A Stable Sexaquark: Overview and Discovery Strategies

The neutral, flavor singlet scalar uuddss bound state -- the sexaquark, S -- may have a low enough mass to be stable or extremely long-lived. Here we review mass estimates and production expectations and show that laboratory experiments to date do not rule out such a long-lived state. An S with mass below 2054 MeV is either absolutely stable or has a lifetime greater than the age of the Universe. Detection of a stable S in accelerator experiments is very challenging. An examination of the experimental literature shows that such an effectively stable state would have escaped detection. The strongest laboratory constraint on a long-lived S comes from the lower-bound on its formation time in a doubly-strange hypernucleus; this constraint is, however, not stringent enough to exclude a stable S. We develop strategies to discover it. A stable S would be an attractive dark matter candidate. Relevant astrophysical and cosmological observations, which show that sexaquark dark matter is consistent with all current knowledge, are briefly reviewed.