9,213 research outputs found
Interactions between Octet Baryons in the SU_6 Quark model
The baryon-baryon interactions for the complete baryon octet (B_8) are
investigated in a unified framework of the resonating-group method, in which
the spin-flavor SU_6 quark-model wave functions are employed. Model parameters
are determined to reproduce properties of the nucleon-nucleon system and the
low-energy cross section data for the hyperon-nucleon interaction. We then
proceed to explore B_8 B_8 interactions in the strangeness S=-2, -3 and -4
sectors. The S-wave phase-shift behavior and total cross sections are
systematically understood by 1) the spin-flavor SU_6 symmetry, 2) the special
role of the pion exchange, and 3) the flavor symmetry breaking.Comment: 11 pages, 6 figures, submitted to Phys. Rev. C (Rapid Communication
Antihydrogen, CPT, and Naturalness
Studying fundamental symmetries of Nature has proven fruitful in particle
physics. I argue that recent results at the LHC, and the naturalness problem
highlighted by them, provide a renewed motivation for tests of CPT symmetry as
a probe for physics beyond quantum field theory. I also discuss prospects for
antihydrogen CPT tests with sensitivities to Planck scale suppressed effects.Comment: Based on an invited talk at CPT'13 -- the Sixth Meeting on CPT and
Lorentz Symmetry, Bloomington, Indiana, June 17-21, 201
Detecting Antihydrogen: The Challenges and the Applications
ATHENA's first detection of cold antihydrogen atoms relied on their
annihilation signatures in a sophisticated particle detector. We will review
the features of the ATHENA detector and its applications in trap physics. The
detector for a new experiment ALPHA will have considerable challenges due to
increased material thickness in the trap apparatus as well as field
non-uniformity. Our studies indicate that annihilation vertex imaging should be
still possible despite these challenges. An alternative method for trapped
antihydrogen, via electron impact ionization, will be also discussed.Comment: Invited paper at International Workshop on Physics with Ultra-Slow
Antiprotons, RIKEN, Japan, March 2005. To be published in AIP Conference
Proceeding
Single-Particle Spin-Orbit Strengths of the Nucleon and Hyperons by SU6 Quark-Model
The quark-model hyperon-nucleon interaction suggests an important
antisymmetric spin-orbit component. It is generated from a color analogue of
the Fermi-Breit interaction dominating in the one-gluon exchange process
between quarks. We discuss the strength S_B of the single-particle spin-orbit
potential, following the Scheerbaum's prescription. Using the SU6 quark-model
baryon-baryon interaction which was recently developed by the Kyoto-Niigata
group, we calculate NN, Lambda N and Sigma N G-matrices in symmetric nuclear
matter and apply them to estimate the strength S_B. The ratio of S_B to the
nucleon strength S_N =~ -40 MeV*fm^5 is (S_Lambda)/(S_N) =~ 1/5 and
(S_Sigma)/(S_N) =~ 1/2 in the Born approximation. The G-matrix calculation of
the model FSS modifies S_Lambda to (S_Lambda)/(S_N) =~ 1/12. For S_N and
S_Sigma, the effect of the short-range correlation is comparatively weak
against meson-exchange potentials with a short-range repulsive core. The
significant reduction of the Lambda single-particle potential arises from the
combined effect of the antisymmetric LS force, the flavor-symmetry breaking
originating from the strange to up-down quark-mass difference, as well as the
effect of the short-range correlation. The density dependence of S_B is also
examined.Comment: 26 page
Rigidity of Orientationally Ordered Domains of Short Chain Molecules
By molecular dynamics simulation, discovered is a strange rigid-like nature
for a hexagonally packed domain of short chain molecules. In spite of the
non-bonded short-range interaction potential (Lennard-Jones potential) among
chain molecules, the packed domain gives rise to a resultant global moment of
inertia. Accordingly, as two domains encounter obliquely, they rotate so as to
be parallel to each other keeping their overall structures as if they were
rigid bodies.Comment: 7 pages, 5 figures, and 2 table
Hyperon Single-Particle Potentials Calculated from SU6 Quark-Model Baryon-Baryon Interactions
Using the SU6 quark-model baryon-baryon interaction recently developed by the
Kyoto-Niigata group, we calculate NN, Lambda N and Sigma N G-matrices in
ordinary nuclear matter. This is the first attempt to discuss the Lambda and
Sigma single-particle potentials in nuclear medium, based on the realistic
quark-model potential. The Lambda potential has the depth of more than 40 MeV,
which is more attractive than the value expected from the experimental data of
Lambda-hypernuclei. The Sigma potential turns out to be repulsive, the origin
of which is traced back to the strong Pauli repulsion in the Sigma N (I=3/2)
^3S_1 state.Comment: 20 pages, 5 figure
Baryon-baryon interactions in the SU6 quark model and their applications to light nuclear systems
Interactions between the octet-baryons (B8) in the spin-flavor SU6 quark
model are investigated in a unified coupled-channels framework of the
resonating-group method (RGM). The interaction Hamiltonian for quarks consists
of the phenomenological confinement potential, the color Fermi-Breit
interaction with explicit flavor-symmetry breaking (FSB), and effective-meson
exchange potentials of scalar-, pseudoscalar- and vector-meson types. The model
parameters are determined to reproduce the properties of the nucleon-nucleon
(NN) system and the low-energy cross section data for the hyperon-nucleon (YN)
interactions. The NN phase shifts and many observables for the NN and YN
interactions are nicely reproduced. Properties of these B8 B8 interactions are
analyzed through the G-matrix calculations. The B8 B8 interactions are then
applied to some of few-baryon systems and light Lambda-hypernuclei in a
three-cluster Faddeev formalism using two-cluster RGM kernels. An application
to the three-nucleon system shows that the quark-model NN interaction can give
a sufficient triton binding energy with little room for the three-nucleon
force. The hypertriton Faddeev calculation indicates that the attraction of the
Lambda N interaction in the 1S0 state is only slightly more attractive than
that in the 3S1 state. In the application to the alpha alpha Lambda system, the
energy spectrum of 9 Lambda Be is well reproduced using the alpha alpha RGM
kernel. The very small spin-orbit splitting of the 9 Lambda Be excited states
is also discussed. In the Lambda Lambda alpha Faddeev calculation, the NAGARA
event for 6 Lambda Lambda He is found to be consistent with the quark-model
Lambda Lambda interaction.Comment: 77 pages, 33 figures, review article to be published in Prog. Part.
Nucl. Phy
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