This was how we built on the idea. Notice Gordon had a lot less gray in his hair!

1. Everything you wanted to know about the LHC but were afraid to askGordon J. Aubrecht, IIPhysics Education Research Group Department of Physics, Ohio State University, former chair of CPEP

2. Abstract: The Large Hadron Collider (LHC) is a particle accelerator based at CERN on the Swiss-French border. The LHC was turned on last September to fears of the “end of the world,” but the experience turned almost into the end of the LHC. An accident took the machine out of service until September 2009. What is the LHC for? Why is it important? What caused the accident? When will it return to service? I hope to address some or all of these issues in this presentation.

3. I have long been associated with the Contemporary Physics Education Project, is known as CPEP for short.CPEP began as a way to bring particle physics into high school (and college) classrooms. At that time, twenty years ago, the Standard Model of particles had jelled into something respectable.We at CPEP thought that presentation of cutting-edge physics and the knowledge that there were still many open questions could lead students to consider future careers as scientists.

4. This was how we built on the idea. Notice Gordon had a lot less gray in his hair!

5. This is the original version of the published chart.

6. I am passing out the CPEP particles and interaction chart for you to look at and keep.

7. This is the newest version of the particles chart, however, I do not have copies of this one with me.

8. There are materials available to help students and teachers as well. CPEP thought that we needed to assist serious study as well as providing visual beauty and provoking curiosity through charts. Amazon.com: The Charm of Strange Quarks: Mysteries and Revolutions of Particle Physics: R Michael Barnett, Henry Muehry, Helen R. Quinn, G. J. Aubrecht, ... www.amazon.com/Charm-Strange-Quarks-Mysteries-Revolutions/dp/0387988971 - 307k -

10. What do we mean by the “hadron” in the Large Hadron Collider?

11. There are two sorts of particles shown on the chart I gave you—leptons and hadrons. They are completely different in their properties from one another, but all leptons behave in certain ways and all hadrons behave in certain other ways.Leptons interact gravitationally, electromagnetically, and via the weak interaction.Hadrons are the only ones that interact via the strong interaction. Quarks are hadrons.

13. The hadrons are the strongly interacting particles.

14. This is important: the hadrons act over really short distances—distances of a femtometer (10-15 m).

15. The Standard Model (see the chart) has been the most successful model ever in describing the actions of particles.The Standard Model explains all the particle physics of the past 30 years. Explorations of the Standard Model have been responsible for 32 Nobel Prizes over the last 30 years.

16. However, there are some little problems …The Standard Model uses as input 24 parameters:12 quark and lepton masses12 coupling constantsWhere should these parameters come from?All fundamental particles start with zero mass, but I’m sure you’re aware that you have mass, as does everything we see around us.Why just quarks and leptons? Why not, say, leptoquarks?

17. In 1964, Peter Higgs proposed a particle to explain the Standard Model (before it really existed in concept).Wikipedia says: “broken symmetry in electroweak theory, explaining the origin of mass of elementary particles in general and of the W and Z bosons in particular. This so-called Higgs mechanism, which had several inventors besides Higgs, predicts the existence of a new particle, the Higgs boson (often described as “the most sought-after particle in modern physics”). Although this particle has not turned up in accelerator experiments so far, the Higgs mechanism is generally accepted as an important ingredient in the Standard Model of particle physics, without which particles would have no mass.”

18. The outstanding problems are there as we saw … and the more complete model, if any, should be able to answer the questions:Why is there an accelerating universe?Why is there so little antimatter in the universe?What is the origin of mass?Where could dark matter come from?Why is there a huge range of masses?

19. The forces of nature are introduced as interactions: gravitational interaction, electroweak interaction, strong interaction.The strong interaction involves hadrons.

20. The Large Hadron Collider (LHC) is a place where interactions can occur through particle collisions. According to Wikipedia, “The Large Hadron Collider (LHC) is the world’s largest and highest-energy particle accelerator, intended to collide opposing particle beams, protons at an energy of 7 TeV/particle or lead nuclei at 574 TeV/particle.”

21. The Higgs particle may soon be discovered at the LHC. The Higgs particle rescues something my colleague Richard Kass at OSU called a physical Ponzi scheme (speaking of the Standard Model). Another colleague once called this the “broom and rug approach” to physics—use the broom to sweep the dirt together, pull up the rug and sweep the dirt under it, then put the rug back down.

22. We hid a lot of dirt in the Standard Model. …We can’t predict the Higgs mass, for example. We don’t know if there’s one Higgs or many.There are those 24 free parameters.Why are the electric charges of e- (a basic lepton) and p (a composite hadron) exactly the same size?There are problematic infinities in the model.

23. Let’s think a bit.The resolution of objects depends on the wavelength of the probing object. A wave of wavelength  bends around objects of size d. Waves and particles are not more than different evocations of some underlying reality. Particles have momentum p that is related to the wavelength : p = h/.

24. Becausep = h/,  is comparable in size to the object (d),and the energy of a particle is given byE = (p2c2 + m2c4)1/2 = mc2, we see that to “see” a small object (d very small), p must be very large, and so in turn E must be very large.

25. This means that particle physicists are always searching to increase the energy of collisions. They do this by accelerating the particles in an accelerator.The first accelerators were designed in the 1920s—Cockroft and Walton designed a linear accelerator (linac), and E. O. Lawrence designed a circular accelerator (cyclotron).

26. Lawrence’s machine was called a cyclotron (not prefix), and today particle physicists use both linacs and synchrocyclotrons to study particle physics.The synchronization is necessary due to the effects of special relativity.

27. This is an experimental sketch from a 1950s paper. Note that the mass energy of the pi particle is ~ 140 MeV, or 0.14 GeV (in the 1950s, this was denoted “Bev”).

28. Here’s another experimental result. See the “resonance” (the particle) in these data?

29. Experiments led to this “particle zoo.”

30. Then, in the 1960s, Murray Gell-Mann, George Zweig, and others invented ways to categorize these many particles and the result is called the quark model. You saw the quarks from the chart earlier.A proton is uud, a neutron is udd, etc.The model also produces mesons—hadrons that are made of quark-antiquark pairs.

31. CERN’s LHC will allow us to glimpse interactions at really high energy. This shows ATLAS, which is one of the detectors at the LHC.

32. The LHC is a circular accelerator ring 27 km around. Particles are steered in both directions using superconducting magnets and made to collide in several regions loaded with detectors like the Atlas detector.Because the ring is so big, the particles’ energies are immense—~10 TeV—and the particles are traveling at essentially the speed of light: E =  mc2 =  1 GeV, so 10 TeV/(1 GeV) = 10,000, givingv = c - 1.5 m/s.

33. LHC preacceleratorsp and Pb: Linear accelerators for protons (Linac 2) and Lead (Linac 3) (not marked) Proton Synchrotron BoosterPS: Proton Synchrotron SPS: Super Proton SynchrotronLHC experimentsATLAS A Toroidal LHC ApparatusCMS Compact Muon SolenoidLHCb LHC-beautyALICE A Large Ion Collider ExperimentTOTEM Total Cross Section, Elastic Scattering and Diffraction DissociationLHCf LHC-forward

35. ATLAS is about 45 meters long, more than 25 meters high, and has a mass of about 7,000 tonnes. More than 1700 physicists work on this collaboration.

36. ALICE is about 26 meters long, and 12 meters high and wide, and has a mass of about 10,000 tonnes. This experiment is a collaboration of over 1000 physicists.

37. The Compact Muon Solenoid (CMS) is 21 meters long and 15 meters wide and high. It has a mass of 12,500 tonnes.

38. LHCb (Large Hadron Collider beauty) is 21 meters long, 10 meters high, and 13 meters wide, with a mass of 5600 tonnes. 650 physicists belong to this experimental collaboration.

39. TOTEM is 440 meters long, 5 meters high and 5 meters wide. It has a mass of 20 tonnes. Fifty physicists work on this experiment. <-- This is CMS. The long red thing is TOTEM. View of one quarter of the CMS detector with the TOTEM forward trackers T1 and T2. The CMS calorimeters, the solenoid and the muon chambers are visible. Note also the forward calorimeter CASTOR.

40. LHCf (Large Hadron Collider forward)LHCf has two detectors, each measuring 30 cm long, 80 cm high, 10 cm wide, with a mass of 40 kg each. Twenty-two physicists work on this experiment, which uses the LHC to simulate cosmic rays.

41. The experiments ALICE, ATLAS, LHCb, etc., will be looking for traces of the Higgs particle(s), and we know that the Tevatron at Fermilab has already constrained the Higgs mass to be above 100 GeV. We need to get to those high energies the LHC promises to see what’s what.We need to look for evidence of what lies beyond the Standard Model …

42. … such as supersymmetry (colloquially known as SUSY) or some more exotic things (whatever they might be). SUSY might be able to explain dark matter, the mysterious extra mass that helps hold galaxies together. As in the Pauli joke explanation, the lowest-mass object is stable; it doesn’t decay. The lowest-mass SUSY particle could be the source of this dark matter.SUSY might tell us that grand unification is correct (the couplings are the same at high enough temperature [energy]).

43. For a circular accelerator, the magnets that bend the particles are situated along the path.

46. The LHC has more than 1600 superconducting magnets (most of which mass over 27 tonnes). Around 96 tonnes of liquid 4He is needed to keep the magnets at their operating temperature of 1.9 K. There are 1232 dipole magnets that keep the beams on their circular path, with an additional 392 quadrupole magnets that steer the beams.

47. To get the high magnetic fields needed, the superconducting magnets carry huge currents (millions of amperes) losslessly. On 19 September 2008 came an unanticipated disaster. A fault occurred in the electrical bus connection in the region between a dipole and a quadrupole. This led to an electric arc, which punctured a helium enclosure. All of a sudden the huge current heated everything up, so the temperature went up, vaporizing the helium and sending it blasting through the tunnel. It spread to other helium enclosures and damage occurred over half a kilometer.

48. A faulty electrical connection between two magnets (in red) was the cause of the incident in sector 3-4 of the LHC.

49. CERN said: “The forces on the vacuum barriers attached to the quadrupoles at the subsector ends were such that the cryostats housing these quadrupoles broke their anchors in the concrete floor of the tunnel and were moved away from their original positions, with the electric and fluid connections pulling the dipole cold masses in the subsector from the cold internal supports inside their undisplaced cryostats. The displacement of the quadrupoles cryostats damaged ‘jumper’ connections to the cryogenic distribution line, but without rupturing its insulation vacuum.”

50. Some of the damage.