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Hard physics in STAR
(2005)
The hot and dense matter created in high-energy nuclear collisions is believed to undergo a transition into a deconfined phase where partonic degrees of freedom determine the dynamics of the medium. High-p⊥ partons, that are produced in the initial collisions between nucleons of the incoming nuclei, lose energy as they propagate through the medium. This effect, called jetquenching, is observed in high-p⊥ particle spectra, in azimuthal correlations with the reaction plane (elliptic flow) and jet-like two-particle correlations.
STAR consists of tracking detectors and electromagnetic calorimetry with large and azimuthally symmetric acceptance and is exceptionally well suited for single particle detection and correlation studies at high p⊥. In the last five years, it has collected a large dataset including Au+Au and Cu+Cu collisions at different energies and reference data from p+p and d+Au collisions.
We present particle spectra and two-particle correlations at high-p⊥, and relate these measurements to the properties of the medium.
A new imaging method that combines high-efficiency fast-neutron detection with sub-ns time resolution is presented. This is achieved by exploiting the high neutron detection efficiency of a thick scintillator and the fast timing capability and flexibility of light-pulse detection with a dedicated image intensifier. The neutron converter is a plastic scintillator slab or, alternatively, a scintillating fibre screen. The scintillator is optically coupled to a pulse counting image intensifier which measures the 2-dimensional position coordinates and the Time-Of-Flight (TOF) of each detected neutron with an intrinsic time resolution of less than 1 ns. Large-area imaging devices with high count rate capability can be obtained by lateral segmentation of the optical readout channels.
The CERN Axion Solar Telescope (CAST) is searching for axions produced in the Sun's core by the Primakoff process. CAST is using a decommissioned Large Hadron Collider (LHC) test magnet where axions could be converted back into X-rays with energies up to 10 keV. Analysis of the 2003 data showed no signal above background implying an upper limit for the axion-photon coupling constant gagg < 1.16 X 10 ^-10 GeV exp -1 at 95% C.L. for ma . 0.02 eV [1]. The higher quality 2004 data is presently under analysis. CAST Phase II is scheduled to start in late 2005. This will be the first step in extending CAST's sensitivity to axion rest masses up to ~ 1 eV.
The freeze out of the expanding systems, created in relativistic heavy ion collisions, is discussed. We combine kinetic freeze out equations with Bjorken type system expansion into a unified model. The important feature of the proposed scenario is that physical freeze out is completely finished in a finite time, which can be varied from 0 (freeze out hypersurface) to infinit. The dependence of the post freeze out distribution function on the freeze out time will be studied. Model allows analytical analyses for the simplest systems such as pion gas. We shall see that the basic freeze out features, pointed out in the earlier works, are not smeared out by the expansion of the system. The entropy evolution in such a scenario is also studied.
We compute neutrino emissivities, specific heat, and the resulting cooling rates in four spin-one color superconductors: color-spin locked, planar, polar, and A phases. In particular, the role of anisotropies and point nodes in the quasiparticle excitation spectra are investigated. Furthermore, it is shown that the A phase exhibits a helicity order, giving rise to a reflection asymmetry in the neutrino emissivity.
The elliptic flow for Lambda hyperons and K0s mesons was measured by the NA49 experiment in semicentral Pb+Pb collisions at 158A GeV. The standard method of correlating particles with an event plane has been used. Measurements of v2 near mid-rapidity are reported as a function of centrality, rapidity and transverse momentum. Elliptic flow of Lambda and K0s particles increases both with the impact parameter and with the transverse momentum. It is compared with v2 for pions and protons as well as with various model predictions. The NA49 results are compared with data from NA45/CERES and STAR experiments.
The multiplicity of hadronic species created in elementary, and in nucleus-nucleus collisions, are known to be well reproduced by the statistical hadronization model, in its canonical and grand-canonical versions.To understand the origin of the implied equilibrium we revisit the hadronization models developed for e+e- annihilation to hadrons which imply spatial color pre-confinement clusters forming at the end of the pQCD evolution, which decays into on-shell hadrons/resonances. The classical ensemble description arises as a consequence of decoherence and phase space dominance during cluster formation, and decay.For A+A collisions we assume that hadronization occurs from similar singlet clusters which will overlap spatially owing to the extreme density. This is imaged in the transition to the grand-canonical ensemble.This transition sets in with increasing A and collision centrality. It can be described by a percolation model.
The effects of the onset of deconfinement on longitudinal and transverse flow are studied. First, we analyze longitudinal pion spectra from Elab = 2A GeV to √sNN = 200 GeV within Landau’s hydrodynamical model and the UrQMD transport approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c2s in the early stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at Ebeam = 30A GeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement. Furthermore, the energy excitation function of elliptic flow (v2) from Ebeam = 90A MeV to √sNN = 200 GeV is explored within the UrQMD framework and discussed in the context of the available data. The transverse flow should also be sensitive to changes in the equation of state. Therefore, the underestimation of elliptic flow by the UrQMD model calculation above Elab = 30A GeV might also be explained by assuming a phase transition from a hadron gas to the quark gluon plasma around this energy. This would be consistent with the model calculations, indicating a transition from hadronic matter to “string matter” in this energy range.
The energy dependence of multiplicity fluctuations was studied for the most central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV by the NA49 experiment at the CERN SPS. The multiplicity distribution for negatively and positively charged hadrons is significantly narrower than Poisson one for all energies. No significant structure in energy dependence of the scaled variance of multiplicity fluctuations is observed. The measured scaled variance is lower than the one predicted by the grand-canonical formulation of the hadron-resonance gas model. The results for scaled variance are in approximate agreement with the string-hadronic model UrQMD.
A new SPS programme
(2006)
A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: (i) search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, (ii) measurements of correlations, fluctuations and hadron spectra at high transverse momentum in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, (iii) measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation.
The J/psi-hadron interaction is a key ingredient in analyzing the J/psi suppression in hot hadronic matter as well as the propagation of J/psi in nuclei. As a first step to clarify the J/psi-hadron interactions at low energies, we have calculated J/psi-pi, J/psi-rho and J/psi-nucleon scattering lengths by the quenched lattice QCD simulations with Wilson fermions for beta=6.2 on 24^3*48 and 32^3*48 lattices. Using the Luscher's method to extract the scattering length from the simulations in a finite box, we find an attractive interaction in the S-wave channel for all three systems: Among others, the J/psi-nucleon interaction is most attractive. Possibility of the J/psi-nucleon bound state is also discussed.
We discuss the present collective flow signals for the phase transition to quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). A study of Mach shocks induced by fast partonic jets propagating through the QGP is given. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. Results of a hydrodynamical study of jet energy loss are presented.
The energy dependence of various hadronic observables is reviewed. The study of their evolution from AGS over SPS to the highest RHIC energy reveals interesting features, which might locate a possible onset of deconfinement. These observables include transverse spectra of different particle types and their total multiplicities, as well as elliptic flow. In this context especially the observation of a maximum of the strangeness to pion ratio is of particular interest, since on one hand it has been predicted as a signal for the onset of deconfinement but on the other hand also statistical model calculations exhibit qualitatively similar structures. The sharpness of these features is however not reproduced by hadronic scenarios. The significance of these structures will be discussed in this contribution. Other observables, such as radius parameters from Bose-Einstein correlations, on the other hand do not exhibit any structure in their energy dependence.
We present quantitative and qualitative arguments in favor of the claim that, within the present cosmological epoch, the U(1)gamma factor in the Standard Model is an effective manifestation of SU(2) pure gauge dynamics of Yang-Mills scale Lambda ~ 10^-4 eV. Results for the pressure and the energy density in the deconfining phase of this theory, obtained in a nonperturbative and analytical way, support this connection in view of large-angle features inherent in the map of the CMB temperature fluctuations and temperature-polarization cross correlations.
A new technique for precision ion implantation has been developed. A scanning probe has been equipped with a small aperture and incorporated into an ion beamline, so that ions can be implanted through the aperture into a sample. By using a scanning probe the target can be imaged in a non-destructive way prior to implantation and the probe together with the aperture can be placed at the desired location with nanometer precision. In this work first results of a scanning probe integrated into an ion beamline are presented. A placement resolution of about 120 nm is reported. The final placement accuracy is determined by the size of the aperture hole and by the straggle of the implanted ion inside the target material. The limits of this technology are expected to be set by the latter, which is of the order of 10 nm for low energy ions. This research has been carried out in the context of a larger program concerned with the development of quantum computer test structures. For that the placement accuracy needs to be increased and a detector for single ion detection has to be integrated into the setup. Both issues are discussed in this thesis. To achieve single ion detection highly charged ions are used for the implantation, as in addition to their kinetic energy they also deposit their potential energy in the target material, therefore making detection easier. A special ion source for producing these highly charged ions was used and their creation and interactions with solids of are discussed in detail.
In the present work we applied the Optically read out PArticle track Chamber, OPAC, for the measurement of radial dose distributions, d(r), around tracks of heavy ions passing through the gas-filled sensitive volume of the chamber. The measured data were compared with d(r) functions derived from data calculated with the Monte Carlo particle transport code, TRAX – which is used for the heavy ion therapy planning at GSI. To measure this quantity we have used here an optically read out time projection chamber (OPAC) with a parallel-drift field and one or several electron and light amplification stages. The two dimensional projection of the three dimensional ionization pattern caused by the ionizing particle passing through the chamber is captured by an image intensified CCD camera. The work is motivated by the role the radial dose distribution plays in the estimation of the relative biological effectiveness (RBE) of heavy ions, e.g. in radiation therapy and in radiation protection. The most successful model for high-dose irradiation with ions (applicable e.g. for heavy ion therapy) is found to be the local effect model (LEM). The present work intends to deliver measured data for one of the basic physical parameters which serve as input for the application of the local effect model: the radial dose distribution, d(r). The first goal of our measurement program was the measurement of d(r) distributions around carbon ions of different energies from 400 MeV/u down to the Bragg peak regions. We found an excellent agreement between the measured and simulated distributions at all carbon energies for the r–range in which the measurements deliver useful results. The lower limit of this range is about 100 nm and the upper limit is 6000 nm at a resolution of down to 33 nm - if scaled to water density. Despite the simplifications in the TRAX code (e.g. binary encounter theory for the emission ionization electrons), the discrepancies between the simulated and measured d(r) distributions are found to be lower than the measurement uncertainties at most measured carbon ion energies in almost the whole observed r-range. Hence, within the limitations of our measurements we can conclude that the precision of TRAX is sufficient to simulate the d(r) distributions around carbon ions to serve as input parameter for therapy planning. However, this conclusion is only valid for larger radial distances (r >100 nm). For smaller radial distances the measured data are dominated by the diffusion. Apart from carbon ion tracks, tracks of very heavy ions (40Ar, 84Kr and 238U) were also measured with OPAC. The simulated d(r) values were typically slightly or significantly higher than the measured data in the 100 nm < r < 5000 nm region. The experience has shown: the heavier or the faster the ion, the higher the discrepancies. On the one hand, we found a surprisingly good agreement between measurements and simulations if the ions had energies of around 50 MeV/u (i.e. relatively low energy). On the other hand, at higher energies, simulated data underestimate the measured ones by up to a factor of two in the region of 100 nm < r < 1000 nm for 84Kr (E = 650 MeV/u) or in the region of 100 nm < r < 6000 nm for 238U (E = 1 GeV/u). A possible reason for these discrepancies is that the BEA model, used in TRAX for the production ionization electrons, is not adequate for very heavy projectiles. The energy values of the very heavy ions were selected with the aim of comparing the track structures - and namely the d(r) distributions - of ions with largely different atomic mass but similar LET values. From the Z-dependency of the stopping power we know that for heavier ions a higher specific ion energy (expressed in MeV/u) is required to provide the same LET. For example the common LET of 315 keV/micro-m was achieved at largely different specific energy levels of 4,4 MeV/u for 12C, 65 MeV/u for 40Ar and 650 MeV/u for 84Kr ions. The difference in the track structures was expected mainly due to the different ion velocities and thus e.g. different ranges of d-electrons. This expectation could be confirmed by the measurements. The reason why - in line with the simulations - no strong differences could be observed in the d(r) distributions of the argon and krypton ions is the relatively small difference in the velocities of the both ion types in conjunction with the limited range in r, where the data can be compared. In contrary, the d(r) function of the carbon ion shows a qualitatively different behavior than the heavier ions inside the observable radius-range - in agreement with the simulations.
In dieser Arbeit wurden zum ersten Mal explizite Ausdrücke für Strahlungskorrekturen zur Grundzustandsenergie der relativistischen Dichtefunktionaltheorie hergeleitet und im Rahmen einer Langwellennäherung ausgewertet. Dazu wurde, ausgehend von einer angemessenen Zerlegung des Wechselwirkungs-Hamiltonians (2.23), ein DFT-Analogon zu Sucher's Level-Shift Formel abgeleitet, G1. (3.54). Mit Hilfe der Ausdrücke für die Gesamtenergie Etd (3.17), die Hartree-Energie EH (3.21) sowie die korrespondierenden Potentiale (3.29), (3.30) und der Grundzustandsenergie des nichtwechselwirkenden KS-Systems, (3.41), kann diese DFT Level-Shift Formel dann mit dem Austauschkorrelationsenergiefunktional in Verbindung gebracht werden. Der resultierende Ausdruck für den Level-Shift, G1. (3.55), liefert eine exakte Darstellung des Austauschkorrelationsenergiefunktionals der RDFT. Dieses Funktional ist ein implizites Dichtefunktional, da es von den KS-Orbitalen und Eigenwerten abhängt. Der Vergleich mit dem Ausdruck für Exc aus Kapitel 6.1, der das Ergebnis des in der DFT weit verbreiteten Kopplungskonstantenintegrations-Schemas ist, zeigt, dass beide Zugänge vollkommen äquivalent sind. Allerdings wurde die in dieser Dissertation erarbeitete DFT Level-Shift Formel analog zur Standard QED-Störungsreihe abgeleitet und stellt damit einen idealen Zugang für , die Untersuchung von QED-Effekten im Rahmen relativistischer DFT dar. Insbesondere beinhaltet unser Zugang das bekannte QED-Schema, wenn man im Störanteil des Hamiltonoperators (3.32) das KS-Potential ... (3.29) durch das Potential eines wasserstoffartigen Systems ersetzt. Eine selbstkonsistente Anwendung dieses Zugangs verlangt jedoch die Lösung der relativistischen OPM-Integralgleichung. Während in Kapitel 4 gezeigt wurde, dass dies für den transversalen Austausch relativ direkt möglich ist, ist bisher noch nicht explizit überprüft worden, wie Vakuumkorrekturen im Zusammenspiel mit der OPM-Integralgleichung zu berücksichtigen sind. Da eine solche Untersuchung den Rahmen der vorliegenden Arbeit gesprengt hätte, haben wir uns auf eine perturbative Auswertung der Ausdrücke für Vakuumpolarisation und Vertexkorrektur beschränkt. .....