ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2016). Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at root s(NN)=5.02 TeV with the ATLAS detector. Eur. Phys. J. C, 76(4), 199–30pp.
Abstract: The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1 μb(-1) of proton-lead collisions at a nucleon-nucleon centre-of-mass energy of root s(NN) = 5.02 TeV using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The p + Pb collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the p + Pb collision have been carried out using the Glauber model as well as two Glauber-Gribov inspired extensions to the Glauber model. Charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon-nucleon collisions in the modelling of the initial state of p + Pb collisions.
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Botella, F. J., Branco, G. C., Nebot, M., & Rebelo, M. N. (2016). Flavour-changing Higgs couplings in a class of two Higgs doublet models. Eur. Phys. J. C, 76(3), 161–17pp.
Abstract: We analyse various flavour-changing processes like t -> hu, hc, h -> t e, tau μas well as hadronic decays h -> bs, bd, in the framework of a class of two Higgs doublet models where there are flavour-changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely determined by the CKM and PMNS matrices as well as tan beta. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalisation group. We show that in some of the models the rates of the above flavour-changing processes can reach the discovery level at the LHC at 13 TeV even taking into account the stringent bounds on low energy processes, in particular μ-> e gamma.
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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. (2016). Identification of boosted, hadronically decaying W bosons and comparisons with ATLAS data taken at root s=8 TeV. Eur. Phys. J. C, 76(3), 154–47pp.
Abstract: This paper reports a detailed study of techniques for identifying boosted, hadronically decaying W bosons using 20.3 fb(-1) of proton-proton collision data collected by the ATLAS detector at the LHC at a centre-of-mass energy root s = 8 TeV. A range of techniques for optimising the signal jet mass resolution are combined with various jet substructure variables. The results of these studies in Monte Carlo simulations show that a simple pairwise combination of groomed jet mass and one substructure variable can provide a 50 % efficiency for identifying W bosons with transverse momenta larger than 200 GeV while maintaining multijet background efficiencies of 2-4% for jets with the same transverse momentum. These signal and background efficiencies are confirmed in data for a selection of tagging techniques.
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Olmo, G. J., Rubiera-Garcia, D., & Sanchez-Puente, A. (2016). Classical resolution of black hole singularities via wormholes. Eur. Phys. J. C, 76(3), 143–6pp.
Abstract: In certain extensions of General Relativity, wormholes generated by spherically symmetric electric fields can resolve black hole singularities without necessarily removing curvature divergences. This is shown by studying geodesic completeness, the behavior of time-like congruences going through the divergent region, and by means of scattering of waves off the wormhole. This provides an example of the logical independence between curvature divergences and space-time singularities, concepts very often identified with each other in the literature.
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Uchino, T., Liang, W. H., & Oset, E. (2016). Baryon states with hidden charm in the extended local hidden gauge approach. Eur. Phys. J. A, 52(3), 43–16pp.
Abstract: The s-wave interaction of (D) over bar Lambda(c), (D) over bar Sigma(c),(D) over bar*Lambda(c), (D) over bar*Sigma(c) and (D) over bar Sigma(c)*, (D) over bar*Sigma(c)*, is studied within a unitary coupled channels scheme with the extended local hidden gauge approach. In addition to the Weinberg-Tomozawa term, several additional diagrams via the pion exchange are also taken into account as box potentials. Furthermore, in order to implement the full coupled channels calculation, some of the box potentials which mix the vector-baryon and pseudoscalar-baryon sectors are extended to construct the effective transition potentials. As a result, we have observed six possible states in several angular momenta. Four of them correspond to two pairs of admixture states, two of (D) over bar Sigma(c) – (D) over bar*Sigma(c) with J – 1/2, and two of (D) over bar Sigma(c)* – (D) over bar*Sigma(c)* with J = 3/2. Moreover, we find a (D) over bar*Sigma(c) resonance which couples to the (D) over bar Lambda(c) channel and one spin degenerated bound state of (D) over bar*Sigma(c)* with J = 1/2, 5/2.
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