration. In particular, we demonstrate that the total cross section at RHIC is strongly dependent on the energy behavior of the dipole-target cross section at low energies, which is not well determined in the dipole a…
By using the NexSPheRIO code, we study the elliptic-flow fluctuations in Au+Au collisions at 200A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudo-rapidity and the transverse-momentum distributions, reasonable agreement of <v_2> with data is obtained, both as function of pseudo-rapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data in experiments.
We suggest to use net-baryon rapidity distributions in central relativistic heavy-ion collisions at SPS, RHIC and LHC energies in order to probe saturation physics. Within the color glass condensate framework based on small-coupling QCD, net-baryon rapidity distributions are shown to exhibit geometric scaling. In a comparison with RHIC data in Au + Au collisions at sqrt(s_NN) = 62.4 GeV and 200 GeV the gradual approach to the gluon saturation regime is investigated. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb + Pb collisions at LHC energies of sqrt (s_N…
We analyze longitudinal pion spectra from \sqrt{s_{NN}}= 2 GeV to \sqrt {s_{\rm NN}}=20 GeV within Landau's hydrodynamical model and the UrQMD hybrid approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c_s^2 in the dense stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at \sqrt{s_{NN}}= 4-9 GeV, an energy range accessible at the Facility for Antiproton and Ion Research (FAIR) as well as the RHIC-Beam Energy Scan (RHIC-BES). This softening of the EoS i…
We report an underlying event tune for the PYTHIA 8 Monte Carlo event generator that is applicable for hadron collisions primarily at $\sqrt{s}$ ranges available at the Relativistic Heavy-Ion Collider (RHIC). We compare our new PYTHIA 8 tuned predictions to mid-rapidity inclusive $π^{\pm}$ spectra, jet sub-structure, Drell-Yan production, and underlying event measurements from RHIC and the Tevatron, as well as underlying event data from the Large Hadron Collider. With respect to the default PYTHIA 8 Monash Tune, the new `Detroit' tune shows significant improvements in the description of the ex…
A kinetic equation approach is applied to model anomalous J/psi suppression at RHIC and SPS by absorption in a hadron resonance gas which successfully describes statistical hadron production in both experiments. The puzzling rapidity dependence of the PHENIX data is reproduced as a geometric effect due to a longer absorption path for J/psi production at forward rapidity.
We discuss the saturation of the parton density in heavy ion collisions at RHIC energiesusing a Pomeron approach. Our predictions for the particle density in ion-ion collisions at RHIC energies can be utilized as the background for the observation of possible quark-gluon plasma production.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at Tevatron energies.
The yields of dibaryon (Omega-Omega) in relativistic heavy ion collisions, especially at RHIC energies, are estimated by statistical model. The yields of hyperon Omega- and the ratio of dibaryon to Omega are also given.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at SSC and LHC energies.
In this work the rapidity and transverse momentum dependence of the nuclear modification ratio is evaluated for the dilepton production at RHIC and LHC, using the Color Glass Condensate (CGC) framework. The ratio is compared for two distinct dilepton mass values, concerning the transverse momentum distribution, and a suppression of the Cronin peak is verified even for large mass. The nuclear modification ratio suppression in the dilepton rapidity spectra, as obtained for hadrons at RHIC, is verified for LHC energies at large transverse momentum, although not present at RHIC energies. These res…
We derive a simple analytical scaling function which embodies the predictions of high density QCD on the energy, centrality, rapidity, and atomic number dependences of hadron multiplicities in nuclear collisions. Both centrality and rapidity dependences of hadron multiplicity in $Au-Au$ collisions as measured at RHIC at $\sqrt{s}= 130 {GeV}$ are well described in this approach. The centrality and rapidity dependences of hadron multiplicity at $\sqrt{s}= 200 \ {GeV}$ run at RHIC are predicted; the variation of these dependences with energy appear different from other approaches, and can be used…
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at very high energies.
Predictions for the pseudorapidity density of charged particles produced in Pb-Pb central collisions at $\sqrt{s_{NN}}=5.5$ TeV are presented. Particle production in such collisions is computed in the framework of k_t-factorization, using running coupling non-linear evolution to determine the transverse momentum and rapidity dependence of the nuclear unintegrated gluon distributions.
The strong suppression of the $J/ψ$ is studied in the framework of hadronic and quark gluon plasma models. Predictions for RHIC energies are presented.
The nuclear modification factor $R_{AA}$ for $π_0$ production in Au+Au collisions at $\sqrt{s}=200$ AGeV is calculated, and studied at high transverse momenta $p_T$. The soft thermalized nuclear medium is described within the framework of relativistic ideal three-dimensional hydrodynamics. The energy loss of partonic jets is evaluated in the context of gluon bremsstrahlung in the thermalized partonic matter. We provide a systematic analysis of the azimuthal asymmetry of $π_0$ suppression at high $p_T$ in central and non-central collisions, at mid and forward rapidity. The determination of $R_{…
Experimental results of the rapidity spectra of protons and net-protons (protons minus antiprotons) emitted in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions, measured by a few collaborations at the alternating gradient synchrotron (AGS), super proton synchrotron (SPS), and relativistic heavy ion collider (RHIC), are described by a three-source distribution. The values of the distribution width $σ_C$ and contribution ratio (relative contribution) $k_C$ of the central rapidity region, and the distribution width $σ_F$ and rapidity shift $Δy$ of the forward/backward rapidity regions, are then…
We show that the whole range of RHIC data for hadron production in d-Au collisions is compatible with geometric scaling. To establish the scaling violations expected from small-x evolution a larger kinematic range in transverse momentum and rapidity would be needed. We point out that the fall-off of the p_t distribution of produced hadrons at large p_t is a sensitive probe of small-x evolution especially at the LHC.
We investigate the energy dependence of stopping and hadron production in high-energy heavy-ion collisions based on a three-sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies (sqrt{s_NN)=19.6 - 200 GeV) to Pb + Pb at LHC energies sqrt{s_NN)= 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.
We analyze long range rapidity correlations observed in the STAR experiment at RHIC. Our goal is to extract properties of the two particle correlation matrix, accounting for the analysis method of the STAR experiment. We find a surprisingly large correlation strength for central collisions of gold nuclei at highest RHIC energies. We argue that such correlations cannot be the result of impact parameter fluctuations.
We investigate consequences of local energy-momentum conservation for initial eccentricity coefficients in heavy ion collisions at not too high energies relevant for CERN SPS and RHIC BES. Different models of energy density available for pion production are considered. We study dependence of eccentricity coefficients on space-time rapidity for different impact parameters. The naive formula how to define eccentricities breaks with our initial conditions and must be corrected. We predict considerable eccentricities for $ε_{1,2,3,4}$ and specific dependence on space-time rapidity as well as on im…
Multiparton interactions modify the high energy hadronic cross section to produce minijets with a rapidity gap in the distribution of secondaries. At Tevatron energy the correction to the single scattering term is large for transverse momenta smaller than 6 GeV.
The midrapidity inclusive densities of different secondaries are calculated in the framework of the Quark-Gluon String Model. The transfer of baryon number in rapidity space due to the gluon string junction propagation leads to a significant effect on the net baryon production. The numerical results are in reasonable agreement with RHIC experimental data.
Starting from the presence of non-ideal plasma effects due to strongly coupled plasma in the early stage of relativistic heavy-ion collisions, we investigate, from a phenomenological point of view, the relevance of non-conventional statistical mechanics effects on the rapidity spectra of net proton yield at AGS, SPS and RHIC. We show that the broad rapidity shape measured at RHIC can be very well reproduced in the framework of a non-linear relativistic Fokker-Planck equation which incorporates non-extensive statistics and anomalous diffusion.
Background: A resonance has been observed by the ANDY Collaboration at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory in Cu+Au collisions at center-of-mass energy $\sqrt{s} = 200$ GeV and at forward rapidity with an average mass of 18.15 GeV. The Collaboration suggests that it is a $b \overline b b \overline b$ tetraquark state decaying to two $Υ$(1S) states, each measured through the $Υ\rightarrow ggg$ channel. Purpose: Their suggestion is investigated assuming that the two $Υ$ states are produced through the materialization of a $|uud b\overline b b \overline b \rangle…
We present our recent results on jet tomography of AA-collisions at RHIC and LHC. We focus on flavor dependence of the nuclear modification factor. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant.
We use the extended statistical thermal model to describe various hadron rapidity spectra at the highest RHIC energy (200 GeV/A). The model assumes the formation of hot and dense regions moving along the beam axis with increasing rapidities, yFB. It has been earlier shown that this model can explain the net proton flow i.e. p minus pbar, ratio pbar/p and the pion rapidity spectra. In this paper we have attempted to show that in addition to these quantities, this model can also successfully describe the individual rapidity spectra of protons, antiprotons, Kaons, antiKaons, pions, the ratios lam…
The impact parameter and rapidity dependence of the Cronin effect for massless pions in $d+Au$ reactions at $\sqrt{s}_{NN}=200$ GeV at RHIC is computed in the framework of pQCD multiple elastic scattering on a nuclear target. We introduce a formalism to incorporate initial state energy loss in perturbative calculations and take into account the elastic energy loss in addition to the transverse momentum broadening of partons.We argue that the centrality dependence of the Cronin effect can distinguish between different hadron production scenarios at RHIC. Its magnitude and rapidity dependence ar…
Forward di-jet production in d+Au collisions at RHIC provides sensitivity to Bjorken-x between 0.001 and 0.02 for the nuclear gluon density . The STAR experiment at RHIC has continuous azimuthal coverage with electromagnetic calorimeters for pseudo-rapidity from -1 to 4. We have measured forward+mid-rapidity $π^{0}-π^{0}$ and $π^{0}-h$ azimuthal correlations and forward+forward rapidity $π^{0}-π^{0}$ azimuthal correlations. Both analyses use the Forward Meson Spectrometer (FMS) triggered data in RHIC 2008 run p+p and d+Au collisions at $\sqrt{s_{NN}}$=200 GeV. The end-cap electromagnetic calor…
It is widely acknowledged that heavy flavor probes are sensitive to the properties of the quark-gluon plasma and are often considered an important tool for the plasma tomography studies. Forward rapidity observables can provide further insight on the dynamics of the medium due to the interplay between the medium size and the differences in the production spectra of heavy quark probes. In this proceedings we present the nuclear modification factor $R_\text{AA}$'s for B and D mesons, as well as heavy flavor leptons, in the rapidity range $-4.0 < y < 4.0$ obtained from relativistic Langevin equat…
We consider production of prompt photons in high energy gold-gold and deuteron-gold collisions in the forward rapidity region of RHIC ($y \sim 3.8$). In this kinematics, the projectile partons typically have large $x_{bj}$ while the target partons are mostly at very small $x_{bj}$ so that the primary partonic collisions involve valence quarks from the projectile and gluons from the target. We take the target nucleus to be a Color Glass Condensate while the projectile deuteron or nucleus is treated as a dilute system of partons. We show that the photon production cross section can be written as…
We calculate ratios of higher-order susceptibilities quantifying fluctuations in the number of net protons and in the net-electric charge using the Hadron Resonance Gas (HRG) model. We take into account the effect of resonance decays, the kinematic acceptance cuts in rapidity, pseudo-rapidity and transverse momentum used in the experimental analysis, as well as a randomization of the isospin of nucleons in the hadronic phase. By comparing these results to the latest experimental data from the STAR collaboration, we determine the freeze-out conditions from net-electric charge and net-proton dis…
We attempt to describe the rapidity and transverse momentum spectra of strange as well as non-strange hadrons e.g. cascade,cascadebar, lambda , lambdabar, proton, protonbar,(omega+omegabar, Kaon, anti-Kaon and their ratios in the ultra-relativistic collisions of gold nuclei at (Root sNN)=200 GeV. This is done by using a statistical thermal freeze-out model which incorporates the rapidity (collision) axis as well as transverse direction boosts developed within an expanding hot and dense hadronic fluid (fireball) till the final freeze-out. We determine the thermo-chemical freeze-out conditions p…
The property of limiting fragmentation of various observables such as rapidity distributions ($dN/dy$), elliptic flow ($v_{2}$), average transverse momentum ($\langle p_{T} \rangle$) etc. of charged particles is observed when they are plotted as a function of rapidity ($y$) shifted by the beam rapidity ($y_{beam}$) for a wide range of energies from AGS to RHIC. Limiting fragmentation (LF) is a well studied phenomenon as observed in various collision energies and colliding systems experimentally. It is very interesting to verify this phenomenon theoretically. We study such a phenomenon for pion…
We compare results of $2 \to 1$ $k_t$-factorization approach with Kwieciński unintegrated parton distributions and the standard collinear factorization approach at RHIC and slightly smaller energies. Our approach contains only one free parameter responsible for internal parton motion in nucleons. In contrast to recent works in the literature our $k_t$-factorization approach includes also quark degrees of freedom in addition to purely gluonic terms. Both mid and forward rapidity regions are considered. We discuss uncertainties due to fragmentation functions. In general, the $k_t$-factorization …
We investigate the consequences of long range rapidity correlations in the Glasma. Particles produced locally in the transverse plane are correlated by approximately boost invariant flux tubes of longitudinal color electric and magnetic fields that are formed when two sheets of Colored Glass Condensate pass through one another, each acquiring a modified color charge density in the collision. We argue that such long range rapidity correlations persist during the evolution of the Quark Gluon Plasma formed later in the collision. When combined with transverse flow, these correlations reproduce ma…
