18689235
Thermal hard-photons probing multifragmentation in nuclear collisions around the fermi energy
Hard-photon (Eγ>30 MeV) emission originating from photon-neutron bremsstrahlung collisions is investigated in four different heavy-ion reactions at intermediate bombarding energies (36Ar+197Au, 107Ag, 58Ni, 12C at 60 A MeV) coupling the TAPS photon spectrometer with two charged-particle multidetectors covering more than 80% of the solid angle. The hard-photon spectra of the three heavier targets result from the combination of two distinct exponential distributions with different slope parameters, a results which deviates from the behaviour expected for hard-photon production just in first-chance proton-neutron collisions. The thermal origin of the steeper bremsstrahlung component is confirmed by the characteristics of its slope and angular distribution. Such thermal hard-photons convey undisturbed information of the thermodynamical state of hot and excited nuclear systems undergoing multifragmentation.
117936465
ALICE, the heavy ion experiment at LHC
ALICE, A Large Ion Collider Experiment, is the future Large Hadron Collider (LHC) experiment at CERN devoted to the physics of Quantum Chromo-thermo-dynamics. Relativistic Heavy-Ion Collisions (HIC) at LHC aim at the production of a plasma of quarks and gluons (QGP). This plasma is expected to be much hotter, bigger and longer than in previous HIC experiments at lower center-of-mass energies. In the ALICE experiment, the ephemeral QGP created during the first stages of the HIC will be studied by the concomitant detection of most of the probes of high temperature strongly interacting matter.
208867779
The Muon Spectrometer of the ALICE experiment
The main goal of the Muon Spectrometer of the ALICE experiment is the measurement of heavy quarks in pp, pA and AA collisions at LHC energies, via the muonic channel. Physics motivations, the apparatus and its physics performances are presented in this talk.
124595639
Hard photons and neutral pions as probes of hot and dense nuclear matter
Abstract The dynamics of heavy-ion collisions is studied in an energy domain in the vicinity of the Fermi energy. The early history of the collision is analyzed from the theoretical and experimental point of view in which the message conveyed by bremsstrahlung photons and neutral pions is exploited. The Boltzmann-Uehling-Uhlenbeck model and the Dubna Cascade Model, both based on similar principles but each adopting different computation technics, are briefly described and their respective predictions are discussed. In particular the emission pattern of bremsstrahlung photons is discussed. The photon production has been measured in the systems 86 Kr+ 58 Ni at 60 A MeV, 181 Ta+ 197 Au at 40 A MeV and 208 Pb+ 197 Au at 30 A MeV and energy spectra, angular distributions and two-photon correlations have been analyzed. We find that bremsstrahlung photons are emitted from two distinct sources that can be correlated with nuclear-matter density oscillations. The properties of photon emission are discussed in terms of collective properties of nuclear matter. The high energy tail of the photon spectrum is interpreted by π 0 and Δ decay but predominantly by radiative capture of pions. The π 0 absorption in the nuclear medium is further analyzed by examining their emission pattern.
122900110
Two-photon Correlations: from Young Experiments to Heavy-ion Collision Dynamics
Abstract Two-photon correlations are discussed within the formalism of Hanbury-Brown and Twiss interferometry and Bose-Einstein correlations. The technique is presented as a universal tool to study the properties of any boson source — light sources such as stars, or photon and meson sources in the early phase of heavy-ion collisions. The formalism is developed starting from optics and quantum statistics and is finally adapted to the dynamics of heavy-ion collisions. Emphasis is put on the experimental methods derived to display the interference between photons from nuclear reactions. The influence of one-dimensional projections and the detector response on the interpretation of the source properties are discussed. The method is illustrated using experimental data, available only in the intermediate (several tens of A MeV) energy domain. The observed interference signal is interpreted, guided by dynamical phase-space calculations, in terms of source size and reaction dynamics. It is found that photons are emitted as brief light flashes, the relative intensity of which can be linked via model calculations to the incompressibility modulus of nuclear matter. At ultrarelativistic energies, two-photon correlations are presented as a tool to observe the phase transition towards the quark-gluon plasma.
116359634
Advances in Quark Gluon Plasma
In the last 20 years, heavy-ion collisions have been a unique way to study the hadronic matter in the laboratory. Its phase diagram remains unknown, although many experimental and theoretical studies have been undertaken in the last decades. The Relativistic Heavy Ion Collider (RHIC) at BNL was the first ever built heavy-ion collider. RHIC delivered its first collisions in June 2000 boosting the heavy-ion community. Impressive amount of experimental results has been obtained. In November 2010, the Large Hadron Collider (LHC) at CERN delivered lead-lead collisions at unprecedented center-of-mass energies, 14 times larger than that at RHIC. Needless to say that the heavy-ion programs at RHIC and LHC promise fascinating and exciting results in the next decade. In the second part, a historical approach will be adopted, starting with the notion of limiting temperature of matter introduced by Hagedorn in the 60's and the discovery of the QCD asymptotic freedom in the 70's. The phase diagram of hadronic matter, conceived as nowadays, will be shown together with the most important predictions of lattice QCD calculations at finite temperature. In the third part, the heavy-ion collisions at ultra-relativistic energies will be proposed as a unique experimental method to study QGP in the laboratory, as suggested by the Bjorken model. In the last part of these lectures, I will present my biased review of the numerous experimental results obtained in the last decade at RHIC which lead to the concept of strong interacting QGP, and the first results obtained at LHC with the 2010 and 2011 PbPb runs. Finally, the last section is devoted to refer to other lectures about quark gluon plasma and heavy ion physics.
122713743
Dark Matter Distributions of the Milky Way Satellites and Implications for Indirect Detection
We review recent progress in understanding the mass distributions of the Milky Way dwarf satellite population, with a specific focus on the implications for gamma-ray fluxes from dark matter. We outline a method that self-consitently predicts the gamma-ray fluxes from the satellites using line-of-sight velocities, the Constrained Minimal Supersymmetric Standard Model (CMSSM), and a model for the boost from substructure in the dark matter halos. Combining all of these ingredients, and accounting for the reduced astrophysical backgrounds relative to the Galactic center, the dwarf satellites make strong candidates for indirect detection with Fermi/GLAST and future Air Cerenkov Telescopes.
119183376
A robust determination of Milky Way satellite properties using hierarchical mass modelling
We introduce a new methodology to robustly determine the mass profile, as well as the overall distribution, of Local Group satellite galaxies. Specifically, we employ a statistical multilevel modelling technique, Bayesian hierarchical modelling, to simultaneously constrain the properties of individual Local Group Milky Way satellite galaxies and the characteristics of the Milky Way satellite population. We show that this methodology reduces the uncertainty in individual dwarf galaxy mass measurements up to a factor of a few for the faintest galaxies. We find that the distribution of Milky Way satellites inferred by this analysis, with the exception of the apparent lack of high-mass haloes, is consistent with the Lambda cold dark matter (Lambda CDM) paradigm. In particular, we find that both the measured relationship between the maximum circular velocity and the radius at this velocity, as well as the inferred relationship between the mass within 300 pc and luminosity, match the values predicted by Lambda CDM simulations for haloes with maximum circular velocities below 20 km s(-1). Perhaps more striking is that this analysis seems to suggest a more cusped 'average' halo shape that is shared by these galaxies. While this study reconciles many of the observed properties of the Milky Way satellite distribution with that of Lambda CDM simulations, we find that there is still a deficit of satellites with maximum circular velocities of 20-40 km s(-1).