Central exclusive diffractive production of theπ+π−continuum, scalar, and tensor resonances inppandp

Abstract

We consider central exclusive diffractive dipion production in the reactions pp → ppπ + π − and pp → ppπ + π − at high energies. We include the dipion continuum, the dominant scalar f 0 (500), f 0 (980), and tensor f 2 (1270) resonances decaying into the π + π − pairs. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in terms of vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The formulae for the dipion continuum and tensor meson production are given here for the first time.The theoretical results are compared with existing STAR, CDF, CMS experimental data and predictions for planned or being carried out experiments (ALICE, ATLAS) are presented. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. Distributions in rapidities and transverse momenta of outgoing protons and pions as well as correlations in azimuthal angle between them are presented. We find that the relative contribution of resonant f 2 (1270) and dipion continuum strongly depends on the cut on proton transverse momenta or four-momentum transfer squared t 1,2 which may explain some controversial observations made by different ISR experiments in the past. The cuts may play then the role of a ππ resonance filter. We suggest some experimental analyses to fix model parameters related to the pomeron-pomeron-f 2 coupling.

Central exclusive production in the STAR experiment at RHIC

“…Between 1 − 1.5 GeV/c 2 a significant resonant structure is present which might represent the f 2 (1270) meson. This result is consistent with the previous measurement by STAR [6] and agrees with predictions of some models [7]. Lack of the peak of ρ 0 meson in π + π − mass spectrum is a proof for insignificant contamination from Reggeon exchanges and photon-Pomeron interactions.…”

Recent diffractive and exclusive results from CMS

“…A decrease is seen above 1 GeV, followed by a local peak at around 1.3 GeV. Excesses above the DIME and PYTHIA8 predictions are observed near 1 GeV and 1.3 GeV, the latter of which is consistent with the f 2 (1270), as seen in previous measurements [7,8,9,10], and at around 1.65 GeV. The local maximum at 1 GeV, followed by a drop, is interpreted as the result of interference between the f 0 (980) and the two-pion continuum.…”

Exclusive diffractive production ofπ+π−continuum and resonances within tensor pomeron approach

“…In Ref. [1] we have considered all possible tensorial structures for the PP f 2 coupling (see Appendix A of [1])…”

“…Central production mediated by the "fusion" of two exchanged pomerons [1,2] is an important diffractive process for the investigation of properties of di-pion resonances, in particular, for search of gluonic bound states (glueballs). The experimental groups such as the COMPASS [3,4], ISR [5,6], STAR [7,8], CDF Tevatron [9], ALICE [10], and CMS [11] all show visible structures in the π + π − invariant mass.…”

“…In most cases one has to add coherently amplitudes for two pomeron-pomeron-meson couplings with different orbital angular momentum and spin of two "pomeron particles". 1 In [22] an extensive study of the photoproduction reaction γp → π + π − p was presented. The resonant (ρ 0 → π + π − ) and non-resonant (Drell-Söding) photon-pomeron/reggeon π + π − production in pp collisions was studied in [23].…”