834 research outputs found
Extended Partial-Wave Analysis of piN Scattering Data
We present results from a comprehensive partial-wave analysis of pi+-p
elastic scattering and charge-exchange data, covering the region from threshold
to 2.6 GeV in the lab pion kinetic energy, employing a coupled-channel
formalism to simultaneously fit pi-p-->eta n data to 0.8 GeV. Our main result,
solution SP06, utilizes a complete set of forward and fixed-t dispersion
relation constraints applied to the piN elastic amplitude. The results of these
analyses are compared with previous solutions in terms of their resonance
spectra and preferred values for couplings and low-energy parameters.Comment: 21 pages, 11 figure
Partial-Wave Analysis of Single-Pion Production Reactions
We present an overview of our efforts to analyze pion-nucleon elastic
scattering data, along with data from related photo- and electroproduction
reactions, in order to study the baryon spectrum. We then focus on the
Delta(1232) resonance. Fits to pion photo- and electroproduction data have been
used to extract values for the R_EM = E2/M1 and R_SM = S2/M1 ratios as
functions of Q^2. These results are compared to other recent determinations.Comment: 7 pages, 9 figures, the Shape of Hadrons Workshop Proceedings (27-29
April, 2006 Athens, Greece
Properties of recent IBAD-MOCVD Coated Conductors relevant to their high field, low temperature magnet use
BaZrO3 (BZO) nanorods are now incorporated into production IBAD-MOCVD coated
conductors. Here we compare several examples of both BZO-free and
BZO-containing coated conductors using critical current (Ic) characterizations
at 4.2 K over their full angular range up to fields of 31 T. We find that BZO
nanorods do not produce any c-axis distortion of the critical current density
Jc(theta) curve at 4.2 K at any field, but also that pinning is nevertheless
strongly enhanced compared to the non-BZO conductors. We also find that the
tendency of the ab-plane Jc(theta) peak to become cusp-like is moderated by BZO
and we define a new figure of merit that may be helpful for magnet design - the
OADI (Off-Axis Double Ic), which clearly shows that BZO broadens the ab-plane
peak and thus raises Jc 5-30{\deg} away from the tape plane, where the most
critical approach to Ic occurs in many coil designs. We describe some
experimental procedures that may make critical current Ic tests of these very
high current tapes more tractable at 4.2 K, where Ic exceeds 1000 A even for 4
mm wide tape with only 1 micron thickness of superconductor. A positive
conclusion is that BZO is very beneficial for the Jc characteristics at 4.2 K,
just as it is at higher temperatures, where the correlated c-axis pinning
effects of the nanorods are much more obvious
Results from the Analysis of Crystal Ball Meson Production Measurements at BNL
The Crystal Ball spectrometer, with its nearly complete angular coverage, is
an efficient detector of photon and neutron final states. While installed in
the C6 beamline of the Alternating Gradient Synchrotron (AGS) of Brookhaven
National Laboratory (BNL), this feature was used in a series of precise
measurements of reactions with all-neutral final states. Here we concentrate on
the analysis of data from the pion-induced reactions: pi- p --> gamma n, pi- p
--> pi0 n, pi- p --> eta n, and pi- p --> pi0 pi0 n.Comment: Conference contribution to MESON 2006 - Krakow, Pola
Baryon Resonance Analysis from SAID
We discuss the analysis of data from piN elastic scattering and single pion
photo- and electroproduction. The main focus is a study of low-lying
non-strange baryon resonances. Here we concentrate on some difficulties
associated with resonance identification, in particular the Roper and higher
P11 states.Comment: 4 pages, 6 figures; Nstar2009 Conf Proceedings; small revisio
Radiation from relativistic jets in blazars and the efficient dissipation of their bulk energy via photon breeding
High-energy photons propagating in the magnetised medium with large velocity
gradients can mediate energy and momentum exchange. Conversion of these photons
into electron-positron pairs in the field of soft photons with the consequent
isotropization and emission of new high-energy photons by Compton scattering
can lead to the runaway cascade of the high-energy photons and
electron-positron pairs fed by the bulk energy of the flow. This is the essence
of the photon breeding mechanism. We study the problem of high-energy emission
of relativistic jets in blazars via photon breeding mechanism using 2D
ballistic model for the jet with the detailed treatment of particle propagation
and interactions. The gamma-ray background of similar energy density as
observed at Earth is sufficient to trigger the photon breeding. As a result, a
jet can convert up to 80 per cent of its total power into radiation. Photon
breeding produces a population of high-energy pairs and predicts the spectra in
agreement with observations of blazars (e.g. the blazar sequence). It also
decelerates the jet at subparsec scales and induces the transversal gradient of
the Lorentz factor which reconcile the discrepancy between the high Doppler
factors determined from the spectra of TeV blazars and the low apparent
velocities observed at VLBI scales. The broad angular distribution of radiation
predicted by the mechanism reconciles the observed statistics and luminosity
ratio of FR I and BL Lac objects with the large Lorentz factors of the jets as
well as explains the high level of the TeV emission in the radio galaxy M87.
(abridged)Comment: 18 pages, 12 figure; replaced with the version accepted to MNRA
Reforming a large lecture modern physics course for engineering majors using a PER-based design
We have reformed a large lecture modern physics course for engineering majors
by radically changing both the content and the learning techniques implemented
in lecture and homework. Traditionally this course has been taught in a manner
similar to the equivalent course for physics majors, focusing on mathematical
solutions of abstract problems. Based on interviews with physics and
engineering professors, we developed a syllabus and learning goals focused on
content that was more useful to our actual student population: engineering
majors. The content of this course emphasized reasoning development, model
building, and connections to real world applications. In addition we
implemented a variety of PER-based learning techniques, including peer
instruction, collaborative homework sessions, and interactive simulations. We
have assessed the effectiveness of reforms in this course using pre/post
surveys on both content and beliefs. We have found significant improvements in
both content knowledge and beliefs compared with the same course before
implementing these reforms and a corresponding course for physics majors.Comment: To be published in the Proceedings of the Physics Education Research
Conference 200
EC-SNe from super-AGB progenitors: theoretical models vs. observations
Using a parametric approach, we determine the configuration of super-AGB
stars at the explosion as a function of the initial mass and metallicity, in
order to verify if the EC-SN scenario involving a super-AGB star is compatible
with the observations regarding SN2008ha and SN2008S. The results show that
both the SNe can be explained in terms of EC-SNe from super-AGB progenitors
having a different configuration at the collapse. The impact of these results
on the interpretation of other sub-luminous SNe is also discussed.Comment: Accepted for publication in ApJ
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