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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for pair production of first or second generation leptoquarks in proton-proton collisions at sqrt(s)=7 TeV using the ATLAS detector at the LHC. Phys. Rev. D, 83(11), 112006–24pp.
Abstract: This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb(-1) of proton-proton collision data recorded by the ATLAS detector at root s = 7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M-LQ < 376 (319) GeV and M-LQ < 422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
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K2K Collaboration(Mariani, C. et al), Cervera-Villanueva, A., Tornero-Lopez, A., Burguet-Castell, J., Catala, J., Gomez-Cadenas, J. J., et al. (2011). Measurement of inclusive pi(0) production in the charged-current interactions of neutrinos in a 1.3-GeV wide band beam. Phys. Rev. D, 83(5), 054023–17pp.
Abstract: In this paper, we report on the measurement of the rate of inclusive pi(0) production induced by charged-current neutrino interactions in a C8H8 target at a mean energy of 1.3 GeV in the K2K near detector. Out of a sample of 11 606 charged- current neutrino interactions, we select 479 pi(0) events with two reconstructed photons. We find that the cross section for the inclusive pi(0) production relative to the charged-current quasielastic cross section is (CC)-C-sigma pi(0)/sigma CCQE = 0.426 +/- 0.032 (stat) +/- 0.035 (syst). The energy-dependent cross section ratio is also measured. The results are consistent with previous experiments for exclusive channels on different targets.
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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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Bernardoni, F., Garron, N., Hernandez, P., Necco, S., & Pena, C. (2011). Probing the chiral regime of N-f=2 QCD with mixed actions. Phys. Rev. D, 83(5), 054503–17pp.
Abstract: We report on our first experiences with a mixed action setup with overlap valence quarks and nonperturbatively O(a) improved Wilson sea quarks. For the latter we employ CLS N-f = 2 configurations with light sea-quark masses at small lattice spacings. Exact chiral symmetry allows to consider very light valence quarks and explore the matching to (partially-quenched) Chiral Perturbation Theory (ChPT) in a mixed epsilon/p-regime. We compute the topological susceptibility and the low-lying spectrum of the massless Neuberger-Dirac operator for three values of the sea-quark mass, and compare the sea-quark mass dependence to NLO ChPT in the mixed regime. This provides two different determinations of the chiral condensate, as well as information about some NLOlow-energy couplings. Our results allow to test the consistency of the mixed-regime approach to ChPT, as well as of the mixed action framework.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Measurement of the inclusive isolated prompt photon cross section in pp collisions at sqrt(s)=7 TeV with the ATLAS detector. Phys. Rev. D, 83(5), 052005–31pp.
Abstract: A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The measurement covers the pseudorapidity ranges vertical bar eta(gamma)vertical bar < 1: 37 and 1: 52 <= vertical bar eta(gamma)vertical bar < 1: 81 in the transverse energy range 15 <= E-T(gamma) < 100 GeV. The results are based on an integrated luminosity of 880 nb(-1), collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading-order perturbative QCD calculations.
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