The Production of Cold Antihydrogen

A Brief History of Antimatter•In 1928, Paul Dirac proposes antimatter with his work in relativistic quantum mechanics

•In 1932 the study of cosmic rays led to the detection of positively charged particles with the mass of an electron (positron)

•With a Bevatron, particles can be collided at GeV energy and create antiprotons ( )

•A high energy photon (>2 x 511 kev) hitting a wall will create a e-\e+ positron pair.

•Spontaneous decay of elements, known as Beta decay (β+ ) also produces positrons.

http://www.euronuclear.org/info/encyclopedia/betaplusdecay.htm

“Man-Made” Antimatter

Antihydrogen Created•The CERN (Conseil Européen pour la Recherche Nucléaire) studies antimatter and has a antiproton factory

•In 1992 CERN was able to create atoms by mixing antiprotons and positrons

•However, due to their high speed, only 9 were created and too fast to make measurements on.

The ATHENA Experiment

An extension of CERN (Athena) is created to produce better amounts of with lower speeds.

The whole apparatus is at a few degrees Kelvin and in a vacuum

The Antiproton Catching Trap

•10^7 of 5 Mev in 200 ns shots.

•A 3T solenoid directs the shot in T<15 K

•They must be slowed down in order to be captured by a Penning trap (E<10KeV).

R=1.25cm

•They hit thin (440 m) aluminium foil that slows then down and sets off the Penning trap (filled with 10^8 electrons)

•~10,000 are captures in the first trap. A series of traps are used, varying potential and size (10 in all).

The Positron Accumulator•A block of Na-22 is surrounded by a solid coat of Ne (e+ moderator) at 5.5 K.

•A 0.14 T field creates a beam of 5 million e+/sec and carries them to the trapping area.

•Nitrogen gas is used to collide and slow down the e+ until they settle in a potential well(~25eV).

•“Rotating wall technique” compresses the e+ cloud into a plasma

www-physics.ucsd.edu/research/surkogroup/positron/buffergas.html

Mixing Trap•The mixing trap is a small Penning trap confined between 2 larger traps.

•10^7 e+ are cooled to 15K

•10^4 (3 shots) are in the surrounding nested traps with E~ev.

•Mixing time is 160s

Antihydrogen Detection•Once a e+ is captured by a , it becomes a neutral and leaves the trap.

•Once it hits the wall, it will annihilate.

•Properties of annihilation is back to back

511KeV photons and 3-4 pions (50 to 900 MeV )

•Surrounding the trap is a series of detectors:

Si strips for the pions followed by CsI crystals for the two 511 KeV.

•It is assumed that is the 511KeV photons are ~2s, then they originate from the same source.

Analysis•Per mixing, between 100 and 150 counts of annihilation are detected.

•Using simulations (Monte Carlo) the efficiency of the detection is 2.5 x 10^-3, putting the actual number of in the thousands.

•In the future, CERN hopes to capture theses in order to make spectroscopic analysis on them.

•ie: 2s -> 1s transition

Referenceshttp://www.euronuclear.org/info/encyclopedia/betaplusdecay.htm

http://athena.web.cern.ch/athena/

http://livefromcern.web.cern.ch/livefromcern/antimatter/

D.S. Hall & G. Gabrielse, Electron cooling of protons in a Nested Penning Trap,77,10,(1996)

M. Amoretti et al., Production and detection of cold antihydrogen atoms, Nature, 2002

M. Amoretti et al., The Athena antihydrogen apparatus, A 518, (2004), p. 679-710.

Images with from athena and cern website