Below is a short animation summarizing the antihydrogen hyperfine spectroscopy technique used in our experiment (the video is taken from the website of the SMI group: http://antimatter.at)
he spectrometer line consists of
- a low Q microwave cavity with a resonance frequency at ~1.42GHz.
- a superconducting sextupole magnet that focuses or defocuses the antihydrogen beam depending on the spin configuration of the atoms.
- an antihydrogen detector.
Fig.1: 3D drawing of the spectrometer beamline assembly after the CUSP
The cavity is a strip-line resonator (see Fig. 2) surrounded by Helmholtz coils that provide a static and homogeneous field inside the cavity volume. Fig. 3 shows a typical frequency scan around the hyperfine transition energy (double-dip structure).
Fig.2 : Picture of the cavity
Fig.3 : Resonance scan of the sigma1 transition at 2
Gauss (simulation)
After passing through the cavity, atoms that have undergone a
spin flip (from low-field seekers to high-field seekers) will be
defocused by the sextupole
field and will annihilate on the bore of the magnet. The low-field
seekers atoms will be focused toward the detector leading to a lower
amount of antihydrogen annihilations when the cavity is on resonance
(see Fig.2) .
Fig 4. shows a Geant4 simulation of low and high field seekers trajectories from the CUSP to the antihydrogen detector.
Fig.4 : Geant 4 simulation of the trajetories of high field seekers (red) and low-field seekers (green) from the CUSP to the detector
The CPT (“Compact Pion Tracker”) detector is designed to detect the charged pions following an antihydrogen annihilation.
It consists of a central segmented array of plastic scintillators read
out by a Multi-Channel PMT. The central detector is surrounded by a
hodoscope consisting of 30 bars of plastic scintillator read out on both
sides by silicon photomultipliers. Fig. 5 shows a picture of the
hodoscope (and the silicon PM pre-amplifier boards). Fig. 6 shows the
online display of a cosmic event passing through the hodoscope and the
central detector. The color coding is proportional to the charge
deposited in the scintillators.
Developement on the detector system for better vertex reconstruction is underway.
Fig. 5 : Picture of the hodoscope detector Fig.6 : Online display of a cosmic event
