Combination of Direct and Indirect CP Violation
(updated 28 December 2011)

 

People working on this:   Marco Gersabeck


Notation: This combination uses measurements of direct and indirect CP violation to extract the level of agreement for a no-CP-violation hypothesis. The observables are:

A Γ ≡ [τ(D0 → K+ K−) − τ(D0 → K+ K− )] / [τ(D0 → K+ K−) + τ(D0 → K+ K− )]

to constrain indirect CP violation via A Γ = -aCPind, and
ΔACP ≡ ACP(KK) - ACP(ππ)

to constrain direct CP violation (aCPdir) via ΔACP = ΔaCPdir + Δ〈t〉/τ aCPind, where Δ〈t〉 is the difference of the average proper time of the KK and ππ modes. A χ2 fit is performed in the plane ΔaCPdir vs. aCPind. For cases where an experiment does not directly quote a value for ΔACP, the difference of the quoted values for ACP(KK) and ACP(ππ) is calculated, adding all uncertainties in quadrature. This may overestimate the systematic uncertainty for the difference as it neglects correlated errors; however, the result is conservative and the effect is small as all measurements are statistically limited. For all measurements, statistical and systematic uncertainties are added in quadrature when calculating the χ2.

For world average values of mixing parameters, click here. For tables of measured CP asymmetries, click here.


Year Experiment Results Δ〈t〉/τ Comment Reference
2007 Belle AΓ = (0.01 ±0.30 (stat.) ±0.15 (syst.))% - 540 fb−1 near Υ(4S) resonance M. Staric et al. (Belle Collab.), Phys. Rev. Lett. 98, 211803 (2007).
2008 BaBar AΓ = (0.26 ±0.36 (stat.) ±0.08 (syst.))% - 384 fb−1 near Υ(4S) resonance B. Aubert et al. (BaBar Collab.), Phys. Rev. D 78, 011105(R) (2008).
2011 LHCb AΓ = (−0.59 ±0.59 (stat.) ±0.21 (syst.))% - 28 pb−1 √ s  = 7 TeV pp collisions R. Aaij et al. (LHCb Collab.), arXiv:1112.4698 (submitted to JHEP).
2008 BaBar ACP(KK) = (0.00 ±0.34 (stat.) ±0.13 (syst.))%
ACP(ππ) = (−0.24 ±0.52 (stat.) ±0.22 (syst.))% 		0.00 385.8 fb−1 near Υ(4S) resonance B. Aubert et al. (BABAR Collab.), Phys. Rev. Lett. 100, 061803 (2008).
2008 Belle ΔACP = (−0.86 ±0.60 (stat.) ±0.07 (syst.))% 0.00 540 fb−1 near Υ(4S) resonance M. Staric et al. (BELLE Collab.), Phys. Lett. B 670, 190 2008).
2011 CDF ΔACP = (−0.46 ±0.31 (stat.) ±0.12 (syst.))% 0.26 5.9 fb−1 √ s  = 1.96 TeV p p  collisions T. Aaltonen et al. (CDF Collab.), arXiv:1111.5023 (submitted to PRD).
2011 LHCb ΔACP = (−0.82 ±0.21 (stat.) ±0.11 (syst.))% 0.10 0.62 fb−1 √ s  = 7 TeV pp collisions R. Aaij et al. (LHCb Collab.), arXiv:1112.0938 (submitted to PRL).
Fit Result
Agreement with no CP violation
CL = 0.00128

 

Combination Plot: The combination plot shows the measurements listed in the Table above for ΔACP and AΓ, where the bands represent ±1σ intervals. The point of no CP violation (0,0) is shown as a filled circle, and two-dimensional 68% CL, 95% CL, and 99.7% CL regions are plotted as ellipses.

 

 

From the fit, the change in χ2 from the minimum value for the no-CPV point (0,0) is 13.33; this corresponds to a CL of 0.00128 for two degrees of freedom. Thus the data is consistent with no CP violation at 0.128% CL. The central values and ± 1σ errors for the individual parameters are:

aCPind = (−0.019 ± 0.232 )%

ΔaCPdir = (−0.645 ± 0.180 )%

 

Comparison Plots: The comparison plots show the measurements listed in the Table above for ΔACP and AΓ, excluding the LHCb result for ΔACP, where the bands represent ±1σ intervals. The point of no CP violation (0,0) is shown as a filled circle, and two-dimensional 68% CL, 95% CL, and 99.7% CL regions are plotted as ellipses. The right-hand plot has the LHCb result for ΔACP superimposed without it being included in the fit.

 

         

 

From the fit, the change in χ2 from the minimum value for the no-CPV point (0,0) is 2.578; this corresponds to a CL of 0.2755 for two degrees of freedom. Thus the data is consistent with no CP violation at 27.6% CL. The central values and ± 1σ errors for the individual parameters are:

aCPind = (−0.030 ± 0.232 )%

ΔaCPdir = (−0.423 ± 0.270 )%

This page is maintained by M. Gersabeck and A. Schwartz and was last updated 11/23/2011 03:04:22