Our interest in strangelets dates back to 1988 when, as members of BNL E814,
we initiated a search for strangelets in the products of heavy ion collisions.
The initial searches set upper limits on positively-charged strangelet
production at the level 
to 
per interaction,
depending on the strangelet's characteristics [8, 9]. These
limits rule out some of the parameter space of the quark-gluon plasma
production models [4]. E814 has recently collected additional data,
which is presently being analyzed. This includes data on negatively-charged
strangelets with expected sensitivity at the level, and data on
positively-charged strangelets with an expected sensitivity between 10 and 30
times better than that of E814's previous result [10].
Complementary data on antiproton production [11] and the coalescence
of light nuclei [10] were also obtained.
Present sensitivity limits must be improved by about 6 orders of magnitude to critically test the existence of strangelets. This motivated a series of meetings in August and December of 1989 to study methods of searching for exotic composite objects in heavy ion collisions. About 35 physicists attended these meetings. In addition to E864's wide-band approach, two other serious designs were proposed. The first, by Hank Crawford, emphasized the measurement of negatively-charged particles in a focussing spectrometer. The second, by Shoji Nagamiya, specifically studied the neutral H-dibaryon. The E864 design emerged as a way to simultaneously study positively- and negatively-charged particles, as well as neutrals. This required a large acceptance so that the complete range of Z/A could be studied in a reasonable running time.
A collaboration formed to pursue the wide-band approach, and a proposal was submitted to Brookhaven's Program Advisory Committee (PAC) on 7 May 1990. The collaboration consisted of 14 physicists from Brookhaven, University of Massachusetts, McGill University, University of New Mexico, and Yale University. The PAC concluded that the wide-band approach was attractive, but that the decision should be deferred until the detectors were better understood and the collaboration was strengthened.
The collaboration, expanded by the addition of the Penn State University group, resubmitted the proposal in November 1990. The update included additional physics goals of the experiment, as well as more complete technical designs and background studies. The PAC concluded that the experiment had merit both for its discovery potential and its study of the production of nuclei and antinuclei. However, the PAC felt a panel of experts should be convened to study the proposal and to determine: (i) if the experiment could achieve the needed sensitivity, (ii) could be constructed within the $6M estimated cost (not including the beam line), and (iii) if the collaboration had sufficient strength to achieve its goals.
The panel, chaired by Doug Bryman (TRIUMF), included Hank Crawford (LBL), Hugh Brown (BNL), and Craig Woody (BNL). This panel concluded that the above three requirements were met, and that the experiment would be an exciting addition to the AGS physics program.
In March 1991, Brookhaven's PAC decided to approve E864 for 1200 hours of running for positive particles; the additional time we requested for negatives was deferred because at the time the Bryman Committee met, only positive running was reviewed.
Since the approval, the MIT group joined the collaboration, and the Brookhaven group was strengthened with the addition of M. Schwartz. Moreover, much progress has been made on background studies and detector development. These developments, along with the physics goals and cost estimates, are the subject of this proposal.