Searching for the Higgs Boson in Pairs of Tau Leptons in Data from the ATLAS Experiment : Automation of the SCT prompt calibration
Bibliographic record
Abstract
One of the key questions in particle physics today, is the origin of the electroweak symmetry breaking. The answer to this question will most likely be solved with the data provided by the Large Hadron Collider which started colliding protons in 2008. Many ideas have been posed to how particles gain their masses. The most promising of these ideas is the Higgs mechanism which predicts the existence of a new massive scalar boson, the Higgs boson. Since the discovery of a new particle consistent with a Standard Model Higgs boson was made on July 4 by the ATLAS and CMS experiment, the solution for the puzzle of the electroweak symmetry breaking might be very near. However, in order to fully claim a discovery of the Standard Model Higgs boson, the new particle has to be proven to be a scalar boson and its decay has to be observed in both bosonic and fermionic final states with the corrected branching ratios predicted by the Standard Model. So far the new boson has only been seen in the bosonic gamma-gamma, ZZ and WW final states, and the new particle is yet to be observed in any fermionic final state. Among the fermionic final states, the largest sensitivity is expected in tau+tau- and bb. In this thesis, a search for the Standard Model Higgs boson in the fully hadronic tau+tau− final state is presented. In the selection of Higgs candidate events, a technique for recreating the rest frame of the tau-pairs is shown to be a powerful tool for discriminating between Higgs and background events. Using the reconstructed rest frame, a new mass estimation technique is developed and compared to the existing methods. Finally, an updated limit on the Higgs production cross section is derived using the data recorded by ATLAS during 2011, and compared to the existing ATLAS limit. The thesis is structured as follows: In the first part a brief introduction to the Standard Model including the Higgs mechanism is given, followed by a description on the production of Higgs bosons at the LHC in the Standard Model. The second part describes the ATLAS experiment in general, but a special emphasis is put on the SCT prompt calibration loop, which a great deal of the work of this thesis has gone into developing. The last part describes in the analysis of τ-pairs using the ATLAS detector. First, general description of the newly developed method for the rest frame reconstruction is given, followed by several chapters on the search for the Higgs boson in the tau+tau− final state. Here, the attention is put on mass estimation, background normalisation and evaluation of the theoretical uncertainties related to categorisation of events based on jet kinematics.
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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 | 0.003 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.003 |
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".