A new probe of dark sector dynamics at the LHC
Received: April
new probe of dark sector dynamics at the LHC
0 College Park, MD 20742 , U.S.A
1 Bandung , Indonesia
2 Baltimore , MD 21218 , U.S.A
3 Department of Physics, Parahyangan Catholic University
4 Maryland Center for Fundamental Physics, Department of Physics, University of Maryland
5 Department of Physics and Astronomy, Johns Hopkins University
We propose a LHC search for dilepton resonances in association with large missing energy as a generic probe of TeV dark sector models. Such resonances can occur if the dark sector includes a U(1) gauge boson, or Z0, which kinetically mixes with the Standard Model U(1). For small mixing, direct 2 → 1 production of the Z0 is not visible in standard resonance searches due to the large Drell-Yan background. However, there may be significant production of the Z0 boson in processes involving other dark sector particles, resulting in final states with a Z0 resonance and missing transverse momentum. Examples of such processes include cascade decays within the dark sector and radiation of the Z0 off of final state dark sector particles. Even when the rate to produce a Z0 boson in a dark sector process is suppressed, this channel can provide better sensitivity than traditional collider probes of dark sectors such as monojet searches. We find that data from the 8 TeV LHC run can be interpreted to give bounds on such processes; more optimized searches could extend the sensitivity and continue to probe these models in the Run II data.
Beyond Standard Model; Cosmology of Theories beyond the SM
1 Introduction 2 3 4
Dileptons plus MET at the LHC
Monte Carlo simulation
There is compelling evidence that most of the matter in the Universe is composed of
nonbaryonic particles, the dark matter (DM), the nature of which is otherwise unknown. One
of the only quantitative data points known about dark matter is its current cosmological
bath of the early Universe, then this relic density can be achieved [2] with a dark matter
vation for considering dark matter production at the LHC. Dark matter candidates of weak
scale mass can also naturally emerge within theories developed to address the electroweak
hierarchy problem, such as supersymmetric models.
Current searches for dark matter at the LHC focus on pair production of invisible DM
particles plus radiation from the initial state in the form of jets, photons, or electroweak
bosons [3–22]. The resulting “monojet”, “monophoton” etc. signatures have considerable
SM background, but still allow for constraints to be placed on dark matter interactions
with quarks and gluons. Within an effective field theory (EFT) framework, these processes
can be correlated with signals from elastic DM scattering in detectors (direct detection)
and astrophysical DM annihilation (indirect detection) [23–28].
This program is appropriate for the minimal assumption of a single DM particle and no
other new physics. However, when one goes beyond this minimal framework, other types
of collider searches may provide much more powerful probes [29–39]. A familiar example
is that of supersymmetric models, in which searching for squarks and gluinos decaying to
a neutralino DM candidate is usually a far more effective probe of the new physics than
searches for direct neutralino production. More generally, any new particles associated
with dark matter can provide additional collider signatures which may greatly enhance
the prospects for discovery. Note that the same enhancement does not extend to direct
and indirect detection of dark matter, which are only sensitive to the actual cosmological
relics. In this respect colliders provide a unique window into the physics associated with
In this work we specialize to the case where all new particles are gauge singlets under
the Standard Model, forming a “dark sector.” Although the model space for such a dark
sector is vast, some well-motivated assumptions greatly narrow down the possible collider
phenomenology. Consistent with renormalizable field theory, we can consider the new
particles to be either fermions, scalars or gauge bosons. Since the coupling of these states
to the SM is generally weak, once dark sector particles are produced at colliders they
will tend to cascade decay within the dark sector until that is no longer kinematically
possible. In particular, particles with arbitrarily weak couplings to the SM can still be
produced through decay of or radiation off of other dark sector particles. If the theory
preserves baryon and lepton number, or an analogous dark fermion number, then the
lightest dark fermion will be absolutely stable and appear as missing energy at colliders.
Dark bosons however may not be protected by any quantum numbers and could decay
into the Standard Model. Although this decay width may be small due to weak couplings,
the branching ratio of the dark boson to the SM can still be large if decays to other
states are suppressed– particularly if they are not kinematically accessible. This (...truncated)