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Seth Zenz | Imperial College London | UK

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The World’s Largest Detector?

This morning, the @CERN_JOBS twitter feed tells us that the ATLAS experiment is the world’s largest detector:

CERN_JOBS Tweet Largest Detector

Weighing over 7,000 tons, 46 meters long, and 25 meters high, ATLAS is without a doubt the particle detector with the greatest volume ever built at a collider. I should point out, though, that my experiment, the Compact Muon Solenoid, is almost twice as heavy at over 12,000 tons:

CMS

CMS is smaller but heavier — which may be why we call it “compact.” What’s the difference? Well, it’s tough to tell from the pictures, in which CMS is open for tours and ATLAS is under construction, but the big difference is in the muon systems. CMS has short gaps between muon-detecting chambers, while ATLAS has a lot of space in order to allow muons to travel further and get a better measurement. That means that a lot of the volume of ATLAS is actually empty air! ATLAS folks often say that if you could somehow make it watertight, it would float; as a CMS member, I heartily recommend attempting to do this and seeing if it works. ;)

But the truth is that all this cross-LHC rivalry is small potatoes compared to another sort of detector: the ones that search for neutrinos require absolutely enormous volumes of material to get those ghostlike particles to interact even occasionally! For example, here’s IceCube:

"Icecube-architecture-diagram2009" by Nasa-verve - IceCube Science Team - Francis Halzen, Department of Physics, University of Wisconsin. Licensed under Creative Commons Attribution 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Icecube-architecture-diagram2009.PNG#mediaviewer/File:Icecube-architecture-diagram2009.PNG

Most of its detecting volume is actually antarctic ice! Does that count? If it does, there may be a far bigger detector still. To follow that story, check out this 2012 post by Michael Duvernois: The Largest Neutrino Detector.

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2 Responses to “The World’s Largest Detector?”

  1. Dan Riley says:

    Presumably testing ATLAS flotation would be easier if it were at P5, with the plentiful Cessy  ground water. Maybe we need a proposal to swap the detectors in order to eliminate any geographical systematics.

    IceCube would, of course, float.

    But what about the atmospheric shower experiments like the Auger Observatory? What counts as the active detector volume?

  2. Kyle Cranmer says:

    It will continue to be tricky to define what you mean by “largest”, but this idea is now in the running and probably takes the cake for most distributed
    http://crayfis.ps.uci.edu
    A network of smart phones to detect ultra high energy cosmic rays

    (all this changes if you count the surface of last scattering as a detector )

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