Mixing and CP Violation in Charm Meson Decays Page: 4 of 7

34th International Conference on High Energy Physics, Philadelphia, 2008

Sample x" y"
D0 and D [ 2.61+0 6(stat.) + 0.39(syst.)]% [-0.06+0 6{(stat.) + 0.34(syst.)]%
D0 only [ 2.53+ . (stat.) + 0.39(syst.)]% [-0.05+.3(stat.) + 0.50(syst.)]%
3 only [ 3.55 08 (stat.) + 0.65(syst.)]% [-0.54 + .4(stat.) + 0.41(syst.)]%

The significance of the mixing signal in the fit to the combined D0 and D0 samples, ignoring CPV, was 3.2-.
Separate fits to each sample show no evidence for CPV.
Two other channels have recently been analyzed in which the mixing signal was of less significance, but where
mixing parameters were, nevertheless, measurable.
3.1. D0 -> Ksr r+ Decays
Analysis of this channel, pioneered by the CLEO collaboration [22] is of great interest due to the presence of
CP-eigenstates in the final state. These tie the phase of the amplitudes for D0 and D0 decay amplitudes together,
so that 3Kn. in Eq. (??) is zero. Thus, measurements of x, y and the two CPV parameters q/pj and OK,,-,+ can
be made free of unknown phases.
CLEO's analysis used a 9f b-1 e+e- sample and found only an upper limit for mixing parameters (-4.7 < x < 8.6)%
and ( 6.1 < y < 3.5)% at 95% CL. The Belle collaboration has repeated the analysis with a 540f b-1 sample (534K
events) [4], observing mixing at the 2.4- significance. The parameter values obtained are summarized in Table II.
It is noteworthy that the value for y here is not consistent with the world average value for y, 1.072 0.275%
discussed in section 2.2.
Table II: Mixing parameters obtained from the Belle analysis of D0 -> Ks -w+ decays. The third error is that due to
uncertainties in the model used to define the Dalitz plot amplitudes.
x y Iq/pl Arg(q/p)
(0.80 + 0.29+00+0.I)% (0.33+0.24+00 .0+0 )% 0.86+0.29+ + + 0.08 (-14++
There was no evidence for CPV since the magnitude of q/p was consistent with unity and its phase was zero.
3.2. CP-odd Final States
A new result from Belle [23]. has examined lifetime differences between the decays to the CP-odd final state
Do -> Ks with decays to the CP-even background and 0 sideband regions. A novel method was chosen over a
time-dependent analysis of the whole KsK-K+ Dalitz plot like that used for the Ks-7r+ channel which required
a flavour-tagged sample of Do's from D* decays. The sample size available was thereby enhanced almost threefold.
Approximately 130K D0 -> K-K+Ks decays were extracted from a 697fb-1 sample of e+e- collisions, with no
attempt to distinguish D0 from D0. Lifetimes TA and TB were measured, respectively, for events in the K- K+ invari-
ant mass regions A (containing the 0) and B (narrow sidebands above and below the 0 where CP-even ao(980)Ks,
fo(980)Ks and non-resonant decays were dominant).
Decay amplitudes A1,2 A(so, s+) A(so, s-)]/2 were obtained from a fit [24, 25] to the distribution of events
in the K-K+Ks Dalitz plot. Here, so, s- and s+ were, respectively, K-K+, KsK- and KsK+ squared invariant
mass combinations. Neglecting CPV, A1,22 should have approximately exponential time-dependences with lifetimes
T1,2 = /(1 y,), and their interference A*A2 should be zero when integrated over the s+ coordinate.


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Meadows, B & U., /Cincinnati. Mixing and CP Violation in Charm Meson Decays, article, August 26, 2010; [California]. (https://digital.library.unt.edu/ark:/67531/metadc1015050/m1/4/ocr/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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