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

Understand

A search for time-integrated $CP$ violation in the Cabibbo-suppressed decay $\mbox{$D^0\rightarrow\pi^+\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 world's best sensitivity to $CP$ violation in this decay is obtained.