The NA52 experiment searches for long-lived massive strange quark matter particles, so-called strangelets, produced in Pb-Pb collisions at a beam momentum of p lab 158 A GeV͞c. Upper limits for the production of strangelets at zero degree production angle covering a mass to charge ratio up to 120 GeV͞c 2 and lifetimes t lab * 1.2 ms are given. The data presented here were taken during the 1994 lead beam running period at CERN. [S0031-9007(96) PACS numbers: 25.75. Dw, 12.38.Mh, 24.85.+p The production of strange quark matter (SQM), socalled strangelets, has long been advertised as an ultimate signature for quark-gluon plasma (QGP) formation in ultrarelativistic heavy ion collisions. Strangelets could be formed from the QGP via a strangeness distillation process [1][2][3][4]. Their production is due to a cooling process of the plasma which results in a strong enhancement of the s quarks in the quark phase. The cooling mechanism of the plasma is started by the evaporation of pions, K 1 and K 0 , which carry entropy and antistrangeness away from the system. The strong s-quark enhancement in the baryon rich environment of the plasma favors the formation of strangelets. In contrast to nuclear matter, strangelets consist of approximately the same number of u, d, and s quarks. On the basis of the Pauli exclusion principle such multiquark states become stable owing to the introduction of strangeness as an additional degree of freedom. Depending on the relative s-quark content, strangelets can exist in neutral or charged form. By virtue of the large s-quark content, the charge to mass ratio of strangelets is expected to be small ͑Z͞A , 0.1͒, which is used as a prominent experimental signature. Bag model calculations indicate that for sufficiently large masses ͑A . 10 GeV͞c 2 ͒ strangelets could be stable with respect to strong and weak nucleon emission and therefore detectable in mass spectrometer experiments [5][6][7][8]. Strangelet formation has also been considered in coalescence models [9]. Strange quark matter could even occur as a decay product of metastable exotic multihypernuclear objects (MEMO's) [10]. The discovery of strangelets would have profound implications beyond the confirmation of the QGP formation: it would establish the existence of strange quark matter (SQM) [11][12][13] [20]. A recent review is given in Ref. [21]. During the 1994 Pb period at CERN, the NA52 Collaboration took data to search for positively and negatively charged strangelets resulting from lead-on-lead collisions at an incident beam momentum of 158A GeV͞c. Preliminary results have been already presented [22]. Now the full statistics have been analyzed and the final results are reported here.The experimental setup (Fig. 1) makes use of the existing H6 beam line at the CERN-SPS to identify the secondary particles produced in the lead target. It is a single particle, double-bend focusing spectrometer transmitting charged particles within a momentum bite of 2.8% for rigidities p͞jZj selectable between 5 and 200 GeV͞c with full particle...

A search for new massive particles vnth a lour charge to mass ratio in S -W collisions at a beam momentum of 200 GeV/c per nucleon is presented. Upper limits for the production of strangelets with a mass to charge ratio of up to 60GeV/c at rigidities of +150GV are reported.

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