209865899
ALICE EMCal Physics Performance Report
7670434
Transverse momentum spectra of charged particles in proton-proton collisions at sqrt(s) = 900 GeV with ALICE at the LHC
The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$~GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|_{\rm INEL}=0.483\pm0.001$~(stat.)~$\pm0.007$~(syst.)~GeV/$c$ and $\left_{\rm NSD}=0.489\pm0.001$~(stat.)~$\pm0.007$~(syst.)~GeV/$c$, respectively. The data exhibit a slightly larger $\left$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET
116971544
Two particle correlations with photon and pi0 triggers in ALICE at LHC
Comparing the measurements of the hadronic final state from partonic showers in proton-proton and heavy-ion collisions will reveal the modifications generated by the medium on partons produced in hard scatterings. This can be achieved by selecting the hard processes in which there is a direct photon in the final state. The experimental technique consists in tagging events with a well identified high energy direct photon and in measuring the azimuthal angle correlation with charged hadrons. To establish a reference measurement for heavy-ion collisions, proton-proton collision data collected with ALICE have been analyzed. Preliminary results are presented together with photon and $\pi^{0}$-charged hadrons correlations showing the characteristic di-jet pattern from where the partonic momentum $k_{T}$ is extracted.
122169643
Photon — jet correlations measurement with ALICE at LHC: a feasibility study in proton-proton collisions
The feasibility to measure the imbalance distribution between direct isolated photons and charged hadrons is discussed within the context of the ALICE experiment at LHC. The case of proton-proton collisions at $\sqrt s $ TeV is studied with Monte-Carlo simulations. Performances for prompt photon identification and rejection of the π0 decay photons are presented. Such a measurement will offer the possibilty to probe the medium formed in AA collisions with jets of energies below 50 GeV, which cannot be reconstructed in the heavy-ion environment.
208868925
High-pT particle correlations in pp collisions at LHC/ALICE*
Two-particle correlation triggered by high-pT particles allows us to study hard scattering phenomena when full jet reconstruction is challenging. An analysis of the first ALICE pp data where charged and neutral particles isolated or not are used as trigger particles is presented. The two-particle correlation between the trigger (t) and the associate (a) particles is studied as a function of the imbalance parameter and interpreted in terms of the jet fragmentation function.
122184484
CHARM QUARK ENERGY LOSS IN DENSE MATTER WITHIN THE LIGHT-CONE PATH INTEGRAL APPROACH
The energy loss of heavy quarks traversing color dense matter is calculated with an analytical formula derived within the light-cone path integral (LCPI) approach. We find that the energy loss mechanism is dominated by gluon radiation and induces a suppression pattern of charm quark different from the suppression of light quarks. We find also that this radiative energy-loss is proportional to L2 for energetic quarks, but changes to a L dependance with decreasing quark energy, where L is the length of the traversed medium.
7859650
Sussing merger trees: the Merger Trees Comparison Project
Merger trees follow the growth and merger of dark-matter haloes over cosmic history. As well as giving important insights into the growth of cosmic structure in their own right, they provide an essential backbone to semi-analytic models of galaxy formation. This paper is the first in a series to arise from the Sussing Merger Trees Workshop in which 10 different tree-building algorithms were applied to the same set of halo catalogues and their results compared. Although many of these codes were similar in nature, all algorithms produced distinct results. Our main conclusions are that a useful merger-tree code should possess the following features: (i) the use of particle IDs to match haloes between snapshots; (ii) the ability to skip at least one, and preferably more, snapshots in order to recover subhaloes that are temporarily lost during merging; (iii) the ability to cope with (and ideally smooth out) large, temporary fluctuations in halo mass. Finally, to enable different groups to communicate effectively, we defined a common terminology that we used when discussing merger trees and we encourage others to adopt the same language. We also specified a minimal output format to record the results.
16094942
Sussing merger trees: the impact of halo merger trees on galaxy properties in a semi-analytic model
A halo merger tree forms the essential backbone of a semi-analytic model for galaxy formation and evolution. Recent studies have pointed out that extracting merger trees from numerical simulations of structure formation is non-trivial; different tree building algorithms can give differing merger histories. These differences should be carefully understood before merger trees are used as input for models of galaxy formation. We investigate the impact of different halo merger trees on a semi-analytic model. We find that the z=0 galaxy properties in our model show differences between trees when using a common parameter set. The star formation history of the Universe and the properties of satellite galaxies can show marked differences between trees with different construction methods. Independently calibrating the semi-analytic model for each tree can reduce the discrepancies between the z=0 global galaxy properties, at the cost of increasing the differences in the evolutionary histories of galaxies. Furthermore, the underlying physics implied can vary, resulting in key quantities such as the supernova feedback efficiency differing by factors of 2. Such a change alters the regimes where star formation is primarily suppressed by supernovae. Therefore, halo merger trees extracted from a common halo catalogue using different, but reliable, algorithms can result in a difference in the semi-analytic model. Given the uncertainties in galaxy formation physics, however, these differences may not necessarily be viewed as significant.
116950669
TWQCD's dynamical DWF project
We present an overview of our project of simulation of unquenched lattice QCD with optimal domain-wall quarks, using a GPU cluster currently constituting of 16 units of Nvidia Tesla S1070 plus 64 graphic cards with Nvidia GTX285 (total 128 GPUs with 128 Teraflops peak), attaining sustained computing power of 15.36 Teraflops. The first production run in two-flavor QCD is on-going, using the Iwasaki gauge action on a set of lattices with sizes $ 16^3 \times (32,10,8,6,4) \times (16,32) $ at the lattice spacing $ a \sim 0.1$ fm, with eight sea quark masses down to $ m_\pi \simeq 200 $ MeV. We outline our simulation algorithm, and describe the present status of the production run. Preliminary results of pseudoscalar mass and decay constant are also presented.
118704966
Lattice QCD with Optimal Domain-Wall Fermion: Light Meson Spectroscopy
We perform lattice simulations of two flavors QCD using the optimal domain-wall fermion, in which the chiral symmetry is preserved to a good precision ($ m_{res} \sim 0.3 $ MeV) on the $ 16^3 \times 32 $ lattice ($ L \sim 2 $ fm) with inverse lattice spacing $ a^{-1} \sim 1.8 $ GeV, and $ N_s = 16 $ in the fifth dimension, for eight sea quark masses corresponding to the pion masses in the range 210-500 MeV. We present our first results of the mass and the decay constant of the pseudoscalar meson, which are in good agreement with the next-to-leading order chiral perturbation theory for $ M_\pi < 450 $ MeV, and from which we determine the low-energy constants $ f $, $ \Sigma $, $ \bar{l}_3 $ and $ \bar{l}_4 $. At the physical pion mass $ M_{\pi} = 135$ MeV, we obtain the pion decay constant $f_\pi =133(1)(2)$ MeV, and the average up and down quark mass $m_{ud}^{\bar{\rm MS}}(\mathrm{2 GeV})=4.09(7)(11)$ MeV, where the first error is statistical, and the second error is systematic due to the truncation of the higher order corrections and the uncertainty in the determination of the lattice spacing. Furthermore, we also obtain the chiral condensate $ \Sigma^{\bar{{\mathrm{MS}}}}(2 GeV) = [250(4)(7) MeV]^3 $.
62834395
SUSSING MERGER TREES: the influence of the halo finder
Merger tree codes are routinely used to follow the growth and merger of dark matter haloes in simulations of cosmic structure formation. Whereas in Srisawat et. al. we compared the trees built using a wide variety of such codes, here we study the influence of the underlying halo catalogue upon the resulting trees. We observe that the specifics of halo finding itself greatly influences the constructed merger trees. We find that the choices made to define the halo mass are of prime importance. For instance, amongst many potential options different finders select self-bound objects or spherical regions of defined overdensity, decide whether or not to include substructures within the mass returned and vary in their initial particle selection. The impact of these decisions is seen in tree length (the period of time a particularly halo can be traced back through the simulation), branching ratio (essentially the merger rate of subhaloes) and mass evolution. We therefore conclude that the choice of the underlying halo finder is more relevant to the process of building merger trees than the tree builder itself. We also report on some built-in features of specific merger tree codes that (sometimes) help to improve the quality of the merger trees produced.