An epic pony particle physics post · 3:11pm April 20th
It’s time for me to properly introduce a future particle physics experiment, which I have been working on for the past two news for a steadily increasing fraction of my time. It’s primarily a US project, but like everything we do in particle physics, it’s a global collaboration, and now has sufficiently secure British funding that I will probably be able keep doing this one for some more years, despite the we-have-no-idea-what-is-going-on status of science in the US at the moment.
Introducing the ePIC experiment. That is, the electron Proton / Ion Collider, a particle detector to be built at the planned Electron Ion Collider (EIC) in Brookhaven, New York. As the name suggests, this will smash a beam of electrons into a beam of protons (or heavier ions) and study the result.
The name is a little problematic as searches for “epic [whatever hardware/software/physics thing I need information about]” do not usually give the answer I want. It also means project managers can’t resist beginning conferences by saying what an epic meeting it is going to be. On the plus side, it means I can fill my blog with some epically contrived cheesy pony references and jokes.
The High Energy Frontier of particle physics at the moment is at the Large Hadron Collider at CERN, where they have been smashing tera-electron-volt proton beams together for the last fifteen years, doing lots of really interesting important measurements, while failing to discovery anything really super-duper exciting since the Higgs boson (in 2012).
With all the High Energy action happening in Europe, US labs have been looking for other projects to do. Fermilab have their muon physics programme. Now the Brookhaven National Laboratory in New York, have found a new project – a electron-proton collider – an asymmetric particle smasher.
Why? Because this is what you need to probe the internal structure of the proton. All matter is made of atoms. Atoms are made from protons, neutrons, and electrons. In the simple model, a proton is made up of three quarks (two Up, one Down). That’s what we learn at particle physics kindergarten. But actually, it’s a bit messier. The quarks radiate virtual gluons, which split into virtual quark-antiquark pairs, so the proton is mostly a messy sea of different colours of quarks, antiquarks, held together with a lot of coloured glue, as described by the theory of quantum chromodynamics (QCD).
To see what’s happening inside this particle requires a high energy electron beam. Fire it at your proton and look at the resulting pattern of electrons scattered at all angles. Scattering experiments like this have a long history. It would be remiss not to mention the Rutherford experiment, which first showed the atom had a nucleus (instead of the previously favoured plum-pudding model). This was shown by firing alpha particles at a gold foil, and showing that a few were knocked back as they hit a tiny gold nucleus containing all the positive charge in the atom. The experiments were done by Geiger and Marsden, but Rutherford made more noise about it.
Fast forward to 1968 and the proton was shown to be made of quarks in a similar experiment at Stanford Laboratory by sending a high energy electron beam into a tank of liquid hydrogen, where they were scattered off the quarks. This was the first direct evidence that quarks were real things and not just a mathematic quirk invented to explain patterns in data.
In the initial model, there were just three quarks– Up, Down, and Strange. Then more flavours were discovered. In 1979 experiments at the DESY laboratory in Hamburg, Germany revealed a new particle: the gluon, which mediates the strong nuclear force that binds the quarks together. The theory developed and the complex picture of the proton interior started to come into focus.
DESY was later the location for the first, and so far, only, electron-proton collider, HERA, which ran from 1992 to 2007, collecting the data to reveal this. The EIC and ePIC will now continue this quest, using more intense polarized beams to make 3D maps of the structure of the proton. It will tackle the mystery of the Proton Spin Crisis – how the intrinsic angular momentum of the quarks and gluons combine to give that of the proton and other hadrons.
It may be able to create a predicted new state of matter, the colour glass condensate, where gluons multiple until they reach a saturation point with a super-high density.
But before we can do all that, we need to design and build the machine. The accelerator engineers at Brookhaven are busy unicycling the Relativistic Heavy Ion Collider (RHIC), (an accelerator which has been smashing ion beams together for over twenty years) and adding a new electron accelerator and storage ring to this.
Meanwhile we detector scientists are working on our epic detector. The detector needs to track every particle flying out from the collision point, which needs multiple layers of silicon wafers. One challenge at the EIC is keeping the amount of stuff inside to a minimum. The low energy electrons will be deflected by any material surrounding the beam pipe, blurring the resulting picture. We need a super light-weight interior structure – carbon fibre supports to hold the silicon in place, as well as cables to supply power and get the signals out, and some sort of cooling to get rid of all the heat. This needs careful design.
Right now, we just hope the project isn’t delayed too much by the chaos in the US. Of course, compared to other researchers, we are in a relatively good position. Mapping the interior structure of the proton isn’t as inconvenient as studying climate or public health. If the current administration wants an America First attitude, then logically that should support a new machine in the US, and it’s our American colleagues working on projects at CERN and other European labs who are more at risk.
Unfortunately, logic does not seem to have much to do with it at the moment.
Worrying times. Good luck to everyone in the US. Let’s keep working together and be friends.
Waiting for the inevitable gluon accelerator to see what's inside those little suckers. I figure there has to be a bottom to the stack of turtles somewhere, and I have a prediction that the last turtle unwrapped will show this:
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But.
Turtles Swim.
(c) Terry Pratchett, All Orangutan Librarians Reserved.
Unless insulted.
Id really love to see a reverse chirped plasma wake accelerator used. Instead of pushing the particles along and geting left behind by relativity, you pull the suckers along and the relativistic slow down in acceleration occurs at the same rate os the decay of the chirp, so you get full energy in a shorter distance, and youre runnign into the pulses meaning they get denser the faster you go.?
As for the coloured glass condensate, thats the Rainbow Jewel,a nd it will be the same point in the equations where the evento horizon of a pure mass energy collection occurs, such as electrons, or plank masses?
An epic pony particle would indeed be a thrilling thing to discover.
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In a way, both the idea that there's no end of ever-smaller turtles stacked under one another, or that there is a fundamental base layer of the smallest thing you can have, that you can't get any deeper from, are weird. Is the spacetime itself pixelated or smoothly continuous ad infinitum?
I just don't know how you always manage to find the most perfect pony pictures to illustrate your text!
I didn't know quarks could be detected that way! I always assumed they were just mathematical abstractions :) That's super cool!
Epic indeed! congrats on the news and here's hoping for at least semi-smooth sailing. n_n
This would be a great April Fools Day joke if it didn't happen to be real physics
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I'm now at a point in my career, where I can think: I'll leave than one for the next generation. When will we reach the next turtle? Well, the timeline of the Future Circular Collider is suggesting proton-proton collisions may start in the 2070s.
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I guess not everyone watches episodes while thinking about what bit of physics could be illustrated by each scene.
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It's no April fool. Particle Physics experiments are no picnic party. Particle physics is epically serious.
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