AGATA Collaboration, Doncel, M., Recchia, F., Quintana, B., Gadea, A., & Farnea, E. (2010). Experimental test of the background rejection, through imaging capability, of a highly segmented AGATA germanium detector. Nucl. Instrum. Methods Phys. Res. A, 622(3), 614–618.
Abstract: The development of highly segmented germanium detectors as well as the algorithms to identify the position of the interaction within the crystal opens the possibility to locate the gamma-ray source using Compton imaging algorithms. While the Compton-suppression shield, coupled to the germanium detector in conventional arrays, works also as an active filter against the gamma rays originated outside the target, the new generation of position sensitive gamma-ray detector arrays has to fully rely on tracking capabilities for this purpose. In specific experimental conditions, as the ones foreseen at radioactive beam facilities, the ability to discriminate background radiation improves the sensitivity of the gamma spectrometer. In this work we present the results of a measurement performed at the Laboratori Nazionali di Legnaro (LNL) aiming the evaluation of the AGATA detector capabilities to discriminate the origin of the gamma rays on an event-by-event basis. It will be shown that, exploiting the Compton scattering formula, it is possible to track back gamma rays coming from different positions, assigning them to specific emitting locations. These imaging capabilities are quantified for a single crystal AGATA detector.
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Batist, L., Gorska, M., Grawe, H., Janas, Z., Kavatsyuk, M., Karny, M., et al. (2010). Systematics of Gamow-Teller beta decay “Southeast” of Sn-100. Eur. Phys. J. A, 46(1), 45–53.
Abstract: The energy centroids and integrated strengths of Gamow-Teller transitions in the beta(+) and electron-capture decay are analyzed for nuclei whose proton number Z and neutron number N are restricted to 44 <= Z <= 50 and 50 <= N <= 58. The analysis is based on data measured both with high-resolution gamma-ray spectrometry and total gamma-ray absorption techniques. The dependence of the considered quantities on the relative neutron excess are established after taking into account the effects due to the Coulomb interaction and mean-field level occupancies. An extrapolation of this dependence to the lightest known tin isotopes is used to estimate the decay characteristics of Sn-100 and Sn-101. The values extrapolated for the half-lives of Sn-100 and Sn-101 agree with experimental data. Using the extrapolated values together with shell model predictions, the Q values for the electron-capture decay of Sn-100 is evaluated. The quenching factor for beta(+) and the electron-capture decay of the nuclei under consideration here is established to be 0.56(2) with a possible weak dependence on N – Z.
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Bouhova-Thacker, E., Kostyukhin, V., Koffas, T., Liebig, W., Limper, M., Piacquadio, G. N., et al. (2010). Expected Performance of Vertex Reconstruction in the ATLAS Experiment at the LHC. IEEE Trans. Nucl. Sci., 57(2), 760–767.
Abstract: In the harsh environment of the Large Hadron Collider at CERN (design luminosity of 10(34) cm(-2) s(-1)) efficient reconstruction of vertices is crucial for many physics analyses. Described in this paper is the expected performance of the vertex reconstruction used in the ATLAS experiment. The algorithms for the reconstruction of primary and secondary vertices as well as for finding photon conversions and vertex reconstruction in jets are described. The implementation of vertex algorithms which follows a very modular design based on object-oriented C++ is presented. A user-friendly concept allows event reconstruction and physics analyses to compare and optimize their choice among different vertex reconstruction strategies. The performance of implemented algorithms has been studied on a variety of Monte Carlo samples and results are presented.
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Bordes, J., Chan, H. M., & Tsun, T. S. (2010). Possible anomalies in Higgs decay: charm-suppression and flavour-violation. Eur. Phys. J. C, 65(3-4), 537–542.
Abstract: It is suggested that the Higgs boson may have a branching ratio into the c (c) over bar c mode suppressed by several orders of magnitude compared with conventional predictions and in addition some small but detectable flavour-violating modes such as b (s) over bar and tau(mu) over bar. The suggestion is based on a scheme proposed and tested earlier for explaining the mixing pattern and mass hierarchy of fermions in terms of a rotating mass matrix. If confirmed, the effects would cast new light on the geometric origin of fermion generations and of the Higgs field itself.
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MiniBooNE Collaboration(Aguilar-Arevalo, A. A. et al), & Sorel, M. (2010). Measurement of the neutrino neutral-current elastic differential cross section on mineral oil at E-nu similar to 1 GeV. Phys. Rev. D, 82(9), 092005–16pp.
Abstract: We report a measurement of the flux-averaged neutral-current elastic differential cross section for neutrinos scattering on mineral oil (CH2) as a function of four-momentum transferred squared, Q(2). It is obtained by measuring the kinematics of recoiling nucleons with kinetic energy greater than 50 MeV which are readily detected in MiniBooNE. This differential cross-section distribution is fit with fixed nucleon form factors apart from an axial mass M-A that provides a best fit for M-A = 1.39 +/- 0.11 GeV. Using the data from the charged-current neutrino interaction sample, a ratio of neutral-current to charged-current quasielastic cross sections as a function of Q(2) has been measured. Additionally, single protons with kinetic energies above 350 MeV can be distinguished from neutrons and multiple nucleon events. Using this marker, the strange quark contribution to the neutral-current axial vector form factor at Q(2) – 0, Delta s, is found to be Delta s = 0.08 +/- 0.26.
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