©2004 Richard E. Hughes Fermilab; p.1 Studying the Fundamental Particles  Particle physicists see the world as made up of a small number of fundamental particles:  QUARKS: up, down, charm, strange, top, and bottom  LEPTONS: electron, electron-neutrino, muon, muon-neutrino, tau, tau-neutrino  Force carrying particles: photon, W/Z boson, gluon, graviton  Special “mass generating particle”: Higgs  Special Features  Only the up and down quarks, and the electron, are in the matter around us  The masses of the particles vary wildly: the up, down and electron are much less massive than a hydrogen atom, while the top quark is more massive than a gold atom!  The Higgs particle – which we think can help explain these masses of the particles – is predicted by our theory, but has not been observed (yet!)

©2004 Richard E. Hughes Fermilab; p.2 The Fundamental Particles

©2004 Richard E. Hughes Fermilab; p.3 Studying the Fundamental Particles  Some reasonable questions to ask:  Are there any other “fundamental particles”?  Why are the masses of these fundamental particles so different?  Why is the top quark so massive?  Does the Higgs particle really exist?  To answer these questions we need:  To be able to make at least some of these fundamental particles  To be able to study them in great detail  Since particles like the top quark are very massive, we will need a lot of energy to do this (Remember, E=mc 2 )  One way to do this:  Use “Particle Accelerators” and “colliders” to get the necessary high energy to make interesting particles  Use “Particle Detectors” to take “photographs” of these newly created particles

©2004 Richard E. Hughes Fermilab; p.4 Particle Accelerators  Accelerators are machines used to speed up particles to very high energies. This way, we achieve two things: We decrease the particle’s wavelength, so we can use it to probe inside atoms, nuclei, even quarks. We increase its energy, and since E = mc 2, we can use that energy to create new, massive particles that we can study. Tevatron Accelerator at Fermilab

©2004 Richard E. Hughes Fermilab; p.5 FNAL: Fermi National Accelerator Laboratory  Fermilab is located in Batavia, Illinois (about an hour west of Chicago).  Fermilab is home to the Tevatron, the world’s highest- energy particle accelerator.  Fermilab is also a park, with 1,100 acres of prairie- restoration land! Danger of working too hard at physics!

©2004 Richard E. Hughes Fermilab; p.6 The Accelerator Complex Linac Cockcroft-Walton Booster Anti-protons Tevatron

©2004 Richard E. Hughes Fermilab; p.7 Practical Facts  FNAL -- about 2500 employees work there on the payroll.  On any given day, there are probably another users on location  FNAL budget is about $320 million dollars per year  Power cost  Is this worth it?  Currently, the US Gov’t spends less than 0.5% of its total GNP on (ALL) knowledge based scientific research.

©2004 Richard E. Hughes Fermilab; p.8 Beam Facts  How many particles in the beam?  10^14 protons  10^14 antiprotons  Grouped in 36 packets  Total collision energy of 1.8TeV  Each packet has the energy of a car!  But the beam has the width of a human hair!  Protons and antiprotons are circulated in opposite directions about a four-mile-long tunnel. The beams are focused and steered by over a thousand superconducting magnets  When running Fermilab uses 60MW of electricity (about what is used by a small city in the summertime)  How fast are they moving?  Really fast! c

©2004 Richard E. Hughes Fermilab; p.9 Collisions are important events!  After particles have been accelerated, they collide either with a target (fixed target experiments) or with each other (colliding beam experiments).  These collisions are called events.  New particles are created in such a collision. Most of them quickly decay, but we can look at their decay products using detectors. More energy in initial state to make new particles

©2004 Richard E. Hughes Fermilab; p.10 Our detectors are HUGE! ALEPH ALEPH detector at CERN CDF CDF detector at FNAL A lot of HEP detectors are as big as a house -- several stories high! A lot of HEP detectors are as big as a house -- several stories high!

©2004 Richard E. Hughes Fermilab; p.11 The CDFII Collaboration 700+ scientists 55+ institutions 11+ countries Students Postdoc’s Professors Research Scientists

©2004 Richard E. Hughes Fermilab; p.12 A brief history of CDF  1985: First collisions with partial detector  1987: Core detector in place. Jet physics  1988/9: “Run 0” – we got 4x the expected data see lots of W/Z’s  : “Run I” – add silicon detector. Discover the top quark  2001-?: Run II era begins with essentially a new detector, higher collision energy, and more data. We want to discover what hasn’t even been thought of.

©2004 Richard E. Hughes Fermilab; p.13 CDF detector roll-in Feb 2001 Detector weight: 5000 tons. Don’t drop on your toe! “Channels”: Approximately 2 million. Cost of detector: About $400 million (materials and construction only, no salaries).

©2004 Richard E. Hughes Fermilab; p.14 Trying to find a top quark!  What happens when we collide a proton and an anti-proton?  Some jargon: a collision is called an “Event”  If they hit nearly head on, then the energy in this collision can turn into new particles.  What kinds of particles are created?  Many different kinds are possible, as long as the total mass is less than what you would get from E=mc 2 !  Aside from this, exactly which kinds of particles are created is random, although some particles are more likely than others to be created. New particles p p

©2004 Richard E. Hughes Fermilab; p.15 Trying to find a top quark!  It is possible that a given proton-antiproton collision could make a pair of top quarks (actually one top and one antitop)  But this is very rare: only 1 in every 10 billion collisions!  Luckily, we have ~2 million collisions/second  (Doing the math: pair of top quarks made every 1½ hours!)  Let’s imagine this happens. How do we know we have a top quark in this “event”? t p t p

©2004 Richard E. Hughes Fermilab; p.16 Pattern Recognition  It turns out that when top quarks are created, they don’t live very long….only about 1 yoctosecond….  Each top quark decays into two other particles: a b quark (or anti-quark) and one of the force carrier particles: the W boson.  Both the W boson and the b quarks also decay  The b’s decay into a spray of particles called a “jet”  The W’s decay in two ways:  Sometimes 2 “jets”  Sometimes a lepton (electron, muon, tau) and a neutrino jet

©2004 Richard E. Hughes Fermilab; p.17 Trying to find a top quark! jet t p p b (jet) W+W+ W-W- electron t So here is what we can look for Events in which one W decayed to a lepton and neutrino, while the other W decayed to two jets Including the two b quarks, we want events which have a lepton, a neutrino, and 4 “jets”

©2004 Richard E. Hughes Fermilab; p.18 What does an event look like? Fermilab; p.18 ©2004 Richard E. Hughes

Fermilab; p.19 A Candidate top-antitop event Jet 1 Jet 3 Jet 2 Jet 4 electron neutrino

©2004 Richard E. Hughes Fermilab; p.20 How do we identify top-antitop events?  Top pair events have an “M.O”: for example: an electron, a neutrino, and 4 “jets”  How hard is it to find them?  BACKGROUND: Things that share the above “M.O.” but are not top events  There are about as many “BACKGROUND” events expected as top events  How do we tell the difference?  We use Advanced Analysis Techniques  Examples:  Genetic algorithms  Neural Networks  …..

©2004 Richard E. Hughes Fermilab; p.21 Artificial Neural Networks

©2004 Richard E. Hughes Fermilab; p.22 Constructing an Artificial Neural Network

©2004 Richard E. Hughes Fermilab; p.23 What does the data look like? Mostly top quarks up here, about 90 total events Mostly background events down here, about 430 total events

©2004 Richard E. Hughes Fermilab; p.24 A more enriched sample?  Remember that every top-antitop event has two b quarks  Background events tend to NOT have b quarks  Is it possible to identify events in which there are 2 b jets?  YES! Use a device called a silicon vertex detector (SVX) q, l - q ’, t p p b W+W+ W-W- b q, l + q ’, t

©2004 Richard E. Hughes Fermilab; p.25 The SVX  About 1 million channels of info  Extremely precise mesaurements  Precision of ~40 microns (width of human hair)  Excellent b-quark “tagger”

©2004 Richard E. Hughes Fermilab; p.26 Hey, that looks just like….top!  Require top “M.O”: an electron, a neutrino, and 4 “jets”  But additionally require that at least 1 of the 4 jets be identifed as a b-quark by the SVX  What does the neural net say for these events?  They are almost ALL top quarks!

©2004 Richard E. Hughes Fermilab; p.27 What Now?  Now we have the world’s largest (only) collection of top quarks. And we are continually adding to the collection. What can we learn about this quark?  Since the top quark is so massive, maybe it can tell us about mass itself.  Theorist Chris Hill of Fermilab claims that an understanding of the origin of mass would rank as "an achievement on a par with the greatest scientific strides in history, like Newton's establishing the universal law of gravitation or Einstein's connection of energy to mass and the speed of light."