I would like to ask what are the experimental evidences that led to the conclusion that QCD is the right theory to describe strong interactions. I know that some of the key point are the decay of $\pi_{0}$ and the measurement of Jets but I'd love to see a full answer to this question. Is there a still a chance to Regge theory nowadays?

  • $\begingroup$ Please, read section IV of "Resource Letter: Quantum Chromodynamics," by Andreas S. Kronfeld, Chris Quigg arxiv.org/abs/1002.5032 $\endgroup$
    – user34944
    Nov 29 '13 at 11:21

Is there a still a chance to Regge theory nowadays?

Regge trajectories are having a revival in string theories. String theories are candidates for the Theory of Everything (TOE) , i.e unification at the quantum level of all four forces, including a quantized gravity.

If you google "regge trajectories and strings 2013" you will get a large number of hits. For example G. S. Sharov (Submitted on 17 May 2013):

The abstract

Various string models of mesons and baryons include a string carrying 2 or 3 massive points (quarks or antiquarks). Rotational states (planar uniform rotations) of these systems generate quasilinear Regge trajectories and may be used for describing excited hadron states on these trajectories. For different string models of baryon we are to solve the problem of choice between them and the stability problem for their rotational states. An unexpected result is that for the Y string baryon model these rotations are unstable with respect to small disturbances on the classical level. This instability has specific feature, disturbances grow linearly, whereas for the linear string baryon model they grow exponentially and may increase predictions for baryon's width Γ. The classical instability of rotational states and nonstandard Regge slope are the arguments in favor of the stable simplest model of string with massive ends both for baryons and mesons. Rotational states of this model with two types of spin-orbit correction are used to describe Regge trajectories for light, strange, charmed, bottom mesons and for N, Δ, Σ, Λ and Λc baryons.

One has to keep in mind that string theoretical models for TOF are at the frontier of research, still and open question on which string theory will describe the Standard Model and a quantized gravity.

Edit: As far as the first question goes

what are the experimental evidences that led to the conclusion that QCD is the right theory to describe strong interactions

The wiki paragraph has the history of emergence of QCD as the theoretical model of the strong interaction force.

The first experimental indication was that no free quarks came out of high energy scatterings, even though looked for extensively in all experiments that could produce them.

As I remember it, the second indications that the simple parton model, as proposed by Feynman, was not a good description of strong interactions came from the high transverse momentum events in high energy scattering experiments, indicative of large angle scatterings from a hard core, not consistent with the simple parton model .

Theorists were looking for a gauge theory similar to the electroweak theory to explain the behavior of the strong interactions, and QCD, as such an SU(3) formulation, could organize observations using asymptotic freedom, that the quarks and gluons in the nucleons had to observe. Once this viable theory was proposed one could calculate the expectation of how the quarks and gluons would behave during scattering, leading to jet model predictions for data. So it was a feedback between data, high p_t and jet structure that led to the establishment of QCD.

The famous mercedes diagram proposed by John Ellis et al at CERN made visual the difference between expectations from the simple parton model and a model where the partons obeyed QCD. You can see the progress in this presentation.. The jet structure is the most solid experimental "proof" of the existence of quarks and gluons.

three jets

Gluon-jet studies developed into a precision technique for testing QCD at LEP. In this event from the OPAL experiment, the most energetic jet (going to the bottom of the picture) is likely to be the quark that didn't radiate a gluon. The jet moving towards the top right can be identified as a b-quark jet, because an energetic muon (red arrow) was produced in the decay of the b-hadron. This leaves the third jet as the gluon jet and permits the comparison of the properties of quark and gluon jets – an important test of QCD.

  • $\begingroup$ on an unrelated note, where does the abbreviation TOF (instead of TOE) come from? I'm guessing it's not 'Totally Obvious Fraud' ;) $\endgroup$
    – Christoph
    Nov 29 '13 at 12:23
  • $\begingroup$ Thanks Anna! To be honest I still want to see an answer to the first question. $\endgroup$
    – Yair
    Nov 29 '13 at 13:01
  • $\begingroup$ @Christoph it is an E that lost a leg :). $\endgroup$
    – anna v
    Nov 29 '13 at 15:10
  • $\begingroup$ Some form of Regge theory probably holds true within QCD. But it would be a very technical topic. $\endgroup$ Nov 30 '13 at 6:51
  • $\begingroup$ @MitchellPorter In my googling I did see such publications. After all the regge trajectories are an experimental fact ( my experimental thesis back in the 1970's is based on that theory), they should appear at some mathematical manipulations of QCD. $\endgroup$
    – anna v
    Nov 30 '13 at 7:22

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