X-ray astronomy in the new Millenium. A Summary

Recent X-ray observations have had a major impact on topics ranging from protostars to cosmology. They have also drawn attention to important and general physical processes that currently limit our understanding of thermal and nonthermal X-ray sources. These include unmeasured atomic astrophysics data (wavelengths, oscillator strengths etc.), basic hydromagnetic processes (e.g. shock structure, reconnection), plasma processes (such as electron-ion equipartition and heat conduction) and radiative transfer (in disks and accretion columns). Progress on these problems will probably come from integrative studies that draw upon observations, throughout the electromagnetic spectrum, of different classes of source. X-ray observations are also giving a new perspective on astronomical subjects, like the nature of galactic nuclei and the evolution of stellar populations. They are contributing to answering central cosmological questions including the measurement of the matter content of the universe, understanding its overall luminosity density, describing its chemical evolution and locating the first luminous objects. X-ray astronomy has a healthy future with several international space missions under construction and in development.Comment: 12 page

Suppression of ϒ(1S) at forward rapidity in Pb–Pb collisions at sNN=2.76 TeV

AbstractWe report on the measurement of the inclusive ϒ(1S) production in Pb–Pb collisions at sNN=2.76 TeV carried out at forward rapidity (2.5<y<4) and down to zero transverse momentum using its μ+μ− decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive ϒ(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon–nucleon collisions. The nuclear modification factor, for events in the 0–90% centrality range, amounts to 0.30±0.05(stat)±0.04(syst). The observed ϒ(1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence

Measurement of visible cross sections in proton-lead collisions at 1asNN= 5.02 TeV in van der Meer scans with the ALICE detector

In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair root s NN=5.02 TeV . Van der Meer scans were performed for both configurations of colliding beams, and the cross section was measured for two reference processes, based on particle detection by the T0 and V0 detectors, with pseudo-rapidity coverage 4.6 < \u3b7 < 4.9, -3.3 < \u3b7 < -3.0 and 2.8 < \u3b7 < 5.1, -3.7 < \u3b7 < -1.7, respectively. Given the asymmetric detector acceptance, the cross section was measured separately for the two configurations. The measured visible cross sections are used to calculate the integrated luminosity of the proton-lead and lead-proton data samples, and to indirectly measure the cross section for a third, configuration-independent, reference process, based on neutron detection by the Zero Degree Calorimeters

Freeze-out radii extracted from three-pion cumulants in pp, p–Pb and Pb–Pb collisions at the LHC

AbstractIn high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose–Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p–Pb and Pb–Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p–Pb collisions are found to be 5–15% larger than those in pp, while those in Pb–Pb are 35–55% larger than those in p–Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p–Pb as compared to pp collisions at similar multiplicity