Title:

Searches for CP violation in D⁰→K⁻K⁺π⁻π⁺ and D⁰→π⁻π⁺π⁺π⁻ decays at the LHCb experiment

A search for CP violation in the phasespace structures of DO and 15° decays to the final states
K K+nn+ and nn+n+n is presented. The search is carried out with a data set corresponding
to an integrated luminosity of 1.0fb1 collected in 2011 by the LHCb experiment in pp collisions
at a centreofmass ellergy of 7 TeV. For the K1(+nn+ final state, the fourbody phase space is
divided into 32 bins, each bin with approximately 1800 decays. The pvalue under the hypothesis
of no CP violation is 9.1%, and in no bin is a CP asymmetry greater than 6.5% observed. The
phase space of the nn+n+n final state is partitioned into 128 bins, each bin with approximately
2500 decays. The pvalue under the hypothesis of no CP violation is 41 %, and in no bin is a CP
asymmetry greater than 5.5% observed.
A complementary search for CP violation is conducted by measuring the difference between
Podd triple product asymmetries for DO and 15° decays to the final state K1(+n n+. The
measurement is carried out with 2.8 x 105 DO ~ 1( K+nn+ candidates from 3 fb 1 of pp
collisions collected by the LHCb experiment during 2011 and 2012. The difference in Podd
triple products asymmetries, AT, is measured to be consistent with zero,
AT =(  0.19 ± 0.20(stat) ± 0.04(sys) ± 0.31(eff))%,
where the first component of the uncertainty is the statistical uncertainty, the second component
is the combination of the systematical uncertainty, and the third component is the uncertainty
associated with the efficiency evaluation, which should decrease significantly with a larger Monte
Carlo sample. AT is also measured in 16 bins of the fourbody phase space, where each bin has
approximately 18,000 DO ~ K K+nn+ candidates. The pvalue under the hypothesis of no CP
violation is 3.2% and no single bin has a value of AT greater than 2.0%. All results are consistent
with the hypothesis of no CP violation at the current sensitivity.
