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arxiv: 1907.01292 · v1 · pith:RP4KTKKWnew · submitted 2019-07-02 · ✦ hep-ex

Measurements of time-dependent C\!P violation and mixing in charm at LHCb

Tommaso Pajero (for the LHCb Collaboration) This is my paper

Pith reviewed 2026-05-25 10:43 UTC · model grok-4.3

classification ✦ hep-ex
keywords charm mixingCP violationA_GammaLHCbD0 decaystime-dependent analysischarm hadron
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0 comments X

The pith

LHCb reports a new measurement of the CP violation parameter A_Γ from 2015-2016 charm decay data.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents LHCb measurements of mixing and time-dependent CP violation in the charm sector based on a large sample of charm hadron decays. It describes in detail a new determination of the parameter A_Γ using data collected in 2015 and 2016. These results test the size of CP-violating effects in charm mixing at a precision that complements the recent observation of direct CP violation. A sympathetic reader would care because any nonzero A_Γ constrains possible extensions of the Standard Model in the up-quark sector. The paper also gives prospects for further gains in precision with future data sets.

Core claim

Using the 2015-2016 LHCb data set the collaboration extracts a new value of the time-dependent CP violation parameter A_Γ together with charm mixing parameters; the analysis selects D0 decays to CP eigenstates and accounts for detector effects and backgrounds to obtain the reported central value and uncertainty.

What carries the argument

The parameter A_Γ, which measures the difference between the effective decay widths of CP-even and CP-odd D0 states.

If this is right

  • The new A_Γ result enters the world average and tightens the constraint on possible new-physics contributions to charm mixing.
  • Combined with existing mixing-parameter measurements it improves the determination of the parameters x and y.
  • The analysis framework developed here will be applied to larger data samples from later LHC runs.
  • The measurement provides a cross-check on the size of indirect CP violation relative to the observed direct CP violation in charm decays.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Combining this LHCb result with independent measurements from Belle II would further reduce the total uncertainty on A_Γ.
  • The same data sample could be re-examined in additional decay channels to test whether A_Γ is consistent across modes.
  • If future precision reaches the 10^{-5} level, the measurement could begin to probe specific classes of new-physics models that predict enhanced charm mixing.

Load-bearing premise

The time-dependent analysis correctly accounts for all detector-related systematic effects and background contributions when extracting A_Γ and mixing parameters from the selected decay samples.

What would settle it

An independent re-analysis of the identical 2015-2016 LHCb data set that yields a statistically incompatible central value for A_Γ after changing only the background model or selection criteria would falsify the reported result.

Figures

Figures reproduced from arXiv: 1907.01292 by Tommaso Pajero (for the LHCb Collaboration).

Figure 1
Figure 1. Figure 1: FIG. 1. (Top) iso-∆ [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Impact of the measurement [14], presented in [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Fitted asymmetry of the primary decays in [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
read the original abstract

The LHCb experiment has opened the possibility to test mixing and $C\!P$ violation in the charm sector with unprecedented precision thanks to the huge number of charm hadron decays collected, $\mathcal{O}(10^8)$. The first observation of $C\!P$ violation in the decay of charm quarks in March 2019 has been a fundamental achievement. The latest LHCb measurements in the complementary sectors of mixing and time-dependent $C\!P$ violation are illustrated in these proceedings. In particular, a new measurement of the $C\!P$ violation parameter $A_\Gamma$ with 2015--2016 data that was presented for the first time at this conference is described. In the last section, prospects are given for the improvements in precision expected in the next few years.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 1 minor

Summary. The manuscript summarizes recent LHCb measurements of time-dependent CP violation and mixing in the charm sector. It highlights a new measurement of the CP violation parameter A_Γ from 2015--2016 data, presented for the first time at the conference, and outlines prospects for improved precision with larger datasets.

Significance. These results add to the precision tests of CP violation in charm decays following the 2019 observation. LHCb's large charm sample enables competitive constraints on mixing and time-dependent CP parameters; the new A_Γ result is a timely contribution to flavor physics.

minor comments (1)
  1. The manuscript is a conference proceedings contribution; the level of detail on data selection, background modeling, and time-dependent systematic uncertainties is necessarily limited. For a journal submission, expand the description of the A_Γ extraction procedure and associated systematics.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our manuscript and the recommendation for minor revision. No specific major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity; data-driven experimental measurement

full rationale

This LHCb proceedings paper reports experimental measurements of time-dependent CP violation and mixing parameters extracted from collision data. The central claim is a new A_Γ measurement from 2015-2016 data. No derivation chain, self-referential equations, fitted parameters renamed as predictions, or load-bearing self-citations exist. Results come from data fits with background and detector corrections; these are standard analysis steps, not circular reductions. The paper is self-contained against external data benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

As an experimental measurement summary, the claims rest on the validity of LHCb detector performance, calibration, and analysis techniques rather than theoretical free parameters, axioms, or invented entities.

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discussion (0)

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Reference graph

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