Spectrometer line

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)

The 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