1. M. Gilchriese - March 2000 ATLAS at the Large Hadron Collider A Particle Physics Detector at the Energy Frontier M. Gilchriese Lawrence Berkeley National Laboratory

2. M. Gilchriese - March 2000 2 Outline Physics motivation - why are we doing this? What is the Large Hadron Collider? Introduction to the ATLAS detector A film interlude The experimental environment Tour of ATLAS detector technology Pointers to additional information

3. M. Gilchriese - March 2000 3 Physics Motivation Experimental and theoretical work over the last three decades has resulted in the “Standard Model” that, so far, describes with remarkable success the “fundamental” particles and the forces that act between them. Nevertheless there many mysteries that are not explained by the “Standard Model”. Among these are –is there a field - the Higgs field or equivalent - that explains the very different masses of the basic building blocks, the quarks, leptons and the quanta of the fundamental forces? If so, find this particle(or particles). –does supersymmetry exist ie. are there partners to each of the known building blocks with different mass and spin? –do the quarks and leptons have substructure? –can we observe direct manifestations of extra dimensions?

4. M. Gilchriese - March 2000 4 Standard Model

5. M. Gilchriese - March 2000 5 Colliding Beams In parallel with the theoretical developments over the last 30- some years, has been the development of colliding beam accelerators to achieve the highest possible energies. During this time, electron-positron, proton-proton and antiproton-proton colliders have been built with ever increasing energies to continue to push the “energy frontier” in particle physics. Many(but definitely not all!) of the discoveries of new quarks(charm, top), leptons(tau) and of the force quanta(gluons, W, Z) have come from experiments at these colliders. The Large Hadron Collider will be the highest energy collider in the world, and is likely to remain so for a long time.

6. M. Gilchriese - March 2000 6 Large Hadron Collider(LHC) Located at the CERN, the European Laboratory for Particle Physics Will be operational by 2006. Collides protons-on- protons(and can also do heavy ions-on-heavy ions). Center-of-mass energy 14 TeV High intensity(luminosity), more than 10x current proton-antiproton colliders.

7. M. Gilchriese - March 2000 7 Aerial View of the LHC Circumference of 27 km Main CERN Site

8. M. Gilchriese - March 2000 8 LHC Underground Layout

9. M. Gilchriese - March 2000 9 LHC Magnets Superconducting dipoles and other magnets guide and focus the proton beams and bring them into collision at multiple points around the ring. Magnets are cooled by superfluid Helium at 1.9 o K to achieve the highest possible magnetic field with the “standard” superconductor used.

10. M. Gilchriese - March 2000 10 A Toroidal LHC ApparatuS Calorimeters Inner Tracking Superconducting Toroids Muon Detectors ATLAS Tall person Superconducting Solenoid

11. M. Gilchriese - March 2000 11 International Collaboration 2000 scientists 150 institutions 35 countries

12. M. Gilchriese - March 2000 Roll the Film!

13. M. Gilchriese - March 2000 13 LHC Experimental Environment Proton collisions are messy! Each proton can(crudely) be thought of as a collection of constituents/virtual particles. The “hard”, high energy(actually transverse momentum) collisions of these constituents are of interest to probe the smallest distances and to produce the highest mass new particles The “soft” collisions are background to the interesting, hard collisions.

14. M. Gilchriese - March 2000 14 Luminosity and Event Rates An interaction between the counter-rotating protons is called an “event”. The rate of these events depends of the type of interaction{the cross section(  )} and the luminosity(L). Rate = L x  LHC luminosity = 10 34 cm -2 sec -1 “Soft” collisions => 10 9 events sec -1 Most interesting events are much, much rarer, few per second or less => on-the-fly filtering of data

15. M. Gilchriese - March 2000 15 A Toroidal LHC ApparatuS Calorimeters Inner Tracking Superconducting Toroids Muon Detectors ATLAS Tall person Superconducting Solenoid

16. M. Gilchriese - March 2000 16 What Is Detected? Detect Electrons Muons Taus(not so easy) Photons Jets(will explain) Original quark type(b,c,s) sometimes Neutrinos or other non-interacting particles How? Electromagnetic calorimetry/tracking Absorber/tracking Tracking/calorimeter Electromagnetic calorimetry/tracking Calorimeter/tracking Secondary vertices/tracking Calorimeter Detection “Onion”

17. M. Gilchriese - March 2000 17 Basics of Particle Detection Liberation and collection(sometimes also amplification) of charge(ionization) in –solid(eg. silicon) –gas(usually argon + other gases) –liquid(eg. liquid argon) or creation of light by ionization(scintillation) that is converted to charge(eg. by photomultiplier tube) Followed by amplification(if needed), storage, processing…in electronics elements. Within ATLAS there are more than 10 8 individual electronics elements. This is only possible by the extensive use of integrated circuit technology.

18. M. Gilchriese - March 2000 18 Tracking Detector Silicon pixel and strip detectors and wire/gas detectors. Inside solenoid(2 Tesla field) to measure momentum of charged particles. 7m Superconducting Solenoid

19. M. Gilchriese - March 2000 19 Elements of the Tracking Detector Strip detector Hybrid Wire bonds Front-end ICs 6cm Higher granularity and resolution near collision point. Granularity sizes are –Silicon pixel detector 50µ x 400µ –Silicon strip detector 80µ x 12cm –Straw tube/wire gas 4mm x 1m Straw tubes Gas-filled tube Wire at HV

20. M. Gilchriese - March 2000 20 Charged Particle Tracking TRT Silicon strip detectors Silicon pixel detectors Computer reconstruction Pattern recognition This particular event shows the characteristics of “jets” Jets are created from the quarks and gluons formed in the collisions. The quarks and gluons combine to form hadrons(pions, kaons, protons…) that are detected(if charged) by the tracking detectors or by the calorimetry(charged or neutral).

21. M. Gilchriese - March 2000 21 Electromagnetic Calorimetry

22. M. Gilchriese - March 2000 22 Liquid Argon Detector Electromagnetic Shower Ionization created by electromagnetic(EM) showers(in lead mostly) is detected in liquid argon.

23. M. Gilchriese - March 2000 23 EM Calorimeter Elements Location and energy of EM showers measured

24. M. Gilchriese - March 2000 24 Detecting Electrons Electrons are identified and their energies measured by combining tracking(is there a track) and the EM calorimeter as shown in this computer simulation of a Higgs particle decay to four electrons.

25. M. Gilchriese - March 2000 25 Hadronic Calorimetry Energy from hadrons is detected in the combination of the the EM and Hadronic calorimetry. Goal is to measure well as much of the energy in an event as possible => smallest possible holes. And the direction and magnitude of the energy. Missing (transverse) energy(eg. from neutrinos) can also be inferred.

26. M. Gilchriese - March 2000 26 Scintillation Tile Calorimeter Scintillating Tile Photomultiplier Tube Scintillating Fiber Steel Hadrons interact in steel producing showers of particles. These create light in the scintillating tiles. The amount of light is proportional to the energy. Light is converted to charge by photomultiplier tubes.

27. M. Gilchriese - March 2000 27 Detecting Muons Combine tracking information with fact that muons penetrate material - see next slides. Computer reconstruction of Higgs particle decay into two muons and two electrons

28. M. Gilchriese - March 2000 28 Big Superconducting Magnets Will be world’s biggest superconducting toroids to measure muon momenta using precision wire/gas tubes - see next page.

29. M. Gilchriese - March 2000 29 Muon Position Measurements Pressurized, gas- filled tube. Wire at HV “Acres” of very precise (100 Micron) measurements

30. M. Gilchriese - March 2000 30 Data Processing The data obtained from all of the detector elements ultimately ends up on permanent storage accessible to computers. Only a small fraction, roughly 1 part in 10 7, of the events created in the proton-proton collisions ends up on permanent storage. Computing power in all of the collaborating countries will be used to analyze the data. The goal(shared with other areas of science) is to make analysis of data possible via a world-wide data network “grid” accessible from as many places as possible.

31. M. Gilchriese - March 2000 31 Additional Information ATLAS has an educational Web Site (under continuous construction/improvement) at http://pdg.lbl.gov/atlas/atlas.html This includes copy of the movie. And there are additional educational resources at http://www-pdg.lbl.gov/