Exotic Meson Production Research Articles

Ultra-peripheral nuclear collisions

This article presents a very brief review of the physics of Ultra-Peripheral Collisions (UPC) at the Large Hadron Collider (LHC) and other nuclear facilities. I discuss several processes of interest such as electron-position pair production, the anti-hydrogen atom, giant resonances, exotic meson production and parton distribution functions.

Nuclear effects on tetraquark production by double parton scattering

In this work we study the nuclear effects in exotic meson production. We estimate the total cross section as a function of the energy for pPb scattering using a version of the color evaporation model (CEM) adapted to Double Parton Scattering (DPS). We fond that the cross section grows significantly with the atomic number, indicating that the hypothesis of tetraquark states can be tested in pA collisions at LHC.

Exotic meson production in the f1(1285)π− system observed in the reaction π−p→ηπ+π−π−p at 18 GeV/c

This Letter reports results from the partial wave analysis of the π−π−π+η final state in π−p collisions at 18GeV/c. Strong evidence is observed for production of two mesons with exotic quantum numbers of spin, parity and charge conjugation, JPC=1−+ in the decay channel f1(1285)π−. The mass M=1709±24±41MeV/c2 and width Γ=403±80±115MeV/c2 of the first state are consistent with the parameters of the previously observed π1(1600). The second resonance with mass M=2001±30±92MeV/c2 and width Γ=333±52±49MeV/c2 agrees very well with predictions from theoretical models. In addition, the presence of π2(1900) is confirmed with mass M=2003±88±148MeV/c2 and width Γ=306±132±121MeV/c2 and a new state, a1(2096), is observed with mass M=2096±17±121MeV/c2 and width Γ=451±41±81MeV/c2. The decay properties of these last two states are consistent with flux tube model predictions for hybrid mesons with non-exotic quantum numbers.

Role of photoproduction in exotic meson searches

We discuss two production mechanisms of the $J^{PC}=1^{-+}$ exotic meson, hadroproduction, using pion beams and photoproduction. We show that the ratio of exotic to non-exotic, in particular the $a_2$, meson production cross sections is expected to be by a factor of 5 to 10 larger, in photoproduction then in hadroproduction. Furthermore we show that the low-t photoproduction of exotic meson is enhanced as compared to hadronic production. This findings support the simple quark picture in which exotic meson production is predicted to be enhanced when the beam is a virtual $Q\bar Q$ pair with a spin-1 (photon) rather then with a spin-0 (pion).

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c.

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.

Search for non-strange exotic mesons produced via baryon exchange

Negative results on backward production, via baryon exchange, of exotic non-strange mesons are presented. The reactions π −p→p forward X −and π −n→ p forward X −− have been studied with a 12 GeV/ c π − beam in the Omega spectrometer at CERN. No resonant peak in X→ p p π −, p p π −π −, p p π −π 0,π +π −π −π 0 has been seen. The upper limits obtained on cross sections for exotic meson production X → N N π, N N π, 4π are lower than the ϱ − backward production cross section in the π −p→p ϱ − reaction; this result seems to contradict the predictions of the two-component duality model. Compared to already published experiments in the search for exotics produced via baryon exchange, the sensitivity of this experiment is increased by an order of magnitude.