1 Particle Physics, The Mysteries of the Universe, and The LHC Nhan Tran Johns Hopkins University

2 “Particle physics is a modern name for the centuries old effort to understand the laws of nature…” Edward Witten What is Particle Physics? We aim to answer 2 questions: Matter: What is the stuff we are made of? Forces: How does the stuff we are made of interact?

3 Matter What are the most elementary constituents of matter?

4 Forces Forces are the interactions between matter - you already know some of them… …like gravity …and electromagnetic How are forces “felt”? Forces are mediated by the exchange of particles or “force carriers”

5 The universe as we know it… The Standard Model Matter: fermions Quarks and Leptons Antimatter: every fermion has an anti-particle Force Carriers: bosons Strong force (gluons) Weak Force (W/Z) Electromagnetic (photon) Gravity (graviton?)

6 A New “Periodic Table” Hadrons are particles made up of combinations of quarks The proton is a hadron made of two u quarks and one d quark

7 But that’s not the whole story… There are still many things we don’t understand

8 Mysteries of the Universe Origin of mass? The SM predicts a particle called the Higgs which is responsible for giving all elementary particles mass - still undiscovered. Higgs field: Imagine running through a pool… Why are the masses what they are? Why are there 3 families of fermions? Why are we here? Matter-antimatter asymmetry: why is there more matter than antimatter in the universe? Gravity? Why so weak? Grand unification?

9 Mysteries of the Universe Cosmological mysteries Dark Matter: more stuff out there than we see Dark Energy: everything is moving away from us faster than we expect

10 Understanding the mysteries of the universe… We need: Accelerators to collide the particles in a controlled environment Detectors to “see” the resulting particles coming from the collision The experimental challenge is getting particles to interact in the lab and precisely detecting the properties of the resulting particles

11 Accelerators More energy means we can probe: Smaller scales: E ~ 1/size Higher masses: E ~ mass (E = mc 2 !!) Earlier conditions of the universe: E ~ temperature de BroglieEinsteinBoltzmann With more energy, we can get even closer to the Big Bang!

12 The LHC: Large Hadron Collider The LHC will collide particles at energies 7 times greater than ever before!

13 The LHC and The Big Bang The LHC will probe the same energy as when the universe was about 1 picosecond ( s) old!

14 The LHC my apartment!

15 The LHC my apartment! The LHC is an accelerating ring 27 km in circumference straddling the Switzerland- France border.

16 The LHC: A Technical Marvel The LHC will accelerate bunches containing 100 billion protons to energies 14,000 times the mass of the proton colliding them every 25 nanoseconds (40 million times/sec) Two proton beams are circulated in opposite directions around the beam to be collided my experiment… we will discuss it soon

17 The LHC: A Technical Marvel The bunches are given “kicks” by a very powerful electric field, accelerated almost to the speed of light. And are guided in their orbits by a magnetic field 200,000 times that of the Earth in superfluid helium at 1.7K.

18 And out comes…

19 Great! …we can get the particles to collide… …but how do we see the results?

20 How do we “see” particles? We see particles by observing their interactions with matter. A simple example… Unfortunately, most heavy particles do not live long enough for us to see directly semi-stableunstable

21 Putting Humpty Dumpty together again: The Modern Particle Detector Detectors are built like onions where each layer is meant to detect a different type of particle We determine: Direction Momentum Energy Charge Type Using this information, we can piece together the decays of certain particles

22 CMS: Compact Muon Solenoid

23 CMS

24 CMS

25 CMS: how does it work? An overview of how CMS is designed to detect particles

26 CMS: what will it look like? SIMULATION

27 Getting the Data Out T. Virdee (Split08) CMS produces about 40 TB (fills 1000 IPods) per second - too much information! We use a computing farm to reduce the data down to those events we want and save them.

28 What do we do with the data? An example…the search for the Higgs… Theory says that the Higgs should decay like this: H->ZZ->4µ We search for events with 4µ. Adding together their momentums, we can determine the mass of a possible parent particle. If we see a lot more at a certain mass than we expect, it could be a new particle! SIMULATION

29 Exciting times ahead! As of November 20th, the LHC has been circulating beam! As of November 23rd, the LHC is colliding beams! FIRST CMS COLLISION EVENT CMS PRELIMINARY On December 14th, the LHC collided beams at 2.36 TeV, surpassing the Tevatron for highest center-of-mass energy collision

30 “I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.” Sir Isaac Newton Conclusion The LHC has been a project more than 15 years in the making and we are on the verge of reaping the benefits! We can tackle some of the biggest questions in physics What is mass? Why is there more matter than antimatter? What is 95% of the universe made of? Only such experiments will help us to answer these questions