Photons and dileptons as probes of early-time dynamics in relativistic heavy-ion collisions
Bibliographic record
Abstract
Vigorous experimental and theoretical programs are underway to study the behaviour of strongly interacting systems in extreme conditions of temperature and density. The only practical way to create such systems in terrestrial laboratories is to collide nuclei at relativistic energies. This is done at accelerator facilities such as the LHC (CERN, Geneva) and RHIC (Brookhaven National Laboratory, USA). These collisions of heavy ions contain so much energy in such a small volume that the colliding nuclei "melt" into a plasma of quarks and gluons. This creates an exotic form of nuclear matter: the quark-gluon plasma (QGP), which exists but for a fleeting moment, and can be studied through the particles that stream to the detectors. Two such particles are leptons and photons, which this research will focus on. As it was discovered that the QGP can be very well modelled by relativistic fluid dynamics, there has been a large theoretical effort to completely characterize this QGP and understand its bulk properties. One of the aims of the McGill group is to obtain a value for the shear and bulk viscosities of the plasma: those are transport coefficients linked to fundamental properties of quantum chromodynamics (QCD), the theory of the nuclear strong interaction. The production of photons and dileptons can be used as probes to study these transport coefficients as they are emitted throughout the out-of-equilibrium evolution of the QGP medium, as well as within thermal equilibrium. In order for such studies to be done, the electromagnetic signal from the pre-equilibrium phase needs to be quantified, which is the topic of this thesis. Using kinetic theory, the production rate of dileptons and photons was calculated for both thermal equilibrium and pre-equilibrium cases. In the thermal equilibrium case, results of the numerical integration of the differential dilepton and photon production rates were matched to the analytical solution. For the out-of-equilibrium case, transport equations derived within the diffusion approximation of the Boltzmann equation were solved numerically to study the thermalization of quarks and gluons in quark-gluon plasma.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".