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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Evidence of W gamma gamma Production in pp Collisions at root s=8 TeV and Limits on Anomalous Quartic Gauge Couplings with the ATLAS Detector. Phys. Rev. Lett., 115(3), 031802–18pp.
Abstract: This Letter reports evidence of triple gauge boson production pp -> W(l nu)gamma gamma + X, which is accessible for the first time with the 8 TeV LHC data set. The fiducial cross section for this process is measured in a data sample corresponding to an integrated luminosity of 20.3 fb(-1), collected by the ATLAS detector in 2012. Events are selected using the W boson decay to e nu or μnu as well as requiring two isolated photons. The measured cross section is used to set limits on anomalous quartic gauge couplings in the high diphoton mass region.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of the B-s(0) -> eta 'eta ' Decay. Phys. Rev. Lett., 115(5), 051801–9pp.
Abstract: The first observation of the B-s(0) -> eta'eta' decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb(-1) of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31 +/- 0.64(stat) +/- 0.28(syst) +/- 0.12(norm)] x 10(-5), where the third uncertainty comes from the B-+/- -> eta'K-+/- branching fraction that is used as a normalization. In addition, the charge asymmetries of B-+/- -> eta'K-+/- and B-+/- -> phi K-+/-, which are control channels, are measured to be (-0.2 +/- 1.3)% and (+1.7 +/- 1.3)%, respectively. All results are consistent with theoretical expectations.
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Tain, J. L. et al, Valencia, E., Algora, A., Agramunt, J., Rubio, B., Estevez, E., et al. (2015). Enhanced gamma-Ray Emission from Neutron Unbound States Populated in beta Decay. Phys. Rev. Lett., 115(6), 062502–5pp.
Abstract: Total absorption spectroscopy is used to investigate the beta-decay intensity to states above the neutron separation energy followed by gamma-ray emission in Br-87,Br-88 and Rb-94. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large. intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The gamma branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For Br-87 and Br-88 the gamma branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich Rb-94 the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proves to be correct, leads to a similar increase in the (n, gamma) cross section that would have an impact on r process abundance calculations.
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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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Maiezza, A., Nemevsek, M., & Nesti, F. (2015). Lepton Number Violation in Higgs Decay at LHC. Phys. Rev. Lett., 115(8), 081802–7pp.
Abstract: We show that within the left-right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs boson with the triplet that breaks parity. As a result, the Higgs boson can act as a gateway to the origin of the heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign dileptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches.
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