Agullo, I., del Rio, A., & Navarro-Salas, J. (2017). Electromagnetic Duality Anomaly in Curved Spacetimes. Phys. Rev. Lett., 118(11), 111301–5pp.
Abstract: The source-free Maxwell action is invariant under electric-magnetic duality rotations in arbitrary spacetimes. This leads to a conserved classical Noether charge. We show that this conservation law is broken at the quantum level in the presence of a background classical gravitational field with a nontrivial Chern-Pontryagin invariant, in parallel with the chiral anomaly for massless Dirac fermions. Among the physical consequences, the net polarization of the quantum electromagnetic field is not conserved.
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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. (2016). Search for Higgs and Z Boson Decays to phi gamma with the ATLAS Detector. Phys. Rev. Lett., 117(11), 111802–19pp.
Abstract: A search for the decays of the Higgs and Z bosons to a phi meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected at root s = 13 TeV with the ATLAS detector at the LHC. No significant excess of events is observed above the background, and 95% confidence level upper limits on the branching fractions of the Higgs and Z boson decays to phi gamma of 1.4 x 10(-3) and 8.3 x 10(-6), respectively, are obtained.
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n_TOF Collaboration(Barbagallo, M. et al), Domingo-Pardo, C., Tain, J. L., & Tarifeño-Saldivia, A. (2016). Be-7(n,alpha)He-4 Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN. Phys. Rev. Lett., 117(15), 152701–7pp.
Abstract: The energy-dependent cross section of the (7)Bed(n,alpha)He-4 reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of Be-7 and by the low reaction cross section have been overcome at nTOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the nTOF facility at CERN, the availability of a sufficient amount of chemically pure Be-7, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si-Be-7-Si arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n_TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2017). Observation of J/psi phi Structures Consistent with Exotic States from Amplitude Analysis of B+ -> J/psi phi K+ Decays. Phys. Rev. Lett., 118(2), 022003–10pp.
Abstract: The first full amplitude analysis of B+ -> J/psi phi K+ with J/psi -> mu(+)mu(-), phi -> K+K- decays is performed with a data sample of 3 fb(-1) of pp collision data collected at root s = 7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into phi K+ , and four J/psi phi structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Evidence for Exotic Hadron Contributions to Lambda(0)(b) -> J/psi p pi(-) Decays. Phys. Rev. Lett., 117(8), 082003–10pp.
Abstract: A full amplitude analysis of Lambda(0)(b) -> J/psi pi(-) decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb(-1). A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations N -> p pi(-), either the P-c(43800)(+) and P-c(4450)(+) -> J/psi p states, previously observed in Lambda(0)(b) -> J/psi pK(-) decays, or the Z(c)(4200)(-) -> J/psi pi(-) state, previously reported in B-0 -> J/psi K+pi(-) decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the P-c(4380)(+) and P-c(4 450)(+) production rates expected from their previous observation taking account of Cabibbo suppression.
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