344 – History and Development of ATLAS
Guests: Peter Jenni Host: Markus Voelter Shownoter: Alexander Grote
ATLAS is one of the two general-purpose experiments at the LHC. It has been conceived, designed, and built over decades by hundreds of scientists and engineers from dozens of countries and hundreds of organizations. My guest, Peter Jenni, has been the head of the ATLAS collaboration for most of this time. In this episode we talk about science and engineering, but mostly about organizational aspects and the “community management” necessary to get such a magnificent machine off the ground.
Introduction Peter Jenni00:02:55
Peter Jenni | LHC | CERN | Atlas | University of Bern | ETH Zürich | SLAC | Fabiola Gianotti | LEP | Intensity | electrons | positrons | protons
The Atlas Experiment Overview00:18:40
solenoid magnet | magnetic field | right hand rule | electromagnetic calorimeter | the Atlas liquid Argon Calorimeter | Hadrons (Mesons and Baryons) | TileCal | Muons | CMS | Particle Collider | ALICE | LHCb | Bottom Quark | Standard Model | Weak interaction / intermediate vector bosons | UA1 | UA2 | SPS | Super Proton–Antiproton Synchrotron | Simon van der Meer | Carlo Rubbia | Dipole Magnet | SSC | Higgs Boson | Luminosity | Higgs Mechanism | Supersymmetry | WIMPs | Supersymmetric Dark Matter
Design Decisions in Atlas01:39:39
Tracking Detector | Atlas Tracker | Decay | Decay length (Lecture Particle Decay Slide 9) | Superconductivity | Atlas Technical Design Report
LS2 | HL-LHC | LHC Quench | European Strategy for Particle Physics | ILC
I’m curious about what Peter said about luminosity not making up for lack of energy. If you had sufficient luminosity, wouldn’t that allow you to measure the effect of arbitrarily massive particles in your scattering cross sections?
In principle, yes: heavy particles have a small effect on physics below their own mass scale. The leading contribution is suppressed like (E / M)^2, where E is the LHC energy and M is the mass of the super-heavy particle – so the effect will be *very* small (and not detectable with the finite datasets we can collect in this universe), unless the energy of your collider is in the same ballpark as the mass of the new particle.
There are many examples where “hints” of new particles have been seen in this indirect way. Perhaps most famously, LEP saw hints of the Higgs boson – in exactly the same mass range where it was later unambiguously discovered by the LHC.
You can also turn the argument around and ask: “given that I don’t see anything strange in my data, how light could a new particle possibly be?” This is how the LHC sets limits on the masses of supersymmetric particles. These limits will continue to become stronger as the LHC accumulates more data, even if the energy will no longer change. But these improvements will be quite minor.
If you want to find heavy particles, invest in a higher-energy collider and don’t keep the old machines running forever!