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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Search for heavy neutral leptons in W plus . μplus μ+/- jet decays. Eur. Phys. J. C, 81(3), 248–15pp.
Abstract: A search is performed for heavy neutrinos in the decay of a W boson into two muons and a jet. The data set corresponds to an integrated luminosity of approximately 3.0 fb-1 of proton-proton collision data at centre-of-mass energies of 7 and 8 TeV collected with the LHCb experiment. Both same-sign and opposite-signmuons in the final state are considered. Data are found to be consistent with the expected background. Upper limits on the coupling of a heavy neutrino with the Standard Model neutrino are set at 95% confidence level in the heavy-neutrino mass range from 5 to 50GeV/c2. These are of the order of 10(-3) for lepton-number-conserving decays and of the order of 10(-4) for lepton-number-violating heavy-neutrino decays.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2021). Searches for 25 rare and forbidden decays of D+ and Ds+ mesons. J. High Energy Phys., 06(6), 044–24pp.
Abstract: A search is performed for rare and forbidden charm decays of the form D+-> hl+l -/+, where h(+/-) is a pion or kaon and l((')+/-) is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of 1.6 fb(-1), collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and 90 % confidence level limits on the branching fractions are set between 1.4 x 10(-8) and 6.4 x 10(-6). In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of new excited Bs0 states. Eur. Phys. J. C, 81(7), 601–11pp.
Abstract: A structure is observed in the B +/- K -/+ mass spectrum in a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb-1. The structure is interpreted as the result of overlapping excited Bs0</mml:msubsup> states. With high significance, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to B +/- K -/+, are determined to be m1 = 6063.5 +/- 1.2 (stat) +/- 0.8 (syst) MeV
Gamma 1 = 26 +/- 4 (stat) +/- 4 (syst) MeV
m2 = 6114 +/- 3 (stat) +/- 5 (syst) MeV
Gamma 2 = 66 +/- 18 (stat) +/- 21 (syst) MeV
Alternative values assuming a decay through B +/- K -/+, with a missing photon from the B +/- -> B +/- gamma decay, which are shifted by approximately 45 MeV, are also determined. The possibility of a single state decaying in both channels is also considered. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed Bs20 state is determined to be 0.87 +/- 0.15 (stat)+/- 0.19 (syst).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Measurement of the relative branching fractions of B+ -> h(+) h('+) h('-) decays. Phys. Rev. D, 102(11), 112010–19pp.
Abstract: The relative branching fractions of B+ -> h(+)h('+)h('-) decays, where h((')) is a pion or kaon, are measured. The analysis is performed with a data sample, collected with the LHCb detector, corresponding to an integrated luminosity of 3.0 fb(-1) of pp collisions. The results obtained improve significantly on previous measurements of these quantities, and are important for the interpretation of Dalitz plot analyses of three-body charmless hadronic decays of B+ mesons.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Strong constraints on the b -> s gamma photon polarisation from B-0 -> K(*0)e(+)e(-) decays. J. High Energy Phys., 12(12), 081–25pp.
Abstract: An angular analysis of the B-0 -> K*(0)e(+)e(-) decay is performed using a data sample corresponding to an integrated luminosity of 9 fb(-1) of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (q(2)) interval between 0.0008 and 0.257 GeV2, where the rate is dominated by the B-0 -> K*(0)gamma transition with a virtual photon. The fraction of longitudinal polarisation of the K*(0) meson, F-L, is measured to be F-L = (4.4 +/- 2.6 +/- 1.4)%, where the first uncertainty is statistical and the second systematic. The A(T)(Re) observable, which is related to the lepton forward-backward asymmetry, is measured to be A(T)(Re) = -0.06 +/- 0.08 +/- 0.02. The A(T)((2)) and A(T)(Im) transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be A(T)((2)) = 0.11 +/- 0.10 +/- 0.02 and A(T)(Im) = 0.02 +/- 0.10 +/- 0.01. The results are consistent with Standard Model predictions and provide the world's best constraint on the b -> s gamma photon polarisation.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of Multiplicity Dependent Prompt chi(c1) (3872) and psi (2S) Production in pp Collisions. Phys. Rev. Lett., 126(9), 092001–11pp.
Abstract: The production of chi(c1)(3872) and psi(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2 fb(-1). For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of chi(c1) (3872) to psi(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the chi(c1) (3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the chi(c1)(3872) state are discussed.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Search for the doubly heavy Xi bc0 baryon via decays to D(0)pK(-). J. High Energy Phys., 11(11), 095–21pp.
Abstract: A search for the doubly heavy Xi bc0 baryon using its decay to the D(0)pK(-) final state is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb(-1). No significant signal is found in the invariant mass range from 6.7 to 7.2 GeV/c(2). Upper limits are set at 95% credibility level on the ratio of the Xi bc0 production cross-section times its branching fraction to D(0)pK(-) relative to that of the Lambda b0 -> D0pK- decay. The limits are set as a function of the Xi bc0 mass and lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and in the transverse momentum region from 5 to 25 GeV/c. Upper limits range from 1.7 x 10(-2) to 3.0 x 10(-1) for the considered Xi bc0 mass and lifetime hypotheses.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Amplitude analysis of the B+ -> D+D-K+ decay. Phys. Rev. D, 102(11), 112003–32pp.
Abstract: Results are reported from an amplitude analysis of the B+ -> D+D-K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at root s = 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1). In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D-K+ channel with masses around 2.9 GeV/c(2), and a new spin-0 charmonium resonance in proximity to the spin-2 chi(c2)(3930) state.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Model-Independent Study of Structure in B+ -> D+D-K+ Decays. Phys. Rev. Lett., 125(24), 242001–10pp.
Abstract: The only anticipated resonant contributions to B+ -> D+D-K+ decays are charmonium states in the D+D- channel. A model-independent analysis, using LHCb proton-proton collision data taken at centerof-mass energies of root s = 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1), is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D+D- pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D-K+ channel with masses around 2.9 GeV/c(2).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). First branching fraction measurement of the suppressed decay Xi(0)(c) -> pi(-) Lambda(+)(c). Phys. Rev. D, 102(7), 071101–11pp.
Abstract: The Xi(0)(c) baryon is unstable and usually decays into charmless final states by the c -> sud transition. It can, however, also disintegrate into a pi(-) meson and a Lambda(+)(c) baryon via s quark decay or via cs -> dc weak scattering. The interplay between the latter two processes governs the size of the branching fraction B(Xi(0)(c) -> pi(-) Lambda(+)(c)), first measured here to be (0.55 +/- 0.02 +/- 0.18)%, where the first uncertainty is statistical and second systematic. This result is compatible with the larger of the theoretical predictions that connect models of hyperon decays using partially conserved axial currents and SU(3) symmetry with those involving the heavy-quark expansion and heavy-quark symmetry. In addition, the branching fraction of the normalization channel, B(Xi(+)(c) -> pK(-) pi(+)) = (1.135 +/- 0.002 +/- 0.387)% is measured.
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