ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Search for the Production of a Long-Lived Neutral Particle Decaying within the ATLAS Hadronic Calorimeter in Association with a Z Boson from pp Collisions at root s=13 TeV. Phys. Rev. Lett., 122(15), 151801–19pp.
Abstract: This Letter presents a search for the production of a long-lived neutral particle (Z(d)) decaying within the ATLAS hadronic calorimeter, in association with a standard model (SM) Z boson produced via an intermediate scalar boson, where Z -> l(+) l(-) (l = e, mu). The data used were collected by the ATLAS detector during 2015 and 2016 pp collisions with a center-of-mass energy of root s = 13 TeV at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 +/- 0.8 fb(-1). No significant excess of events is observed above the expected background. Limits on the production cross section of the scalar boson times its decay branching fraction into the long-lived neutral particle are derived as a function of the mass of the intermediate scalar boson, the mass of the long-lived neutral particle, and its c tau from a few centimeters to one hundred meters. In the case that the intermediate scalar boson is the SM Higgs boson, its decay branching fraction to a long-lived neutral particle with a c tau approximately between 0.1 and 7 m is excluded with a 95% confidence level up to 10% for m(zd) between 5 and 15 GeV.
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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. (2019). First Measurement of Charm Production in its Fixed-Target Configuration at the LHC. Phys. Rev. Lett., 122(13), 132002–12pp.
Abstract: The first measurement of heavy-flavor production by the LHCb experiment in its fixed-target mode is presented. The production of J/psi and D-0 mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon center-of-mass energies of root s(NN) = 86.6 and 110.4 GeV, respectively. The J/psi and D-0 production cross sections in pHe collisions in the rapidity range [2, 4.6] are found to be sigma(J/psi) = 652 +/- 33(stat) +/- 42(syst) nb/nucleon and sigma(D0) = 80.8 +/- 2.4(syst) +/- 6.3(syst) μb/nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-x region.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2019). Observation of the Decay D-0 -> K- pi(+) e(+) e(-). Phys. Rev. Lett., 122(8), 081802–8pp.
Abstract: We report the observation of the rare charm decay D-0 -> K-pi(+)e(+)e(-), based on 468 fb(-1) of e(+)e(-) annihilation data collected at or close to the center-of-mass energy of the (sic)(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675 < m(e(+)e(-)) < 0.875 GeV/c(2) of the electron-positron pair to be B(D-0 -> K-pi(+)e(+)e(-)) = (4.0 +/- 0.5 +/- 0.2 +/- 0.1) x 10(-6), where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D-0 -> K-pi(+)pi(+)pi(-) used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D-0 -> K-pi(+)mu(+)mu(-) branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m(e(+)e(-)), where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B(D-0 -> K-pi(+)e(+)e(-)) < 3.1 x 10(-6).
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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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Timar, J. et al, & Algora, A. (2019). Experimental Evidence for Transverse Wobbling in Pd-105. Phys. Rev. Lett., 122(6), 062501–6pp.
Abstract: New rotational bands built on the nu(h(11/2)) configuration have been identified in Pd-105. Two bands built on this configuration show the characteristics of transverse wobbling: the Delta I = 1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the A similar to 100 mass region.
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