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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 stable hadronising squarks and gluinos with the ATLAS experiment at the LHC. Phys. Lett. B, 701(1), 1–19.
Abstract: Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton-proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb(-1). No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.
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Mangano, G., Miele, G., Pastor, S., Pisanti, O., & Sarikas, S. (2012). Updated BBN bounds on the cosmological lepton asymmetry for non-zero theta(13). Phys. Lett. B, 708(1-2), 1–5.
Abstract: We discuss the bounds on the cosmological lepton number from Big Bang Nucleosynthesis (BBN), in light of recent evidences for a large value of the neutrino mixing angle theta(13), sin(2) theta(13) greater than or similar to 0.01 at 2 sigma. The largest asymmetries for electron and mu, tau neutrinos compatible with He-4 and H-2 primordial yields are computed versus the neutrino mass hierarchy and mixing angles. The flavour oscillation dynamics is traced till the beginning of BBN and neutrino distributions after decoupling are numerically computed. The latter contains in general, non-thermal distortion due to the onset of flavour oscillations driven by solar squared mass difference in the temperature range where neutrino scatterings become inefficient to enforce thermodynamical equilibrium. Depending on the value of theta(13), this translates into a larger value for the effective number of neutrinos, N-eff. Upper bounds on this parameter are discussed for both neutrino mass hierarchies. Values for N-eff which are large enough to be detectable by the Planck experiment are found only for the (presently disfavoured) range sin(2) theta(13) <= 0.01.
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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). Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC. Phys. Lett. B, 716(1), 1–29.
Abstract: A search for the Standard Model Higgs boson in proton-proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb(-1) collected at, root s = 7 TeV in 2011 and 5.8 fb(-1) at root s = 8 TeV in 2012. Individual searches in the channels H -> ZZ(()*()) -> 4l, H -> gamma gamma and H -> WW (()*()) -> ev μv in the 8 TeV data are combined with previously published results of searches for H -> ZZ(()*()), WW(*()), b (b) over bar and tau(+)tau(-) in the 7 TeV data and results from improved analyses of the H -> ZZ(()*()) -> 4l and H -> gamma gamma channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of 126.0 +/- 0.4 (stat) +/- 0.4 (sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7 x 10(-9), is compatible with the production and decay of the Standard Model Higgs boson. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Determination of gamma and-2 beta(s) from charmless two-body decays of beauty mesons. Phys. Lett. B, 741, 1–11.
Abstract: Using the latest LHCb measurements of time-dependent CP violation in the B-s(0) -> K+K- decay, a U-spin relation between the decay amplitudes of B-s(0) -> K+K- and B-0 -> p(+)p(-) decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B-s(0) mixing phase -2 beta(s). Results from an extended approach, which uses additional inputs on B-0 -> pi(0)pi(0) and B+ -> pi(+)pi(0) decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of U-spin breaking is studied. At 68% probability, the value gamma =( 63.5(-6.7)(+7.2))degrees modulo 180 degrees is determined. In an alternative analysis, the value -2 beta(s)= – 0.12(-0.16)(+ 0.14) rad is found. In both measurements, the uncertainties due to U-spin breaking effects up to 50% are included.
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Roy, S., Morisi, S., Singh, N. N., & Valle, J. W. F. (2015). The Cabibbo angle as a universal seed for quark and lepton mixings. Phys. Lett. B, 748, 1–4.
Abstract: A model-independent ansatz to describe lepton and quark mixing in a unified way is suggested based upon the Cabibbo angle. In our framework neutrinos mix in a “Bi-Large” fashion, while the charged leptons mix as the “down-type” quarks do. In addition to the standard Wolfenstein parameters (lambda, A) two other free parameters (psi, delta) are needed to specify the physical lepton mixing matrix. Through this simple assumption one makes specific predictions for the atmospheric angle as well as leptonic CP violation in good agreement with current observations.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurement of the W-+/- Z boson pair-production cross section in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 762, 1–22.
Abstract: The production of W-+/- Z events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb(-1). The W-+/- Z candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is sigma(fid.)(W +/- Z -> L'vll) = 63.2 +/- 3.2 (stat.) +/- 2.6 (sys.) +/- 1.5 (lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is 53.4(-2.8)(+3.6) fb. The extrapolation of the measurement from the fiducial to the total phase space yields sigma(tot.)(W +/- Z) = 50.6 +/- 2.6 (stat.) +/- 2.0 (sys.) +/- 0.9 (th.) +/- 1.2 (lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of 48.2(-1.0)(+1.1) pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent W+ Z and W- Z cross sections and their ratio.
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n_TOF Collaboration(Massimi, C. et al.), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2017). Neutron spectroscopy of Mg-26 states: Constraining the stellar neutron source Ne-22(alpha, n)Mg-25. Phys. Lett. B, 768, 1–6.
Abstract: This work reports on accurate, high-resolution measurements of the Mg-25(n, gamma)Mg-26 and Mg-25(n, tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved Mg-25(n, gamma)Mg-26 parametrization. The relevant resonances for n+Mg-25 were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in Mg-26. With this information experimental upper limits of the reaction rates for Ne-22(alpha, n)Mg-25 and Ne-22(alpha, gamma)Mg-26 were established, potentially leading to a significantly higher (alpha, n)/(alpha, gamma) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M-circle dot. (C) 2017 The Author(s). Published by Elsevier B.V.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Search for Higgs boson decays into a pair of light bosons in the bb μμfinal state in pp collision at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 790, 1–21.
Abstract: A search for decays of the Higgs boson into a pair of new spin-zero particles, H -> aa, where the a-bosons decay into a b-quark pair and a muon pair, is presented. The search uses 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio (sigma(H)/sigma(SM)) x B(H -> aa -> bb μmu), ranging from 1.2 x 10(-4) to 8.4 x 10(-4) in the a-boson mass range of 20-60 GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the bb μμfinal state for new physics, sigma(vis)(X) x B(X -> bb μmu), ranging from 0.1 fb to 0.73 fb for m(mu mu) between 18 and 62 GeV.
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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. (2014). Search for Higgs boson decays to a photon and a Z boson in pp collisions at root s=7 and 8 TeV with the ATLAS detector. Phys. Lett. B, 732, 8–27.
Abstract: A search is reported for a neutral Higgs boson in the decay channel H -> Z gamma, Z -> l(+)l(-) (l = e, mu), using 4.5 fb(-1) of pp collisions at root s = 7 TeV and 20.3 fb(-1) of pp collisions at root s = 8 TeV, recorded by the ATLAS detector at the CERN Large Hadron Collider. The observed distribution of the invariant mass of the three final-state particles, m(ll gamma), is consistent with the Standard Model hypothesis in the investigated mass range of 120-150 GeV. For a Higgs boson with a mass of 125.5 GeV, the observed upper limit at the 95% confidence level is 11 times the Standard Model expectation. Upper limits are set on the cross section times branching ratio of a neutral Higgs boson with mass in the range 120-150 GeV between 0.13 and 0.5 pb for root s = 8 TeV at 95% confidence level.
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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 gamma(1S) production cross-section in pp collisions at sqrt(s)=7 TeV in ATLAS ATLAS Collaboration. Phys. Lett. B, 705(1-2), 9–27.
Abstract: A measurement of the cross-section for gamma(1S) -> mu(+)mu(-) production in proton-proton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the gamma(1S) transverse momentum in two bins of rapidity, vertical bar y(gamma(1S))vertical bar < 1.2 and 1.2 < vertical bar y(gamma(1S))vertical bar < 2.4. The measurement requires that both muons have transverse momentum p(T)(mu) > 4 GeV and pseuclorapidity vertical bar eta(mu)vertical bar < 2.5 in order to reduce theoretical uncertainties on the acceptance, which depend on the poorly known polarisation. The results are based on an integrated luminosity of 1.13 pb(-1), collected with the ATLAS detector at the Large Hadron Collider. The cross-section measurement is compared to theoretical predictions: it agrees to within a factor of two with a prediction based on the NRQCD model including colour-singlet and colour-octet matrix elements as implemented in PYTHIA while it disagrees by up to a factor of ten with the next-to-leading order prediction based on the colour-singlet model.
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