arXiv subjects

Barbara Betz

Publications and source records attributed to Barbara Betz.

30 records · Page 2Linked to original sources

arXiv2010

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

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.

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arXiv2009

Jet Propagation and Mach-Cone Formation in (3+1)-dimensional Ideal Hydrodynamics

This thesis investigates the jet-medium interactions in a Quark-Gluon Plasma using a hydrodynamical model. It deals with the creation of Mach cones which are supposed to exhibit a characteristic structure in the measured angular particle distributions allowing for direct conclusions about the Equation of State and in particular about the speed of sound of the medium. Several different scenarios of jet energy loss are examined and different mechanisms of energy and momentum loss are analyzed, ranging from weak interactions (based on calculations from perturbative Quantum Chromodynamics, pQCD) to strong interactions (formulated using the Anti-de-Sitter/Conformal Field Theory Correspondence, AdS/CFT). Though they result in different angular particle correlations which could in principle allow to distinguish the underlying processes, it is shown that the characteristic structure observed in experimental data can be obtained due to the different contributions of several possible jet trajectories through an expanding medium. Such a structure cannot directly be connected to the Equation of State. In this context, the impact of a strong flow created behind the jet (the diffusion wake) is examined which is common to almost all jet deposition scenarios. Besides that, the transport equations for dissipative hydrodynamics are discussed which are fundamental for any numerical computation of viscous effects in a Quark-Gluon Plasma.

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arXiv2009

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

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.

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arXiv2009

Anomalous Conical Di-jet Correlations in pQCD vs AdS/CFT

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.

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arXiv2009

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

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.

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arXiv2009

Mach cones in heavy ion collisions

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.

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arXiv2008

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

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.

hep-ph↗

arXiv2008

Jet Propagation and Mach Cones in (3+1)d Ideal Hydrodynamics

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, 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. However, a combined study of energy deposition and fluid response is needed. We solve numerically 3--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.

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arXiv2007

Polarization probes of vorticity in heavy ion collisions

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.

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arXiv2007

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

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.

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arXiv2007

Are there plasminos in superconductors?

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.

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arXiv2007

Hydrodynamic Flow and Jet Induced Mach Shocks at RHIC and LHC

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.

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