2,345 research outputs found
Putin und die Raketenabwehr: Moskaus Haltung zu NMD im Kontext der russisch-amerikanischen Beziehungen
Bereits in der Amtszeit Jelzins und Clintons haben die Auseinandersetzungen über die amerikanischen Pläne zum Aufbau einer nationalen (»strategischen«) Raketenabwehr die russisch-amerikanischen Beziehungen stark belastet. Auch unter Putin hat Moskau auf dem Standpunkt beharrt, das NMD-Projekt solle dazu dienen, den Vereinigten Staaten eine globale politische und militärstrategische Vorherrschaft zu verschaffen. Die Bedrohung, die von sogenannten »Schurkenstaaten« ausgehe, werde von Washington bewußt übertrieben; im Grunde genommen richte sich NMD gegen Rußland und auch gegen China. Der Aufbau eines Raketenabwehrsystems und die Verletzung beziehungsweise Aufkündigung des ABM-Vertrags durch die Vereinigten Staaten würde die Gefahren eines Wettrüstens und der Weiterverbreitung von Massenvernichtungswaffen und ihrer Trägermittel verstärken und die internationale strategische Stabilität unterhöhlen. Die Studie weist auf, daß die den Vereinigten Staaten mit dem NMD-Projekt unterstellten Absichten zwar zum Teil wirklichen Überzeugungen in Moskau entsprechen, andererseits aber wegen beabsichtigter politischer Nutzeffekte überzeichnet werden. Eine in Moskau angestellte, wohlverstandene Kosten/Nutzen-Rechnung würde zugunsten einer Modifikation des ABM-Vertrags ausfallen. Tatsächlich geht die Tendenz im Kreml in Richtung auf eine Vertragsanpassung. Die Terroranschläge vom 11. September haben diese Tendenz weiter gestärkt. "Gegenmaßnahmen" wie beispielsweise eine Vermehrung der Offensivwaffen wären dagegen nicht oder nur zu Lasten anderer wichtiger Vorhaben finanzierbar; sie würden die strategische Gleichung auch nicht wesentlich zugunsten Rußlands verändern. Im Interesse der Bundesregierung dürfte es liegen, sich bei der NMD/ABM-Frage zurückzuhalten. Vorteilhaft könnte es allerdings sein, sich in Moskau für eine einvernehmliche Lösung mit Washington einzusetzen
Partial wave analysiss of pbar-p -> piminus-piplus, pizero-pizero, eta-eta and eta-etaprime
A partial wave analysis is presented of Crystal Barrel data on pbar-p ->
pizero-pizero, eta-eta and eta-etaprime from 600 to 1940 MeV/c, combined with
earlier data on d\sigma /d\Omega and P for pbar-p->piminus-piplus. The
following s-channel I=0 resonances are identified: (i) J^{PC} = 5^{--} with
mass and width (M,\Gamma) at (2295+-30,235^{+65}_{-40}) MeV, (ii) J^{PC} =
4^{++} at (2020+-12, 170+-15) MeV and (2300+-25, 270+-50) MeV, (iii) 3D3 JPC =
3^{--} at (1960+-15, 150+-25) MeV and (2210+-4$, 360+-55) MeV, and a 3G3 state
at (2300 ^{+50}_{-80}, 340+-150) MeV, (iv) JPC = 2^{++} at (1910+-30, 260+-40)
MeV, (2020+-30, 275+-35) MeV, (2230+-30, 245+-45) MeV, and (2300+-35, 290+-50)
MeV, (v) JPC = 1^{--} at (2005+-40, 275+-75) MeV, and (2165+-40, 160
^{+140}_{-70}) MeV, and (vi) JPC = 0^{++} at (2005+-30, 305+-50) MeV,
(2105+-15, 200+-25) MeV, and (2320+-30, 175+-45) MeV. In addition, there is a
less well defined 6^{++} resonance at 2485+-40 MeV, with Gamma = 410+-90 MeV.
For every JP, almost all these resonances lie on well defined linear
trajectories of mass squared v. excitation number. The slope is 1.10+-0.03
Gev^2 per excitation. The f_0(2105) has strong coupling to eta-\eta, but much
weaker coupling to pizero-pizero. Its flavour mixing angle between q-qbar and
s-sbar is (59-71.6)deg, i.e. dominant decays to s-sbar. Such decays and its
strong production in pbar-p interactions strongly suggest exotic character.Comment: Makes available the combined fit to Crystal Barrel data on pbar-p ->
2-body final states. 29 pages, 11 figures. Typo corrected in version
SU(3) Mixing for Excited Mesons
The SU(3)-flavor symmetry breaking and the quark-antiquark annihilation
mechanism are taken into account for describing the singlet-octet mixing for
several nonets assigned by Particle Data Group(PDG). This task is approached
with the mass matrix formalism
Search for new phenomena in dijet angular distributions in proton-proton collisions at root s =8 TeV measured with the ATLAS detector
A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of sqrt[s]=8 TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb^{-1}. The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the standard model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95% C.L.; median expected limits are 8.9 TeV for the destructive interference scenario and 14.1 TeV for the constructive interference scenario.G. Aad … P. Jackson … L. Lee … A. Petridis … N. Soni ... M. White ... et al. (The ATLAS Collaboration
Search for the standard model higgs boson produced in association with top quarks and decaying into bb in pp collisions at root s = 8 TeV with the ATLAS detector
A search for the Standard Model Higgs boson produced in association with a top-quark pair, t ¯tH, is presented. The analysis uses 20.3 fb−1 √ of pp collision data at s = 8 TeV, collected with theATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H → b¯b decay mode and uses events containing one or two electrons or muons. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by t ¯t+jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible t ¯t+b¯b background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the StandardModel cross section is obtained at 95% confidence level. The ratio of the measured t ¯tH signal cross section to the StandardModel expectation is found to be μ = 1.5±1.1 assuming a Higgs boson mass of 125 GeV .G. Aad ... P. Jackson ... L. Lee ... A. Petridis ... N. Soni ... M.J. White ... et al. (ATLAS Collaboration
Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson pp collisions at root s = 8 TeV with the ATLAS detector
A search for Higgs boson decays to invisible particles is performed using 20.3 fb−1 of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115 < mH < 300 GeV. The 95%confidence-level observed upper limit on σV H × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78%at 95%confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.G. Aad ... P. Jackson ... L. Lee ... A. Petridis ... N. Soni ... M.J. White ... et al. (ATLAS Collaboration
Search for heavy lepton resonances decaying to a Z boson and a lepton in pp collisions at root s = 8 TeV with the ATLAS detector
A search for heavy leptons decaying to a Z boson and an electron or a muon is presented. The search is based on pp collision data taken at √s = 8 TeV by the ATLAS experiment at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb⁻¹. Three high-transverse-momentum electrons or muons are selected, with two of them required to be consistent with originating from a Z boson decay. No significant excess above Standard Model background predictions is observed, and 95% confidence level limits on the production cross section of high-mass trilepton resonances are derived. The results are interpreted in the context of vector-like lepton and type-III seesaw models. For the vector-like lepton model, most heavy lepton mass values in the range 114–176 GeV are excluded. For the type-III seesaw model, most mass values in the range 100–468 GeV are excluded.G. Aad ... P. Jackson ... L. Lee ... A. Petridis ... N. Soni ... M.J. White ... et al. (ATLAS Collaboration
Measurement of the charge asymmetry in top-quark pair production in the lepton-plus-jets final state in pp collision data at root s = 8 TeV with the ATLAS detector
Published online: 19 February 2016This paper reports inclusive and differential measurements of the tt¯ charge asymmetry AC in 20.3 fb−1 of s√=8 TeVpp collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the tt¯ system. The tt¯ pairs are selected in the single-lepton channels (e or μ) with at least four jets, and a likelihood fit is used to reconstruct the tt¯ event kinematics. A Bayesian unfolding procedure is performed to infer the asymmetry at parton level from the observed data distribution. The inclusive tt¯ charge asymmetry is measured to be AC=0.009±0.005 (stat. + syst.). The inclusive and differential measurements are compatible with the values predicted by the Standard Model.G. Aad … P. Jackson … L. Lee ... A. Petridis... N. Soni … M. J. White … et al. (ATLAS collaboration
Measurements of the nuclear modification factor for jets in Pb+Pb collisions at root sNN =2.76 TeV with the ATLAS detector
Measurements of inclusive jet production are performed in pp and Pb+Pb collisions at √(s)NN=2.76 TeV with the ATLAS detector at the LHC, corresponding to integrated luminosities of 4.0 and 0.14 nb(-1), respectively. The jets are identified with the anti-k(t) algorithm with R=0.4, and the spectra are measured over the kinematic range of jet transverse momentum 32<p(T)<500 GeV and absolute rapidity |y|<2.1 and as a function of collision centrality. The nuclear modification factor R(AA) is evaluated, and jets are found to be suppressed by approximately a factor of 2 in central collisions compared to pp collisions. The R(AA) shows a slight increase with p(T) and no significant variation with rapidity.G. Aad … P. Jackson … L. Lee … A. Petridis … N. Soni ... M. White ... et al. (The ATLAS Collaboration
- …