0000000000653392
AUTHOR
T. A. Trainor
First Antiprotons in an Ion Trap
Measurements of the antiproton mass[2,3,4,5] are represented in Fig. 1. All of these are deduced from measurements of the energy of x-rays radiated from highly excited exotic atoms. For example, if an antiproton is captured in a Pb atom, it can make radiative transitions from its n = 20 to n = 19 state. The antiproton is still well outside the nucleus in this case, so that nuclear effects can be neglected. The measured transition energy is essentially proportional to the reduced mass of the nucleus and hence the antiproton mass can be deduced by comparing the measured values with theoretical values, corrected for QED effects. The most accurate quoted uncertainty is 5 × 10-5 and is consisten…
Barkas effect with use of antiprotons and protons.
The difference in the range of protons and antiprotons in matter, an example of the Barkas effect, is observed in a simple time-of-flight apparatus. The ranges of 5.9-MeV antiprotons and protons differ by about 6% in a degrader made predominantly of aluminum.
Thousandfold improvement in the measured antiproton mass
Comparisons of antiproton and proton cyclotron frequencies yield the ratio of inertial masses M(p¯)/M(p)=0.999 999 977 ±0.000 000 042. The fractional uncertainty of 4×10−8 is 1000 times more accurate than previous measurements of this ratio using exotic atoms and is the most precise test of CPT invariance with baryons. Independent comparisons to electrons yield the mass ratios M(p¯)/M(e−)=1836.152 660±0.000 083 and M(p)/M(e−) =1836.152 680±0.000 088. Cryogenic antiprotons (near 4 K) stored in a Penning trap for 2 months establish directly a lifetime greater than 3.4 months.
Cooling and slowing of trapped antiprotons below 100 meV
Electron cooling of trapped antiprotons allows their storage at energies 10 million times lower than is available in any antiproton storage ring. More than 60 000 antiprotons with energies from 0 to 3000 eV are stored in an ion trap from a single pulse of 5.9-MeV antiprotons from LEAR. Trapped antiprotons maintain their initial energy distribution over a storage lifetime exceeding 50 h unless allowed to collide with a cold buffer gas of trapped electrons, where- upon they cool dramatically to 1 eV in tens of seconds. The cooled antiprotons can be stacked into a harmonic potential well suited for long-term storage and precision measurements.
First Capture of Antiprotons in a Penning Trap: A Kiloelectronvolt Source
Antiprotons from the Low Energy Antiproton Ring of CERN are slowed from 21 MeV to below 3 keV by being passed through 3 mm of material, mostly Be. While still in flight, the kiloelectronvolt antiprotons are captured in a Penning trap created by the sudden application of a 3-kV potential. Antiprotons are held for 100 s and more. Prospects are now excellent for much longer trapping times under better vacuum conditions. This demonstrates the feasibility of a greatly improved measurement of the inertial mass of the antiproton and opens the way to other intriguing experiments.
First Capture of Antiprotons in an Ion Trap: Progress Toward a Precision Mass Measurement and Antihydrogen
Antiprotons from the Low Energy Antiproton Ring of CERN are slowed from 21 MeV to below 3 keV by being passed through 3 mm of material, mostly Be. While still in flight, the kilo-electron volt antiprotons are captured in a Penning trap created by the sudden application of a 3-kV potential. Antiprotons are held for 100 s and more. Prospects are now excellent for much longer trapping times under better vacuum conditions. This demonstrates the feasibility of a greatly improved measurement of the inertial mass of the antiproton and opens the way to other intriguing experiments. The possibility of producing antihydrogen by merging cold, trapped plasmas of positrons and antiprotons is discussed.