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Xie, J. J., Wang, E., & Nieves, J. (2014). Re-analysis of the A(1520) photoproduction reaction. Phys. Rev. C, 89(1), 015203–10pp.
Abstract: Based on previous studies that support the important role of the N*(2120)D-13 resonance in the gamma p -> K+ A(1520) reaction, we make a re-analysis of this A(1520) photoproduction reaction taking into account the recent CLAS differential cross-section data. In addition to the contact, t-channel (K) over bar exchange, s-channel nucleon pole, and N*(2120) [previously called N*(2080)] resonance contributions, which have been considered in previous works, we also study the u-channel A(1115) hyperon pole term. The latter mechanism has always been ignored in all theoretical analysis, which has mostly relied on the very forward K+ angular LEPS data. It is shown that when the contributions from the N*(2120) resonance and the A(1115) hyperon are taken into account, both the new CLAS and the previous LEPS data can be simultaneously described. We also show that the contribution from the u-channel A(1115) pole term produces an enhancement for large K+ angles, and it becomes more and more relevant as the photon energy increases, being essential to describe the CLAS differential cross sections at backward angles. Furthermore, we find that the new CLAS data also favor the existence of the N*(2120) resonance and that these measurements can be used to further constrain its properties.
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Campanario, F., Kaiser, N., & Zeppenfeld, D. (2014). W gamma production in vector boson fusion at NLO in QCD. Phys. Rev. D, 89(1), 014009–5pp.
Abstract: The next-to-leading order QCD corrections to W-+/-gamma. production in association with two jets via vector boson fusion are calculated, including the leptonic decay of the W with full off-shell effects and spin correlations. The process lends itself to a test of quartic gauge couplings. The next-to-leading order corrections reduce the scale uncertainty significantly and show a nontrivial phase space dependence.
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Campanario, F., Rauch, M., & Sapeta, S. (2014). W+W- production at high transverse momenta beyond NLO. Nucl. Phys. B, 879, 65–79.
Abstract: Pair production of W gauge bosons is an important process at the LHC entering many experimental analyses, both as background in new-physics searches or Higgs measurements and as signal in precision studies and tests of the Standard Model. Therefore, accurate predictions for this class of processes are of great interest in order to exploit the full potential of LHC measurements. We use the LoopSim method to combine NLO QCD results for WW and WW + jet, as well as the loop-squared gluon-fusion contribution, to obtain approximate NNLO predictions for WW production. The cross sections are calculated with VBFNLO and include leptonic decays of the W bosons as well as finite-width and off-shell effects. We find that the size of the additional corrections beyond NLO can be significant and well outside of the NLO error bands given by renormalization and factorization scale variation. Applying a jet veto, we observe further negative corrections at NNLO. which we relate to the presence of large Sudakov logarithms.
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Juste, A., Mantry, S., Mitov, A., Penin, A., Skands, P., Varnes, E., et al. (2014). Determination of the top quark mass circa 2013: methods, subtleties, perspectives. Eur. Phys. J. C, 74(10), 3119–14pp.
Abstract: We present an up-to-date overview of the problem of top quark mass determination. We assess the need for precision in the top mass extraction in the LHC era together with the main theoretical and experimental issues arising in precision top mass determination. We collect and document existing results on top mass determination at hadron colliders and map the prospects for future precision top mass determination at e(+)e(-) colliders. We present a collection of estimates for the ultimate precision of various methods for top quark mass extraction at the LHC.
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Garzon, E. J., Molina, R., Hosaka, A., & Oset, E. (2014). Strategies for an accurate determination of the X(3872) energy from QCD lattice simulations. Phys. Rev. D, 89(1), 014504–9pp.
Abstract: We develop a method to determine accurately the binding energy of the X( 3872) from lattice data for the D (D) over bar* interaction. We show that, because of the small difference between the neutral and charged components of the X( 3872), it is necessary to differentiate them in the energy levels of the lattice spectrum if one wishes to have a precise determination of the the binding energy of the X( 3872). The analysis of the data requires the use of coupled channels. Depending on the number of levels available and the size of the box, we determine the precision needed in the lattice energies to finally obtain a desired accuracy in the binding energy.
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Martinez Torres, A., Khemchandani, K. P., Navarra, F. S., Nielsen, M., & Oset, E. (2014). Reanalysis of the e(+)e(-) -> (D*(D*)over-bar)(+/-)pi(-/+) reaction and the claim for the Z(c)(4025) resonance. Phys. Rev. D, 89(1), 014025–9pp.
Abstract: In this paper we study the reaction e(+)e(-) -> (D*(D*) over bar (+/-)pi(-/+) in which the BESIII collaboration has claimed the existence of a 1(+) resonance, named Z(c)(4025), in the (D*(D*) over bar invariant mass spectrum with a mass around 4026 MeV and width close to 26 MeV. We determine the (D*(D*) over bar invariant mass distribution and find that although the explanation considered by the BESIII collaboration is plausible, there are others which are equally possible, like a 2(+) resonance or a bound state. Even more, we find that the data can be explained without the existence of a resonance/bound state. In view of the different possible interpretations found for the BESIII data, we try to devise a strategy which could help in identifying the origin of the signal reported by the BESIII collaboration. For this, we study the dependence of the (D*(D*) over bar spectrum considering the different options as a function of the total center-of-mass energy. We arrive at the conclusion that increasing the center-of-mass energy from 4.26 GeV to 4.6 GeV can be useful to distinguish between a resonance, a bound state or just a pure background as being responsible for the signal found. This information should be useful for future experiments.
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Pich, A., Rosell, I., & Sanz-Cillero, J. J. (2014). Oblique S and T constraints on electroweak strongly-coupled models with a light Higgs. J. High Energy Phys., 01(1), 157–35pp.
Abstract: Using a general effective Lagrangian implementing the chiral symmetry breaking SU(2)(L) circle times SU(2)(R) -> SU(2)(L+R), we present a one-loop calculation of the oblique S and T parameters within electroweak strongly-coupled models with a light scalar. Imposing a proper ultraviolet behaviour, we determine S and T at next-to-leading order in terms of a few resonance parameters. The constraints from the global fit to electroweak precision data force the massive vector and axial-vector states to be heavy, with masses above the TeV scale, and suggest that the W+W- and and ZZ couplings of the Higgs-like scalar should be close to the Standard Model value. Our findings are generic, since they only rely on soft requirements on the short-distance properties of the underlying strongly-coupled theory, which are widely satisfied in more specific scenarios.
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Stuhl, L., Krasznahorkay, A., Csatlos, M., Algora, A., Gulyas, J., Kalinka, G., et al. (2014). A neutron spectrometer for studying giant resonances with (p,n) reactions in inverse kinematics. Nucl. Instrum. Methods Phys. Res. A, 736, 1–9.
Abstract: A neutron spectrometer, the European Low-Energy Neutron Spectrometer (ELENS), has been constructed to study exotic nuclei in inverse-kinematics experiments. The spectrometer, which consists of plastic scintillator bars, can be operated in the neutron energy range of 100 keV-10 MeV. The neutron energy is determined using the time-of-flight technique, while the position of the neutron detection is deduced from the time-difference information from photomultipliers attached to both ends of each bar. A novel wrapping method has been developed for the plastic scintillators. The array has a larger than 25% detection efficiency for neutrons of approximately 500 keV in kinetic energy and an angular resolution of less than 1 degrees. Details of the design, construction and experimental tests of the spectrometer will be presented.
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Pich, A. (2014). Precision tau physics. Prog. Part. Nucl. Phys., 75, 41–85.
Abstract: Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of tau physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the tau lepton probe the structure of the weak currents and the universality of their couplings to the W boson. The universality of the leptonic Z couplings has also been tested through Z -> l(+)l(-) decays. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the Cabibbo mixing V-us have been obtained with tau data. The large mass of the tau opens the possibility to study many kinematically-allowed exclusive decay modes and extract relevant dynamical information. Violations of flavour and CP conservation laws can also be searched for with tau decays. Related subjects such as μdecays, the electron and muon anomalous magnetic moments, neutrino mixing and B-meson decays into tau leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the tau lepton is playing now a very important role at the LHC as a tool to test the Higgs properties and search for new physics at higher scales.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Search for lepton-number violating B+ -> X(-)l(+)l '(+) decays. Phys. Rev. D, 89(1), 011102–8pp.
Abstract: We report on a search for eleven lepton-number violating processes B+ -> X(-)l(+)l'(+) with X- = K-, pi(-), rho(-), K*(-), or D- and l(+)/l'(+) = e(+) or mu(+), using a sample of 471 +/- 3 million B (B) over bar events collected with the BABAR detector at the PEP-II e(+)e(-) collider at the SLAC National Accelerator Laboratory. We find no evidence for any of these modes and place 90% confidence level upper limits on their branching fractions in the range (1.5-26) x 10(-7).
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