Experiment VI-10

High Energy Frontier

anticipated results from the Large Hadronic Collider


mailInput to our minds is extremely limited to only what our few types of sense organs provide.  But in the last several centuries we have discovered ways to drastically surpass that restriction using elaborate and remote equipment which provides additional information in formats our sense organs can assimilate.  (A trivial example: the author has a remote television camera mounted in a tree so that it displays on the corner of his computer monitor a live view of the nearby country road.  Such expanded vision permits remote witness of such events as mail delivery.→)

papyrus & cave paintingsEarlier humans devised ways to paint images inside caves, record symbols on papyrus (←e.g.) and utter audible sounds to convey earlier experiences of one person for later gain by another listener, viewer or reader.  In the last century we have discovered that by capturing extremely faint light traveling the largest astronomical distances, we can study information about events which occurred very near the beginning of the universe.  And by colliding the tiniest of particles together at the highest energies, we can gather information about the things that inhabited such early universe, and surmise the rules and restrictions which govern both the early and current universe.

today's frontier

Currently the premier physics laboratory, of many around the world, for providing such information is the Large Hadron Collider (LHC).  This, the world's largest particle accelerator, is located at the European Organization for Nuclear Research (CERN) straddling the border between France and Switzerland near Geneva (as shown below; click image to access details).  Bunches of protons travel in a pair of 8.6 km diameter circular vacuum tubes in opposite directions, colliding at intersecting locations where detectors have been constructed to study what new particles are formed from the high energy.  The actual tubes, with bending magnets and accelerating klystrons, are located in a tunnel about 100 meters underground (below the yellow circle superimposed on the photograph below).  The Compact Muon Solenoid detector (CMS) is located about the 9 o'clock position and the Atlas detector is opposite at 2 o'clock on this circle.

LHC from air

Besides the CMS and Atlas detectors, Alice is a collaboration building a dedicated heavy-ion detector at the 3 o'clock position to investigate nucleus-nucleus interactions at energies the LHC will employ.  They plan to occasionally study the physics of strongly interacting matter at extreme energy densities where the phase of matter called quark-gluon plasma, is formed following collisions of beams of heavy atomic nuclei such Lead ions.  The existence of such a phase and its properties are key issues in Quantum Chromo Dynamics (QCD) for the understanding of confinement and of chiral-symmetry restoration.

Fourteen billion years ago, the Universe began with a bang, forming exactly EQUAL quantities of matter and antimatter within an extremely small volume.  As the Universe cooled and expanded in the first second, matter annihilating ALL the antimatter.  Somehow a small excess of matter remained to form everything that we see around us from the stars and galaxies, to the Earth and life.  The Large Hadron Collider beauty (LHCb) experiment is a collaboration established to explore what happened just after the Big Bang which allowed the tiny fraction of matter to be in excess, survive and build the Universe we inhabit today.  Located at pit 8 (near the visible Geneva airport, slightly clockwise from the 12 o'clock position), the experiment utilized the access excavation of one of CERN's previous experiments, DELPHI.

TOTEM is an experiment extension at the CMS detector dedicated to the measurement of total cross section, elastic scattering and diffractive processes at the LHC.  TOTEM is designed to measure the total cross section using the simultaneous detection of elastic scattering at low momentum transfer and of the inelastic interactions.  This method also provides an absolute calibration of the LHC luminosity.  The experimental apparatus includes telescopes of Roman pots, movable detectors placed symmetrically inside the vacuum chamber a meager 1 mm on both sides of the beam at an intersection region.  (These Roman pots have to be movable because when particles are first injected to form the beams, the beams occupy a larger cross section which is only compressed as higher energies are achieved.) The Roman pots will detect protons scattered at very small angles in elastic or quasi-elastic reactions.  Also part of the apparatus is a forward inelastic detector with full azimuthal acceptance.  This detector will measure the overall rate of inelastic reactions.  The other fixed larger detectors have larger vacuum tubes passing through them and therefore miss detecting any collision products that are emitted nearly in line with the beams.

a bit of how we got here

Following discussions among Raoul Dautry, Pierre Auger and Lew Kowarski in France, Edoardo Amaldi in Italy and Niels Bohr in Denmark after the second world war, the French physicist Louis de Broglie put forward the first official proposal for the creation of a European atomic physics laboratory to the European Cultural Conference in Lausanne in December 1949.  The following June, the American Nobel laureate physicist, Isidor I. Rabi tabled a resolution authorizing UNESCO to assist and encourage the formation of regional research laboratories in order to increase international scientific collaboration...  At a UNESCO meeting in Paris in December 1951, the first resolution concerning the establishment of a European Council for Nuclear Research was adopted.  Two months later, 11 countries signed an agreement establishing the provisional Council with the acronym CERN.  Geneva was chosen as the site of the future laboratory in October 1952.  A 600 MeV synchrocyclotron, completed in 1957, was CERN's first accelerator, providing beams of electrons for CERN's first experiments.  An additional synchrotron began accelerating protons in 1959 with a beam energy of 28 GeV.  A set of 300 m diameter intersecting storage rings were completed in 1971 allowing for the full kinetic energy of the colliding proton beams to be used to create new particles.  In 1976 a super proton synchrotron was commissioned, built in a tunnel measuring 7 km in circumference crossing the Franco-Swiss border, with an original beam energy of 300 GeV.  That apparatus was modified in 1981 to also study collisions of protons with antiprotons.  A 100 GeV Electron-Positron collider was commissioned in 1989 in a 27 km circumference tunnel.  That excavation was Europe's largest civil-engineering project prior to the Channel Tunnel.  That apparatus consisted of 5176 magnets, 128 accelerating cavities and four enormous detectors called ALEPH, DELPHI, L3 and OPAL.  The Large Electron-Positron collider was shut down in 2000 so that the same tunnel could be used for installation of the Large Hadron Collider using much more powerful superconducting magnets.

LHC beam pipebeam pipe cross section

The Large Hadron Collider (shown above) has 1232 dipole magnets maintaining the twin beams on their nearly circular paths, while 392 quadrupole magnets refocus the beams.  Not only is the LHC the world's largest particle accelerator, it is by a factor of 8 the world's largest refrigeration system.  In order to maintain the flow of electricity without resistance needed for the magnets to maintain the protons in the circular paths, all magnets must be pre-cooled to -193.2°C (80 K) using 10,080 tons of liquid Nitrogen, before they are further cooled with 60 tons of liquid Helium necessary to reach -271.3°C (1.9 K).  To avoid colliding with gas molecules inside the accelerator, the two beams of particles travel in opposite directions in two intersecting, ultra-highly evacuated tubes at a pressure of 10-13 atm.  Rather than continuous beams, the protons are lumped together into 2,808 bunches, never closer than 25 ns and 7.5 m together, so that the detectors and computers can keep track of each collision.  At full beam density there are potentially 600 million collisions per second.  While each proton will be accelerated to a kinetic energy of 7 TeV (1 TeV = 1012electron Volts) providing the head-on collisions of 14 TeV, what will actually collide are the constituent particles inside protons, quarks and the gluons which bond them together.  And those collisions will seldom have more than about 1 TeV.  The enormous detectors have been engineered to measure particle locations down to micron precision in the inner most detectors in order to determine their paths and energies and keep each event distinct.  The amount of data collected will exceed that of all previous experiments.  So a system to disseminate, store and eventually study the data involves supercomputers located around the world connect by the Grid, the worlds largest distributed computing network.  Most collisions will produce only common reactions.  The most interesting results will be rare.  So the detectors and computers attempt to sift through the data, only saving and disseminating the most interesting and unusual results.  First beam is scheduled for 10 September 2008.

why do it?  what else might be discovered?

understanding gravity

There is considerable confidence that the LHC should improve our understanding of the force of gravity.  The typical person probably thinks that gravity is already well understood.  Certainly Isaac Newton (1642-1727) figured out the basic equations for determining the relations between the strength of gravity and the related masses and distance.  In his 1687 Principia, he explained how gravity curved the paths of earthly projectiles.  In 1905 Albert Einstein (1879-1955) wrote three papers, one of which proposed a theory of Special Relativity.  Einstein suspected that while Special Relativity was formulated on the basis of electricity and magnetism, all forces must be consistent with Special Relativity and the exchange of information at the speed of light.  So the remaining force, gravity, would also be governed by similar equations.  Einstein was also aware that inertial mass that resists acceleration in Newtons dynamics, F = ma, seems to be experimentally equivalent to gravitational mass which causes gravitational force in Newton's law of gravity: F = Gm1m2/d2.  This seemed to imply an equivalence principle stating that there would be no experimental way to every distinguish the difference between the effects of gravity and those observed in other accelerated frames of reference.  In 1915 Einstein announced his general theory of relativity which suggests that mass deforms the surrounding space so that, contrary to Euclid's geometry where the shortest distance between two points is a straight line, the shortest distance between two locations near any mass would be a curved pathway.  For nearly all situations Einstein's theory makes identical predictions to Newton's theory.  But the real nature of mass, and the cause of gravity remained elusive.

Peter HiggsTheorists have suspected that mass is not actually a property of objects.  A mechanism for mass was postulated by British physicist Peter Higgs (b 1929 ←photo at left) in 1964 while walking the Scottish mountains.  He returned to his lab declaring he had had his one big idea.  His theory hypothesizes that a sort of lattice, now referred to as the Higgs field, fills the universe.  This is a bit like an electromagnetic field, in that it affects particles that move through it.  It functions like a famous person moving with a throng of fans has inertia created by the surrounding crowd; it is hard for the famous person to start moving, or once in motion, change course or speed.  Higgs suggested the same could be true for particles in a Higgs field: a particle moving through it creates a little bit of distortion and that provides mass to the particle depending on the amount of attraction by the Higgs field.

Just as particles are created by high enough energy accelerations in other types of force fields, it seems likely that acceleration in the Higgs field could create the Higgs boson, the last remaining class of particle needed to complete the Standard Model.  The lightest Higgs particle is predicted to be within the energy range the LHC will provide.  Many scientists are eagerly awaiting what they expect to be the discovery of the first Higgs boson!

dark matter

Fritz ZwickyIn 1933 the very creative maverick, but often offensively brash Fritz Zwicky (b1898 in Bulgaria, d1974 shown right), Swiss astronomer working at CalTech, calculated the orbital speeds of outlying stars in the Coma cluster of galaxies (from their spectral shifts).  He compared those speeds with the masses of the clusters (calculated from their brightness).  He found the masses to be only 1/10 to 1/100 of what was needed.  Because there must be enough mass to keep the parts of each cluster in orbit, Zwicky proposed the existence of what he termed dark matter.  More recent observations confirm the existence of such missing mass and provides details about how much is needed.  But the actual nature of this dark matter continues to be an enigma.

The current explanation of the known matter in the universe in encapsulated by the Standard Model's table of known particles.  But to provide the necessary dark matter, the Standard Model must be incomplete.  Perhaps there are yet undiscovered kinds of particles which compose this dark matter.  In the higher energy collisions, there is some hope that clues about such particles might be discovered.

dark energy

Before the expansion of the universe was discovered, at a time when nearly everyone believed the heavens were static and pertinent, Albert Einstein attempted to understand gravity and proposed his theory of general relativity.  Einstein realized that gravity caused by the mass of the universe would attract all objects in the heavens perhaps causing the universe to eventually collapse together.  Since the universe continued to exist and at that time showed no evidence of any ongoing collapse, Einstein proposed a repulsive term in his gravity equations called the cosmological constant.  When Hubble and Humason discovered that the universe is expanding, Einstein realized the cosmological constant was unneeded and declared it the biggest mistake of his life.  But a graph of the distances (observed magnitudes) of type Ia supernovae verses their red shifts shows that the most distant ones seem to be moving faster away from us.  One possible explanation of their acceleration of the universe revealed by this new data is a repulsive force with a cosmological constant.  The data seems to fit a cosmological constant (ΩΛ = 0.75) requiring a repulsive force with an associated dark energy of about 75% of the energy of the universe, eventually enough to overwhelm all other forces we know.

Very little is known about this dark energy, but the LHC could potentially provide some clues.

additional dimensions of reality

Albert Einstein spent the latter part of his life trying to unify gravity equations with the equations for the other forces.  This notion that all the forces are fundamentally related (i.e., find what things have alike) is a claim by Nature Philosophy that developed partially as a counter view to Newton's very successful analytical method of physics (i.e., take things apart and determine their differences).  Over the past two centuries this effort at unification has inspired a large number of physics discoveries.  Superstring theory is a possible unified theory of all fundamental forces, but superstring theory requires a 10 dimensional spacetime.  Much of the effort has been to establish if Strings might be able to explain what we already know about out universe.

Basically String Theory suggests that instead of Euclid's view that space is composed of point locations which can specified by 3 dimensions (or 4 dimensions if time is added as suggested by Einstein), there may be 7 or more additional dimensions which are degenerate or hidden from our normal perceptions.  (Think of a thread as having a dimension, length, that is easily perceived from some distance, but other dimensions, such as thickness, which are harder to perceive from that distance.)  These degenerate dimensions contain the essential properties of reality.  But there is also the possibility that hidden in the degenerate dimensions might be aspects of reality for which we now know nothing.  Each string has two properties, mass and tension, governing the vibration of the string.

One of the predictions of string theory is that at higher energy scales we should start to see evidence of a symmetry that gives every particle that transmits a force (a boson) a partner particle that makes up matter ( a fermion), and vice versa.  This symmetry between forces and matter is called supersymmetry.  One big problem with supersymmetry: in the particle physics that is observed in today's accelerators, every boson most definitely does NOT have a matching fermion with the same mass and charge.  So if supersymmetry exists in reality, the symmetry must somehow be broken.  Some string theorists hope the LHC will find some signs of supersymmetry, thereby providing new clues about additional dimensions.

end of the universe?

There has been some speculation that at the increased energy of the LHC, colliding particles might force particles close enough to create the conditions of a mini-black hole, which would then consume surrounding matter, eventually destroying the Earth.  Of course no involved scientists want to do an experiment which not only destroys themselves, but our world as well.  So theorists have considered the possibility and found it unlikely. (Of course by using the tools of science, it is not possible to say it is absolutely impossible.  Unlikely is the strongest statement that science can make.)  But considering that our best understanding is that these conditions were universally true shortly after the Big Bang, and believed to still occur occasionally elsewhere in the universe, we find no evidence that such destruction occurs.  (But perhaps a reader might want to create a fictional game based on this speculation?)

It is much more likely that evolution will continue on Earth by the same natural processes much as it has in past, except in the near future more influenced by the exploding human population.  In the long run the Earth is likely to be consumed roughly 5 billion years from now when the Sun evolves to a red giant star.  A bit later the Sun will collapse to a white dwarf while the Milky Way galaxy continued on pretty much as it has.  Perhaps the far distant end of the universe is still beyond our comprehension?


The detectors are built in layers (like an onion) with the most expensive, track detectors closest to the beam pipe to precisely determine collision location and direction particles begin traveling.  Layers further from the beam pipe track the particles as they curve in strong magnetic fields.  And particle absorbing materials slow most particles, extracting and measuring their energy.  (Shown below during construction, the ATLAS calorimeter to measure particle energy is being inserted from far end between the eight torodial magnets.  Note apparatus size compared to workman standing in foreground and stairways on sides.)


When one reflects back on the discoveries about elementary particles of a century ago, one might notice they often were the result of a single discrepant event, confirmed by rare reoccurrences.  (Consider the observation by Rutherford's group of an α particle reflecting back from a thin Gold foil.)  Later discoveries were more likely to be the result of the number of events deviating from what was anticipated.  (Consider the discovery by Raymond Davis, Jr. that the number of neutrinos from the Sun was short, later to be explained as neutrinos morphing to cousin particles.)  Most of the discoveries anticipated from experiments using the Large Hadronic Collider may be found in variation in patterns assembled by computers from the enormous number of tracks detected following each collision.


The LHC experiments using the full collider ring begin data collection September 2008.  Events have been simulated which allows you to begin to understand data generated by the ATLAS detector at LHC. The software HYPATIA was written to allow you to download event files and identify particles.  If you haven't done so previously, you may wish to first do the less complex Experiment VI-9.

  1. Download the needed files and follow the directions provided.  The simple version comes with 5 events in the "events" folder.  Drag or move he additional Hypatia events into that same folder.

  2. To understand Hypatia and what to do, load the Simplified_Basics web page (which will load in a new Tab or Window).

Communicating technical information such as observations and findings is a skill used by scientists but useful for most others.  If you need course credit, use your observations in your journal to construct a formal report.



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initial draft 20 May 2008
latest addition 26 February 2009
by D Trapp
Mac made