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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. (2014). Search for nonpointing and delayed photons in the diphoton and missing transverse momentum final state in 8 TeV pp collisions at the LHC using the ATLAS detector. Phys. Rev. D, 90(11), 112005–29pp.
Abstract: A search has been performed, using the full 20.3 fb(-1) data sample of 8 TeV proton-proton collisions collected in 2012 with the ATLAS detector at the LHC, for photons originating from a displaced vertex due to the decay of a neutral long-lived particle into a photon and an invisible particle. The analysis investigates the diphoton plus missing transverse momentum final state, and is therefore most sensitive to pair production of long-lived particles. The analysis technique exploits the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction, as well as the time of flight, of photons. No excess is observed over the Standard Model predictions for background. Exclusion limits are set within the context of gauge mediated supersymmetry breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying into a photon and gravitino with a lifetime in the range from 250 ps to about 100 ns.
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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. (2015). Measurements of Higgs boson production and couplings in the four-lepton channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector. Phys. Rev. D, 91(1), 012006–47pp.
Abstract: The final ATLAS Run 1 measurements of Higgs boson production and couplings in the decay channel H -> ZZ* -> l(+)l(-)l(+)l'(-), where l, l' = e or mu, are presented. These measurements were performed using pp collision data corresponding to integrated luminosities of 4.5 and 20.3 fb(-1) at center-of-mass energies of 7 and 8 TeV, respectively, recorded with the ATLAS detector at the LHC. The H -> ZZ* -> 4l signal is observed with a significance of 8.1 standard deviations, with an expectation of 6.2 standard deviations, at m(H) = 125.36 GeV, the combined ATLAS measurement of the Higgs boson mass from the H -> gamma gamma and H -> ZZ* -> 4l channels. The production rate relative to the Standard Model expectation, the signal strength, is measured in four different production categories in the H -> ZZ* -> 4l channel. The measured signal strength, at this mass, and with all categories combined, is 1.44(-0.33)(+0.40). The signal strength for Higgs boson production in gluon fusion or in association with (tt) over bar or (bb) over bar pairs is found to be 1.7(-0.4)(+0.5), while the signal strength for vector-boson fusion combined with WH/ZH associated production is found to be 0.3(-0.9)(+1.6).
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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. (2014). Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector. Phys. Rev. D, 90(11), 112015–44pp.
Abstract: A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb(-1) of proton-proton collisions data at root s = 7 TeV and 20.3 fb(-1) at root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be μ= 1.17 +/- 0.27 at the value of the Higgs boson mass measured by ATLAS, m(H) = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m(H). They are found to be mu(ggF) = 1.32 +/- 0.38, mu(VBF) = 0.8 +/- 0.7, mu(WH) = 1.0 +/- 1.6, mu(ZH) = 0.1(-0.1)(+3.7), and μt (t) over barH = 1.6(-1.8)(+2.7), for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.
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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. (2015). Observation of top-quark pair production in association with a photon and measurement of the t(t)over-bar gamma production cross section in pp collisions at root s=7 TeV using the ATLAS detector. Phys. Rev. D, 91(7), 072007–28pp.
Abstract: A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events, respectively. The production of t (t) over bar gamma events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t (t) over bar gamma production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is sigma(fid)(t (t) over bar gamma) x BR = 63 +/- 8(stat)(-13)(+17) (syst) +/- 1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 +/- 10 fb.
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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. (2012). Underlying event characteristics and their dependence on jet size of charged-particle jet events in pp collisions at root(s)=7 TeV with the ATLAS detector. Phys. Rev. D, 86(7), 072004–34pp.
Abstract: Distributions sensitive to the underlying event are studied in events containing one or more chargedparticle jets produced in pp collisions at root s = 7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 μb(-1) of data taken during 2010. Jets are reconstructed using the anti-k(t) algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle p(T) are measured as functions of p(T)(jet) in regions transverse to and opposite the leading jet for 4 GeV < p(T)(jet) < 100 GeV. In addition, the R dependence of the mean values of these observables is studied. In the transverse region, both the multiplicity and the scalar sum of the transverse momentum at fixed p(T)(jet) vary significantly with R, while the average charged- particle transverse momentum has a minimal dependence on R. Predictions from several Monte Carlo tunes have been compared to the data; the predictions from Pythia 6, based on tunes that have been determined using LHC data, show reasonable agreement with the data, including the dependence on R. Comparisons with other generators indicate that additional tuning of soft-QCD parameters is necessary for these generators. The measurements presented here provide a testing ground for further development of the Monte Carlo models.
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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. (2012). ATLAS measurements of the properties of jets for boosted particle searches. Phys. Rev. D, 86(7), 072006–30pp.
Abstract: Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of root s = 7 TeV. The data correspond to an integrated luminosity of 35 pb(-1) and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-k(t) algorithm with distance parameters R 0: 6 and 1.0, with transverse momentum p(T) > 300 GeV and pseudorapidity vertical bar eta vertical bar < 2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.
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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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Ayala, C., & Mikhailov, S. V. (2015). How to perform a QCD analysis of DIS in analytic perturbation theory. Phys. Rev. D, 92(1), 014028–11pp.
Abstract: We apply (fractional) analytic perturbation theory (FAPT) to the QCD analysis of the nonsinglet nucleon structure function F-2(x, Q(2)) in deep inelastic scattering up to the next leading order and compare the results with ones obtained within the standard perturbation QCD. Based on a popular parametrization of the corresponding parton distribution we perform the analysis within the Jacobi polynomial formalism and under the control of the numerical inverse Mellin transform. To reveal the main features of the FAPT two-loop approach, we consider a wide range of momentum transfer from high Q(2) similar to 100 GeV2 to low Q(2) similar to 0.3 GeV2 where the approach still works.
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Azizi, K., Bayar, M., Ozpineci, A., Sarac, Y., & Sundu, H. (2012). Semileptonic transition of Sigma(b) to Sigma in light cone QCD sum rules. Phys. Rev. D, 85(1), 016002–8pp.
Abstract: We use distribution amplitudes of the light Sigma baryon and the most general form of the interpolating current for heavy Sigma(b) baryon to investigate the semileptonic Sigma(b) -> Sigma l(+)l(-) transition in light cone QCD sum rules. We calculate all 12 form factors responsible for this transition and use them to evaluate the branching ratio of the considered channel. The order of branching fraction shows that this channel can be detected at LHC.
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BABAR and Belle Collaborations(Adachi, I. et al), Martinez-Vidal, F., & Oyanguren, A. (2018). Measurement of cos 2 beta in B-0 -> D((*))h(0) with D -> K-S(0)pi(+) pi(-) decays by a combined time-dependent Dalitz plot analysis of BABAR and Belle data. Phys. Rev. D, 98(11), 112012–29pp.
Abstract: We report measurements of sin 2 beta and cos 2 beta using a time-dependent Dalitz plot analysis of B-0 -> D((*))h(0) with D -> K-S(0)pi(+)pi(-) decays, where the light unflavored and neutral hadron h(0) is a pi(0),eta, or omega meson. The analysis uses a combination of the final data sets of the BABAR and Belle experiments containing 471 x 10(6) and 772 x 10(6) B (B) over bar pairs collected at the gamma(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We measure sin 2 beta = 0.80 +/- 0.14(stat) +/- 0.06(syst) +/- 0.03(model) and cos 2 beta = 0.91 +/- 0.22(stat) +/- 0.09(syst) +/- 0.07(model). The result for the direct measurement of the angle is beta = (22.5 +/- 4.4(stat) +/- 1.2(syst) +/- 0.6(model))degrees. The last quoted uncertainties are due to the composition of the D-0 -> K-S(0)pi(+)pi(-) decay amplitude model, which is newly established by a Dalitz plot amplitude analysis of a high-statistics e(+) e(-) -> c (c) over bar data sample as part of this analysis. We find the first evidence for cos 2 beta > 0 at the level of 3.7 standard deviations. The measurement excludes the trigonometric multifold solution pi/2 – beta = (68.1 +/- 0.7)degrees at the level of 7.3 standard deviations and therefore resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The hypothesis of beta = 0 degrees is ruled out at the level of 5.1 standard deviations, and thus CP violation is observed in B-0 -> D-(*) h(0) decays. The measurement assumes no direct CP violation in B-0 -> D-(*) h(0) decays.
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