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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). Search for CP violation in the phase space of D-0 -> pi(+)pi(-)pi(+)pi(-) decays. Phys. Lett. B, 769, 345–356.
Abstract: A search for time-integrated CP violation in the Cabibbo-suppressed decay D-0 -> pi(+)pi(-)pi(+)pi(-) is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for P-even CP asymmetries and, for the first time, is extended to probe the P-odd case. Using proton proton collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb detector at centre-of-mass energies of root s = 7 TeV and 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (4.6 +/- 0.5)% in the P-even case, and marginally consistent with a p-value of (0.6 +/- 0.2)% in the P-odd case, corresponding to a significance for CP non -conservation of 2.7 standard deviations.
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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2017). Online Rn-222 removal by cryogenic distillation in the XENON100 experiment. Eur. Phys. J. C, 77(6), 358–8pp.
Abstract: We describe the purification of xenon from traces of the radioactive noble gas radon using a cryogenic distillation column. The distillation column was integrated into the gas purification loop of the XENON100 detector for online radon removal. This enabled us to significantly reduce the constant Rn-222 background originating from radon emanation. After inserting an auxiliary 222Rn emanation source in the gas loop, we determined a radon reduction factor of R > 27 (95% C.L.) for the distillation column by monitoring the Rn-222 activity concentration inside the XENON100 detector.
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NA48/2 Collaboration(Batley, J. R. et al), & Fiorini, L. (2017). Searches for lepton number violation and resonances in K-+/- -> pi μμdecays. Phys. Lett. B, 769, 67–76.
Abstract: The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003-2004. A new upper limit on the rate of the lepton number violating decay K-+/- -> pi(+/-)mu(+/-)mu(+/-) is reported: B( K-+/- -> pi(+/-)mu(+/-)mu(+/-)) < 8.6 x 10(-11) at 90% CL. Searches for two-body resonances X in K-+/- -> pi μμdecays (such as heavy neutral leptons N-4 and inflatons chi) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K-+/- -> μN-+/-(4))B(N-4 -> pi mu) and B(K-+/- ->pi X-+/-)B(X -> mu(+),mu(-)) for ranges of assumed resonance masses and lifetimes. The limits are in the (10(-11),10(-9)) range for resonance lifetimes below 100 ps.
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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). Measurement of matter-antimatter differences in beauty baryon decays. Nat. Phys., 13(4), 391–396.
Abstract: Differences in the behaviour of matter and antimatter have been observed in K and B meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined chargeconjugation and parity transformations, known as CP violation. Here, using data from the LHCb experiment at the Large Hadron Collider, we search for CP-violating asymmetries in the decay angle distributions of A(b)(0) baryons decaying to p pi(-)pi(+)pi(-) and p pi-K+K- final states. These four-body hadronic decays are a promising place to search for sources of CP violation both within and beyond the standard model of particle physics. We find evidence for CP violation in A(b)(0) to p pi(-)pi(+)pi(-) decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for CP violation in the baryon sector.
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Escudero, M., Rius, N., & Sanz, V. (2017). Sterile neutrino portal to Dark Matter II: exact dark symmetry. Eur. Phys. J. C, 77(6), 397–11pp.
Abstract: We analyze a simple extension of the standard model (SM) with a dark sector composed of a scalar and a fermion, both singlets under the SM gauge group but charged under a dark sector symmetry group. Sterile neutrinos, which are singlets under both groups, mediate the interactions between the dark sector and the SM particles, and generate masses for the active neutrinos via the seesaw mechanism. We explore the parameter space region where the observed Dark Matter relic abundance is determined by the annihilation into sterile neutrinos, both for fermion and scalar Dark Matter particles. The scalar Dark Matter case provides an interesting alternative to the usual Higgs portal scenario. We also study the constraints from direct Dark Matter searches and the prospects for indirect detection via sterile neutrino decays to leptons, which may be able to rule out Dark Matter masses below and around 100 GeV.
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