Nuclear Theory·nucl-th

Wednesday·October 11, 2017

8 papers—4 primary·4 cross-listed

01
Evolution of the Mean Jet Shape and Dijet Asymmetry Distribution of an Ensemble of Holographic Jets in Strongly Coupled Plasma
Jasmine Brewer🇺🇸 · Krishna Rajagopal🇺🇸 · Andrey Sadofyev🇺🇸 · Wilke van der Schee🇺🇸
Some of the most important probes of the quark-gluon plasma (QGP) produced in heavy ion collisions come from the analysis of how the shape and energy of jets are modified by passage through QGP. We model an ensemble of back-to-back dijets to gain a qualitative understanding of how the shapes of the individual jets and the asymmetry in the energy of the pairs of jets are modified by passage through an expanding droplet of strongly coupled plasma, as modeled in a holographic gauge theory. We do so by constructing an ensemble of strings in the gravitational description of the gauge theory. We model QCD jets in vacuum using strings whose endpoints move "downward" into the gravitational bulk spacetime with some fixed small angle that represents the opening angle (ratio of jet mass to jet energy) that the QCD jet would have in vacuum. Such strings must be moving through the gravitational bulk at (close to) the speed of light; they must be (close to) null. This condition does not specify the energy distribution along the string, meaning that it does not specify the shape of the jet being modeled. We study the dynamics of strings that are initially not null and show that strings with a wide range of initial conditions rapidly accelerate and become null and, as they do, develop a similar distribution of their energy density. We use this distribution of the energy density along the string, choose an ensemble of strings whose opening angles and energies are distributed as in perturbative QCD, and show that we can then fix one model parameter such that the mean jet shape in our ensemble matches that measured in p-p collisions reasonably well. We send our strings through the plasma, choosing the second model parameter to get a reasonable suppression in the number of jets, and study how the mean jet shape and the dijet asymmetry are modified, comparing both to data from LHC heavy ion collisions.
nucl-thhep-phhep-thJHEP(2018)·50 citations
02
Causal Electric Charge Diffusion and Balance Functions in Relativistic Heavy Ion Collisions
Joseph I. Kapusta🇺🇸 · Christopher Plumberg🇺🇸
We study the propogation and diffusion of electric charge fluctuations in high energy heavy ion collisions using the Cattaneo form for the dissipative part of the electric current. As opposed to the ordinary diffusion equation this form limits the speed at which charge can propagate. Including the noise term in the current, which arises uniquely from the fluctuation-dissipation theorem, we calculate the balance functions for charged hadrons in a simple 1+1 dimensional Bjorken hydrodynamical model. Limiting the speed of propagation of charge fluctuations increases the height and reduces the width of these balance functions when plotted versus rapidity. We also estimate the numerical value of the associated diffusion time constant from AdS/CFT theory.
nucl-thnucl-exPRC(2018)·35 citations
03
Nuclear clustering and the electron screening puzzle
C.A. Bertulani · C. Spitaleri
Electron screening changes appreciably the magnitude of astrophysical nuclear reactions within stars. This effect is also observed in laboratory experiments on Earth, where atomic electrons are present in the nuclear targets. Theoretical models were developed over the past 30 years and experimental measurements have been carried out to study electron screening in thermonuclear reactions. None of the theoretical models were able to explain the high values of the experimentally determined screening potentials. We explore the possibility that the "electron screening puzzle" is due to nuclear clusterization and polarization effects in the fusion reactions. We will discuss the supporting arguments for this scenario.
nucl-thnucl-exEPJ Web Conf.(2017)·3 citations
04
Simultaneous Production of Lepton Pairs at Ultra-peripheral Relativistic Heavy Ion Collisions
Erkan Kurban🇹🇷 · Mehmet Cem Guclu🇹🇷
We calculate the total cross sections and probabilities of electromagnetic productions of electron, muon and tauon pair productions simultaneously. At the Large Hadron Collider (LHC), the available electromagnetic energy is sufficient to produce all kind of leptons coherently. The masses of muon and tauon are large, so their Compton wavelengths are small enough to interact with the colliding nuclei. Therefore, the realistic nuclear form factors are included in the calculations of electromagnetic pair productions. The cross section calculations show that, at the LHC energies, the probabilities of simultaneous productions of all kind of leptons are increased significantly compare to the RHIC energies. Experimentally, observing this simultaneous production can give us important informations about the strong QED.
nucl-thhep-phPRC(2017)·2 citations
05
Electric Dipole Moments of the Atoms, Molecules, Nuclei and Particles
Timothy Chupp🇺🇸 · Peter Fierlinger🇩🇪 · Michael Ramsey-Musolf🇺🇸 · Jaideep Singh🇺🇸
A permanent electric dipole moment (EDM) of a particle or system is a separation of charge along its angular-momentum axis and is a direct signal of T-violation and, assuming CPT symmetry, CP violation. For over sixty years EDMs have been studied, first as a signal of a parity-symmetry violation and then as a signal of CP violation that would clarify its role in nature and in theory. Contemporary motivations include the role that CP violation plays in explaining the cosmological matter-antimatter asymmetry and the search for new physics. Experiments on a variety of systems have become ever-more sensitive, but provide only upper limits on EDMs, and theory at several scales is crucial to interpret these limits. Nuclear theory provides connections from Standard-Model and Beyond-Standard-Model physics to the observable EDMs, and atomic and molecular theory reveal how CP-violation is manifest in these systems. EDM results in hadronic systems require that the Standard Model QCD parameter of $θ ˉ$ must be exceptionally small, which could be explained by the existence of axions - also a candidate dark-matter particle. Theoretical results on electroweak baryogenesis show that new physics is needed to explain the dominance of matter in the universe. Experimental and theoretical efforts continue to expand with new ideas and new questions, and this review provides a broad overview of theoretical motivations and interpretations as well as details about experimental techniques, experiments, and prospects. The intent is to provide specifics and context as this exciting field moves forward.
↳ physics.atom-phhep-phnucl-exnucl-thRMP(2019)·477 citations
06
N-Jettiness Subtractions for $g g \to H$ at Subleading Power
Ian Moult🇺🇸 · Lorena Rothen🇩🇪 · Iain W. Stewart🇺🇸 · Frank J. Tackmann🇩🇪 · Hua Xing Zhu🇺🇸
$N$ -jettiness subtractions provide a general approach for performing fully-differential next-to-next-to-leading order (NNLO) calculations. Since they are based on the physical resolution variable $N$ -jettiness, $T_{N}$ , subleading power corrections in $τ = T_{N} / Q$ , with $Q$ a hard interaction scale, can also be systematically computed. We study the structure of power corrections for $0$ -jettiness, $T_{0}$ , for the $g g \to H$ process. Using the soft-collinear effective theory we analytically compute the leading power corrections $α_{s} τ ln τ$ and $α_{s}^{2} τ ln^{3} τ$ (finding partial agreement with a previous result in the literature), and perform a detailed numerical study of the power corrections in the $g g$ , $g q$ , and $q q ˉ$ channels. This includes a numerical extraction of the $α_{s} τ$ and $α_{s}^{2} τ ln^{2} τ$ corrections, and a study of the dependence on the $T_{0}$ definition. Including such power suppressed logarithms significantly reduces the size of missing power corrections, and hence improves the numerical efficiency of the subtraction method. Having a more detailed understanding of the power corrections for both $q q ˉ$ and $g g$ initiated processes also provides insight into their universality, and hence their behavior in more complicated processes where they have not yet been analytically calculated.
↳ hep-phnucl-thPRD(2018)·97 citations
07
Relativistic Hydrodynamic Attractors with Broken Symmetries: Non-Conformal and Non-Homogeneous
Paul Romatschke🇺🇸
Standard textbooks will state that hydrodynamics requires near-equilibrium to be applicable. Recently, however, out-of-equilibrium attractor solutions for hydrodynamics have been found in kinetic theory and holography in systems with a high degree of symmetry, suggesting the possibility of a genuine out-of-equilibrium formulation of hydrodynamics. This work demonstrates that attractor solutions also occur in non-conformal kinetic theory and spatially non-homogeneous systems, potentially having important implications for the interpretation of experimental data in heavy-ion and proton-proton collisions and relativistic fluid dynamics as a whole.
↳ hep-thgr-qcnucl-thJHEP(2017)·117 citations
08
Medium modification of strange hadronic resonances at SIS, RHIC and LHC energies
Laura Tolos🇪🇸
The properties of strange pseudoscalar and vectors mesons as well as strange baryon resonances in dense matter are reviewed. Some open questions on the properties of strange hadrons in medium are addressed, such as the experimental signatures of in-medium effects coming from the hadronic phase on the final observables in heavy-ion collisions for the experimental conditions at SIS, RHIC and LHC energies.
↳ hep-phnucl-thEPJ Web Conf.(2018)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE