The Phenomenology of Scalar Colour Octets

We discuss the phenomenology of colour scalar octet particles. Namely, we consider the discovery potential of scalar octets at LEP, FNAL and LHC. Octet scalars decay mainly into two gluino and new hadrons composed from scalar coloured octets are rather longlived (Γ ≤ O(10)Kev). For the scalar octet masses(M ≥ O(50)Gev) the scalar octets producing at FNAL or LHC will decay into two gluons that leads to additional four-jet events. We propose to look for the scalar octets by the measurement of the distributions of the four-jet differential cross section on the invariant two-jet masses. Scalar octets naturally arise in models with compactification of additional dimensions. In such models the branching ratio for the scalar octet bound state into 2 photons is O(10) that leads to the events with two photons and two jets. We also point out that the current experimental data don’t contradict to the existence of light (M ∼ O(1)Gev) scalar octets. Light scalar colour octets give additional contribution to the QCD β -function and allow to improve agreement between deep inelastic and LEP data. 1 On leave of absence from Institute for Nuclear Research, Moscow 117312, Russia. e-mail: [email protected] The aim of this note is the discussion of the phenomenology of scalar colour octets. The relatively light (M ≤ O(1)Tev) scalar colour octets are predicted in some nonsupersymmetric and supersymmetic GUTs [1, 2]. Here we consider the discovery potential of scalar octets at LEP, FNAL and LHC. Colour octet scalars decay mainly into two gluons with rather small decay width (Γ ≤ O(10)Kev), so new hadrons composed from colour scalar octets are longlived. The scalar octets producing at FNAL or LHC (for scalar octet masses M ≥ O(50)Gev) decay into two gluino that leads to additional four-jet events. We propose to look for scalar octets by the measurement of the distributions of the four-jet differential cross section on the invariant two-jet masses. At least, the accurate measurement of the four-jet differential cross section allows to extract the lower bound for the octet scalar cross section. Scalar octets naturally arise in models with compactification of additional dimensions. In such models the branching ratio for the scalar octet bound state into two photons is Br(Φg → γγ) ∼ O(10). For such models we shall have the events with two photons and two jets that allows to detect scalar octets using this mode. We also point out that the current experimental data don’t contradict to the existence of light (M ∼ O(1)Gev) scalar octets. Light scalar octets give additional contribution to the QCD β-function and allow to improve agreement between deep inelastic and LEP data. To be precise in this paper we consider colour light scalar octets neutral under SU(2)⊗ U(1) electroweak gauge group. Such particles are described by the selfconjugate scalar field Φβ(x) ((Φ α β(x)) + = Φα(x), Φ α α(x) = 0) interacting only with gluons. Here α = 1, 2, 3; β = 1, 2, 3 are SU(3) indices. The scalar potential for the scalar octet field Φβ(x) has the form V (Φ) = M 2 Tr(Φ) + λ1M 6 Tr(Φ) + λ2 12 Tr(Φ) + λ3 12 (TrΦ) (1) The term λ1M 6 Tr(Φ) in the scalar potential (1) breaks the discrete symmetry Φ → −Φ. The existence of such term in the lagrangian leads to the decay of the scalar octet mainly into two gluons through one-loop diagrams similar to the corresponding one-loop diagrams describing the Higgs boson decay into two photons. One can find that the decay width of the scalar octet is determined by the formula Γ(Φ → g g) = 15 4096π3 α sc λ1M , (2)