Topic of the Week : Peaks, Valleys, Deserts: Searching for the invisible at the LHC

Sunrise - WH11NE (Fermilab)

Sunrise - WH11NE


Javier Mauricio Duarte (Fermi National Accelerator Lab. (US)), Si Xie (California Institute of Technology (US))

At the Large Hadron Collider (LHC), many new physics
signatures feature pair-production of massive particles with
subsequent direct or cascading decays to weakly interacting particles,
such as SUSY scenarios with conserved R-parity, or Higgs decaying to
two leptons and two neutrinos through W bosons, often motivated by
models of new physics which attempt to mitigate the hierarchy problem
in the Standard Model and explain the identity of Dark Matter. While final states containing multiple invisible particles represent an opportunity for discovery of new
physics phenomena, they also present a unique experimental challenge;
the kinematic information lost through particles escaping detection
makes fully reconstructing these collision events impossible. In order
to address this shortcoming special kinematic variables are used to
partially reconstruct these events, providing sensitivity to
properties of the particles appearing in them, including masses and
even their spin correlations.

We introduce a systematic prescription, Recursive Jigsaw
Reconstruction, for generating a preferred kinematic basis of observables developed to study final states with invisible particles at HEP experiments, specifically catered to each
case of interest. Using the examples of single W boson production and slepton pair production at the
LHC, the motivation and derivation of these observables are described,
along with comparisons to previously existing approaches.
Generalizations to more complicated decay topologies are also
discussed, including fully leptonic top quark pair production
(resonant and non-resonant), its supersymmetric analogue of stop
pair-production with subsequent decays to b-quarks, leptons, and
neutrinos, examples involving both SM and BSM Higgs
decays, and strategies for compressed mass-spectra scenarios.