Negative Mass Masquerading as Positive Mass; and What Happened to All the Antimatter?

All masses measured in a laboratory using simple measurement methods must give outcomes as positive or zero masses. A method is given in principle to determine between negative and positive masses for matter and antimatter particle pairs. Negative mass masquerades as positive mass and simple measurements would always show negative mass to have apparent positive mass. This means that antimatter particles could have negative masses despite measurements showing them to have positive masses. If antimatter has negative mass masquerading as positive mass then antimatter cannot form lumps in the same way that matter does. Antimatter would then be the main component of dark energy, which would answer the question of what happened to all the antimatter.