  A Higgs boson lighter than 2 m_W that decays mostly into invisible channels
(e.g., dark matter particles) is theoretically well-motivated. We study the
prospects for discovery of such an invisible Higgs, h_inv, at the LHC and the
Tevatron in three production modes: (1) in association with a Z, (2) through
Weak Boson Fusion (WBF), and (3) accompanied by a jet. In the Z+h_inv channel,
we show that the LHC can yield a discovery signal above 5 sigma with 10 fb-1 of
integrated luminosity for a Higgs mass of 120 GeV. With 30 fb-1 the discovery
reach extends up to a Higgs mass of 160 GeV. We also study the extraction of
the h_inv mass from production cross sections at the LHC, and find that
combining WBF and Z+h_inv allows a relatively model-independent determination
of the h_inv mass with an uncertainty of 35-50 GeV (15-20 GeV) with 10 (100)
fb-1. At the Tevatron, a 3 sigma observation of a 120 GeV h_inv in any single
channel is not possible with less than 12 fb-1 per detector. However, we show
that combining the signal from WBF with the previously-studied Z+h_inv channel
allows a 3 sigma observation of h_inv with 7 fb-1 per detector. Because of
overwhelming irreducible backgrounds, h_inv+j is not a useful search channel at
either the Tevatron or the LHC, despite the larger production rate.

High Energy Physics - Phenomenology;High Energy Physics - Experiment