<P> The biggest limiting factor in the large - scale production of antimatter is the availability of antiprotons . Recent data released by CERN states that, when fully operational, their facilities are capable of producing ten million antiprotons per minute . Assuming a 100% conversion of antiprotons to antihydrogen, it would take 100 billion years to produce 1 gram or 1 mole of antihydrogen (approximately 7023602000000000000 ♠ 6.02 × 10 atoms of anti-hydrogen). </P> <P> Antihelium - 3 nuclei (3 He) were first observed in the 1970s in proton--nucleus collision experiments at the Institute for High Energy Physics by Y . Prockoshkin's group (Protvino near Moscow, USSR) and later created in nucleus--nucleus collision experiments . Nucleus--nucleus collisions produce antinuclei through the coalescense of antiprotons and antineutrons created in these reactions . In 2011, the STAR detector reported the observation of artificially created antihelium - 4 nuclei (anti-alpha particles) (4 He) from such collisions . </P> <P> Antimatter cannot be stored in a container made of ordinary matter because antimatter reacts with any matter it touches, annihilating itself and an equal amount of the container . Antimatter in the form of charged particles can be contained by a combination of electric and magnetic fields, in a device called a Penning trap . This device cannot, however, contain antimatter that consists of uncharged particles, for which atomic traps are used . In particular, such a trap may use the dipole moment (electric or magnetic) of the trapped particles . At high vacuum, the matter or antimatter particles can be trapped and cooled with slightly off - resonant laser radiation using a magneto - optical trap or magnetic trap . Small particles can also be suspended with optical tweezers, using a highly focused laser beam . </P> <P> In 2011, CERN scientists were able to preserve antihydrogen for approximately 17 minutes . </P>

Which of the following particles is considered to be a form of antimatter