CERN bids farewell to the LHC and enters Long Shutdown 3

I was visiting CERN on one of their Open Days during the previous shutdown. This is one of the rare occasion where visitors can enter the LHC. I walked for about 500m along the beam which is remarkably small despite all its protection. Standing inside LHCb (one of the experiments where they track collisions) was one of my most awe-inspiring moments about science and technology. Photos don’t do it justice. It’s a multi-story building underground, but every inch is covered with cables, sensors etc. Seeing it on photos is one thing, standing inside the biggest machine built by humankind is a completely different experience and hard to put into words. The amount of thinking and planning that went into it is insane. CERN staff is super-friendly and open to talk and explain. If you have the possibility to visit, do it - especially with guided tours and on their annual Open Days.

I wonder whether the cancellation of the superconducting supercollider was a net positive or negative for science. If it continued to completion, it would have had almost 3x the beam energy of even the upgraded LHC in 2030 (20TeV vs. 7TeV). But the questions are fundamentally political, not scientific: Would SSC operations and funding have continued through the US economic challenges of 2001, 2008, and 2020? I could see a timeline in which the SSC got built and discovered the Higgs boson before LHC came online, causing the LHC to be canceled, delayed, and/or starved of funding -- only for the SSC to be shuttered during the "great recession" of 2008 or during any other US Gov't belt tightening exercise. Today we would have neither the SSC nor the LHC. Or, perhaps SSC would have accelerated other discoveries by 10 to 15 years (SSC go-live was to be in the late-1990's versus LHC's Higgs discovery in 2012).

I feel like the title is a little overdramatic. They’re not saying goodbye to the LHC, they’re upgrading it to have 10x the power.

I worked on a tiny, tiny part of the research for the insertable B layer in ATLAS during long shutdown one as an undergraduate - the 3 year period allowed all the detectors to be upgraded significantly! It will be interesting to see how the current systems are upgraded during this shutdown. Sounds like the ITK for ATLAS is absolutely _insane_ compared to the insertable B layer - 5 billion channels, up from 8 million. I wonder if ITKpix is at all similar to the T3MAPs cmos or FEI4 sensors we worked with… Edit Looks like it’s very different; and really cool: https://cds.cern.ch/record/2928802/files/ATL-ITK-PROC-2025-0...

I visited CERN last July. Was lucky enough to get into a group tour. The tour guide was a postdoc researcher who said the only times that public tours are allowed to take an elevator down is during long shutdowns. So while they do this work on LHC might be the best time to swing by for a tour (I might even try to return). Even without the descent, my tour was great with showing the 70 year timeline, historical early particle accelerator equipment, and a cool view of the ATLAS control room. The facility is awe inspiring and a testament to Europe's willingness to make long-term commitments to furthering science research for the public good.