Browsing by Subject "COLOR GLASS CONDENSATE"

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Now showing items 1-14 of 14
  • Adam, J.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2017)
    We present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V.
  • Mäntysaari, Heikki; Roy, Kaushik; Salazar, Farid; Schenke, Björn (2021)
    We study coherent diffractive photon and vector meson production in electron-proton and electron-nucleus collisions within the Color Glass Condensate effective field theory. We show that electron-photon and electron-vector meson azimuthal angle correlations are sensitive to nontrivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerran-Venugopalan initial color charge configurations coupled to the numerical solution of small x JIMWLK evolution equations. We compute the cross-section differentially in Q(2) and vertical bar t vertical bar and find sizeable anisotropies in the electron-photon and electron-J/psi azimuthal correlations (v(1,2) approximate to 2-10%) in electron-proton collisions for the kinematics of the future Electron-Ion Collider. In electron-gold collisions these modulations are found to be significantly smaller (v(1,2) < 0.1%). We also compute incoherent diffractive production where we find that the azimuthal correlations are sensitive to fluctuations of the gluon distribution in the target.
  • Lappi, Tuomas (2017)
    A full understanding of the spacetime evolution of the QCD matter created in a heavy ion collision requires understanding the properties of the initial stages. In the weak coupling picture these are dominated by classical gluon fields, whose properties can also be studied via the scattering of dilute probes off a high energy hadron or nucleus. A particular challenge is understanding small systems, where LHC data is also showing signs of collective behavior. We discuss some recent results of on the initial matter production and thermalization in heavy ion collisions, in particular in the gluon saturation framework.
  • Ducloué, B.; Lappi, T.; Mäntysaari, H. (2018)
    We calculate isolated photon production at forward rapidities in proton-nucleus collisions in the color glass condensate framework. Our calculation uses dipole cross sections solved from the running coupling Balitsky-Kovchegov equation with an initial condition fit to deep inelastic scattering data. For comparison, we also update the results for the nuclear modification factor for pion production in the same kinematics. We present predictions for future forward RHIC and LHC measurements at root s(NN) = 200 GeV and root s(NN) = 8 TeV.
  • Weigert, Heribert; Lappi, Tuomas; Ramnath, Andrecia; Rummukainen, Kari (2016)
    The Color Glass Condensate and its associated evolution equation, the JIMWLK equation have applications to many observables far beyond totally inclusive observables. The phenomenology is so rich that little has been done to explore beyond scaling behavior of correlators. We show first examples that exemplify the considerations necessary to access additional information both experimentally and theoretically and demonstrate that the Wilson line correlators appearing throughout make it imperative to consistently take into account that one is dealing with correlators of group elements and demonstrate how this imposes physical and phenomenological constraints. Similar considerations apply also to jet observables at finite N-c.
  • Lappi, T.; Ramnath, A.; Rummukainen, K.; Weigert, H. (2016)
    We study the effects of a parity-odd "odderon" correlation in Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner renormalization group evolution at high energy. Firstly we show that in the eikonal picture where the scattering is described by Wilson lines, one obtains a strict mathematical upper limit for the magnitude of the odderon amplitude compared to the parity-even Pomeron one. This limit increases with N-c, approaching infinity in the infinite N-c limit. We use a systematic extension of the Gaussian approximation including both two-and three-point correlations which enables us to close the system of equations even at finite N-c. In the large-N-c limit we recover an evolution equation derived earlier. By solving this equation numerically we confirm that the odderon amplitude decreases faster in the nonlinear case than in the linear Balitsky-Fadin-Kuraev-Lipatov limit. We also point out that, in the three-point truncation at finite N-c, the presence of an odderon component introduces azimuthal angular correlations similar to cos(n phi) at all n in the target color field. These correlations could potentially have an effect on future studies of multiparticle angular correlations.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2019)
    Measurements of differential cross sections for inclusive very forward jet production in proton-lead collisions as a function of jet energy are presented. The data were collected with the CMS experiment at the LHC in the laboratory pseudorapidity range 6 : 6 < < 5 : 2. Asymmetric beam energies of 4TeV for protons and 1.58TeV per nucleon for Pb nuclei were used, corresponding to a center-of-mass energy per nucleon pair of p sNN = 5 : 02TeV. Collisions with either the proton (p+ Pb) or the ion (Pb+ p) traveling towards the negative hemisphere are studied. The jet cross sections are unfolded to stable-particle level cross sections with pT & 3 GeV, and compared to predictions from various Monte Carlo event generators. In addition, the cross section ratio of p+ Pb and Pb+ p data is presented. The results are discussed in terms of the saturation of gluon densities at low fractional parton momenta. None of the models under consideration describes all the data over the full jet-energy range and for all beam con fi gurations. Discrepancies between the di ff erential cross sections in data and model predictions of more than two orders of magnitude are observed.
  • Jokela, Niko; Kajantie, K.; Sarkkinen, Miika (2021)
    We study the empirical realization of the memory effect in Yang-Mills theory with an axionlike particle, especially in view of the classical vs quantum nature of the theory. We solve for the coupled equations of motion iteratively in the axionic contributions and explicitly display the gauge-invariant effects in terms of field strengths. We apply our results in the context of heavy-ion collisions, in the thin nuclear sheet limit, and point out that a probe particle traversing radiation train acquires a longitudinal null memory kick in addition to the usual transverse kick.
  • Mäntysaari, Heikki; Paukkunen, Hannu (2019)
    We investigate the forward-jet energy spectrum within the color glass condensate framework at 5 TeV center-of-mass energy. In particular, we focus on the kinematic range covered by the CMS-CASTOR calorimeter. We show that our saturation-model calculations are compatible with the CASTOR measurements and that to optimally reproduce the data, effects of multiparton interactions need to be included. We predict a significant nuclear suppression-reaching down to 50% at the lowest considered jet energies E-jet similar to 500 GeV.
  • Boussarie, Renaud; Mäntysaari, Heikki; Salazar, Farid; Schenke, Björn (2021)
    We compute the differential yield for quark anti-quark dijet production in high-energy electron-proton and electron-nucleus collisions at small x as a function of the relative momentum P-perpendicular to and momentum imbalance k(perpendicular to) of the dijet system for different photon virtualities Q(2), and study the elliptic and quadrangular anisotropies in the relative angle between P-perpendicular to and k(perpendicular to). We review and extend the analysis in [1], which compared the results of the Color Glass Condensate (CGC) with those obtained using the transverse momentum dependent (TMD) framework. In particular, we include in our comparison the improved TMD (ITMD) framework, which resums kinematic power corrections of the ratio k(perpendicular to) over the hard scale Q(perpendicular to). By comparing ITMD and CGC results we are able to isolate genuine higher saturation contributions in the ratio Q(s)/Q(perpendicular to) which are resummed only in the CGC. These saturation contributions are in addition to those in the Weizsacker-Williams gluon TMD that appear in powers of Q(s)/k(perpendicular to). We provide numerical estimates of these contributions for inclusive dijet production at the future Electron-Ion Collider, and identify kinematic windows where they can become relevant in the measurement of dijet and dihadron azimuthal correlations. We argue that such measurements will allow the detailed experimental study of both kinematic power corrections and genuine gluon saturation effects.
  • Lappi, T.; Paatelainen, R. (2017)
    Light cone perturbation theory has become an essential tool to calculate cross sections for various small-x dilute-dense processes such as deep inelastic scattering and forward proton-proton and proton-nucleus collisions. Here we set out to do one loop calculations in an explicit helicity basis in the four dimensional helicity scheme. As a first process we calculate light cone wave function for one gluon emission to one-loop order in Hamiltonian perturbation theory on the light front. We regulate ultraviolet divergences with transverse dimensional regularization and soft divergences using a cut-off on longitudinal momentum. We show that when all the renormalization constants are combined, the ultraviolet divergences can be absorbed into the standard QCD running coupling constant, and give an explicit expression for the remaining finite part. (C) 2017 Elsevier Inc. All rights reserved.
  • Lappi, T.; Ramnath, A. (2019)
    We study unequal rapidity correlators in the stochastic Langevin picture of Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner (JIMWLK) evolution in the color glass condensate effective field theory. We discuss a diagrammatic interpretation of the long-range con elators. By separately evolving the Wilson lines in the direct and complex conjugate amplitudes, we use the formalism to study two-particle production at large rapidity separations. We show that the evolution between the rapidities of the two produced particles can be expressed as a linear equation, even in the full nonlinear limit. We also show how the Langevin formalism for two-particle correlations reduces to a Balitsky-Fadin-Kuraev-Lipatov (BFKL) picture in the dilute limit and in momentum space, providing an interpretation of BFKL evolution as a stochastic process for color charges.
  • Ducloue, B.; Iancu, E.; Lappi, T.; Mueller, A. H.; Soyez, G.; Triantafyllopoulos, D. N.; Zhu, Y. (2018)
    We address and solve a puzzle raised by a recent calculation [1] of the cross section for particle production in proton-nucleus collisions to next-to-leading order: the numerical results show an unreasonably large dependence upon the choice of a prescription for the QCD running coupling, which spoils the predictive power of the calculation. Specifically, the results obtained with a prescription formulated in the transverse coordinate space differ by 1 to 2 orders of magnitude from those obtained with a prescription in momentum space. We show that this discrepancy is an artifact of the interplay between the asymptotic freedom of QCD and the Fourier transform from coordinate space to momentum space. When used in coordinate space, the running coupling can act as a fictitious potential which mimics hard scattering and thus introduces a spurious contribution to the cross section. We identify a new coordinate-space prescription, which avoids this problem, and leads to results consistent with those obtained with the momentum-space prescription.