Constituent Gluons Research Articles

LOW-LYING MESON SPECTROSCOPY AND CONFINEMENT

The paper is devoted to the construction of low-energy quark-scattering amplitudes. The amplitudes of dressed quarks qq→qq and [Formula: see text] are calculated in the framework of the dispersion N/D method with the help of the iteration bootstrap procedure including two types of point-like input interactions, namely the four-fermion interaction with quantum numbers of the gluon and four-fermion interaction induced by instantons (the exchanges of white states with JP=0±). The mass values of the lowest mesons (JP=0−, 1−, 0+) and their quark content are obtained. In the colour meson channel a bound state was found which corresponds to the constituent gluon with the mass MG=0.67 GeV . The qq-amplitudes in the colour state [Formula: see text] have the diquark levels with JP=0+ and the masses mud=0.72 GeV and mus=mds=0.86 GeV . The interaction of dressed quarks appeared to be an effectively short-range one. The calculated amplitudes satisfy the Okubo-Zweig-Iisuka rule. The creation of mesons (pion included) is mainly due to the gluon exchange. The mesons with heavy quarks (c and b) are considered also, using the calculated forces. We discuss the possibility of constructing the amplitudes which take into account the quark confinement.

A dynamical mechanism for the hairpin diagram

Based on the nonvalence quark-antiquark and gluon constituent structure of mesons we give a reasonable dynamical mechanism which can induce the hairpin diagram without violating the well-observed OZI rule. We calculate the hairpin amplitudes of D(o)-->KBAR(o)eta and KBAR(o)eta' normalized D(o)-->KBAR(o)pi(o) and have found that the hairpin diagram can give rise to substantial contributions to the decays where a meson with a SU(3) flavor singlet component is involved in the final state. In this scenario, we also obtain the branching ratio of D(o)-->KBAR(o)phi as 0.55% in comparison with the experimental data of 0.83%.

A test of the glueball theory for the ξ(2230)

The possibility that the ξ(2230) is considered as a glueball is discussed in the framework of a nonrelativistic potential model [D. Robson, Nucl. Phys. B 130 (1977) 328] of the glueball with massive constituent gluons by using the experimental data from the Mark III Collaboration. The ratios of the helicity amplitude are calculated. The results are that the theoretical values cannot be consistent with the data if the ξ(2230) is a 2 ++ glueball in a pure S wave and the theoretical values are in excellent agreement with the data if the ξ(2230) is a 2 ++ glueball in a mixture between the S wave and two D waves or a 4 ++ glueball in a pure D wave.

Evidence for non-q $$\bar q$$ mesons

The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. In addition,q\(\bar q\)q\(\bar q\) states are also predicted. This paper describes a search for these non-q\(\bar q\)q mesons performed by experiment WA 76 using the CERN Omega Spectrometer and discusses three candidates which have been observed.

Expectations for two- and three-jet events at HERA

We calculate cross-sections for two- and three-jet events ine − p collisions at $$\sqrt s $$ =314 GeV. We include contributions from point-like photon interactions, as well as contributions from when the photon is resolved into constituent quarks and gluons. It is shown that measurements of the angular distribution of the dijet system in two-jet events as a function of the dijet mass will assist in the separation of these two components. Aside from being a direct test of QCD photoproduction subprocesses, measurement of these events will yield information on the hadronic structure of the photon.

Studies in $$\bar p$$ p annihilation

Evidence is presented that\(\bar p\)p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the\(\bar p\)p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the\(\bar p\)p experiments at the highest available energies.

The spin-zero glueballs ( C = + 1)

The production of the 0 − glueball in J/ψ radiative decays is calculated using effective lagrangians describing its non-local interactions with the constituent gluons. Local effective lagrangians, respecting U(3) L × U(3) R chiral symmetry and the U(1) anomaly, are then used to describe the glueball interactions with the light mesons and photons. The main decay mode of a 0 − glueball with a mass around 1460 MeV is found to be K K π . The 2γ and vector meson radiative widths, as well as the stickness of the glueball, are calculated. The glueball identification of ι(1460) is strongly supported, and further tests are provided. The interaction of the 0 + glueball with its constituent gluons is also studied, and the effective potential describing its self-interactions is calculated in the special case of glueballs made out of two gluons. We conclude that a narrow 0 + glueball cannot exist.

Two- gamma decay widths of glueballs.

Using a nonrelativistic gluon bound-state model, we compute GAMMA(G..--> gamma gamma..), where G is a pseudoscalar, tensor, or scalar digluon, starting from the amplitudes of the process ..gamma gamma -->..g/sup */g/sup */ at threshold, the g/sup */'s being massive constituent gluons. Those amplitudes are obtained, at lowest order in perturbative QCD, by deriving them from a QED calculation performed many years ago by Constantini, de Tollis, and Pistoni. The unknown parameter (the digluon wave function, or its first or second derivative, at the origin) is determined by using measured values of GAMMA(J/psi..-->..G..gamma..). Our predictions are compared, for various glueball candidates, with present experimental limits.

Qq̄g hybrid and qqq̄q̄ diquonium interpretation of the GAMS 1 −+ resonance

We study the possible interpretation of the exotic 1400 MeV resonance decaying into ηπ recently discovered in the GAMS experiment in π −p→ ηπ 0n. This state is claimed to have J PC I G = 1 −+1 −. If confirmed this state could only be interpreted as an hybrid (qq̄g) or a diquonium ( qq qq ) state. However, the quark model with constituent gluons, forbids, under rather general assumptions, the decay into ηπ of both hybrids and diquonia. We generalize a selection rule previously derived for diquonia. We then discuss a possible breaking mechanism of these selection rules. Our conclusion is that all interpretations predict an ηπ branching ratio of 1% to a few %. An hybrid with l g = 1 would lead to BR ( ηπ)<BR( η' π) and a large b 1 (1235) π branching ratio. But no b 1 π resonance has been seen in photoproduction. On the other hand an hybrid with l q q ̄ = 1 would lead to a large πϱ branching ratio, in contradiction with experiment. A qqq̄q̄ diquonin would lead to a very large b 1 π branching ratio and no η' π enhancement versus ηπ.

Test of the transverse magneticity of the xi (2.23).

We propose the Jacob-Wick helicity-amplitude ratios x\ifmmode\bar\else\textasciimacron\fi{}=${A}_{1}$/${A}_{0}$ and y\ifmmode\bar\else\textasciimacron\fi{}=${A}_{2}$/${A}_{0}$ for \ensuremath{\psi}/J\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\xi}, \ensuremath{\xi}\ensuremath{\rightarrow}${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, as a test of the transverse magneticity of the two gluon constituents of the \ensuremath{\xi}(2.23) under the assumption that the latter state is in fact a spin-2 bound state of two constituent gluons. Here ${A}_{j}$ is the amplitude for \ensuremath{\xi} helicity j, j=0,1,2. We therefore encourage experimentalists to measure these ratios.

Constituent gluons in the presence of heavy quarks

The formalism necessary to describe bag model constituent gluons in the presence of heavy sources is presented. Numerical values for energies and magnetic moments of low-lying modes are given, as well as some applications relevant to the phenomenology of hybrid\(\bar QqG\) states.

Erratum: Are there baryons which contain constituent gluons?

Erratum: Are there baryons which contain constituent gluons?

Constituent gluons and a new mechanism for radiative weak decays of hyperons

An effective quark-gluon-photon operator is considered as the mechanism for radiative weak decays of hyperons. The coefficient function is unsuppressed by GIM cancellations, suggesting a significant decay rate, and a substantial amount of parity violation (large decay asymmetry) is expected. Attempted model calculations confirm this last feature but fail to provide an adequate absolute decay rate.

Density of pseudoscalar states: Evidence for valence glue.

We claim that experimental meson spectroscopy now requires the existence of constituent gluons. Drawing from several models, we study the number of mesons with given quantum numbers that can be expected in a given mass range, concentrating on pseudoscalars below 2 GeV. Counting only quark-antiquark states gives fewer mesons than are now seen, but including gluon degrees of freedom so that glueballs and hybrid states are allowed remedies this situation.

Are there baryons with constituent glue?

We point out that Λ-like baryons with a constituent gluon can be light because of large color electromagnetic attractions. Mass estimates from the MIT bag model suggest that some observed baryons may be (qqqg) states.

Are there baryons which contain constituent gluons?

A study of three-quark---one-gluon configurations in the zero-strangeness, positive-parity sector is carried out. The quantum numbers of the ground-state levels in this system are identified. The mass spectrum is analyzed in both the bag-model and harmonic-oscillator dynamical frameworks. Mixing between the ${Q}^{3}$ and ${Q}^{3}G$ sectors is determined, and implications of ${Q}^{3}\ensuremath{-}{Q}^{3}G$ mixing are explored.

Adjoint Wilson lines and the effective gluon mass

The effective mass of the gluon is defined in terms of the energy stored in the string between adjoint sources. For SU(2) lattice gauge theory, I present Monte Carlo evidence that this mass scales correctly in the weak coupling regime and hence is non-zero and finite in the continuum limit. Various systematic errors (chief among them are temperature effects) still make it difficult to give a precise numerical value for this mass at zero temperature, but a range of 500 to 800 MeV seems reasonable (using a value for the string tension of (420 MeV) 2). Some attempt is made to relate this quantity to a true “constituent gluon mass.”

Anomalous mass dependence of glueball exclusive decay rates

Exclusive decays such as G → ππ are studied in the framework ofperturbative QCD. We discuss the possibility of the constituent gluons' virtualness scaling as the glueball mass M G, which is a picture equivalent to a glueball containing a few slow-moving, heavy gluons. In this case, the decay rate exhibits a pinch singularity which enhances it by a factor of order ( M G 2/ m q 2) 2 over the dimensional scaling expectation. This singularity is partially suppressed by Sudakov effects which reduce the enhancement factor to (M G 2/m q 2) 2n, where n ⋍ 0.4 .

The magnitude of annihilation and penguin contributions to charm-meson decays

A consistent treatment of color singlet and octet contributions in the spectator constituent gluon model for pseudoscalar meson decays is attempted. The result comes out one order of magnitude too small to explain the observed life-time difference of D 0 and D +. Furthermore, it is found that ‘penguin’ interactions in the annihilation channel may give contributions to the asymmetry of the (D 0 → K +K −)/(D 0 → π + π −) ratio of the order of the phase-space difference or larger. Finally, it is argued that annihilation cannot explain the ΔI = 1 2 rule for kaon decays; dynamical effects including the penguin interactions seem still to be needed.

On hadronic production of the η c and other cc̄ bound states

We discuss various mechanisms for inclusive production of cc̄ bound states in hadron-hadron interactions. We conclude that for η c, η′ c alone, among the bound states, the cross section for production is mainly due to the annihilation of two constituent gluons in a color singlet state. We give detailed results for η c production cross sections.