Discovering an Invisibly Decaying Higgs at Hadron Colliders
Abstract
A Higgs boson lighter than 2 mW 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, hinv, 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+hinv 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 hinv mass from production cross sections at the LHC, and find that combining WBF and Z+hinv allows a relatively model-independent determination of the hinv 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 hinv 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+hinv channel allows a 3 sigma observation of hinv with 7 fb-1 per detector. Because of overwhelming irreducible backgrounds, hinv+j is not a useful search channel at either the Tevatron or the LHC, despite the larger production rate.
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