Observation of Time-Reversal Violation in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>B</mml:mi><mml:mn>0</mml:mn></mml:msup></mml:math>Meson System
Bibliographic record
Abstract
Although $CP$ violation in the $B$ meson system has been well established by the $B$ factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral $B$ mesons into definite flavor states (${B}^{0}$ or ${\overline{B}}^{0}$), and $J/\ensuremath{\psi}{K}_{L}^{0}$ or $c\overline{c}{K}_{S}^{0}$ final states (referred to as ${B}_{+}$ or ${B}_{\ensuremath{-}}$), allow comparisons between the probabilities of four pairs of $T$-conjugated transitions, for example, ${\overline{B}}^{0}\ensuremath{\rightarrow}{B}_{\ensuremath{-}}$ and ${B}_{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{B}}^{0}$, as a function of the time difference between the two $B$ decays. Using $468\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs produced in $\ensuremath{\Upsilon}(4S)$ decays collected by the BABAR detector at SLAC, we measure $T$-violating parameters in the time evolution of neutral $B$ mesons, yielding $\ensuremath{\Delta}{S}_{T}^{+}=\ensuremath{-}1.37\ifmmode\pm\else\textpm\fi{}0.14(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{syst})$ and $\ensuremath{\Delta}{S}_{T}^{\ensuremath{-}}=1.17\ifmmode\pm\else\textpm\fi{}0.18(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.11(\mathrm{syst})$. These nonzero results represent the first direct observation of $T$ violation through the exchange of initial and final states in transitions that can only be connected by a $T$-symmetry transformation.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.002 |
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".