Prospects for sgoldstino search at the LHC

In this paper we estimate the LHC sgoldstino discovery potential for the signatures with γγ and ZZ in a final state. It is well known, that exist models of supergravity breaking with relatively light sgoldstinos (scalar S and pseudoscalar P particles — superpartners of goldstino ψ). Such pattern emerges in a number of non-minimal supergravity models [1] and also in gauge mediation models if supersymmetry is broken via non-trivial superpotential (see, Ref. [2] and references therein). To the leading order in 1/F , where F is the parameter of supersymmetry breaking, and to zero order in MSSM gauge and Yukawa coupling constants, the interactions between the component fields of goldstino supermultiplet and MSSM fields have been derived in Ref. [3]. They correspond to the most attractive for collider studies processes where only one of these new particles appears in a final state. In this case light gravitino behaves exactly as goldstino. For sgoldstinos, as they are R-even, only sgoldstino couplings to goldstino and sgoldstino couplings to SM fields have been included as the most interesting phenomenologically. All relevant sgoldstino coupling constants presented in Ref. [3] are completely determined by the MSSM soft terms and the parameter of supersymmetry breaking F , but sgoldstino masses (mS, mP ) remain free. If sgoldstino masses are of the order of electroweak scale and √ F ∼ 1 TeV — sgoldstino may be detected in collisions of high energy particles at supercolliders [4, 5]. There are flavor-conserving and flavor-violating interactions of sgoldstino fields. As concerns flavor-conserving interactions, the strongest bounds arise from astrophysics and cosmology, that is √ F & 10 GeV [6, 7], or m3/2 > 600 eV, for models with mS(P ) < 10 keV and MSSM soft flavor-conserving terms being of the order of electroweak scale. For the intermediate sgoldstino masses (up to a few MeV) constraints from the study of SN explosions and reactor experiments lead to √ F & 300 TeV [7]. For heavier sgoldstinos, low energy processes (such as rare decays of mesons) provide limits at the level of √ F & 500 GeV [7]. The collider experiments exhibit the same level of sensitivity to light sgoldstinos as rare meson decays. Indeed the studies [8, 9, 10, 11] of the light sgoldstino (mS,P . a few MeV) phenomenology based on the effective low-energy Lagrangian derived from N=1 linear supergravity yield the bounds: √ F & 500 GeV (combined bound on Z → Sf̄f, P f̄f [10]; combined bound on ee → γS, γP [9]) at Msoft ∼ 100 GeV, √ F & 1 TeV [11] (combined bound on pp̄ → gS, gP ) at gluino mass M3 ≃ 500 GeV. Searches for heavier sgoldstinos at colliders, though exploiting another technique, results in similar bounds on the scale of supersymmetry breaking. Most powerful among the operating machines, LEP and Tevatron, give a constraint of the order of 1 TeV on supersymmetry breaking scale in models with light sgoldstinos. Indeed, the analysis carried out by DELPHI Collaboration [12] yields the limit 1 e-mail: [email protected] 2 e-mail: [email protected] 1 √ F > 500÷200 GeV at sgoldstino massesmS,P = 10÷150 GeV andMsoft ∼ 100 GeV. The constraint depends on the MSSM soft breaking parameters. In particular, it is stronger by about a hundred GeV in the model with degenerate gauginos. At Tevatron, a few events in pp̄ → Sγ(Z) channel, and about 10 events in pp̄ → S channel would be produced at √ F = 1 TeV and Msoft ∼ 100 GeV for integrated luminosity L = 100 pb and sgoldstino mass of the order of 100 GeV [5]. This gives rise to a possibility to detect sgoldstino, if it decays inside the detector into photons and √ F is not larger than 1.5÷ 2 TeV. In this note we estimate the LHC sgoldstino discovery potential using as a signature the decay of sgoldstino into two photons or(and) two Z-bosons. In terms of SU(3)c × SU(2)L × U(1)Y fields the sgoldstino effective lagrangian reads [3]: LS = − ∑ all gauge fields Mα 2 √ 2F S · F α a μνF α μν a − Aab √ 2F y ab · S(ǫijl aebhD + h.c.) − A D ab √ 2F y ab · S(ǫijq adbhD + h.c.)− Aab √ 2F y ab · S(ǫijq aubhjU + h.c.) , LP = ∑ all gauge fields Mα 4 √ 2F P · F α a μνǫF α a λρ − i Aab √ 2F y ab · P (ǫijl aebhD − h.c.) − i A D ab √ 2F y ab · P (ǫijq adbhD − h.c.)− i Aab √ 2F y ab · P (ǫijq aubhjU − h.c.) . Lψ,S,P = i∂μψ̄σ̄ψ + 1 2 ∂μS∂ S − 1 2 mSS 2 + 1 2 ∂μP∂ P − 1 2 mPP 2 + mS 2 √ 2F S ( ψψ + ψ̄ψ̄ ) − i m 2 P 2 √ 2F P ( ψψ − ψ̄ψ̄ )