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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2013). Measurement of CP asymmetries and branching fractions in charmless two-body B-meson decays to pions and kaons. Phys. Rev. D, 87(5), 052009–16pp.
Abstract: We present improved measurements of CP-violation parameters in the decays B-0 -> pi(+)pi(-), B-0 -> K+pi(-), and B-0 -> pi(0)pi(0), and of the branching fractions for B-0 -> pi(0)pi(0) and B-0 -> K-0 pi(0). The results are obtained with the full data set collected at the Upsilon(4S) resonance by the BABAR experiment at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory, corresponding to (467 +/- 5) x 10(6) B (B) over bar pairs. We find the CP-violation parameter values and branching fractions: S pi+pi- = -0.68 +/- 0.10 +/- 0.03, C-pi+pi(-) = -0.25 +/- 0.08 +/- 0.02, A(K+pi-) = -0.107 +/- 0.016(-0.004)(+0.006), C pi(0)pi(0) = -0.43 +/- 0.26 +/- 0.05, B(B-0 -> pi(0)pi(0)) = (1.83 +/- 0.21 +/- 0.13) x 10(-6), B(B-0 -> pi(0)pi(0)) = (10.1 +/- 0.6 +/- 0.4) x 10(-6), where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for B-0 -> pi(+)pi(-) and 6.1 standard deviations for B-0 -> K+pi(-), including systematic uncertainties. Constraints on the unitarity triangle angle alpha are determined from the isospin relations among the B -> pi pi rates and asymmetries. Considering only the solution preferred by the Standard Model, we find alpha to be in the range [71 degrees,109 degrees] at the 68% confidence level.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2013). Evidence of B+ -> tau(+)nu decays with hadronic B tags. Phys. Rev. D, 88(3), 031102–9pp.
Abstract: We present a search for the decay B+ -> tau(+)nu using 467.8 x 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II B-Factory. We select a sample of events with one completely reconstructed B- in the hadronic decay mode (B- -> D-(*X-)0(-) and B- -> J/psi X-). We examine the rest of the event to search for a B+ -> tau(+)nu decay. We identify the tau(+) lepton in the following modes: tau(+) -> e(+)nu(nu) over bar, tau(+) -> mu(+)nu(nu) over bar, tau(+) -> pi(+)(nu) over bar and tau(+) -> rho(+)(nu) over bar. We find an excess of events with respect to the expected background, which excludes the null signal hypothesis at the level of 3.8 sigma (including systematic uncertainties) and corresponds to a branching fraction value of B(B+ -> tau(+)nu) = (1.83(-0.49)(+0.53)(stat) +/- 0.24(syst)) x 10(-4).
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Bertone, V., Carrasco, N., Ciuchini, M., Dimopoulos, P., Frezzotti, R., Gimenez, V., et al. (2013). Kaon mixing beyond the SM from N-f=2 tmQCD and model independent constraints from the UTA. J. High Energy Phys., 03(3), 089–53pp.
Abstract: We present the first unquenched, continuum limit, lattice QCD results for the matrix elements of the operators describing neutral kaon oscillations in extensions of the Standard Model. Owing to the accuracy of our calculation on Delta S = 2 weak Hamiltonian matrix elements, we are able to provide a refined Unitarity Triangle analysis improving the bounds coming from model independent constraints on New Physics. In our non-perturbative computation we use a combination of N-f = 2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks in order to achieve both O(a)-improvement and continuum-like renormalization properties for the relevant four-fermion operators. The calculation of the renormalization constants has been performed non-perturbatively in the RI-MOM scheme. Based on simulations at four values of the lattice spacing and a number of quark masses we have extrapolated/interpolated our results to the continuum limit and physical light/strange quark masses.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2013). Measurement of the Lambda(0)(b) lifetime and mass in the ATLAS experiment. Phys. Rev. D, 87(3), 032002–19pp.
Abstract: A measurement of the Lambda(0)(b) lifetime and mass in the decay channel Lambda(0)(b) -> J/psi (mu(+) mu(-))Lambda(0)(p pi(-)) is presented. The analysis uses a signal sample of about 2200 Lambda(0)(b) and (Lambda) over bar (0)(b) decays that are reconstructed in 4.9 fb(-1) of ATLAS pp collision data collected in 2011 at the LHC center-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the Lambda(0)(b) lifetime and mass. They are measured to be tau(Lambda b) = 1.449 +/- 0.036(stat) +/- 0.017(syst) ps and m(Lambda b) = 5619.7 +/- 0.7(stat) +/- 1.1(syst) MeV.
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Perez-Ramos, R., & Mathieu, V. (2013). Collimation of energy in medium-modified QCD jets. Phys. Lett. B, 718(4-5), 1421–1424.
Abstract: The collimation of energy inside medium-modified jets is investigated in the leading logarithmic approximation of QCD. The Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations are slightly modified by introducing splitting functions enhanced in the infrared sector. As compared to elementary collisions in the vacuum, the angular distribution of the jet energy is found to broaden in QCD media.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2013). Measurements of top quark pair relative differential cross-sections with ATLAS in pp collisions at root s=7 TeV. Eur. Phys. J. C, 73(1), 2261–28pp.
Abstract: Measurements are presented of differential cross-sections for top quark pair production in pp collisions at root s = 7 TeV relative to the total inclusive top quark pair production cross-section. A data sample of 2.05 fb(-1) recorded by the ATLAS detector at the Large Hadron Collider is used. Relative differential cross-sections are derived as a function of the invariant mass, the transverse momentum and the rapidity of the top quark pair system. Events are selected in the lepton (electron or muon) + jets channel. The background-subtracted differential distributions are corrected for detector effects, normalized to the total inclusive top quark pair production cross-section and compared to theoretical predictions. The measurement uncertainties range typically between 10 % and 20 % and are generally dominated by systematic effects. No significant deviations from the Standard Model expectations are observed.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurement of charged-particle event shape variables in inclusive root(s)=7 TeV proton-proton interactions with the ATLAS detector. Phys. Rev. D, 88(3), 032004–25pp.
Abstract: The measurement of charged-particle event shape variables is presented in inclusive inelastic pp collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the LHC. The observables studied are the transverse thrust, thrust minor, and transverse sphericity, each defined using the final-state charged particles' momentum components perpendicular to the beam direction. Events with at least six charged particles are selected by a minimum-bias trigger. In addition to the differential distributions, the evolution of each event shape variable as a function of the leading charged-particle transverse momentum, charged-particle multiplicity, and summed transverse momentum is presented. Predictions from several Monte Carlo models show significant deviations from data.
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Bernabeu, J., Di Domenico, A., & Villanueva-Perez, P. (2013). Direct test of time reversal symmetry in the entangled neutral kaon system at a phi-factory. Nucl. Phys. B, 868(1), 102–119.
Abstract: We present a novel method to perform a direct T (time reversal) symmetry test in the neutral kaon system, independent of any CP and/or CPT symmetry tests. This is based on the comparison of suitable transition probabilities, where the required interchange of in <-> out states for a given process is obtained exploiting the Einstein-Podolski-Rosen correlations of neutral kaon pairs produced at a phi-factory. In the time distribution between the two decays, we compare a reference transition like the one defined by the time-ordered decays (l(-), pi pi) with the T-conjugated one defined by (3 pi(0), l(+)). With the use of this and other T-conjugated comparisons, the KLOE-2 experiment at DA Phi NE could make a statistically significant test.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using 4.7 fb(-1) of root s=7 TeV proton-proton collision data. Phys. Rev. D, 87(1), 012008–34pp.
Abstract: A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-p(T) electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 4.7 fb(-1). No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In minimal supergravity/constrained minimal supersymmetric Standard Model models with tan beta = 10, A(0) = 0 and μ> 0, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of supersymmetric models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
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Antonelli, V., Miramonti, L., Pena-Garay, C., & Serenelli, A. (2013). Solar Neutrinos. Adv. High. Energy Phys., 2013, 351926–34pp.
Abstract: The study of solar neutrinos has given a fundamental contribution both to astroparticle and to elementary particle physics, offering an ideal test of solar models and offering at the same time relevant indications on the fundamental interactions among particles. After reviewing the striking results of the last two decades, which were determinant to solve the long standing solar neutrino puzzle and refine the Standard Solar Model, we focus our attention on the more recent results in this field and on the experiments presently running or planned for the near future. The main focus at the moment is to improve the knowledge of the mass and mixing pattern and especially to study in detail the lowest energy part of the spectrum, which represents most of the solar neutrino spectrum but is still a partially unexplored realm. We discuss this research project and the way in which present and future experiments could contribute to make the theoretical framework more complete and stable, understanding the origin of some “anomalies” that seem to emerge from the data and contributing to answer some present questions, like the exact mechanism of the vacuum to matter transition and the solution of the so-called solar metallicity problem.
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