2,879 research outputs found
LPM-Effect in Monte Carlo Models of Radiative Energy Loss
Extending the use of Monte Carlo (MC) event generators to jets in nuclear
collisions requires a probabilistic implementation of the non-abelian LPM
effect. We demonstrate that a local, probabilistic MC implementation based on
the concept of formation times can account fully for the LPM-effect. The main
features of the analytically known eikonal and collinear approximation can be
reproduced, but we show how going beyond this approximation can lead to
qualitatively different results.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee; v2: removed line
number
Coherent Radiative Parton Energy Loss beyond the BDMPS-Z Limit
It is widely accepted that a phenomenologically viable theory of jet
quenching for heavy ion collisions requires the understanding of medium-induced
parton energy loss beyond the limit of eikonal kinematics formulated by
Baier-Dokshitzer-Mueller-Peigne-Schiff and Zakharov (BDMPS-Z). Here, we
supplement a recently developed exact Monte Carlo implementation of the BDMPS-Z
formalism with elementary physical requirements including exact energy-momentum
conservation, a refined formulation of jet-medium interactions and a treatment
of all parton branchings on the same footing. We document the changes induced
by these physical requirements and we describe their kinematic origin.Comment: 8 pages, 4 figure
Medium Modification of the Jet Properties
In the case that a dense medium is created in a heavy ions collision,
high-E_t jets are expected to be broadened by medium-modified gluon emission.
This broadening is directly related, through geometry, to the energy loss
measured in inclusive high-p_t particle suppression. We present here the
modifications of jet observables due to the presence of a medium for the case
of azimuthal jet energy distributions and k_t-differential multiplicities
inside the jets.Comment: 4 pages, 3 postscript figures. Proceedings for Quark Matter 200
The variety show: Why classical string musicians are exploring a multistyle approach to teaching
The Variety Show: Why Classical String Musicians are
Exploring a Multistyle Approach to Music
Kelly C. Wiedemann
This case study examines the experiences of five classically trained string teachers who now include alternative styles in their teaching. The research questions are: (1) What factors inspire a classically trained string educator to begin teaching alternative styles to their students? (2) Why is it important to keep classical music in string pedagogy? (3) How have these teachers, their peers, students, and community reacted to multistylism? The interviews revealed four major points of motivation: Opportunities for developing creativity and finding a personal voice on their instrument, freedom to make mistakes without criticism, higher enrollment and retention rates, and increased job opportunities.
Participants were committed to keeping classical music as a core part of their curriculum. Upon implementing a diverse curriculum, participants felt some resistance from students and peers, but for them, the positive reactions outweigh the negative. Based on the findings of this study, I argue that including alternative styles in a classical string curriculum, whatever the style may be, greatly increase professional & personal potential for both teacher and student
How sensitive are high-pt electron spectra at RHIC to heavy quark energy loss?
In nucleus-nucleus collisions, high-pt electron spectra depend on the medium
modified fragmentation of their massive quark parents, thus giving novel access
to the predicted mass hierarchy of parton energy loss. Here we calculate these
spectra in a model, which supplements the perturbative QCD factorization
formalism with parton energy loss. In general, we find - within large errors -
rough agreement between theory and data on the single inclusive electron
spectrum in pp, its nuclear modification factor, and its azimuthal anisotropy.
However, the nuclear modification factor depends on the relative contribution
of charm and bottom production, which we find to be affected by large
perturbative uncertainties. In order for electron measurements to provide a
significantly more stringent test of the expected mass hierarchy, one must then
disentangle the b- and c-decay contributions, for instance by reconstructing
the displaced decay vertices.Comment: 9 pages RevTex, 4 eps-figures, asci-file containing numerical tables
of results include
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.
Jet quenching via jet collimation
The strong modifications of dijet properties in heavy ion collisions measured
by ATLAS and CMS provide important constraints on the dynamical mechanisms
underlying jet quenching. In this work, we show that the transport of soft
gluons away from the jet cone - jet collimation - can account for the observed
dijet asymmetry with values of that lie in the expected order of
magnitude. Further, we show that the energy loss attained through this
mechanism results in a very mild distortion of the azimuthal angle dijet
distribution.Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conferenc
Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data
The solutions of the Balitsky-Kovchegov evolution equations are studied
numerically and compared with known analytical estimations. The rapidity and
nuclear size dependences of the saturation scale are obtained for the cases of
fixed and running coupling constant. These same dependences are studied in
experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus
collisions, through geometric scaling and compared with the theoretical
calculations.Comment: 8 pages, 8 figures. Contribution based on talks given by J. G.
Milhano and C. A. Salgado to the proceedings of ``Hard Probes 2004'',
Ericeira (Portugal), November 4-10, 200
The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry
Context: Stars on the asymptotic giant branch (AGB) show broad evidence of
inhomogeneous atmospheres and circumstellar envelopes. These have been studied
by a variety of methods on various angular scales. In this paper we explore the
envelope of the well-studied carbon star TX Psc by the technique of
spectro-astrometry. Aims: We explore the potential of this method for detecting
asymmetries around AGB stars. Methods:We obtained CRIRES observations of
several CO v=1 lines near 4.6 m and HCN lines near 3 m in
2010 and 2013. These were then searched for spectro-astrometric signatures. For
the interpretation of the results, we used simple simulated observations.
Results: Several lines show significant photocentre shifts with a clear
dependence on position angle. In all cases, tilde-shaped signatures are found
where the positive and negative shifts (at PA 0deg) are associated with blue
and weaker red components of the lines. The shifts can be modelled with a
bright blob 70 mas to 210 mas south of the star with a flux of several percent
of the photospheric flux. We estimate a lower limit of the blob temperature of
1000 K. The blob may be related to a mass ejection as found for AGB stars or
red supergiants. We also consider the scenario of a companion object.
Conclusions: Although there is clear spectro-astrometric evidence of a rather
prominent structure near TX Psc, it does not seem to relate to the other
evidence of asymmetries, so no definite explanation can be given. Our data thus
underline the very complex structure of the environment of this star, but
further observations that sample the angular scales out to a few hundred
milli-arcseconds are needed to get a clearer picture
On the jet spectrum in nucleus-nucleus interactions
We derive the inclusive transverse spectrum of minijets in nuclear collisions
at very high energies by assuming that the nuclear S-matrix factorizes into a
product of elastic S-matrices for elementary partonic collisions. Interference
effects and, in particular, the contribution of loop diagrams are fully taken
into account in the derivation of the spectrum, which is shown to coincide with
the result earlier obtained by superposing the elementary interactions
incoherently. A quantitative analysis confirms that the deformation induced by
multiple collsions is a large effect at RHIC and LHC energies, for transverse
momenta ~ 20 GeV.Comment: text in LaTex, 4 figures in P
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