LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). First Observation of a Baryonic B-c(+) Decay. Phys. Rev. Lett., 113(15), 152003–9pp.
Abstract: A baryonic decay of the B-c(+) meson, B-c(+) -> J/psi p (p) over bar pi(+) is observed for the first time, with a significance of 7.3 standard deviations, in pp collision data collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb(-1) taken at center-of-mass energies of 7 and 8 TeV. With the B-c(+) -> J/psi pi(+) decay as the normalization channel, the ratio of branching fractions is measured to be B(B-c(+) -> J/psi p (p) over bar pi(+)) /B(B-c(+) -> J/psi pi(+)) = 0.143(-0.034)(+0.039) (stat) +/- 0.013 (syst). The mass of the B-c(+) messon is determined as M(B-c(+)) = 6274.0 +/- 0.4 (sysst) MeV/c(2), using the B-c(+) -> J/psi p (p) over bar pi(+) channel.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Test of lepton universality using B+ -> K(+)l(+)l(-) decays. Phys. Rev. Lett., 113(15), 151601–10pp.
Abstract: A measurement of the ratio of the branching fractions of the B+ -> K+mu(+)mu(-) and B+ -> K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV2/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) +/- 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Evidence for Electroweak Production of W(+/-) W(+/-) jj in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 113(14), 141803–19pp.
Abstract: This Letter presents the first study of W(+/-)W(+/-)jj, same-electric-charge diboson production in association with two jets, using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons (e(+/-)e(+/-), e(+/-)mu(+/-), and mu(+/-)mu(+/-)) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for W(+/-)W(+/-)jj production and electroweak-only W(+/-)W(+/-)jj production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.
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Hernandez, P., Kekic, M., & Lopez-Pavon, J. (2014). N_eff in low-scale seesaw models versus the lightest neutrino mass. Phys. Rev. D, 90(6), 065033–12pp.
Abstract: We evaluate the contribution to N_eff of the extra sterile states in low-scale type I seesaw models (with three extra sterile states). We explore the full parameter space and find that at least two of the heavy states always reach thermalization in the early Universe, while the third one might not thermalize provided the lightest neutrino mass is below O(10(-3) eV). Constraints from cosmology therefore severely restrict the spectra of heavy states in the range 1 eV-100 MeV. The implications for neutrinoless double beta decay are also discussed.
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Ullan, M., Benitez, V., Quirion, D., Zabala, M., Pellegrini, G., Lozano, M., et al. (2014). Low-resistance strip sensors for beam-loss event protection. Nucl. Instrum. Methods Phys. Res. A, 765, 252–257.
Abstract: AC coupled silicon strip sensors can be damaged in case of a beam loss due to the possibility of a large charge accumulation in the bulk, developing very high voltages across the coupling capacitors which can destroy them. Punch-through structures are currently used to avoid this problem helping to evacuate the accumulated charge as large voltages are developing. Nevertheless, previous experiments, performed with laser pulses, have shown that these structures can become ineffective in relatively long strips. The large value of the implant resistance can effectively isolate the “far” end of the strip from the punchthrough structure leading to large voltages. We present here our developments to fabricate lowresistance strip sensors to avoid this problem. The deposition of a conducting material in contact with the implants drastically reduces the strip resistance, assuring the effectiveness of the punch-through structures. First devices have been fabricated with this new technology. Initial results with laser tests show the expected reduction in peak voltages on the low resistivity implants. Other aspects of the sensor performance, including the signal formation, are not affected by the new technology.
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