Search for $CP$ violation in the phase space of $D^0rightarrowpi^+pi^-pi^+pi^-$ decays

A search for time-integrated $CP$ violation in the Cabibbo-suppressed decay $mbox{$D^0rightarrowpi^+pi^-pi^+pi^-$}$ is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for $P$-even $CP$ asymmetries and, for the first time, is extended to probe the $P$-odd case. Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb detector at centre-of-mass energies of $sqrt{s}=$7 TeV and 8 TeV, the worlds best sensitivity to $CP$ violation in this decay is obtained. The data are found to be consistent with the hypothesis of $CP$ symmetry with a $p$-value of $(4.6pm0.5)%$ in the $P$-even case, and marginally consistent with a $p$-value of $(0.6pm0.2)%$ in the $P$-odd case, corresponding to a significance for $CP$ non-conservation of 2.7 standard deviations.