Podolyak, Z. (2016). Role of the Delta Resonance in the Population of a Four-Nucleon State in the Fe-56 -> Fe-54 Reaction at Relativistic Energies. Phys. Rev. Lett., 117(22), 222302–6pp.
Abstract: The Fe-54 nucleus was populated from a Fe-56 beam impinging on a Be target with an energy of E/A = 500 MeV. The internal decay via gamma-ray emission of the 10(+) metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the Fe-56 ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of Fe-54, suggesting that it was populated via the decay of the Delta(0) resonance into a proton. This process allows the population of fournucleon states, such as the observed isomer. Therefore, it is concluded that the observation of this 10(+) metastable state in Fe-54 is a consequence of the quark structure of the nucleons.
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Euve, L. P., Robertson, S., James, N., Fabbri, A., & Rousseaux, G. (2020). Scattering of Co-Current Surface Waves on an Analogue Black Hole. Phys. Rev. Lett., 124(14), 141101–6pp.
Abstract: We report on what is to our knowledge the first scattering experiment of surface waves on an accelerating transcritical flow, which in the analogue gravity context is described by an effective spacetime with a black-hole horizon. This spacetime has been probed by an incident co-current wave, which partially scatters into an outgoing countercurrent wave on each side of the horizon. The measured scattering amplitudes are compatible with the predictions of the hydrodynamical theory, where the kinematical description in terms of the effective metric is exact.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Search for A ' -> mu(+)mu(-) Decays. Phys. Rev. Lett., 124(4), 041801–12pp.
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. These searches look for A '->mu(+)mu(-) decays using a data sample corresponding to an integrated luminosity of 5.5 fb(-1) collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the gamma-A ' kinetic mixing strength. The promptlike A ' search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with 214 < m(A ') less than or similar to 740 MeV and 10.6 < m(A ') less than or similar to 30 GeV. The search for long-lived A '->mu(+)mu(-) decays places world-leading constraints on low-mass dark photons with lifetimes O(1)ps.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for a Charged Higgs Boson Produced in the Vector-Boson Fusion Mode with Decay H-+/- -> W(+/-)Z using pp Collisions at root S=8 TeV with the ATLAS Experiment. Phys. Rev. Lett., 114(23), 231801–18pp.
Abstract: A search for a charged Higgs boson, H-+/-, decaying to a W-+/- boson and a Z boson is presented. The search is based on 20.3 fb(-1) of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H-+/- boson is assumed to be produced via vector-boson fusion and the decays W-+/- -> q (q') over bar and Z -> e(+)e(-)/mu(+)mu(-) are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H+ boson is observed. Upper limits of 31-1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H-+/- boson times its branching fraction to W(+/-)Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2020). Search for a Dark Leptophilic Scalar in e(+) e(-) Collisions. Phys. Rev. Lett., 125(18), 181801–8pp.
Abstract: Many scenarios of physics beyond the standard model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an e(+) e(-) collider, such a leptophilic scalar (phi(L)) would be produced predominantly through radiation from a tau lepton. We report herein a search for e(+) e(- )-> tau(+) tau(-)phi(L), phi(L)-> l(+) l(-) (l = e, mu) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the phi(L) coupling to leptons in the range 0.04 < m phi(L) < 7.0 GeV. These bounds significantly improve upon the current constraints, excluding almost entirely the parameter space favored by the observed discrepancy in the muon anomalous magnetic moment below 4 GeV at 90% confidence level.
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