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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2017). Search for Invisible Decays of a Dark Photon Produced in e(+)e(-) Collisions at BABAR. Phys. Rev. Lett., 119(13), 131804–7pp.
Abstract: We search for single-photon events in 53 fb(-1) of e(+)e(-) collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A' through the process e(+)e(-) -> gamma A'; A' -> invisible. Such particles, referred to as “dark photons,” are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A' to e(+)e(-) in the mass range m(A') <= 8 GeV. In particular, our limits exclude the values of the A' coupling suggested by the dark-photon interpretation of the muon (g – 2)(mu) anomaly, as well as a broad range of parameters for the dark-sector models.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for Dark Matter Produced in Association with a Higgs Boson Decaying to b(b)over-bar Using 36 fb(-1) of pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 119(18), 181804–21pp.
Abstract: Several extensions of the standard model predict associated production of dark-matter particles with a Higgs boson. Such processes arc searched for in final states with missing transverse momentum and a Higgs boson decaying to a b (b) over bar pair with the ATLAS detector using 36.1 fb(-1) of pp collisions at a center-of mass energy of 13 TeV at the LHC. The observed data are in agreement with the standard model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for Heavy Higgs Bosons A/H Decaying to a Top Quark Pair in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 119(19), 191803–20pp.
Abstract: A search for heavy pseudoscalar (A) and scalar (H) Higgs bosons decaying into a top quark pair (t (t) over bar) has been performed with 20.3 fb(-1) of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy root s = 8 TeV. Interference effects between the signal process and standard model t (t) over bar production, which are expected to distort the signal shape from a single peak to a peak-dip structure, are taken into account. No significant deviation from the standard model prediction is observed in the t (t) over bar invariant mass spectrum in final states with an electron or muon, large missing transverse momentum, and at least four jets. The results are interpreted within the context of a type-II two-Higgs-doublet model. Exclusion limits on the signal strength are derived as a function of the mass m(A/H) and the ratio of the vacuum expectation values of the two Higgs fields, tan beta, for m(A/H) > 500 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. (2017). Search for Baryon-Number Violating Xi(0)(b) Oscillations. Phys. Rev. Lett., 119(18), 181807–9pp.
Abstract: A search for baryon-number violating Xi(0)(b) oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The baryon number at the moment of production is identified by requiring that the Xi(0)(b) come from the decay of a resonance Xi(b)*(-) -> Xi(0)(b)pi(-) or Xi(b)'(-) -> Xi(0)(b)pi(-) and the baryon number at the moment of decay is identified from the final state using the decays Xi(0)(b) -> Xi(0)(c)pi(-) , Xi(+-)(c) -> pK(-)pi(+). No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of omega < 0.08 ps(-1), where. is the associated angular frequency.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2017). Measurement of the D* (2010)(+) -D+ Mass Difference. Phys. Rev. Lett., 119(20), 202003–7pp.
Abstract: We measure the mass difference, Delta m(+), between the D* (2010)(+) and the D+ using the decay chain D* (2010)(+) -> D+ pi(0) with D+ -> K- pi(+)pi(+). The data were recorded with the BABAR detector at center-of-mass energies at and near the (sic)(4S) resonance, and correspond to an integrated luminosity of approximately 468 fb(-1). We measure Delta m(+) = (140601.0 +/- 6.8[stat] +/- 12.9[syst]) keV. We combine this result with a previous BABAR measurement of Delta m(0) = m(D* (2010)(+)) – m(D-0) to obtain Delta m(D) = m(D+) – m(D-0) = (4824.9 +/- 6.8[stat] +/- 12.9[syst]) keV. These results are compatible with and approximately five times more precise than the Particle Data Group averages.
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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. (2017). chi(c1) and chi(c2) Resonance Parameters with the Decays chi(c1,c2) -> J/psi mu(+)mu(-). Phys. Rev. Lett., 119(22), 221801–9pp.
Abstract: The decays chi(c1) -> J/psi mu(+)mu(-) and chi(c1) -> J/psi mu(+)mu(-) are observed and used to study the resonance parameters of the chi(c1) and chi(c2) mesons. The masses of these states are measured to be m(chi(c1)) = 3510.71 +/- 0.04(stat) +/- 0.09(syst) MeV and m(chi(c2)) = 3556.10 +/- 0.06(stat) +/- 0.11(syst) MeV, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(chi(c2)) – m(chi(c1)) = 45.39 +/- 0.07(stat) +/- 0.03(syst) MeV. The natural width of the chi(c2) meson is measured to be Gamma(chi(c2)) = 2.10 +/- 0.20(stat) +/- 0.02(syst) MeV. These results are in good agreement with and have comparable precision to the current world averages.
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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. (2017). First Observation of the Rare Purely Baryonic Decay B0 -> p p-bar. Phys. Rev. Lett., 119(23), 232001–10pp.
Abstract: The first observation of the decay of a B0 meson to a purely baryonic final state, B-0 -> p$(p)over-bar-$ , is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb(-1). The branching fraction is determined to be B(B-0 -> p$(p)over-bar-$) = (1.25 +/- 0.27 +/- 0.18) x 10(-8), where the first uncertainty is statistical and the second systematic. The decay mode B-0 -> p$(p)over-bar-$ is the rarest decay of the B-0 meson observed to date. The decay B-s(0 )-> p$(p)over-bar-$ is also investigated. No signal is seen and the upper limit B(B-s(0) -> p$(p)over-bar-$) < 1.5 x 10(-8) at 90% confidence level is set on the branching fraction.
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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. (2017). Observation of D-0 meson decays to pi(+) pi(-) mu(+) mu(-) and K+ K- mu(+) mu(-) final states. Phys. Rev. Lett., 119(18), 181805–10pp.
Abstract: The first observation of the D-0 -> pi(+) pi(-) mu(+) mu(-) and D-0 -> K+ K- mu(+) mu(-) decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2 fb(-1) of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay D-0 -> K- pi(+) [mu(+) mu(-)](rho 0/omega), where the two muons are consistent with coming from the decay of a rho(0) or omega meson. The results are B(D-0 -> pi(+) pi(-) mu(+) mu(-)) = (9.64 +/- 0.48 +/- 0.51 +/- 0.97) x 10(-7) and B(D-0 -> K+ K- mu(+) mu(-)) = (1.54 +/- 0.27 +/- 0.09 +/- 0.16) x 10(-7), where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.
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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). Search for Dark Photons Produced in 13 TeV pp Collisions. Phys. Rev. Lett., 120(6), 061801–11pp.
Abstract: Searches are performed for both promptlike and long-lived dark photons, A', produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A' -> mu(+)mu(-) decays and a data sample corresponding to an integrated luminosity of 1.6 fb(-1) collected with the LHCb detector. The promptlike A' search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A' search is restricted to the low-mass region 214 < mo(A') < 350 MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the gamma-A' kinetic-mixing strength. The constraints placed on promptlike dark photons are the most stringent to date for the mass range 10.6 < m(A') < 70 GeV, and are comparable to the best existing limits for m(A') < 0.5 GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.
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NEXT Collaboration(McDonald, A. D. et al), Alvarez, V., Benlloch-Rodriguez, J. M., Botas, A., Carcel, S., Carrion, J. V., et al. (2018). Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging. Phys. Rev. Lett., 120(13), 132504–6pp.
Abstract: A new method to tag the barium daughter in the double-beta decay of Xe-136 is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba++) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (similar to 2 nm), and detected with a statistical significance of 12.9 sigma over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.
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