Monday, August 8

“Everyone wants to look for a signal that goes beyond the standard physics model”: Scientist at Large Hadron Collider

Nicola Neri, a senior member of the LHCb experiment, spoke to indianexpress.com about the Large Hadron Collider, the three new particles it discovered and why scientists are hoping it will yield discoveries that break the standard model of particle physics.

The Large Hadron Collider (LHC), the biggest and most complex machine ever built by mankind, began operations again in April this year after nearly three years of maintenance and upgrades. After the particle accelerator began smashing together particles at an unprecedented energy level, CERN (the European Organisation for Nuclear Research) announced that the LHC has helped find three previously never-before-seen particles: a new kind of “pentaquark” and a pair of “tetraquarks,” which have never been observed before.

Nicola Neri, a senior member of the LHCb (LHC beauty) experiment spoke to indianexpress.com about the new discovery, the future of particle accelerators and why scientists are hoping that the next discovery from the LHC will break down the standard model, a model of particle physics that seems to accommodate all the discoveries made by LHC so far. Here is an edited version of the interview.

Q: What is this new pentaquark and the pair of tetraquarks?
We discovered some exotic particles, which means they don’t exist naturally and are not ordinary matter. Quarks are fundamental particles and they combine together to form hadrons like baryons with three quarks and mesons with a quark and anti-quark. These are particles that we study and we know their properties very well.

But exotics are different and they are made differently. In the case of the newly-discovered pentaquark, it is still a baryon but with the three quarks, it has an extra pair consisting of a quark and an anti-quark. The two tetraquarks are within the family of mesons but instead of having pairs of quarks and anti-quarks, it has two pairs of quarks. These states were predicted in the nominal quark model introduced in the sixties but these states were not found until now.

Q: How do you detect these particles when they have such a short life span?
Their lifetime is very short. They are produced and they decay almost immediately. The technique we use is the reconstruction of the decay process. The exotic particles decay into more stable charged particles that move within the tracking volume of our detectors. When they do that, they bend inside the magnetic field we have and release energy in the detectors. We can detect this energy signal to calculate their position and trajectory, thereby helping us reconstruct the decay process and understand what exotic particles they came from.

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Of course, this is a very complex process. We use pattern recognition techniques to make sure that we assign the right hits to the right track. It requires very advanced detectors, very advanced data processing, and very advanced reconstruction software that we have developed.

Q: What is the importance of the discovery of these particles?
This is very intriguing from a particle physics theory perspective. We currently do not know what is the mechanism that binds the quarks in these states together. That is why there is a lot of interest. We know that these particles exist, we can detect them, and we can measure their properties, but we really don’t know how these particles are bound together.

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