Updated measurement of decay-time-dependent CP asymmetries in D0→K+

Abstract

A search for decay-time-dependent charge-parity (CP) asymmetry in D 0 → K þ K − and D 0 → π þ π − decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb −1. The D 0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D 0 andD 0 mesons are determined to be A Γ ðK þ K − Þ ¼ ð−4.3 AE 3.6 AE 0.5Þ × 10 −4 and A Γ ðπ þ π − Þ ¼ ð2.2 AE 7.0 AE 0.8Þ × 10 −4 , where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A Γ ðK þ K − Þ ¼ ð−4.4 AE 2.3 AE 0.6Þ × 10 −4 and A Γ ðπ þ π − Þ ¼ ð2.5 AE 4.3 AE 0.7Þ × 10 −4 .

A Review of CP Violation Measurements in Charm at LHCb

“…Assuming no final-state dependency, and taking account of the correlation between the systematic uncertainties, the combination of the two values gives ∆Y = (−2.7 ± 1.3 ± 0.3) × 10 −4 , consistent with zero within two standard deviations [80]. The combination with previous LHCb measurements [25,26,28] leads to…”

“…The production cross-section of charm in proton-proton (pp) (or proton-antiproton) collisions is much larger than that at the B-factories, for example σ(pp → ccX) = (2369 ± 12) µb at √ s = 13 TeV in the LHCb acceptance [21], whereas σ(e + e − → γ * → cc) = 1.3 nb at √ s = 10.58 GeV. Despite the large hadronic background, not present in the low-multiplicity environment of the e + e − machines, LHCb was therefore able to collect the largest sample ever produced of charm-hadron decays, performing a number of measurements of observables related to CP violation in the charm sector, such as: searches for direct CP asymmetry in D + (s) decays [22][23][24]; time-dependent CP violation in singly Cabibbo suppressed (SCS) D 0 decays [25][26][27][28]; direct CP asymmetries in SCS D 0 decays [29][30][31]; CP violation in mixing using D 0 → K + π − decays [32,33]; CP violation in multi-body D 0 decays [34][35][36][37][38][39]; CP violation in D 0 decays into final states with K 0 s [40,41]; and CP violation in baryon decays [42,43]. The measurement of…”

“…The ∆Y f parameter is approximately equal, up to 1% relative corrections (For a detailed description of the theoretical parametrisation of mixing in D 0 decays, see Refs [56,[25,26,28] collaborations, and the world average, assuming no difference is present between the K + K − and π + π − final states, is ∆Y = (3.1 ± 2.0) × 10 −4 [79]. The measurement of ∆Y f performed by LHCb with data collected during the LHC Run 2, corresponding to an integrated luminosity of 6 fb −1 , using D * + → D 0 π + decays originated from primary pp interactions, is reported here.…”

Mixing and indirect CP violation in charm decays at LHCb

“…The final value measured by the LHCb experiment with the Run 1 and 2 data samples, corresponding to 9 fb −1 of integrated luminosity, is obtained by combining the two above measurements with those reported in Refs. [20][21][22], and is equal to…”

Mixing and $CP$ violation in $D^0 \to K^- π^+$ decays

“…The y f CP parameter has been analogously measured from the time-dependent ratio of the decay rates of CS to RS decays [18],…”