Search for CP violation in the phase space of $$ {D}^0\to {K}_S^0{K}^{\pm }{\pi}^{\mp } $$ decays with the energy test

Abstract

A search for CP violation in

D 0

→

K S 0

K +

π −

$$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ and

D 0

→

K S 0

K −

π +

$$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ 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

$$ \sqrt{s} $$ = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the

D 0

→

K S 0

K −

π +

$$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and

D 0

→

K S 0

K +

π −

$$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ modes, respectively. The method is validated using D0 → K−π+π−π+ and

D 0

→

K S 0

π +

π −

$$ {D}^0\to {K}_S^0{\pi}^{+}{\pi}^{-} $$ 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

D 0

→

K S 0

K −

π +

$$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and the

D 0

→

K S 0

K +

π −

$$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively.