Mixing and CP Violation in Charm Meson Decays Page: 5 of 7

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

A value for y, was extracted from the difference between (TA and TB) and the "CP-ness", of each region, obtained
by integration of these amplitudes.
The result, y, (0.21 0.63 0.78 0.01, where the third uncertainty accounts for uncertainties in the decay
model used to describe the decay amplitude A, was included in Fig. 1(c). This result ranks third in precision for
measurements of yip. It is important that it agrees quite well with all other results from the CP-even modes.
SM expectations for CP asymmetries in time-integrated decays in the charm sector are small. Singly-Cabibbo-
Suppressed (SCS) decays are of particular interest since these allow for asymmetries, at the ~ 0.1% level, from gluonic
penguins [12, 26 28]. Observation of CPV at current sensitivities would be an indication for new physics.
The asymmetry is defined as
Af = F(D-f)F(D-f)
c F(D -f) + F(D ->f)
For D0 asymmetries, there could be contributions from both direct CPV and from mixing. The latter is small since
A1 ~ 0.1%.
Experimentally, measurement of asymmetries at the 10-3 level are limited by uncertainties in asymmetries in
the detection and reconstruction of particles of opposite charge. Also, for D0 decays, efficiencies for D*+ tagging
cannot be assumed to be the same as that for D*-. Forward-backward production asymmetries, resulting from Z0/-
interference and higher order loops in the production of cc quarks, results in asymmetries in the distribution of D
decay products in regions of varying efficiency in the detector.
Calibration of these factors used to rely upon Monte Carlo simulated event (MC) studies, with questionable
assumptions about charge-dependent interaction effects, resulting in systematic uncertainties in A0P's in the 1 - 5%
range. In the past year, new insights in using data rather than MC have led to reduction of these uncertainties to
the 0.2 - 0.4% range [29].
Large samples of CF D0 -> K--r+ decays, selected from the BABAR 386fb-1- data sample, were used to provide
information on the efficiency asymmetries in small momentum and angular range. The underlying assumption was
that the integrated production rates for D0 and D0 were the same. Forward-backward production asymmetries were
dealt with by measuring event yields in forward and backward separately.
Asymmetries obtained in this way, are summarized in Table III. Other, recent measurements are also included.
Table III: Recent measurements of CP decay asymmetries x 10-2. The first uncertainty is statistical, the second is systematic.
Data were used to estimate asymmetries in efficiency in all but ref. [30].
Mode BABAR x10-2 Belle x10-2 CLEO x10-2
D - K-K+ 0.00 + 0.34 + 0.13 [29] -0.43 + 0.30 + 0.11 [31]
D c ->-'+ -0.24 + 0.52 + 0.22 [29] 0.43 + 0.52 + 0.12 [31]
D -> K-K+ O 1.00 + 1.67 + 0.25 [32]
D c ->-0+, -0.31 + 0.41 + 0.17 [32] -0.43 + 0.41 + 1.23 [30]
D+ ->K-K++ -0.03 + 0.84 + 0.29 [33]
These asymmetries are consistent with zero, with most systematic uncertainties much less than 1%. Of particular
interest is the observation that both statistical and systematic uncertainties should scale with the square root of
the number of events. Future measurements from flavour factories may well detect asymmetries at or above the SM

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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/m1/5/ocr/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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