107 research outputs found
Edge Detection, Cosmic Strings and the South Pole Telescope
We develop a method of constraining the cosmic string tension which
uses the Canny edge detection algorithm as a means of searching CMB temperature
maps for the signature of the Kaiser-Stebbins effect. We test the potential of
this method using high resolution, simulated CMB temperature maps. By modeling
the future output from the South Pole Telescope project (including anticipated
instrumental noise), we find that cosmic strings with
could be detected.Comment: 27 pages, 5 figures, reference and minor notes added, discussion of
noise expanded, explanation of equation (4) expande
Measurement of qubits
We describe in detail the theory underpinning the measurement of density matrices of a pair of quantum two-level systems (qubits). Our particular emphasis is on qubits realized by the two polarization degrees of freedom of a pair of entangled photons generated in a down-conversion experiment; however, the discussion applies in general, regardless of the actual physical realization. Two techniques are discussed, namely, a tomographic reconstruction (in which the density matrix is linearly related to a set of measured quantities) and a maximum likelihood technique which requires numerical optimization (but has the advantage of producing density matrices that are always non-negative definite). In addition, a detailed error analysis is presented, allowing errors in quantities derived from the density matrix, such as the entropy or entanglement of formation, to be estimated. Examples based on down-conversion experiments are used to illustrate our results
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Specific oligomerization of the 5-HT1A receptor in the plasma membrane
In the present study we analyze the oligomerization of the 5-HT1A receptor within living cells at the sub-cellular level. Using a 2-excitation Förster Resonance Energy Transfer (FRET) method combined with spectral microscopy we are able to estimate the efficiency of energy transfer based on donor quenching as well as acceptor sensitization between CFP-and YFP-tagged 5-HT1A receptors at the plasma membrane. Through the analysis of the level of apparent FRET efficiency over the various relative amounts of donor and acceptor, as well as over a range of total surface expressions of the receptor, we verify the specific interaction of these receptors. Furthermore we study the role of acylation in this interaction through measurements of a palmitoylation-deficient 5-HT1A receptor mutant. Palmitoylation increases the tendency of a receptor to localize in lipid rich microdomains of the plasma membrane. This increases the effective surface density of the receptor and provides for a higher level of stochastic interaction
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays
The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where
Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL
detector at LEP. Lambda_b are selected by the presence of energetic Lambda
particles in bottom events tagged by the presence of displaced secondary
vertices. A fit to the momenta of the Lambda particles separates signal from B
meson and fragmentation backgrounds. The measured product branching ratio is
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))%
Combined with a previous OPAL measurement, one obtains
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European
Physical Journal
Measurement of the Michel Parameters in Leptonic Tau Decays
The Michel parameters of the leptonic tau decays are measured using the OPAL
detector at LEP. The Michel parameters are extracted from the energy spectra of
the charged decay leptons and from their energy-energy correlations. A new
method involving a global likelihood fit of Monte Carlo generated events with
complete detector simulation and background treatment has been applied to the
data recorded at center-of-mass energies close to sqrt(s) = M(Z) corresponding
to an integrated luminosity of 155 pb-1 during the years 1990 to 1995. If e-mu
universality is assumed and inferring the tau polarization from neutral current
data, the measured Michel parameters are extracted. Limits on non-standard
coupling constants and on the masses of new gauge bosons are obtained. The
results are in agreement with the V-A prediction of the Standard Model.Comment: 32 pages, LaTeX, 9 eps figures included, submitted to the European
Physical Journal
Multiplicities of , , and of charged particles in quark and gluon jets
We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction.We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction
Measurements of , and in Collisions at 130-189 GeV
The cross-section ratio Rb=sigma(e+e- to b-antib)/sigma(e+e- to q-antiq) andthe bottom and charm forward-backward asymmetries AFB^b and AFB^c are measuredusing event samples collected by the OPAL detector at centre-of-mass energiesbetween 130 and 189 GeV. Events with bottom quark production are selected witha secondary vertex tag, and a hemisphere charge algorithm is used to extractAFB^b. In addition, the bottom and charm asymmetries are measured using leptonsfrom semileptonic decays of heavy hadrons and pions from D*+ to D0pi+ decays.The results are in agreement with the Standard Model predictions.The cross-section ratio Rb=sigma(e+e- to b-antib)/sigma(e+e- to q-antiq) and the bottom and charm forward-backward asymmetries AFB^b and AFB^c are measured using event samples collected by the OPAL detector at centre-of-mass energies between 130 and 189 GeV. Events with bottom quark production are selected with a secondary vertex tag, and a hemisphere charge algorithm is used to extract AFB^b. In addition, the bottom and charm asymmetries are measured using leptons from semileptonic decays of heavy hadrons and pions from D*+ to D0pi+ decays. The results are in agreement with the Standard Model predictions
Inclusive production of charged hadrons and mesons in photon-photon collisions
The production of charged hadrons and K_s mesons in the collisions of quasi-real photons has been measured using the OPAL detector at LEP. The data were taken at e+e- centre-of-mass energies of 161 and 172 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the charged hadrons and K_s mesons have been compared to the leading order Monte Carlo simulations of PHOJET and PYTHIA and to perturbative next-to-leading order (NLO) QCD calculations. The distributions have been measured in the range 10-125 GeV of the hadronic invariant mass W. By comparing the transverse momentum distribution of charged hadrons measured in gamma-gamma interactions with gamma-proton and meson-proton data we find evidence for hard photon interactions in addition to the purely hadronic photon interactions.The production of charged hadrons and K_s mesons in the collisions of quasi-real photons has been measured using the OPAL detector at LEP. The data were taken at e+e- centre-of-mass energies of 161 and 172 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the charged hadrons and K_s mesons have been compared to the leading order Monte Carlo simulations of PHOJET and PYTHIA and to perturbative next-to-leading order (NLO) QCD calculations. The distributions have been measured in the range 10-125 GeV of the hadronic invariant mass W. By comparing the transverse momentum distribution of charged hadrons measured in gamma-gamma interactions with gamma-proton and meson-proton data we find evidence for hard photon interactions in addition to the purely hadronic photon interactions
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