InvisibleZ′at the CERN LHC

Abstract

We study the feasibility of observing an invisibly decaying Z 0 at the LHC through the process pp ! ZZ 0 ! ' þ ' À XX y , where X is any neutral, (quasi-) stable particle, whether a standard model neutrino or a new state. The measurement of the invisible width through this process facilitates both a modelindependent measurement of À Z 0 ! " and potentially detection of light neutral hidden states. Such particles appear in many models, where the Z 0 is a messenger to a hidden sector, and also if dark matter is charged under the Uð1Þ 0 of the Z 0 . We find that with as few as 30 fb À1 of data the invisibly decaying Z 0 can be observed at 5 over standard model background for a 1 TeV Z 0 with reasonable couplings. If the Z 0 does not couple to leptons and therefore cannot be observed in the Drell-Yan channel, this process becomes a discovery mode. For reasonable hidden sector couplings, masses up to 2 TeV can be probed at the LHC. If the Z 0 does couple to leptons, then the rate for this invisible decay is predicted by on-peak data and the presence of additional hidden states can be searched for. With 100 fb À1 of data, the presence of excess decays to hidden states can be excluded at 95% C.L., if they comprise 20-30% of the total invisible cross section.

Monojet versus the rest of the world I: t-channel models

“…4 For masses larger than 2 TeV all the limits converge towards the EFT line and the dependence on the mediator width becomes negligible. The first message from these figures is that there is no such a thing as a lower bound on Λ; instead, there are bands, parameterized by the details of the theory.…”

“…function effects), and on resonance [4,7,20,21,[23][24][25][26][27]. On the other hand, production at low √ s is the most contaminated by SM backgrounds.…”

“…The basic idea is to make use of crossing symmetry to relate the scattering cross-section of DM off of nucleons to the production of DM at colliders. The DM is produced with initial state radiation (ISR), whether that be a Z [4,5], photon [6][7][8], jet [9][10][11][12][13][14][15], top [16] or Higgs [17][18][19], allowing a measurement of the missing transverse energy (MET) carried by the DM. The strongest constraints are derived from a jet in the initial state.…”

Constraining light dark matter with diffuse X-ray and gamma-ray observations

“…Such DM can be probed at colliders [10][11][12][13][14][15], at direct detection experiments [9,16,17], and at proton-and electron-beam dumps [18][19][20][21][22][23]. Constraints from the Cosmic Microwave Background (CMB) already limit the s-wave DM annihilation cross section to SM matter to be below that of a thermal WIMP, for DM masses below ∼ 7 GeV [24][25][26][27].…”

Surprises from complete vector portal theories: New insights into the dark sector and its interplay with Higgs physics

“…This Z boson could also provide a portal to the dark matter sector -another robust motivation for physics beyond the SM [2,3]. Extensive studies have pursued this scenario, with simplified models as a commonly employed tool [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Although this approach is advantageous as it allows to study phenomenology with a handful of masses and couplings, some key issues may be missed unless a UV-complete theory is specified.…”