Hunting for Glueballs in Electron-Positron Annihilation

Abstract

We calculate the cross section for the exclusive production of J P C = 0 ++ glueballs G0 in association with the J/ψ in e + e − annihilation using the pQCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative Υ decay. The cross section for e + e − → J/ψ + G0 at √ s = 10.6 GeV is similar to exclusive charmonium-pair production e + e − → J/ψ + h for h = ηc and χc0, and is larger by a factor 2 than that for h = ηc(2S). As the subprocesses γ * → (cc)(cc) and γ * → (cc)(gg) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e + e − → J/ψX may actually be due to the production of charmonium-glueball J/ψGJ pairs.Bound states of gluons provide an explicit signature of the non-Abelian interactions of quantum chromodynamics. In fact, in a model universe without quarks, the hadronic spectrum of QCD would consist solely of color-singlet glueball states. In the physical world, the purely gluonic components mix with qq pairs, leading to an enriched spectrum of isospin-zero states as well as qqg hybrids. The existence of this exotic spectrum is as essential a prediction of QCD as the Higgs particle is for the electroweak theory.Lattice gauge theory predicts the spectrum and quantum numbers of gluonic states. According to a recent calculation [1], the ground-state masses for the J P C = 0 ++ and 2 ++ glueballs G J are 1.73 and 2.40 GeV, respectively.Thus far, the empirical evidence for glueballs is not decisive, probably because of complications from mixing with the quark degrees of freedom, but there are indications of an extra neutral scalar state perhaps due to a glueball of mass (before mixing) near 1.7 GeV [2].An important mechanism for producing glueballs is the radiative decay of heavy quarkonium, particularly J/ψ → γG J and Υ → γG J [3]. In these reactions, the quarkonium decays to an intermediate γgg state which then can couple to any charge conjugation parity C = + isospin I = 0 gluonic or hybrid state. For example, the BES Collaboration [4] has observed the radiative decays of the J/ψ and the ψ(2S) to γf 0 (1710), a glueball candidate. In this Letter we focus on another optimal mechanism for the production of G 0 and G 2 at e + e − colliders, the reaction e + e − → γ * → HG J , H = J/ψ or Υ [5], in which a C = + glueball can be produced in association with a quarkonium state from the subprocess γ * → (QQ)(gg). Two-gluon components in η particles have been estimated recently [6]. One of the six Feynman diagrams for the subprocess is shown in Fig. 1; the remaining diagrams are permutations of the photon and the two gluons. A related reaction γbeen considered [7] as a source of pseudoscalar glueballs. We shall show that these reactions satisfy perturbative QCD (pQCD) factorization. Unlike radiative quarkonium decay, this channel imposes no a priori limit on the mass of the glueball. The main background to charmonium-glueball production e + ...

Study of double charmonium production ine+e−annihilation ats≈10.6 GAbe1, Aihara2, Asano3 et al. 2004Phys. Rev. D1422360View full textAdd to dashboardCite

“…There is no evidence for the sharp rise in cross-section for large | cos(θ prod )| expected for J/ψ J/ψ production via two virtual photons [3]. The prediction for a spin-0 glueball contribution (e + e − → J/ψ G 0 ) to the J/ψ η c peak, 4], is also disfavored. The process e + e − → γ * → J/ψ χ c0 can proceed via both S-and D-wave amplitudes, and predictions for the resulting angular distributions are therefore model dependent.…”

“…[3] have proposed that processes proceeding via two virtual photons may be important. Other authors [4] suggest that since the dominant mechanism for charmonium production in e + e − annihilation is expected to be the color-singlet process e + e − → ccgg, the final states observed by Belle contain a charmonium state and a M ∼ 3 GeV/c 2 glueball. Such glueball states are predicted by lattice QCD and can have masses around 3 GeV/c 2 .…”

Next-to-Leading-Order QCD Correction toe+e−→J/ψ+ηcats=

“…In particular, Bodwin, Braaten, and Lee proposed [9,10] that processes proceeding via two virtual photons may be important, and Belle data for J/ψ + η c might essentially include the J/ψ + J/ψ events which were produced via two photons. Brodsky, Goldhaber, and Lee suggested that since the dominant mechanism for charmonium production in e + e − annihilation is expected to be the color-singlet process e + e − → ccgg, the final states observed by Belle might contain J/ψ and a M ∼ 3GeV spin-J glueball G J (J = 0, 2) [11]. Motivated by these proposals, Belle presented an updated analysis [12], and ruled out the J/ψ +J/ψ and spin-0 glueball scenarios.…”

BelleJ/ψ+ηcanomaly and a very light scalar boson

“…Thus, the anomalous production remains one of the challenging problems in QCD, and arouses speculations. For example, a heavy glueball of a mass very near m ηc with a rather large matrix amplitude has been proposed [10] to account for the excess.…”