463 research outputs found
Space Launch System Advanced Development Office, FY 2013 Annual Report
The Advanced Development Office (ADO), part of the Space Launch System (SLS) program, provides SLS with the advanced development needed to evolve the vehicle from an initial Block 1 payload capability of 70 metric tons (t) to an eventual capability Block 2 of 130 t, with intermediary evolution options possible. ADO takes existing technologies and matures them to the point that insertion into the mainline program minimizes risk. The ADO portfolio of tasks covers a broad range of technical developmental activities. The ADO portfolio supports the development of advanced boosters, upper stages, and other advanced development activities benefiting the SLS program. A total of 34 separate tasks were funded by ADO in FY 2013
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An Overview of Major Tax Proposals in the President's FY2012 Budget
The Obama Administration released the President's FY2012 budget proposal on February 14, 2011. According to the Administration's estimates, the tax proposals in the budget would increase revenues $280 billion over the next 10 years. This report provides a broad overview of the provisions included in the President's FY2012 budget request
Collision geometry scaling of Au+Au pseudorapidity density from sqrt(s_NN) = 19.6 to 200 GeV
The centrality dependence of the midrapidity charged particle multiplicity in
Au+Au collisions at sqrt(s_NN) = 19.6 and 200 GeV is presented. Within a simple
model, the fraction of hard (scaling with number of binary collisions) to soft
(scaling with number of participant pairs) interactions is consistent with a
value of x = 0.13 +/- 0.01(stat) +/- 0.05(syst) at both energies. The
experimental results at both energies, scaled by inelastic p(pbar)+p collision
data, agree within systematic errors. The ratio of the data was found not to
depend on centrality over the studied range and yields a simple linear scale
factor of R_(200/19.6) = 2.03 +/- 0.02(stat) +/- 0.05(syst).Comment: 5 pages, 4 figures, submitted to PRC-R
Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at sqrt(sNN) = 200 GeV
This paper describes the measurement of elliptic flow for charged particles
in Au+Au collisions at sqrt(sNN)=200 GeV using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). The measured azimuthal anisotropy is
presented over a wide range of pseudorapidity for three broad collision
centrality classes for the first time at this energy. Two distinct methods of
extracting the flow signal were used in order to reduce systematic
uncertainties. The elliptic flow falls sharply with increasing eta at 200 GeV
for all the centralities studied, as observed for minimum-bias collisions at
sqrt(sNN)=130 GeV.Comment: Final published version: the most substantive change to the paper is
the inclusion of a complete description of how the errors from the hit-based
and track-based analyses are merged to produce the 90% C.L. errors quoted for
the combined results shown in Fig.
Elliptic Flow in Au+Au Collisions at RHIC
Elliptic flow is an interesting probe of the dynamical evolution of the dense
system formed in the ultrarelativistic heavy ion collisions at the Relativistic
Heavy Ion Collider (RHIC). The elliptic flow dependences on transverse
momentum, centrality, and pseudorapidity were measured using data collected by
the PHOBOS detector, which offers a unique opportunity to study the azimuthal
anisotropies of charged particles over a wide range of pseudorapidity. These
measurements are presented, together with an overview of the analysis methods
and a discussion of the results.Comment: Presented at Hot Quarks 2004; 7 pages, 6 figure
Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC
This paper describes the measurement of the energy dependence of elliptic
flow for charged particles in Au+Au collisions using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of
19.6, 62.4, 130 and 200 GeV are shown over a wide range in
pseudorapidity. These results, when plotted as a function of
, scale with approximate linearity throughout ,
implying no sharp changes in the dynamics of particle production as a function
of pseudorapidity or increasing beam energy.Comment: 5 pages, 4 figure
The significance of the fragmentation region in ultrarelativistic heavy ion collisions
We present measurements of the pseudorapidity distribution of primary charged
particles produced in Au+Au collisions at three energies, sqrt(s_{NN}) = 19.6,
130, and 200 GeV, for a range of collision centralities. The centrality
dependence is shown to be non-trivial: the distribution narrows for more
central collisions and excess particles are produced at high pseudorapidity in
peripheral collisions. For a given centrality, however, the distributions are
found to scale with energy according to the "limiting fragmentation"
hypothesis. The universal fragmentation region described by this scaling grows
in pseudorapidity with increasing collision energy, extending well away from
the beam rapidity and covering more than half of the pseudorapidity range over
which particles are produced. This approach to a universal limiting curve
appears to be a dominant feature of the pseudorapidity distribution and
therefore of the total particle production in these collisions.Comment: 5 pages, 4 figure
Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at sqrt(s_NN) = 200 GeV
This paper presents the first measurement of event-by-event fluctuations of
the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a
function of collision centrality. The relative non-statistical fluctuations of
the v_2 parameter are found to be approximately 40%. The results, including
contributions from event-by-event elliptic flow fluctuations and from azimuthal
correlations that are unrelated to the reaction plane (non-flow correlations),
establish an upper limit on the magnitude of underlying elliptic flow
fluctuations. This limit is consistent with predictions based on spatial
fluctuations of the participating nucleons in the initial nuclear overlap
region. These results provide important constraints on models of the initial
state and hydrodynamic evolution of relativistic heavy ion collisions.Comment: 5 pages, 2 figures, Published in Phys. Rev. Lett
Centrality dependence of charged hadron transverse momentum spectra in d+Au collisions at sqrt(s_NN) = 200 GeV
We have measured transverse momentum distributions of charged hadrons
produced in d+Au collisions at sqrt(s_NN) = 200 GeV. The spectra were obtained
for transverse momenta 0.25 < p_T < 6.0 GeV/c, in a pseudorapidity range of 0.2
< eta < 1.4 in the deuteron direction. The evolution of the spectra with
collision centrality is presented in comparison to p+pbarcollisions at the same
collision energy. With increasing centrality, the yield at high transverse
momenta increases more rapidly than the overall particle density, leading to a
strong modification of the spectral shape. This change in spectral shape is
qualitatively different from observations in Au+Au collisions at the same
energy. The results provide important information for discriminating between
different models for the suppression of high-p_T hadrons observed in Au+Au
collisions.Comment: 5 pages, 4 figures, submitted to PR
Non-flow correlations and elliptic flow fluctuations in gold-gold collisions at sqrt(s_NN)= 200 GeV
This paper presents results on event-by-event elliptic flow fluctuations in
Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow
correlations has been subtracted. An analysis method is introduced to measure
non-flow correlations, relying on the assumption that non-flow correlations are
most prominent at short ranges (Delta eta < 2). Assuming that non-flow
correlations are of the order that is observed in p+p collisions for long range
correlations (Delta eta > 2), relative elliptic flow fluctuations of
approximately 30-40% are observed. These results are consistent with
predictions based on spatial fluctuations of the participating nucleons in the
initial nuclear overlap region. It is found that the long range non-flow
correlations in Au+Au collisions would have to be more than an order of
magnitude stronger compared to the p+p data to lead to the observed azimuthal
anisotropy fluctuations with no intrinsic elliptic flow fluctuations.Comment: 9 pages, 7 figures, Published in Phys. Rev.
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