ATLAS on-Z excess via gluino-Higgsino-singlino decay chains in the NMSSM

Journal of High Energy Physics, Jan 2016

Recently the ATLAS experiment has reported 3.0 σ excess in an on-Z signal region in searches for supersymmetric particles. We find that the next-to-minimal supersymmetric standard model can explain this excess by the production of gluinos which mainly decay via \( \tilde{g}\to g{\tilde{\chi}}_{2,3}^0\to gZ{\tilde{\chi}}_1^0 \) where \( {\tilde{\chi}}_{2,3}^0 \) and \( {\tilde{\chi}}_1^0 \) are the Higgsino and the singlino-like neutralinos, respectively. We show that the observed dark matter density is explained by the thermal relic density of the singlino-like neutralino, simultaneously. We also discuss the searches for the Higgs sector of this scenario at the Large Hadron Collider.

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ATLAS on-Z excess via gluino-Higgsino-singlino decay chains in the NMSSM

HJE ATLAS on-Z excess via gluino-Higgsino-singlino decay chains in the NMSSM Keisuke Harigaya 1 2 5 6 7 8 9 10 Masahiro Ibe 1 2 3 6 8 9 10 Teppei Kitahara 0 1 2 4 8 9 10 0 Institute for Nuclear Physics (IKP), Karlsruhe Institute of Technology 1 Kashiwa , Chiba 277-8582 , Japan 2 Berkeley , California 94720 , U.S.A 3 Kavli IPMU (WPI), UTIAS, University of Tokyo 4 Institute for Theoretical Particle Physics (TTP), Karlsruhe Institute of Technology 5 Theoretical Physics Group, Lawrence Berkeley National Laboratory 6 ICRR, University of Tokyo 7 Department of Physics, University of California 8 Tsukuba , Ibaraki 305-0801 , Japan 9 Engesserstra e 7 , D-76128 Karlsruhe , Germany 10 Kashiwa , Chiba 277-8583 , Japan Recently the ATLAS experiment has reported 3.0 mainly decay via g~ ! g ~02;3 ! gZ ~01 where ~2;3 and ~01 are the Higgsino and the singlino0 like neutralinos, respectively. We show that the observed dark matter density is explained by the thermal relic density of the singlino-like neutralino, simultaneously. We also discuss the searches for the Higgs sector of this scenario at the Large Hadron Collider. Supersymmetry Phenomenology - We nd that the next-to-minimal supersymmetric standard model can explain this excess by the production of gluinos which 1 Introduction NMSSM 2 3 4 5 6 1 Explanation of the ATLAS on-Z excess Dark matter property Higgs sector searches at the LHC Conclusion Introduction model. A drawback of the MSSM is, however, that it contains a dimensionful parameter , the mass term of the Higgs multiplets. This reintroduces an additional ne-tuning problem, the so-called problem [1]. The size of is required to be of the order of other soft SUSY breaking parameters for successful electroweak symmetry breaking whereas they are essentially unrelated with each other. The simplest solution of the problem is to introduce an additional gauge-singlet super eld S^ [2] whose vacuum expectation value (VEV) is controlled by soft SUSY breaking parameters. By making an e ective term generated by the VEV of S^, the size of is naturally interrelated to the size of the soft SUSY breaking parameters. The next-tominimal SUSY standard model (NMSSM) is one of the simplest singlet extensions of the MSSM where a discrete Z3 symmetry is imposed [2{4]. Recently, the ATLAS experiment has reported excess events in the SUSY particle p searches with dileptons, jets and missing transverse energy (ETmiss) in data of 20.3 fb 1 at s = 8 TeV [5]. They have observed 29 (16 for ee and 13 for ) same- avour oppositesign dilepton pairs whose invariant masses are in the Z boson mass window, 81 GeV < m`` < 101 GeV (\on-Z" signal region). The expected number of SM background events is 10:6 3:2 pairs. The observed event number corresponds to excess of 3.0 local signi cance (3.0 for ee and 1.7 for , separately). In this paper, we call this excess \ATLAS onZ excess". This excess seems to imply an existence of a gluino whose mass is lighter experiment has also analyzed the dileptons+jets+ETmiss nal state using p than 1.2 TeV or squarks lighter than 1.4 TeV [6]. The caveat is, though, that the CMS s = 8 TeV data { 1 { in which the kinematical cut is di erent from the ATLAS one, and a signi cant excess has not been observed in the on-Z signal region [7]. After the report, many scenarios in the MSSM as well as in the NMSSM have been proposed to explain the ATLAS on-Z excess without con icting with constraints from various SUSY searches including the CMS on-Z result [6, 8{20]. To have on-shell Z bosons in nal states while escaping other SUSY search constraints, scenarios with a gravitino as the lightest SUSY particle (LSP) seems to be one of the simplest possibilities. The lightest neutralino decays into a pair of a Z boson and a gravitino, while the decay of colored SUSY particles into the gravitino with a large ETmiss are suppressed. Unfortunately, however, the simpli ed general gauge mediation model with the gravitino LSP cannot explain the ATLAS on-Z excess [9, 10], where the produced Z bosons are rather hard due to the lightness of the gravitino and are caught in the mesh of the SUSY searches with multi jets + ETmiss. In ref. [16], it has been shown that this problem can be evaded by introducing a nonMSSM massive particle, a goldstini G~0, into which the lightest neutralino mainly decays. Due to the massiveness of the goldstini, the Z bosons are emitted softly, and hence, the constraints from 0 lepton + multi jets + ETmiss searches become weaker. In this scenario, similar to the gravitino LSP scenario, the couplings between the goldstini and the MSSM particles are suppressed. Besides, the sfermion masses are assumed to be rather larger than the gaugino masses and the lightest neutralino is assumed to be the Higgsino-like. With this setup, the ATLAS on-Z excess is successfully explained by the gluino production via a decay chain, g~ ! g ~01;2 ! gZG~0, where ~1;2 are the Higgsino-like neutralinos. 0 The above goldst (...truncated)


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Keisuke Harigaya, Masahiro Ibe, Teppei Kitahara. ATLAS on-Z excess via gluino-Higgsino-singlino decay chains in the NMSSM, Journal of High Energy Physics, 2016, pp. 30, Volume 2016, Issue 1, DOI: 10.1007/JHEP01(2016)030