6,376 research outputs found
Annihilation-Gamma-based Diagnostic Techniques for Magnetically Confined Electron-Positron Pair Plasma
Efforts are underway to magnetically confine electron--positron pair plasmas
to study their unique behavior, which is characterized by significant changes
in plasma time and length scales, supported waves, and unstable modes. However,
use of conventional plasma diagnostics presents challenges with these
low-density and annihilating matter-antimatter plasma. To address this problem,
we propose to develop techniques based on the distinct emission provided by
annihilation. This emission exhibits two spatial correlations: the distance
attenuation of isotropic sources and the back-to-back propagation of
momentum-preserving 2- annihilation. We present the results of our
analysis of the emission rate and the spatial profile of the
annihilation in a magnetized pair plasma from direct pair collisions, from the
formation and decay of positronium, as well as from transport processes. In
order to demonstrate the effectiveness of annihilation-based techniques, we
tested them on annular emission profiles produced by a
radioisotope on a rotating turntable. Direct and positronium-mediated
annihilation result in overlapping volumetric sources, and the
2- emission from these volumetric sources can be tomographically
reconstructed from coincident counts in multiple detectors. Transport processes
result in localized annihilation where field lines intersect walls, limiters,
or internal magnets. These localized sources can be identified by the
fractional counts on spatially distributed detectors.Comment: 21 pages, 11 figures, 2 tables, contribution to the 13th
International Workshop on Non-Neutral Plasma
Injection of Positrons into a Dense Electron Cloud in a Magnetic Dipole Trap
The creation of an electron space charge in a dipole magnetic trap and the
subsequent injection of positrons has been experimentally demonstrated.
Positrons (5eV) were magnetically guided from their source and injected into
the trapping field generated by a permanent magnet (0.6T at the poles) using a
cross field E B drift, requiring tailored electrostatic and magnetic
fields. The electron cloud is created by thermionic emission from a tungsten
filament. The maximum space charge potential of the electron cloud reaches
-42V, which is consistent with an average electron density of ()
and a Debye length of () .
We demonstrate that the presence of this space potential does not hamper
efficient positron injection. Understanding the effects of the negative space
charge on the injection and confinement of positrons represents an important
intermediate step towards the production of a confined electron-positron pair
plasma
A Measurement of the Ds+ Lifetime
A high statistics measurement of the Ds+ lifetime from the Fermilab
fixed-target FOCUS photoproduction experiment is presented. We describe the
analysis of the two decay modes, Ds+ -> phi(1020)pi+ and Ds+ ->
\bar{K}*(892)0K+, used for the measurement. The measured lifetime is 507.4 +/-
5.5 (stat.) +/- 5.1 (syst.) fs using 8961 +/- 105 Ds+ -> phi(1020)pi+ and 4680
+/- 90 Ds+ -> \bar{K}*(892)0K+ decays. This is a significant improvement over
the present world average.Comment: 5 pages, 3 figures, 2 tables, submitted to PR
Dalitz Plot Analysis of the Decay D^+ --> K^- pi^+ pi^+ and Indication of a Low-Mass Scalar K pi Resonance
We study the Dalitz plot of the decay D^+ --> K^- pi^+ pi^+ with a sample of
15090 events from Fermilab experiment E791. Modeling the decay amplitude as the
coherent sum of known K pi resonances and a uniform nonresonant term, we do not
obtain an acceptable fit. If we allow the mass and width of the K^*_0(1430) to
float, we obtain values consistent with those from PDG but the chi^2 per degree
of freedom of the fit is still unsatisfactory. A good fit is found when we
allow for the presence of an additional scalar resonance, with mass 797 +/- 19
+/- 43 MeV/c^2 and width 410 +/- 43 +/- 87 MeV/c^2. The mass and width of the
K^*_0(1430) become 1459 +/- 7 +/- 5 MeV/c^2 and 175 +/- 12 +/- 12 MeV/c^2,
respectively. Our results provide new information on the scalar sector in
hadron spectroscopy.Comment: Accepted for publication in Physical Review Letter
A High Statistics Measurement of the Lambdac+ Lifetime
A high statistics measurement of the Lambdac+ lifetime from the Fermilab
fixed-target FOCUS photoproduction experiment is presented. We describe the
analysis technique with particular attention to the determination of the
systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat.) +/- 2.5
(syst.) fs from 8034 +/- 122 Lambdac -> pKpi decays represents a significant
improvement over the present world average.Comment: Submitted to Physical Review Letter
Study of the decay and measurement of masses and widths
From a sample of 848 44 decays, we find
. Using a Dalitz plot analysis of this
three body decay, we find significant contributions from the channels
, , , , and
. We present also the values obtained for masses and widths of
the resonances and .Comment: 10 pages, 3 eps figure
Direct measurement of the pion valence quark momentum distribution, the pion light-cone wave function squared
We present the first direct measurements of the pion valence quark momentum
distribution which is related to the square of the pion light-cone wave
function. The measurements were carried out using data on diffractive
dissociation of 500 GeV/c into di-jets from a platinum target at
Fermilab experiment E791. The results show that the light-cone
asymptotic wave function, which was developed using perturbative QCD methods,
describes the data well for or more. We also
measured the transverse momentum distribution of the diffractive di-jets.Comment: 13 pages, 4 figure
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