242 research outputs found
Photon tagged correlations in heavy ion collisions
A detailed study of various two-particle correlation functions involving
photons and neutral pions is presented in proton-proton and lead-lead
collisions at the LHC energy. The aim is to use these correlation functions to
quantify the effect of the medium (in lead-lead collisions) on the jet decay
properties. The calculations are carried out at the leading order in QCD but
the next-to-leading order corrections are also discussed. The competition
between different production mechanisms makes the connection between the jet
energy loss spectrum and the gamma-pi correlations somewhat indirect while the
gamma-gamma correlations have a clearer relation to the jet fragmentation
properties.Comment: 32 pages, 19 figures. Minor changes, published versio
Design methodology for the development of variable stiffness devices based on layer jamming transition
Variable stiffness mechanisms as Jamming Transition draw huge attention recently in Soft Robotics. This paper proposes a comprehensive design methodology for developing variable stiffness devices based on layer jamming. Starting from pre-existing modelling, we highlight the design parameters that should be considered, extracting them from literature and our direct experience with the phenomenon. Then we validated the methodology applying the design process to previous layer jamming cases presented in literature. The comparison between the results obtained from our methodology and those presented in the analyzed previous works highlights a good predictive capability, demonstrating that this methodology can be used as a valid tool to design variable stiffness devices based on layer jamming transition. Finally, in order to provide the scientific community with an easily usable tool to design variable stiffness structures based on layer jamming transition, we have elaborated a Matlab script that guides the user through the main design parameters implementing the proposed methodology in an interactive process
Charmonium suppression in p-A collisions at RHIC
We discuss charmonium production in proton-nucleus collisions at RHIC
energies under the assumption of xF and x2 scaling. We find that all the
ambiguities due to energy loss are gone at this energy and therefore data will
reveal the scaling law, if any. These p-A data will also be crucial to
interpret nucleus-nucleus data with respect to a possible formation of a quark
gluon plasma because the extrapolations for charmonium production from the
present p-A data to RHIC energies, based on the two scaling laws, differ by a
factor of four.Comment: 6 pages, 3 figures. New section on shadowing and energy loss,
References adde
Energy Loss Effect in High Energy Nuclear Drell-Yan Process
The energy loss effect in nuclear matter, which is another nuclear effect
apart from the nuclear effect on the parton distribution as in deep inelastic
scattering process, can be measured best by the nuclear dependence of the high
energy nuclear Drell-Yan process. By means of the nuclear parton distribution
studied only with lepton deep inelastic scattering experimental data, measured
Drell-Yan production cross sections for 800GeV proton incident on a variety of
nuclear targets are analyzed within Glauber framework which takes into account
energy loss of the beam proton. It is shown that the theoretical results with
considering the energy loss effect are in good agreement with the FNAL E866
Application of the Two-Scale Model to the HERMES Data on Nuclear Attenuation
The Two-Scale Model and its improved version were used to perform the fit to
the HERMES data for (the virtual photon energy) and z (the fraction of
carried by hadron) dependencies of nuclear multiplicity ratios for
and mesons electro-produced on two nuclear targets (N
and Kr). The quantitative criterium was used for the first
time to analyse the results of the model fit to the nuclear multiplicity ratios
data. The two-parameter's fit gives satisfactory agreement with the HERMES
data. Best values of the parameters were then used to calculate the - and
- dependencies of nuclear attenuation for , K, K and
produced on Kr target, and also make a predictions for ,
z and the Q (the photon virtuality) - dependencies of nuclear attenuation
data for those identified hadrons and nuclea, that will be published by HERMES
Medium-induced gluon radiation and jet quenching in heavy ion collisions
In this brief review, I summarize the new developments on the description of
gluon radiation by energetic quarks traversing a medium as well as the
observable consequences in high-energy heavy ion collisions. Information about
the initial state is essential for a reliable interpretation of the
experimental results and will also be reviewed. Comparison with experimental
data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern
Physics Letters
GiViP: A Visual Profiler for Distributed Graph Processing Systems
Analyzing large-scale graphs provides valuable insights in different
application scenarios. While many graph processing systems working on top of
distributed infrastructures have been proposed to deal with big graphs, the
tasks of profiling and debugging their massive computations remain time
consuming and error-prone. This paper presents GiViP, a visual profiler for
distributed graph processing systems based on a Pregel-like computation model.
GiViP captures the huge amount of messages exchanged throughout a computation
and provides an interactive user interface for the visual analysis of the
collected data. We show how to take advantage of GiViP to detect anomalies
related to the computation and to the infrastructure, such as slow computing
units and anomalous message patterns.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Gluon Shadowing in DIS off Nuclei
Within a light-cone quantum-chromodynamics dipole formalism based on the
Green function technique, we study nuclear shadowing in deep-inelastic
scattering at small Bjorken xB < 0.01. Such a formalism incorporates naturally
color transparency and coherence length effects. Calculations of the nuclear
shadowing for the \bar{q}q Fock component of the photon are based on an exact
numerical solution of the evolution equation for the Green function, using a
realistic form of the dipole cross section and nuclear density function. Such
an exact numerical solution is unavoidable for xB > 0.0001, when a variation of
the transverse size of the \bar{q}q Fock component must be taken into account.
The eikonal approximation, used so far in most other models, can be applied
only at high energies, when xB < 0.0001 and the transverse size of the \bar{q}q
Fock component is "frozen" during propagation through the nuclear matter. At xB
< 0.01 we find quite a large contribution of gluon suppression to nuclear
shadowing, as a shadowing correction for the higher Fock states containing
gluons. Numerical results for nuclear shadowing are compared with the available
data from the E665 and NMC collaborations. Nuclear shadowing is also predicted
at very small xB corresponding to LHC kinematical range. Finally the model
predictions are compared and discussed with the results obtained from other
models.Comment: 29 pages including 7 figures; Fig.7 modified, some references and
corresponding discussion adde
Electromagnetic Emission and Energy Loss in the QGP
I discuss why photon production from the Quark Gluon Plasma (QGP) presents an
interesting problem, both experimentally and theoretically. I show how the
photon emission rate can be computed under the simplifying assumption that the
QGP fully thermalizes. The theoretical issues are very similar to those for jet
energy loss; so it should be possible to treat them in a common formalism and
relate the predictions of one phenomenon to those of the other.Comment: 8 pages, invited talk at Quark Matter 200
Next-to-MLLA corrections to single inclusive kt-distributions and 2-particle correlations in a jet
The hadronic kt-spectrum inside a high energy jet is determined including
corrections of relative magnitude O{\sqrt{\alpha_s}} with respect to the
Modified Leading Logarithmic Approximation (MLLA), in the limiting spectrum
approximation (assuming an infrared cut-off Q0 =Lambda_{QCD}) and beyond
Q_0\ne\Lambda_{QCD}. The results in the limiting spectrum approximation are
found to be, after normalization, in impressive agreement with preliminary
measurements by the CDF collaboration, unlike what occurs at MLLA, pointing out
small overall non-perturbative contributions. Within the same framework,
2-particle correlations inside a jet are also predicted at NMLLA and compared
to previous MLLA calculations.Comment: 35 pages and 39 figures. Comments, appendices, figures, references
added. Version to appear in Phys. Rev.
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