ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2012). Performance of the ATLAS Trigger System in 2010. Eur. Phys. J. C, 72(1), 1849–61pp.
Abstract: Proton-proton collisions at root s = 7 TeV and heavy ion collisions at root(NN)-N-s = 2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the evolution of the system during 2010 and the performance of the trigger system components and selections based on the 2010 collision data are shown. A brief outline of plans for the trigger system in 2011 is presented.
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Cappiello, L., Cata, O., D'Ambrosio, G., & Gao, D. N. (2012). K+ -> pi(+) pi(0)e(+) e(-): a novel short-distance probe. Eur. Phys. J. C, 72(1), 1872–16pp.
Abstract: We study the decay K+ -> pi(+) pi(0)e(+) e(-), currently under analysis by the NA62 Collaboration at CERN. In particular, we provide a detailed analysis of the Dalitz plot for the long-distance, gamma*-mediated, contributions (Brems-strahlung, direct emission and its interference). We also examine a set of asymmetries to isolate genuine short-distance effects. While we show that charge asymmetries are not required to test short distances, they provide the best environment for its detection. This constitutes by itself a strong motivation for NA62 to study K- decays in the future. We therefore provide a detailed study of different charge asymmetries and the corresponding estimated signals. Whenever possible, we make contact with the related processes K+ -> pi(+) pi(0)gamma and K-L -> pi(+) pi(0)e(+) e(-) and discuss the advantages of K+ -> pi(+) pi(0)e(+) e(-) over them.
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Al-Dahan, N. et al, Algora, A., Molina, F., & Rubio, B. (2012). Multiple beta(-) decaying states in Re-194: Shape evolution in neutron-rich osmium isotopes. Phys. Rev. C, 85(3), 034301–9pp.
Abstract: beta decays from heavy, neutron-rich nuclei with A similar to 190 have been investigated following their production via the relativistic projectile fragmentation of an E/A = 1 GeV Pb-208 primary beam on a similar to 2.5 g/cm(2) Be-9 target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. gamma decays were observed and correlated with these secondary ions on an event-by-event basis such that gamma-ray transitions following from both internal (isomeric) and beta decays were recorded. A number of discrete, beta-delayed gamma-ray transitions associated with beta decays from Re-194 to excited states in Os-194 have been observed, including previously reported decays from the yrast I-pi = (6(+)) state. Three previously unreported gamma-ray transitions with energies 194, 349, and 554 keV are also identified; these transitions are associated with decays from higher spin states in Os-194. The results of these investigations are compared with theoretical predictions from Nilsson multi-quasiparticle (MQP) calculations. Based on lifetime measurements and the observed feeding pattern to states in Os-194, it is concluded that there are three beta(-)-decaying states in Re-194.
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de Angelis, G. et al, & Gadea, A. (2012). Shape isomerism and shape coexistence effects on the Coulomb energy differences in the N = Z nucleus As-66 and neighboring T=1 multiplets. Phys. Rev. C, 85(3), 034320–7pp.
Abstract: Excited states of the N = Z = 33 nucleus As-66 have been populated in a fusion-evaporation reaction and studied using gamma-ray spectroscopic techniques. Special emphasis was put into the search for candidates for the T = 1 states. A new 3(+) isomer has been observed with a lifetime of 1.1(3) ns. This is believed to be the predicted oblate shape isomer. The excited levels are discussed in terms of the shell model and of the complex excited Vampir approaches. Coulomb energy differences are determined from the comparison of the T = 1 states with their analog partners. The unusual behavior of the Coulomb energy differences in the A = 70 mass region is explained through different shape components (oblate and prolate) within the members of the same isospin multiplets. This breaking of the isospin symmetry is attributed to the correlations induced by the Coulomb interaction.
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Roca, L., & Oset, E. (2012). Scattering of unstable particles in a finite volume: The case of pi rho scattering and the a(1)(1260) resonance. Phys. Rev. D, 85(5), 054507–13pp.
Abstract: We present a way to evaluate the scattering of unstable particles quantized in a finite volume with the aim of extracting physical observables for infinite volume from lattice data. We illustrate the method with the pi rho scattering which generates dynamically the axial-vector a(1)(1260) resonance. Energy levels in a finite box are evaluated both considering the rho as a stable and unstable resonance and we find significant differences between both cases. We discuss how to solve the problem to get the physical scattering amplitudes in the infinite volume, and hence phase shifts, from possible lattice results on energy levels quantized inside a finite box.
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