A striking confirmation

On arxiv today it is appeared a paper by Stephan Narison,  Gerard Mennessier and Robert Kaminski (see here). Stephan Narison is the organizer of QCD Conferences series and I attended one of this, QCD 08, last year. Narison is located in Montpellier (France) and, together with other researchers, is carrying out research aimed to an understanding of low-energy phenomenology of QCD. So, there is a strong overlapping between their work and mine. Their tools are QCD spectral sum rules and low energy theorems and the results they obtain are quite striking. Narison has written a relevant handbook of QCD (see here) that is a worthwhile tool for people aimed to work with this theory.

The paper gives further support to the idea that the resonance f0(600)/ is indeed a glueball. Currently, researchers have explored another possibility, that this particle is a four quark state. Narison, Mennessier and Kaminski consider that, if this would be true, being this a state with u and d quarks, coupling with K mesons should be suppressed. This would imply that, in a computation for the rates of decays, the contribution coming in the case of K mesons in the final state should be really small. But, for a glueball state, these couplings for and decays should be almost the same.

Indeed, they get the following

that is quite striking indeed. They do the same for f0(980) and, even if they get a similar result, they draw no conclusion about the nature of this resonance.

This, together with the small decay rate in , gives a really strong support to the conclusion that is indeed a glueball. At this stage, we would like to see an improved support from lattice computations. Surely, it is time to revise some theoretical computations of the gluon propagator.

Update: I have received the following correction to above deleted sentence by Stephan Narison. This is the right take:

One should take into account that the sigma to KK is suppressed due to phase space BUT the coupling to KK is very strong. The non-observation of sigma to KK has been the (main) motivation that it can be pi-pi or 4-quark states and nobody has payed attention to this (unobserved) decay.

Nature of f0(980)

As pointed out in my recent post (see here), f0(980) can be a glueball and an excited state of resonance. I have found some theoretical support for this. But it would be enough to have some support from experimental data just for this resonance being a glueball. Such an evidence exists. Firstly I would like to insert here a conclusion from the beautiful paper by Caprini, Colangelo and Leutwyler (see here and here)

“The physics of the σ is governed by
the dynamics of the Goldstone bosons: The properties of
the interaction among two pions are relevant… The properties of the resonance f0(980) are also governed by Goldstone
boson dynamics – two kaons in that case.”

This is just the scenario I depicted in my papers. But I was also able to find a very smart paper by Baru, Haidenbauer, Hanhart, Kalashnikova and Kydryavtsev (see here and here) where a proof is given that this resonance has not a quark structure. This is accomplished through an approach devised by Steven Weinberg that applies to unstable particles.

This is a strong support to our scenario that appears consistently built. In turn, this implies that a clear understanding of the very nature of light unflavored scalar mesons is at hand.