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Comment by iamthepieman | Hacker News Reader

I followed the links to the CMS, Atlas and other detectors that the images appear to be from but couldn't find any information on what these images actually mean. By reading the layman's descriptions (which I most certainly am) I assume that the images show where along the "surface", if there is such a thing, of the detector various particles were detected and the length of the bars show either how much energy the particle(s) have or the density of particles at that point.

Is there anywhere I can go to get a more detailed description of these without delving into academic papers that I have no hope of understanding?

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A detector is typically a series of concentric cylinders, with the beam pipe, where the collisions occur, running through the center. The inner layers are tracking chambers, which detect the paths of charged particles. This is what produces all the curved lines radiating from the center.

The outer layers are calorimeters, which catch particles and measure their kinetic energy. As you correctly assumed, these produce the bar plots. Often there will be one layer of calorimeters for photons and electrons, and a second for hadrons (protons, mesons, etc.)

This Wikipedia article is a good starting point: https://en.wikipedia.org/wiki/Hermetic_detector

Very helpful, thank you. Do you know if they have the ability to plot the various events of the collision by time, such that the bar plots could be shown appearing one after another as collision events are recorded?

I'm not familiar with the nitty-gritty of the LHC experiments, but in general the various detector subsystems have different response times and rate capabilities. There are certain types of detectors with explicit time granularity (e.g. time of flight) but for most detectors there would be no time structure within a single collision record ("event").

But you could work backwards to make an animation for each event. From a scientific perspective it's not that interesting though.

I'd expected it to be trivial to hunt down some animated gifs, but to no avail.

Here's a movie derived from an actual event that will give you a feel for things: http://www.atlas.ch/multimedia/proton-event.html

CMS, too: https://www.youtube.com/watch?v=poNftWVbwmM

Wow, thank you. That CMS video is awesome! This really gives me more of a foothold on what is going on.

You've got the right general idea. It's a tricky thing to simultaneously display three-dimensional tracks and the amount of energy deposited in each detector system.

I'm surprised that Atlas and CMS don't have a better viewer's guide immediately at hand, but perhaps this article will help:

http://www.symmetrymagazine.org/breaking/2010/03/18/atlas-ev...

I've worked at two accelerator facilities (RHIC and CEBAF) writing software for doing particle tracking and pseudo-data generation, and I always wished that they could divert more time into preparing articles like the one you linked. They're super helpful to laypeople, especially family and friends, but they're also great for getting students at universities interested in maybe coming to pitch in.

Sadly, the lab personnel (especially those coordinating outreach) are generally crazy overworked and don't have a lot of time, and the interns are just too inexperienced and lack the requisite domain knowledge to do it themselves.

If you ever feel like writing a paper on this I can highly suggest Ludwik Fleck as a starting point (his writing on thought collectives). At least that's where I started when I needed a concept of marketplace for ideas and why laypeople matter.

Thanks! this is exactly what I was looking for. I may be missing something but I found it odd that the CERN website didn't have any more detailed breakdowns of the experiments and setups like the article you linked.

The amount of data that comes out of the different detectors on the LHC is staggering. It takes a fair amount of post processing to get meaningful results from collisions, and there can be millions of collisions in a run. There's some more information about how they process these results on the LHC computing grid page: http://wlcg-public.web.cern.ch/.

When I did my traineeship at ATLAS DAQ around 10 years ago, one issue was how to per-process the data that could be considered invalid fast enough, to be able to throw it away before it arrived into the cluster.

Talking about ATLAS experiment: protons in LHC collide 40 million times a second, but "only" around 100 events per second are stored for later analysis. LHC grid concerns the 100; three levels of trigger (one hardware and two software levels) are used to select the useful 100 out of 40 millions, in real time.

That's insane.

I understood more after using some citizen science project where you classified particles by their trajectories using images like these. Basically, if you didn't figure out that part, the images are cross sections of the vacuum pipe and show the trajectories of the particles that come to exist in the collision of the accelerated particles

(Copying from elsewhere:) I highly recommend the "Particle Adventure" for lots of info about basic particles physics that's accessible to the layman

http://www.particleadventure.org/

In particular, starting at this page should give you an idea of how many components there are and what sorts of information come out of them:

http://www.particleadventure.org/component_detector.html

Although the cartoons seem a bit silly, this is what my professor gave me as an undergrad to get oriented, and it was really helpful.

http://www.extremetech.com/extreme/206123-first-images-of-re...

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