Gaseous AntiParticle Spectrometer (GAPS)(GAPS
We propose a novel antimatter detection scheme. The gaseous antiparticle spectrometer (GAPS) effects particle identification through the characteristic X-rays emitted by antiparticle when it forms exotic atoms in gases. The resulting instrument can provide more than an order of magnitude improvement in sensitivity over the forthcoming missions in the next decade. GAPS will draw several significant cosmological consequences, most prominently the indirect detection of dark matter in the Galactic halo through measuring low energy antideuterons. In addition, GAPS will elucidate a source of antiprotons and significantly extend a searching power of antihelium to probe the baryonic symmetry of the Universe. Based on the full understanding of relevant physics, we have simulated several potential applications of GAPS for measurement of different types of cosmic antiparticles.
2. Science of GAPS
GAPS is tuned to detect
cosmic antibaryons at low energy band (< fewx100 MeV/nuc).
|Primary source||WIMP annihilation||WIMP annihilation||Antimatter domain in the universe|
|Previous measurements||Detected at E=0.2-20 GeV||No detection||No detection|
|Scientific study||Solar modulation
||Dark matter||Baryonic (a)symmetry|
3. Detection scheme of GAPS
The GAPS detector operates on a straightforward scheme. An antiparticle that passes through a TOF system is slowed down by dE/dx losses in a degrader block. The thickness of this block is tuned to select the sensitive energy range of the detector. The antiparticle is eventually stopped in the gas chamber, forming an exotic atom with probability of order unity (excluding a small fraction of loss by the direct annihilation in degrader block and gas). Once the antiparticle is captured into an bound state of the atom due to its negative charge, it starts decaying toward the nucleus. Through proper selection of gas and its density, the absorption of the antiparticle can be tailored to produce 3 to 4 well-defined hard X-ray transitions in the decay chain. Coincidence of deexcitation X-rays unique to antiparticle type register a valid event and the particle type is identified through energy measurement of characteristic X-rays. Incident energy is reconstructed from the velocity measurement by TOF system. Promptly after the release of these X-rays, the antiparticle annihilates with the proton producing a shower of pions. The coincident signal between the TOF system, the characteristic decay X-rays and the energy deposition induced by the pions is an extremely clean criterion for the presence of the antiparticle.
Each surface of GAPS detector is readily open to half of the sky due to the excellent background rejection power. Therefore, the effective grasp of GAPS is significantly larger than a detector of same size based on the other detection schemes. Also, by varying the thickness of the degrader block, separate energy channels can be defined and optimized. A typical GAPS implementation would have 2 to 5 such channels. In principle, there is no inherent lower limit on the detectable energy of cosmic antiparticles. Instead, it is set by the geomagnetic rigidity and the particle degradation by the materials (e.g. TOF system) outside the absorbing material.
other detector schemes
|Detectors||GAPS||AMS, PAMELA, BESS||BGO|
|Particle identification||Characteristic X-rays||Momentum + velocity||Total deposited energy|
|Total energy band width||~400 MeV/nuc||~10 GeV/nuc||~200 MeV/nuc|
|Lower energy limit||~ 50 MeV/nuc||~200 MeV/nuc||~ 50 MeV/nuc|
|BKG rejection power||Excellent||Medium||Poor|
|Background source||Cosmic hard X-rays||Multi-scattering||Protons|
|Identifiable particles||Antibaryons||All cosmic-rays||Antiproton|
5. Potential mission
|Mission type||Balloon||Space mission||Interplanetary mission|
|Purpose||Spectroscopy of low energy antiprotons||Search for antideuterons and antiheliums||Spectroscopy of very low energy antiprotons|
|Scientific objectives||Low energy antiprotons,
|Primary antiproton sources, Solar modulation|
|Observation point||High latitude
(Canada, North poles)
|Low earth orbit
|Beyond solar system|
|Size (cube)||2 m||5 m||6 cm|
|Weight||< 1 ton||< 5 ton||~ 1 kg|
|Energy band||100-400 MeV/nuc||100-400 MeV/nuc||< 100 MeV|
|Observation time||1 day||3 years||1 year|
6. Current status
7. Publications and talks
Last updated on 12/07/03.