What would happen if Large Hadron Collider would collide electrons? After some reading about the Large Hadron Collider and it's very
impressive instruments to detect and investigate the collision results,
there is a remaining question.
What would happen if the scientists would use leptons instead of hadrons?
Especially: What would happen if they would collide electrons?
Isn't it intrinsic that all particles consist of smaller particles?
With current technology, could we detect them?
 A: The very basic reason LEP stopped going to higher energies ( it reached over 200GeV center of mass, at the last stage, LEPII) and the tunnel was used for LHC is synchrotron radiation .

Note that radiated power is proportional to 1/m^4

It is not possible to feed a circular beam of electrons the energy needed to raise it to higher energies at the radius of LEP, it is a loosing game, The energy would go into feeding synchrotron radiation. The reason the same radius can be used for much higher energy protons is the ratio of the masses of electron to proton.
Synchrotron radiation is not present in linear colliders and that is why the next electron positron accelerator will be a linear collider the ILC.
Edit

What would happen if the scientists would use leptons instead of hadrons?

It has happened at LEP and LEPII with electrons on positrons. If the scattering is not elastic a lot of hadrons appear, as well as leptons and Z bosons. The data from LEP confirmed the calculations of the standard model for elementary particles to great accuracy. 

Especially: What would happen if they would collide electrons?

from the previous paragraph, the standard model predicts what would happen if electrons were scattered on electrons : all the variants of the feynman diagram possibilities would appear also.
A: First of all -- it wouldn't be called "the Large Hadron Collider", right?
Looks like one would rather call it something like "Large Electron-Positron Collider".
In that case one definitely would need another abbreviation for it. Something like "LEP" instead of "LHC"...
Now, guess what was there in the same tunnel before?

Edit: since my shenanigan got popular, I'll elaborate. 


*

*Yes, they actually was colliding electrons and positrons, not electrons-electrons. Mainly because of the richer physics of such collisions. (But for my theoristish point of view: positron is just an electron going back in time.)

*Why the same tunnel? Perhaps surprisingly, tunnel is taking a substantial part of the cost of an accelerator. Digging a new one for LHC would have definitely burnt a large hole in CERN's pocket.

*Given a fixed  circular tunnel (it's radius) you actually have a bound on energy you can have for your particles. Due to synchrotron radiation -- see @emarti answer for more. 

*27 kilometers seems to be a reasonable limit on the size of a circular tunnel. (Actually people think about 233 km, but that sounds crazy to me.) So the next accelerator most probably will be linear and it will be electron-positron.

P.S. Have you heard of a Photon Collider?
A: 
Especially: What would happen if they would collide electrons?

In case you really meant electron on electron (and not electron on positron): for a 'discovery' machine it is useful to have a initial state which is 'neutral' in all respects: no net charge (electrons and positrons have opposite charge; protons not only contain quarks but also a significant amount of anti-quarks and gluons), no net lepton flavour etc. 
So far, lepton flavour is almost entirely conserved, so an e-e- collider would predominantly produce final states with an electron flavour number of two which would be quite unnatural for a new fundamental particle.

What would happen if the scientists would use leptons instead of hadrons?

Others have pointed out that this happened until the year 2000 in the LHC tunnel (LEP) and is limited by the synchrotron radiation losses (while LHC is limited by the achievable fields in the bending magnets). 
There is also the concept of a muon collider which would have features similar to an e+ e- collider (known initial state four momentum etc.) but this is technologically very challenging, mainly due to the liftetime of the muon of only two microseconds. It would however for example allow to measure the mass of the Higgs particle to keV precision if I remember well (through scanning of the beam energy, similar to the determination of the mass and decay width of the Z particle at LEP).
A: There are two points in answering this question:


*

*Design: The design of the collider would have to be different. Electrons/positrons in a cyclotron radiate synchrotron radiation when they are accelerated (which itself is a useful device). To get above a few GeV, researchers use linear accelerators, such as SLAC. The proposed International Linear Collider is a design intended to reach TeV energies, close to what the LHC already achieves with protons. 

*Science: Yes, electron-electron or electron-positron collisions are very useful in studying particle physics. The signal is 'cleaner', since electrons are are not composite particles, and it's easier to calculate the cross-sections. By contrast, it is very challenging to calculate how two colliding protons, with six quarks, will decay, to say the least. A classic story of electron-electron and proton-proton colliders complement each other was the discovery of the J/psi meson. The general idea I've heard is that proton-proton colliders can reach higher energies, but electron-positron colliders tend to have better energy resolution and cleaner signals.
A: 
What would happen if the scientists would use leptons instead of hadrons? 

They would go in the opposite direction - electrons are the opposite charge to protons. The LHC doesn't use electrons because protons are 2000x heavier so you get a lot more energy in the collision. 

Especially: What would happen if they would collide electrons?              

Not a lot - they would bounce off each other. Electrons (as far as we know) don't break apart (and not at these low energies) 

Isn't it intrinsic that all particles consist of smaller particles?             

Probably not. We don't know of any components of an electron, but we also don't know why it should have the same charge as a proton when it's not made of the same stuff - so I wouldn't take any bets.

With current technology, could we detect them?

Then logically those would be the smallest particles we could detect ... and so  on ....
A: This is an interesting question, for which some interesting answers have been given from various points of view.
I am intrested in what will happen in the case of the electron-electron collisions at these high energies. It is true that at low energies the two electrons will bounce of each other, not much happening. At very high energies, however, I thought that the following outcome might be possible (it is possible to draw a Feynman diagram, to calculate the probability amplitude for such an event.) Sorry I have not learnt how to bring in drawings, so I will just describe it: 
As the $e^-$ and $e^-$ approach each other they could interact via the weak force. Electron 1 would emit a $W^-$ and turn into a $\nu_e$ which would emerge as a free particle. The $W^-$ could interact electromagnetically with electron 2 and both particles would scatter at some other directions. The $W^-$ would then decay into $e^-+\bar{\nu_e}$. Therefore, the $e^--e^-$ collision could serve as a $\nu_e-\bar{\nu_e}$ generating machine? 
$e^-+e^- -->e^-+e^- + \nu_e+\bar{\nu_e}$.
Unfortunately, we don't know of any other mechanism to forcast entirely new physics.
