377 research outputs found
Energy dependence of transverse mass spectra of kaons produced in p+p and p+pbar interactions.A compilation
The data on m_T spectra of K0S K+ and K- mesons produced in all inelastic p+p
and p+pbar interactions in the energy range sqrt(s)NN=4.7-1800GeV are compiled
and analyzed. The spectra are parameterized by a single exponential function,
dN/(m_T*dm_T)=C exp(-m_T/T), and the inverse slope parameter T is the main
object of study. The T parameter is found to be similar for K0S, K+ and K-
mesons. It increases monotonically with collision energy from T~30MeV at
sqrt(s)NN=4.7GeV to T~220MeV at sqrt(s)NN=1800GeV. The T parameter measured in
p+p and p+pbar interactions is significantly lower than the corresponding
parameter obtained for central Pb+Pb collisions at all studied energies. Also
the shape of the energy dependence of is different for central Pb+Pb
collisions and p+p(pbar) interactions.Comment: more differential analysis adde
Kaonen-Produktion in C+C und Si+Si Kollisionen bei 40A und 158A GeV
In dieser Arbeit wurde die Produktion geladener Kaonen in C+C und Si+Si- Kollisionen bei Strahlenergien von 40A und 158A GeV untersucht, die verwendeten Daten stammen vom CERN Experiment NA49. Die Kaonen wurden über den mittleren Energieverlust in den TPCs identifiziert, was die Messung der Phasenraumverteilung in einem großen Bereich möglich machte. Die Analyse basiert auf der dE/dx Auswertung aller NA49 TPCs (globale Analyse). Es wurde herausgefunden, dass bei den C+C und Si+Si Datensätzen die MTPC dE/dx Information unvollständig auf den DSTs gespeichert wurde. Da die Auflösung bei der Bestimmung des mittleren Energieverlusts beschränkt ist, ist die Teilchenidentifikation nur über statistische Methoden möglich. Im Kapitel 4 wird diese von Marco van Leeuwen mitentwickelte Methode beschrieben. Für die endgültigen Werte der Phasenraumverteilung der Teilchen müssen die identifizierten Kaonen noch auf Effekte korrigiert werden, die durch den Aufbau des Detektors und die verwendete Analysesoftware hervorgerufen werden. Die Korrekturen werden im Kapitel 5.4 beschrieben und angewandt, dies sind unter anderem geometrische Korrekturen, Akzeptanz und Zerfallskorrekturen. Die Ergebnisse bei 158A GeV wurden mit C.Höhnes Ergebnissen verglichen und stimmen im Rahmen der Fehler überein. Zur Übersicht wurden die Daten mit den anderen NA49-Daten zusammengefasst. Dabei ist zu erkennen dass die Verhältnisse / , / , / und / im Bereich zwischen p+p und Si+Si schnell ansteigen und im weiterem Verlauf bis Pb+Pb kaum weiter ansteigen. Im Rahmen des Statistical Model of the Early Stage sind dies Anzeichen für einen Übergang in das Quark-Gluon-Plasma bei 40A GeV in Si+Si Kollisionen. Für eine Bestätigung dieser Vermutung sind jedoch weitere Messungen bei unterschiedlichen Energien und Systemen notwendig
Strangeness dynamics in relativistic nucleus-nucleus collision
We investigate hadron production as well as transverse hadron spectra in
nucleus-nucleus collisions from 2 GeV to 21.3 TeV within two
independent transport approaches (UrQMD and HSD) that are based on quark,
diquark, string and hadronic degrees of freedom. The comparison to experimental
data demonstrates that both approaches agree quite well with each other and
with the experimental data on hadron production. The enhancement of pion
production in central Au+Au (Pb+Pb) collisions relative to scaled
collisions (the 'kink') is well described by both approaches without involving
any phase transition. However, the maximum in the ratio at 20 to 30
AGeV (the 'horn') is missed by 40%. A comparison to the
transverse mass spectra from and C+C (or Si+Si) reactions shows the
reliability of the transport models for light systems. For central Au+Au
(Pb+Pb) collisions at bombarding energies above 5 AGeV, however,
the measured -spectra have a larger inverse slope parameter
than expected from the calculations. The approximately constant slope of
spectra at SPS (the 'step') is not reproduced either. Thus the pressure
generated by hadronic interactions in the transport models above 5
AGeV is lower than observed in the experimental data. This finding
suggests that the additional pressure - as expected from lattice QCD
calculations at finite quark chemical potential and temperature - might be
generated by strong interactions in the early pre-hadronic/partonic phase of
central Au+Au (Pb+Pb) collisions.Comment: 10 pages, 5 figures, Invited talk presented by H. Stocker at
ERICE-2003 (Sep. 2003, Erice, Italy), to be published in Prog. Part. Nucl.
Phys. 52 (2004
System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy
Measurements of charged pion and kaon production are presented in centrality
selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in
semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra,
rapidity spectra and total yields are determined as a function of centrality.
The system-size and centrality dependence of relative strangeness production in
nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from
the data presented here and published data for C+C and Si+Si collisions at 158A
GeV beam energy. At both energies a steep increase with centrality is observed
for small systems followed by a weak rise or even saturation for higher
centralities. This behavior is compared to calculations using transport models
(UrQMD and HSD), a percolation model and the core-corona approach.Comment: 32 pages, 14 figures, 4 tables, typo table II correcte
High p_T Spectra of Identified Particles Produced in Pb+Pb Collisions at 158GeV/nucleon Beam Energy
Transverse momentum spectra of pi^{+/-}, p, pbar, K^{+/-}, K^0_s and Lambda
at midrapidity were measured at high p_T in Pb+Pb collisions at 158GeV/nucleon
beam energy by the NA49 experiment. Particle yield ratios (p/pi, K/pi and
Lambda/K^0_s) show an enhancement of the baryon/meson ratio for p_T>2GeV/c. The
nuclear modification factor R_{CP} is extracted and compared to RHIC
measurements and pQCD calculations.Comment: Quark Matter 2005 parallel section proceeding
NA49 results on hadron production: indications of the onset of deconfinement ?
The NA49 experiment at the CERN SPS measured the energy and system size
dependence of particle production in A+A collisions. A change of the energy
dependence of several hadron production properties at low SPS energies is
observed which suggests a scenario requiring the onset of deconfinement.Comment: XXXV International Symposium on Multiparticle Dynamics 200
Energy dependence of particle ratio fluctuations in central Pb+Pb collisions from ~6.3 to 17.3 GeV
We present measurements of the energy dependence of event-by-event
fluctuations in the K/pi and (p + \bar{p})/pi multiplicity ratios in heavy ion
collisions at the CERN SPS. The particle ratio fluctuations were obtained for
central Pb+Pb collisions at five collision energies, \sqrt{s_{_{NN}}}, between
6.3 and 17.3 GeV. After accounting for the effects of finite-number statistics
and detector resolution, we extract the strength of non-statistical
fluctuations at each energy. For the K/pi ratio, larger fluctuations than
expected for independent particle production are found at all collision
energies. The fluctuations in the (p + \bar{p})/pi ratio are smaller than
expectations from independent particle production, indicating correlated pion
and proton production from resonance decays. For both ratios, the deviation
from purely statistical fluctuations shows an increase towards lower collision
energies. The results are compared to transport model calculations, which fail
to describe the energy dependence of the K/pi ratio fluctuations.Comment: 11 pages, 10 figures, update to published versio
Bose-Einstein correlations of pion pairs in central Pb+Pb collisions at CERN SPS energies
Measurements of Bose-Einstein correlations of pion pairs in central Pb+Pb
collisions were performed with the NA49 detector at the CERN SPS for beam
energies of 20A, 30A, 40A, 80A, and 158A GeV. Correlation functions were
measured in the longitudinally co-moving ``out-side-long'' reference frame as a
function of rapidity and transverse momentum in the forward hemisphere of the
reaction. Radius and correlation strength parameters were obtained from fits of
a Gaussian parametrization. The results show a decrease of the radius
parameters with increasing transverse momentum characteristic of strong radial
flow in the pion source. No striking dependence on pion-pair rapidity or beam
energy is observed. Static and dynamic properties of the pion source are
obtained from simultaneous fits with a blast-wave model to radius parameters
and midrapidity transverse momentum spectra. Predictions of hydrodynamic and
microscopic models of Pb+Pb collisions are discussed.Comment: 22 pages, 23 figure
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