REPORT OF DISCUSSION CLUB



SESSION NO.7(B)

Topic : Experimental approach to Dark Matter

Presenter:Sakshi Bhise

Date:25th February,2020.





DARK MATTER

EXPERIMENTS AND RESEARCHES





Physicists from Brown university (A university in US) devised a strategy in 2017 (1st August 2017) in order to detect interactions between dark matter particles(WIMP's) and helium superfluid.





What are WIMP's?

WIMP stands for weakly interacting massive particles.As the name suggests, these are particles that are weakly interacting, they only interact through Gravitational force or the Weak force, not with Electromagnetic force(light) or the Strong Nuclear Force. These are the best candidates for Dark Matter Particles, but since they do not interact , they are really hard to detect. Also, the massive implies they have more mass than protons.





Fun Fact: Neutrinos are not WIMP's as they are weakly interacting, but they are not massive.





Hellium superfluid: Superfluids are liquids that remain in liquid state at very low temperature and have zero viscosity. Liquid hellium can remain in liquid state upto 4.2K (-268.93 C).

An image that depicts that the superfluid defies Gravity as it crawls through the inner layer of the tube and slides down the outer layer in the form of drops.





It does not turns into solid at atmospheric pressure, the pressure needs to be about 20 times the atmospheric pressure to make it into solid hellium. Superfluid helium-4 is an example of a superfluid, where hellium-4 is an isotope of helium with 2 protons and 2 neutrons and it is way more abundant than the other isotope, helium-3 with 2 protons and 1 neutron.





EXPERIMENTS TO DETECT DARK MATTER.

When a particle dark matter is passed through a tub of superfluid helium atoms, it should collide with atleast one helium nucleus. This collision should produce phonons(quantum of vibrational mechanical energy like photons are quantum of electromagnetic or light energy) and rotons(excitations with very short wavelength) which propagate through the fluid without loss of kinetic energy.When these excitations reach the surface of the superfluids they’ll cause helium atom to be released into vaccum space.

When the vacuum space is filled with array of positively charged metal pins, as the atom is released it goes near the pin and pulls an electrom from the atom creating a positively charged helium atom. And since its near the positively charged pin it will fly off (since two positive charges will repel each other)with enough energy to be detected by a calorimeter(a device that detects heat change during chemical reactions),so even if theres only 1 atom and 10000volts on pins .. positive ion will hold 10000volts on it (as it is being repelled by all those 1000 positive charges)and will be detected.