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The strong nuclear force is described by Quantum Chromodynamics (QCD), the parallel field theory to Quantum Electrodynamics (QED) that describes the electromagnetic force. It is propagated by gluons analogously to photons in the electromagnetic force, but unlike photons, which do not carry electric charge, gluons carry color, and they can self-interact. However, as individual quarks have never been observed in nature, it is postulated that the color charge itself is confined, and hence all baryons and mesons must be colorless objects. To study nuclear matter under extreme conditions, it is necessary to create hot and dense nuclear matter in the laboratory. In such conditions the confinement between quarks and gluons is cancelled (deconfinement). This state is characterized with a qusi-free behavior of quarks and gluons. The strange (s) and anti-strange (anti-s) quarks are not contained in the colliding nuclei, but are newly produced and show up in the strange hadrons in the final state. It was suggested that strange particle production is enhanced in the QGP with respect to that in a hadron gas. This enhancement is relative to a collision where a transition to a QGP phase does not take place, such as p+p collisions where the system size is very small. Therefore the energy- and system size dependence is studied to receive a picture about the initial state. In this thesis experimental results on the energy- and system size dependence of Xi hyperon production at the CERN SPS is shown. All measurements were performed with the NA49 detector at the CERN SPS. NA49 took central lead-lead collisions from 20 - 158 AGeV, minimus bias lead-lead collisions at 40 and 158 AGeV, and semi-central silicon-silicon colisions at 158 AGeV. The NA49 experiment features a large acceptance in the forward hemisphere allowing for measurements of Xi rapidity spectra. At the SPS accelerator at CERN Pb+Pb collisions are performed with beam energies to 158 AGeV. The analyzed data sets were taken in the period from 1999 to 2002. The NA49 experiment is a large acceptance hadron spectrometer, which measures charged hadrons in a wide acceptance. The main components are the four TPCs (Time Projection Chamber). The centrality of nucleon-nucleon collisions was done by measuring the not in the collision participating (spectator-) nucleons in the VETO-calorimeter. The study of strangeness is motivated by its role as a signature for the Quark Gluon Plasma. Any enhancement in the yield must be with respect to a ’normal’ yield, where a QGP is not formed. This is usually taken to mean suitably scaled p+p collisions, where the volume of the system created is too small for a QGP to occur. The results at SPS and RHIC energies show an enhancement, with the doubly strange Xi? being enhanced more than the Lambda, in accordance with the original prediction. However, the enhancement at SPS energies is higher than at RHIC energies.
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.
Results are presented from a search for the decays D0 -> K min pi plus and D0 bar -> K plus pi min in a sample of 3.8x10^6 central Pb-Pb events collected with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed. An upper limit on D0 production is derived and compared to predictions from several models.
Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.
System-size dependence of strangeness production in nucleus-nucleus collisions at √sNN = 17.3 GeV
(2005)
Emission of pi, K, phi and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as onset of the formation of coherent partonic subsystems of increasing size. PACS numbers: 25.75.-q
Results are presented on Omega production in central Pb+Pb collisions at 40 and 158 AGeV beam energy. Given are transverse-mass spectra, rapidity distributions, and total yields for the sum Omega+Antiomega at 40 AGeV and for Omega and Antiomega separately at 158 AGeV. The yields are strongly under-predicted by the string-hadronic UrQMD model and are in better agreement with predictions from a hadron gas models. PACS numbers: 25.75.Dw
Particle production in central Pb+Pb collisions was studied with the NA49 large acceptance spectrometer at the CERN SPS at beam energies of 20, 30, 40, 80, and 158 GeV per nucleon. A change of the energy dependence is observed around 30A GeV for the yields of pions and strange particles as well as for the shapes of the transverse mass spectra. At present only a reaction scenario with onset of deconfinement is able to reproduce the measurements.
In dieser Arbeit wurde die Produktion von Omega und Anti-Omega Hyperonen in zentralen Pb+Pb-Kollisionen bei 40 A GeV am CERN SPS mit dem NA49 Experiment untersucht. Der in dieser Arbeit verwendete Datensatz wurde während einer 4 wöchigen Strahlzeit 1999 aufgenommen. Dabei wurden 579446 Zentrale (7.2 % des totalen Wirkungsquerschnitts) Ereignisse, bei zwei verschiedenen Polarit aten (std+ und std-), aufgezeichnet. Die Omega Produktion bei 40 A GeV wird mit Messungen bei anderen Energien verglichen, um damit die Energieabhangigkeit der Omega Produktion zu untersuchen. Das Experiment NA49 erlaubt genaue Messungen in einem weiten Akzeptanzbereich. Man misst die Zerfallstochter des Omegas und die Zerfallstochter des Omegas mit hochauflösenden TPCs. Mehrfach seltsame Teilchen (Theta, Omega) werden durch ihre Zerfallstopologie identifiziert. Es wurden verschieden Qualitatskriterien verwendet, um den kombinatorischen Untergrund zu reduzieren. NA49 hat nur eine endliche geometrische Akzeptanz und kann deshalb nicht den ganzen Phasenraum abdecken. Außerdem wurden verschiedene Qualitatskriterien verwendet, um ein akzeptables Signal zu Untergrund Verhaltnis zu erhalten. Da es wegen der Akzeptanz und der Qualitatskriterien zu Verlusten kommt, muss man darauf korrigieren. Dies macht man mittels einer Simulation, in der man Omega Hyperonen simuliert. Die Omega Hyperonen werden uber drei Rapiditatseinheiten um den Bereich zentraler Rapiditat und mit Transversalimpulsen von 0.9 bis 2.4 GeV/c gemessen. Es wurde der Temperaturparameter des Omega Hyperons bei 40 A GeV bestimmt. Im Rahmen der Fehler ist der Temperaturparameter der 40 A GeV dem der 158 A GeV gleich. Betrachtet man den Temperaturparameter der Omegas als Funktion der Schwerpunktenergie, gibt es einen Anstieg des Temperaturparameters von SPS- zu RHIC-Energien. Es wurden jeweils die Multiplizitaten bei mittlerer Rapiditat für Omega und Anti-Omega bestimmt. Die Multiplizität vom Omega betragt 0.068 +- 0.020 (stat.) +- 0.019 (sys.) und vom Anti-Omega 0.027 +- 0.008 (stat.) +- 0.007 (sys.). Die Multiplizitaten bei mittlerer Rapiditat steigen für Omega und Anti-Omega mit der Schwerpunktenergie von SPS- zu RHIC-Energien. Die Ergebnisse stimmen mit den Messungen der NA57 Kollaboration überein. Bei 40 A GeV wurde erstmals eine Rapiditatsverteilung gemessen. Die daraus resultierende totale Multiplizitat fur Omega + Anti-Omega betragt 0.20 +- 0.03 (stat.) +- 0.04 (sys.). Mit steigender Schwerpunktenergie steigt die totale Multiplizität und die Rapiditätsverteilung wird breiter. Um den systematischen Fehler zu bestimmen, wurde eine Stabilität-Analyse des mt-Spektrums und der Rapiditatsverteilung durchgefuhrt. Der systematische Fehler der mt-Spektren betragt 18 % und der totalen Multiplizitat 21 %. Schaut man sich die Anregungsfunktion der Omega und Anti-Omega als Funktion der Schwerpunktenergie an, erkennt man, dass es eine leichte Energieabhängigkeit beim Anti-Omega / Pi-Minus ....
System size and centrality dependence of the balance function in A + A collisions at √sNN = 17.2 GeV
(2004)
Electric charge correlations were studied for p+p, C+C, Si+Si and centrality selected Pb+Pb collisions at sqrt s_NN = 17.2$ GeV with the NA49 large acceptance detector at the CERN-SPS. In particular, long range pseudo-rapidity correlations of oppositely charged particles were measured using the Balance Function method. The width of the Balance Function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.
System size dependence of multiplicity fluctuations of charged particles produced in nuclear collisions at 158 A GeV was studied in the NA49 CERN experiment. Results indicate a non-monotonic dependence of the scaled variance of the multiplicity distribution with a maximum for semi-peripheral Pb+Pb interactions with number of projectile participants of about 35. This effect is not observed in a string-hadronic model of nuclear collision HIJING.