**QUARK FUSION**

**By Suvir Rathore**

Physicists use the standard model to describe the interactions between the fundamental elementary particles of our universe, which is split into three main sections: **Quarks **(matter), which come in 6 flavours that come in 3 different colours[1] and mix to form colourless composite particles – Mesons and Baryons; **Leptons** (matter), which are arranged in 3 main generations that increase in mass and instability where electrons are the lightest out of the 3 in its family (Electron, Muon and Tau). Each is ‘paired’ with a distinct neutrino which are electrically neutral and have close to zero mass and finally the **force carriers**, where a specific boson (integer spin particles) carries out a force. For example, Gluons carry the strong force, Photons the electromagnetic force, W and Z bosons the weak force and the recently ‘discovered’ Higgs Boson (however it currently aids understanding into the origin of the mass of particles, not necessarily the force, as gravity still remains mathematically incompatible with quantum theory).

Our current understanding of nuclear fusion means that it would release around 4 times more energy that fission (per unit mass) however in order to allow fusion to happen here on Earth, more energy would have to be put in than we get out of it, rendering the process useless as of current. Nevertheless potentially viable methods such as magnetic or inertial confinement are continuously being developed so that in the future we can harness the energy released.

The sun uses fusion reactions to sustain itself where the energy released counters the force of gravity hence preventing the star from collapsing in on itself. The core of the sun is almost 10 times cooler than the required temperature of fusion, however fusion of the initial hydrogen nuclei is achieved through quantum tunnelling as a result of Heisenberg’s Uncertainty Principle as due to an uncertainty in momentum, particles can gain an immense momentum and fuse (this also works for the uncertainty of their position). This can’t be done on Earth, largely due to the fact that the sun is enormous, so the probability of a particle exceeding the barrier is much higher than one on Earth, especially in lab conditions.

One theoretical method of fusion is by using quarks. A ‘doubly charmed’ baryon (Xicc++) consists of 2 charm quarks and 1 lighter (up) quark, where the two charm quarks have a binding energy of 130 MeV therefore releasing (the ‘leftover’) 12 MeV, which is approximately two-thirds of a deuterium-helium 3 fusion reaction (D + 3He -> 4He + p + 18.35 MeV). Although this method is far cooler it is not viable at all.

However, there is a far more energetic quark-fusion reaction: the fusion of 2 bottom quarks. The two bottom quarks have a binding energy of 280 MeV, releasing (+) 138 MeV when they fuse. Here the two heavy quark baryons fuse to form a neutron (bottom right of the image) and a doubly bottom baryon (top right) with up to 8 times more energy being released then the deuterium-tritium fusion reaction.

Heavy quarks such as the bottom and charm, however, are very unstable where the bottom quark decays quickly usually after just 1 picosecond (~1.3 x 10−12 s half-life). This means that practical applications of such fusion reactions are far from viable and appropriate. Fortunately, the quick decay of these baryons into smaller lighter and more stable quarks means chain reactions (which is essentially the main principle of hydrogen fusion in hydrogen bombs) won’t occur. These reactions are purely theoretical and have not been tested in any lab, although such a reaction may feature at The European Organisation for Nuclear Research (CERN) in the upcoming years.

[1] The 6 flavours of quarks do not have this as their visible colour, instead they have a colour charge which is essentially the source of the strong force in quantum chromodynamics.