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.
122411213
Potential physics measurement with ALICE electromagnetic calorimeters
Abstract We present the two electromagnetic calorimeters of the ALICE (A Large Ion Collider Experiment) experiment at LHC (Large Hadron Collider). One is the high-resolution PHOton Spectrometer (PHOS) made of lead tungsten crystals and the other is the ElectroMagnetic Calorimeter (EMCal), a Lead-Scintillator sampling calorimeter. They are dedicated to the measurement and identification of direct photons, light neutral mesons such as π 0 , η and ω ( 782 ) , and jets emitted in proton-proton and heavy-ion collisions at the LHC energies. The PHOS is capable of precisely detecting photons with momentum range between 0.1 GeV/c and 100 GeV/c and the EMCal can extend the prompt photon and light neutral meson momentum measurement beyond 200 GeV/c. The objective of the study is to explore the physics of strongly interacting QCD matter under extreme conditions of energy density.
12396289
Two particle correlations: A probe of the LHC QCD medium
The properties of γ-jet pairs emitted in heavy-ion collisions provide an accurate mean to perform a tomographic measurement of the medium created in the collision through the study of the medium modified jet properties. The idea is to measure the distribution of hadrons emitted on the opposite side of the direct photon. The feasibility of such measurements is studied by applying the approach on the simulation data, we have demonstrated that this method allows us to measure, with a good approximation, both the jet fragmentation 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 reveals the modifications induced by the medium on the jet structure and consequently allows us to infer the medium properties. In this contribution, we discuss a first attempt of such measurements applied to real proton-proton data from the ALICE experiment.
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.
202135211
Evidence of b-Jet Quenching in PbPb Collisions at $\sqrt{s_{NN}}=2.76$ TeV
125350395
Gamma-hadrons and hadrons-hadrons correlation measurements in pp collisions at 7TeV to study jet fragmentation with ALICE at LHC
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.
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.
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 $.
118724716
Halo-to-halo Similarity and Scatter in the Velocity Distribution of Dark Matter
We examine the velocity distribution function (VDF) in dark matter halos from Milky Way to cluster mass scales. We identify an empirical model for the VDF with a wider peak and a steeper tail than a Maxwell-Boltzmann distribution, and discuss physical explanations. We quantify sources of scatter in the VDF of cosmological halos and their implication for direct detection of dark matter. Given modern simulations and observations, we find that the most significant uncertainty in the VDF of the Milky Way arises from the unknown radial position of the solar system relative to the dark matter halo scale radius.