Particle Physics at the Energy Frontier

1. Particle Physics at the Energy Frontier Tevatron→LHC & The Very Early Universe Tony Liss Air Force Institute of Technology April 10, 2008

2. Two Views of the Universe • High energy physicists study the smallest, most fundamental objects and the forces between them. • Cosmologists study what there is on the largest possible scales and try to understand how it got that way. But these two very different approaches address many of the same questions: What is the Universe made of & how does it behave?

3. The High-Energy View A proton is made of U U D Add an electron to make a hydrogen atom The matter around us is made up of “quarks” and “leptons” Electromagnetic Strong Weak Gravity And held together by four forces, each with a force carrier: ????

4. Unification of the Forces Higgs Bosons born here Electric Magnetic Weak Strong Electromagnetic Electroweak ? “Very (very)High Energy” “Low Energy” “High Energy” Part way to Einstein’s dream! Theory (“Standard Model”) works up to ~here …And you may notice that gravity isn’t in this picture… STRING THEORY???

5. Cosmology, Particle Physics, the Universe and All That

7. Successes of Particle Physics + Big Bang • Light elements (H to Li) were made in the early universe • And we can calculate how much! About 1 He nucleus for every 10 protons (25% by mass) Predicted abundance depends on density of “baryons” – particles made of 3 quarks (like a proton or a neutron) astron.berkeley.edu/~mwhite/darkmatter/bbn.html The grey band is where the measured & calculated abundances are.

8. But Wait! Recent cosmological measurements put the density of the universe here. Most of the universe is not normal (“baryonic”) matter!

9. Dark Matter (Not a New Idea) Speed of stuff out here Doesn’t match luminous matter in here! There’s DARK MATTER in Galaxies!!

10. Dark Matter In Between Galaxies Too! Motion of a galaxy out here Doesn’t agree with luminous matter in here Wmatter ~ 0.3 from galactic clusters The “Hydra” Galactic Cluster

11. Studying the Universe at Accelerators Accelerate particles to very high energies and smack them together. E=Mc2 : Make new stuff and study how it behaves. Fermi National Accelerator Laboratory This picture shows a proton and antiproton colliding to make a pair of top quarks. Top quarks were discovered 14 years ago at Fermilab Michael Goodman

12. Hadron-Hadron Collisions • Proton-antiproton (Tevatron) or proton-proton (LHC) collisions: Each collision (“event”) is between the hadron constituents. What can happen is…EVERYTHING

13. Cross Sections The total pp cross section is here at ~1011!

14. This happens only once in ~1010 collisions

15. Data Taking (TeVatron) Protons & antiprotons collide at ~2.5 MHz 0.25Hz of W/Z production ~100 Hz of high ET jets ~100 Hz of b-quark production .0002 Hz of top quark production ?? Hz of new physics 20% “Acceptance” Prescale/20 10% “Acceptance” 1% “Acceptance” 10% “Acceptance” ?? “Acceptance” ~20% Analysis Mode 85% to analysis ~1% Analysis Mode ~40% Analysis Mode ?? Analysis Mode ~10-2 Hz for analysis ~10-2 Hz for analysis ~10-5 Hz for analysis ~0.4 Hz for analysis

16. The CDF Detector at FNAL

17. The Mass of the Top Quark • The Mass of the W Boson

18. Measuring the Top Mass There are many subtleties to improve S/B and resolution, but basically… Measure for each of the decay objects

20. Measuring the Top Mass

21. Measuring the W Boson Mass

22. A Window on the Higgs! H t W W W W b W Experimental bound (LEP) The result is marginally inconsistent with the SM… SUSY????

23. Making Higgs Bosons

24. Finding The Higgs The Higgs “couples to mass”, so it’s preferred decay channel depends on its (unknown) mass. As if life were not difficult enough…

25. Looking for Higgs (is hard)

26. No Higgs…yet

27. SUSY Make SUSY particles at an accelerator: • Every quark, lepton and force carrier has a SUSY partner (sparticles). • Sparticles would be made copiously in the early (HOT) universe. • They all decay away quickly, except for the lightest one (neutralino), which can’t. • The dark matter might be made up of neutralinos!! E=Mc2 happening here! www.science.doe.gov/hep/EME2004/03-what-is.html

28. Another Reason to Believe in SUSY? • Einstein’s dream of a “Unified Field Theory”, now needs SUSY: No SUSY SUSY EM Strength of force Strength of force weak strong Energy Energy

29. Searching for SUSY – an example SUSY models come in many different flavors, but one characteristic of many of them is signatures with large “Missing ET” – Undetectable particles whose momentum is unmeasured. In these diagrams “charginos” and “neutralinos” are produced. In their subsequent decay, the lightest “neutralino” is produced but remains undetected.

30. Searching for Charginos & Neutralinos The data Backgrounds What the signal would look like (if it were there)

31. No SUSY So Far • Many searches, no sightings… • The hunt continues… • At LHC there is 7x more “reach” (E=Mc2) for making SUSY particles. • But maybe SUSY isn’t the right model… • We can find it anyway if M<E/c2!

32. On to the LHC!

33. ATLAS Detector at CERN

34. ATLAS is VERY BIG

35. ATLAS

36. A (simulated) Higgs event in ATLAS

37. A Black Hole in ATLAS

38. The Universe as We Know It This is NOT what we thought as recently as 10 years ago!! Atoms Dark Matter 4% 23% 73% Our fabulously successful “Standard Model of particle physics” explains only 4% of the universe… So far… Dark Energy

39. Perspective • Our theories of cosmology and particle physics are extremely successful, but leave significant open questions. • As new phenomena are discovered, we adapt the theories and test them with experiments & observations. • The next ten years of accelerator experiments and cosmological measurements are guaranteed to bring new insights and new surprises!