Antimatter particles do not have negative mass. The concept of negative mass is not a property of antimatter or matter. In our current understanding of physics, mass is always positive, regardless of whether the particle is made of matter or antimatter.
When matter and antimatter particles come into contact, they can annihilate each other, converting their mass into energy according to Einstein's famous equation E=mc². This process releases a large amount of energy in the form of gamma rays or other particles, depending on the specific particles involved.
For example, when an electron (matter) and a positron (antimatter) collide, they annihilate each other, resulting in the production of high-energy photons (gamma rays). The mass of the electron and positron is completely converted into energy during this annihilation process.
The conservation of mass-energy is a fundamental principle in physics, and it holds true during interactions involving matter and antimatter. So, rather than the antimatter particle losing its negative mass, the combined system (matter and antimatter) undergoes annihilation, converting their mass into energy.
It's worth noting that while the concept of negative mass is not applicable to matter or antimatter, theoretical physics does explore exotic ideas like negative mass in certain contexts. However, these concepts are currently speculative and not directly related to the behavior of antimatter in our known universe.