3 ms·

You're reading a bit too much into the "raw data" part. An average event that is saved to disk is about 1MB in size but that is with compression. The uncompress

• DoctorOetker 8y ago
  Hi, thanks for your response! I have the impression that the reason the data for a single event is so large is because it is ambiguous, i.e. the uncertainty of a possibly incorrect interpretation forces you to store a lot of analog values (so that the interesting events can be checked or re-interpreted later on), and this size is what forces you to store a lot of data, and this forces you to triage for interesting events. Assuming this is correct, then if the uncertainty of the tracks and their energies could be decreased, the data would be much more compact (i.e. only store location, momentum, energy/mass of incoming and decay particles as opposed to all the possibly relevant for later analysis ADC values) Assuming that this level of correctness could be achieved by solid-state track detectors [0], where the particles leave tracks throughout a solid material, would it not (in theory) make sense to 1) continuously pass a such a detector material above and below the collision point, 2) at high speed slice, 3) in massively parallel etch, 4) microscopically examine the accurate tracks (bubble chamber style) 5) digitally store them compactly by the above assumption that the event size in bytes would be much lower if we only needed to store few but exact parameters per event 6) remelt the preferably low melting point etched track detector material 7) feed the erased etched track detector back to the collision point in a continuous fashion. Either the speed of the material should be quite high or the illumination zone or collision point engineered very compact. Different collision bunches would be disambiguated because the tracks point to a different origin point (since the material has moved in the 25 ns @ 40 MHz, so for sub micrometer collision point that is 40 meters per second! obviously the detector would benefit from being designed to steer the collision point so it alternates to different positions) Obviously the biggest issue with this approach is needing a huge facility for parallel etching and inspecting the slices the cooling time should not be an issue, since the circular buffer of remelted material could be made arbitrarily long do you think it could make sense for a future detector to temporarily store the tracks physically in a solid-state nuclear track detector ? [0] https://en.wikipedia.org/wiki/Solid-state_nuclear_track_detector https://en.wikipedia.org/wiki/Solid-state_nuclear_track_dete... Edit: I forgot to mention that energy could then be determined from the change in curvature as the particle loses energy
  • Analog24 8y ago
    It's an interesting idea but, if I understand it correctly, I don't think it would be able to capture the majority of particles emitted from the collision zone. Modern detectors are designed to be as hermetic as possible so they can capture as much of the transverse energy as possible. This is crucial because in the plane perpendicular to the beam axis (i.e. line of collision) the total momentum is zero. Thus we can use conservation of momentum to infer the presence of particles that the detectors struggle to find (like neutrinos). This, of course, only works if we're confident that we accounted for (almost) all of the particles coming out of the collision. Here is a picture of a heavy-ion collision reconstructed from the CMS detectors to give you an idea of how much needs to be accounted for [0]. The light orange lines are the particle tracks in the tracker, the red boxes indicate the amount of energy deposited in the EM calorimeter, and the blue boxes indicate the amount of energy deposited in the hadronic calorimeter. I should note that normal proton-proton collisions do not produce anywhere near this number of particles (what we call the event "multiplicty") but they can still produce a few hundred. Furthermore, there are, on average, 40 proton-proton collisions per bunch crossing (which is what dictates the 40 MHz rate). So every 25ns there is a bunch crossing and the detector "snaps an image". In that image there are typically about 40 different collisions. Correlating tracks to vertices is not that easy given these conditions and is further complicated by the fact that particles can decay mid flight, causing their track to suddenly change. It would be great if we could be absolutely confident about the physical quantities associated with all of the particles produced in a collision, that's all we would need to know and this is essentially what's produced in high-energy physics simulations. However, reality is a lot messier. In addition to what I previously mentioned, the interactions between the detector material and the particles themselves also creates a lot of noise in the system. All of these uncertainties make it infeasible to compress an event down to just the reconstructed physical quantities, there is too much uncertainty and I don't think it will ever be overcome. Lastly, I should mention that the energy densities reached in the immediate vicsinity of the collision zones is high enough to destroy any material known to man. The center of heavy-ion collisions reach a temperature of over a trillion degrees. That's 100,000 times hotter than the center of the Sun. No instrument could ever be placed there to make an accurate reading. The best we can do is place detectors a decent distance away (IIRC it's about a few cm) and try to catch what comes out. [0] http://cms.web.cern.ch/sites/cms.web.cern.ch/files/styles/large/public/field/image/hiY1.jpg?itok=yHZVPXLh http://cms.web.cern.ch/sites/cms.web.cern.ch/files/styles/la...