Expected Tracking Performance of the ATLAS Inner Tracker at the High-Luminosity LHC
Bibliographic record
Abstract
Following the discovery of the Higgs boson, the precise measurement of its properties and their consistency with Standard Model (SM) predictions remains a central goal of the physics program at the Large Hadron Collider (LHC). While current measurements align with the SM predictions, unanswered questions suggest the potential for new physics beyond the SM (BSM). The first part of this thesis presents the first ATLAS search for Higgs boson pair production ($HH$) associated with top quarks ($t\bar{t}HH$), a rare process that provides direct access to BSM physics through the quartic top-Higgs coupling, offering unique opportunities to probe the Higgs sector of the SM and the electroweak symmetry breaking (EWSB) mechanism. This thesis establishes observed (expected) 95% confidence level upper limits on the SM $t\bar{t}HH$ production cross-sections of 30.8 (24.6) times the SM in leptonic final states, using the full Run 2 and partial Run 3 datasets, corresponding to integrated luminosities of 140 and 59 fb$^{-1}$, respectively. No significant excess in data above the SM expectations is seen. Additionally, the results are interpreted within the framework of Effective Field Theories by establishing limits on the top-Higgs quartic interaction. The second part of this dissertation also discusses the experimental challenges and opportunities presented by the High-Luminosity LHC (HL-LHC). The increased luminosity will enable precision measurements of the Higgs self-coupling and provide enhanced sensitivity to BSM physics. Key detector upgrades, such as the Inner Tracker (ITk) and improved $b$-jet tagging, photon reconstruction, and tau identification, are crucial for maximising the sensitivity of $HH$ searches, including $t\bar{t}HH$.This thesis describes ongoing efforts to address the computational challenges of Phase-II tracking at the HL-LHC. The expected Phase-II ITk tracking physics and computational performance is evaluated. It details improvements in the A Common Tracking Software (ACTS) framework, focusing on the implementation and optimization of the ITk seeding algorithm. Finally, the current expected tracking performance of the ACTS algorithms are presented together with a discussion on CPU optimisation.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".