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Discovering an Invisibly Decaying Higgs at Hadron Colliders

Hooman Davoudiasl, Tao Han, Heather E. Logan

TL;DR

The paper investigates the discovery potential for an invisibly decaying Higgs h_inv at hadron colliders, focusing on three production modes: Z+h_inv, h_inv via Weak Boson Fusion, and h_inv+ j. Using realistic cuts and backgrounds, it finds that the Z+h_inv channel yields a >5σ discovery at the LHC with 10 fb−1 for m_h ≈ 120 GeV and can extend to ≈160 GeV with 30 fb−1; it also shows how cross-section measurements can be used to extract the Higgs mass, particularly via a ratio of Zh_inv and WBF rates that is less model-dependent. At the Tevatron, WBF combined with Z+h_inv can achieve a 3σ observation for mh ≈ 120 GeV with about 7 fb−1 per detector, though h_inv+ j is not a viable channel due to large backgrounds. Collectively, the study demonstrates complementary discovery avenues and a pathway to mh determination for invisible Higgs scenarios, while highlighting the limited utility of the h_inv+ j channel.

Abstract

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.

Discovering an Invisibly Decaying Higgs at Hadron Colliders

TL;DR

The paper investigates the discovery potential for an invisibly decaying Higgs h_inv at hadron colliders, focusing on three production modes: Z+h_inv, h_inv via Weak Boson Fusion, and h_inv+ j. Using realistic cuts and backgrounds, it finds that the Z+h_inv channel yields a >5σ discovery at the LHC with 10 fb−1 for m_h ≈ 120 GeV and can extend to ≈160 GeV with 30 fb−1; it also shows how cross-section measurements can be used to extract the Higgs mass, particularly via a ratio of Zh_inv and WBF rates that is less model-dependent. At the Tevatron, WBF combined with Z+h_inv can achieve a 3σ observation for mh ≈ 120 GeV with about 7 fb−1 per detector, though h_inv+ j is not a viable channel due to large backgrounds. Collectively, the study demonstrates complementary discovery avenues and a pathway to mh determination for invisible Higgs scenarios, while highlighting the limited utility of the h_inv+ j channel.

Abstract

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.

Paper Structure

This paper contains 7 sections, 14 equations, 1 figure, 7 tables.

Table of Contents

  1. Introduction
  2. Associated $Z + h_{inv}$ Production at the LHC
  3. Signal for $h_{inv}$
  4. Higgs boson mass
  5. Production of $h_{inv}$ via WBF at the Tevatron
  6. The $h_{inv} + j$ signal
  7. Discussion and Conclusions

Figures (1)

  • Figure 1: Missing $p_T$ distribution for $Z(\to e^+e^-)+h_{inv}$ signal (solid lines, with $m_h = 120$, 140 and 160 GeV top to bottom) and backgrounds from $WW$ and $ZZ$ (dotted lines) at the LHC, after applying the cuts in Eqs. (\ref{['mincuts']}), (\ref{['mllcut']}) and (\ref{['dphicut']}).