Strange Quark Matter (SQM) is a proposed state of hadronic matter made up of roughly one-third each of up, down, and strange quarks in a single hadronic bag. For the last three decades, a wide range of experimental searches for strangelets (small lumps of SQM with baryon number less than 106) have been conducted but all failed to give a definite answer to the existence of SQM. We report results from a search for strangelets in a lunar soil sample, in which the predicted strangelet concentration is about 104 times higher than that on the Earth. The search used the tandem Van-de-Graaff accelerator at Yale as an ultra-sensitive mass spectrometer. We have searched for strangelets with nuclear charges 5, 6, 8. 9, and 11 over a range in mass from A = 42 to A = 70 amu. No strangelets were found in the experiment. For strangelets with nuclear charge 8, usually called strangelet oxygen, a concentration in the lunar soil sample higher than 10-16 per normal atom is excluded at the 95% confidence level. The implied limits on the strangelet flux in cosmic rays are the most sensitive to date for the covered range and are relevant to both recent theoretical flux predictions and a strangelet candidate event found by the Alpha Magnetic Spectrometer collaboration.
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