1. Hadron Collider Physics Jay Hauser UCLA Some slides copied from Peter Richardson (Durham U.)

2. Outline 1) A short physics introduction  Electroweak unification and the Higgs Boson 2) Why Hadron Colliders?  Going beyond fixed-target and e + e - circular colliders.  Constituents of the proton.  How to calculate cross-sections in proton collisions. 3) Current generation of hadron colliders  Tevatron at Fermilab near Chicago.  Large Hadron Collider at CERN (Switzerland) 4) Future linear e + e - and muon colliders

3. Ideas of Force Unification - 18731967 theory 1983 expt. 1686, 1915

4. Weak + Electromagnetic Unification Energy scale about 100 GeV. The theory hinges on the “Higgs” particle, energy<1000 GeV. Enigmatic Higgs particle is not yet observed, does it exist? If the Higgs doesn’t exist, there is a theorem that there must be some additional force to be discovered, with effects visible in the <1000 GeV range. Goal of the “current” generation of colliders is to find the Higgs or its replacement. Current “Tevatron” probably can’t find the Higgs, future “LHC” probably will (year ~2009).

5. Why Hadron Colliders (I)? Before colliders, there was “fixed-target” – a beam of particles hits a block of matter. Before colliders, there was “fixed-target” – a beam of particles hits a block of matter. –Modern era of accelerators started in 1931. –Relativistic disadvantage: E CM increases slowly as sqrt(E beam ) Colliders: counter-rotating beams within a vacuum pipe. Colliders: counter-rotating beams within a vacuum pipe. –Advantage: E CM = 2*E beam increases faster –Developed around 1970. –Need pretty intense beams for a worthwhile rate of interactions.

6. Accelerators: Bigger, and Stronger Magnets  Higher Energy Berkley 11 inch This is still pre-WW II 1931 Lawrence and Livingston operate the first Cyclotron

7. Modern Particle Accelerators The particles gain energy by surfing on the electric fields of well-timed radio oscillations (in a cavity like a microwave oven) The particles are guided around a ring by strong magnets so they can gain energy over many cycles and then remain stored for days

8. Historical Development of Colliders Beam More energy: colliding beams Beam hits matter (fixed-target)

9. Why Hadron Colliders (II)? Electron-positron (e + e - ) colliders (>1970) are excellent! Electron-positron (e + e - ) colliders (>1970) are excellent! –The Feynman diagrams are simple. –Positrons circulate in the same set of magnets as the electrons. –You know the initial state energy and momentum (zero) precisely by the magnetic field and the radius of the electron path. Many great things were discovered with e + e -, but… Many great things were discovered with e + e -, but… e-e+ 

10. Why Hadron Colliders (III)? Electrons are by far the lightest particles. Electrons are by far the lightest particles. Therefore, magnetic fields accelerate them a lot, and acceleration of charges results in electromagnetic “synchrotron” radiation. Therefore, magnetic fields accelerate them a lot, and acceleration of charges results in electromagnetic “synchrotron” radiation. For highly relativistic particles, this radiation depends on the relativistic  =E/mc 2 factor as: For highly relativistic particles, this radiation depends on the relativistic  =E/mc 2 factor as: So electrons, having the lowest mass, radiate like crazy if E (hence  ) is high. So electrons, having the lowest mass, radiate like crazy if E (hence  ) is high. Circular e + e - machines topped out with the LEP accelerator, which reached about 200 GeV energy, which required massive amounts of power to keep the electrons going around. Circular e + e - machines topped out with the LEP accelerator, which reached about 200 GeV energy, which required massive amounts of power to keep the electrons going around. So if you want more center-of-mass energy than that, use protons, which are 2000 times more massive than the electron. So if you want more center-of-mass energy than that, use protons, which are 2000 times more massive than the electron.

11. Colliding Proton/Antiproton Beams No problem with synchrotron radiation energy loss, but… Like throwing bags of marbles at each other at high velocity: Marble-marble collisions are interesting, not bag-bag collisions Fortunately, the number and arrangements of the “marbles” has been measured by other experiments

12. Proton Constituent Particles Proton internal structure is quarks and gluons Also, there are 2 up (u) and 1 down (d) “valence” quarks There are also gluons, holding them together, that carry 50% of the proton momentum! There are also “sea” quarks! Argh – at a fundamental level, what is the beam??

13. Probability Functions Suppose the beam energy was 1000 GeV, and you knew that each valence quark carried 1/6 of the proton momentum, and there were 5 gluons carrying 1/10 of the proton momentum, and there were no sea quarks. Then you would have 2 u and 1 d quarks of 167 GeV, and 5 gluons of 100 GeV in each proton. Assuming no multiple scattering (Born approximation of scattering Quantum Mechanics), you could calculate all the scattering.

14. Real Hadron Scattering The constituents don’t take on exact fractions of proton momentum, but have probability functions called “parton distribution functions” (PDFs) PDFs measured in high-energy electron-proton and neutrino- proton experiments. Good cross-checks between them, so it all makes sense. The initial state is a probability function you have to integrate over. For example, for quark-antiquark scattering:  = Integral [ (fundamental cross-section) * (prob that beam A has quark with momentum P A ) * (prob that beam B has antiquark with momentum P B ) ]

15. Top Events Let’s start by thinking about how the top quark is produced Let’s start by thinking about how the top quark is produced The top quark is produced by the strong interaction. The top quark is produced by the strong interaction.

16. Collider Experiments

17. Particle Physics Detectors A tracking chamber measures the energies of charged particles (with aid of a big magnet to bend them) A calorimeter measures energies of neutral particles A muon system sees only penetrating muon particles Used to take pictures (bubble chambers), now we use fully electronic readout

18. Timeline of Proton Collider Discoveries 1975198019851990199520002005201020152020 W/Z bosonsTop quarkHiggs Supersymmetry Proton- proton Proton-antiproton Proton-proton

19. Proton-Antiproton Collisions at Fermilab (Chicago) The Tevatron accelerator, 6 km circumference The CDF (Collider Detector at Fermilab) experiment

20. The LHC (Large Hadron Collider) at the CERN Laboratory

21. The CERN Laboratory near Geneva, Switzerland France Switzerland

22. The LHC The LHC is built in the old LEP tunnel at CERN near Geneva. The LHC is built in the old LEP tunnel at CERN near Geneva. It will collide protons at an energy of 14 TeV starting in 2007. It will collide protons at an energy of 14 TeV starting in 2007. There will be four experiments. There will be four experiments. Two ATLAS and CMS to look for the Higgs, LHCB to look at B physics and ALICE for heavy ion physics. Two ATLAS and CMS to look for the Higgs, LHCB to look at B physics and ALICE for heavy ion physics. Here I will concentrate on the physics for ATLAS and CMS. Here I will concentrate on the physics for ATLAS and CMS.

23. LHC Experiments The two general purpose LHC experiments ATLAS and CMS follow the general design we have just considered. The two general purpose LHC experiments ATLAS and CMS follow the general design we have just considered. ATLAS CMS

24. The CMS Endcap Muon System Chambers produced at Fermilab Equipping with electronics and testing at UCLA 300,000 data channels “trigger” electronics built by UCLA Support from UC Riverside and UC Davis scientists

25. Start from: 40 million events/sec x10 million sec/year (30% run eff.) x10 years =4x10 15 events Data Analysis End result: Search for Higgs particle Look for data > background rate ~40 events excess 10 -14 factor: Each Higgs event is like a 1g needle in a 100 million metric ton haystack

26. How to Find Needles in Large Haystacks... Multi-step approach: I) Special-purpose 40 MHz Electronics “Level 1 Trigger” II) Fast “online” Computers “Level 2 Trigger” III) “Offline” Analysis Crunch Petabyte data store (1 Million Gigabytes) UCLA UCSD & UCLA Caltech

27. Higgs Signals By looking at a large number of different signals the LHC can discover the Higgs over a wide mass range. By looking at a large number of different signals the LHC can discover the Higgs over a wide mass range. This range more than covers the mass excepted from the precision electroweak data. This range more than covers the mass excepted from the precision electroweak data. The LHC should discover the Higgs. The LHC should discover the Higgs.

28. Hadron vs. Lepton Collisions The Tevatron is currently running at 1.96TeV centre-of- mass energy colliding protons and antiprotons. Will continue till LHC start up in 2007. The Tevatron is currently running at 1.96TeV centre-of- mass energy colliding protons and antiprotons. Will continue till LHC start up in 2007. The LHC will start in 2007 and run for about 10 years colliding protons at 14 TeV. The LHC will start in 2007 and run for about 10 years colliding protons at 14 TeV. People are working hard on the design of electron- positron Linear Colliders for the future. People are working hard on the design of electron- positron Linear Colliders for the future. –No synchrotron radiation –But have to accelerate the particles very forcefully to reach high energy in one pass (linear accelerator already many km long)

29. The Long-Term Future of Colliders A future linear collider (ILC for International Linear Collider) operating between 500 GeV and 1 TeV will hopefully be built to start data taking some time after LHC start-up. A future linear collider (ILC for International Linear Collider) operating between 500 GeV and 1 TeV will hopefully be built to start data taking some time after LHC start-up. A second generation linear collider operating at energies of up to 5 TeV could then be built to explore higher energies (e.g. the CLIC research project at CERN). A second generation linear collider operating at energies of up to 5 TeV could then be built to explore higher energies (e.g. the CLIC research project at CERN). These machines will measure the properties in more detail. These machines will measure the properties in more detail. There are other proposals to build a neutrino factory as the first step towards a muon collider. This would be on the same sort of timescale as a second generation linear collider. There are other proposals to build a neutrino factory as the first step towards a muon collider. This would be on the same sort of timescale as a second generation linear collider.