Reconstructing the Source in Heavy Ion Collisions from Particle Interferometry

The preliminary CERN SPS NA49 Pb+Pb 158 GeV/A negative one- and two-particle spectra at mid-rapidity are consistent with a source of temperature 130 MeV, lifetime 9 fm/c, transverse flow 0.35, and a transverse geometric size which is twice as large as the cold Pb nucleus.Comment: Proceedings for Quark Matter 97; 4 pages, 2 eps-figure

Multiparticle Bose-Einstein Correlations

Multiparticle symmetrization effects are contributions to the spectra of Bose-symmetrized states which are not the product of pairwise correlations. Usually they are neglected in particle interferometric calculations which aim at determining the geometry of the boson emitting source from the measured momentum distributions. Based on a method introduced by Zajc and Pratt, we give a calculation of all multiparticle symmetrization effects to the one- and two-particle momentum spectra for a Gaussian phase space distribution of emission points. Our starting point is an ensemble of N-particle Bose-symmetrized wavefunctions with specified phase space localization. In scenarios typical for relativistic heavy ion collisions, multiparticle effects steepen the slope of the one-particle spectrum for realistic particle phase space densities by up to 20 MeV, and they broaden the relative momentum dependence of the two-particle correlations. We discuss these modifications and their consequences in quantitative detail. Also, we explain how multiparticle effects modify the normalization of the two-particle correlator. The resulting normalization conserves event probabilities, which is not the case for the commonly used pair approximation. Finally, we propose a new method of calculating Bose-Einstein weights from the output of event generators, taking multiparticle correlations into account.Comment: 17 pages RevTeX, 8 eps-figures, replaced by published version, one typo [sigma^2 --> 1/sigma^2] corrected w.r.t. Erratum. All statements unchanged, as publishe

Opportunities for Heavy Ion Physics at the Large Hadron Collider LHC

This talk discusses extrapolations to the LHC of several, apparently universal trends, seen in the data on relativistic nucleus-nucleus collisions up to RHIC energies. In the soft physics sector, such extrapolations to the LHC are typically at odds with LHC predictions of the dynamical models, advocated to underlie multi-particle production up to RHIC energies. I argue that due to this, LHC is likely to be a discovery machine not only in the hard, but also in the soft physics sector.Comment: Plenary talk given at Quark Matter 2006, Shanghai, China, 14-20 Nov 2006; to appear in the conference proceeding

Energy Loss of Hard Partons in Nuclear Matter

We report on recent calculations of the medium-induced gluon radiation off hard partons. The employed path-integral formalism reduces in limiting cases to the main ``jet quenching'' results of the existing literature. Moreover, it describes destructive interference effects between medium-independent and medium-induced radiation amplitudes. These affect the angular distribution and $L$-dependence of the medium-induced gluon bremsstrahlung spectrum significantly.Comment: 4 pages LaTeX, invited talk given at the 15th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM 2001), Long Island, New York, January 15 - 20, 200

Introductory Overview of Quark Matter 2012

The two arguably most generic phenomena seen in ultra-relativistic heavy ion collisions are the flow of essentially all soft hadronic observables and the quenching of essentially all hard hadronic observables. Limiting the discussion to these two classes of phenomena, I review what can be said so far about the properties of hot and dense QCD matter from the heavy ion programs at RHIC and at the LHC, and I discuss the opportunities for further progress in the coming years.Comment: 8 pages, write-up of plenary talk at Quark Matter 2012 in Washington, to appear in the QM12 conference proceeding

From Leading Hadron Suppression to Jet Quenching at RHIC and at the LHC

In nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC), one generically observes a strong medium-induced suppression of high-pT hadron production. This suppression is accounted for in models which assume a significant medium-induced radiative energy loss of high-pT parent partons produced in the collision. How can we further test the microscopic dynamics conjectured to underly this abundant high-pT phenomenon? What can we learn about the dynamics of parton fragmentation, and what can we learn about the properties of the medium which modifies it ? Given that inelastic parton scattering is expected to be the dominant source of partonic equilibration processes, can we use hard processes as an experimentally well-controlled window into QCD non-equilibrium dynamics ? Here I review what has been achieved so far, and which novel opportunities open up with higher luminosity at RHIC, and with the wider kinematical range accessible soon at the LHC.Comment: 8 pages Latex, 4 eps-figures, contribution to the proceedings of the "Hard Probes 2004" conference in Ericeira, Portugal, November 4-10, 200

Jet Tomography in Heavy Ion Collisions

We review recent calculations of the probability that a hard parton radiates an additional energy fraction due to scattering in spatially extended matter, and we discuss their application to the suppression of leading hadron spectra in heavy ion collisions at collider energies.Comment: 10 pages, 5 figures, Talk given at Workshop on Strong and Electroweak Matter (SEWM 2002), Heidelberg, Germany, 2-5 Oct 200

Determination of the position angle of stellar spin axes

Measuring the stellar position angle provides valuable information on binary stellar formation or stellar spin axis evolution. We aim to develop a method for determining the absolute stellar position angle using spectro-astrometric analysis of high resolution long-slit spectra. The method has been designed in particular for slowly rotating stars. We investigate its applicability to existing dispersive long-slit spectrographs, identified here by their plate scale, and the size of the resulting stellar sample. The stellar rotation induces a tilt in the stellar lines whose angle depends on the stellar position angle and the orientation of the slit. We developed a rotation model to calculate and reproduce the effects of stellar rotation on unreduced high resolution stellar spectra. Then we retrieved the tilt amplitude using a spectro-astrometric extraction of the position of the photocentre of the spectrum. Finally we present two methods for analysing the position spectrum using either direct measurement of the tilt or a cross-correlation analysis. For stars with large apparent diameter and using a spectrograph with a small plate scale, we show that it is possible to determine the stellar position angle directly within 10deg with a signal-to-noise ratio of the order of 6. Under less favourable conditions, i.e. larger plate scale or smaller stellar diameter, the cross-correlation method yields comparable results. We show that with the currently existing instruments, it is possible to determine the stellar position angle of at least 50 stars precisely, mostly K-type giants with apparent diameter down to 5 milliarcseconds. If we consider errors of around 10deg still acceptable, we may include stars with apparent diameter down to 2 mas in the sample that then comprises also some main sequence stars.Comment: 10 pages, 9 figures, A&A (in press