Anatomy of a collider detector

1. Anatomy of a collider detector Silicon vertex detectors- small but important

2. Inquiring minds want to know… • the energy of the final state particles (calorimeters) • the momentum of the final state particles (tracking detector surrounded by a magnetic field) • the trajectory of the final state particles (tracking detector) One more thing: you would like to know the identity of the final state particles. Once these quantities are known, one can apply conservation of energy and momentum and reconstruct the collision “event”. This is basically freshman physics, with some relativistic corrections thrown in.

4. Resonance particles

5. The Z resonance

6. Z decay into leptons

7. There are a huge number of known particles

8. Nature tends to be simple…following in the tradition of Mendeleev, assume the large number of observed particles are just different combinations of a few fundamental building blocks.

9. Evidence for quarks

10. As with the periodic table, this chart predicted that there should be certain combinations of quark states that had not been discovered yet…and these predictions have turned out to be correct.

12. Quantum chromodynamics Governs how quarks can be combined into composite particles. Gluons are the force carriers for the color force. A color interaction In analogy with electric charge, except there are more than two Particles are color neutral.

13. color force and pion interactions

14. High energy particle collisions and Jets Example: decay of the Z into jets

15. Good "quantum numbers" Like the conservation of mass-energy, momentum and charge, there are other quantum numbers that are conserved in an interaction. Lepton number Baryon number

16. The last quark? The tau lepton was discovered in 1977. If there are three generations of leptons, there must be three generations of quarks! Since then, the “botton” and the “top” have been discovered.

17. W b t • The top was the last quark to be discovered • It weighs 175 times more than the proton! • It has essentially no lifetime.

18. What is a b quark and why do we care? b 500 microns • b quarks are very massive- more than 4 times the proton mass • b quarks are relatively long lived ~1 picosecond • can travel a measurable distance (about 500 microns before decaying)

19. Electroweak theory Just as the electric and magnetic force were discovered to be related by electromagnetism (and now we know tat they are both carried by the photon). The weak and the electromagnetic force have been discovered to be different manifestation of the same thing. The weak force is weak and short ranged because its carriers are heavy. At high energies (where the force carriers are real, and their rest mass energies are negligible) the weak and electromagnetic forces have the same strength. These conditions occurred in the early universe.

20. Grand unified theories …and the history of the universe… If the weak and electromagnetic forces are different manifestations of the same underlying force, are they all? Was there just one force in the early universe?

21. How do we "see" a neutrino? In physics, any possible interaction can proceed backwards. The process of neutrino capture is the same as the beta decay of a neutron, but in reverse time. The interaction is rare because the W mass is really heavy…80 times the mass of a proton!

22. ne m- e- The neutrino is observed by “seeing” the product of its interaction with matter. Electron neutrino nm Muon We don’t see the neutrino coming in, but its products are charged particles.

23. Cable that carries power in and information out digital optical modules (essentially a camera) The “wake” of a muon traveling through the ice

24. Are neutrinos their own antiparticles? The results of searches for “neutrino-less” double beta decay may give us a clue. In this reaction, two beta decays occur simultaneously (a very rare event!) and if they are one another’s own antiparticle, they can annihilate.

25. How do we know how the sun works? The sun is a fusion reactor Neutrinos are produced in fusion reactions, so for many years people counted the number of neutrinos coming from the sun. They saw too few until they realized that neutrinos are “shape-shifters” and can assume different identities. e n

26. an image of the Sun in neutrinos

27. Our current view of matter (subject to change)