Model-independent measurement of the CKM angle γ using B0 → DK∗0 decays with D → K S 0 π + π − and K S 0 K+K−

Abstract

A binned Dalitz plot analysis of the decays B 0 → DK * 0 , with D → K 0 S π + π − and D → K 0 S K + K − , is performed to measure the observables x ± and y ± , which are related to the CKM angle γ and the hadronic parameters of the decays. The D decay strong phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of the D decay model. With a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb −1 , collected by the LHCb experiment, the values of the CP violation parameters are found to be x + = 0.05 ± 0.35 ± 0.02, x − = −0.31 ± 0.20 ± 0.04, y + = −0.81 ± 0.28 ± 0.06 and y − = 0.31 ± 0.21 ± 0.05, where the first uncertainties are statistical and the second systematic. These observables correspond to values γ = (71 ± 20) • , r B 0 = 0.56 ± 0.17 andThe parameters r B 0 and δ B 0 are the magnitude ratio and strong phase difference between the suppressed and favoured B 0 decay amplitudes, and have been measured in a region of ±50 MeV/c 2 around the K * (892) 0 mass and with the magnitude of the cosine of the K * (892) 0 helicity angle larger than 0.4.

Averages of b-hadron, c-hadron, and $$\tau $$ τ -lepton properties as of summer 2016

“…Both Belle [463] and LHCb [464] have also used this approach to study B 0 → DK * (892) 0 decays. In both cases, the experiments use (150), are determined from the data.…”

“…This procedure should be conservative. In the LHCb B 0 → DK * (892) 0 results [464], the values of c i and s i are constrained to their measured values within uncertainties in the fit to data, and hence the effect is absorbed in their statistical uncertainties. The B 0 → DK * (892) 0 average is performed neglecting the model uncertainties on the Belle results.…”

Measurement of the CKM angle γ at LHCb

“…This is an advantage as the subsequent measurement of γ has well-defined uncertainties and is not subject to uncertainties from phases determined in amplitude models of the D decay which can be difficult to assign. The interference in this B 0 → DK * 0 is rich, and allows for a standalone determination of γ =(71 ± 20) • [10] with a further solution at (71 + 180) • . The 1 and 2 σ contours of γ vs r B 0 and γ vs δ B 0 are depicted in Fig.…”

Determination of Strong-Phase Parameters in D→KS,L0π+π−

“…The total integrated luminosity of our sample is 2.93 fb −1 [17], 3.6 times that of the CLEO measurement. The expected improvement in precision of the strong-phase parameters will significantly reduce the uncertainties of determinations of γ [15,[18][19][20][21] that utilize D → K 0 S;L π þ π − . Additionally, improved knowledge of these strong-phase parameters will have significant impact in other applications, including measurements of the CKM angle β (also denoted ϕ 1 ) through time-dependent analyses of B 0 → Dh 0 [22] (where h is a light meson) and B 0 → Dπ þ π − [23], as well as measurements of charm mixing and CP violation [24][25][26][27].…”

“…Therefore, the uncertainty on γ arising from knowledge of the charm strong phases is approximately a factor of three smaller than was possible with the CLEO measurements. For the first time, the dominant systematic uncertainty for γ measurement from the strong-phase parameters will be constrained to around 1°, or less, for γ measurements with future B experiments [15,[18][19][20][21]. The predicted statistical uncertainties on γ from LHCb prior to the start of highluminosity LHC operation in the mid 2020s, and from Belle II are expected to be around 1.5° [35,36].…”