151 research outputs found
T-Odd Correlations in pi->e nu_e gamma and pi->mu nu_mu gamma Decays
The transverse lepton polarization asymmetry in pi_l2gamma decays may probe
T-violating interactions beyond the Standard Model. Dalitz plot distributions
of the expected effects are presented and compared to the contribution from the
Standard Model final state interactions. We give an example of a
phenomenologically viable model, where a considerable contribution to the
transverse lepton polarization asymmetry arises.Comment: 19 pages, 5 figures. To be published in Phys.Rev.D. Fixed sign in FSI
contribution figure, fixed formulas in K-bar{K} mixing analysis, added some
minor comment
Ratios of Elastic Scattering of Pions from 3H and 3He
We have measured the elastic-scattering ratios of normalized yields for
charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we
completed the angular distribution begun with our earlier measurements, adding
six data points in the angular range of 119 deg to 169 deg in the pi-nucleus
center of mass. We also measured an excitation function with data points at
142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle
for each energy between 160 deg and 170 deg in the pi-nucleus center of mass.
This excitation function corresponds to the energies of our forward-hemisphere
studies. The data, taken as a whole, show an apparent role reversal of the two
charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data >
100 deg we observe a strong dependence on the four-momentum transfer squared
(-t) for all of the ratios regardless of pion energy or scattering angle, and
we find that the superratio R data match very well with calculations based on
the forward-hemisphere data that predicts the value of the difference between
the even-nucleon radii of 3H and 3He. Comparisons are also made with recent
calculations incorporating different wave functions and double scattering
models.Comment: RevTex 8pages, 12 figure file
Charge-Symmetry Violation in Pion Scattering from Three-Body Nuclei
We discuss the experimental and theoretical status of charge-symmetry
violation (CSV) in the elastic scattering of pi+ and pi- on 3H and 3He.
Analysis of the experimental data for the ratios r1, r2, and R at Tpi = 142,
180, 220, and 256 MeV provides evidence for the presence of CSV. We describe
pion scattering from the three-nucleon system in terms of single- and
double-scattering amplitudes. External and internal Coulomb interactions as
well as the Delta-mass splitting are taken into account as sources of CSV.
Reasonable agreement between our theoretical calculations and the experimental
data is obtained for Tpi = 180, 220, and 256 MeV. For these energies, it is
found that the Delta-mass splitting and the internal Coulomb interaction are
the most important contributions for CSV in the three-nucleon system. The CSV
effects are rather sensitive to the choice of pion-nuclear scattering
mechanisms, but at the same time, our theoretical predictions are much less
sensitive to the choice of the nuclear wave function. It is found, however,
that data for r2 and R at Tpi = 142 MeV do not agree with the predictions of
our model, which may indicate that there are additional mechanisms for CSV
which are important only at lower energies.Comment: 26 pages of RevTeX, 16 postscript figure
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
A deep cut ellipsoid algorithm for convex programming
This paper proposes a deep cut version of the ellipsoid algorithm for solving a general class of continuous convex programming problems. In each step the algorithm does not require more computational effort to construct these deep cuts than its corresponding central cut version. Rules that prevent some of the numerical instabilities and theoretical drawbacks usually associated with the algorithm are also provided. Moreover, for a large class of convex programs a simple proof of its rate of convergence is given and the relation with previously known results is discussed. Finally some computational results of the deep and central cut version of the algorithm applied to a min—max stochastic queue location problem are reported
One-loop corrections to omega photoproduction near threshold
One-loop corrections to photoproduction near threshold have been
investigated by using the approximation that all relevant transition amplitudes
are calculated from the tree diagrams of effective Lagrangians. With the
parameters constrained by the data of , , and reactions, it is found that the one-loop effects
due to the intermediate and states can significantly change
the differential cross sections and spin observables. The results from this
exploratory investigation suggest strongly that the coupled-channel effects
should be taken into account in extracting reliable resonance parameters from
the data of vector meson photoproduction in the resonance region.Comment: 19 pages, REVTeX, 14 figures, title changed, revised version to
appear in Phys. Rev.
Manufacturing flow line systems: a review of models and analytical results
The most important models and results of the manufacturing flow line literature are described. These include the major classes of models (asynchronous, synchronous, and continuous); the major features (blocking, processing times, failures and repairs); the major properties (conservation of flow, flow rate-idle time, reversibility, and others); and the relationships among different models. Exact and approximate methods for obtaining quantitative measures of performance are also reviewed. The exact methods are appropriate for small systems. The approximate methods, which are the only means available for large systems, are generally based on decomposition, and make use of the exact methods for small systems. Extensions are briefly discussed. Directions for future research are suggested.National Science Foundation (U.S.) (Grant DDM-8914277
Correlated Production of p and p^bar in Au+Au Collisions at sqrt(s_NN) = 200 GeV
Correlations between p and pbar's at transverse momenta typical of enhanced
baryon production in Au+Au collisions are reported. The PHENIX experiment
measures same and opposite sign baryon pairs in Au+Au collisions at sqrt(s_NN)
= 200 GeV. Correlated production of p and p^bar with the trigger particle from
the range 2.5 < p_T < 4.0 GeV/c and the associated particle with 1.8 < p_T <
2.5 GeV/c is observed to be nearly independent of the centrality of the
collisions. Same sign pairs show no correlation at any centrality. The
conditional yield of mesons triggered by baryons (and anti-baryons) and mesons
in the same pT range rises with increasing centrality, except for the most
central collisions, where baryons show a significantly smaller number of
associated mesons. These data are consistent with a picture in which hard
scattered partons produce correlated p and p^bar in the p_T region of the
baryon excess.Comment: 420 authors from 58 institutions, 21 pages,5 figures. Submitted to
Physics Letters B. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
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