342 research outputs found
Quenching of high-pT hadrons: Energy Loss vs Color Transparency
High-pT hadrons produced in hard collisions and detected inclusively bear
peculiar features: (i) they originate from jets whose initial virtuality and
energy are of the same order; (ii) such jets are rare and have a very biased
energy sharing among the particles, namely, the detected hadron carries the
main fraction of the jet energy. The former feature leads to an extremely
intensive gluon radiation and energy dissipation at the early stage of
hadronization, either in vacuum or in a medium. As a result, a leading hadron
must be produced on a short length scale. Evaluation within a model of
perturbative fragmentation confirms the shortness of the production length.
This result is at variance with the unjustified assumption of long production
length, made within the popular energy loss scenario. Thus we conclude that the
main reason of suppression of high-pT hadrons in heavy ion collisions is the
controlled by color transparency attenuation of a high-pT dipole propagating
through the hot medium. Adjusting a single parameter, the transport
coefficient, we describe quite well the data from LHC and RHIC for the
suppression factor R_{AA} as function of pT, collision energy and centrality.
We observe that the complementary effect of initial state interaction causes a
flattening and even fall of R_{AA} at large pT. The azimuthal anisotropy of
hadron production, calculated with no further adjustment, also agrees well with
data at different energies and centralities.Comment: 17 pages, 19 figure
Diffractive Excitation of Heavy Flavors: Leading Twist Mechanisms
Diffractive production of heavy flavors is calculated within the light-cone
dipole approach. Novel leading twist mechanisms are proposed, which involve
both short and long transverse distances inside the incoming hadron.
Nevertheless, the diffractive cross section turns out to be sensitive to the
primordial transverse momenta of projectile gluons, rather than to the hadronic
size. Our calculations agree with the available data for diffractive production
of charm and beauty, and with the observed weak variation of the
diffraction-to-inclusive cross section ratios as function of the hard scale.Comment: Latex, 19 pages, 12 figures. A short commenting on previously done
computations is adde
Collective quantization of axially symmetric gravitating B=2 skyrmion
In this paper we perform collective quantization of an axially symmetric
skyrmion with baryon number two.The rotational and isorotational modes are
quantized to obtain the static properties of a deuteron and other dibaryonic
objects such as masses, charge densities, magnetic moments. We discuss how the
gravity affects to those observables.Comment: 13 pages, 13 figures, 1 table, accepted to Physical Review
Gluon Shadowing and Heavy Flavor Production off Nuclei
Gluon shadowing which is the main source of nuclear effects for production of
heavy flavored hadrons, remains unknown. We develop a light-cone dipole
approach aiming at simplifying the calculations of nuclear shadowing for heavy
flavor production, as well as the cross section which does not need
next-to-leading and higher order corrections. A substantial process dependence
of gluon shadowing is found at the scale of charm mass manifesting a deviation
from QCD factorization. The magnitude of the shadowing effect correlates with
the symmetry properties and color state of the produced c-cbar pair. It is
about twice as large as in DIS, but smaller than for charmonium production. The
higher twist shadowing correction related to a nonzero size of the c-cbar pair
is not negligible and steeply rises with energy. We predict an appreciable
suppression by shadowing for charm production in heavy ion collisions at RHIC
and a stronger effect at LHC. At the same time, we expect no visible difference
between nuclear effects for minimal bias and central collisions, as is
suggested by recent data from the PHENIX experiment at RHIC. We also
demonstrate that at medium high energies when no shadowing is possible, final
state interaction may cause a rather strong absorption of heavy flavored
hadrons produced at large x_F.Comment: Preprint NSF-ITP-02-40, ITP, UCSB, Santa Barbara; Latex 52 pages and
8 figure
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