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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. (2018). Measurement of colour flow using jet-pull observables in in t(t)over-bar events with the ATLAS experiment at root s=13 TeV. Eur. Phys. J. C, 78(10), 847–31pp.
Abstract: Previous studies have shown that weighted angular moments derived from jet constituents encode the colour connections between partons that seed the jets. This paper presents measurements of two such distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the Wboson and the two b-jets from the top-quark decays, which are not expected to be colour connected. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables.
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Romero-Lopez, F., Rusetsky, A., & Urbach, C. (2018). Two- and three-body interactions in phi 4 theory from lattice simulations. Eur. Phys. J. C, 78(10), 846–15pp.
Abstract: We calculate the one-, two- and three-particle energy levels for different lattice volumes in the complex phi(4) theory on the lattice. We argue that the exponentially suppressed finite-volume corrections for the two- and three-particle energy shifts can be reduced significantly by using the single particle mass, which includes the finite-size effects. We show numerically that, for a set of bare parameters, corresponding to the weak repulsive interaction, one can reliably extract the two- and three-particle energy shifts. From those, we extract the scattering length, the effective range and the effective three-body coupling. We show that the parameters, extracted from the two- and three-particle energy shifts, are consistent. Moreover, the effective three-body coupling is significantly different from zero.
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Pavao, R., & Oset, E. (2018). Coupled channels dynamics in the generation of the Omega (2012) resonance. Eur. Phys. J. C, 78(10), 857–8pp.
Abstract: We look into the newly observed Omega (2012) state from the molecular perspective in which the resonance is generated from the (K) over bar Xi*, eta Omega and (K) over bar Xi channels. We find that this picture provides a natural explanation of the properties of the Omega (2012) state. We stress that the molecular nature of the resonance is revealed with a large coupling of the Omega (2012) to the (K) over bar Xi* channel, that can be observed in the Omega (2012) -> (K) over bar pi Xi decay which is incorporated automatically in our chiral unitary approach via the use of the spectral function of Xi* in the evaluation of the (K) over bar Xi* loop function.
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Baines, S., Mavromatos, N. E., Mitsou, V. A., Pinfold, J. L., & Santra, A. (2018). Monopole production via photon fusion and Drell-Yan processes: MadGraph implementation and perturbativity via velocity-dependent coupling and magnetic moment as novel features. Eur. Phys. J. C, 78(11), 966–36pp.
Abstract: In this work we consider point-like monopole production via photon-fusion and Drell-Yan processes in the framework of an effective U(1) gauge field theory obtained from conventional models describing the interaction of magnetically-charged fields with ordinary photons, upon electric-magnetic dualisation. We present arguments based on such dualities which support the conjecture of an effective monopole-velocity-dependent magnetic charge. For the cases of 1 monopoles, we also include a magnetic-moment which is treated as a new phenomenological parameter and, together with the velocity-dependent coupling, allows for a perturbative treatment of the cross-section calculation. We discuss unitarity issues within these effective field theories, in particular we point out that in the spin-1 monopole case only the may restore unitarity. However from an effective-field-theory point of view, this lack of unitarity should not be viewed as an impediment for the phenomenological studies and experimental searches of generic spin-1 monopoles, given that the potential appearance of new degrees of freedom in the ultraviolet completion of such models might restore it. The second part of the paper deals with an appropriate implementation of photon-fusion and Drell-Yan processes based on the above theoretical scenarios into MadGraph UFO models, aimed to serve as a useful tool in interpretations of monopole searches at colliders such as LHC, especially for photon fusion, given that it has not been considered by experimental collaborations so far. Moreover, the experimental implications of such perturbatively reliable monopole searches have been laid out.
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Dai, L. R., & Oset, E. (2018). Helicity amplitudes in B -> D*(nu)over-barl decay. Eur. Phys. J. C, 78(11), 951–11pp.
Abstract: We use a recent formalism of the weak hadronic reactions that maps the transition matrix elements at the quark level into hadronic matrix elements, evaluated with an elaborate angular momentum algebra that allows finally to write the weak matrix elements in terms of easy analytical formulas. In particular they appear explicitly for the different spin third components of the vector mesons involved. We extend the formalism to a general case, with the operator parameter, which suggest to use this magnitude to test different models beyond the standard model. We show that our formalism implies the heavy quark limit and compare our results with calculations that include higher order corrections in heavy quark effective theory. We find very similar results for both approaches in normalized distributions, which are practically identical at the end point of M-inv((nu l)) = m(B) – m(D)*
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