Exclusivepp→ppπ+π−reaction: From the threshold to LHC

Abstract

We evaluate differential distributions for the four-body pp ! pp þ À (and p " p ! p " p þ À ) reaction which constitutes an irreducible background to three-body processes pp ! ppM, where M are a broad resonances in the þ À channel, e.g., M ¼ , 0 , f 0 ð980Þ, f 2 ð1275Þ, f 0 ð1500Þ. We include both double-diffractive contribution (both Pomeron and Reggeon exchanges) as well as pion-pion rescattering contribution. The first process dominates at higher energies and small pion-pion invariant masses while the second becomes important at lower energies and higher pion-pion invariant masses. The amplitude(s) is(are) calculated in the Regge approach. We compare our results with measured cross sections for the Intersecting Storage Ring and Fermi National Accelerator Laboratory experiments. We make predictions for future experiments at the anti-Proton ANnihilation at DArmstadt (PANDA), Relativistic Heavy Ion Collider, Tevatron, and LHC energies. Differential distributions in invariant two-pion mass, pion rapidities and transverse momenta of pions are presented. The two-dimensional distribution in ðy þ ; y À Þ is particularly interesting. The higher the incident energy, the higher preference for the same-hemisphere emission of pions. The processes considered constitute a sizeable contribution to the total nucleon-nucleon cross section as well as to pion inclusive cross section.

QCD diffractive mechanism of exclusive pair production at high energies

“…Different representations of the phase space depending on a particular kinematical distributions needed can be found in Ref. [43].…”

“…Ref. [43]). However, the evaluation of the corresponding hard subprocess amplitude V λ + λ − , its subsequent convolution with the gluon UPDFs in the diffractive amplitude (2.7) and the full phase space integration (3.1) is extremely time consuming.…”

Measurement of the Central Exclusive Production of pion pairs using tagged forward protons at the STAR detector at RHIC

“…Due to high gluon density in the Pomeron, glueball formation might be enhanced in DPE. Another topic of interest is a non-perturbative aspect of meson production [3,5,4].…”

Diffractive mechanisms in pp\rightarrow pp pi0 reaction at high energies

“…2 In the past we have studied exclusive pion/kaon pairs in the pp → ppπ + π − [15,16], pp → nnπ + π + [17] and pp → ppK + K − [18] processes. There pomeron-pomeron and pomeron-reggeon exchanges are the dominant mechanisms.…”