Search for a Light Higgs boson in the Z boson plus a Photon Decay Channel

This is a condensed description with plots for the analysis CMS-HIG-13-006

Abstract

A search for a Higgs boson decaying into a Z boson and a photon is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from proton-proton collisions at a centre-of-mass energy of 7 and 8 TeV, corresponding to an integrated luminosity of 5.0 and 19.6 fb^-1, respectively. Limits are set on the cross section of a standard model Higgs boson decaying to opposite-sign electron or muon pairs and a photon. The expected exclusion limits at 95% confidence level are between 6 and 19 times the standard model cross section in the mass range of 120 and 150 GeV, and the observed limits are between about 3 and 31 times the standard model cross section.

Main result

A search has been made for a Higgs boson decaying into a Z boson plus a photon in the CMS detector at a centre-of-mass energy of 7 and 8 TeV, and the data sample corresponds to 24.6 fb-1 of integrated luminosity. Events are classified in four categories according to topology of the leptons and the photon, and the photon shower shape. The main backgrounds (pp to Zg and Drell-Yan+jets) are estimated with data-driven techniques.

The search discussed here is performed over the mass range 120--150 GeV. No excess been found in the current data sample and the first limits on the Higgs production cross-section times the H to Zg branching fraction at the LHC have been derived. The upper cross-section limits for the Higgs production times branching fraction decays into Z plus photon are about an order of magnitude larger than the standard model expectation for mH = 125 GeV.

PAS Figures:

Figure	Label	Description
	png, pdf	mllg spectrum in the electron and the muon channels for the 7 and 8 TeV data combined. Also shown is the expected signal due to a 125 GeV standard model Higgs scale by 100 and the sum of the individual fits made to the data for each channel and event class at 7 and 8 TeV.
	png, pdf	Background model fit to the m_eeg distribution for Event classes 1 and 2 for the year 2011
	png, pdf	Background model fit to the m_eeg distribution for Event classes 3 and 4 for the year 2011
	png, pdf	Background model fit to the m_eeg distribution for Event classes 1 and 2 for the year 2012
	png, pdf	Background model fit to the m_eeg distribution for Event classes 3 and 4 for the year 2012
	png, pdf	Background model fit to the m_mumug distribution for Event classes 1 and 2 for the year 2011
	png, pdf	Background model fit to the m_mumug distribution for Event classes 3 and 4 for the year 2011
	png, pdf	Background model fit to the m_mumug distribution for Event classes 1 and 2 for the year 2012
	png, pdf	Background model fit to the m_mumug distribution for Event classes 3 and 4 for the year 2012
	png, pdf	Exclusion limit on the cross section of a SM Higgs boson decaying into Z-boson and a photon as a function of the boson mass based on 5.0 fb-1 at of data taken at 7 TeV and 19.6 fb-1 at 8 TeV.

PAS Tables:

Table	Label	Description
	png	Definition of event classes.
	png	Luminosity and observed data yields used in the analysis. Expected signal yields are for a 125 GeV SM Higgs boson.
	png	Systematic uncertainties.

Additional Figures:

Figure	Label	Description
	png, pdf	mllg spectrum in the electron and the muon channels for the 7 and 8 TeV data combined and weighted by the significance [S/(S+B)] expected at 125 GeV. Also shown is the expected signal due to a 125 GeV standard model Higgs scale by 100 and the sum of the individual fits made to the data for each channel and event class at 7 and 8 TeV. The combined reweighted distributions are then normalized to the original data yield.
	png, pdf	Exclusion limit on the cross section of a SM Higgs boson decaying into Z-boson and a photon as a function of the boson mass based on 5.0 fb-1 at of data taken at 7 TeV and 19.6 fb-1 at 8 TeV and the expect exclusion limit from our previous analysis (HIG-12-049) based on 5.0 fb-1 at of data taken at 7 TeV and 5.0 fb-1 at 8 TeV. * Alternative colors for the one and two sigma band -- used in HIG-12-049. *
	png, pdf	Exclusion limit on the cross section of a SM Higgs boson decaying into Z-boson and a photon as a function of the boson mass based on 5.0 fb-1 at of data taken at 7 TeV and 19.6 fb-1 at 8 TeV and the expect exclusion limit from our previous analysis (HIG-12-049) based on 5.0 fb-1 at of data taken at 7 TeV and 5.0 fb-1 at 8 TeV. * Alternative colors for the one and two sigma band. *
	png, pdf	Exclusion limit on the cross section of a SM Higgs boson decaying into Z-boson and a photon as a function of the boson mass based on 5.0 fb-1 at of data taken at 7 TeV and 19.6 fb-1 at 8 TeV and the expect exclusion limit from our previous analysis (HIG-12-049) based on 5.0 fb-1 at of data taken at 7 TeV and 5.0 fb-1 at 8 TeV.

png, pdf

The observed local p-value p0 as a function of the SM Higgs boson mass in the range 120–150 GeV.