118357623
Pseudoscalar Meson in Two Flavors QCD with the Optimal Domain-Wall Fermion
Abstract We perform hybrid Monte Carlo (HMC) simulations of two flavors QCD with the optimal domain-wall fermion (ODWF), on the 16 3 × 32 lattice (with lattice spacing a ∼ 0.1 fm ), for eight sea-quark masses corresponding to pion masses in the range 228–565 MeV. We calculate the mass and the decay constant of the pseudoscalar meson, and compare our data with the chiral perturbation theory (ChPT). We find that our data is in good agreement with the sea-quark mass dependence predicted by the next-to-leading order (NLO) ChPT, and provides a determination of the low-energy constants l ¯ 3 and l ¯ 4 , the pion decay constant, the chiral condensate, and the average up and down quark mass.
118618637
The Dependence of Subhalo Abundance on Halo Concentration
Hierarchical structure formation implies that the number of subhalos within a dark matter halo depends not only on halo mass, but also on the formation history of the halo. This dependence on the formation history, which is highly correlated with halo concentration, can account for the super-Poissonian scatter in subhalo occupation at a fixed halo mass that has been previously measured in simulations. Here we propose a model to predict the subhalo abundance function for individual host halos that incorporates both halo mass and concentration. We combine results of cosmological simulations with a new suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We show that the model can successfully reproduce the mean and the scatter of subhalo occupation in these simulations. The implications of this correlation between subhalo abundance and halo concentration are further investigated. We also discuss cases in which inferences about halo properties can be affected if this correlation between subhalo abundance and halo concentration is ignored; in these cases, our model would give a more accurate inference. We propose that with future deep surveys, satellite occupation in the low-mass regime can be used to verify the existence of halo assembly bias.
118618046
RHAPSODY. I. STRUCTURAL PROPERTIES AND FORMATION HISTORY FROM A STATISTICAL SAMPLE OF RE-SIMULATED CLUSTER-SIZE HALOS
We present the rst results from the Rhapsody cluster re-simulation project: a sample of 96 \zoom-in" simulations of dark matter halos of 10 14:8 0:05 h 1 M , selected from a 1 h 3 Gpc 3 volume. This simulation suite is the rst to resolve this many halos with 5 10 6 particles per halo in the cluster mass regime, allowing us to statistically characterize the distribution of and correlation between halo properties at xed mass. We focus on the properties of the main halos and how they are aected by formation history, which we track back to z = 12, over ve decades in mass. We give particular attention to the impact of the formation history on the density proles of the halos. We nd that the deviations from the Navarro{Frenk{White (NFW) model and the Einasto model depend on formation time. Late-forming halos tend to have considerable deviations from both models, partly due to the presence of massive subhalos, while early-forming halos deviate less but still signicantly from the NFW model and are better described by the Einasto model. We nd that the halo shapes depend only moderately on formation time. Departure from spherical symmetry impacts the density proles through the anisotropic distribution of massive subhalos. Further evidence of the impact of subhalos is provided by analyzing the phase-space structure. A detailed analysis of the properties of the subhalo population in Rhapsody is presented in a companion paper.
119269420
Topological susceptibility to the one-loop order in chiral perturbation theory
We derive the topological susceptibility to the one-loop order in the chiral effective theory of QCD, for an arbitrary number of flavors.
119242151
Topological susceptibility in two flavors lattice QCD with the optimal domain-wall fermion
Abstract We determine the topological susceptibility of the gauge configurations generated by lattice simulations using two flavors of optimal domain-wall fermion on the 16 3 × 32 lattice with length 16 in the fifth dimension, at the lattice spacing a ≃ 0.1 fm . Using the adaptive thick-restart Lanczos algorithm, we project the low-lying eigenmodes of the overlap Dirac operator, and obtain the topological charge of each configuration, for eight ensembles with pion masses in the range 220–550 MeV. From the topological charge, we compute the topological susceptibility and the second normalized cumulant. Our result of the topological susceptibility agrees with the sea-quark mass dependence predicted by the chiral perturbation theory and provides a determination of the chiral condensate, Σ MS ¯ ( 2 GeV ) = [ 259 ( 6 ) ( 7 ) MeV ] 3 , and the pion decay constant F π = 92 ( 12 ) ( 2 ) MeV .
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.
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.
118373519
QGP tomography with photon tagged jets in ALICE
γ+jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies. Tagging events with a well identified high pT direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon in ALICE, allows us to determine, with a good approximation, both the jet fragmentation function and the back-to-back azimuthal alignment of the direct photon and the jet. Comparing these two observables measured in pp collisions with the ones measured in AA collisions will reveal the modifications of the jet structure induced by the medium formed in AA collisions and consequently will infer the medium properties.
202135211
Evidence of b-Jet Quenching in PbPb Collisions at $\sqrt{s_{NN}}=2.76$ TeV
208867768
Inclusive $J/\psi$ production in $pp$ collisions at $\sqrt{s} = 2.76$ TeV
The ALICE Collaboration has measured inclusive J/psi production in pp collisions at a center of mass energy sqrt(s)=2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges |y|<0.9 and 2.5
121353892
Measurements of jet shape in 2.76 TeV PbPb collisions with CMS
Abstract The fragmentation properties of inclusive jets produced in PbPb collisions at a center of mass energy of s N N = 2.76 TeV are characterized by measuring differential jet shapes. The jet shape is defined as the fractional jet transverse momentum carried by charged particles emitted at a distance r from the jet axis, with jets reconstructed using the anti- k T clustering algorithm. The jet shapes are measured for reconstructed jet p T , jet > 100 GeV / c and charged hardons with p T > 1 GeV / c . Different background subtraction methods are employed to remove the contribution from the underlying events. The results obtained for PbPb collisions as a function of collision centrality are compared to reference distributions from pp data collected at the same collision energy. For the most central collisions, the jet shapes are found to be modified at large distance from the jet axis.