the great party story of the young girl-electron which was going to a party story of the young girl-electron which was going to a party

Questions & Answers


(Credit: CERN) 		 

Nega makes things clear
  • The story says that Scientists, through experiments, study elementary particles and the forces that keep them together to form matter. How do they do this? Can you give me an example of an experiment?
    Imagine the long empty pipe (ring shaped) of a Machine designed to accelerate particles, called an Accelerator. Inside this pipe Scientists circulate protons, for example, which can reach extremely high speed, close to the speed of light, and therefore with very high energy. Then the protons are driven to collide with a motionless target or against antiprotons moving at high energy but in the opposite direction to that of the incoming protons.

    Do you remember the formula E = mc2 mentioned in the story? From this formula it's evident that energy and mass are two exchangeable forms of the same realty. That's why, in the impact between protons and antiprotons at high energy, new matter is created in the form of many particles, sometimes new or predicted by some Theory. From a study of the particles produced, you can get information on the properties of the particles and on the forces they interact with.

    The figure above, from a CERN publication, shows clearly what happens in a collision between two particles with a fanciful image of everyday objects. Two strawberries, travelling at high speed and with great energy, collide: their energy changes into matter and creates many fruits that didn't exist before, some similar to the previous ones and some completely new.

  • What is the reason for making protons come into collision with moving antiprotons instead of motionless protons? This seems strange.
    This serves to have more energy in the collision. Think back again to the already mentioned formula E = mc2 which tells us that energy and mass can be converted one into the other. Well, keeping this in mind, Scientists learned many decades ago to use collisions at high energy between elementary particles to "create" matter.

    However, in the case of the collision of a moving proton with a motionless target, only a part of the energy of the bullet-particle is available to transform into matter. Let's see why.

    A bullet proton, accelerated to a speed close to that of light, increases its mass considerably. In other words, the bullet proton, which can be considered as a bike at rest, becomes 500 times heavier; it becomes a truck. So, just as a moving truck can't be stopped by the impact against a bike, which is dragged away, the proton coming at high speed against a motionless brother drags it along with it. Its initial energy is mainly spent on making the target-bullet system move.

    Now, let's suppose that two particles, both at high energy (two trucks), collide frontally. Let's also suppose, for example, that they stop in the position of the impact, losing all their moving energy. So, in this case, all their initial energy can be used to produce matter. The saving in terms of energy is enormous.

    That's why a "colliding beams Machine" (collider) has been designed in which beams of protons and antiprotons at extremely high energy are driven to collide frontally. In this way the energy available for the transformation into matter is higher, much higher, compared to the energy available when a proton beam strikes against a motionless target.
  • Has the idea of the frontal collision between protons and antiprotons at high energy led to any interesting results?
    Scientists have used this idea to "create" some particles (that had only been hypothesised before) in the laboratory, confirming a very important theory which tries to explain our World.

    In 1983, in the CERN Laboratories of Geneva, a group of Scientists (led by the Italian C. Rubbia, Nobel Prize for Physics in 1984) verified the so called "Electroweak Theory".

    Based on this theory the electromagnetic and weak interactions are two different aspects of the same force called "electroweak" interaction. In other words, the theory gives a "unified" description of the two forces and supposes that these two forces are not "distinguishable" at higher energies.

    The experimental confirmation of this hypothesis has been a fundamental step in the story of Physics. Note that  they are two of the four "fundamental interactions" of Nature.

    It's important to keep in mind that it's experimental verification which establishes, by means of a concrete fact, the truth of a theory, and also that a theory describes a real situation that can be observed in Nature.

    One curious fact to note: Scientists gave these particles, that in some way tell us about our World, very strange names such as Z0 particle, W+ boson and W- boson.