Galactic constraints on supernova progenitor models

Aims. To estimate the mean masses of oxygen and iron ejected per each type of supernovae (SNe) event from observations of the elemental abundance patterns in the Galactic disk and constrain the relevant SNe progenitor models. Methods. We undertake a statistical analysis of the radial abundance distributions in the Galactic disk within a theoretical framework for Galactic chemical evolution which incorporates the influence of spiral arms. This framework has been shown to recover the non-linear behaviour in radial gradients, the mean masses of oxygen and iron ejected during SNe explosions to be estimated, and constraints to be placed on SNe progenitor models. Results. (i) The mean mass of oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated within spiral arms) is similar to 0.27 M-circle dot; (ii) the mean mass of iron ejected by tardy Type Ia SNe (SNeIa, whose progenitors are older/longer-lived stars with ages greater than or similar to 100 Myr and up to several Gyr, which do not concentrate within spiral arms) is similar to 0.58 M-circle dot; (iii) the upper mass of iron ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars with ages less than or similar to 100 Myr, which are concentrated within spiral arms) is <= 0.23 M-circle dot per event; (iv) the corresponding mean mass of iron produced by CC SNe is <= 0.04 M-circle dot per event; (v) short-lived SNe (core-collapse or prompt SNeIa) supply similar to 85% of the Galactic disk's iron. Conclusions. The inferred low mean mass of oxygen ejected per CC SNe event implies a low upper mass limit for the corresponding progenitors of similar to 23 M-circle dot, otherwise the Galactic disk would be overabundant in oxygen. This inference is the consequence of the non-linear dependence between the upper limit of the progenitor initial mass and the mean mass of oxygen ejected per CC SNe explosion. The low mean mass of iron ejected by prompt SNeIa, relative to the mass produced by tardy SNeIa (similar to 2.5 times lower), prejudices the idea that both sub-populations of SNeIa have the same physical nature. We suggest that, perhaps, prompt SNeIa are more akin to CC SNe, and discuss the implications of such a suggestion

Energetic constraints to chemo-photometric evolution of spiral galaxies

The problem of chemo-photometric evolution of late-type galaxies is dealt with relying on prime physical arguments of energetic self-consistency between chemical enhancement of galaxy mass, through nuclear processing inside stars, and luminosity evolution of the system. Chemical enhancement is assessed in terms of the so-called "yield metallicity", that is the metal abundance of processed mass inside stars, as constrained by the galaxy photometric history.Comment: Ready to appear in the MNRAS. A total of 24 pages with 17 figures & 6 tables. Further info at author's web site (see http://www.bo.astro.it/~eps/home.html

Predictors of the Uptake of A (H1N1) Influenza Vaccine: Findings from a Population-Based Longitudinal Study in Tokyo

BACKGROUND: Overall pandemic A (H1N1) influenza vaccination rates remain low across all nations, including Japan. To increase the rates, it is important to understand the motives and barriers for the acceptance of the vaccine. We conducted this study to determine potential predictors of the uptake of A (H1N1) influenza vaccine in a cohort of Japanese general population. METHODOLOGY/PRINCIPAL FINDINGS: By using self-administered questionnaires, this population-based longitudinal study was conducted from October 2009 to April 2010 among 428 adults aged 18-65 years randomly selected from each household residing in four wards and one city in Tokyo. Multiple logistic regression analyses were performed. Of total, 38.1% of participants received seasonal influenza vaccine during the preceding season, 57.0% had willingness to accept A (H1N1) influenza vaccine at baseline, and 12.1% had received A (H1N1) influenza vaccine by the time of follow-up. After adjustment for potential confounding variables, people who had been vaccinated were significantly more likely to be living with an underlying disease (p = 0.001), to perceive high susceptibility to influenza (p = 0.03), to have willingness to pay even if the vaccine costs ≥ US$44 (p = 0.04), to have received seasonal influenza vaccine during the preceding season (p<0.001), and to have willingness to accept A (H1N1) influenza vaccine at baseline (p<0.001) compared to those who had not been vaccinated. CONCLUSIONS/SIGNIFICANCE: While studies have reported high rates of willingness to receive A (H1N1) influenza vaccine, these rates may not transpire in the actual practices. The uptake of the vaccine may be determined by several potential factors such as perceived susceptibility to influenza and sensitivity to vaccination cost in general population

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde