Meanwhile at CERN

The Joke

Two scientists at CERN:

- Bob, look at the data, it's scary! These two particle fields are anti-commuting but they have 0-spin. I am afraid, Bob. I am telling you, there must be ghosts in this lab. Run away!

Picture is taken from http://www.toonpool.com/cartoons/God%20particle%20found_172865 and is modified.

Background
Only theoretical physicists can get it right away. Everybody else should go through a standard textbook of quantum field theory and then read the joke again.

However, we will attempt to give a glimpse of theory. According to the spin-statistics theorem, the spin of a particle is related to the statistics it follows. For example, particles with half-integer spin follow the Fermi-Dirac statistics and they are categorised as Fermions. Furthermore, particles with integer spin follow the Bose-Einstein statistics and they are named Bosons.

Now, in quantum field theory, the quantisation of a gauge field through the path-integral formalism requires the exclusion of the all gauge-equivalent contributions to the path integral. This is achieved by the so called Faddeev-Popov trick, introduced by Faddeev and Popov.  This trick gives rise to fictitious fields, which are anti-commuting (i.e. obey Fermi-Dirac statistics) and have 0-spin. 


We emphasize that these fields are fictitious, they do not correspond to real field (particles) and have been introduced as part of a mathematical trick, they can't appear in any observation and carry no physical content or information. This is probably the reason that have been given the provocative name ghosts.

A theoretical physicist at interview

The Joke

A brown hair male theoretical physicist, named X, has applied for a position in a research institution. The time for the interview has come and the physicist is a bit anxious.

The scientific committee checks his CV, asks him some questions regarding his research and interests. The candidate has an excellent background, but the members of the committee seem to have a problem. One of them tells him

- Well, Dr X, you have a brilliant background, but we are looking for a blonde, female and experimental physicist.  How do you meet these criteria?

and Dr X replies after some thought,
- Hmm, I could negotiate the first two points, but definitely not the third.


Background

There is no math background here, but you should know what theoretical physicists think about experimentalists.

Maybe a funny example (bonus joke)

Functions in a bar

The Joke

All the function are gathered in a bar, drinking, chatting and relaxing. Suddenly, the $x^2$ function enters the bar shouting with scare

- Run, run quickly, derivatives are coming and they are angry.

Then the exponential function, $e^x$ stands up, makes a step and says proudly

- Let them come, I am not afraid!

Background
When a derivative acts on function it usually changes the function's form. For example the derivative of the polynomial function decreases its order, e.g. $d/dx (x^n) = n x^{n-1}$, where $n$ is integer, but the result is valid for non-polynomial functions ($n$ real) too. Other common derivatives regard the $sin x$ and $cos x$ functions, where $d/dx (sin x) = cos x$ and $d/dx (cos x) = - sin x $.

The only exception is the exponential function $e^x$ whose derivatives always give the exponential function again, i.e. $d/dx (e^x) = e^x$.

It works, ...

PS: Apologies, we couldn't resist the temptation. 

Interest fluctuations during a physics talk

Picture taken from http://backreaction.blogspot.co.uk/2007/12/cmb-power-spectrum.html. All the credits belong to the authors of the blog Backreaction

We found it on the internet and wanted to share it with the physics geeks.

A helium walks into a bar

The Joke

Helium walks into a bar and orders a beer.

The bartender says “We don’t serve noble gases in here.”

The Helium doesn’t react.




Background

Helium is one of the the least reactive elements in nature, because it is a noble gas. The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence (outer) electrons is considered to be "full", giving them little tendency to participate in chemical reactions.

STOP found at CERN

Despite the recent rumors and disappointment about the absence of super-symmetric hints in LHC data (see for example https://www.scientificamerican.com/article/supersymmetry-fails-test-forcing-physics-seek-new-idea/),

our blog has an exclusive picture of the stop found in CERN

STOP found at CERN:

(image taken from http://cp3-origins.dk/a/4276)


Background

In a glimpse: s-top is the supersymmetric partner of top quark. (funny, isn't it?)

In more details:

The Standard Model of Particle Physics.
The standard model of particle physics refers to the theory that describes the elementary particles of our world and the interactions among them. This model has been successfully confirmed in a series of experiments over the last 50 years. It can be summarised in the following picture

Fermions
The first three columns correspond to the elementary particles that constitute the (ordinary) matter around us.  They are named fermions. You might notice the electron at the bottom left corner which, together with the nucleus, make the atom. You might know that the nucleus is not elementary but consists of  protons and nucleons. The latter are not again the most elementary particles, that's why you do not see them in the above table. Protons and nucleons are made of three quarks each.

You might also observe that the particles in the first three columns are separated into two classes, quarks and leptons. However, they all come in three generations, each generation having two particles. Between generations, particles differ by their quantum number, mass, but they "feel" same interactions. You might ask why there are only three generations. This is an open question in theoretical physics, and physicists seek for an dynamical selection rule which picks only three generations. Nevertheless the possibility of a fourth generation has almost been ruled out by experiments.

Notice the top quark at the first row, third column in above table.

Bosons
The last column in the table above consists of the force carriers. Those particle carry the three interactions of nature. The photon, denoted by $\gamma$, is the carrier of the electromagnetic interaction, W and Z are the carriers of the weak interaction and the gluon, $g$, is the carrier of the strong nuclear interaction (plus gravity makes us four). Those particles are called bosons. For example, two electrons interact by exchanging a photon, which carries the interaction. In other words, the electrons interact without "touching" each other, but rather exchanging "messengers" (the force carriers)  which have the information of the interaction, see the picture below.

Supersymmetry (a.k.a SUSY)
Although the great experimental success of the standard model, it is understood only as an effective theory. which means a theorythat is valid up to some energy scale and breaks down beyond it. Theoretical physicists have come up with several extensions of the standard model, the most popular of which is supersymmetry. This theory provides satisfactory explanations for a numbers of problems of the Standard model, such as the fine-tuning and the gauge-coupling unification.

As the name reveals, SUSY is an extended symmetry of space-time and fundamental fields which relates bosons to fermions and vice versa. In particular in SUSY, every particle has its supersymmetric partner, which has the opposite statistics.  For example the superpartners of fermions are bosons and the superpartners of bosons are fermions .The superpartners of the standard model particles are named with the prefix 's-'particle, so the superpartner of electron, is the selectron, the superpartner of top quark is the stop quark and so on (see the table below).

Picture taken from http://www.particleadventure.org/supersymmetry.html. It shows that every standard model particle, has supersymmetric "shadow" particle. The size of the "balls" indicates that the supersymmetric partners are much heavier because SUSY is broken. It is the role of the experiment to probe high energy and discover new particles, if there are any.

When the theory is full and unbroken each pair of superpartners shares the same mass and other quantum numbers. However if that was case in our world we would have detected the selectron, for example, simply because it has the same energy with the electron, it wouldn't be heavier! But this is not the case! This is one of the reasons why supersymmetry must be broken. While the theory is being broken the superpartners acquire higher masses and this is the reason we haven't detected them yet. This is illustrated in the following picture

Although supersymmetry is considered an elegant and rich theory, there is no experimental evidence for its existence at the moment. Moreover, the current search in LHC seems to rule out the simplest supersymmetric extension of the standard model, named the MSSM.