Nucleus to Quark Gluon Plasma -- Popular talk

This is in continuation of the earlier lecture in the camp. The youtube link of the first lecture is in the first comment below. Starting from the atom, we had talked about how we learnt about the constituents of nucleus. We learnt how the different discoveries unfolded the secrets of nature at the subatomic level. Towards the end of the lecture, we saw that there are many different nuclei, more than one corresponding to each element ( these are isotopes – same proton number, different neutron number). We also saw that as the size of the nucleus increases, the number of neutrons far exceed the number of protons. The larger number of neutrons help to overcome the increasing coulomb repulsive force and keep the nucleons bound together in the nucleus. Binding energy (BE) reveals how tightly the nuclei are bound. With such a large number of nuclei across the periodic table, and isotopes, it is so interesting to note that the BE is nearly a constant, within about 10-15 percent for most part of the periodic table. This is very interesting and makes us curious to know how this happens. So we gave some arguments and wrote five terms semi-intuitively. Each term had some dependence on the number of protons or neutrons, and some constant. And just 5 constants could explain the observed values of binding energy over such a large range. This is remarkable. Probing deeper, we learn that the neutrons and protons are arranged in shells, meaning that the nuclei also have a shell-like structure. Continuing with more scattering experiments, we learnt that there are large number of particles and resonances. And as in periodic table, these particles were classified. Their constituents were proposed and observed. These are quarks --- fractionally charged particles. And these come in six different kinds. Each of the six kinds of quarks has properties like charge, spin and another property which we call as the colour quantum of the quark. All this is fine, but how do we really know all this? How do we measure the particles and determine any information about them Just like contrails in the sky convey a passing plane, similarly when elementary particles pass through material sensitive to their properties, they create a track. Using the thickness (meaning ionization) and curvature of the track, we can identify the particle that caused it. Repeating such experiments with collisions of different particles and nuclei reveal a lot of information about the structure of matter and of subatomic matter at extreme conditions. One such phase is called Quark Gluon Plasma which is created in collision of two heavy ions at high energy. And in the same spirit, there is much more to learn and discover. In addition to the topic, we also talk about some other issues and address the questions sent by the students. There are two unanswered questions in this talk which we shall talk about another time. Also, some opined that parts of it should have been made more pedagogical :-) If you enjoy these, please write in the comments what you enjoyed and what else should we talk about. Enjoy.