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.
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.
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.
15558797
A New contribution to the nuclear modification factor of non-photonic electrons in Au+Au collisions at s(NN)**(1/2) = 200 GeV
We investigate the effect of the so-called anomalous baryon/meson enhancement to the nuclear modification factor of non-photonic electrons in Au+Au collisions at sqrt(s) = 200 GeV. It is demonstrated that an enhancement of the charm baryon/meson ratio, as it is observed for non-strange and strange hadrons, can be responsible for part of the amplitude of the nuclear modification factor of non-photonic electrons. About half of the measured suppression of non-photonic electrons in the 2-4 pt range can be explained by a charm baryon/meson enhancement of 5. This contribution to the non-photonic electron nuclear modification factor has nothing to do with heavy quark energy loss.
92826748
Dependance de la production de photons durs avec le parameetre d'impact dans les collisions entre ions lourds aux energies intermediaires
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.
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.
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.