Eric Prebys Fermilab 4/15/2008

 430 BCE – Greek Philosopher Empedocles theorizes that all things are made of four elements: Air, Earth, Fire, and Water  ~400 BCE – Democritus (as in “Democracy”) hypothesizes that everything can be cut into smaller and smaller pieces, until you get to “atomos”, the smallest possible piece (not too far off the mark)  Unfortunately, Aristotle didn’t accept this, and little happened for the next 2000 years  17 th and 18 th century: lots of important experiments resurrect “atomic theory”  Much work done by Alchemists searching for “The Philosopher’s Stone”  1808 – Robert Dalton publishes “A New System of Chemical Philosophy”  Matter consists of fundamental “elements”, which are comprised of a individual “atoms”  Different Atoms combine to form “molecules” 4/15/ Rotolo Middle School

 1896 – Henri Becquerel discovers radioactivity  1897 – J.J. Thompson discovers the electron  1911 – Ernest Rutherford probes the structure of the atom in the first true “particle physics experiment” Backward scattered particles prove small, positive nucleus, and disprove “plum pudding” model (where positive and negative charge are mixed) The “accelerator” was a natural radioactive source 4/15/ Rotolo Middle School

 Classical Physics:  “Fields” produce continuous “forces”  Forces produce “acceleration”  Example: electric field + + Electric field Charged particle 4/15/ Rotolo Middle School

 Quantum Physics  Discrete interactions produce changes in “state”. The “field” determines the probability this will happen.  Interactions mediated by “virtual particles”  Each has a momentum + + Charged particle “Planck’s Constant” Wavelength 4/15/ Rotolo Middle School

 In quantum mechanics, “observation” requires “interaction”. Example: We see because light is reflected into our eyes Light is made up of photons, which carry momentum and can therefore move what we are looking at (at least a little) Observation always affects what is observed!! 4/15/ Rotolo Middle School

 We can use light to measure down to the size of its wavelength:  Quantum-mechanically, not just light, but all particles have a wavelength, determined by momentum Resolution of measurement Particle wavelength “Planck’s Constant” momentum  The smaller the scale we want to probe, the higher the momentum (and energy) we need 4/15/ Rotolo Middle School

 Einstein tells is mass is energy  Particle accelerators use energy to create mass Energetic, light particles come in Heavy, less energetic particles out 4/15/ Rotolo Middle School

 First predicted by Paul Dirac in 1930, as the result of a mathematical equation  Postulated that “beta+” particle was an anti-electron  Predicted “antiproton”, which as discovered in 1955  Generally, for any matter, there is antimatter, with equal mass and opposite charge  Some particles are their own antiparticle example: photon  Energy produces equal amounts of matter and antimatter  Matter and antimatter can annihilate to produce energy. 4/15/2008 Rotolo Middle School 9

 We normally measure particle energy in “electron volts” (eV), where this is the energy of a particle with an electron charge accelerated through 1 volt electrical potential  1 eV = 1.6x Joules  Also use standard multiples  1 keV = 1,000 eV  1 MeV = 1,000,000 eV  1 GeV = 1,000,000,000 eV  1 TeV = 1,000,000,000,000 eV  Because energy is related to mass (E=mc 2 ) we also use “equivalent energy” to express mass  1 eV/c^2 = 1*1.6x /(3x10 8 ) 2 = 1.77x kg  Some typical masses  Electron: 511 keV/c 2  Proton: 935 MeV/c 2 ~ 2000 x (electron)  Top Quark: 171 GeV/c 2 ~ 200 x (proton) 4/15/ Rotolo Middle School

The simplest accelerators accelerate charged particles through a static (constant) field. Example: vacuum tubes Cathode Anode Limited by magnitude of static field: - TV Picture tube ~keV - X-ray tube ~10’s of keV - Van de Graaf ~MeV’s Solutions: - Alternate fields to keep particles in accelerating fields -> “Radio Frequency (RF) acceleration” - Bend particles so they see the same accelerating field over and over - > cyclotrons, synchrotrons 4/15/ Rotolo Middle School

Fermilab Linac Stanford Linear Accelerator Center (SLAC) 4/15/ Rotolo Middle School

 1930 (Berkeley)  Lawrence and Livingston  K=80KeV ” Cyclotron –Lawrence, et al. (LBL) –~19 MeV (D 2 ) –Prototype for many 4/15/ Rotolo Middle School

14  Fermilab  Built ~1970  200 GeV Protons  Later 400 GeV  Later 980 GeV x 980 GeV collider  Alternating Gradient Synchrotron (AGS)  Built at Brookhaven in 1960  33 GeV protons  Later converted to ions (RHIC) 4/15/2008

 CERN  On Swiss-French border  LEP  27 km in circumference!!  Built in 1980’s as an electron positron collider  Large Hadron Collider (LHC)  Being built in LEP tunnel  Will start up later this year  About 7 times more energy that Fermilab /LHC My House ( ) 4/15/ Rotolo Middle School

 One very important parameter of an interaction is the center of mass energy. For a relativistic beam hitting a fixed target, the center of mass energy is: For 1TeV beam on H, E CM =43.3 GeV!! On the other hand, for colliding beams (of equal mass and energy): All the highest energy accelerators are colliders 4/15/ Rotolo Middle School E m E E

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Weak forces cause transitions between fundamental “fermions” Electromagnetic Interaction: Weak Interaction: 4/15/ Rotolo Middle School

e + e - scattering e + e - annihilation particle anti-particle 4/15/ Rotolo Middle School

 The Standard Model actually has a problem with mass  The calculations blow up unless all the particles are massless  Unfortunately, the particles aren’t massless.  Putting in mass while still getting sensible answers required a special “trick”, invented by Peter Higgs  His theory predicts one more particle, yet to be discovered, which is named after him.  The last piece of “The Standard Model” 4/15/ Rotolo Middle School

Stuff we understand (stars, planets, gas) Unknown stuff kind of like ordinary matter No idea what this is 4/15/ Rotolo Middle School

 The Big Bang should have produced equal amounts of matter and antimatter.  Somehow, the universe became primarily matter.  This must be due to some small difference between matter and antimatter.  This is known as “CP Violation”  CP Violation has been observed, but not at a level that would explain the matter dominance of the universe.  What’s going on? 4/15/ Rotolo Middle School

 Even with the Higgs mechanism, the Standard Model eventually fails.  Doesn’t explain  Generations  Quarks vs. leptons  Lots of new theories  Supersymmetry  Extra dimensions  String Theory  To find the truth, we must got to energies beyond those currently available. 4/15/ Rotolo Middle School

 This is the most popular new theory, but there are many others Ordinary particles Gauge bosons SUSY partners Higgs bosons Gauginos Dark Matter Candidates Higgs and SUSY are LHC/ILC issues Leptons and Quarks Scalar Fermions Higgsinos 4/15/ Rotolo Middle School

 Will be built in the LEP tunnel at CERN (27 km circumference)  7 times the energy of the Tevatron  Proton on proton  Should definitely find the Higgs  Hopefully, will find other things 4/15/ Rotolo Middle School

 Remember, protons are made up of quarks, gluons, and other virtual particles  Interactions take place between these constituents,which carry only a fraction of the total energy.  In other words… 4/15/ Rotolo Middle School

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 Unlike protons, electron and positrons are “point-like”  That is, they have no sub-structure (that we know of)  They carry the entire beam energy  Lower energy electron beams have the same “reach” as much higher energy proton beams.  Events are much simpler and “cleaner”  So why don’t we just build e + e - colliders?  Well, there are some problems… 4/15/ Rotolo Middle School

 Protons: synchrotron radiation not important  Electrons: beyond very low energy, synchrotron radiation dominates kinematics  Beyond ~200 GeV, circular accelerators no longer win, because all the energy radiates away each turn.  Must go to a “linear collider” Whenever you accelerate a charged particle, it radiates energy. This is called “bremsstrahlung” or “synchrotron radiation”. A particle being bent through a radius of curvature  will radiate energy at a rate An electron will radiate about times more power than a proton of the same energy!!!! 4/15/ Rotolo Middle School

 Two 15 km linear accelerators  One electrons  One positrons (anti-electrons)  Each accelerates to 250 GeV  500 GeV at the collision point  Can potentially be upgrade (lengthened) to 500 GeV+ 500 GeV = 1 TeV  You’ll hear more about this from Dr. Garbincius 4/15/ Rotolo Middle School

 Because of the high energy, the Higgs particle and other new physics will probably be discovered at the LHC  Because of the complex environment, it will be difficult to the details of this physics.  Once we know what to look for, the ILC will be a platform for precision studies  For example, we can tune the energy to be precisely precisely study the Higgs particle  Hopefully other new physics, too! 4/15/ Rotolo Middle School

 ILC will cost about $15B, hopefully shared by several countries  Is this knowledge worth the cost?  Ultimately, society must decide the value of such pure research, relative to, say Healthcare Energy Defense Other research  That’s why we do talks like this  Scientifically, is it the right machine to build?  If Higgs + new physics is within reach? Yes!!  If no Higgs and no new physics? No!!  If Higgs, but nothing else Big arguments!!  Unfortunately, we won’t know which scenario it is until the LHC has been running a few years  Have to do at least some R&D to be ready to build. 4/15/2008 Rotolo Middle School 33

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 We can use light to measure down to the size of its wavelength:  But the smaller the wavelength, the higher the momentum, which can “knock the target around” Position uncertainty 4/15/ Rotolo Middle School

 This relationship between position and momentum measurement leads to a fundamental uncertainty  With a little bit of algebra, we can also express this as an uncertainty in energy The better we measure position The worse we measure momentum  can violate energy conservation – for a very short time 4/15/ Rotolo Middle School

 Because energy and mass are related  We can talk about the uncertainty principle as an uncertainty in mass  can make very heavy particles for a very short time 4/15/ Rotolo Middle School