41 research outputs found
Heavy ion event generator HYDJET++ (HYDrodynamics plus JETs)
HYDJET++ is a Monte-Carlo event generator for simulation of relativistic
heavy ion AA collisions considered as a superposition of the soft, hydro-type
state and the hard state resulting from multi-parton fragmentation. This model
is the development and continuation of HYDJET event generator (Lokhtin &
Snigirev, 2006, EPJC, 45, 211). The main program is written in the
object-oriented C++ language under the ROOT environment. The hard part of
HYDJET++ is identical to the hard part of Fortran-written HYDJET and it is
included in the generator structure as a separate directory. The soft part of
HYDJET++ event is the "thermal" hadronic state generated on the chemical and
thermal freeze-out hypersurfaces obtained from the parameterization of
relativistic hydrodynamics with preset freeze-out conditions. It includes the
longitudinal, radial and elliptic flow effects and the decays of hadronic
resonances. The corresponding fast Monte-Carlo simulation procedure, C++ code
FAST MC (Amelin et al., 2006, PRC, 74, 064901; 2008, PRC, 77, 014903) is
adapted to HYDJET++. It is designed for studying the multi-particle production
in a wide energy range of heavy ion experimental facilities: from FAIR and NICA
to RHIC and LHC.Comment: 44 pages including 6 figures as EPS-files; prepared using LaTeX
package for publication in Computer Physics Communication
Progress in jet reconstruction and heavy ion collisions
We review recent developments related to jet clustering algorithms and jet
reconstruction, with particular emphasis on their implications in heavy ion
collisions. These developments include fast implementations of sequential
recombination algorithms, new IRC safe algorithms, quantitative determination
of jet areas and quality measures for jet finding, among many others. We also
show how jet reconstruction provides a useful tool to probe the characteristics
of the hot and dense medium created in heavy ion collisions, which allows one
to distinguish between different models of parton-medium interaction.Comment: 7 pages, 4 figures, to appear in the proceedings of the 13th
International Conference on Elastic & Diffractive Scattering, CERN, 29th June
- 3rd July 200
"Jets" and their distortion in heavy-ion collisions
After a discussion on the meaning of "jets" in the context of nucleus-nucleus
collisions, the distortions of the profile of a parton shower induced by the
presence of a medium is investigated in a QCD-inspired model that implements
the conservation of energy at each step of the shower evolution.Comment: 10 pages, 4 figures; talk given at the workshop "High-pT physics at
LHC 2009", February 4-7, Prague, Czech Republi
Fabrication and Characterization of CMOS-MEMS Thermoelectric Micro Generators
This work presents a thermoelectric micro generator fabricated by the commercial 0.35 ÎŒm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 ÎŒV at the temperature difference of 1 K
Seeing jets in heavy-ion collisions
In these proceedings, we briefly review how jets can be reconstructed in
heavy-ion collisions. The main point we address is the subtraction of the large
contamination from the underlying event background. We first present the main
ingredients needed to define the jets and perform the background subtraction
and then discuss the efficiency of the subtraction for different jet algorithms
and background-estimation methods.Comment: 7 pages, 4 figures. Contribution to the Hard Probes 2010 conference,
October 10-15 2010, Eilat, Israe
Jet formation and interference in a thin QCD medium
In heavy-ion collisions, an abundant production of high-energy QCD jets
allows to study how these multiparticle sprays are modified as they pass
through the quark-gluon plasma. In order to shed new light on this process, we
compute the inclusive two-gluon rate off a hard quark propagating through a
color deconfined medium at first order in medium opacity. We explicitly impose
an energy ordering of the two emitted gluons, such that the "hard" gluon can be
thought of as belonging to the jet substructure while the other is a "soft"
emission (which can be collinear or medium-induced). Our analysis focusses on
two specific limits that clarify the modification of the additional angle- and
formation time-ordering of splittings. In one limit, the formation time of the
"hard" gluon is short compared to the "soft" gluon formation time, leading to a
probabilistic formula for production of and subsequent radiation off a
quark-gluon antenna. In the other limit, the ordering of formation is reverted,
which automatically leads to the fact that the jet substructure is resolved by
the medium. We observe in this case a characteristic delay: the jet radiates as
one color current (quark) up to the formation of the "hard" gluon, at which
point we observe the onset of radiation of the new color current (gluon). Our
computation supports a picture in which the in-medium jet dynamics are
described as a collection of subsequent antennas which are resolved by the
medium according to their transverse extent.Comment: 33 page
The radiation pattern of a QCD antenna in a dense medium
We calculate the radiation spectrum off a qq-bar pair of a fixed opening
angle theta_qq-bar traversing a medium of length L. Multiple interactions with
the medium are handled in the harmonic oscillator approximation, valid for soft
gluon emissions. We discuss the time-scales relevant to the decoherence of
correlated partons traversing the medium and demonstrate how this relates to
the hard scale that govern medium-induced radiation. For large angle radiation,
the hard scale is given by Qhard = max(r_perp^{-1}, Qs), where r_perp =
theta_qq-bar L is the probed transverse size and Qs is the maximal transverse
momentum accumulated by the emitted gluon in the medium. These situations
define in turn two distinct regimes, which we call "dipole" and "decoherence"
regimes, respectively, and which are discussed in detail. A feature common to
both cases is that coherence of the radiation is restored at large transverse
momenta, k_\perp > Qhard.Comment: 44 pages, 8 figure
Search for medium effects using jets from bottom quarks in PbPb collisions at âs\u3csub\u3eNN\u3c/sub\u3e=5.02TeV
The first study of the shapes of jets arising from bottom (b) quarks in heavy ion collisions is presented. Jet shapes are studied using charged hadron constituents as a function of their radial distance from the jet axis. Lead-lead (PbPb) collision data at a nucleon-nucleon center-of-mass energy of âsNN=5.02TeVwere recorded by the CMS detector at the LHC, with an integrated luminosity of 1.69nbâ1. Compared to proton-proton collisions, aredistribution of the energy inbjets to larger distances from the jet axis is observed in PbPb collisions. This medium-induced redistribution is found to be substantially larger forbjets than for inclusive jets