A search for the pair production of scalar top quarks,t, has been performed in 360 pb −1 of data from pp collisions at a center-of-mass energy of 1.96 TeV, collected by the DØ detector at the Fermilab Tevatron collider. Thet decay mode considered ist → cχ 0 1 , whereχ 0 1 is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data and standard model expectation are in agreement, and a 95% C.L. exclusion domain in the (mt , mχ0 ciated with the left-and right-handed degrees of freedom of each ordinary quark. The mass eigenstates result from the diagonalization of a mass matrix, with elements determined by the specific SUSY-breaking pattern. A light SUSY partner of the top quark, or stop, is a generic prediction of models in which the scalar quark masses are equal at the grand unification scale. A first reason is that, due to the impact of the large top quark Yukawa coupling in the renormalization group equations, DØ Collaboration / Physics Letters B 645 (2007) 119-127 123 the diagonal elements of the mass matrix are driven to values smaller than those for the other scalar quarks at the electroweak scale [2]. A second reason is that the off-diagonal terms are proportional to the relevant quark mass, and hence are much larger in the case of the top quark. The mass eigenstates are therefore broadly split, with the mass of the lighter stopt thus driven to an even lower value [3]. Finally, a light stop is a necessary ingredient in the context of electroweak baryogenesis [4].In models with R-parity conservation [5], the lightest SUSY particle (LSP) is stable, and cosmological constraints imply that it should be neutral and colorless [6]. In a large class of SUSY models, the lightest of the neutralinos-the mass eigenstates resulting from the mixing of the SUSY partners of the neutral gauge and Higgs bosons-is the LSP, which furthermore appears as a viable dark matter candidate. In the following, it will be assumed that R-parity is conserved and that the LSP is the lightest neutralinoχ is considered, and it is assumed that t → cχ 0 1 , a flavor-changing loop decay [7], is the only relevant decay mode, i.e., that the tree-level four-body decays [8] t → bff χ 0 1 can be neglected. In pp collisions, stop pair production proceeds via qq annihilation and gluon-gluon fusion. The cross section has very little dependence on SUSY parameters other than the stop mass. At the center-of-mass energy of 1.96 TeV available in Run II of the Fermilab Tevatron collider, it ranges from 15 to 2.25 pb for stop masses from 100 to 140 GeV, as calculated at nextto-leading order (NLO) with PROSPINO [9], for equal renormalization and factorization scales μ rf = mt and using the CTEQ6.1M parton distribution functions (PDFs) [10]. The final state topology resulting from thet → cχ 0 1 decay is a pair of acoplanar jets, with large missing transverse energy / E T carried away by the two weakly interacting LSPs. Previous searches in this...

Boundary integral analysis of scattering from rigid bodies is well known. Analysis often proceeds along the following lines: representation of the geometry using a collection of triangles, representation of physics using low order ansatz functions defined on each triangle, and then solving the resulting discrete system. This prescription for the common solution stands out in terms of the low-order approximation of both geometry and representation of physics; specifically, both are C0. Taking inspiration from computer graphics literature, a framework wherein continuity of representation (both geometry and physics) can be as high as C2 is developed. In this paper, the steps necessary to develop such a iso-geometric (i.e., using the same basis functions for representing both geometry and physics) boundary integral solver are elucidated. In doing so, an efficient method based on a wideband fast multipole method to evaluate the required inner products and matrix vector products is proposed and demonstrated. Numerous examples are presented to highlight the benefits of the proposed approach.

Neuroprosthetics can benefit greatly from area and power efficient signal processing circuitry suitable for implanting alongside miniature neural probes that interface to the nervous system. This work identifies an optimal VLSI architecture for computing a I-dimensional multilevel discrete wavelet transform for multiple electrode channels simultaneously. The architecture is based on the lifting-scheme for wavelet computation and integer fixed-point precision for real-time processing under constraints imposed by implantability requirements. Two different computational node designs have been explored and compared to identify an optimal approach that minimizes power and chip area for a given number of levels and channels. Results demonstrate that on-chip computation is feasible prior to data transmission.

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