397 research outputs found
Proton Differential Elliptic Flow and the Isospin-Dependence of the Nuclear Equation of State
Within an isospin-dependent transport model for nuclear reactions involving
neutron-rich nuclei, we study the first-order direct transverse flow of protons
and their second-order differential elliptic flow as a function of transverse
momentum. It is found that the differential elliptic flow of mid-rapidity
protons, especially at high transverse momenta, is much more sensitive to the
isospin dependence of the nuclear equation of state than the direct flow.
Origins of these different sensitivities and their implications to the
experimental determination of the isospin dependence of the nuclear equation of
state by using neutron-rich heavy-ion collisions at intermediate energies are
discussed.Comment: 15 pages, 6 figures. Phys. Rev. C (2001) in pres
Formation of superdense hadronic matter in high energy heavy-ion collisions
We present the detail of a newly developed relativistic transport model (ART
1.0) for high energy heavy-ion collisions. Using this model, we first study the
general collision dynamics between heavy ions at the AGS energies. We then show
that in central collisions there exists a large volume of sufficiently
long-lived superdense hadronic matter whose local baryon and energy densities
exceed the critical densities for the hadronic matter to quark-gluon plasma
transition. The size and lifetime of this matter are found to depend strongly
on the equation of state. We also investigate the degree and time scale of
thermalization as well as the radial flow during the expansion of the
superdense hadronic matter. The flow velocity profile and the temperature of
the hadronic matter at freeze-out are extracted. The transverse momentum and
rapidity distributions of protons, pions and kaons calculated with and without
the mean field are compared with each other and also with the preliminary data
from the E866/E802 collaboration to search for experimental observables that
are sensitive to the equation of state. It is found that these inclusive,
single particle observables depend weakly on the equation of state. The
difference between results obtained with and without the nuclear mean field is
only about 20\%. The baryon transverse collective flow in the reaction plane is
also analyzed. It is shown that both the flow parameter and the strength of the
``bounce-off'' effect are very sensitive to the equation of state. In
particular, a soft equation of state with a compressibility of 200 MeV results
in an increase of the flow parameter by a factor of 2.5 compared to the cascade
case without the mean field. This large effect makes it possible to distinguish
the predictions from different theoretical models and to detect the signaturesComment: 55 pages, latex, + 39 figures available upon reques
Study of Dipole Resonance Strength in 12-C via the Reactions 12-C(pol.p,p'c)
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Isospin Response of the 4-He Continuum
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
"Sixth root of unity" and Feynman diagrams: hypergeometric function approach point of view
We briefly discuss the transcendental constants generated through the
epsilon-expansion of generalized hypergeometric functions and their
interrelation with the "sixth root of unity."Comment: 6 pages, presented at "Loops and Legs in Quantum Field Theory 2010",
Woerlitz, Germany, April 2010; v2: Eq.(2) is improve
On the Standard Model prediction for BR(B{s,d} to mu+ mu-)
The decay Bs to mu+ mu- is one of the milestones of the flavor program at the
LHC. We reappraise its Standard Model prediction. First, by analyzing the
theoretical rate in the light of its main parametric dependence, we highlight
the importance of a complete evaluation of higher-order electroweak
corrections, at present known only in the large-mt limit, and leaving sizable
dependence on the definition of electroweak parameters. Using insights from a
complete calculation of such corrections for K to pi bar{nu} nu decays, we find
a scheme in which NLO electroweak corrections are likely to be negligible.
Second, we address the issue of the correspondence between the initial and the
final state detected by the experiments, and those used in the theoretical
prediction. Particular attention is devoted to the effect of the soft
radiation, that has not been discussed for this mode in the previous
literature, and that can lead to O(10%) corrections to the decay rate. The
"non-radiative" branching ratio (that is equivalent to the branching ratio
fully inclusive of bremsstrahlung radiation) is estimated to be (3.23 +/- 0.27)
x 10^{-9} for the flavor eigenstate, with the main uncertainty resulting from
the value of f_{Bs}, followed by the uncertainty due to higher order
electroweak corrections. Applying the same strategy to Bd to mu+ mu-, we find
for its non-radiative branching ratio (1.07 +/- 0.10) x 10^{-10}.Comment: 15 pages. v3: very minor changes to match the journal version (EPJC
Precision Electroweak Data and Unification of Couplings in Warped Extra Dimensions
Warped extra dimensions allow a novel way of solving the hierarchy problem,
with all fundamental mass parameters of the theory naturally of the order of
the Planck scale. The observable value of the Higgs vacuum expectation value is
red-shifted, due to the localization of the Higgs field in the extra dimension.
It has been recently observed that, when the gauge fields propagate in the
bulk, unification of the gauge couplings may be achieved. Moreover, the
propagation of fermions in the bulk allows for a simple solution to potentially
dangerous proton decay problems. However, bulk gauge fields and fermions pose a
phenomenological challenge, since they tend to induce large corrections to the
precision electroweak observables. In this article, we study in detail the
effect of gauge and fermion fields propagating in the bulk in the presence of
gauge brane kinetic terms compatible with gauge coupling unification, and we
present ways of obtaining a consistent description of experimental data, while
allowing values of the first Kaluza Klein mode masses of the order of a few
TeV.Comment: 32 pages, 7 figures. References adde
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