Particle Detectors Overview

1. Particle Detectors Overview Dave Barney, CERN (biased towards the CMS detector!) David Barney, CERN

2. Particle Detectors Overview • What does a particle detector need to do? • The first particle detectors • The challenges of modern detectors • Rising to the challenge - let’s design a detector! • The LHC detectors and components • What might physicists get excited about in a few years from now? David Barney, CERN

3. What we do at CERN: Smash things together and see what happens! David Barney, CERN

4. Spherical Detector Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

5. Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Forward Detector David Barney, CERN

6. What does a particle detector need to do? • Need to determine: • What particles do we see? • Where did they come from and where do they go? • What were their energies and momenta? • In order to understand: • What happened in a collision between particles? • Has something interesting been created? Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

7. The first particle detectors Cloud chamber (1911 by Charles T. R. Wilson, Nobel Prize 1927)chamber with saturated water vapour;originally developed to study formation of rain clouds Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Positron loses energy in lead: narrower curvature lead plate Was used at discovery of the positron (1932 by Carl Anderson, Nobel Prize 1936) upward going positron David Barney, CERN

8. The first particle detectors Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Liquid hydrogen “bubble chamber” The hydrogen acts as a target (for incoming particles) and a detector David Barney, CERN

9. The first particle detectors Particle colliding with a proton in liquid hydrogen - A “Bubble Chamber” Many people employed to look through these photos to understand what happened! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

10. Scanning Photographs Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

11. The first particle detectors Spark Chambers Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Big one in the CERN microcosm David Barney, CERN

12. The first particle detectors • Phil. Mag. Xiii (1896)392 • Conduction of electricity through gases (Ist ed 1903) • Proc. of Royal Soc. A81(1908)14 1 • The Geiger-Müller tube – 1928 • Tube filled with inert gas+ organic vapour • Central thin wire (20 – 50 µm) • High voltage between wire and tube Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts • Strong increase of E-field close to the wire • electron gains more and more energy • above some threshold (>10 kV/cm) • electron energy high enough to ionize other gas molecules • newly created electrons also start ionizing • avalanche effect: exponential increase of electrons (and ions) • measurable signal on wire • organic substances responsible for “quenching” (stopping) the discharge David Barney, CERN

13. E E The first particle detectors • Geiger-Müller tube just good for single tracks with limited precision (no position information) • Multi Wire Proportional Chamber (MWPC) • (1968 by Georges Charpak, Nobel Prize 1992) Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts cathode plane (-) anode plane (+), many wires, a few mm apart charged particle cathode plane (-) Georges Charpak, Fabio Sauli and Jean-Claude Santiard David Barney, CERN

14. The challenges of modern detectors • We don’t really know what we are looking for! • The “interesting” things we are looking for are very rare • Need to make millions of collisions every second! • Cannot use conventional photography • They are also unstable….. Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

15. Unstable Interesting Particles Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts The interesting things (the dinosaurs!) disappear almost instantly. We “see” the resulting particles – so we have to be like detectives – look at the evidence to see what happened! David Barney, CERN

16. The challenges of modern detectors • Each collision produces many hundreds of particles • The energies/momenta of the particles involved are huge • The detectors are very complex and have many layers • They also need to be big! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts VERY BIG!! David Barney, CERN

17. The challenges of modern detectors Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Have to understand this sort of image 40 million times per second! David Barney, CERN

18. A “simple” collision at LHC (simulation) Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Higgs  4 muons Where are the muons? Red lines show the muons (cheating!) David Barney, CERN

19. Let’s add a magnetic field! Charged particles bend in the magnetic field Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts The lower the particle momentum (~speed) the more they bend. Now the muons are clear! David Barney, CERN

20. A typical detector for the LHC #1 Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts The “CMS” detector for LHC Each colour shows a different layer This is the view along the beam direction David Barney, CERN

21. Let’s design a detector #1 • Start with a BIG and powerful magnet! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

22. The “Gothic Cathedrals of the 21st Century” ATLAS Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

23. Transporting and constructing the CMS solenoid Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

24. “Swivelling the CMS solenoid” Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Coil is constructed vertically but needs to be horizontal! David Barney, CERN

25. Inserting the CMS solenoid into the yoke Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

26. Standing in the CMS solenoid – at 100K! CMS solenoid is 13m long, 6m diameter and provides a magnetic field of 4 teslas when a current of ~19500 Amps is passed down it – coil is made of superconducting niobium-titanium and operates at -269oC With the return yoke it weighs around 12000 tonnes! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

27. Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Tracking Detectors To measure the direction and momenta of charged particles Thin sensors – do not disturb the trajectories of the particles: must go on the inside of the detector David Barney, CERN

28. A basic “Tracker” Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Multiple thin layers of, for example, silicon sensors David Barney, CERN

29. Example Silicon Detector Construction 25mm thick wires ultrasonically bonded David Barney, CERN

30. CMS Tracker Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Many layers of silicon sensors Silicon sensors are reverse-biased diodes. Electrons & holes created in the extended depletion region due to the passage of a charged particle make a signal David Barney, CERN

31. Calorimeters • Electromagnetic Calorimeters – sensitive to photons, electrons, positrons • Hadronic Calorimeters – sensitive to “hadrons” (particles containing quarks) such as protons, neutrons, pions etc. • The calorimeters “stop” the incoming particles so must go outside of the “tracker” To measure the energies of different types of particle David Barney, CERN

32. A basic “sampling” calorimeter Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Total # of particles is proportional to energy of incoming particle Light materials (green) produce a signal proportional to the number of charged particles traversing David Barney, CERN

33. ATLAS tile calorimeter Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

34. CMS Electromagnetic Calorimeter Crystals Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Lead tungstate (PbWO4) crystalsnearly as dense as lead! Crystals initiate showers and produce light David Barney, CERN

35. Let’s design a detector #3 • Need to identify the different types of particle • Combination of signals in the tracker and calorimeters can identify many particles • Also have dedicated sensors for muons • These are the only particles that travel all the way through the calorimeters without stopping Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

36. RESISTIVE PLATE CHAMBERS • Place resistive plates (Bakelite or window glass) in front of the metal electrodes • Sparks cannot develop because the resistivity and capacitance will allows only a very localized discharge • Large area detectors can be made • Fast – kHz/cm2 Muon Detectors – e.g. RPCs Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

37. Muon Detectors • ATLAS 1200 muon chamber with 5500 m2 Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts CMS muon detectors in magnet yoke Muondetectors 37 David Barney, CERN

38. Particle Identification Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

39. LHC Detectors 39 David Barney, CERN

40. LHC Detectors ATLAS CMS Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts LHCb ALICE David Barney, CERN

41. ATLAS CMS The two giant detectors for the LHC Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

42. Lowering CMS underground Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

43. The “Gothic Cathedrals of the 21st Century” The ATLAS detector 100m underground Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

44. In the CMS cavern Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

45. What might a real Higgs event look like? 2 muons Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts 2 electrons David Barney, CERN

46. The physicist’s gold! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts IF the Higgs particle exists & IF it has a mass around 130 GeV This is the signal we will see after about a year of running! David Barney, CERN

47. Some final thoughts on the technology • The LHC detectors are the most complex scientific instruments ever made • A typical LHC detector has about 100 million individual sensors (c.f. a typical digital camera with ~6 Mpixels) • But it takes a “digital photo” 40 million times every second! • The detectors have to operate for at least ten years with little or no intervention • Technology – sensors and electronics – are cutting-edge Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN

48. People • CMS and ATLAS have about 2500 collaborators each, including more than 1000 students! • They come from all over the world - about 80 countries • We have been working on these detectors for the past ~15 years – and they haven’t even started operation yet! Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts David Barney, CERN