Lepton flavour violating signature in supersymmetric U(1)′ seesaw models at the LHC
Received: January
Lepton flavour violating signature in supersymmetric
U 0 1 2
seesaw 0 1 2
Priyotosh Bandyopadhyay 0 1 2 4
Eung Jin Chun 0 1 2 3
Open Access 0 1 2
c The Authors. 0 1 2
0 Hoegiro 85 , Dongdaemun-gu, Seoul 130-722 , South Korea
1 Via Arnesano , 73100, Lecce , Italy
2 FIN-00014 , Helsinki , Finland
3 Korea Institute for Advanced Study
4 Department of Physics, University of Helsinki and Helsinki Institute of Physics
We consider a U(1)0 supersymmetric seesaw model in which a right-handed sneutrino is a thermal dark matter candidate whose relic density can be in the right range due to its coupling to relatively light Z0, the superpartner of the extra gauge boson Z0. Such light Z0 can be produced at the LHC through cascade decays of colored superparticles, in particular, stops and sbottoms, and then decay to a right-handed neutrino and a sneutrino dark matter, which leads to lepton flavor violating signals of same/opposite-sign dileptons (or multileptons) accompanied by large missing energy. Taking some benchmark points, we analyze the opposite- and same-sign dilepton signatures and the corresponding flavour difference i.e., (2e 2). It is shown that 5 signal significance can be reached for some benchmark points with very early data of 2 fb1 integrated luminosity. In addition, 3` and 4` signatures also look promising to check the consistency in the model prediction, and it is possible to reconstruct the Z0 mass from jj` invariant mass distribution.
Supersymmetry Phenomenology
1 Introduction
2 Z0 phenomenology
3 Experimental bounds and benchmark points
4 Production rates and decays 5 LHC phenomenology 5.1 5.2
Reconstruction of RHN
6 Conclusion
Introduction
Among various reasons for requiring theories beyond the Standard Model (SM),
experimental evidences for tiny neutrino masses and dark matter, and a theoretical requirement for
naturalness of the electroweak scale would be key elements and related to each other. The
first candidate model addressing these features would be Minimal Supersymmetric
Standard Model (MSSM) where the neutrino masses and mixing are explained by R-parity and
lepton-number violation [1] and the dark matter consists of a slowly decaying gravitino as
the lightest supersymmetric particle (LSP). In this paper, we wish to explore another
possibility which can provide richer collider signatures. A sumpersymmetric seesaw model [2]
associated with an additional gauge symmetry U(1)0 [3] would be one of such examples.
In supersymmetric theories with R-parity, the LSP is stable and thus a neutral LSP,
typically a linear combination of neutral gauginos and Higgsinos, becomes a good thermal
dark matter (DM) candidate if supersymmetry (SUSY) is broken around the TeV scale [4].
The SUSY breaking can radiatively induce the U(1)0 breaking in addition to the usual
electroweak symmetry breaking, which determines the seesaw scale also at O(TeV) [5]. A
the presence of right-handed neutrinos (RHNs) for the anomaly-free condition, and thus
realizes the TeV-scale seesaw mechanism. Let us note that we do not assume any grand
unification theory as the origin of our model and the grand unification structure will be
used for a convenient guide to a theoretically consistent model gauranteeing the anomaly
free condition, and so on. In our framework, a right-handed sneutrino (RHsN) can be
the LSP and thus another good dark matter candidate whose thermal relic density is in
the right range if the U(1)0 gaugino Z0, the superpartner of the U(1)0 gauge boson Z0, is
relatively light [6].
In this paper, we analyze LHC signatures of the extra gaugino Z0 which can be pairly
produced mainly through third generation squark cascades and then decay to a RHN
and a RHsN DM. Due to the Majorana nature of a RHN, N , it can decay to
bothdilepton (SSD) events in addition to the usual opposite-sign dilepton (OSD) events [7].
Furthermore, Yukawa couplings of a RHN are generically flavour-dependent and thus lead
benchmark points, we carry out a Pythia-FastJet level collider simulation at the 14 TeV
LHC for multilepton final states to study the prospect for detecting such lepton flavour
opposite-sign dilepton final states. Similar phenomenon should appear also in multi-lepton
integrated luminosity at the very early stage of LHC14. It is straightforward to follow the
Br(N eW ) resulting in
a similar conclusion.
Let us here recall that the neutrino mass models with R-parity and lepton number
violating couplings lead to similar signatures [8, 9]. In particular, there could appear an
interesting connection of the electron excess assumed in this work and the neutrinoless
double-beta decay caused by R-parity violation as pointed out by Allanach et al. [10, 11].
Furthermore, the supersymmetric left-right symmetric model [12] can also lead to the
similar signatures except a possible W 0 appearance in the next LHC run.
This paper is organized as follows. In section 2, we describe a general Z0
phenomenology by taking (...truncated)