고에너지 물리 특강

1. 고에너지 물리 특강 Lecture 1: Experimental Tools for HEP - Accelerators & Detectors - Observation of fundamental particles Lecture 2: Some recent/future HEP experiments - Belle for heavy-flavor physics and CP violation - COREA for UHECR Experiments of High-Energy Physics

2. Theory vs. Experiment theory calculate physical observables QFT experiment with any necessary approximations

3. Experimental tools • Particle Accelerators • Particle interactions inside matter • Particle detectors

4. Particle Accelerators • “precision instruments constructed on a gigantic scale” • particles are traversing ~106 km for a few seconds while maintaining the path within ~mm • “modern accelerators are like great Gothic cathedrals of mediaeval Europe…” (R. Wilson) • Why accelerate? the more energy, the deeper structure we can probe r p  ħ/2

5. Why not use high-E particles in the cosmic ray?  low flux ;  energies cannot be controlled

6. Electrostatic Accelerators T = qV limited to ~ 1 MeV  voltage breakdown & discharge

7. Linear Accelerator • potential difference b/w the ends of drift tubes • the fields oscillate, but • the particles are protected (from decelerating phase) by the metallic drift tube • the distance b/w gap increases • but soon saturates an everyday proof of special relativity!

8. An example: Stanford Linear Accelerator Center

9. SLAC linear acc.

10. Circular Accelerators cyclotron

11. Cyclotron

12. Cyclotron [Ex] a cyclotron, with extraction radius R = 0.4 m & B = 1.5T fAC = ? Tmax = ? (for p) fAC = fc = qB/2pm = 22.9 MHz Tmax = (qBR)2/2m = 17 MeV • As we increase the energy, relativity must be considered. • fixed freq. cyclotron would not work for very high E • synchronous acceleration is needed!

13. Consider we already attained the desired energy (g = constant) and the particle goes through a circular orbit under B  Synchrotron • f or B (or both) should be changed synchronously with the particle velocity; hence it is called a “synchrotron”

14. a “magic formula” for charged particles Then, for v c, and we obtain a very useful formula [Ex] p = 3 GeV/c, B = 2T; R = ?

15. Synchrotron If we build a cyclotron-style machine,  too much steel (and cost!) is needed… hence, a new design! The beam particles take many turns to achieve the design energy. Q: is it possible to maintain the beam size (within the vac. chamber) for so many turns?beam stability ??

16. Focusing of beams • Phase stability • edge focusing • Strong focusing - FODO lattice F O D O

17. focusing with quadrupole magnet flux return steel

18. Collider vs. fixed target How to derive ?

19. Livingston Plot

20. Colliders

21. Particle Detectors • Detector system: an overview • Particle interaction inside matter • dE/dx • Multiple Coulomb scattering • photon interaction inside matter • Charged particle detection : • Neutral particle detection : • Detector system for real experiment

22. On experimental resolution

23. Detector System • What do we want to measure in a detector system? • position ; event topology, intermediate particle state • momentum ; need “tracking” • energy ; deposited in a localized place ; “calorimetry” • mass ; i.e. particle identification (PID) • charge ; from the curve orientation in the tracking chamber • Constructing (E, ) 4-vector for each particle: • charged : tracking & PID => , m => E=(p2+m2) • neutral : (E, q, f) => is deduced by assuming m and origin

24. How a detector system works For colliding beam experiments For fixed-target experiments Pt=0.3BR

26. Particle interaction inside matter • Energy loss of charged particle • Before a particle can be detected, it must first undergo some sort of interaction in the material of a detector. • EM interaction is the most important • Energy loss as a function of travel distance

27. dE/dx (brief derivation) • Coulomb interaction b/w incident charged particle & another charged particle in the detector material • by transverse Then, in the Lab. frame, (t=0 @ r=b) (Jackson) m = target mass

28. [Ex] energy loss due to bound electrons vs. nuclei

29. dE/dx (brief derivation) • For dE/dx, count the number of interacting particles in the target! bminandbmax ?

30. bmax for dE/dx • consider interaction w/ free electron only if

31. bmin for dE/dx • DE cannot exceed the max. allowed energy transfer for a head-on collision (let Z2 = 1)

32. Bethe-Bloch formula I = ionization potential • dE/dx calculation with quantum correction For small v, For large v, “relativistic rise” minimum ionization

33. Particle ID by dE/dx

34. I p p K p Additional tools for charged particle ID • Time of flight mass p from tracking Mass (GeV) • Cherenkov radiation

35. Multiple Coulomb scattering • energy loss in Coulomb collision with nuclei is small ping-pong ball bowling ball Note: Rutherford scattering formula

36. Multiple Coulomb scattering In any given layer of material, the net scattering is the result of a large # of small-angle deviations (indep. of one another) => “ Multiple Scattering ” a Gaussian distribution for details, see “Intro. to Exp. P.P.” by R. Fernow, Sec.2-7

37. Multiple Coulomb scattering In a layer of thickness deflection angle

38. Multiple Coulomb scattering Ec = “critical energy”

39. B Multiple Coulomb scattering In practice, multiple scattering limits the precision of [ex] determine inside of a solenoid if no scattering, pc = BeR(Gaussian unit) or p = BeR(SI unit) • Traversing a distance x, the angulardeflection is [ p(MeV/c), x(m), B(T) ]

40. Tracking error due to multiple scattering Compare with • why 1/2 ? • consider only projection onto the plane of the trajectory where

41. Energy loss via radiation

43. C Pb Photon interactions in matter

44. Pair production In the high energy limit (Eg>>2me), the mean distance a photon will travel before pair producing is “conversion length” Note: Why are XP and X0 similar? => because bremsstrahlung and pair production are simply time and space rearrangements of the same process

45. Photon interactions in matter

46. Calorimetry • Most calorimeters measure the ionization energy deposited by all the charged particles in the "showers" produced as the particle is absorbed. • EM shower • Hadronic shower • The scale length • EM: radiation length, X0 (~2cm in Fe); • relevant for both bremsstrahlung & pair production • Hadronic: mean hadronic interaction length, lI (0.2m in Fe).

47. Scintillation detectors

48. PhotoMultiplier Tube

49. Belle EM Calorimeter Tower structure projected to the vicinity of IP. 30 cm long (16.2 X0), 8736 CsI(Tl) crystals (6624 in barrel). 12<  < 155 (lab frame) Inner radius – 1250 mm