Lambda Produktion in Pb-Au Kollisionen bei 40 A GeV

The CERES-experiment at the CERN-SPS investigates the production of electron-positron pairs in ultrarelativistic nuclear collisions. The CERES spectrometer was upgraded during 1998 by the addition of a Time Projection Chamber (TPC) with a radial electric drift field and two coils of a warm magnet to provide a momentum analysis. This thesis deals with the design and construction of the CERES TPC and a first $Lambda$-analysis in 40 A,GeV Pb+Au collisions. The relative momentum resolution $sigma (dp/p)^2$ = $0.027^2+(0.024 ~ p)^2$ (in GeV/c) was determined using the measured width of the $Lambda$ invariant mass spectrum ($sigma$ = 12 MeV/c$^2$) and comparing it to a TPC simulation containing all measured distortions of a trajectory. The resolution is about a factor of 2.5 worse compared to its design value due to the still incomplete calibration. Analysing the fully corrected $Lambda$ transverse momentum spectra in a rapidity interval 2.0 $<$ $y_{m {Lambda}}$ $<$ 2.4 close to midrapidity for centralities $sigma / sigma _{ m {geo}} < 5 $ the inverse slope parameter and the rapidity density were measured in a $p_t$ interval 0.9 $<$ $p_{t}^{Lambda}$ $<$ 2.5 GeV/c$^2$: $T$ = 273 $pm$ 22 MeV/c$^2$, $dN/dy_{Lambda}$ = 5 $pm$ 0.5. Extrapolations over the whole $p_t$ region from zero to $infty$ the rapidity density was determined to be $dN/dy_{Lambda}$ = 11 $pm$ 2. Using the measurement of $ ar{Lambda}$ yield and a separate analysis of the net-proton production close to midrapidity it was possible to calculate particle ratios $ ar {Lambda}/Lambda ~ = ~ 0.024 pm 0.01$ and $Lambda/ m p ~ = ~ 0.22 ~ pm ~ 0.05$. Comparing these ratios to a thermal model the baryo-chemical potential and the temperature at hadro-chemical freeze-out were determined as $mu _B ~ = ~ (440 ~ pm 60) ~ m {MeV/c} ^2$ and $T ~ = ~( 140 ~ pm 5)~ m {MeV/c}^2$.