ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., Costa, M. J., et al. (2016). Measurements of top-quark pair differential cross-sections in the lepton plus jets channel in pp collisions at root s=8 TeV using the ATLAS detector. Eur. Phys. J. C, 76(10), 538–39pp.
Abstract: Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, t (t) over bar system and event-level kinematic observables in proton-proton collisions at a centre-of-mass energy of root s = 8 TeV. The observables have been chosen to emphasize the t (t) over bar production process and to be sensitive to effects of initial-and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb(-1), recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.
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Ortega, P. G., Segovia, J., Entem, D. R., & Fernandez, F. (2016). Canonical description of the new LHCb resonances. Phys. Rev. D, 94(11), 114018–7pp.
Abstract: The LHCb Collaboration has recently observed four J/psi phi structures called X(4140), X(4274), X(4500), and X(4700) in the B+ -> J/psi phi K+ decays. We study them herein using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components. The X(4140) resonance appears as a cusp in the J/psi phi channel due to the near coincidence of the D-s(+/-) D-s(*+/-) and J/psi phi mass thresholds. The remaining three [X(4274), X(4500), and X(4700)] appear as conventional charmonium states with quantum numbers 3(3)P(1), 4(3)P(0), and 5(3)P(0), respectively, and their masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds. A particular feature of our quark model is a lattice-based screened linear confining interaction that has been constrained in the light-quark sector and usually produces higher excited heavy-quark states with lower masses than standard quark model predictions.
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Kim, J. S., Rolbiecki, K., & Ruiz de Austri, R. (2016). Model-independent combination of diphoton constraints at 750 GeV. Eur. Phys. J. C, 76(5), 251–8pp.
Abstract: Motivated by the recent diphoton excess reported by both the ATLAS and CMS collaborations, we provide a model-independent combination of diphoton results obtained at root s = 8 and 13 TeV at the LHC. We consider resonant s-channel production of a spin-0 and spin-2 particle with a mass of 750 GeV that subsequently decays to two photons. The size of the excess reported by ATLAS appears to be in a slight tension with other measurements under the spin-2 particle hypothesis.
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Feijoo, A., Magas, V. K., Ramos, A., & Oset, E. (2016). A hidden-charm S =-1 pentaquark from the decay Lambda(b) into J/psi eta Lambda states. Eur. Phys. J. C, 76(8), 446–12pp.
Abstract: The hidden-charm pentaquark P-c(4450) observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness S = -1 sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the Lambda b, just as in the case of the non-strange P-c(4450), but looking into the J/psi eta Lambda decay mode and forming the invariant mass spectrum of J/psi Lambda pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and final-state interaction effects, we find the J/psi eta Lambda final states to be populated with similar strength as the J/psi K- p states employed for the observation of the non-strange pentaquark. This makes the Lambda b -> J/psi eta Lambda decay to be an interesting process to observe a possible strange partner of the P-c(4450). We study the dependence of the J/psi Lambda mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.
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Liang, W. H., Xie, J. J., & Oset, E. (2016). f(0)(500), f(0)(980), and a(0)(980) production in the chi(c1) -> eta pi(+)pi(-) reaction. Eur. Phys. J. C, 76(12), 700–7pp.
Abstract: We study the chi(c1) -> eta pi(+)pi(-) decay, paying attention to the production of f(0)(500), f(0)(980), and a(0)(980) from the final state interaction of pairs of mesons that can lead to these three mesons in the final state, which is implemented using the chiral unitary approach. Very clean and strong signals are obtained for the a(0)(980) excitation in the eta pi invariant mass distribution and for the f(0)(500) in the pi(+)pi(-) mass distribution. A smaller, but also clear signal for the f(0)(980) excitation is obtained. The results are contrasted with experimental data and the agreement found is good, providing yet one more test in support of the picture where these resonances are dynamically generated from the meson-meson interaction.
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