HIG-12-022

"Search for the fermiophobic model Higgs boson decaying into two photons"

This is a condensed description with plots for the analysis HIG-12-022 with 2012 (8 TeV) data.

Results for the analyis on 2011 data are availalble in HIG-12-002

Table of contents

Abstract

Search for a fermiophobic Higgs boson in proton-proton collisions at √s = 7 and 8 TeV in the diphoton decay mode is reported. The data analysed correspond to an integrated luminosity of 5.1 fb^–1, recorded in 2011 at √s = 7 TeV and of 5.3 fb^–1, recorded in 2012 at √s = 8 TeV by the CMS experiment at the LHC. The Higgs boson mass range explored is 110–150 GeV. A fermiophobic Higgs boson is excluded at 95% confidence level in the mass range 110–147 GeV. In the mass ranges 110–134 GeV a fermiophobic Higgs boson is excluded at 99% confidence level.

Further details

This search for the FP Higgs is performed using 4 sub-channels (dijet tag, lepton tag, MET tag, and untagged). With respect to the earlier public results on the FP search in CMS HIG-12-002, one more exclusive sub-channel is added, the MET tag. Techiniques used in this analysis are the same as in the FP search reported previously, except for the lepton tag where now the background model is obtained from a fit to the observed data, where in the past a combination of MC and data from control sample were used.

To improve the sensitivity of the search, selected diphoton events are subdivided into mutually exclusive classes tagged in four different channels

• dijet tag sub-channel: two event classes
• lepton tag sub-channel: electron and muon classes
• MET tag sub-channel: one event class using only di-photons from the barrel (EBEB)
• inclusive channel: four classes according to photon eta and R9 variables: EBEB highR9, EBEB lowR9, NotEBEB highR9, NotEBEB lowR9. Events already tagged by dijet- or lepton-tag are removed from this class.

The background model is obtained by fitting polynomial to the observed diphoton mass distributions in the dijet and MET tag sub-channel. A power law function is used in the lepton tag sub-channel. In the untagged channel we use two physical observables, diphoton mass and piT (piT is defined as the ratio of the diphoton pT and mass), and build a 2D maximum likelihood model. We explicitely account for the correlations between the observables in the background model. We fit the the observed diphoton mass by a power law function with a linear correlation term in the power. The higher order correlation terms can be neglected. The observed diphoton piT is modeled with a sum of an exponential and a gaussian function centered at zero. 2D compared to 1D treatment is 30% more sensitive in terms of cross section measurement.

Figures

Image	File links	Description

	pdf png	Figure 1(a): Dijet-tagged diphoton with dijet mass > 500 GeV event class. Fit with a 3rd order polynomial
	pdf png	Figure 1(b): Dijet-tagged diphoton with dijet mass > 250 GeV event class. Fit with a 4rd order polynomial. Common events between the dijet tagged event classes are removed from this event class
	pdf png	Figure 2(a): Muon-tagged diphoton event class. Bkg model is a power law function obtained from a fit to observed data.
	pdf png	Figure 2(b): Electron-tagged diphoton event class. Bkg model is a power law function obtained from a fit to data.
	pdf png	Figure 3: MET-tagged diphoton event class. Bkg model is a 3rd order polynomial.

	pdf png	Figure 4(a): The best inclusive channel event class defined by diphoton EBEB HighR9.
	pdf png	Figure 4(b): The inclusive channel event class defined by diphoton EBEB LowR9.
	pdf png	Figure 4(c): The inclusive channel event class defined by diphoton NotEBEB HighR9.
	pdf png	Figure 4(d): The inclusive channel event class defined by diphoton NotEBEB LowR9.

	pdf png	Figure 5(a): The best inclusive channel event class defined by diphoton EBEB HighR9.
	pdf png	Figure 5(b): The inclusive channel event class defined by diphoton EBEB LowR9.
	pdf png	Figure 5(c): The inclusive channel event class defined by diphoton NotEBEB HighR9.
	pdf png	Figure 5(d): The inclusive channel event class defined by diphoton NotEBEB LowR9.

	pdf png	Figure 6: Exclusion limit on the cross section of a FG Higgs boson decaying into two photons as a function of the boson mass relative to the FP cross section, where the theoretical uncertainties on the cross section have been included in the limit setting. The limit is calculated in the asymptotic CLs approximation. The expected limit is provided for the combined sub-channels and the indiviudal channels (dijet-tag, lepton-tag, MET-tag and untagged
	pdf png	Figure 8: Combined 2011 and 2012 exclusion limit on the cross section of a FG Higgs boson decaying into two photons as a function of the boson mass relative to the FP cross section.
	pdf png	Figure 7: Observed local p-values in the 5.3 fb–1 of 2012 data for the four sub-channels combined is shown in black line. P-value is also shown for individual channels: dijet-tagged class, lepton-tagged classes, MET-tagged and untagged 2D classes.
	pdf png	Figure 9: Observed local p-values in the 5.1 fb–1 of 2011 (7 TeV) data and 5.3 fb–1 of 2012 (8 TeV) data combined is shown in black line. P-value is also shown for each 2011 and 2012 data
	pdf png	Figure 10: The best fit signal strength, in terms of the standard model Higgs boson cross section, for the combined 2011 and 2012 data. The band corresponds to ±1σ uncertainties on the μ̂ value.

-- VladimirRekovic - 05-Jul-2012