A Strangelet and Particle Search in Pb-Pb Collisions

%NA52 %title\\ \\The NA52 experiment aims to detect strangelets, \textit{i.e.} small drops of strange quark matter, which might result from the extreme energy and baryon densities attained in Pb+Pb collisions at a beam momentum of 158~A GeV/c. The experiment uses the H6 beam line as a spectrometer equipped with wire chambers, time of flight measurements over a path of 524~m and a hadronic calorimeter which is placed at the end of the setup.\\ \\During the 17 day run in fall of 1994 we accumulated data of 1.8~\cdot~10$^{12}$~Pb ions on our Pb targets. The average beam intensity was 2~\cdot~10$^{7}$~ions per spill for the NA52 experiment. We were running mainly with a 40~mm target at spectrometer rigidities of $\pm$100 and $-$200~GeV/c and with a 16~mm target at $+$200~GeV/c. Per setting 10$^{11}$ Pb+Pb collisions were recorded. During the Pb-ion run in 1995 the statistics for the strangelet search at a rigidity of $-$200~GeV/c has been improved by about one order of magnitude. This was mainly due to a factor of 10~higher beam intensity.\\ \\We did not observe any heavy object with a mass to charge ratio $m/|Z|$ between 8 and 120~GeV/c$^{2}$ at $p/|Z|$~=~200~GeV/c and between 5 and 60~GeV/c$^{2}$ at a rigidity $p/|Z|$~=~100~GeV/c, for particles which reach at least TOF3. This leads to an experimental sensitivity of about 10$^{-8}$ to 10$^{-7}$ per interaction depending on the assumed phase space distribution.\\ \\To improve the particle identification and background rejection capabilities for shorter tracks in the H6 beam line two additional scintillator counters BT and BS providing time of flight measurements and two multiwire proportional chambers W0B and WSB were added. See the figure for the updated beam line configuration.\\ \\In our 33 day data taking during the 1998 lead beam period we concentrated on the search for negatively charged strangelets. Several 10$^{12}$~lead-lead interactions were recorded at the rigidity settings of $-20, -40, -70, -100$ and $-$200~GeV/c. We had a mean intensity of 2~\cdot~10$^{8}$ lead ions per spill on the T4 target. Currently the analysis of this data is in progress.\\ \\During the 1996 lead beam period a segmented quartz-fibre lead calorimeter intended for event plane and centrality analysis was successfully tested. Additional physics data was taken in 1998 concerning the centrality dependence of K$^{-}$ and K$^{+}$ and flow studies of $\overline{p}$ and $\overline{d}$. Also this analysis is in progress.