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muon spectrometer,
upgrade,
HL-LHC

First ATLAS New Small Wheel nears completion

4 June 2021 | By

Katarina Anthony

On Friday 28 May 2021, teams of physicists and engineers installed the final "wedge" of the first ATLAS New Small Wheel detector. This was an important milestone for the Collaboration, in preparation for the wheel’s installation in the ATLAS cavern later this summer.

These now-iconic detectors are critical to a new era of exploration for the ATLAS experiment. In the coming years, a major upgrade to the LHC – known as the High-Luminosity LHC – aims to crank up the collider's luminosity by a factor of ten beyond its design value. This will generate even more collisions, allowing ATLAS physicists to probe phenomena that are even rarer in nature.

A massive upgrade of the ATLAS experiment is underway to prepare for this increased luminosity. The first major system to be upgraded is the muon spectrometer, with the New Small Wheels set to be installed on either end of the experiment in summer and autumn 2021. The wheels use novel small-strip Thin Gap Chambers (sTGC) and Micromegas detectors. These new technologies will give ATLAS much more stringent selection criteria for muons, and better handle high background and pile-up rates – the two main requirements for the High-Luminosity LHC.

The New Small Wheels were built in ATLAS institutes around the world and mounted on the wheels at CERN over the course of several years. Following the installation of the last "wedge" of detectors, the first New Small Wheel is now complete, with just final testing and commissioning pending.

The photos below showcase the logistical complexity behind this milestone. Look forward to watching the installation of this “small” behemoth, set to be broadcast live on CERN and ATLAS channels this summer.

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The final wedge of the muon detector is mounted onto the crane, ready to be moved from the test area and to the wheel itself. (Image: CERN)
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The wedge is lifted up and over to the other side of the construction hall. Both New Small Wheels can be seen: the wheel on the left will be installed into side-A of the ATLAS cavern this summer, the wheel on the right will go to side-C later this year. (Image: CERN)
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The wedge is lifted up to position, with scientists on cherry pickers alongside. (Image: CERN)
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View from the top of an ATLAS New Small Wheel inside CERN's building 191. The wheels themselves are some 10 metres in diameter. (Image: CERN)
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The wedges are made of multiple layers of detectors, with small Thin Gap Chambers (sTGC) sandwiching two layers of Micromegas detectors. (Image: CERN)
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While the installation progresses, teams on the ground prepare their stations to run tests of the new wedge once it is in its final position. In the background are large doors, through which the New Small Wheels will leave the construction hall. (Image: CERN)
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View of the completed "A-side" New Small Wheel – soon to be installed in the ATLAS experiment. (Image: CERN)