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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Observation of the decay Lambda(0)(b) -> pK(-)mu(+)mu(-) and a search for CP violation. J. High Energy Phys., 06(6), 108–17pp.
Abstract: A search for CP violation in the decay Lambda(0)(b) -> pK(-)mu(+)mu(-) is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The Lambda(0)(b) -> pK(-)mu(+)mu(-) decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, Delta A(CP) equivalent to A(CP) (Lambda(0)(b) -> pK(-)mu(+)mu(-)) – A(CP) (Lambda(0)(b) -> pK(-)J/psi) and a(CP)((T) over cap -odd), where the latter is based on asymmetries in the angle between the mu(+)mu(-) and pK(-) decay planes. These are measured to be Delta A(CP) = (-3.5 +/- 5.0 (stat) +/- 0.2 (syst)) x 10(-2), a(CP)((T) over cap -odd) = (1.2 +/- 5.0 (stat) +/- 0.7 (syst)) x 10(-2), and no evidence for CP violation is found.
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Caputo, A., Hernandez, P., Lopez-Pavon, J., & Salvado, J. (2017). The seesaw portal in testable models of neutrino masses. J. High Energy Phys., 06(6), 112–20pp.
Abstract: A Standard Model extension with two Majorana neutrinos can explain the measured neutrino masses and mixings, and also account for the matter-antimatter asymmetry in a region of parameter space that could be testable in future experiments. The testability of the model relies to some extent on its minimality. In this paper we address the possibility that the model might be extended by extra generic new physics which we parametrize in terms of a low-energy effective theory. We consider the effects of the operators of the lowest dimensionality, d = 5, and evaluate the upper bounds on the coefficients so that the predictions of the minimal model are robust. One of the operators gives a new production mechanism for the heavy neutrinos at LHC via higgs decays. The higgs can decay to a pair of such neutrinos that, being long-lived, leave a powerful signal of two displaced vertices. We estimate the LHC reach to this process.
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Ballesteros, G., Carmona, A., & Chala, M. (2017). Exceptional composite dark matter. Eur. Phys. J. C, 77(7), 468–18pp.
Abstract: We study the darkmatter phenomenology of non-minimal composite Higgs models with SO(7) broken to the exceptional group G(2). In addition to the Higgs, three pseudo-Nambu-Goldstone bosons arise, one of which is electrically neutral. A parity symmetry is enough to ensure this resonance is stable. In fact, if the breaking of the Goldstone symmetry is driven by the fermion sector, this Z(2) symmetry is automatically unbroken in the electroweak phase. In this case, the relic density, as well as the expected indirect, direct and collider signals are then uniquely determined by the value of the compositeness scale, f. Current experimental bounds allow one to account for a large fraction of the dark matter of the Universe if the dark matter particle is part of an electroweak triplet. The totality of the relic abundance can be accommodated if instead this particle is a composite singlet. In both cases, the scale f and the dark matter mass are of the order of a few TeV.
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Gnendiger, C., Signer, A., Stockinger, D., Broggio, A., Cherchiglia, A. L., Driencourt-Mangin, F., et al. (2017). To d, or not to d: recent developments and comparisons of regularization schemes. Eur. Phys. J. C, 77(7), 471–39pp.
Abstract: We give an introduction to several regularization schemes that deal with ultraviolet and infrared singularities appearing in higher-order computations in quantum field theories. Comparing the computation of simple quantities in the various schemes, we point out similarities and differences between them.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Observation of the decay B-s(0) -> eta(c)phi and evidence for B-s(0) -> eta(c)pi(+)pi(-). J. High Energy Phys., 07(7), 021–33pp.
Abstract: A study of B-s(0) -> eta(c)phi and B-s(0) -> eta(c)pi(+)pi(-) decays is performed using pp collision data corresponding to an integrated luminosity of 3.0 fb(-1), collected with the LHCb detector in Run 1 of the LHC. The observation of the decay B-s(0) -> eta(c)phi is reported, where the eta(c) meson is reconstructed in the p (p) over bar, K+K-pi(+)pi(-), pi(+)pi(-)pi(+)pi-and K+K-K+K-decay modes and the phi(1020) in the K+K-decay mode. The decay B-s(0) -> J/psi phi is used as a normalisation channel. Evidence is also reported for the decay B-s(0) -> eta(c)pi(+)pi(-), where the eta(c) meson is reconstructed in the p (p) over bar decay mode, using the decay B-s(0) -> J/psi phi pi(+)pi-as a normalisation channel. The measured branching fractions are B(B-s(0) -> eta(c)phi) = (5 : 01 +/- 0 : 53 +/- 0 : 27 +/- 0 : 63) x 10(-4), B(B-s(0) -> eta(c)pi(+)pi(-)) = (1 : 76 +/- 0 : 59 +/- 0 : 12 +/- 0 : 29) x 10(-4), where in each case the fi rst uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.
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