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Question - I understand that the particles are guided into collisions by using magnets and directing the path of the two particles. What I don't understand is,

Question - I understand that the particles are guided into collisions by using magnets and directing the path of the two particles. What I don't understand is, how do the researchers know exactly where the particles are located before they have collided? Would not their exact position have to be known to record the collision data and for taking pictures of the collision? Thank you ahead of time for any explanation you provide.

pjc50 8y ago
They're two beams of particles that cross at a point. It's not adequately captioned but I think the image is a cross-section view, with the beam direction "into/outof" the screen.
JshWright 8y ago
They aren't tracking individual particles, they are tracking "packets" of many particles. There are many packets in flight at any time.
kryptiskt 8y ago
They don't take pictures, the particles are recorded by a variety of detectors. For example, a wire chamber records particles through the ionization they cause in a very diluted gas, those ions are then accelerated by the electric field in the chamber and causes a blip when they hit one of the wires. As the particles are tracked all the way through the detector, they can know the state both before and after the collision. Then there are calorimeters that absorbs the debris from the collision and measures the energy of it.
mng2 8y ago
It's essentially statistical. First, the beam. The beam at a collider is actually made out of longitudinal 'buckets' of particles. The buckets are timed to cross at the interaction point inside the detector, where magnetic lens arrangements squeeze the beam as far down in physical size as is practical. By controlling the beam, you know when exactly to look for collision products, and expected collision rates are calculated from particle distributions and cross-sections. Next, the detectors. There are a variety of detectors around the interaction point that serve different purposes. Broadly speaking, they measure deposited energy, and in which direction it is going. That's what physicists are interested in, so they can work out what those particles were. Everything at an experiment like this is modeled and calculated. At the very bottom you have fundamental physics, particles being created and destroyed, modeled in a simulation tool such as Pythia. Once you know what's supposed to come out, you can simulate how the products behave in your detectors, by building a model in a tool like Geant. If you model from end to end, you essentially test physics theory against the hard bedrock of reality.

pjc50 8y ago

They're two beams of particles that cross at a point. It's not adequately captioned but I think the image is a cross-section view, with the beam direction "into/outof" the screen.

JshWright 8y ago

They aren't tracking individual particles, they are tracking "packets" of many particles. There are many packets in flight at any time.

kryptiskt 8y ago

They don't take pictures, the particles are recorded by a variety of detectors. For example, a wire chamber records particles through the ionization they cause in a very diluted gas, those ions are then accelerated by the electric field in the chamber and causes a blip when they hit one of the wires. As the particles are tracked all the way through the detector, they can know the state both before and after the collision. Then there are calorimeters that absorbs the debris from the collision and measures the energy of it.

mng2 8y ago

It's essentially statistical. First, the beam. The beam at a collider is actually made out of longitudinal 'buckets' of particles. The buckets are timed to cross at the interaction point inside the detector, where magnetic lens arrangements squeeze the beam as far down in physical size as is practical. By controlling the beam, you know when exactly to look for collision products, and expected collision rates are calculated from particle distributions and cross-sections. Next, the detectors. There are a variety of detectors around the interaction point that serve different purposes. Broadly speaking, they measure deposited energy, and in which direction it is going. That's what physicists are interested in, so they can work out what those particles were. Everything at an experiment like this is modeled and calculated. At the very bottom you have fundamental physics, particles being created and destroyed, modeled in a simulation tool such as Pythia. Once you know what's supposed to come out, you can simulate how the products behave in your detectors, by building a model in a tool like Geant. If you model from end to end, you essentially test physics theory against the hard bedrock of reality.