On the hunt for dark matter

This week two news items have focused on the Large Hadron Collider (LHC) of the European Laboratory for Particle Physics (CERN). One is the death of Peter Higgs, Nobel Prize winner and discoverer of the Higgs boson, popularly known as “the God particle.” Another is the solar eclipse. This has generated a shower of speculation due to its coincidence with the restart of operations of the LHC (Large Hadron Collider. However, “it must be clarified that there is no link between the solar eclipse and what we do in the laboratory, which has little to do directly with astrophysics. Every year, after a brief winter technical stop, we restart our accelerator complex and this work requires a start-up time to verify that all the equipment works correctly. After carrying out all the checks, The first collisions of this year actually occurred a few days ago and will continue throughout the year,” says the laboratory spokesperson.

The LHC is not the only accelerator at CERN, but it is the largest. It is located one hundred meters deep at a point on the map between Switzerland and France and is 27 km in diameter. It is made up, says the CERN spokesperson, of “superconducting magnets that drive the energy of particles such as protons within the accelerator. Two beams of these high-energy particles travel at close to the speed of light before colliding. “These particles are so tiny that the task of colliding them is similar to shooting two needles 10 kilometers away with such precision that they meet halfway.”

Thousands of researchers from more or less twenty countries around the world participate in the laboratory experiments. “Here matter is created from energy, following postulates that have their origin in Einstein's theory of relativity,” says Aurelio Juste, researcher at the Institute of High Energy Physics (IFAE) of the Autonomous University of Barcelona. His current research focuses on the Atlas experiment, one of the large particle detectors built at the LHC, because apart from producing particles, they have to be observed to be able to determine what they are like, for example, what their mass is… .

The divine particle

In short, the Swiss particle accelerator reproduces the conditions in the universe immediately after the Big Bang so that we can understand why it is such and how we know it, that is, what matter is like, its structure and the fundamental forces of nature, «A physics that is not accessible under normal conditions. Thanks to the LHC we can analyze those physical processes that have had consequences throughout the evolution of the universe, such as the creation of dark matter,” says Aurelio Juste of the IFAE.

Part of what happened at the time of the Big Bang has been explained with the so-called standard model. «Thanks to experiments it is known that the protons and neutrons that make up the nucleus of atoms can be divided into even smaller particles. The discovery of these subatomic particles was the beginning of the development of one of the most important theories in physics, the standard model. This contemplates 17 fundamental particles that, when interacting with each other through the influence of forces, make up the universe we know. The last piece that was missing to complete this model was the Higgs Boson finally discovered in 2012,” explains Dr. Raquel González Arrabal of the “Guillermo Velarde” Nuclear Fusion Institute and the Department of Energy Engineering of the Polytechnic University of Madrid.

All the particles of the standard model that make it up have been detected, including the Higgs boson. In the 1960s, Peter Higgs, who died this week, began working on a theory about an elementary particle that would allow us to understand the origin of mass in the universe. Something that could not be demonstrated until the appearance of the LHC (in operation since 2008). In 2012, evidence of this particle capable of giving mass to the rest was detected, which is why it was popularly named “The God Particle.” In 2013, scientists François Englert and Peter Higgs were awarded the Nobel Prize in Physics for this discovery.

Dark matter and a 10-dimensional universe

The standard model, however, has reached its limit and is no longer useful for knowing, for example, what happens inside a black hole or what dark matter is. «It is a very interesting moment in research because there are many enigmas and many theories such as the superstring theory that maintains that we live in a 10-dimensional universe (beyond that of space and time that humans perceive). To prove these theories, such as supersymmetry, we need to find the ingredients that make them up,” says Juste.

The nature of dark matter is one of these great pending enigmas of physics; It is known that it exists, that it is the dominant matter in the universe and that it influences it, but for now there is no indication of the existence of dark matter particles in collisions, although the search continues. To understand the complexity of the operation of the large collider in its search for particles, the words of CERN are enough: “Only a few of the 1 billion collisions every second have the special characteristics that can lead to new discoveries.” «The standard model is now complete, but it is only capable of predicting 4% of the known universe. There are still questions to be resolved that this model does not explain, such as neutrinos and their masses, why there is more matter than antimatter, the presence of dark matter or why gravity is so weak compared to other forces. These unknowns make us think that what has been seen so far is not all there is, for example, the deformations in the path of light observed with the Hubble telescope, the rotation of galaxies, etc., give clues about the existence of dark matter. This means that what is happening is that we have reached the limit of what we can observe with the tools we currently have,” explains Raquel González from the UPM.

Technological applications

Why is it so important to know what happened in the first moments of the universe? In addition to why human beings want to understand, some of these big questions involve technological developments or commercial applications. «Particle physics tries to answer these questions and that forces us to develop technology. Examples of applications arising from physics are the internet or proton therapies. Some of the pending questions will take us hundreds of years and may bring about applications for interstellar travel or to generate energy using the cosmos,” says Juste, to which Raquel González adds other uses such as “the development of large-scale superconductivity for its application in the generation of high magnetic fields, which could not be achieved in any other way.

In this desire to understand how and why matter in the universe is the way it is, CERN has set itself a new challenge: increasing the luminosity of the LHC to continue searching for particles that until now have not been recorded. «The achievement of these energies could give us access to the discovery of new particles that would contribute to the development of a unified theory of physics. Another objective is to increase the energy at which the particles collide, the idea is to do so until achieving energies of at least 100 TeV, the current LHC works with an energy of 16 TeV. for which it is necessary to build a new hadronic collider,” concludes UPM researcher Raquel González.

Particle acceleratorCERN

The gravitational effect of the moon

The operation of the accelerator is complex and delicate. Not only, as CERN says, because a few of the thousands of collisions that take place every second will lead to discoveries, but also because there are natural and distant phenomena that affect it, such as the gravitational effect of the moon. The accelerator is so large that the gravitational force exerted by our satellite is not the same at all points, which creates small distortions within the tunnel. The machine perceives them due to its high sensitivity. This occurs as the moon rises in the sky; The force it exerts changes sufficiently to require a periodic correction of the orbit of the particle beams in the accelerator: “the orbits change, and not only that, they do it in a different way throughout the passage of the particles.” , they say from CERN and add that all experiments need these corrections.