Wednesday, 25 March 2015

Antimatter and CERN's Large Hadron Collider

If you watch a lot of the popular sitcom, 'The Big Bang Theory' or if you're a big science nerd like me, you've probably heard about these terms, but failed to understand. Let's see if I can be of any help :)

So, lets start with the most popular physics equation, E=mc².It basically says that mass is concentrated energy and mass and energy are interchangeable, kind of like two currencies but with a huge exchange rate. 90 trillion joules of energy is equivalent to 1g of standard mass. If we concentrate huge amounts of energy in a tiny space, new particles will come into existence. If we look closer we see that these particles always come in pairs, like twins. That's because particles( each and every one of them) always have their counterpart an 'antiparticle' and these are always produced in exactly equal amounts (1:1 ratio). This might sound like science fiction, but it's actually true and is the daily life at particle accelerators, CERN LHC  (We'll discuss that soon). 
 In the collisions between two protons between CERN's LHC, billions of particles and antiparticles are produced every second. Consider for example the electron. It has a very small mass ( in physics we call it infinitely small)  and a negative charge. It's anti particle, the positron has exactly the same mass but an opposite positive charge. But apart from the opposite charges, both particles are identical and perfectly stable. And the same is true for the heavy cousins, the proton and the anti-proton. Therefore, scientists are convinced that a world made of antimatter would look, feel and smell just like our world. In this anti-world, we might find anti-water, anti-gold, anti-food and maybe anti-you & me! 
Now imagine a matter and an antimatter particle are brought together. These two apparently if are in contact, would completely disappear into a big flash of energy, equivalent to an atomic bomb! Because combining matter and antimatter would create so much energy that it can run future spaceships like in Star Wars, cause energy content of antimatter is a billion times more than the conventional fuel. The energy of 1g of antimatter would be enough to put a rocket in our orbit. So why not use antimatter in energy production? Well, antimatter isn't just sitting around. We have to make antimatter before we can combust it. 

And creating antimatter takes a billion times more energy to make antimatter than you get back. So some of us might say that why don't we just dig some antimatter from the space? A few decades ago, many scientists believed that this might be possible. But today, observations have shown that there is no significant amounts of antimatter out there, which is weird cause it was already established that there should be equal amounts of matter and antimatter. Now that is a real mystery. To understand this better, let us go back to the Big Bang.
                                                                                                                                                               The Big Bang suggests that the universe was created in an instant as huge amounts of energy transformed into  mass, and our initial universe contained equal amounts of matter and antimatter. But just a second latter, most  of the matter and all of the antimatter had destroyed one another producing enormous amounts of energy in forms of radiation, that can be still observed today. Now you might say,"Where the hell did all that antimatter  disappear and only matter was left? It seems that we were somehow lucky that there existed a tiny amount of asymmetry between few of the matter and antimatter particles which when collided, matter won and was left.   Hadn't been so, there would no matter at all, and obviously you wouldn't be able to read this right now cause you don't exist. But what causes this asymmetry? This is one of the biggest mysteries of the universe ( Baryogenesis- for which the  the CERN LHC was created.  

                                                  CERN, or the Conseil EuropĂ©en pour la Recherche NuclĂ©aire  is actually the worlds largest physics laboratory located at Geneva, Switzerland. The 'LHC' stands for the Large Hadron Collider. It basically a particle accelerator, and serves as Mecca to all the physicists around the world. The whole setup is actually of a circle, 27 kilometers in circumference! What it does is pretty neat.

Hydrogen atoms from a gas cylinder are fed at a precisely controlled rate into the source chamber of the LHC, from where their electrons are stripped off leaving only the protons, or the hydrogen nuclei. These protons are then accelerated using an electric field. This acceleration from the external electric field has caused the protons to attain the speed of a rocket. The packet of protons then slowly reach 1/3rd the speed of light and enters a booster which is another small part-circle(157 m in circumference) of the LHC circle which increases the speed of the photons to 91.6 % of the speed of light and squeezes them closer together , using powerful magnets and electric fields. From there, it enters into another part-circle of the LHC called the proton synchrotron. Let us follow two such protons. Proton is 627m in circumference and they circulate for 1.2 seconds, reaching about 99.9% of the velocity of light. It's here that a point of transition is reached (this is crucial), a point where the energy added to the protons by the electric field cannot increase the velocity of the protons, cause they are already reaching the limiting speed of light(which is maximum). Instead the added energy increases the mass of the protons. In short, the protons can't go faster so they get heavier. At this point, the energy of each proton is measured as 'electronVolts' and is 25 giga eV. The protons now become 25 times heavier then they are at rest. 

LHC. Notice the small Proton Synchroton(PS)

The protons are now transferred to the main orbit of the Large Hadron Collider, circumference of 27 kilometers. There are two vacuum pipes in the LHC, containing the proton beams travelling in opposite directions, clockwise and anticlockwise. For half an hour, the PS keeps transferring protons in the LHC. The velocity of the protons is now so high, that it goes round the 27 km circumference, over 11,000 times per second, becoming 7000 times heavier than at rest. The magnetic force needed to bend the protons in the right circular direction of the orbit is so high that the entire LHC is kept colder than the outer space so that the elector magnets present inside the circular tubes become superconducting.

 Now the protons are made to collide. The collisions emit matter and antimatter particles similar to that of the big bang and the asymmetry is studied.