From particle colliders to automated computer simulations

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Initially, I wanted to propose to build a community-based participatory research project on Hive (and STEMsocial). From my experience with students with no advanced knowledge in physics (and no knowledge in particle physics at all), I am quite convinced that such a project could work. This could yield a great outcome, not only scientifically but also in terms of introducing a way to use the chain to record systematically and transparently how a scientific project evolves. This would be, in my opinion, a cool precedent for Hive.

However, this requires that there are participants ready to invest a few hours of their time per week, and this during a few months. This is where I started to hesitate. After having slept several nights on this matter, I am still completely undecided about proposing this project or not. I will continue debating with myself this week, and anyone is free to enter the debate in the comment section of this blog (even if it is finally a bit far from the subject of the day).

I therefore needed to find something different to write about today. This is a piece of cake, as there are so many interesting particle physics topics that I work on. After having spent the last two weeks discussing neutrinos, it is time to change gears and focus on a different topic.

The idea I want to discuss is about how particle physics simulations can be easily achieved on computers such as those that can be bought in regular shops, and how there is no need to know anything about quantum field theory magic to run those simulations. As a matter of fact, my older son managed to simulate thousands of Large Hadron Collider collisions giving rise to the production of a Higgs boson when he was six. It is obviously clear that he didn’t know anything about physics at this age…

In this blog I discuss how collisions such as those ongoing at CERN’s Large Hadron Collider (the LHC) work. I focus in particular how and where new phenomena beyond the Standard Model of particle physics are expected to occur, and why we need high-energy collisions to explore territories beyond the Standard Model. Any excuse is good to provide bits of information on my world. From there, we naturally move on with computer codes, whose development consists of a sub-topic of my research work.


[Credits: Original image by phsymyst (CC BY 2.0)]


Accelerated protons as a probe of the high-energy frontier


In a circular particle collider such as the LHC, protons are accelerated and collimated in two intense beams that are then smashed in different points of the machine. Whereas this sentence does not look like a special sentence, it introduces two important concepts: high energy and high intensity.

First of all, let’s focus on high-energy collisions. We have currently explored the Standard Model of particle physics quite deeply at all energies reached so far in an experiment. We however know that once extrapolated to higher energies, this very successful theoretical framework has conceptual issues and practical limitations. It is thus important to explore the high-energy regime as much as we can by tracking new particles and new phenomena (that may also not be directly associated with a new particle). This may reveal how the Standard Model should be extended to accommodate some of its current problems.

However, we should keep in mind that an exploration process is always paved with unknowns and no guarantee… This is why it is so exciting, in my opinion. We have no idea about what we will find, if anything.

Particle colliders consist of some of the tools we use to open a window on this high-energy world. Thanks to powerful electromagnetic fields (electric fields to be precise), it is possible to accelerate charged particles to an incredible speed. In the tunnel of the Large Hadron Collider, bunches of protons are accelerated to 6.5 TeV. This means that every proton has a kinetic energy equal to 6500 times its mass, reaching a speed of 99.99999896% the speed of light. We can thus see the LHC as the fastest racetrack on the planet (to take the expression found on this webpage).

This is where special relativity enters the game. A very energetic collision can lead to the production of very massive particles. Mass is indeed one of the three forms of energy that exist in the microscopic world. As already mentioned several times in other blogs, the golden rule of physics states that total energy is conserved in any process. This means that one form of energy (i.e. kinetic energy) can be converted into any other form of energy (i.e. mass energy) in a process, provided that their sum is constant. This is exactly what we expect to happen at particle colliders, namely the conversion of the protons’ kinetic energy into something new.


[Credits: P. Stroppa (CEA)]

Any particle collider also relies on powerful magnetic fields. Whereas electric fields are required to accelerate particles, magnetic fields are needed to control their trajectories. We indeed do not want to send our beams to the moon. Instead, we want to collide them in very well defined points. Moreover, magnetic fields are additionally used to collimate the beams as much as possible, so that we could reach a high intensity of particle collisions.

New phenomena are expected to be rare, and very intense beams are necessary to reach a satisfactory amount of collisions. Out of this large amount, there are hopes that a few collisions will be connected to those rare events. Of course, it is then crucial to have a good strategy to see them from an often overwhelming background. This is however a different story.


High-energy proton-proton collisions in a nutshell


For the sake of keeping the discussion as clear as possible, I consider from now on the Large Hadron Collider and assume that two beams of highly-accelerated protons collide.

As already mentioned in this earlier blog, protons are made of three smaller entities called quarks. When protons are accelerated at very high speed, the picture changes a little. They become complex systems made of a huge number of quarks, antiquarks (antiparticles corresponding to quarks) and gluons (the mediators of the strong force). This originates from the behaviour of the strong force itself, and I won’t enter into the details as this deserves an entire blog by itself.

In a high-energy collision, the constituents of the protons scatter, instead of the protons themselves. Therefore, at the LHC we have collisions of quarks, antiquarks and gluons. Whereas most the time, nothing happens when two protons cross each other, once in a while one of the constituents of the first proton interacts with one of the constituents of the second proton, to produce some final state.

Many final states are possible, especially if we consider theories extending the Standard Model of particle physics. Not all final states are however equal. Some of them are associated with a copious rate, and some are rarer. In order to know this, we rely on the ‘master equation governing the world’ (that could be the one of either the Standard Model, or of any other particle physics model). This equation contains all the ingredients to calculate the rate associated with any given process that could happen at a particle collider.

However, it is impossible to tell the outcome of a specific collision. From the knowledge of the rates of all possible processes, we can only associate a probability with each of the possible outcomes. Large rates correspond to large probabilities, while small rates correspond to small probabilities. We naturally go back to the reason of having a lot of collisions happening in an experiment. To be able to observe a rare final state in a few collisions, it is important to have a very large number of collisions in total. The small associated probability and the huge total number of collisions then guarantee that in a few cases, the rare final state considered is produced.


[Credits: CERN]

This probabilistic nature stems from the quantum nature of the microscopic world. The result of a given collision is not deterministic, but probabilistic. Therefore, we need to re-run experiments many many times (i.e. to have tons of collisions) to have a good idea of what is going on. Probabilities are naturally related to occurrence rates when collision statistics is large. Whereas this may sound weird, hundreds of years of data have proven it to work…

God is actually playing dice with the universe! We know today that the 20th was a quantum century. However, it is also clear that the 21st century will even be more quantum (quantum computers are coming…)!


A master equation to rule all calculations!


What about this master equation that I mentioned above? Do we really only need a single equation to be able to calculate anything relevant for particle colliders? The answer is positive, and this equation is called the Lagrangian of the particle physics model.

The Lagrangian contains all the building blocks of the theory: the manner each particle propagates, which particle interacts with which particle, which particle has a mass and which one has not, etc. Everything is in there. Everything. The Lagrangian is a unique way to fully define a theory.

So we have a model of particle physics, and therefore we have a Lagrangian. We are moreover interested in many collider processes. How can we relate the probabilities and the rates associated with these processes (which consist of the information relevant for a particle collider experiment) to the Lagrangian?

This answer originates from the concept of Feynman rules, as well as to the calculation of very highly-dimensional integrals. I skip any detail here, as this could become quite cumbersome. At the end of the day, what matters is that regardless of the process of interest, there are well-defined quantum field theory recipes that can be followed. Having recipes means that we can teach a computer how to do this systematically (and correctly).

This has been done, and the resulting computer codes (yes we even have several of them) are used on a daily basis by physicists from all over the world. An example of such a code is [email protected]. In this code, users input details about their favourite collider, particle physics model and process of interest through a human-friendly Python interface.


[Credits: Edward Tufte (Twitter)]

The rest is automated. This means that anyone could run this code. Me, my son or even my bachelor students who don’t not know much about particle physics yet. What is needed to be known is the final state that we are interested in producing in a collider experiment, for a given particle physics model. That’s all. Really!

Obviously, this can be done only because the code has been carefully validated against tons of non-automated calculations and results coming from the hard work of many generations of physicists. This is however how progress is built. We move on from bases established by others to reach new summits.

By running these simulation code, we end up in a few minutes with predictions for the production rate of the process considered, but also with thousands of simulated collisions related to this process. The latter is a bonus coming from the implemented numerical adaptive integration procedure. This is a Monte Carlo integration procedure, that is the only way to solve a highly-dimensional integral numerically. In practice, it explores all configurations of the final state and assesses which ones are the most probable ones and which ones the rarest. We can then extract simulated collisions with configurations occurring in a satisfactory manner related to their level of rarity, or in other words as they occur in nature.


Summary: particle physics simulations on regular computers


In this blog, I started to discuss how particle collisions as happening in colliders such as the Large Hadron Collider at CERN work. I wrote ‘started’ as there is in fact much more to write on this topic, which is left for a future blog. Thanks to very energetic electric and magnetic fields, protons can be accelerated to very high speeds. And by high speed, we actually mean it. At the LHC, they reach 99.99999986% the speed of light. A world record!

When two of such accelerated protons collide, the reaction occurs at the level of their constituents (fundamental particles called quarks, antiquarks and gluons). Thanks to special relativity, the energy in the process can be converted into mass energy, and thus possibly yield the production of new particles beyond the Standard Model.

As a theorist, it is important to be able to calculate the production rates of those new processes, and to simulate collisions as they would occur in nature. This relies on possibly complex quantum field theory calculations. However, there are ways to automate them so that they become fully transparent to anyone. We did this and have taught quantum field theory recipes once and for all to various public computer codes.

In this way, users (who could be physicists or anyone, like my teenager son) only need to provide information about the particle physics model and process of interest. The code then deals with the rest, and in particular with the quantum field theory part. In other words, anyone could investigate any process of any model and see what would be the impact on present and future LHC data by means of easy-made computer simulations.

What I have not said is how this simple picture is getting messy by virtue of the strong interaction. This story will however be the topic of a next blog.

For now, I hope you enjoyed reading this post. On my side, it was quite a good fun to write. Please don’t hesitate to ask questions or provide comments. Feel also free to give some insight on setting up a stage for a community-based participatory research on Hive. I am wondering how doing so would be perceived…

See you next week for the next episode!



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Building a community-based participatory research project on hive will be quite interesting and will further project hive to the world. You can say this is me being selfish as a hive user.

On the other hand, your students also stand to benefit from the immutability of the blockchain or even get exposed to blockchain tech for the first time. If you ask me, I will say bring it on.

As a matter of fact, my older son managed to simulate thousands of Large Hadron Collider collisions giving rise to the production of a Higgs boson when he was six.

Really? Would be interesting to see what else he can do at an older age. Was it intentional or just some surreptitious discoveries?

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My youngest students (i.e. the bachelor ones) already use my blogs as a basis to get details on particle physics. At such a level of study in which they are not experts in quantum mechanics, special relativity and field theory (and the associated math background), this is by far sufficient. Moreover, if is good to mention at this stage that the research project is fully adapted to this.

I am still unsure about injecting the students in any process that could be ported to Hive. Their internship is quite advanced already, and I don't want to change the habits they built during the last two months. However, constructing something from scratch on Hive may be what I will try, if I (we?) decide to move on.

Really? Would be interesting to see what else he can do at an older age. Was it intentional or just some surreptitious discoveries?

In fact, I just asked him to type this and that. He did it and then I explained him what he did. At the end, this was just to show off ;)

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Doing something on hive would be great.

I hope you'll tell the story to your son of how he was able to model collision at a tender age. 😅

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This could yield a great outcome, not only scientifically but also in terms of introducing a way to use the chain to record systematically and transparently how a scientific project evolves.

The idea is very interesting, it's as you mentioned though about the participation and time. Especially if they have no idea about Hive. But definitely worth a shot.

Maybe you can kick it off as a tag or few tags and see the participation from there?

I am wondering how doing so would be perceived…

On Hive? Hivers are very welcoming for all new ideas I think, so there's no issue there. From outside Hive? I don't see how here would differ from any other stage or platform, be it forums or blogs or what have you. The immutability is a big plus too.

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As I mentioned it to @gentleshaid, I do not think that I will involve my current pair of bachelor students to any long-term participatory research project we may build on Hive (if any). The reason is that they have their habits, and that I don't want to mess them up. The internship is supposed to end in a couple of months, and they need to stay focused.

However, we could build something fresh with the Hive community directly. The required level of expertise will be very low (similar to that of my bachelor students), and only motivation will be mandatory. At the end of the day, we only need a few people who have a few hours per week to start the experiment. What makes me hesitating about proposing it more loudly, ... is that I am very unsure that I can find those 4-5 people (in fact, even having two participants would be sufficient to motivate me to run the experiment to the end).

On Hive? Hivers are very welcoming for all new ideas I think, so there's no issue there. From outside Hive? I don't see how here would differ from any other stage or platform, be it forums or blogs or what have you. The immutability is a big plus too.

I meant on Hive, as outside Hive things are pretty clear. I guess many Hive users may be interested... But without crossing the line and actually playing the game (and doing some work), this will not be sufficient to create a precedent. This is the full source of my hesitation. Running a project without participants makes no sense.

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without crossing the line and actually playing the game (and doing some work), this will not be sufficient to create a precedent

I totally get your hesitation, and I think it's a valid one.

At least the idea is out there now, and I'm sure it will be brewed into something eventually in this form or another.

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Indeed. I will let it get more mature during a week, and I definitely thank you and @gentleshaid for your contribution to the debate :)

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interesting concept, seems it would be much more cost effective indeed !1UP

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Glad to read that you have liked the concept.

Note that I am not sure to understand to which costs you actually refer. Do you mind clarifying or elaborating a bit? Thanks in advance.

Cheers!

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running computer simulations vs running the colliders :)

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Ah yeah, this is definitely waaaaaaaay cheaper. However... we eventually need the colliders to very the simulations are realised in nature (or not) ;)

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I really understand you, relying on voluntary work is really complicated, even more if you need a sustained medium level of effort for a long period.

But who knows, maybe the incentives produced by hive could maintain the effort without having to change continuously the people participating in the experiment.

I hope one day we get to know what is it about!

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You definitely coined my fears very well, even if in principle, a few hours a week is not a big deal. The real problem is that the effort has to be provided on a decent period (a few months probably, with breaks being of course allowed).

On the other hand, I didn't even think about providing any incentive. We are talking about the beauty of research, and having a scientific publication advancing science as a reward. This being said, it is clear that I will support this myself as much as I can, and that STEMsocial will follow (if the project ever starts). I didn't plan to look for any other source of support, although anyone interested is free to help.

As a side note, we may naively think that with this project I will have people working for me for free. This is very untrue, as organising such a project will actually require much more from me than from all participants combined, knowing that I will have to verify every single finding, coordinate everything, etc. I can come back with a huge list of tasks. However, I think that having this happening on Hive may be cool.

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Really agree with what you say that this is going to be a lot of work for you and that you just do it thinking on provinding back to the community.

When I was speaking about incentives I was more thinking on that if it is done creating interesting content in hive, it may generate some attention and contributors will see how they get rewarded.

It is a big decision because once you start it is going to be a lot of work and it would be a shame if the effort is wasted

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I agree with everything that you wrote.

We have handles on incentives that could serve as extra bits to motivate people to participate, as well as an extra way to generate attention both from inside the Hive community and from outside it.

I will continue thinking about it and will make my decision over the week-end. Or maybe, I will just continue thinking for another week. Let's see. I am still very undecided, as can be guessed, although the "no no" is now mostly a "maybe" thanks to the positive feedback I got in the comments to this blog. ;)

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Hello @lemouth,
I enjoyed this blog very much. My physics literacy is increasing, I think (or your writing is getting better😇), because I pretty much got it as I went through the blog. It makes sense that you would need a high number of collisions in order to see a rare event. One question I have is about electric fields and magnetic fields. The electric fields accelerate particles and magnetic fields are used to control their trajectories. I understand that the magnetic fields collimate the particle beams, and that this intensifies the collisions. What I don't understand (this may frustrate you) is the difference between an electric field and a magnetic field.

If you have a science project that you would like to involve the lay (non-science) community in, I would be willing to be a participant. Know this though: my computer skills are extremely limited. I would be willing to put in the time (a few hours a week) but might be challenged by the the required skill level.

Thank you for another great blog. It's a pleasure to learn about stuff I never would have attempted to learn otherwise.

Hope everyone is well in this crazy world of ours. Tense night (geopolitically speaking).

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Thanks for this interesting question, and the nice comments towards this blog and my writing ;) This is always appreciated!

Electric and magnetic fields are two facets of the same phenomenon: electromagnetism. Let me try to explain how they work with more details.

The first thing to keep in mind is that two electric charges of the same sign repel each other, while two electric charges of different signs attract each other. The strength of this attraction/repulsion strongly depends on the distance between the charges. The closer they are, the stronger is the phenomenon.

Let's now assume that we have a bunch of charges present at different positions in space. If I take a fresh charge and put it somewhere, it will start to move. This motion is charaterised by the sum of the electric forces coming from the different charges already present. The electric field is a quantity characterising this force. It tells us in advance which motion any charge put in a given place will have, from the knowledge of the charges already present.

At colliders, we can create strong electric fields in well-defined regions of space so that any charge going through them will feel an important electric force that will accelerate their motion.

Magnetic fields are a bit different (and in fact more complicated to explain), and they are related to magnets and electric currents (charges in motion). Those fields have an impact on the motion of an electric charge. This time, it won't however change the speed of this motion, but only act on its trajectory. Therefore, we can use appropriate magnets to have a magnetic field that will be such that accelerated particle stays within the collider. We can moreover collimate a bunch of particles by forcing their trajectories to be very close to each other.

Does it clarify?

If you have a science project that you would like to involve the lay (non-science) community in, I would be willing to be a participant. Know this though: my computer skills are extremely limited. I would be willing to put in the time (a few hours a week) but might be challenged by the the required skill level.

The only requirement is time (and patience), and obviously a computer that does not necessarily need to be a super computer. Anything from a regular shop works. In this sense, if I start the experiment you can definitely be part of the game! From then, we will see how this evolves.

PS: I am very scary by all of what is currently going on... next door... Crazy world, indeed!

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Geopolitically, things have accelerated from yesterday. Once the machine is in motion, no one can predict the outcome. Unlike introducing an electrical charge into a clearly defined space. I get it. You know exactly the nature of what you are adding and what already exists. You can predict the outcome. And I get it about the magnetic field. It pushes and pulls the charges in a defined way so that these behave predictably.

Thank you @lemouth for the explanation.

As for the project. I am game. Hope I will be a worthy participant.

Have a great, and I hope peaceful, week.

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I have indeed noticed the evolution, I am afraid war is there, unstoppable... :(

PS: glad to read that you are part of the game! I will probably give it a try, and announce it either with the blog of next week or with the next-to-next one (in two weeks).

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Yeah, time is becoming an increasingly scarce resource, and convincing people to invest it will be a tall order.

I wonder if experiments in simulations will slowly replace experiments in the real world!

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In fact, I don't want to convince anyone to do it. I only want people interested in it genuinely to onboard. That is the almost the same, but with a slight difference ;)

I wonder if experiments in simulations will slowly replace experiments in the real world!

Probably not as you need both to verify the status of simulations. This is especially true when they target new phenomena that could possibly exist or not, and when we need an actual confirmation.

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Hello @lemouth I find it very interesting that you can implement a participatory project through the hive blockchain, Undoubtedly this platform has allowed us to interact with our students has become a space where we shelter our academic information to be consulted by them.

You can start by conducting a small pilot test with a small group of students, conducting a survey to see who is interested, in this way you begin to create a precedent and possibly in the future it will become one of the evaluations that you make in your curriculum unit.

I hope you implement it, you would also be a reference for us and see what methods you use to reach students. I hope you will succeed with this idea and make it happen.

So long, have a great weekend.

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In fact, as I have only two of them (who by the way know I write on Hive but didn't ask to join), it is not necessary to implement any interaction on a social medium (we have live discussions instead). The fact is while I would be very happy to see my students here, I won't force them if they don't feel that necessary.

What I had in mind was really a project where we could offer to Hive users who are not scientific to participate and contribute to a scientific project. As the level on physics of any "lambda" person may be similar that of my bachelor students, I imagine that this would be something possible to achieve on Hive.

Sorry for not having been clearer on this. Have a good week-end!

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