Time Dependent Analysis of B<sup>0</sup> →ρ<sup>0</sup>ρ<sup>0</sup> Decays
Bibliographic record
Abstract
The BABAR detector at the PEP-II asymmetric-energy e+e- collider is located at the Stanford Linear Accelerator Center. It has been gathering data on the Υ(4S) resonance from 2000 until 2007 with the primary objective of studying CP violation in B-meson decays. In this thesis they provide a theoretical overview of how CP violation arises in the context of the Standard Model, why B decays are relevant, and how BABAR gathers the necessary data. Specifically, they present the analysis of B0 →ρ0ρ0 decays in a sample of 465 x 106 Υ(4S) → B$\bar{B}$. They measure the corresponding branching fraction β = (0.92 ± 0.32(stat.) ± 0.14(syst.)) x 10-6 and the longitudinal polarization fraction fL = 0.75-0.14+0.11(stat.) ± 0.04(syst.). The evidence for the B0→ ρ0ρ0 signal has a significance of 3.1 standard deviations (σ), when the systematic uncertainties are included. There is insufficient evidence for B decays into similar modes and the corresponding upper limits are determined to be βρ0f0 < 0.34 x 10-6, βf0f0 < 0.16 x 10-6, βρ0π+π- < 8.7 x 10-6, B π+π-π+π- < 21.1 x 10-6 at the 90% Confidence Level (CL). They also investigate the proper-time dependence of the longitudinal component in the decay and measure the Cp-violating coefficients SL = 0.3± 0.7(stat.) ± 0.2(syst.) and CL = 0.2 ± 0.8(stat.) ± 0.3(syst.). By combining these results with other measurements from the B → ρρ processes and performing an Isospin Analysis, they are able to restrict the unitarity angle α as well as its uncertainty due to penguin contributions, Δα. Namely, α = (92.4-6.5+6.0)° with -1.8° < Δα < 6.7° at 1σ CL.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".