Soft physics at the LHC

Abstract

We recall the main features of the Regge approach used to understand soft interactions at LHC and higher energies. Unitarity tames the power growth of the elastic protonproton scattering amplitude with energy, and leads to the migration of the secondary particles produced in high-energy proton-proton collisions to larger transverse momenta. We discuss, in qualitative terms, the role of processes containing large rapidity gaps (LRG), and the probability that the gaps survive population by secondaries produced in additional soft interactions. We explain how the Regge diagram corresponding to a LRG event simultaneously describes events with different (single, double, etc.) particle density in the same rapidity interval. We show that the role of these, enhanced, multi-Pomeron diagrams can be studied by measuring multiplicity fluctuations and long-range rapidity correlations between secondaries produced at the Tevatron and the LHC. Finally, we make a list of the characteristic features of the multi-Pomeron description of soft interactions that may be observed at the high energies accessible at the Tevatron and the LHC.

Basic features of proton-proton interactions at ultra-relativistic energies and RFT-based quark-gluon string model

“…2 with the predictions of other RFT-based models [14,[17][18][19][20]. At Tevatron energy √ s = 1.8 TeV all models agree within 5% accuracy limit for all cross sections except of the double-diffraction one, whereas at √ s = 14 TeV the model predictions start to deviate.…”

“…Finally, the Field-Feynman algorithm [21] is employed to describe the fragmentation of strings into hadrons. Here the hadron emission proceeds from both ends of the string with equal probabilities under imposed conditions of the preservation of the quark numbers and the energy-momentum conser- The models are as follows: GLMM (circles) [17], GLM (squares) [18], QGSM (crosses), KMR-1 (triangles) [19], KMR-2 (diamonds) [20], and QGSJET-2 (stars) [14]. Dashed lines between the QGSM points are drawn to guide the eye.…”

Several Effects Unexplained by QCD

“…3). It is quite well fitted by various phenomenological models using mostly the reggeon approach [12]. The slope B of the diffractiom peak dσ/dt ∝ exp(Bt) (where −t = 2p 2 (1 − cos θ) ≈ p 2 θ 2 , p is the c.m.s.…”

“…It was shown that simplest approximations of the QCD-approach with the two-gluon exchange can lead to the power-law behavior [11]. The rise of hadronic cross sections is understood within scattering theory as being due to a virtual exchange of vacuum quantum numbers, known in Regge theory as a Pomeron (for a review see [12]). The power-like dependence can be ascribed to the exchange of the so-called supercritical Pomeron, i.e., the pole singularity with intercept exceeding 1.…”

N=4 SYM model for soft interactions at high energy

“…8 we can conclude that the average B at large momentum scale (short distances), is about 4 ÷ 5 GeV −2 . We made estimates for One can see that we obtain the value for S 2 , which is 2 ÷ 3 times larger than all previous estimates [31,32].…”