Considerations concerning diffraction scattering in quantum chromodynamics

Odderon in the color glass condensate

The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark states X(2900) and Tcc+(3875) as well as the hidden heavy flavor multiquark states X(6900), Pcs(4459)0 , Zcs(3985)− , Zcs(4000)+ , and Zcs(4220)+ . We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-Abelian SU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.

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An updated review of the new hadron states

The TOTEM experiment at the LHC has performed the first measurement at $$\sqrt{s} = 13\,\mathrm{TeV}$$ of the $$\rho $$ parameter, the real to imaginary ratio of the nuclear elastic scattering amplitude at $$t=0$$, obtaining the following results: $$\rho = 0.09 \pm 0.01$$ and $$\rho = 0.10 \pm 0.01$$, depending on different physics assumptions and mathematical modelling. The unprecedented precision of the $$\rho $$ measurement, combined with the TOTEM total cross-section measurements in an energy range larger than $$10\,\mathrm{TeV}$$ (from 2.76 to $$13\,\mathrm{TeV}$$), has implied the exclusion of all the models classified and published by COMPETE. The $$\rho $$ results obtained by TOTEM are compatible with the predictions, from other theoretical models both in the Regge-like framework and in the QCD framework, of a crossing-odd colourless 3-gluon compound state exchange in the t-channel of the proton–proton elastic scattering. On the contrary, if shown that the crossing-odd 3-gluon compound state t-channel exchange is not of importance for the description of elastic scattering, the $$\rho $$ value determined by TOTEM would represent a first evidence of a slowing down of the total cross-section growth at higher energies. The very low-|t| reach allowed also to determine the absolute normalisation using the Coulomb amplitude for the first time at the LHC and obtain a new total proton–proton cross-section measurement $$\sigma _{\mathrm{tot}} = (110.3 \pm 3.5)\,\mathrm{mb}$$, completely independent from the previous TOTEM determination. Combining the two TOTEM results yields $$\sigma _{\mathrm{tot}} = (110.5 \pm 2.4)\,\mathrm{mb}$$.

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First determination of the ρ parameter at √s = 13 TeV – probing the existence of a colourless three-gluon bound state

A model for soft high-energy scattering: Tensor pomeron and vector odderon

The experimental data on the charge exchange differential cross-section and on the difference of the π+p and π−p total cross-sections in the rangep

 L
 =5 GeV/c to 200 GeV/c are shown to be incompatible with conventional Regge asymptotic behaviour. It is shown that an additional term is required which grows in importance with energy. The precise form of the new term cannot be ascertained, but it is shown that it corresponds to a singularity atJ =1 in the complex-angular-momentum plane. Amongst the possible types of additional term there are two which are aesthetically favoured and which have been closely analysed. These correspond to i) a non-Regge behaviour associated with the maximal growth permitted in axiomatic field theory; ii) a «hyper-Regge» term,i.e. an odd-signatured Regge pole, the analogue of the pomeron pole, with interceptα =1 att =0. Very striking predictions, in particular for the charge exchange polarization, follow as a consequence of the non-Regge or hyper-Regge asymptotic behaviour of the crossing-odd amplitude.

C. Lopez

Papers

Non-regge and hyper-regge effects in pion-nucleon charge exchange scattering at high energies

Striking polarization effects in π(su-)p»(su0)n as a test of unconventional asymptotic behaviour