# Are there new physics scenarios that predict low lying hadrons?

There is a significant ongoing experimental effort to search for new hadrons with masses in the GeV range. This is used to find the spectra of QCD bound states, with a particular emphasis on finding exotic resonances such as the tetraquark. To my knowledge, they have not found any state whose mass is in contradiction with the theoretical prediction using lattice QCD thus far (though e.g., there are a few tetraquark candidates, such objects are not in conflict with lattice predictions).

These searches are clearly very important as they confirm our understanding of QCD and in particular, they verify the validity of lattice QCD, which can subsequently be used to study new phenomena. But my question is, are there any mainstream new physics scenarios which predict a deviation in the spectra of QCD and could be found at for example, LHCb?

EDIT: I'm interested in changes to the low energy ($\sim$ GeV) bound state spectrum measured by these experiments

• I am not a theorist, so I can only give a gut-feeling answer. I think the model for the color force is pretty solid at this point. Like conventional nuclear physics it suffers from numerical prediction problems but lattice qcd seems to have made real progress. The "IR end" of the standard model is probably close to watertight at this point. The vital questions of interest are still at the electroweak scale (precision characterization of the Higgs) and whether there is any new physics at the TeV scale. It doesn't seem to look good at that end, but the next LHC run will answer that. – CuriousOne Jan 6 '15 at 13:49
• Sorry misread your question (didn't see the b in LHCb), so I now see my answer isn't appropriate! Hope someone with expertise in GeV scale physics has an answer - I'd be interested to see it. – Edward Hughes Jan 6 '15 at 14:21

There are none. The reason is that the mainstream extensions of the Standard Model leave its gauge group intact at LHC energies and only add matter to the spectrum.

Such a modification will not lead to new hadronic states. Exotic particles with masses comparable to quark masses are mostly excluded (unless there is some intricate hiding scheme, e.g. for light stops).

In general mingling with the ingredients of the low energy bound spectrum is both "dangerous" and not very fruitful from a model building point of view - the low energies is not where the SM has its troubles; on the contrary it is the low energy bound spectrum where the Standard Model shines.

tl;dr:

Since there is no need (and little room) to build models affecting the low energy spectrum nobody does.

Some popular supersymmetric extensions of the Standard Model predict masses of the squarks (superpartners of the quarks) that could be detected with the LHC.

If you mean any mainstream model that predicts a different mass spectrum of the quarks than observed at LHC? I don't know of such a model and if there would be any I would say it conflicts experimental data and won't become mainstream for that reason anyway.

• Thanks for the response, but I'm interested in effects to the low energy bound state spectrum. I am well aware of the searches done by CMS and ATLAS – JeffDror Jan 14 '15 at 11:13

If you mention about exotic state hadrons which are composite of two anti quarks and two quarks, yes there are some new observations. The recent and approved one is Z(4430) which observed by LHCb group from CERN http://home.web.cern.ch/about/updates/2014/04/lhcb-confirms-existence-exotic-hadrons It consists $c^-cdu^-$ quarks and anti quarks.

There is also an on-going research from CMS group which is not approved yet, but supported by a group from Fermilab as well, they expect to see resonance through the $B^±$ meson decays and called the observed particle Y(4140) http://news.discovery.com/space/lhc-spots-mysterious-y4140-particle-121120.htm

These new hadrons are mostly called by their own mass as Y(4140) $mass = 4.4140 GeV/c^2$ and Z(4430) $mass = 4.430 GeV/c^2$ and we would say they are in low energy scale

I am not theoretical physicist mostly works experimental but I know the importance of these kind of hadrons because they seem like two mesons compositions but theoretically they are not at all.

• Thanks for the response, but I wouldn't consider the tetraquark states new physics. They are still QCD but just with a quark structure we've never seen before. – JeffDror Jan 14 '15 at 11:14
• Could you please emphasize what you mean by "new hadron" ? – aQuestion Jan 14 '15 at 11:26
• I meant either a "hadron" composed of a new particle not in the SM, or shifts the the mass spectrum of hadrons due to virtual corrections of new BSM particles. A tetraquark is still bound with QCD interactions, just with not-yet-seen group structure. – JeffDror Jan 14 '15 at 11:35