New upper limit on strange quark matter flux with the PAMELA space experiment

Abstract

In this work we present results for direct search of Strange Quark Matter in cosmic rays with the PAMELA space spectrometer. If this state of matter exists it may be present in cosmic rays as particles, called strangelets, having an anomalously high mass-to-charge (A/Z) ratio. A direct search in space is complementary to those from ground based spectrometers. Furthermore, it has the advantage of being potentially capable of directly identifying these particles, without any assumption on their interaction model with Earth's atmosphere and the long term stability in terrestrial and lunar rocks. In the energy range from 1 to ∼ 1.0 × 10 3 GV no such particles were found in the data collected by PAMELA between 2006 and 2009. An upper limit on the strangelet flux in cosmic rays was therefore set for particles with charge 1 ≤ Z ≤ 8 and in mass 4 ≤ A ≤ 1.2 × 10 5 . This limit as a function of mass and as a function of magnetic rigidity allows to constrain models of SQM production and propagation in the Galaxy.