Recent “Discoveries” in Particle Physics

1. Recent “Discoveries” in Particle Physics An introduction for MARSEF 2012

2. Tiny Neutrinos May Have Broken Cosmic Speed Limit New York Times, September 22, 2011 The physics world is abuzz with news that a group of European physicists plans to announce Friday that it has clocked a burst of subatomic particles known as neutrinos breaking the cosmic speed limit — the speed of light — that was set by Albert Einstein in 1905. If true, it is a result that would change the world. But that “if” is enormous.

3. At Particle Lab, a Tantalizing Glimpse Has Physicists Holding Their BreathsNew York Times, 5 April 2011 Physicists at the Fermi National Accelerator Laboratory are planning to announce Wednesday that they have found a suspicious bump in their data that could be evidence of a new elementary particle or even, some say, a new force of nature…. “Nobody knows what this is,” said Christopher Hill, a theorist at Fermilab who was not part of the team. “If it is real, it would be the most significant discovery in physics in half a century.” One possible explanation for this mysterious bump, scientists say, is that it is evidence of a new and unexpected version of the long-sought Higgs boson. This is a hypothetical elementary particle that, according to the reigning theory known as the Standard Model, is responsible for endowing other elementary particles with mass.

4. How Science is Done

5. Background on Particle Physics, Part I Albert Einstein 1905Speed of Light from EM does not match Newtonian Mechanics Hypothesis: Special Relativity Result of Hypothesis: Matter Energy Equivalence Matter  Energy Energy  Matter

6. Background on Particle Physics, Part I • Particle Colliders: • Accelerate electrons and protons to very high speeds - this gives the particles high kinetic energy • Collide the particles head-on to convert the kinetic energy into mass Animation

7. Background on Particle Physics, Part I Examine the particles created by the collisions. Trajectory of particle is used to determine its charge and mass/energy. Length of path tells particle stability. Repeated experiments allow us to identify many different types of particles and the conditions under which they are created. Results used to form a theory of fundamental particles.

8. How Science is Done

9. The Standard Model • Four Fundamental Forces in Nature Gravity, Electromagnetic, Strong Nuclear, and Weak Nuclear • Six Fundamental Leptons (Light Particles) Electron, e-Neutrino, Muon, µ-Neutrino, Tau, -Neutrino • Six Fundamental Quarks Up, Down, Strange, Charmed, Top, Bottom • Each Lepton and Quark has a standard form and an anti-form.

11. Conservation Laws When particles collide and energy is converted to matter, certain quantities must remain conserved. Energy/Mass Momentum Lepton Number (within flavors) Baryon Number Charm Strangeness Topness Bottomness When a fundamental particle is created, an antiparticle is also created to maintain the conservation laws.

12. Background on Particle Physics: Part II • Where did everything come from? • Isaac Newton: Static Universe • Edwin Hubble: Expanding Universe

13. Background on Particle Physics: Part II • To understand origin, imagine time running backwards from where we are now. • What conditions would have had to exist in the past for the universe to look like it does today?

14. Background on Particle Physics: Part II Light takes time to reach the Earth from distant objects. Therefore, as we look at more distant objects we are also looking back in time.

17. Questions on Big Bang Theory • If all particles were initially created from pure energy, and the create of particles requires an equal creation of anti-particles, where did all of the anti-particles go? • Where does mass come from? • Hypothesis: Higgs Field – non-zero vacuum field that “sticks” to particles to give them their mass.

18. Theoretical Properties of Higg’s Field • The Standard Model predicts four Higg’s Field Bosons, two with charge and two without. • The W+, W-, and Z are three of the bosons and are well understood and experimentally verified. • The 4th is the Higg’s Boson,which is currently theoretical. • Many properties are predicted but not the mass. • Higg’s Boson decays to rapidly to be detected bytracks – must look at decayproducts to predict its existence.

19. Status of the Search • Before 2000: Experiments at Fermilab ruled out the Higg’s Boson having a mass less than 114.4 GeV • July 2011: Fermilab ruled out the region 156 – 177 GeV. The LHC ruled out the region 149-206 GeV (95% Confidence) • December 2011: LHC has narrowed the possible region to 115-130 GeV (125 GeV most probable). Experiments have shown an “excess of events.” at this energy that could be caused by the Higg’s Boson. • March 7, 2012: Fermilab analysis shows excess activity in 115 – 135 GeV that could be Higg’s Boson, but not enough data to rule out that the activity is due to statistical fluctuations (noise). • December 2012?: LHC expected to have enough data by end of 2012 to confirm or reject the existence of the Higg’s Boson.

20. How Science is Done

21. Neutrino Experiment CERN Laboratories • Created Neutrinos • Sent them down 450 mile tunnel between Switzerland and Italy • Recorded Time of Travel. • Resulting Speed: Distance/Time = 300,006,000 m/s • Greater than the Speed of Light. • Repeated the experiment 15,000 times over 3 years before announcing results

22. Neutrino Experiment 22 September 2011: Antonio Ereditato: "We have high confidence in our results. We have checked and rechecked for anything that could have distorted our measurements but we found nothing. We now want colleagues to check them independently." 22 February 2012: Discovery retracted, as researchers found a faulty connection in one of the pieces of equipment. This would have produced a time delay. Correcting for this time delay would put the speed of the neutrinos slower than the speed of light.

23. Lessons from the Neutrino Experiment • Check your connections. • Sometimes the results make giant leaps forward in our understanding. Many times they must be retracted. • Don’t be afraid to publish your findings, but don’t be overconfident in the results.

24. Questions?