The Large Hadron Collider is back

IPPOG communication, 16 March 2022

There is an exciting amount of activity at CERN these days, even more so, than usual. And it is not only because Covid-19 restrictions have been loosened. In fact, many of the scientists working on the Large Hadron Collider (LHC) have been working throughout the pandemic, despite the challenging conditions. This was necessary to prepare the accelerator and its detectors during the planned machine shut down.

These days, however, the activity has markedly increased, as the startup of LHC Run 3 approaches. When it does, (it’s currently planned for the beginning of April), proton beams will once again circulate through its 27 km of superconducting magnets located in a tunnel 100m underground. The newly revamped detectors, located at the 4 LHC beam collision points, need to be closed up and ready to go.

As you follow the startup #restartingLHC there are several phrases that will appear in the communications coming from CERN and its experiments. In this short article, we want to introduce you to the one called Beam Splash (#BeamSplash). This term comes up every time the accelerator restarts in the spring. Beam Splash is a means of filling up the detectors with controlled showers of particles, so the experiments can test their detectors, electronics and software before data taking gets underway.

As simple as this sounds, the detectors are very sensitive instruments, so the job is a delicate one. During normal collisions, devices called collimators are used to clean up the edges of the proton beams to shield the detectors from stray protons. They are essentially narrow passages located upstream from the entrances to the detectors. Any protons outside of the diameter of the collimator’s passage will run into its walls and be absorbed, leaving two fine needles of beam to enter the detector at each side.

In order to create a beam splash, the collimator on one side is moved very slightly, so that its inner edge just passes into the beam. The beam interacts with that edge, creating a spray of particles that continues on into the detector, effectively lighting up all of its sensitive components in a controlled manner. Any sensors that are not working or which might be problematic can then be detected and repaired or adjusted before the experiments start to take data for physics.

Not only is the beam splash a great way to assure the scientists that their detectors are in great shape for the new run, it also produces a number of beautiful event displays for our enjoyment. Here is an example of a beam splash event from the restart in 2018.

This next run promises to be an exciting one. During the past Long Shutdown 2 (LS2), the magnets in the accelerator were upgraded to provide higher energy (6.8 TeV per beam compared to 6.5 TeV in Run 2) and higher luminosity, possibly yielding up to 3 times as many more proton collisions per second, as in the previous run. This higher rate will not only greatly improve the precision of current measurements, but will allow the LHC scientists to search for rare phenomena they have never seen before.

To do all this, a long preparation has been needed at CERN. Engineers, technicians, researchers, and many others have worked for years to get ready for  Run 3. Covid-19 didn’t make things easy during the Long Shutdown 2. Delays, closures, absences and supply shortages were among the challenges. Despite this, the force that pushes science to take other great steps has never stopped, and Run 3 is now only days away.

The experiments will have a lot to test in the early days of the run. Each has a number of very important upgrades needed to handle the higher collision rates. The ALICE experiment has a large number of new detector components. LHCb has new silicon and scintillating fibres, CMS has new GEM detectors and ATLAS has new small wheels for its muon spectrometer.

The entire world of physicists and scientists looks forward to recording high-quality physics data from the LHC RUN 3. Let's open our eyes and ears, who knows what will happen during this new era of the LHC.

In the meantime, if you are a student or teacher, take a look at our masterclasses and experience particle physics like real scientists! More info at www.ippog.org

 

 

 

  

Links:

https://news.fnal.gov/2021/11/lhc-is-making-a-splash-as-cms-prepares-for-run-3/

https://atlas.cern/updates/news/beams-return-atlas-experiment