Quantum Physics I — the CERN data workflow in new Physics discoveries.
HOW DATA ANALYSIS AT CERN CAN HELP DETECT DARK MATTER
A comprehensive guide of the CERN workflow in new Physics discoveries.
Are you interested in learning more about particle physics? You might have heard terms like neutrinos, quarks, or dark matter mentioned before and want to know more about them. However, the literature and articles involved mainly use terms and concepts that the reader is supposed to already know, which makes them inaccessible to anyone not in this field.
In this article, I’ll provide an easy-to-understand explanation about everything you’d need to know to understand the main points of these articles: the main results, how they’ve been obtained, and the methodology behind their collection. It will be divided into two parts:
- The first one will focus on the basic concepts regarding this subject: a basic Standard Model (SM) overview and a description of dark matter and the Compact Muon Solenoid (CMS) detector.
- The second one will focus on the details of data collection and analysis at CERN; this one is where the Data Science component will be.
My experience with this subject comes from my undergraduate project in Physics dedicated to a dark matter model verification with LHC Run 2 data, where my love for experimental particle physics was consolidated. I hope this article will help you understand the basics of these studies at CERN and get you started in further publications on this topic.
Standard Model Basics
We’ll start with a short description of the Standard Model (SM), the theory that describes the structure of matter and its interactions. It’s worth noting that the terminology model comes from the 1970s, when this theory didn’t have enough experimental evidence to support it as such, while nowadays it does.
The SM postulates the existence of two kinds of particles: fermions, which compose all visible matter, and baryons, that mediate the fundamental interactions (ElectroMagnetism, Strong and Weak forces, and Gravity; integrating this last one is still one of the biggest mysteries of modern physics). According to this theory, every interaction between two particles is mediated via the exchange of a boson. Below you can see a simple diagram of these particles and their classifications. The main difference between these two types of particles is their spin: fermions have half-integer spins, while bosons have integer spins, and this is the main reason the physics around these particles are so different.
- ElectroMagnetism: this force is mediated by the photon (γ) between particles that share electric charge; this includes all quarks, all leptons except neutrinos, and both bosons W⁺ and W⁻.
- Weak force: this is the main force behind the decay of some particles into others, like radioactivity, and is mediated by the bosons W⁺, W⁻, and the boson Z⁰ (the superscript indicates their electric charge). The charge needed for this interaction is the weak charge, and all fermions have it.
- Strong force: this is the force that binds the atomic nucleus together, and is mediated by the gluon (g), which has no electric or weak charges. However, a big difference with the previous interactions is that the gluon possesses colour (this is the name given to the strong charge). Its name comes from the fact that this interaction is several times stronger than electromagnetism, thus showing how the nucleus can exist even when it’s made out of protons that should be repelling one another. Only quarks have colour, and as such are the only particles affected by the strong force.
What is Dark Matter?We’ve talked about dark matter in this article before, but we haven’t really given any sort of description of it; we’ll tackle this briefly in this section, discussing the evidence that supports its existence as well.
Several sources, even going back as far as the 1930s, show that astronomical calculations involving galaxy masses and rotational speeds don’t match with the expected results from the observable masses they have. One example of this is the Cosmic Microwave Background or CMB, where we learned that baryonic matter (meaning stars, planets, humans, etc.) only makes up ~5% of the total universe mass; here is some documentation on CMB, gravitational lensing and the Hubble Law that expands on this matter.Is there a possibility that this is actually some sort of known particle? Some possible candidates could be :
- Antimatter: this is impossible since the matter-antimatter annihilation process shows very characteristic 𝜸-rays, and these are not seen.
- Black holes: again, it can’t be since black holes curve light around them, and dark matter doesn’t affect photons.