BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2020). Search for Rare or Forbidden Decays of the D-0 Meson. Phys. Rev. Lett., 124(7), 071802–8pp.
Abstract: We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type D-0 -> h'(-) h(-) l'(+) l(+) and D-0 -> h'(-) h(+) l'(+/-) l(-/+), where h and h' represent a K or pi meson and l and l' an electron or muon. The analysis is based on 468 fb(-1) of e(+) e(-) annihilation data collected at or close to the Upsilon(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range (1.0-30.6) x 10(-7). The limits are between 1 and 3 orders of magnitude more stringent than 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). Observation of a Resonant Structure near the Ds+Ds- Threshold in the B+ -> Ds+Ds- K+ Decay. Phys. Rev. Lett., 131(7), 071901–12pp.
Abstract: An amplitude analysis of the B thorn & RARR; D thorn s D-s K thorn decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A near-threshold peaking structure, referred to as X(3960), is observed in the D thorn s D-s invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width, and the quantum numbers of the structure are measured to be 3956 1 5 1 10 MeV, 43 1 13 1 8 MeV, and JPC = 0 thorn thorn , respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of cc over bar ss over bar quarks. Evidence for an additional structure is found around 4140 MeV in the D thorn s D-s invariant mass, which might be caused either by a new resonance with the 0 thorn thorn assignment or by a J=& psi;& phi; & LRARR; D thorn s D-s coupled-channel effect.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of J/psi p Resonances Consistent with Pentaquark States in Lambda(0)(b) -> J/psi K(-)p Decays. Phys. Rev. Lett., 115(7), 072001–15pp.
Abstract: Observations of exotic structures in the J/psi p channel, which we refer to as charmonium-pentaquark states, in Lambda(0)(b) --> J/psi K(-)p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb(-1) acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/psi p mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380 +/- 8 +/- 29 MeV and a width of 205 +/- 18 +/- 86 MeV, while the second is narrower, with a mass of 4449.8 +/- 1.7 +/- 2.5 MeV and a width of 39 +/- 5 +/- 19 MeV. The preferred J(P) assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
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LHCb Collaboration, Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Observation of a New Xi(-)(b) Resonance. Phys. Rev. Lett., 121(7), 072002–12pp.
Abstract: From samples of pp collision data collected by the LHCb experiment at root s = 7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb(-1), respectively, a peak in both the Lambda(0)(b) K- and Xi(0)(b)pi(-) invariant mass spectra is observed. In the quark model, radially and orbitally excited Xi(-)(b) resonances with quark content bds are expected. Referring to this peak as Xi(b)(6227)(-), the mass and natural width are measured to be m(Xi b(6227))(-) = 6226.9 +/- 2.0 +/- 0.3 +/- 0.2 MeV/c(2) and Gamma(Xi b(6227))- = 18.1 +/- 5.4 +/- 1.8 MeV/c(2), where the first uncertainty is statistical, the second is systematic, and the third, on m(Xi b(6227))(-), is due to the knowledge of the Lambda(0)(b) baryon mass. Relative production rates of the Xi(b)(6227)(-) -> Lambda K-0(b)- and Xi(b)(6227)(-) -> Xi(0)(b)pi(-) decays are also reported.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2019). Search for a Stable Six-Quark State at BABAR. Phys. Rev. Lett., 122(7), 072002–7pp.
Abstract: Recent investigations have suggested that the six-quark combination uuddss could be a deeply bound state (S) that has eluded detection so far, and a potential dark matter candidate. We report the first search for a stable, doubly strange six-quark state in (sic) > S (Lambda) over bar(Lambda) over bar decays based on a sample of 90 x 10(6)(sic)(2S) and 110 x 10(6)(sic)(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined (sic)(2S, 3S) -> S (Lambda) over bar(Lambda) over bar branching fraction in the range (1.2-1.4) x 10(-7) are derived for m(s) < 2.05 GeV. These bounds set stringent limits on the existence of such exotic particles.
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