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Techniques to generate intense isolated attosecond pulses from relativistic plasma mirrors
Not Available
Underdense relativistically thermal plasma produced by magnetically assisted direct laser acceleration
Not Available
Investigation on laser absorption and x-ray radiation in microstructured titanium targets heated by short-pulse relativistic laser pulses
The enhancement effect of a microstructured surface on laser absorption and characteristic K α emission has been investigated by measuring K-shell emission from titanium (Ti) targets irradiated with high-intensity ( ∼ 10 20 W cm − 2 ), subpicosecond (500 fs) laser pulses. The experimental results indicate a modest enhancement ( 1.6 × ) of K α emission from microstructured targets compared to flat foils, but with a similar intensity and profile of He α and Li-like satellites. Particle-in-cell (PIC) simulations are implemented to further understand the underlying physical processes in the laser interaction with both targets, interpreting the mechanisms responsible for the K α enhancement. The reasons for the lower-than-expected enhancement of K α emission are discussed. The rapid heating of the bulk plasma might result in the premature shutdown of K α emission before the thermalization of hot electrons or even the end of laser pulses, suggesting that the use of K α emission as a diagnostic of the hot-electron yield or relaxation could lead to a misinterpretation. Published by the American Physical Society 2024
Symmetrizing relativistic three-body partial wave amplitudes
S matrix principles and symmetries impose constraints on three-particle scattering amplitudes, which can be formulated as a class of integral equations for their partial wave projections. However, these amplitudes are typically expressed in an asymmetric basis, where one of the initial and final state particles is singled out, and all quantum numbers are defined relative to this spectator. In this work, we show how to construct symmetric partial wave amplitudes, which have been symmetrized over all possible spectator combinations, using their asymmetric counterparts and sets of recoupling coefficients. We derive these recoupling coefficients for arbitrary angular momentum and isospin for arbitrary systems of spinless particles with SU(2) flavor symmetry. We propose a simple intensity observable suitable for visualizing the structure of three-body dynamics in Dalitz distributions. Finally, we provide some numerical examples of Dalitz distributions relevant for future lattice QCD calculations of 3𝜋 systems and provide numerical evidence that the symmetrization procedure is consistent with expected symmetries of Dalitz plots.
Identifying the nature of the QCD transition in relativistic collision of heavy nuclei with deep learning
Using deep convolutional neural network (CNN), the nature of the QCD transition can be identified from the final-state pion spectra from hybrid model simulations of heavy-ion collisions that combines a viscous hydrodynamic model with a hadronic cascade “after-burner”. Two different types of equations of state (EoS) of the medium are used in the hydrodynamic evolution. The resulting spectra in transverse momentum and azimuthal angle are used as the input data to train the neural network to distinguish different EoS. Different scenarios for the input data are studied and compared in a systematic way. A clear hierarchy is observed in the prediction accuracy when using the event-by-event, cascade-coarse-grained and event-fine-averaged spectra as input for the network, which are about 80%, 90% and 99%, respectively. A comparison with the prediction performance by deep neural network (DNN) with only the normalized pion transverse momentum spectra is also made. High-level features of pion spectra captured by a carefully-trained neural network were found to be able to distinguish the nature of the QCD transition even in a simulation scenario which is close to the experiments.
Fireball tomography from bottomonia elliptic flow in relativistic heavy-ion collisions
Abstract We calculate the elliptic flow of bottomonia produced in Pb $$\,+\,$$ + Pb collisions at $$\sqrt{s_{\mathrm{NN}}}=5.02$$ s NN = 5.02 TeV. We consider temperature-dependent decay widths for the anisotropic escape of various bottomonium states and observe that the transverse momentum dependence of bottomonia elliptic flow provides a tomographic information about the QGP fireball at different stages of its evolution. For the space-time evolution of the fireball, we employ simulation results from the 3 + 1 D quasiparticle anisotropic hydrodynamic model. We find that our results for transverse momentum dependence of bottomonia elliptic flow are in reasonable agreement with experimental results from the ALICE and CMS collaborations.
An improved method to access initial states in relativistic heavy-ion collisions
Abstract Observables in heavy-ion collisions are generally categorized into centralities, which reflect an average over events within a range of impact parameters including a wide variety of initial-state configurations. A multiple binning method using spectator neutrons within each centrality has been shown to provide access to events with rare initial-state conditions. This work suggests an improvement in quantifying the difference between standard centrality and spectator neutron binning towards accessing the initial-state properties. A selection of events with higher initial-state density at a fixed participating nucleon number was observed to result in larger final-state particle production and smaller elliptic flow. The relative difference between observables in centrality and spectator binning shows reduced sensitivity for the observables dominated by impact parameter fluctuations in the initial state, such as triangular flow. This property renders the spectator binning method a good candidate for separating geometric contributions from random fluctuations in the initial state towards final-state observables.
Flavour-dependent chemical freeze-out of light nuclei in relativistic heavy-ion collisions
We study the production of light nuclei in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7–200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 and 5.02 TeV within a flavour-dependent chemical freeze-out scenario, assuming different flavoured hadrons undergo separate chemical freeze-out. Using the Thermal-FIST package, thermal parameters extracted from fits to various sets of hadron yields, including and excluding light nuclei, are used to calculate the ratios of the yields of light nuclei, namely, d/p, $\overline{d}$/$\overline{p}$, t/p, t/d, 4 He/ 3 He, and 3 H Λ / 3 He. A comparison with experimental data from the STAR and ALICE collaborations shows that a sequential freeze-out scenario provides a better description of light nuclei yield ratios than the traditional single freeze-out approach. These results suggest the flavour-dependent chemical freeze-out for final state light nuclei production persists in heavy-ion collisions at both RHIC and LHC energies.
Impact of a minority relativistic electron tail interacting with a thermal plasma containing high-atomic-number impurities [Slides]
Abstract not provided.
First Principles Kinetic Simulations of Relativistic Collisionless Shocks and Their Particle Acceleration (2019)
Abstract not provided.
First Principles Kinetic Simulations of Relativistic Collisionless Shocks and Their Particle Acceleration
Abstract not provided.
The LLNL Program in Relativistic Heavy-Ion Physics: FY20 Annual Laboratory Continuation Progress Report
The LLNL Heavy-Ion Group has research interests in the features and phenomena of nuclear matter at extreme temperatures and densities. It pursues these interests through participation in two experimental collaborations (ATLAS and sPHENIX) and one joint theory/experiment topical collaboration (JETSCAPE). The group is funded through a combination of LDRD, DOE-SC NP and an award from US ATLAS Software and Computing Operations, which is ultimately funded through HEP. The group's activities in FY20 were oriented around beginning a new LDRD project and fi lling two open postdoc positions while contributing to the ATLAS jet and UPC programs as well as participating in sPHENIX. Both postdoc positions were lled, effectively doubling the side of the LLNL Heavy-Ion Group, by Qipeng Hu (starting 6/20) and Dhanush Hangal (starting 8/20).