Cornering compressed gluino at the LHC
Received: February
Cornering compressed gluino at the LHC
Natsumi Nagata 0 1 3 4 5
Hidetoshi Otono 0 1 2 4 5
Satoshi Shirai 0 1 4 5
Open Access 0 1 4 5
c The Authors. 0 1 4 5
0 The University of Tokyo Institutes for Advanced Study, The University of Tokyo
1 Fukuoka 819-0395 , Japan
2 Research Center for Advanced Particle Physics, Kyushu University
3 Department of Physics, University of Tokyo
4 [59] J. Hisano , S. Matsumoto, M. Nagai, O. Saito and M. Senami, Non-perturbative e ect on
5 [95] M.A. Ajaib, T. Li and Q. Sha , Stop-neutralino coannihilation in the light of LHC , Phys
We discuss collider search strategies of gluinos which are highly degenerate with the lightest neutralino in mass. This scenario is fairly di cult to probe with conventional search strategies at colliders, and thus may provide a hideaway of supersymmetry. Moreover, such a high degeneracy plays an important role in dark matter physics as the relic abundance of the lightest neutralino is signi cantly reduced via coannihilation. In this paper, we discuss ways of uncovering this scenario with the help of longevity of gluinos; if the mass di erence between the lightest neutralino and gluino is . 100 GeV and squarks are heavier than gluino, then the decay length of the gluino tends to be of the order of the detector-size scale. Such gluinos can be explored in the searches of displaced vertices, disappearing tracks, and anomalously large energy deposit by (meta)stable massive charged particles. We nd that these searches are complementary to each other, and by combining their results we may probe a wide range of the compressed gluino region in the LHC experiments.
Supersymmetry Phenomenology
1 Introduction 2 3 2.1
Properties of compressed gluino
Conclusion and discussion
Supersymmetric (SUSY) extensions of the Standard Model (SM) have been thought of as
the leading candidate of physics beyond the SM. In particular, weak-scale SUSY has various
attractive features | the electroweak scale is stabilized against quantum corrections, gauge
coupling uni cation is achieved, and so on | and therefore has widely been studied so far.
This paradigm is, however, under strong pressure from the results obtained at the Large
Hadron Collider (LHC). Direct searches of SUSY particles impose stringent limits on their
masses, especially those of colored particles such as squarks and gluino [1{3]. In addition,
the observed value of the mass of the SM-like Higgs boson [4{6], mh ' 125 GeV, may also
imply that SUSY particles are rather heavy. In the minimal supersymmetric Standard
Model (MSSM), the tree-level value of the SM-like Higgs boson mass is smaller than the
Z-boson mass [7, 8], and we need sizable quantum corrections in order to explain the
discrepancy between the tree-level prediction and the observed value. It turns out that
su ciently large radiative corrections are provided by stop-loop diagrams [9{13] if the stop
masses are much larger than the electroweak scale.
The SUSY SM with heavy SUSY particles (or, equivalently, with a high SUSY-breaking
scale) have various advantages from the phenomenological point of view [14{28]; i ) severe
limits from the measurements of avor-changing processes and electric dipole moments can
be evaded [29{33]; ii ) heavy sfermions do not spoil successful gauge coupling uni cation if
gauginos and Higgsinos remain around the TeV scale [34]; iii ) the dimension- ve proton
decay caused by the color-triplet Higgs exchange [35, 36], which was problematic for
weakscale SUSY [37, 38], is suppressed by sfermion masses and thus the current proton decay
bound can be evaded if SUSY particles are heavy enough [39{47], making the minimal
SUSY SU(5) grand uni cation [48, 49] viable; iv ) cosmological problems in SUSY theories,
the requirement of
SUSY breaking.1
such as the gravitino problem [50{54] and the Polonyi problem [55] can be avoided.
Nevertheless, high-scale SUSY models may have a potential problem regarding dark matter. In
SUSY SMs with R-parity conservation, the lightest SUSY particle (LSP) is stable and thus
can be a dark matter candidate. In particular, if the LSP is the lightest neutralino, its relic
abundance is determined by the ordinary thermal freeze-out scenario. Then, it turns out
that if the mass of the neutralino LSP is well above the weak scale, its thermal relic
abundance tends to exceed the observed value of dark matter density, DMh2
DMh2 . 0:12 imposes a severe constraint on models with high-scale
In order to avoid over-production of the neutralino LSP in the high-scale SUSY
scenario, it is necessary to assure a large annihilation cross section for the LSP. A simple
way to do that is to assume the neutralino LSP to be an almost pure SU(2)L multiplet,
i.e., a wino or Higgsino. In such cases, the LSP has the electroweak interactions and thus
has a relatively large annihilation cross section, which is further enhanced by the so-called
Sommerfeld e ects [57, 58]. Indeed, the thermal relic abundance of wino (...truncated)