6827655
Physics of the Muon Spectrometer of the ALICE Experiment
The main goal of the ALICE Muon spectrometer experiment is the measurement of heavy quark production in p+p, p+A and A+A collisions at LHC energies, via the muonic channel. Physics motivations and expected performances have been presented in this talk.
121006890
Identification of photons and particles in the segmented electromagnetic calorimeter TAPS
Abstract The algorithms devellped for the identification of one and two hard-photon events detected with TAPS are presented. After a presentation of the energy and time calibrations, the identification of single module events and the shower reconstruction, special emphasis is given to the rejection of the background generated by cosmic rays, π 0 decay and e ± conversion pairs. The effect of discontinuous showers is also discussed. The method was tested on data taken with TAPS at GANIL for heavy-ion collisions at energies of several tens of A MeV.
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.
123696609
Identification of hydrogen isotopes with the BaF2 electromagnetic calorimeter TAPS
Abstract The mass spectrum of hydrogen isotope was deduced from the kinetic energy and time-of-flight (TOF) measured with the segmented electromagnetic calorimeter TAPS. The reactions studied were Kr + Ni at 60 A MeV and Ar + Ca at 180 A MeV. Proper corrections for the energy lost by charged particles in passive absorbers between the target and the scintillator are essential to improve greatly the mass resolution. Extension of the capabilities of TAPS to identify light charged particles allows one to study correlations between photons or neutral pions and charged particles.
122373827
Pion reabsorption in heavy-ion collisions interpreted in terms of the Delta capture process
We have measured energy-differential cross sections for pi(0) production in Ar-36 + (197)AU collisions at 95 MeV/u. From an analysis of spectral features due to pion final-state interactions we have estimated the cross section of the capture process Delta + N --> N + N in the center-of-mass energy range root s similar or equal to 2.05-2.25 GeV. Within the frame of BUU calculations, our results support the extension of the detailed-balance principle to broad-width resonances.
18444522
Thermal bremsstrahlung probing the nuclear liquid-gas phase transition
We present the results of the analysis of the hard photon production in the $^{129}${Xe}+$^{\rm nat}${Sn} at 50{\it A} MeV system studied in the GANIL E300 experiment. The energy and angular hard photon distributions confirm the existence of a thermal component which follows the recently measured thermal bremsstrahlung systematics. Exploiting the performances of our complete detection system, consisting of TAPS and 3 charged particle multidetectors, we have also measured the hard photon multiplicity as a function of the charged particle multiplicity.
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).
11410109
Evidence for substructure in Ursa minor dwarf spheroidal galaxy using a Bayesian object detection method
We present a method for identifying localized secondary populations in stellar velocity data using Bayesian statistical techniques. We apply this method to the dwarf spheroidal galaxy Ursa Minor and find two secondary objects in this satellite of the Milky Way. One object is kinematically cold with a velocity dispersion of 4.25 ± 0.75 km s-1 and centred at (9.1 arcmin ± 1.5, 7.2 arcmin ± 1.2) in relative RA and Dec. with respect to the centre of Ursa Minor. The second object has a large velocity offset of -12.8+1.75-1.5 km s-1 compared to Ursa Minor and centred at (-14.0 arcmin+2.4-5.8,-2.5 arcmin+0.4-1.0). The kinematically cold object has been found before using a smaller data set, but the prediction that this cold object has a velocity dispersion larger than 2.0 kms-1 at 95 per cent confidence level differs from previous work. We use two- and three-component models along with the information criteria and Bayesian evidence model selection methods to argue that Ursa Minor has additional localized secondary populations. The significant probability for a large velocity dispersion in each secondary object raises the intriguing possibility that each has its own dark matter halo, that is, it is a satellite of a satellite of the Milky Way. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.