187 research outputs found
Charmonium suppression by gluon bremsstrahlung in p-A and A-B collisions
Prompt gluons are an additional source for charmonium suppression in nuclear
collisions, in particular for nucleus-nucleus collisions. These gluons are
radiated as bremsstrahlung in N-N collisions and interact inelastically with
the charmonium states while the nuclei still overlap. The spectra and mean
number of the prompt gluons are calculated perturbatively and the
gluon-Psi inelastic cross section is estimated. The integrated cross sections
for AB --> J/Psi (Psi')X for p-A and A-B collisions and the dependence on
transverse energy for S-U and Pb-Pb can be described quantitatively with some
adjustment of one parameter \sigma(gPsi).Comment: 17 pages of Latex including 10 figure
Electroproduction of Charmonia off Protons and Nuclei
Elastic virtual photoproduction of charmonia on nucleons is calculated in a
parameter free way with the light-cone dipole formalism and the same input:
factorization in impact parameters, light-cone wave functions for the photons
and the charmonia, and the universal phenomenological dipole cross section
which is fitted to other data. The charmonium wave functions are calculated
with four known realistic potentials, and two models for the dipole cross
section are tested. Very good agreement with data for the cross section of
charmonium electroproduction is found in a wide range of and . Using
the ingredients from those calculations we calculate also exclusive
electroproduction of charmonia off nuclei. Here new effects become important,
(i) color filtering of the pair on its trajectory through nuclear
matter, (ii) dependence on the finite lifetime of the fluctuation
(coherence length) and (iii) gluon shadowing in a nucleus compared to the one
in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as
functions of are presented. The results can be tested with future
electron-nucleus colliders or in the peripheral collisions of relativistic
heavy ions.Comment: Talk at 2-nd International Workshop on Hadron Physics, 25-29
September 2002, Coimbra, Portugal. To appear in the Workshop Proceedings
(will be published by the American Institute of Physics
Imaging Localized States in Graphene Nanostructures
Probing techniques with spatial resolution have the potential to lead to a
better understanding of the microscopic physical processes and to novel routes
for manipulating nanostructures. We present scanning-gate images of a graphene
quantum dot which is coupled to source and drain via two constrictions. We
image and locate conductance resonances of the quantum dot in the
Coulomb-blockade regime as well as resonances of localized states in the
constrictions in real space.Comment: 18 pages, 7 figure
For cost-reducing technologies, knowing markets is to change them
Journal ArticleSponsored research from a NSF Foundation/Whitaker Foundation initiative on cost-reducing technologies brought together faculty from engineering, medicine, and social sciences to link economic and policy assessments to engineering design. The technology under development is to be an inexpensive, easy-to-use monitor for self-management of metabolic diseases by patients, with specific application to phenylketonuria (PKU). While the technology remains in development, the experience, including discussions with others in the Whitaker and National Science foundations' program, raised interesting issues about economics, policy, and cost-reducing technologies
suppression in Pb+Pb collisions and broadening
We have analysed the NA50 data, on the centrality dependence of
broadening of 's, in Pb+Pb collisions, at the CERN-SPS. The data were
analysed in a QCD based model, where 's are suppressed in 'nuclear'
medium. Without any free parameter, the model could explain the NA50
broadening data. The data were also analysed in a QGP based threshold model,
where suppression is 100% above a critical density. The QGP based
model could not explain the NA50 broadening data. We have also predicted
the centrality dependence of suppression and broadening at RHIC
energy. Both the models, the QGP based threshold model and the QCD based
nuclear absorption model, predict broadening very close to each other.Comment: The paper was completely revised. The conclusion is also changed. 5
pages, 4 figure
- …