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I understand that the LHC can collide protons with protons, heavy ions with heavy ions, or protons with heavy ions, giving three main configurations. But, I'm wondering: is that the only property that physicists would vary in order to perform different experiments?

For example, might they run the LHC at less than the maximum energy in order to facilitate a certain kind of experiment? Or, use different heavy ions? Or, vary the beam collision parameters in some way?

If not, then do they just fire up the LCH and continuously collect data for months at a time, only stopping to switch the particles used?

(Note that I'm not talking about the probably millions of properties that must be tweaked to get it running at its best; I'm only asking about properties where the optimal value depends on the experiment being run.)

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  • $\begingroup$ They do some of the things you have suggested. The wikipedia page on the large hardon collider is helpful, though an experimental physicist at stack exchange could provide a better answer than that provided by wikipedia. $\endgroup$
    – Cicero
    Jun 3, 2015 at 22:21
  • $\begingroup$ Only three things matter for high energy collider physics: what you collide, energy, and luminosity. And you want as much of both energy and luminosity as you can get, because more luminosity means more data and higher energy means a higher fraction of the rare and interesting events. For the choice of colliding particles my understanding (but I've never done heavy ions so grain of salt time) is that interest in heavy ions is in the best approximation to extended nuclear matter which means you use the heaviest ions you can manage. Other facilities, of course, have other priorities. $\endgroup$
    – dmckee --- ex-moderator kitten
    Jun 4, 2015 at 0:02

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Components:

Muon Spectrometer: (1) Monitored Drift Tube (2) Thin Gap Chamber Magnet system: (3) End-Cap Toroid Magnet (4) Barrel Toroid Magnet Inner Detector: (5) Transition Radiation Tracker (6) Semi-Conductor Tracker (7) Pixel Detector Calorimeters: (8) Electromagnetic Calorimeter (9) Hadronic Calorimeter

The detectors are complementary: the Inner Detector tracks particles precisely, the calorimeters measure the energy of easily stopped particles, and the muon system makes additional measurements of highly penetrating muons. The two magnet systems bend charged particles in the Inner Detector and the Muon Spectrometer, allowing their momenta to be measured.

The only established stable particles that cannot be detected directly are neutrinos; their presence is inferred by measuring a momentum imbalance among detected particles. For this to work, the detector must be "hermetic", meaning it must detect all non-neutrinos produced, with no blind spots. Maintaining detector performance in the high radiation areas immediately surrounding the proton beams is a significant engineering challenge.

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  • $\begingroup$ Good information, but not what I was looking for. $\endgroup$
    – Daniel Griscom
    Jun 10, 2015 at 0:51
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    $\begingroup$ The list of components you give in the first paragraph is for one of the experiments installed on the machine, and the @James' original question seems to be about the operation of the accelerator. $\endgroup$
    – dmckee --- ex-moderator kitten
    Jun 11, 2015 at 22:48

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