679 research outputs found
Constrained MC for QCD evolution with rapidity ordering and minimum kT
With the imminent start of LHC experiments, development of phenomenological
tools, and in particular the Monte Carlo programs and algorithms, becomes
urgent. A new algorithm for the generation of a parton shower initiated by the
single initial hadron beam is presented. The new algorithm is of the class of
the so called ``constrained MC'' type algorithm (an alternative to the backward
evolution MC algorithm), in which the energy and the type of the parton at the
end of the parton shower are constrained (predefined). The complete kinematics
configurations with explicitly constructed four momenta are generated and
tested. Evolution time is identical with rapidity and minimum transverse
momentum is used as an infrared cut-off. All terms of the leading-logarithmic
approximation in the DGLAP evolution are properly accounted for. In addition,
the essential improvements towards the so-called CCFM/BFKL models are also
properly implemented. The resulting parton distributions are cross-checked up
to the 0.1% precision level with the help of a multitude of comparisons with
other MC and non-MC programs. We regard these tests as an important asset to be
exploited at the time when the presented MC will enter as a building block in a
larger MC program for W/Z production process at LHC.Comment: Submitted to Computer Physics Communication
Solving QCD evolution equations in rapidity space with Markovian Monte Carlo
This work covers methodology of solving QCD evolution equation of the parton
distribution using Markovian Monte Carlo (MMC) algorithms in a class of models
ranging from DGLAP to CCFM. One of the purposes of the above MMCs is to test
the other more sophisticated Monte Carlo programs, the so-called Constrained
Monte Carlo (CMC) programs, which will be used as a building block in the
parton shower MC. This is why the mapping of the evolution variables (eikonal
variable and evolution time) into four-momenta is also defined and tested. The
evolution time is identified with the rapidity variable of the emitted parton.
The presented MMCs are tested independently, with ~0.1% precision, against the
non-MC program APCheb especially devised for this purpose.Comment: version compatible with with the erratum in Acta Physica Polonic
Two real parton contributions to non-singlet kernels for exclusive QCD DGLAP evolution
Results for the two real parton differential distributions needed for
implementing a next-to-leading order (NLO) parton shower Monte Carlo are
presented. They are also integrated over the phase space in order to provide
solid numerical control of the MC codes and for the discussion of the
differences between the standard factorization and Monte Carlo
implementation at the level of inclusive NLO evolution kernels. Presented
results cover the class of non-singlet diagrams entering into NLO kernels. The
classic work of Curci-Furmanski-Pertonzio was used as a guide in the
calculations.Comment: 34 pages, 3 figure
Proceedings of the Workshop on Monte Carlo's, Physics and Simulations at the LHC PART II
These proceedings collect the presentations given at the first three meetings
of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC",
held at the Frascati National Laboratories in 2006. The first part of these
proceedings contains pedagogical introductions to several basic topics of both
theoretical and experimental high pT LHC physics. The second part collects more
specialised presentations.Comment: 157 pages, 136 figures; contribution by M. Grazzini has been adde
Jet Quenching in Heavy Ion Collisions
This review article was prepared for the Landolt-Boernstein volume on
Relativisitc Heavy Ion Physics.Comment: Review articel accepted for publication in the Landolt-Boernstein
Handbook of Physics, ed. R. Stock. 41 pages LaTex, 7 eps-figure
Azimuthal jet flavor tomography with CUJET2.0 of nuclear collisions at RHIC and LHC
A perturbative QCD based jet tomographic Monte Carlo model, CUJET2.0, is
presented to predict jet quenching observables in relativistic heavy ion
collisions at RHIC/BNL and LHC/CERN energies. This model generalizes the DGLV
theory of flavor dependent radiative energy loss by including multi-scale
running strong coupling effects. It generalizes CUJET1.0 by computing jet path
integrations though more realistic 2+1D transverse and longitudinally expanding
viscous hydrodynamical fields contrained by fits to low flow data. The
CUJET2.0 output depends on three control parameters, ,
corresponding to an assumed upper bound on the vacuum running coupling in the
infrared and two chromo-electric and magnetic QGP screening mass scales where is the 1-loop Debye mass. We compare
numerical results as a function of for pure and deformed HTL
dynamically enhanced scattering cases corresponding to to
data of the nuclear modification factor, for
jet fragment flavors at ATeV c.m. energies
per nucleon pair and with impact parameter fm. A analysis
is presented and shows that data from RHIC and LHC are consistent
with CUJET2.0 at the level for . The
corresponding effective jet transport coefficient
field of this model is computed to facilitate comparison to other jet
tomographic models in the literature. The predicted elliptic asymmetry,
is, however, found to significantly underestimated
relative to RHIC and LHC data. We find the analysis shows that
is very sensitive to allowing even as little as 10\% variations of the
path averaged along in and out of reaction plane paths.Comment: 87 pages, 32 figures; v3: typos corrected, new references and
discussions included; accepted by JHE
Markovian MC simulation of QCD evolution at NLO level with minimum k_T
We present two Monte Carlo algorithms of the Markovian type which solve the
modified QCD evolution equations at the NLO level. The modifications with
respect to the standard DGLAP evolution concern the argument of the strong
coupling constant alpha_S. We analyze the z - dependent argument and then the
k_T - dependent one. The evolution time variable is identified with the
rapidity. The two algorithms are tested to the 0.05% precision level. We find
that the NLO corrections in the evolution of parton momentum distributions with
k_T - dependent coupling constant are of the order of 10 to 20%, and in a small
x region even up to 30%, with respect to the LO contributions.Comment: 32 pages, 9 pdf figure
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