Conveners
EM Probes: (1)
- Anne Marie Sickles (Univ. Illinois at Urbana Champaign (US))
EM Probes: (2)
- Raimond Snellings (Nikhef National institute for subatomic physics (NL))
Photonuclear reactions are induced by the strong electromagnetic field generated by ultrarelativistic heavy-ion collisions. These processes have been extensively studied in ultraperipheral collisions, in which the impact parameter is larger than twice the nuclear radius. In recent years, the observation of coherent J/$\psi$ photoproduction has been claimed in nucleus--nucleus (A--A) collisions...
Dileptons are an invaluable tool for mapping out the phase diagram of QCD because they grant observational access to the entire space-time history of heavy-ion collisions. We calculate thermal dilepton yields from Au+Au collisions at BES energies -- $\sqrt{s_{NN}}$=7.7, 19.6, 27, 54.4, 62.4, 130, and 200 GeV -- using a realistic (3+1)-dimensional multistage dynamical framework. The underlying...
Photons provide snapshots of the evolution of relativistic heavy-ion collisions as they are emitted at all stages and do not interact with the medium strongly. Measurements of low momentum direct photons at PHENIX across different systems, from $p+p$, $p/d/^3$He$+$Au to Au$+$Au have been made possible due to the versatility of RHIC. An excess of direct photons, above prompt photon production...
Measurements of direct photons provide valuable information on the properties of the quark-gluon plasma (QGP) because they are colour-neutral and created during all phases of the collision. Sources of photons include initial hard scatterings, Bremsstrahlung and the fragmentation process, jet-medium interactions, and radiation from the medium.
Direct thermal photons, produced by the plasma,...
Electromagnetic probes such as photons and dielectrons (e$^{+}$e$^{-}$ pairs) are a unique tool to study the space-time evolution of the hot and dense matter created in ultra-relativistic heavy-ion collisions. They are produced at all stages of the collision with negligible final-state interactions. At intermediate dielectron invariant mass ($m_{\rm ee} > 1$ GeV/$c^{2}$), thermal radiation...
Dielectrons emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions offer an effective way to probe the medium properties, as they do not interact via the strong force. The rate of the dielectron emission is proportional to the medium's electromagnetic spectral function. In the dielectron mass range from $400$ MeV/$c^{2}$ to $800$ MeV/$c^{2}$,...
Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents a series of measurements of dilepton production from photon fusion performed by the ATLAS Collaboration. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. These processes provide...
In-medium modifications of vector spectral functions are anticipated to carry imprints of restoration of chiral symmetry at high temperature/baryon density. Strong modifications have been indeed measured via dimuon production at the CERN SPS, whereas it remains inconclusive how to quantify those changes as the direct consequence of chiral symmetry restoration. Given the difficulty that it is...
We use QCD kinetic theory to compute photon and dilepton production in the chemically equilibrating out-of-equilibrium Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We compare the non-equilibrium rates to the production in a thermal QGP and extract the dependence of pre-equilibrium photon and dilepton production on the kinetic and chemical equilibration...
We calculate how the critical fluctuations of the QCD critical point (CP) and the color superconducting (CSC) phase transition affect the dilepton production rate (DPR) and the associated transport coefficients, the electric conductivity and relaxation time. We examine the modification of the photon self-energy by the so-called Aslamazov-Larkin, Maki-Thompson, and Density of States terms on...
Thermal photon emission from the QGP is visible in the $p_T$ spectrum of direct photons measured in heavy-ion collisions, producing a characteristic exponential dependence of the spectrum at low $p_T$. The ALICE, PHENIX and STAR Collaboration have quantified this inverse slope $T_{eff}$, measuring $\approx 200$-$400$ MeV, close to the range of QGP temperatures seen in hydrodynamic simulations...
As dileptons are radiated from the extreme states of matter created in heavy-ion collisions with negligible final-state interactions, they retain the information imprinted on them at the time of their creation. Multi-differential measurements of dilepton invariant mass, momentum, and angular distributions can therefore serve as a unique tool to characterize the properties of matter in the...
