4,230 research outputs found
Leading-particle suppression in high energy nucleus-nucleus collisions
Parton energy loss effects in heavy-ion collisions are studied with the Monte
Carlo program PQM (Parton Quenching Model) constructed using the BDMPS
quenching weights and a realistic collision geometry. The merit of the approach
is that it contains only one free parameter that is tuned to the high-pt
nuclear modification factor measured in central Au-Au collisions at sqrt{s_NN}
= 200 GeV. Once tuned, the model is coherently applied to all the high-pt
observables at 200 GeV: the centrality evolution of the nuclear modification
factor, the suppression of the away-side jet-like correlations, and the
azimuthal anisotropies for these observables. Predictions for the
leading-particle suppression at nucleon-nucleon centre-of-mass energies of 62.4
and 5500 GeV are calculated. The limits of the eikonal approximation in the
BDMPS approach, when applied to finite-energy partons, are discussed.Comment: 28 pages, 14 figures, final version, accepted by Eur. Phys. J.
Numerical Study of Finite Size Scaling for First Order Phase Transitions
I present results of simulations of the q=10 and q=20 2-d Potts models in the
transition region. The asymptotic finite size behavior sets in only for
extremely large lattices. We learn from this simulation that finite size
scaling cannot be used to decide that a transition is first order.Comment: Talk presented at the Workshop on Dynamics of First Order
Transitions, HLRZ, Forschungszentrum J\"ulich,Germany, June 1-3, 1992, 7
pages, 2 PostScript Figures (typing mistakes in figure captions corrected
American Legion Race Program
The official race program and score card for the August 17, 1932 Anderson-Mayberry Post No. 91 American Legion Races. The Anderson-Mayberry Post of the American Legion is located in Yarmouth, Maine but the location of the races is not identified in the program.
The program includes the race day\u27s line up of horses and drivers. Kendall\u27s handwritten notes on changes in the field as well as race results appear in the score card. Kendall also mounted photographs on the interior of the program. The program was printed by Elbridge A. Reed, of Yarmouth and provided to race-goers, compliments of Judge Joseph E. F. Connolly, Candidate for Congress
Effect of the lattice alignment on Bloch oscillations of a Bose-Einstein condensate in a square optical lattice
We consider a Bose-Einstein condensate of ultracold atoms loaded into a
square optical lattice and subject to a static force. For vanishing atom-atom
interactions the atoms perform periodic Bloch oscillations for arbitrary
direction of the force. We study the stability of these oscillations for
non-vanishing interactions, which is shown to depend on an alignment of the
force vector with respect to the lattice crystallographic axes. If the force is
aligned along any of the axes, the mean field approach can be used to identify
the stability conditions. On the contrary, for a misaligned force one has to
employ the microscopic approach, which predicts periodic modulation of Bloch
oscillations in the limit of a large forcing.Comment: 4 pages, 3 figure
Accurate spectroscopy of Sr atoms
We report the frequency measurement with an accuracy in the 100 kHz range of
several optical transitions of atomic Sr : at 689 nm, at 688 nm and at 679 nm. Measurements are performed with
a frequency chain based on a femtosecond laser referenced to primary frequency
standards. They allowed the indirect determination with a 70 kHz uncertainty of
the frequency of the doubly forbidden 5s^2^1S_0- 5s5p^3P_0 transition of
Sr at 698 nm and in a second step its direct observation. Frequency
measurements are performed for Sr and Sr, allowing the
determination of , and isotope shifts, as well as the
hyperfine constants.Comment: 12 pages, 16 figure
Bragg spectroscopy of discrete axial quasiparticle modes in a cigar-shaped degenerate Bose gas
We propose an experiment in which long wavelength discrete axial
quasiparticle modes can be imprinted in a 3D cigar-shaped Bose-Einstein
condensate by using two-photon Bragg scattering experiments, similar to the
experiment at the Weizmann Institute [J. Steinhauer {\em et al.}, Phys. Rev.
Lett. {\bf 90}, 060404 (2003)] where short wavelength axial phonons with
different number of radial modes have been observed. We provide values of the
momentum, energy and time duration of the two-photon Bragg pulse and also the
two-body interaction strength which are needed in the Bragg scattering
experiments in order to observe the long wavelength discrete axial modes. These
discrete axial modes can be observed when the system is dilute and the time
duration of the Bragg pulse is long enough.Comment: 5 pages, 3 figures, title, abstract, results changed, references
added. to appear in The European Physical Journal
Do we understand the single-spin asymmetry for inclusive production in pp collisions?
The cross section data for inclusive production in collisions is
considered in a rather broad kinematic region in energy , Feynman
variable and transverse momentum . The analysis of these data is
done in the perturbative QCD framework at the next-to-leading order. We find
that they cannot be correctly described in the entire kinematic domain and this
leads us to conclude that the single-spin asymmetry, for this process,
observed several years ago at FNAL by the experiment E704 and the recent result
obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5
figure
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Melting and evaporation transitions in small Al clusters: canonical Monte-Carlo simulations
A dimer of bound atoms cannot melt, only dissociate. Bulk metals show a well
defined first order transition between their solid and liquid phases. The
appearance of the melting transition is explored for increasing clusters sizes
via the signatures in the specific heat and the root mean square of the bond
lengths (Berry parameter) by means of Monte-Carlo simulations
of Al clusters modelled by Gupta potentials. Clear signatures of a melting
transition appear for atoms. Closed-shell effects are shown for
clusters with up to 56 atoms. The melting transition is compared in detail with
the dissociation transition, which induces a second and possibly much larger
local maximum in the specific heat at higher temperatures. Larger clusters are
shown to fragment into dimers and trimers, which in turn dissociate at higher
temperatures.Comment: 6 pages, 7 figure
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