605 research outputs found
Two-Dimensional Diffusion in the Presence of Topological Disorder
How topological defects affect the dynamics of particles hopping between
lattice sites of a distorted, two-dimensional crystal is addressed.
Perturbation theory and numerical simulations show that weak, short-ranged
topological disorder leads to a finite reduction of the diffusion coefficient.
Renormalization group theory and numerical simulations suggest that
longer-ranged disorder, such as that from randomly placed dislocations or
random disclinations with no net disclinicity, leads to subdiffusion at long
times.Comment: 10 pages, 6 figure
Resonant x-ray diffraction study of the magnetoresistant perovskite Pr0.6Ca0.4MnO3
We report a x-ray resonant diffraction study of the perovskite
Pr0.6Ca0.4MnO3. At the Mn K-edge, this technique is sensitive to details of the
electronic structure of the Mn atoms. We discuss the resonant x-ray spectra
measured above and below the charge and orbital ordering phase transition
temperature (TCOO = 232 K), and present a detailed analysis of the energy and
polarization dependence of the resonant scattering. The analysis confirms that
the structural transition is a transition to an orbitally ordered phase in
which inequivalent Mn atoms are ordered in a CE-type pattern. The Mn atoms
differ mostly by their 3d orbital occupation. We find that the charge
disproportionation is incomplete, 3d^{3.5-\delta} and 3d^{3.5+\delta} with
\delta\ll0.5 . A revised CE-type model is considered in which there are two Mn
sublattices, each with partial e_{g} occupancy. One sublattice consists of Mn
atoms with the 3x^{2}-r^{2} or 3y^{2}-r^{2} orbitals partially occupied, the
other sublattice with the x^{2}-y^{2} orbital partially occupied.Comment: 15 pages, 15 figure
Partial Îł-ray production cross sections for (n,xnÎł) reactions in natural argon at 1-30 MeV
Background: Neutron-induced backgrounds are a significant concern for experiments that require extremely low levels of radioactive backgrounds such as direct dark matter searches and neutrinoless double-ÎČ decay experiments. Unmeasured neutron scattering cross sections are often accounted for incorrectly in Monte Carlo simulations.Purpose: The purpose of this article is to determine partial Îł-ray production cross sections for (n,xnÎł) reactions in natural argon for incident neutron energies between 1 and 30 MeV.Methods: The broad-spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used used for the measurement. Neutron energies were determined using time of flight, and resulting Îł rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE).Results: Partial Îł-ray cross sections were measured for six excited states in 40Ar and two excited states in 39Ar. Measured (n,xnÎł) cross sections were compared to the talys and CoH3 nuclear reaction codes.Conclusions: These new measurements will help to identify potential backgrounds in neutrinoless double-ÎČ decay and dark matter experiments that use argon as a detection medium or shielding. The measurements will also aid in the identification of neutron interactions in these experiments through the detection of Îł rays produced by (n,xnÎł) reactions
Measurement of the Ds lifetime
We report precise measurement of the Ds meson lifetime. The data were taken
by the SELEX experiment (E781) spectrometer using 600 GeV/c Sigma-, pi- and p
beams. The measurement has been done using 918 reconstructed Ds. The lifetime
of the Ds is measured to be 472.5 +- 17.2 +- 6.6 fs, using K*(892)0K+- and phi
pi+- decay modes. The lifetime ratio of Ds to D0 is 1.145+-0.049.Comment: 5 pages, 2 figures submitted to Phys. Lett.
Confirmation of the Double Charm Baryon Xi_cc+ via its Decay to p D+ K-
We observes a signal for the double charm baryon Xi_cc+ in the charged decay
mode Xi_cc+ -> p D+ K- to complement the previously reported decay Xi_cc+ ->
Lambda_c K- pi+ in data from SELEX, the charm hadro-production experiment
(E781) at Fermilab. In this new decay mode we observe an excess of 5.62 events
over an expected background estimated by event mixing to be 1.38+/-0.13 events.
The Poisson probability that a background fluctuation can produce the apparent
signal is less than 6.4E-4. The observed mass of this state is
(3518+/-3)MeV/c^2, consistent with the published result. Averaging the two
results gives a mass of (3518.7+/-1.7)MeV/c^2. The observation of this new weak
decay mode confirms the previous SELEX suggestion that this state is a double
charm baryon. The relative branching ratio Gamma(Xi_cc+ -> pD+K-)/Gamma(Xi_cc+
-> Lambda_c K- pi+) = 0.36+/-0.21.Comment: 11 pages, 6 included eps figures. v2 includes improved statistical
method to determine significance of observation. Submitted to PL
Time-integrated luminosity recorded by the BABAR detector at the PEP-II e+e- collider
This article is the Preprint version of the final published artcile which can be accessed at the link below.We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the Ï(4S), Ï(3S), and Ï(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e-âe+e- and (for the Ï(4S) only) e+e-âÎŒ+ÎŒ- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross-sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross-sections of e+e-âe+e- and e+e-âÎŒ+ÎŒ-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross-sections. For data collected on the Ï(3S) and Ï(2S) resonances, an additional uncertainty arises due to Ïâe+e-X background. For data collected off the Ï resonances, we estimate an additional uncertainty due to time dependent efficiency variations, which can affect the short off-resonance runs. The relative uncertainties on the luminosities of the on-resonance (off-resonance) samples are 0.43% (0.43%) for the Ï(4S), 0.58% (0.72%) for the Ï(3S), and 0.68% (0.88%) for the Ï(2S).This work is supported by the US Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat Ă lâEnergie Atomique and Institut National de Physique NuclĂ©aire et de Physiquedes Particules (France), the Bundesministerium fĂŒr Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (The Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Ciencia e InnovaciĂłn (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation (USA)
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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