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), Jaimes Elles, S. J., Jashal, B. K., Martinez Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Test of lepton flavor universality using B0→D*−τ+ντ decays with hadronic τ channels. Phys. Rev. D, 108, 012018–18pp.
Abstract: The branching fraction B(B0→D*−τ+ντ) is measured relative to that of the normalization mode B0→D*−π+π−π+ using hadronic τ+→π+π−π+(π0)¯ντ decays in proton-proton collision data at a center-of-mass energy of 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 2 fb−1. The measured ratio is B(B0→D*−τ+ντ)/B(B0→D*−π+π−π+)=1.70±0.10+0.11−0.10, where the first uncertainty is statistical and the second is related to systematic effects. Using established branching fractions for the B0→D*−π+π−π+ and B0→D*−μ+νμ modes, the lepton universality test R(D*−)≡B(B0→D*−τ+ντ)/B(B0→D*−μ+νμ) is calculated, R(D*−)=0.247±0.015±0.015±0.012, where the third uncertainty is due to the uncertainties on the external branching fractions. This result is consistent with the Standard Model prediction and with previous measurements.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). First observation of the B+→D+sD−sK+ decay. Phys. Rev. D, 108, 034012–14pp.
Abstract: The B+→D+sD−sK+ decay is observed for the first time using proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. Its branching fraction relative to that of the B+→D+D−K+ decay is measured to be B(B+→D+sD−sK+)B(B+→D+D−K+)=0.525±0.033±0.027±0.034, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the D±s→K∓K±π± and D±→K∓π±π± decays. This measurement fills an experimental gap in the knowledge of the family of Cabibbo-favored ¯b→¯cc¯s transitions and opens the path for unique studies of spectroscopy in future.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Search for K0S(L)→μ+μ−μ+μ− decays at LHCb. Phys. Rev. D, 108, L031102–12pp.
Abstract: A search for K0S(L)→μ+μ−μ+μ− decays is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.1 fb−1. No evidence for signal is found. The 90% confidence level upper limits are the first set for both decays and are B(K0S→μ+μ−μ+μ−)<5.1×10−12 and B(K0L→μ+μ−μ+μ−)<2.3×10−9.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). First observation of B+ -> D-s(+) K+ K- decays and a search for B+ -> D-s(+) phi decays. J. High Energy Phys., 01(1), 131–22pp.
Abstract: A search for B+ -> D-s(+) K+ K- decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb(-1), collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be B(B+ -> D-s(+) K+ K-) = (7.1 +/- 0.5 +/- 0.6 +/- 0.7) x 10(-6), where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+ -> D-s(+)(D) over bar (0). A search is also performed for the pure annihilation decay B+ -> D-s(+)(D) over bar (0). No significant signal is observed and a limit of B(B+ -> D-s(+) phi) < 4.9 x 10(-7) (4.2 x 10(-7)) is set on the branching fraction at 95% (90%) confidence level.
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