347,050 research outputs found
Heavy quarkonium production: Nontrivial transition from pA to AA collisions
Two novel QCD effects, double color filtering and mutual boosting of the
saturation scales in colliding nuclei, affect the transparency of the nuclei
for quark dipoles in comparison with proton-nucleus collisions. The former
effect increases the survival probability of the dipoles, since color filtering
in one nucleus makes the other one more transparent. The second effect acts in
the opposite direction and is stronger, it makes the colliding nuclei more
opaque than in the case of pA collisions. As a result of parton saturation in
nuclei the effective scale is shifted upwards, what leads to an increase of the
gluon density at small x. This in turn leads to a stronger transverse momentum
broadening in AA compared with pA collisions, i.e. to an additional growth of
the saturation momentum. Such a mutual boosting leads to a system of
reciprocity equations, which result in a saturation scale, a few times higher
in AA than in pA collisions at the energies of LHC. Since the dipole cross
section is proportional to the saturation momentum squared, the nuclei become
much more opaque for dipoles in AA than in pA collisions. For the same reason
gluon shadowing turns out to be boosted to a larger magnitude compared with the
product of the gluon shadowing factors in each of the colliding nuclei. All
these effects make it more difficult to establish a baseline for anomalous
J/Psi suppression in heavy ion collisions at high energies.Comment: 10 pages 8 figures. The accuracy of calculations is improve
On the sine-Gordon--Thirring equivalence in the presence of a boundary
In this paper, the relationship between the sine-Gordon model with an
integrable boundary condition and the Thirring model with boundary is discussed
and the reflection -matrix for the massive Thirring model, which is related
to the physical boundary parameters of the sine-Gordon model, is given. The
relationship between the the boundary parameters and the two formal parameters
appearing in the work of Ghoshal and Zamolodchikov is discussed.Comment: 14 pages, Latex, to be published in Int. J. Mod. Phys. A. Two
references adde
Quantum-mechanical description of in-medium fragmentation
We present a quantum-mechanical description of quark-hadron fragmentation in
a nuclear environment. It employs the path-integral formulation of quantum
mechanics, which takes care of all phases and interferences, and which contains
all relevant time scales, like production, coherence, formation, etc. The cross
section includes the probability of pre-hadron (colorless dipole) production
both inside and outside the medium. Moreover, it also includes inside-outside
production, which is a typical quantum-mechanical interference effect (like
twin-slit electron propagation). We observe a substantial suppression caused by
the medium, even if the pre-hadron is produced outside the medium and no energy
loss is involved. This important source of suppression is missed in the usual
energy-loss scenario interpreting the effect of jet quenching observed in heavy
ion collisions. This may be one of the reasons of a too large gluon density,
reported by such analyzes.Comment: 20 pages, 7 figure
Recent BES measurements and the hadronic contribution to the QED vacuum polarization
We have updated our evaluation of the hadronic contribution to the running of
the QED fine structure constant using the recent precise measurements of the
e+e- annihilation at the center-of-mass (c.m.s.) energy region between 2.6 and
3.65 GeV performed by the BES collaboration. In the low energy region, around
the rho resonance, we include the recent measurements from the BABAR, CDM-2,
KLOE and SND collaborations. We obtain Delta alpha (5)_had (s) = 0.02750 +/-
0.00033 at s = m_Z^2.Comment: 3 pages, 1 figur
Dynamic Monte Carlo Study of the Two-Dimensional Quantum XY Model
We present a dynamic Monte Carlo study of the Kosterlitz-Thouless phase
transition for the spin-1/2 quantum XY model in two dimensions. The short-time
dynamic scaling behaviour is found and the dynamical exponent , and
the static exponent are determined at the transition temperature.Comment: 6 pages with 3 figure
Beltrami-like fields created by baroclinic effect in two-fluid plasmas
A theory of two-dimensional plasma evolution with Beltrami-like flow and
field due to baroclinic effect has been presented. Particular solution of the
nonlinear two-fluid equations is obtained. This simple model can explain the
generation of magnetic field without assuming the presence of a seed in the
system. Coupled field and flow naturally grow together. The theory has been
applied to estimate B-field in laser-induced plasmas and the result is in good
agreement with experimental values.Comment: 3 page
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An investigation into the effects of computer integrated manufacturing systems in the productivity of SMEs in Pakistan
The current dynamic and turbulent manufacturing environment has forced companies that compete globally to change their traditional methods of conducting business [Producer to consumer]. Recent developments in manufacturing and business operations have lead to the adoption of Computer Integrated Manufacturing (CIM) technologies that are based on systems and processes that support global competitiveness, especially for Small and Medium Enterprises (SMEs). Organizations and SMEs in particular need to re-evaluate every aspect of their manufacturing strategy and quickly move towards a CIM based environment where manufacturing technologies, business strategies and processes are integrated together. This paper highlights the development of a CIM adoption model that has resulted from empirical work generated from SMEs in Pakistan. The model consists of the parameters such as Top Management Support, System Integration, Marketing, and over all performance
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