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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. (2017). Measurement of the cross-section for electroweak production of dijets in association with a Z boson in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 775, 206–228.
Abstract: The cross-section for the production of two jets in association with a leptonically decaying Z boson (Zjj) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb(-1). The electroweak Zjj cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan Zjj process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is sigma(Zjj)(EW) = 119 +/- 16 (stat.) +/- 20 (syst.) +/- 2 (lumi.) fb for dijet invariant mass greater than 250 GeV, and 34.2 +/- 5.8 (stat.) +/- 5.5 (syst.) +/- 0.7 (lumi.) fb for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive Zjj cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan Zjj production.
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Ortega, P. G., Entem, D. R., & Fernandez, F. (2017). LHCb pentaquarks in constituent quark models. Phys. Lett. B, 764, 207–211.
Abstract: The recently discovered P-c(4380)(+) and P-c(4450)(+) states at LHCb have masses close to the (D) over bar Sigma(C)* and (D) over bar*Sigma(C) thresholds, respectively, which suggest that they may have significant meson-baryon molecular components. We analyze these states in the framework of a constituent quark model which has been applied to a wide range of hadronic observables, being the model parameters, therefore, completely constrained. The P-c(4380)(+) and P-c(4450)(+) are studied as molecular states composed by charmed baryons and open charm mesons. Several bound states with the proper binding energy are found in the (D) over bar Sigma(C)* and (D) over bar*Sigma(C) chennels. We discuss the possible assignments of these states from their decay widths. Moreover, two more states are predicted, associated with the (D) over bar Sigma(C) and (D) over bar*Sigma*(C) thresholds. (C) 2016 Published by Elsevier B.V.
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Centelles Chulia, S., Ma, E., Srivastava, R., & Valle, J. W. F. (2017). Dirac neutrinos and dark matter stability from lepton quarticity. Phys. Lett. B, 767, 209–213.
Abstract: We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type-I seesaw mechanism as a result of a Z(4) discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos.
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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). Dijet production in root s=7 TeV pp collisions with large rapidity gaps at the ATLAS experiment. Phys. Lett. B, 754, 214–234.
Abstract: A 6.8 nb(-1) sample of pp collision data collected under low-luminosity conditions at root s = 7 TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with p(T) > 20 GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in Delta eta(F), the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, (xi) over tilde, of the fractional momentum loss of the proton assuming single diffractive dissociation (pp -> pX). Model comparisons indicate a dominant non-diffractive contribution up to moderately large Delta eta(F) and small (xi) over tilde, with a diffractive contribution which is significant at the highest Delta eta(F) and the lowest (xi) over tilde. The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions.
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Boucenna, S. M., Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2016). Non-abelian gauge extensions for B-decay anomalies. Phys. Lett. B, 760, 214–219.
Abstract: We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic b -> sl(+)l(-) and b -> cl nu decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the SU(2)(L) factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the B-decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.
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