A new probe of dark sector dynamics at the LHC

Journal of High Energy Physics, Sep 2015

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 Z′, which kinetically mixes with the Standard Model U(1). For small mixing, direct 2 → 1 production of the Z′ is not visible in standard resonance searches due to the large Drell-Yan background. However, there may be significant production of the Z′ boson in processes involving other dark sector particles, resulting in final states with a Z′ resonance and missing transverse momentum. Examples of such processes include cascade decays within the dark sector and radiation of the Z′ off of final state dark sector particles. Even when the rate to produce a Z′ 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.

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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)


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Arpit Gupta, Reinard Primulando, Prashant Saraswat. A new probe of dark sector dynamics at the LHC, Journal of High Energy Physics, 2015, pp. 79, Volume 2015, Issue 9, DOI: 10.1007/JHEP09(2015)079