Projected exclusion limits on the SM Higgs boson cross sections obtained by combining the H→WW→2l2v and H→ZZ→4l decay channels

Main Results

• Combined exclusion limits for WW+ZZ decay channels using two statistical approaches, Bayesian and CL_s, for 1 fb^-1 luminosity: the differences are typically less than 10%
• Impact of changing the center of mass energy from 14 to 10 TeV: running at 10 TeV requires about 2 times larger integrated luminosity to reach the same sensitivity for a SM Higgs boson
• At 10 TeV, an exclusion of the SM Higgs boson with m_H~160-170 GeV is projected to be possible with ~200 pb^-1

Public Note: N/A

This study is based on the H→WW→2l2v and H→ZZ→4l results that can be found in CMS PAS HIG-08/006 and CMS PAS HIG-08/003. The combination and extrapolation to lower LHC energies was done on a very short notice in preparations for the Chamonix workshop on LHC startup in 2009. The very short time scale did not allow for carrying out the exercise with a full rigor and a comprehensive review/approval process. Hence, there is not a public note available for these studies; however, the plots shown below are approved for conferences (approved in February 2009). CMS collaborators can refer to an internal note CMS AN-2009/020, where more details can be found.

Public plots recommended for conferences:

	The plot on the left (eps format) shows the relative change in cross sections for signal (mH=160 GeV) and main backgrounds for the H→WW→2l2v search as the pp center-of-mass energy changes from 14 to 10 TeV. The results are obtained with MCFM.
	The plot on the left (eps format) shows the relative change in cross section for signal and the main ZZ-background for the H→ZZ→4l search as the pp center-of-mass energy changes from 14 to 10 TeV. The results are obtained with Pythia. The ZZ cross sections are evaluated for 4-lepton invariant masses with ±10 GeV window around the chosen Higgs boson masses.
	The plot on the left (eps format) shows the relative change in CMS acceptance for signal and the main ZZ-background for the H→ZZ→4l search as the pp center-of-mass energy changes from 14 to 10 TeV. The results are obtained with Pythia. The ZZ acceptance is evaluated for 4-lepton invariant masses within ±10 GeV windows around the chosen Higgs boson masses.
	The plot on the left (eps format) shows the projected 95% CL exclusion limits in terms of a ratio of an excluded cross section to the Standard Model Higgs boson cross section for the 14 and 10 TeV center-of-mass energies and an amount of data corresponding to an integrated luminosity of 1 fb-1. Only H→ZZ→4l and H→WW→2l2v were combined. Two different statistical approaches, Bayesian and CLs, give consistent results, the differences being typically less than 10% (even though correlations between errors in this exercise were treated somewhat differently). Overall, the relative difference in the ratio r for 14 and 10 TeV pp-colision energies is approximately a factor of 1.5, which means that it would take twice as much luminosity at 10 TeV to match the sensitivity attainable in 14-TeV collisions. For Higgs masses 160-170 GeV, 10 TeV collisions, and 1 fb-1 luminosity, the ratio r is ~0.4. Using a simple statistical extrapolation in the form r~r0/sqrt(L/L0), one can project that one would need 200 pb-1 to be able to exclude the SM Higgs boson in this mass range at the 10-TeV LHC. Detailed full simulation studies for the CMS reach at 10 TeV and 200 pb-1are underway.

-- AndreyKorytov - 11-Apr-2010