LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Angular Analysis of D0 -> x plus x-mu plus mu- and D0 -> K plus K-mu plus mu- Decays and Search for CP Violation. Phys. Rev. Lett., 128(22), 221801–11pp.
Abstract: The first full angular analysis and an updated measurement of the decay-rate CP asymmetry of the D0→π+π−μ+μ− and D0→K+K−μ+μ− decays are reported. The analysis uses proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data set corresponds to an integrated luminosity of 9 fb−1. The full set of CP-averaged angular observables and their CP asymmetries are measured as a function of the dimuon invariant mass. The results are consistent with expectations from the standard model and with CP symmetry.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Vidal, J., et al. (2022). Measurement of the charm mixing parameter y(CP)-y(CP)(K pi) using two-body D-0 meson decays. Phys. Rev. D, 105(9), 092013–17pp.
Abstract: A measurement of the ratios of the effective decay widths of D-0 -> pi(-)pi(+) and D-0 -> K- K+ decays over that of D-0 -> K-pi(+) decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb(-1). These observables give access to the charm mixing parameters y(CP)(pi pi) – y(CP)(K pi )and y(CP)(KK) -y(CP)(K pi), and are measured as y(CP)(pi pi) – y(CP)(K pi) = (6.57 +/- 0.53 +/- 0.16) x 10(-3), y(CP)(KK) – y(CP)(K pi) = (7.08 +/- 0.30 +/- 0.14) x 10(-3), where the first uncertainties are statistical and the second systematic. The combination of the two measurements is Y-CP – y(CP)(K pi) = (6.96 +/- 0.26 +/- 0.13) x 10(-3), which is four times more precise than the previous world average.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Observation of an exotic narrow doubly charmed tetraquark. Nat. Phys., 18, 751–754.
Abstract: Conventional, hadronic matter consists of baryons and mesons made of three quarks and a quark-antiquark pair, respectively(1,2). Here, we report the observation of a hadronic state containing four quarks in the Large Hadron Collider beauty experiment. This so-called tetraquark contains two charm quarks, a (u) over bar and a (d) over tilde quark. This exotic state has a mass of approximately 3,875 MeV and manifests as a narrow peak in the mass spectrum of (DD0)-D-0 pi(+) mesons just below the D*D-+(0) mass threshold. The near-threshold mass together with the narrow width reveals the resonance nature of the state.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Study of the doubly charmed tetraquark T-cc(+). Nat. Commun., 13(1), 3351–19pp.
Abstract: Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the (DD0)-D-0 pi(+) mass spectrum just below the D*+D-0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T-cc(+), tetraquark with a quark content of cc (u) over bar(d) over bar and spin-parity quantum numbers J(P) =1(+). Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*(+) mesons is consistent with the observed D-0 pi(+) mass distribution. To analyse the mass of the resonance and its coupling to the DID system, a dedicated model is developed under the assumption of an isoscalar axial-vector T-cc(+), state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T-cc(+), state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Constraints on the CKM angle gamma from B-+/- -> Dh(+/-) decays using D -> h(+/-)h '(-/+)pi(0) final states. J. High Energy Phys., 07(7), 099–24pp.
Abstract: A data sample collected with the LHCb detector corresponding to an integrated luminosity of 9 fb(-1) is used to measure eleven CP violation observables in B-+/- -> Dh(+/-) decays, where h is either a kaon or a pion. The neutral D meson decay is reconstructed in the three-body final states: K-+/-pi(-/+)pi(0); pi(+)pi(-)pi(0); K+ K- pi(0) and the suppressed pi K-+(-/+)pi(0) combination. The mode where a large CP asymmetry is expected, B-+/- -> [K-+/-pi(-/+)pi(0)] K-D(+/-), is observed with a significance greater than seven standard deviations. The ratio of the partial width of this mode relative to that of the favoured mode, B-+/- -> [K-+/-pi(-/+)pi(0)] K-D(+/-), is R-ADS(K) = (1.27 +/- 0.16 +/- 0.02) x 10(-2). Evidence for a large CP asymmetry is also seen: A(ADS(K)) = – 0.38 +/- 0.12 +/- 0.02. Constraints on the CKM angle gamma are calculated from the eleven reported observables.
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