Image: A screen shot of the “LHC Page 1” (accessible here), which is our real-time window on LHC operation (or lack thereof). This page is shown on screen all around CERN, including, most importantly, the coffee area.
It’s now been three weeks since the LHC collided its last hadrons. After a bumpy start in 2008, the Large Hadron Collider began taking physics-quality data in 2010. So after 16 years of hard labour, the most important workhorse of modern particle physics has been put out to pasture. The famous “LHC Page 1” (https://op-webtools.web.cern.ch/vistar/, which is bookmarked by physicists the world over, to know what the current status of collisions is), has gone blank. “So long LHC and thanks for all the collisions!” says the final comment (usually used to report faulty magnets, power trips, or emergency beam dumps).
On the day the collisions ended (and that fact was reported in the media), my mum sent me a WhatsApp message “is CERN shutting down today? How are you feeling about it? “. It is of course a milestone, but I answered “we’ll be analysing the data for years, while installing the new detectors, it’s all part of the plan so doesn’t feel like a big transition. It will be more of a party when the upgraded instruments are installed and working”.
It’s an important message, and that’s a sentiment you can get from the LHC page 1 screenshot: the second line on the final sign-off comment reads “Let’s follow the road to HiLumi LHC”. Indeed, while the LHC is now over (and that is an important and solemn moment) it is in the NOT end of the LHC journey, but more like an extended pit stop. The LHC is getting a makeover and a rebrand. From the ashes of the LHC will be born the “High Luminosity LHC”, HL-LHC. When it switches on after a four-year installation period, it will be able to produce collisions at the same energy as the LHC, but at much, much higher intensities, meaning that we can collect data at a vastly improved rate. The final HL-LHC dataset will be about 6 times larger than the (already record-breaking) dataset collected by the LHC, collected over fewer years.
In order to make the most of the high-intensity collisions, our detectors need a makeover too. New instruments like the HGTD, which I have written about before, and a band new tracker will be needed: the old one is basically shot from 16 years of radiation damage. Moreover, the parts of ATLAS which we are replacing were designed in the 90s, with the technology available at the time. If you compare the Nokia 3310 you may have had in 1996 to the smartphone you have in your pocket now, you will probably see why it is exciting to us that we get a chance to swap out obsolete components in our detector: the technological improvements in the intervening 30 years have been eye-watering, and the physics we will be able to do with a new detector using up to date technologies is incredibly exciting.
During the four-year shutdown, the particle physicists of the world will not be on vacation: if anything, we will be working more intensely than ever. Not only do we have the largest dataset ever collected to analyse, we also need to finalise construction of our new instruments, and install them. And before we install the new instruments, we need to a) get the old ones out and b) finish building the replacements. It’s a daunting task, and one fraught with unexpected dangers (for example, geopolitical events have impacted the price of silicon chips, the availability of components, and hence, budgets). But a challenge which is rich in opportunity. Everyone needs to get on board. That last point is why, for instance, my PhD student is on his way to CERN for three months, to help with the HGTD Data Acquisition software development on our test prototype.
I was in Glasgow in June for an ATLAS Collaboration meeting, and I got to speak to my former manager (and expert blog writer) Jon Butterworth*, who is now the ATLAS outreach coordinator. During the meeting’s social activity (a hike up Conical Hill) I asked him what the biggest outreach challenges on his plate were at the moment and he replied (I am paraphrasing) that we needed to make sure people did not think we were resting on our laurels now that the LHC collisions have ended. We need to remind the public that we are actually entering one of the most intense periods in our history where we need to get a new detector in the ground while analysing the huge dataset we have at our disposal, which could contain unexpected discoveries. And that we are doing all this because we are still trying to answer some of the most fundamental question about the universe: what is dark matter? where is all the antimatter? why are there such enormous differences in the masses of the particles we know about ?
In summary, the LHC is over, but we will be busier than ever over the next four years. So, I hope that with this article, I play my own little role in expressing that message.
*I’m glad to say Jon and I made it to the top in one piece 🙂 It’s Loch Lomond you can see in the background.
