Search for invisible decay of orthopositronium

Abstract

Orthopositronium (o-Ps) decay or conversion into "invisible" final states is searched for by measuring the energy deposited in a hermetic photon detector for each positron produced from p + decay of 22 Na and stopped by an aerogel target. No invisible event is detected for a total of 10 8 stopping positrons, thereby giving an upper limit of 2.8xl0 -6 on the o-Ps branching ratio, which is 200 times more stringent than previous limits. This experiment excludes an invisible decay as the origin of the reported discrepancy on o-Ps lifetime, provides a limit of e < 1.5 x 10 ~~8 on the photon-mirror-photon mixing, and rules out millicharged particles lighter than 500 keV.

Experimental progress in positronium laser physics

“…Various violations would manifest themselves as forbidden decay modes [39,[203][204][205][206][207][208][209][210][211][212][213][214][215]. Moreover, because it has no net additive quantum numbers, Ps can in principle couple to Dark Matter or other exotic systems that provide a mechanism for invisible decays [216][217][218][219]. Many possible scenarios have been proposed and studied in experiments, including Ps coupling to extra dimensions, unparticles, milli-charged particles, gauge bosons or mirror matter [220][221][222][223][224][225][226].…”

Positronium as a Probe for New Physics Beyond the Standard Model

“…Some of these searches are reported in Table 3. Note that best present limit for the branching ratio for invisible channels of o − P s is [27] Br(o − P s → invisible) < 2.8 × 10 …”

“…Experiments differed substantially in the technique of formation of o-Ps. To elucidate discrepancies, a variety of experiments have been carried out to search for the exotic decay mode of o-Ps, resulting in no evidence [25,26,27,28,29,30,31]. Some of these searches are reported in Table 3.…”

Solution of the Orthopositronium Lifetime Puzzle

“…This discrepancy has been referred as 'orthopositronium lifetime puzzle', and was long-standing problem. To elucidate discrepancies, a variety of experiments have since been carried out to search for the exotic decay mode of o-Ps, resulting in no evidence so far [5,6,7,8,9,10].…”