Searches for new physics phenomena with jet final states in the ATLAS detector
Bibliographic record
Abstract
Collimated sprays of particles, known as $jets$, are abundantly produced in high-energy proton-proton ($pp$) collisions, and predicted by many theories of physics beyond the Standard Model. This thesis reports first on the calibration of jets with focus on the data-driven insitu calibration. Two searches for new physics phenomena in events with jets in the final state are then presented. The analyses use $\sqrt s = 13$ TeV $pp$ collision data collected by the ATLAS experiment at the LHC. The response to small- and large-radius jets is measured insitu using data collected between 2015 and 2017. The jet energy scales are measured in events where a jet recoils against a calibrated reference object. The mass scale of large-radius jets is measured with two methods: one uses track jets to provide an independent measurement of the jet mass, the other uses $t\overline{t}$-events with boosted, hadronically decaying $W$-bosons and top quarks. The first analysis is a search for massive coloured objects which are pair-produced and decay to two jets. The data was recorded between 2015 and 2016, corresponding to an integrated luminosity of 36.7 fb$^{-1}$ of data. Two selections of four-jet events are defined; one with two $b$-tagged jets and one inclusive. No significant deviation from the expected background of Standard Model processes is observed in either of the event selections. The results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is a stop squark, which decays to two quarks through $R$-parity violating couplings. Limits are derived on the the stop squark mass and on the mass of pair -produced colour-octet resonances. The scenario where the two squarks decays to a $b$-quark and a lighter quark is considered separately using the $b$-tagged event selection. The second analysis is still ongoing and using data collected between 2015 and 2018, which corresponds to an integrated luminosity of 139 fb$^{-1}$. The search looks for a resonance, which could be a mediator between a confined hidden sector and the Standard Model sector. The mediator decays to two dark partons which shower and hadronise according to the dynamics of the hidden sector. The search targets a selection of model parameters where all dark hadrons decay promptly to visible particle. The signature is a pair of ``dark jets'' with different characteristics than Standard Model QCD-jets. An mass-decorrelated tagger is defined based on the number of tracks associated with the jet. The tagger is designed to distinguish dark jets from the QCD background, without distorting the smoothly falling background distribution.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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; 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".