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