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Baron, R., Boucaud, P., Dimopoulos, P., Frezzotti, R., Palao, D., Rossi, G., et al. (2010). Light meson physics from maximally twisted mass lattice QCD. J. High Energy Phys., 08(8), 097–41pp.
Abstract: We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for N-f = 2 mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 less than or similar to m(PS) less than or similar to 650MeV we control the major systematic effects of our calculation. This enables us to confront our N-f = 2 data with SU(2) chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass.
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Belver, D., Cabanelas, P., Castro, E., Garzon, J. A., Gil, A., Gonzalez-Diaz, D., et al. (2010). Performance of the Low-Jitter High-Gain/Bandwidth Front-End Electronics of the HADES tRPC Wall. IEEE Trans. Nucl. Sci., 57(5), 2848–2856.
Abstract: A front-end electronics (FEE) chain for accurate time measurements has been developed for the new Resistive Plate Chamber (RPC)-based Time-of-Flight (TOF) wall of the High Acceptance Di-Electron Spectrometer (HADES). The wall covers an area of around 8 m(2) divided in 6 sectors. In total, 1122 4-gap timing RPC cells are read-out by 2244 time and charge sensitive channels. The FEE chain consists of 2 custom-made boards: a 4-channel Daughter BOard(DBO) and a 32-channel MotherBOard (MBO). The DBO uses a fast 2 GHz amplifier feeding a dual high-speed discriminator. The time and charge information are encoded, respectively, in the leading edge and the width of an LVDS signal. Each MBO houses up to 8 DBOs providing them regulated voltage supply, threshold values via DACs, test signals and, additionally, routing out a signal proportional to the channel multiplicity needed for a 1st level trigger decision. The MBO delivers LVDS signals to a multi-purpose Trigger Readout Board (TRB) for data acquisition. The FEE allows achieving a system resolution around 75 ps fulfilling comfortably the requirements of the HADES upgrade [1]. The commissioning of the whole RPC wall is finished and the 6 sectors are already mounted in their final position in the HADES spectrometer and ready to take data during the beam-times foreseen for 2010.
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CDF Collaboration(Aaltonen, T. et al), Cabrera, S., & Cuenca Almenar, C. (2010). Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV using soft electron b-tagging. Phys. Rev. D, 81(9), 092002–18pp.
Abstract: We present a measurement of the top-quark pair-production cross section in p (p) over bar collisions at root s = 1.96 TeV using a data sample corresponding to 1.7 fb(-1) of integrated luminosity collected with the Collider Detector at Fermilab. We reconstruct t (t) over bar events in the lepton + jets channel, consisting of e nu + jets and μnu + jets final states. The dominant background is the production of W bosons in association with multiple jets. To suppress this background, we identify electrons from the semileptonic decay of heavy-flavor jets ("soft electron tags''). From a sample of 2196 candidate events, we obtain 120 tagged events with a background expectation of 51 +/- 3 events, corresponding to a cross section of sigma(t (t) over bar) = 7.8 +/- 2.4(stat) +/- 1.6(syst) +/- 0.5(lumi) pb. We assume a top-quark mass of 175 GeV/c(2). This is the first measurement of the t (t) over bar cross section with soft electron tags in run II of the Tevatron.
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de Azcarraga, J. A., Izquierdo, J. M., & Picon, M. (2011). Contractions of Filippov algebras. J. Math. Phys., 52(1), 013516–24pp.
Abstract: We introduce in this paper the contractions B-c of n-Lie (or Filippov) algebras B and show that they have a semidirect structure as their n = 2 Lie algebra counterparts. As an example, we compute the nontrivial contractions of the simple A(n+1) Filippov algebras. By using the. Inonu-Wigner and the generalized Weimar-Woods contractions of ordinary Lie algebras, we compare (in the B = A(n+1) simple case) the Lie algebras Lie B-c (the Lie algebra of inner endomorphisms of B-c) with certain contractions (Lie B)(IW) and (Lie B)(W-W) of the Lie algebra Lie B associated with B.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Direct Top-Quark Width Measurement at CDF. Phys. Rev. Lett., 105(23), 232003–7pp.
Abstract: We present a measurement of the top-quark width in the lepton + jets decay channel of t (t) over bar events produced in p (p) over bar collisions at Fermilab's Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4.3 fb(-1) of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths (Gamma(t)) and deviations from nominal jet energy scale (Delta(JES)) to perform a simultaneous fit for both parameters, where Delta(JES) is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of Gamma(t) < 7.6 GeV and a two-sided 68% CL interval of 0.3 GeV < Gamma(t) < 4.4 GeV for a top-quark mass of 172.5 GeV/c(2), which are consistent with the standard model prediction.
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Noguera, S., & Vento, V. (2010). The pion transition form factor and the pion distribution amplitude. Eur. Phys. J. A, 46(2), 197–205.
Abstract: Recent BaBar data on the pion transition form factor, whose Q(2)-dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism based on a model-independent description for low photon virtuality and a high photon virtuality description based on QCD, which match at a scale Q(0). The high photon virtuality description incorporates a flat pion distribution amplitude, phi(x) = 1, at the matching scale Q(0) and QCD evolution from Q(0) to Q > Q(0). The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valence parton distribution at the same low scale Q(0). The procedure leads to a good description of the data, and by incorporating additional twist-three effects, to an excellent description of the data.
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Kaskulov, M., Hernandez, E., & Oset, E. (2010). On the background in the gamma p -> omega(pi(0)gamma)p reaction and mixed event simulation. Eur. Phys. J. A, 46(2), 223–230.
Abstract: In this paper we evaluate sources of background of the gamma p -> omega p reaction, with the omega detected through its pi(0)gamma decay channel, to compare with the experiment carried out at ELSA. We find background from gamma p -> pi(0)pi(0)p followed by decay of a pi(0) into two gamma, recombining one pi(0) and one gamma, and from the gamma p -> pi(0)eta p reaction with subsequent decay of the eta into two photons. This background accounts for the data at pi(0)gamma invariant masses beyond 700 MeV, but strength is missing at lower invariant masses which was attributed to photon misidentification events, which we simulate to get a good reproduction of the experimental background. Once this is done, we perform an event mixing simulation to reproduce the calculated background and we find that the method provides a good description of the background. A closer look reveals this is accidental. We show that the mixed event generated background in the region of the omega mass and beyond is completely tied to the events at low pi(0)gamma invariant masses where the d sigma/dM(pi 0 gamma) distribution is much larger. This has as a consequence that the mixed event method produces the same background at high invariant masses independently of the actual background in that region, as a consequence of which, the method is unsuited to give the background at energies around the peak of the omega and beyond.
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Doring, M., Oset, E., & Meissner, U. G. (2010). Evaluation of the polarization observables I-S and I-C in the reaction gamma p -> pi(0)eta p. Eur. Phys. J. A, 46(2), 315–323.
Abstract: We evaluate the polarization observables I-S and I-C for the reaction gamma p -> pi(0)eta p, using a chiral unitary framework developed earlier. The I-S and I-C observables have been recently measured for the first time by the CBELSA/TAPS Collaboration. The theoretical predictions of I-S and I-C, given for altogether 18 angle-dependent functions, are in good agreement with the measurements. Also, the asymmetry d Sigma/dcos theta evaluated here agrees with the data. We show the importance of the Delta(1700) D-33-resonance and its S-wave decay into eta Delta(1232). The result can be considered as a further confirmation of the dynamical nature of this resonance. At the highest energies, deviations of the predictions from the data start to become noticeable, which leaves room for additional processes and resonances such as a Delta(1940) D-33. We also point out how to further improve the calculation.
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Girones, Z., Marchetti, A., Mena, O., Pena-Garay, C., & Rius, N. (2010). Cosmological data analysis of f(R) gravity models. J. Cosmol. Astropart. Phys., 11(11), 004–18pp.
Abstract: A class of well-behaved modified gravity models with long enough matter domination epoch and a late-time accelerated expansion is confronted with SNIa, CMB, SDSS, BAO and H(z) galaxy ages data, as well as current measurements of the linear growth of structure. We show that the combination of geometrical probes and growth data exploited here allows to rule out f(R) gravity models, in particular, the logarithmic of curvature model. We also apply solar system tests to the models in agreement with the cosmological data. We find that the exponential of the inverse of the curvature model satisfies all the observational tests considered and we derive the allowed range of parameters. Current data still allows for small deviations of Einstein gravity. Future, high precision growth data, in combination with expansion history data, will be able to distinguish tiny modifications of standard gravity from the Lambda CDM model.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for single top quark production in p(p)over-bar collisions at root s=1.96 TeV in the missing transverse energy plus jets topology. Phys. Rev. D, 81(7), 072003–24pp.
Abstract: We report a search for single top quark production with the CDF II detector using 2: 1 fb(-1) of integrated luminosity of p (p) over bar collisions at root s = 1.96 TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W -> tau nu decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without single top quark production by 2.1 standard deviations (sigma), with a median expected sensitivity of 1.4 sigma. Assuming a top quark mass of 175 GeV/c(2) and ascribing the excess to single top quark production, the cross section is measured to be 4.9(-2.2)(+2.5) (stat + syst) pb, consistent with measurements performed in independent data sets and with the standard model prediction.
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