1,018 research outputs found
New Insight into Antiproton Production and Reabsorption Using Proton-Nucleus Collisions at the AGS
Antiproton () yields are presented for proton-nucleus collisions,
with targets Be, Cu, and Au, at beam momenta of 12.3 and 17.5 GeV/c. In
addition to target size and beam momentum, the number of projectile collisions
, as derived from the number of ``grey'' tracks (slow protons and
deuterons), is used to disentangle the reabsorption from the
production. By quantifying the amount of reabsorption of the within
the nucleus as a function of , the annihilation within the nucleus is
estimated and compared to the free annihilation cross section. Preliminary
results on antilambda () production as a function of are
also presented for comparison.Comment: 4 pages including 4 figure
The Gould's Belt distance survey
Very Long Baseline Interferometry (VLBI) observations can provide the
position of compact radio sources with an accuracy of order 50
micro-arcseconds. This is sufficient to measure the trigonometric parallax and
proper motions of any object within 500 pc of the Sun to better than a few
percent. Because they are magnetically active, young stars are often associated
with compact radio emission detectable using VLBI techniques. Here we will show
how VLBI observations have already constrained the distance to the most often
studied nearby regions of star-formation (Taurus, Ophiuchus, Orion, etc.) and
have started to provide information on their internal structure and kinematics.
We will then briefly describe a large project (called The Gould's Belt Distance
Survey) designed to provide a detailed view of star-formation in the Solar
neighborhood using VLBI observations.Comment: To be published in the Revista Mexicana de Astronomia y Astrofisica
(Serie de Conferencias
Centrality-dependence of Particle Production at RHIC and the Combinational Approach
The newly proposed combinational approach, called the grand combinational
model (GCM), as would be described in detail in the text, is still under our
careful scrutiny. By applying it, we have attempted to analyze here the
characteristics of both the transverse momentum()-, and
centrality-dependence of production of the main varieties of the secondaries
measured in collisions at BNL-RHIC at both GeV
and GeV by PHENIX Collaboration. Besides, with the
help of it, we have also investigated the nature of centrality-dependence of
the average transverse momenta of the various major categories of particles in
collisions at RHIC. The model seems to survive quite smoothly the acid
tests of the latest PHENIX data, as it accommodates data modestly well on these
twin aspects. The study reveals a kind of universality of nature of the
hadronic secondaries and also of the basic particle and nuclear interactions at
high energies. However, in the end, we precisely point out both the strengths
and limitations of the specific model under consideration here.Comment: 13 pages, 17 figures, accepted for publication in EPJ
Progress in Measurements of the Gravitational Bending of Radio Waves Using the VLBA
We have used the Very Long Baseline Array (VLBA) at 43, 23 and 15 GHz to
measure the solar gravitational deflection of radio waves among four radio
sources during an 18-day period in October 2005. Using phase-referenced radio
interferometry to fit the measured phase delay to the propagation equation of
the parameterized post-Newtonian (PPN) formalism, we have determined the
deflection parameter gamma = 0.9998 +/- 0.0003$ (68% confidence level), in
agreement with General Relativity. The results come mainly from 43 GHz
observations where the refraction effects of the solar corona were negligible
beyond 3 degrees from the sun. The purpose of this experiment is three-fold: to
improve on the previous results in the gravitational bending experiments near
the solar limb; to examine and evaluate the accuracy limits of terrestrial VLBI
techniques; and to determine the prospects and outcomes of future experiments.
Our conclusion is that a series of improved designed experiments with the VLBA
could increase the presented accuracy by at least a factor of 4.Comment: 22 pages, 3 figure
Direct Photons at RHIC
The PHENIX experiment has measured direct photons in
GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct
production in Au+Au collisions is shown as a function of and centrality.
This measurement is compared with expectation from pQCD calculations. Other
possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N
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