Search for CP violation in the phase space of D0 → K0 SK±π ∓ decays with the energy test

Abstract

A search for CP violation in D0 → K0 SK+π − and D0 → K0 SK−π + decays is reported. The search is performed using an unbinned model-independent method known as the energy test that probes local CP violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 fb−1 collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of √ s = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the D0 → K0 SK−π + and D0 → K0 SK+π − modes, respectively. The method is validated using D0 → K−π +π −π + and D0 → K0 Sπ +π − decays, where CP-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP symmetry in both the D0 → K0 SK−π + and the D0 → K0 SK+π − decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively.