8,165 research outputs found
Semileptonic Hyperon Decays
We review the status of hyperon semileptonic decays. The central issue is the
element of the CKM matrix, where we obtain . This
value is of similar precision, but higher, than the one derived from ,
and in better agreement with the unitarity requirement,
. We find that the Cabibbo model gives an
excellent fit of the existing form factor data on baryon beta decays ( for 3 degrees of freedom) with , , and no indication of flavour-SU(3)-breaking effects. We
indicate the need of more experimental and theoretical work, both on hyperon
beta decays and on decays.Comment: 37 pages, 8 figures, 4 tables, Final version of this material is
scheduled to appear in the Annual Review of Nuclear and Particle Science Vol.
5
Semileptonic Hyperon Decays and CKM Unitarity
Using a technique that is not subject to first-order SU(3) symmetry breaking
effects, we determine the element of the CKM matrix from data on
semileptonic hyperon decays. We obtain =0.2250(27). This value is of
similar precision to the one derived from , but higher and in better
agreement with the unitarity requirement, .Comment: 3 pages, 1 tabl
Reducing Disparities in the Burden of Cancer: The Role of Patient Navigators
Many racial and ethnic minority patients with cancer face barriers related to access to health care and information. Patient navigators, say the authors, could help to overcome these barriers
Post Deposition Heat Treatment Effects on Ceramic Superconducting Films Produced by Infrared Nd:YAG Pulsed Laser Deposition
A Systematic Approach For Kinematic Design Of Upper Limb Rehabilitation Exoskeletons
Kinematic structure of an exoskeleton is the most fundamental block of its
design and is determinant of many functional capabilities of it. Although
numerous upper limb rehabilitation devices have been designed in the recent
years, there is not a framework that can systematically guide the kinematic
design procedure. Additionally, diversity of currently available devices and
the many minute details incorporated to address certain design requirements
hinders pinpointing the core kinematics of the available devices to compare
them against each other. This makes the review of literature for identifying
drawbacks of the state of the art systems a challenging and puzzling task. In
fact, lack of a unifying framework makes designing rehabilitation devices an
intuitive process and prone to biases from currently available designs. This
research work proposes a systematic approach for kinematic design of upper limb
rehabilitation exoskeletons based on conceptual design techniques. Having
defined a solution neutral problem statement based on the characteristics of an
ideal device, the main functionality of the system is divided into smaller
functional units via the Functional Decomposition Method. Various directions
for concept generation are explored and finally, it has been shown that a vast
majority of the current exoskeleton designs fit within the proposed design
framework and the defined functionalities
Phase ordering in chaotic map lattices with conserved dynamics
Dynamical scaling in a two-dimensional lattice model of chaotic maps, in
contact with a thermal bath, is numerically studied. The model here proposed is
equivalent to a conserved Ising model with coupligs which fluctuate over the
same time scale as spin moves. When couplings fluctuations and thermal
fluctuations are both important, this model does not belong to the class of
universality of a Langevin equation known as model B; the scaling exponents are
continuously varying with the temperature and depend on the map used. The
universal behavior of model B is recovered when thermal fluctuations are
dominant.Comment: 6 pages, 4 figures. Revised version accepted for publication on
Physical Review E as a Rapid Communicatio
Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt{s_NN} = 130 GeV
This paper describes the measurement of collective flow for charged particles
in Au+Au collisions at sqrt{s_NN}} = 130 GeV using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). An azimuthal anisotropy is observed in
the charged particle hit distribution in the PHOBOS multiplicity detector. This
anisotropy is presented over a wide range of pseudorapidity (eta) for the first
time at this energy. The size of the anisotropy (v_{2}) is thought to probe the
degree of equilibration achieved in these collisions. The result here,averaged
over momenta and particle species, is observed to reach 7% for peripheral
collisions at mid-rapidity, falling off with centrality and increasing |eta|.
Data are presented as a function of centrality for |eta|<1.0 and as a function
of eta, averaged over centrality, in the angular region -5.0<eta<5.3. These
results call into question the common assumption of longitudinal boost
invariance over a large region of rapidity in RHIC collisions.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
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
Energy dependence of particle multiplicities in central Au+Au collisions
We present the first measurement of the pseudorapidity density of primary
charged particles in Au+Au collisions at sqrt(s_NN) = 200GeV. For the 6% most
central collisions, we obtain dN_ch/deta|_|eta|<1 = 650 +/- 35 (syst). Compared
to collisions at sqrt(s_NN) = 130GeV, the highest energy studied previously, an
increase by a factor of 1.14 +/- 0.05 is found. The energy dependence of the
pseudorapidity density is discussed in comparison with data from proton-induced
collisions and theoretical predictions.Comment: 4 pages, 6 figures, submitted to PR
Universal Behavior of Charged Particle Production in Heavy Ion Collisions
The PHOBOS experiment at RHIC has measured the multiplicity of primary
charged particles as a function of centrality and pseudorapidity in Au+Au
collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Two kinds of universal
behavior are observed in charged particle production in heavy ion collisions.
The first is that forward particle production, over a range of energies,
follows a universal limiting curve with a non-trivial centrality dependence.
The second arises from comparisons with pp/pbar-p and e+e- data.
N_tot/(N_part/2) in nuclear collisions at high energy scales with sqrt(s) in a
similar way as N_tot in e+e- collisions and has a very weak centrality
dependence. This feature may be related to a reduction in the leading particle
effect due to the multiple collisions suffered per participant in heavy ion
collisions.Comment: 4 Pages, 5 Figures, contributed to the Proceedings of Quark Matter
2002, Nantes, France, 18-24 July 200
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