Hold on! ATLAS has already started detecting particles? Yes, indeed it has. Particle collisions don’t only happen inside particle accelerators such as the Large Hadron Collider (LHC); they happen all the time in the Earth’s atmosphere. High energy protons (or larger ions) generated by the Sun or other cosmic phenomenon (such as a supernova) bathe local space, passing through matter and colliding with atoms and molecules. Should a natural collision event occur in our atmosphere, billions of particles cascade from the point of collision, creating an “air shower.” Muons are one product of this air shower (in fact, the only natural muon production processes known are cosmic ray collisions) and some have been captured, making a fast-dash across the sensors in the recently completed A Toroidal LHC ApparatuS (ATLAS for short) detector at the LHC. It’s unexpected observations like these that really excite me, especially when we are a (possible) few weeks away from the first injection of particles into the LHC…
Three images have been posted on the US LHC Blog (is there any experiment out there without a blog these days?!) of the computational reconstruction of muon events as the energetic particles passed through the ATLAS detector. Although it is not specified, these muons will have originated somewhere in the atmosphere above the Swiss countryside, just after a cosmic ray impact with an atmospheric particle.
The resulting cascade of particles (of lower energy than the relativistic parent cosmic ray) will have included some muons which found their way through ATLAS and detected by the highly sensitive sensors. ATLAS has a devoted muon detector installed, reading the spectrum of radiation from the particle. In the image left, the muon sensors that detected the event are highlighted and software is then used to “connect the dots,” thus deriving the muon path. The top panel shows the axis of the core of the detector (i.e. from an accelerated proton-eye-view) and the middle panel shows a side-on view of ATLAS. It is clear from all three muon events that they originated from above the detector.
It’s great to see ATLAS is good to go! All we need now are some relativistic protons and we’re set…
More articles on the LHC ATLAS detector:
- Why is the LHC so Important? I’ll let Brian Cox Explain… | Astroengine.com | Brian Cox, ATLAS physicist, gives an inspirational lecture on the LHC
- The LHC ATLAS homepage
Source: US LHC Blog