Barbara Betz

Publications (18)11.55 Total impact

• Article: Quantifying a Possibly Reduced Jet-Medium Coupling of the sQGP at the LHC

  Barbara Betz, Miklos Gyulassy
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  ABSTRACT: The nuclear modification factor R_{AA} measured in Pb+Pb collisions at the Large Hadron Collider (LHC) suggests that the jet-medium coupling in a Quark-Gluon Plasma at LHC energies is reduced as compared to energies reached at the Relativistic Heavy Ion Collider (RHIC). We estimate the reduction factor using a simple generic energy-loss model and find that the jet-medium coupling at the LHC is approximately 10% smaller than at RHIC. Moreover, we examine different jet-energy loss prescriptions with $dE/dx\sim E^a$ and show that the measured momentum dependence of the nuclear modification factor at the LHC rules out any model with $E^{a>1/3}$.
  11/2012;
• Article: Scaling of elliptic flow in heavy ion collisions

  Giorgio Torrieri, Barbara Betz, Miklos Gyulassy
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  ABSTRACT: The common interpretation of $v_2$ in heavy ion collisions is that it is produced by hydrodynamic flow at low transverse momentum and by parton energy loss at high transverse momentum. In this talk we discuss this interpretation in view of the dependence of $v_2$ with energy, rapidity and system size, and show that it might not be trivial to reconcile these models with the relatively simple scaling found in experiment
  08/2012;
• Source

  Available from: ArXiv

  Article: Examining a reduced jet-medium coupling in Pb+Pb collisions at the Large Hadron Collider

  Barbara Betz, Miklos Gyulassy
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  ABSTRACT: Recent data on the nuclear modification factor $R_{AA}$ of jet fragments in 2.76 ATeV Pb+Pb collisions at the Large Hadron Collider (LHC) indicate that the jet-medium coupling in a Quark-Gluon Plasma (QGP) is reduced at LHC energies and not compatible with the coupling deduced from data at the Relativistic Hadron Collider (RHIC). We estimate the reduction factor from a combined fit to the available data on $R_{AA}(\sqrt{s},p_T,b)$ and the elliptic flow $v_2(\sqrt{s},p_T,b)$ at $\sqrt{s}=0.2,2.76$ ATeV over a transverse momentum range $p_T$ 10-100 GeV and a broad impact parameter, b, range. We use a simple analytic "polytrope" model ($dE/dx=- \kappa E^{a} x^z T^{c}$) to investigate the dynamical jet-energy loss model dependence. Varying a=0-1 interpolates between weakly-coupled and strongly-coupled models of jet-energy dependence while z=0-2 covers a wide range of possible jet-path dependencies from elastic and radiative to holographic string mechanisms. Our fit to LHC data indicates an approximate 40% reduction of the coupling $\kappa$ from RHIC to LHC and excludes energy-loss models characterized by a jet-energy exponent with a>1/3. In particular, the rapid rise of $R_{AA}$ with $p_T$>10 GeV combined with the slow variation of the asymptotic $v_2(p_T)$ at the LHC rules out popular exponential geometric optics models (a=1). The LHC data are compatible with $0\leq a\leq 1/3$ pQCD-like energy-loss models where the jet-medium coupling is reduced by approximately 10% between RHIC and LHC.
  12/2011;
• Source

  Available from: Giorgio Torrieri

  Article: Sensitivity of Azimuthal Jet Tomography to Early Time Energy-Loss at RHIC and LHC

  Barbara Betz, Miklos Gyulassy, Giorgio Torrieri
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  ABSTRACT: We compute the jet path-length dependence of energy-loss for higher azimuthal harmonics of jet-fragments in a generalized model of energy-loss that can interpolate between pQCD and AdS/CFT limits and compare results with Glauber and CGC/KLN initial conditions. We find, however, that even the high-pT second moment is most sensitive to the poorly known early-time evolution during the first fm/c. Moreover, we demonstrate that quite generally the energy and density-dependence leads to an overquenching jet fragments relative to the first LHC $R_{AA}$-data, once the parameters of the energy-loss model are fixed from $R_{AA}$-data at RHIC.
  06/2011;
• Source

  Available from: Giorgio Torrieri

  Article: Fourier Harmonics of High-pT Particles Probing the Fluctuating Intitial Condition Geometries in Heavy-Ion Collisions

  Barbara Betz, Miklos Gyulassy, Giorgio Torrieri
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  ABSTRACT: Second Fourier harmonics of jet quenching have been thoroughly explored in the literature and shown to be sensitive to the underlying jet path-length dependence of energy loss and the differences between the mean eccentricity predicted by Glauber and CGC/KLN models of initial conditions. We compute the jet path-length dependence of energy-loss for higher azimuthal harmonics of jet-fragments in a generalized model of energy-loss for RHIC energies and find, however, that even the high-$p_T$ second moment is most sensitive to the poorly known early-time evolution during the first fm/c. Moreover, we demonstrate that higher-jet harmonics are remarkably insensitive to the initial conditions, while the different $v_n(N_{part})$ vs. $v_n^{I_{AA}}(N_{part})$ correlations between the moments of monojet and dijet nuclear modifications factors remain a most sensitive probe to differentiate between Glauber and CGC/KLN initial state sQGP geometries.
  02/2011;
• Source

  Available from: arxiv.org

  Article: Universal flow-driven conical emission in ultrarelativistic heavy-ion collisions.

  Barbara Betz, Jorge Noronha, Giorgio Torrieri, Miklos Gyulassy, Dirk H Rischke
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  ABSTRACT: The double-peak structure observed in soft-hard hadron correlations is commonly interpreted as a signature for a Mach cone generated by a supersonic jet interacting with the hot and dense medium created in ultrarelativistic heavy-ion collisions. We show that it can also arise due to averaging over many jet events in a transversally expanding background. We find that the jet-induced away-side yield does not depend on the details of the energy-momentum deposition in the plasma, the jet velocity, or the system size. Our claim can be experimentally tested by comparing soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets.
  Physical Review Letters 11/2010; 105(22):222301. · 7.37 Impact Factor
• Source

  Available from: Hannah Petersen

  Article: Conical Emission from Shock Waves in Ne(1-20 AGeV)+U Collisions

  Philip Rau, Jan Steinheimer, Barbara Betz, Hannah Petersen, Marcus Bleicher, Horst Stöcker
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  ABSTRACT: The formation and propagation of high-density compression waves, e.g. Mach shock waves, in cold nuclear matter is studied by simulating high-energy nucleus-nucleus collisions of Ne with U in the energy range from E_lab = 0.5 AGeV to 20 AGeV. In an ideal hydrodynamic approach, the high-density shock wave created by the small Ne nucleus passing through the heavy U nucleus is followed by a slower and more dilute Mach shock wave which causes conical emission of particles at the Mach cone angle. The conical emission originates from low-density regions with a small flow velocity comparable to the speed of sound. Moreover, it is shown that the angular distributions of emitted baryons clearly distinguish between a hydrodynamic approach and binary cascade processes used in the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport model. Comment: 8 pages, 9 figures
  03/2010;
• Source

  Available from: Giorgio Torrieri

  Article: Conical Correlations, Bragg Peaks, and Transverse Flow Deflections in Jet Tomography

  Barbara Betz, Jorge Noronha, Giorgio Torrieri, Miklos Gyulassy, Dirk H. Rischke
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  ABSTRACT: We use (3+1)-dimensional ideal hydrodynamics to describe a variety of different jet energy loss scenarios for a jet propagating through an opaque medium. The conical correlations obtained for fully stopped jets, revealing a Bragg peak, are discussed as well as results from pQCD and AdS/CFT. Moreover, we investigate transverse flow deflection. It is demonstrated that a double-peaked away-side structure can be formed due to the different contributions of several possible jet trajectories through an expanding medium. Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee, revised version
  07/2009;
• Source

  Available from: Giorgio Torrieri

  Article: Mach cones in heavy ion collisions

  Giorgio Torrieri, Barbara Betz, Jorge Noronha, Miklos Gyulassy
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  ABSTRACT: We study the fate of the energy deposited by a jet in a heavy ion collision assuming that the medium created is opaque (jets quickly lose energy) and its viscosity is so low that the energy lost by the jet is quickly thermalized. The expectation is that under these conditions the energy deposited gives rise to a Mach cone. We argue that, in general, the behavior of the system is different from the naive expectation and it depends strongly on the assumptions made about the energy and momentum deposited by the jet into the medium. We compare our phenomenological hydrodynamic calculations performed in a static medium for a variety of energy-momentum sources (including a pQCD-based calculation) with the exact strong coupling limit obtained within the AdS/CFT correspondence. We also discuss the observability of hydrodynamical features triggered by jets in experimentally measured two-particle correlations at RHIC.
  02/2009;
• Source

  Available from: Giorgio Torrieri

  Article: Universality of the Diffusion Wake from Stopped and Punch-Through Jets in Heavy-Ion Collisions

  Barbara Betz, Jorge Noronha, Giorgio Torrieri, Miklos Gyulassy, Igor Mishustin, Dirk H. Rischke
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  ABSTRACT: We solve (3+1)-dimensional ideal hydrodynamical equations with source terms that describe punch-through and fully stopped jets in order to compare their final away-side angular correlations in a static medium. For fully stopped jets, the backreaction of the medium is described by a simple Bethe-Bloch-like model which leads to an explosive burst of energy and momentum (Bragg peak) close to the end of the jet's evolution through the medium. Surprisingly enough, we find that the medium's response and the corresponding away-side angular correlations are largely insensitive to whether the jet punches through or stops inside the medium. This result is also independent of whether momentum deposition is longitudinal (as generally occurs in pQCD energy loss models) or transverse (as the Bethe-Bloch formula implies). The existence of the diffusion wake is therefore shown to be universal to all scenarios where momentum as well as energy is deposited into the medium, which can readily be understood in ideal hydrodynamics through vorticity conservation. The particle yield coming from the strong forward moving diffusion wake that is formed in the wake of both punch-through and stopped jets largely overwhelms their weak Mach cone signal after freeze-out. Comment: 9 pages, 6 figures, revised version, main results unchanged
  12/2008;
• Source

  Available from: Giorgio Torrieri

  Article: Jet Energy Loss and Mach Cones in pQCD vs. AdS/CFT

  Barbara Betz, Jorge Noronha, Miklos Gyulassy, Giorgio Torrieri
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  ABSTRACT: We compare away-side hadron correlations with respect to tagged heavy quark jets computed within a weakly coupled pQCD and a strongly coupled AdS/CFT model. While both models feature similar far zone Mach and diffusion wakes, the far zone stress features are shown to be too weak to survive thermal broadening at hadron freeze-out. Observable away-side conical correlations are dominated by the jet-induced transverse flow in near zone "Neck" region, which differs significantly for both models. Unlike in AdS/CFT, the induced transverse flow in the Neck zone is too weak in pQCD to produce conical correlations after Cooper-Frye freeze-out. The observation of conical correlations violating Mach's law would favor the strongly-coupled AdS/CFT string drag dynamics, while their absence would favor weakly-coupled pQCD-based hydrodynamics. Comment: 5 pages, 2 figures, proceedings of the Confinement8 Conference, Mainz, Germany, Sept. 1-6, 2008
  12/2008;
• Source

  Available from: ArXiv

  Article: Jet propagation and Mach cones in (3+1)d ideal hydrodynamics

  Barbara Betz, Miklos Gyulassy, Dirk H Rischke, Horst Stöcker, Giorgio Torrieri
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  ABSTRACT: The observation of jet quenching and associated away-side Mach cone-like correlations at RHIC provide powerful 'external' probes of the sQGP produced in A+A reactions [1], but it simultaneously raises the question where the jet energy was deposited. The nearly perfect bulk fluidity observed via elliptic flow suggests that Mach cone-like correlations may also be due to rapid local equilibration in the wake of penetrating jets. Multi-particle correlations lend further support to this possibility [2]. However, a combined study of energy deposition and fluid response is needed. We solve numerically three-dimensional ideal hydrodynamical equations to compute the flow correlation patterns resulting from a variety of possible energy–momentum deposition models. Mach-cone correlations are shown to depend critically on the energy and momentum deposition mechanisms. They only survive for a special limited class of energy–momentum loss models, which assume significantly less longitudinal momentum loss than energy loss per unit length. We conclude that the correct interpretation of away-side jet correlations will require improved understanding and independent experimental constraints on the jet energy–momentum loss to fluid couplings.
  Journal of Physics G Nuclear and Particle Physics 09/2008; 35(10):104106. · 4.18 Impact Factor
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  Available from: Giorgio Torrieri

  Article: Anomalous conical di-jet correlations in pQCD vs AdS/CFT

  Barbara Betz, Miklos Gyulassy, Jorge Noronha, Giorgio Torrieri
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  ABSTRACT: We propose an identified heavy quark jet observable to discriminate between weakly coupled pQCD and strongly coupled AdS/CFT models of quark–gluon plasma dynamics in ultra-relativistic nuclear collisions at RHIC and LHC energies. These models are shown to predict qualitatively different associated hadron correlations with respect to tagged heavy quark jets. While both models feature similar far zone Mach and diffusion wakes, the far zone stress features are shown to be too weak to survive thermal broadening at hadron freeze-out. However, these models differ significantly in a near zone “Neck” region where strong chromo-fields sourced by the heavy quark jet couple to the polarizable plasma. Conical associated correlations, if any, are shown to be dominated by the jet induced transverse flow in the Neck zone and unrelated to the weak far zone wakes. Unlike in AdS/CFT, we show that the induced transverse flow in the Neck zone is too weak in pQCD to produce conical correlations after Cooper–Frye freeze-out. The observation of conical correlations violating Mach's law would favor the strongly-coupled AdS/CFT string drag dynamics, while their absence would favor weakly-coupled pQCD-based chromo-hydrodynamics.
  Physics Letters B. 07/2008;
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  Available from: ArXiv

  Article: Polarization probes of vorticity in heavy ion collisions

  Barbara Betz, Miklos Gyulassy, Giorgio Torrieri
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  ABSTRACT: We discuss the information that can be deduced from a measurement of particle (hyperon or vector meson) polarization in ultrarelativistic nuclear collisions. We describe the sensitivity of polarization to initial conditions, hydrodynamic evolution and mean free path, and find that the polarization observable is sensitive to all details and stages of the system's evolution. We suggest that an experimental investigation covering production plane and reaction plane polarizations, as well as the polarization of jet-associated particles in the plane defined by the jet and particle direction, can help in disentangling the factors contributing to this observable. Scans of polarization in energy and rapidity might also point to a change in the system's properties.
  09/2007;
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  Available from: ArXiv

  Article: Mach Cones and Hydrodynamic Flow: Probing Big Bang Matter in the Laboratory

  Barbara Betz, Philip Rau, Horst Stöcker
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  ABSTRACT: A critical discussion of the present signals for the phase transition to quark-gluon plasma (QGP) is given. Since hadronic rescattering models predict much larger flow than observed from 1 to 50 A GeV laboratory bombarding energies, this observation is interpreted as potential evidence for a first-order phase transition at high baryon density. A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Here, hadronic rescattering models can explain < 30 % of the observed elliptic flow v_2 for $p_T > 2$ GeV/c. This is interpreted as an evidence for the production of superdense matter at RHIC. The connection of v_2 to jet suppression is examined. A study of Mach shocks generated by fast partonic jets propagating through the QGP is given. The main goal is to take into account different types of collective motion during the formation and evolution of this matter. A significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium is predicted. A new hydrodynamical study of jet energy loss is presented.
  08/2007;
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  Available from: uni-frankfurt.de

  Article: Hydrodynamic Flow and Jet Induced Mach Shocks at RHIC and LHC

  Horst Stöcker, Barbara Betz, Philip Rau
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  ABSTRACT: We discuss the present collective flow signals for the phase transition to quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). A study of Mach shocks induced by fast partonic jets propagating through the QGP is given. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. Results of a hydrodynamical study of jet energy loss are presented.
  04/2007;
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  Available from: uni-frankfurt.de

  Article: Mach Cones and Jet Energy Loss Studies in Full (3+ 1) DIMENSIONAL Ideal Hydrodynamics

  Barbara Betz, Kerstin Paech, Dirk H Rischke, Horst Stöcker
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  ABSTRACT: A vigorous debate has recently concerned the quenching of jets by the expanding hot and dense medium created in high–energy nuclear collisions accompanied by Mach-cone-like structures at STAR and PHENIX 1,2 . Large angle (w.r.t. the jet axis) peaks in the angular distribution of the particles created in the jet show up in both, 2– and 3–particle correlations. It is assumed that this reflects the interaction of the jet with the medium 3,4 . However, the jet interactions with the medium are theoretically not understood well enough. Therefore, we present a first ideal (3+1)dimensional hydrodynamics approach with a sudden jet–energy deposition. Clearly, the hydrodynamical evolution strongly depends on the underlying equation of state (EoS) of the medium and therefore the influcence of the EoS on the evolution of the jet through the medium is of great interest for probing the EoS, the nature of the phase transition.
  03/2007;
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  Available from: arxiv.org

  Article: Are there plasminos in superconductors?

  Barbara Betz, Dirk H. Rischke
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  ABSTRACT: Hot and/or dense, normal-conducting systems of relativistic fermions exhibit a particular collective excitation, the so-called plasmino. We compute the one-loop self-energy, the dispersion relation and the spectral density for fermions interacting via attractive boson exchange. It is shown that plasminos also exist in superconductors.
  10/2006;