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Aguilar, A. C., Binosi, D., & Papavassiliou, J. (2011). Dynamical equation of the effective gluon mass. Phys. Rev. D, 84(8), 085026–19pp.
Abstract: In this article, we derive the integral equation that controls the momentum dependence of the effective gluon mass in the Landau gauge. This is accomplished by means of a well-defined separation of the corresponding “one-loop dressed” Schwinger-Dyson equation into two distinct contributions, one associated with the mass and one with the standard kinetic part of the gluon. The entire construction relies on the existence of a longitudinally coupled vertex of nonperturbative origin, which enforces gauge invariance in the presence of a dynamical mass. The specific structure of the resulting mass equation, supplemented by the additional requirement of a positive-definite gluon mass, imposes a rather stringent constraint on the derivative of the gluonic dressing function, which is comfortably satisfied by the large-volume lattice data for the gluon propagator, both for SU(2) and SU(3). The numerical treatment of the mass equation, under some simplifying assumptions, is presented for the aforementioned gauge groups, giving rise to a gluon mass that is a nonmonotonic function of the momentum. Various theoretical improvements and possible future directions are briefly discussed.
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Wu, J. J., Molina, R., Oset, E., & Zou, B. S. (2011). Dynamically generated N* and Lambda* resonances in the hidden charm sector around 4.3 GeV. Phys. Rev. C, 84(1), 015202–15pp.
Abstract: The interactions of (D) over bar Sigma(c)-(D) over bar Lambda(c), (D) over bar*Sigma(c)-(D) over bar*Lambda(c), and related strangeness channels, are studied within the framework of the coupled-channel unitary approach with the local hidden gauge formalism. A series of meson-baryon dynamically generated relatively narrow N* and Lambda* resonances are predicted around 4.3 GeV in the hidden charm sector. We make estimates of production cross sections of these predicted resonances in (p) over barp collisions for the experiment of antiproton annihilation at Darmstadt (PANDA) at the forthcoming GSI Facility for Antiproton and Ion Research (FAIR) facility.
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Montanari, D. et al, & Gadea, A. (2011). Elastic, inelastic, and one-nucleon transfer processes in (48)Ca+(64)Ni. Phys. Rev. C, 84(5), 9pp.
Abstract: Elastic, inelastic, and one-nucleon transfer channels in the (48)Ca+(64)Ni reaction have been measured at approximate to 6 MeV/nucleon with the PRISMA-CLARA setup, at Legnaro National Laboratory, consisting of the coupling of a large solid angle magnetic spectrometer with a germanium array. By trajectory reconstruction the reaction products have been fully identified in mass, nuclear charge, and kinetic energy, while coincident gamma spectra of binary partners have been constructed after Doppler correction. Absolute differential cross sections have been extracted for the inelastic excitation and one-nucleon transfer, also for specific excited states. The data are in good agreement with semiclassical calculations and distorted wave Born approximation predictions. The work outlines an experimental method which can become valuable to extract structural information from heavy-ion reaction studies.
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Cata, O., & Kamenik, J. F. (2011). Electroweak precision observables at one loop in Higgsless models. Phys. Rev. D, 83(5), 053010–9pp.
Abstract: We study the viability of generic Higgsless models at low energies when compliance with electroweak precision observables and unitarity constraints up to the TeV scale are imposed. Our analysis shows that consistency with S and T can be achieved at the one-loop level even with a single light vector state, m(V) less than or similar to 500 GeV. However, this scenario turns out to be strongly disfavored when direct resonance searches at the Tevatron are also taken into account. We show that a fully consistent picture can be obtained if an axial state is introduced. Interestingly, mV is still predicted to be light (below 1 TeV) while typical values of m(A) span over the window 1.2m(V) <= m(A) <= 1.4m(V). Our results for the vector channel are rather robust and well within the reach of present-day colliders, while the axial channel is more loosely constrained.
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Oliveira, C. A. B., Sorel, M., Martin-Albo, J., Gomez-Cadenas, J. J., Ferreira, A. L., & Veloso, J. F. C. A. (2011). Energy resolution studies for NEXT. J. Instrum., 6, P05007–13pp.
Abstract: This work aims to present the current state of simulations of electroluminescence (EL) produced in gas-based detectors with special interest for NEXT – Neutrino Experiment with a Xenon TPC. NEXT is a neutrinoless double beta decay experiment, thus needs outstanding energy resolution which can be achieved by using electroluminescence. The process of light production is reviewed and properties such as EL yield and associated fluctuations, excitation and electroluminescence efficiencies, and energy resolution, are calculated. An EL production region with a 5 mm width gap between two infinite parallel planes is considered, where a uniform electric field is produced. The pressure and temperature considered are 10 bar and 293 K, respectively. The results show that, even for low values of VUV photon detection efficiency, good energy resolution can be achieved: below 0.4% (FWHM) at Q(beta beta) = 2.458 MeV.
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Cederwall, B. et al, Algora, A., & Gadea, A. (2011). Evidence for a spin-aligned neutron-proton paired phase from the level structure of Pd-92. Nature, 469(7328), 68–71.
Abstract: Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work(1) that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing(2-6), in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus Pd-92. Gamma rays emitted following the Ni-58(Ar-36,2n)Pd-92 fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution c-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction(2-6). We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling(7,8)) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
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BABAR Collaboration(Lees, J. P. et al), Lopez-March, N., Martinez-Vidal, F., & Oyanguren, A. (2011). Evidence for the h(b)(1P) meson in the decay Y(3S) -> pi(0)h(b)(1P). Phys. Rev. D, 84(9), 091101–8pp.
Abstract: Using a sample of 122 x 10(6) Y(3S) events recorded with the BABAR detector at the PEP-II asymmetric-energy e(+)e(-) collider at SLAC, we search for the h(b)(1P) spin-singlet partner of the P-wave X(bJ)(1P) states in the sequential decay Y(3S) -> pi(0)h(b) (1P), hb(1P) -> gamma eta(b)(1S). We observe an excess of events above background in the distribution of the recoil mass against the pi(0) at mass 9902 +/- 4(stat) +/- 2(syst) MeV/c(2). The width of the observed signal is consistent with experimental resolution, and its significance is 3.1 sigma, including systematic uncertainties. We obtain the value (4.3 +/- 1.1(stat) +/- 0.9(syst) x 10(-4) for the product branching fraction B(Y(3S) -> pi(0)h(b)) XB (h(b) -> gamma eta(b))
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Albertus, C., Hernandez, E., & Nieves, J. (2011). Exclusive c -> s, d semileptonic decays of ground-state spin-1/2 doubly charmed baryons. Phys. Lett. B, 704(5), 499–509.
Abstract: We evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons driven by a c -> s, d transition at the quark level. Our results for the form factors are consistent with heavy quark spin symmetry constraints which are valid in the limit of an infinitely massive charm quark and near zero recoil. Only a few exclusive semileptonic decay channels have been theoretically analyzed before. For those cases we find that our results are in a reasonable agreement with previous calculations.
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Rodriguez-Alvarez, M. J., Sanchez, F., Soriano, A., Iborra, A., & Mora, C. (2011). Exploiting symmetries for weight matrix design in CT imaging. Math. Comput. Model., 54(7-8), 1655–1664.
Abstract: In this paper we propose several methods of constructing the system matrix (SM) of a Computed Tomography (CT) scanner with two objectives: (1) to construct SMs in the shortest possible time and store them in an ordinary PC without losing quality, (2) to analyze the possible applications of the proposed method to 3D, taking into account SMs' sizes, computing time and reconstructed image quality. In order to build the SM, we propose two new field of view (FOV) pixellation schemes, based on a polar coordinate system (polar grid) by taking advantage of the polar rotation symmetries of CT devices. Comparisons between the SMs proposed are performed using two phantom and a real CT-simulator images. Global error, contrast, noise and homogeneity of the reconstructed images are discussed.
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Bandos, I. A., de Azcarraga, J. A., & Meliveo, C. (2011). Extended supersymmetry in massless conformal higher spin theory. Nucl. Phys. B, 853(3), 760–776.
Abstract: We propose superfield equations in tensorial N-extended superspaces to describe the N = 2,4,8 supersymmetric generalizations of free conformal higher spin theories. These can be obtained by quantizing a superparticle model in N-extended tensorial superspace. The N-extended higher spin supermultiplets just contain scalar and 'spinor' fields in tensorial space so that, in contrast with the standard (super)space approach, no nontrivial generalizations of the Maxwell or Einstein equations to tensorial space appear when N > 2. For N = 4,8, the higher spin-tensorial components of the extended tensorial superfields are expressed through additional scalar and spinor fields in tensorial space which obey the same free higher spin equations, but that are axion-like in the sense that they possess Peccei-Quinn-like symmetries.
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