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 according to 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. Recent theoretical interpretation of the LHC Higgs data that suggests the Higgs to Zg partial widths is significantly enhanced with respect to standard model expectation can be excluded.

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	Luminosity and observed data yields used in the analysis. Expected signal yields are for a 125 GeV SM Higgs boson.
	png	Definition of event classes.
	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.
	png, pdf	The observed local p-value p0 as a function of the SM Higgs boson mass in the range 120–150 GeV.