LHC probes the hidden sector

TL;DR

The paper evaluates LHC constraints on hidden-sector scenarios, focusing on hidden U(1) gauge bosons with kinetic mixing, dimension-6 portal operators, axion-like particles with dimension-5 couplings, and minicharged particles. It leverages 2011–2012 ATLAS/CMS data, reinterpreting di-lepton and diphoton searches (and VBF-like photon processes) to derive bounds on mixing parameters, couplings, and masses across GeV–TeV scales. The study demonstrates that the LHC can probe very small hidden-sector couplings, extending beyond previous low-energy limits and offering complementary coverage to high-precision experiments. It also outlines future prospects at 14 TeV with higher luminosity and more exclusive analyses to further tighten these constraints.

Abstract

In this note we establish LHC limits on a variety of benchmark models for hidden sector physics using 2011 and 2012 data. First, we consider a "hidden" U(1) gauge boson under which all Standard Model particles are uncharged at tree-level and which interacts with the visible sector either via kinetic mixing or higher dimensional operators. Second, we constrain scalar and pseudo-scalar particles interacting with the Standard Model via dimension five operators and Yukawa interactions, in particular including so-called axion-like particles. In both cases we consider several different final states, including photons, electrons, muons and taus, establishing new constraints for a range of GeV to TeV scale masses. Finally, we also comment on particles with electric charges smaller than e that arise from hidden sector matter.

Figures (9)

• Figure 1: 95% exclusion limits on the kinetic mixing parameter $\chi_{_{Y}}$ from the ATLAS (dashed) and CMS (solid) $Z^{\prime}$ searches. The thin lines correspond to the $\mu^{+}\mu^{-}$ channel only, while the thick lines result from a combination of the $\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ channels.
• Figure 2: Combination of the new LHC limits with a range of other constraints on hidden photons (see refs. Jaeckel:2010niAndreas:2012mt for details). The new "LHC" region is marked in orange and extends the existing bounds to a previously uncovered range of high masses. Note that the limits are with respect to the hypercharge mixing parameter $\chi_{_{Y}}$. For small hidden photon masses the kinetic mixing parameter with the ordinary photon is related to $\chi_{_{Y}}$ through $\chi=\cos(\theta_{W})\chi_{_{Y}}$.
• Figure 3: 95% exclusion limits on the coupling constants $\tau_{l_{j}}$ in the case that $\tau_{l_{j}}=\tau_{q}$ with all other lepton couplings switched off. Results from ATLAS are shown as dashed lines, while results from CMS are shown as solid lines. Red, blue and green correspond to the $e^{+}e^{-}$, $\mu^{+}\mu^{-}$ and $\tau^{+}\tau^{-}$ channels, respectively. The gray area indicates where $\Gamma_X>0.03\,m_{X}$ and the limits need to be treated with caution. See Eq. \ref{['dim6lagsimple']} for the definition of the couplings.
• Figure 4: 95% exclusion limits on the dimension five coupling constant $g_{\phi BB}$ assuming pure photon production (blue) and gluon production with $g_{\phi gg}=g_{\phi BB}$ (red). The limits arise from a combination of different datasets (for details see text). The two gray regions indicate where the $\phi$ decay width $\Gamma_\phi$ exceeds $0.05\, m_\phi$ for the case of pure $g_{\phi BB}$ (dark gray) and $g_{\phi gg}=g_{\phi BB}$ (light gray). The limits need to be interpreted with care in these regions.
• Figure 5: Summary of cosmological and astrophysical constraints for (pseudo-)scalars coupled to two photons (compilation adapted from Jaeckel:2010niCadamuro:2011fdHewett:2012ns). The new constraints are marked in blue (pure $g_{\phi BB}$) and red (assuming a gluon coupling with $g_{\phi gg}=g_{\phi BB}$).