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
astroengine.com 
Events like this are by no means unexpected to us here at the ATLAS collaboration. We’ve been planning to use cosmic rays to align and commission our tracking sub-detectors for many years now, and we’ve actually been seeing cosmic rays for quite some time. The exciting part for us about the pictures that Adam posted is that they show that the components of our detector are working well and better-integrated than ever before, so we’re close to being ready for beam!
Here’s an article about the first time one of our sub-detectors saw a cosmic ray in the ATLAS cavern, in 2005:
http://cerncourier.com/cws/article/cern/29389
For some information about what we do with cosmic rays to prepare our detector, see for example:
Click to access jpconf8_110_092028.pdf
The neutron star and cosmic ray safety arguments in the 2008 LHC Safety Report were deemed “unverified” by CERN’s Scientific Policy Committee.
Credible arguments that neutron stars do not prove safety may be found in points 5, 6 and 7 of http://www.wissensnavigator.com/documents/spiritualottoeroessler.pdf
Hi Seth!
Thank you so much for your insight. It is very interesting to me that you have been able to test the sensors in ATLAS with cosmic ray muons. I feel another article coming on 😉
Many thanks for taking the time to comment.
Cheers, Ian
Beware JTankers continual misquotation of the SPC report. They do not use the word ‘unverified’ at all.
The report actually says:
“…at the LHC energy, any danger for the Earth on time scales lower than or
comparable to the natural lifetime of the solar system can be ruled out on the basis of its
contradiction with the observation of white dwarf stars of known mass, age and other
properties. This conclusion, while entirely valid for the LHC, would need further work to
be extended to conceivable future colliders of much higher energies. A powerful
argument applicable also to higher energies is formulated making reference to observed
neutron stars, but this argument relies on properties of cosmic rays and neutrinos that,
while highly plausible, do require confirmation, as can be expected in the coming years.
On the basis of all these findings, we can conclude that there is no danger of whatever
kind from the hypothetical production of black holes at the LHC.”
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Although it is not specified,these muons will have originated somewhere in the atmosphere above the Swiss countryside to be taken care of.
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