# Detection of Gluons

1. Feb 6, 2009

### ghery

Hi to everyone:

Does anybody of you know when was the gluon detected?, and how do you detect gluons?

I hope you can answer
Thank you

2. Feb 6, 2009

### vanesch

Staff Emeritus
You detect gluons with a stick-o-meter of course :tongue:

Seriously, I think it is considered that the first "direct" experimental observation of gluons is the 3-jet events discovered in e+e- collisions at PETRA (DESY, Hamburg, Germany) in 1979. There's a not too bad Wiki entry on it http://en.wikipedia.org/wiki/Three_jet_event

Personally, I find this kind of explanation a bit handwaving of course, but it is the kind of stuff that people tell experimentalist-students when they enter the field. A better explanation is of course that a Monte Carlo simulation based upon QCD containing gluons was statistically in agreement with the data taken there.

After this, there have been several other experimental confirmations of gluons, the most accurate being, I think, deep inelastic e p collisions (again, at DESY but with HERA this time). There are tons of publications by the two collaborations there (H1 and ZEUS).

3. Feb 6, 2009

### humanino

I completely agree with vanesh's answer. I only want to add to his last point that the DIS results can be gazed at here. The amount of data is stupendous. The fact that the points are not located on an horizontal line, called scaling violation, is in perfect agreement with QCD. To fully appreciate the extent of this data set, please take time to realize that we have logarithmic scales in two dimensions $(x_B,Q^2)$.

4. Feb 7, 2009

### Vanadium 50

Staff Emeritus
I kind of like the hand-wavy stuff. I think about it this way - suppose QCD were incorrect. Then you wouldn't have this kind of numerical agreement you mention, but you would still need something very much like the gluon to explain the three-jet events. So the observation of these events tells you something about the kinds of theories that are supported by the data.

5. Feb 7, 2009

### Sideways

vanesch is right. 3-jet events are the first and strongest evidence for the existence of gluons, but certainly aren't the only evidence. Validation of the quark-gluon (DGLAP) evolution equations in multiple high-energy phenomena (to at least 2nd order in perturbative QCD) is pretty solid evidence that the theory is correct, at least at high energy.

Go to lower energies (say, a virtual photon energy of less than 800 MeV), and the models get more controversial, due to the non-perturbative behavior of QCD at low energies. (Things get VERY difficult to calculate in that realm.)

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