Exclusive dimuon production in ultraperipheral Pb+Pb collisions at $\\sqrt{s_{\\mathrm{NN}}} = 5.02$ TeV with ATLAS
Bibliographic record
Abstract
Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, $\\mathrm{PbPb}(\\gamma\\gamma) \\rightarrow \\mu^+\\mu^- (\\mathrm{Pb}^{(\\star)}\\mathrm{Pb}^{(\\star)} )$, is studied using $\\mathcal{L}_{\\mathrm{int}} = 0.48$ nb$^{-1}$ of $\\sqrt{s_\\mathrm{NN}}=5.02$ TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region $p_{\\mathrm{T}\\mu} > 4$ GeV, $|\\eta_{\\mu}| < 2.4$, invariant mass $m_{\\mu\\mu} > 10$ GeV, and $p_{\\mathrm{T,\\mu\\mu}} < 2$ GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of $m_{\\mu\\mu}$, absolute pair rapidity ($|y_{\\mu\\mu}|$), scattering angle in the dimuon rest frame ($|\\cos \\vartheta^{\\star}_{\\mu\\mu}|$) and the colliding photon energies. The total cross section of the UPC $\\gamma \\gamma \\rightarrow \\mu^{+}\\mu^{-}$ process in the fiducial volume is measured to be $\\sigma_{\\mathrm{fid}}^{\\mu\\mu} = 34.1 \\! \\pm \\! 0.3 \\mathrm{(stat.)} \\! \\pm \\! 0.7 \\mathrm{(syst.)}$ $\\mu\\mathrm{b}$. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger $|y_{\\mu\\mu}|$ are found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.002 | 0.002 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.002 | 0.005 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.007 |
| Open science | 0.007 | 0.008 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
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; both teacher heads agree on what is shown here.
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".