HIG-12-002

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

This is a condensed description with plots for the analysis HIG-12-002.

Table of contents

Abstract

A search for a Higgs boson decaying into two photons is described. The analysis is performed using a dataset recorded in 2011 by the CMS experiment at the LHC from pp collisions at a centre-of-mass energy of 7 TeV, and corresponds to an integrated luminosity of 4.8 /fb Limits are set on the cross section of the fermiophobic model Higgs boson decaying to two photons. The expected exclusion limit at 95\% confidence level increases monotonically between 0.1 and 3.0 times the fermiophobic model cross section in the mass range between 110 and 150~GeV, while the expected exclusion range is below 136 GeV. The observed limit excludes at 95\% confidence level the fermiophobic model Higgs boson decaying into two photons in the mass range 110 to 124~GeV and 128-136 GeV. The largest excess of events over the expected background is observed around 126 GeV. The excess has a local significance of 2.7. When taking in consideration the look-elsewhere effect in the search range 100-150 GeV, the global significance is 1.2 sigma. More data are required to ascertain the origin of this excess.

Further details

This search for the FP Higgs is performed using 3 channels (dijet-tag, lepton-tag, inclusive channel. Techiniques used in this analysis are fundamentally different from the FP search reported previously, HIG-11-021. Due to 2D method in the inclusive channel and the use of the exclusive channels, the limit is improved by significantly in terms of cross section.

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

  • dijet-tag channel: one event class
  • lepton-tag channel: electron and muon-class
  • 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-tag channel. In the lepton-tag channel the model is obtained by fitting the exponential which is obtained from MC due to extremely low statistic in data. In the inclusive channle 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
BkgFitExcl.png pdf png Figure 1: Background model fit to the mgg distribution for the three event classes of the exclusive channels. We also show a simulated signal (mH=120 GeV). The magnitude of the simulated signal is what would be expected if its cross section were equal to the FP expectation. (top) dijet-tag: observed diphoton mass is fit with a 2nd order polynomial, (midle) muon-tag: observed diphoton mass is fit with an exponential with shape derived from irreducible background MC , (bottom) electron-tag: observed diphoton mass is fit with an exponential with shape derived from a combination of ireducible background MC and a control sample defined by requiring one of the photons to be matched with a track. For the top plot the statistical uncertainty bands shown are computed from the data fit uncertainty on the background yield. For the two bottom plots the dominant uncertainty comming from the nor- malization to the data is not shown. Signal of FP Higgs at m=120 GeV (red line) is overlaid for reference. Individual plots are given for each event class of this inclusive channel.
Dijet-tag.png pdf png a) Dijet-tagged diphoton event class. Fit with a 2nd order polynomial
Muon-tag.png pdf png b) Muon-tagged diphoton event class. Fit from MC, normalized to data.
Ele-tag.png pdf png c) Electron-tagged diphoton event class. Fit from MC and CS, normalized to data.

piT_4780pb_removed.png pdf png Observed piT distribution in inclusive channel after dijet-tagged and lepton-tagged events have been removed. We also show a simulated signal (mH=120 GeV). The magnitude of the simulated signal is normalized to data. Discriminating power of this observable's shape between background and signal is evident and motivates the use of this observable together with the diphoton mass to build a 2D likelihood model. Not shown on this plot, but the function used to model the signal piT distributions is a sum of a Gaussian and Bifurcated Gaussian.
cLinearCorrel.png pdf png Bias observed if correaltion not included in the 2D background model of the inclusive channel. Bias is defined the mean of the pull distribution of signal strength relative to statistical error of pseudo-experiment.

BkgFitMass-2D.png pdf png Figure 2: Background model fit projected to the mgg distribution for the four event classes of the inclusive channel after the dijet-tagged and lepton-tagged events have been removed. In the power we use a term linear with piT to account for the correlation between the two observables. We also show a simulated signal (mH=120 GeV). The magnitude of the simulated signal is what would be expected if its cross section were equal to the FP expectation. Individual plots are given for each event class of this inclusive channel.
databkgoversig_cat0.png pdf png a) The best inclusive channel event class defined by diphoton EBEB HighR9.
databkgoversig_cat1.png pdf png b) The inclusive channel event class defined by diphoton EBEB LowR9.
databkgoversig_cat2.png pdf png c) The inclusive channel event class defined by diphoton NotEBEB HighR9.
databkgoversig_cat3.png pdf png d) The inclusive channel event class defined by diphoton NotEBEB LowR9.

BkgFitPiT-2D.png pdf png Fig 3. Background model fit to the piT distribution for the four event classes of the inclusive channel after the dijet-tagged and lepton-tagged events have been removed. We also show a simulated signal (mH=120 GeV). The magnitude of the simulated signal is normailzed to data to better ilustrated the difference in shape between the signal and backround.

LimitFP_4780pb_comb.png pdf png Figure 4: 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 channels and the indiviudal channels (dijet-tag, lepton-tag and inclusive (with events removed) is also shown for reference, with the following paticipation in the combined limit (dijet 65%, lepton 17%, inclusive 17%).
LimitFP_pvalue.png pdf png Figure 5: Observed local p-values for the three channels combined is shown in black line. P-value is also shown for individual channels: dijet-tagged class, lepton-tagged classes, and inclusive 2D classes.
BestFit_FP.png pdf png Figure 6: The best fit signal strength, in terms of the standard model Higgs boson cross section, for the combined fit to the five classes (vertical line) and for the individual contributing classes (points) for the hypothesis of a FP Higgs boson mass of 126 GeV. The band corresponds to +- 1sigma uncertainties on the overall value. The horizontal bars indicate +-sigma uncertainties on the values for individual classes.
Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf BestFit_FP.pdf r1 manage 14.3 K 2012-03-03 - 07:01 VladimirRekovic  
PNGpng BestFit_FP.png r1 manage 90.6 K 2012-03-03 - 07:00 VladimirRekovic  
PDFpdf BkgFitExcl.pdf r1 manage 39.2 K 2012-03-03 - 07:10 VladimirRekovic  
PNGpng BkgFitExcl.png r1 manage 124.8 K 2012-03-03 - 07:10 VladimirRekovic  
PDFpdf BkgFitExclWithErroBands.pdf r1 manage 42.8 K 2012-03-04 - 18:32 VladimirRekovic  
PNGpng BkgFitExclWithErroBands.png r1 manage 126.5 K 2012-03-04 - 18:33 VladimirRekovic  
PDFpdf BkgFitMass-2D.pdf r1 manage 140.3 K 2012-03-03 - 06:30 VladimirRekovic  
PNGpng BkgFitMass-2D.png r1 manage 214.0 K 2012-03-03 - 06:28 VladimirRekovic  
PDFpdf BkgFitPiT-2D.pdf r1 manage 95.0 K 2012-03-03 - 06:29 VladimirRekovic  
PNGpng BkgFitPiT-2D.png r1 manage 166.6 K 2012-03-03 - 06:29 VladimirRekovic  
PDFpdf Dijet-tag.pdf r1 manage 30.5 K 2012-03-05 - 17:02 VladimirRekovic  
PNGpng Dijet-tag.png r1 manage 124.3 K 2012-03-05 - 17:01 VladimirRekovic  
PDFpdf Ele-tag.pdf r1 manage 16.8 K 2012-03-05 - 17:02 VladimirRekovic  
PNGpng Ele-tag.png r1 manage 88.9 K 2012-03-05 - 17:00 VladimirRekovic  
PNGpng ExclVBF_SigBkgFitCat_m120.png r1 manage 124.3 K 2012-03-05 - 17:00 VladimirRekovic  
PDFpdf LimitFP_4780pb_comb.pdf r1 manage 19.9 K 2012-03-03 - 06:57 VladimirRekovic  
PNGpng LimitFP_4780pb_comb.png r1 manage 269.4 K 2012-03-03 - 06:56 VladimirRekovic  
PDFpdf LimitFP_pvalue.pdf r1 manage 19.1 K 2012-03-03 - 07:00 VladimirRekovic  
PNGpng LimitFP_pvalue.png r1 manage 212.8 K 2012-03-03 - 07:01 VladimirRekovic  
PDFpdf MassFit-2D_4780pb_allCat.pdf r1 manage 33.2 K 2012-03-03 - 06:24 VladimirRekovic  
PNGpng MassFit-2D_4780pb_allCat.png r1 manage 98.5 K 2012-03-03 - 06:36 VladimirRekovic  
PDFpdf Muon-tag.pdf r1 manage 16.5 K 2012-03-05 - 17:02 VladimirRekovic  
PNGpng Muon-tag.png r1 manage 90.9 K 2012-03-05 - 17:00 VladimirRekovic  
PDFpdf cLinearCorrel.pdf r1 manage 16.0 K 2012-03-03 - 07:54 VladimirRekovic  
PNGpng cLinearCorrel.png r1 manage 119.0 K 2012-03-03 - 07:54 VladimirRekovic  
PDFpdf databkgoversig_cat0.pdf r1 manage 45.9 K 2012-03-02 - 18:19 VladimirRekovic  
PNGpng databkgoversig_cat0.png r1 manage 167.3 K 2012-03-02 - 18:33 VladimirRekovic  
PDFpdf databkgoversig_cat1.pdf r1 manage 45.4 K 2012-03-02 - 18:20 VladimirRekovic  
PNGpng databkgoversig_cat1.png r1 manage 152.4 K 2012-03-03 - 06:17 VladimirRekovic  
PDFpdf databkgoversig_cat2.pdf r1 manage 45.5 K 2012-03-02 - 18:20 VladimirRekovic  
PNGpng databkgoversig_cat2.png r1 manage 158.4 K 2012-03-03 - 06:17 VladimirRekovic  
PDFpdf databkgoversig_cat3.pdf r1 manage 44.6 K 2012-03-02 - 18:20 VladimirRekovic  
PNGpng databkgoversig_cat3.png r1 manage 146.3 K 2012-03-03 - 06:18 VladimirRekovic  
PNGpng piT_4780pb_removed.png r1 manage 141.1 K 2012-03-03 - 08:09 VladimirRekovic  
Edit | Attach | Watch | Print version | History: r7 < r6 < r5 < r4 < r3 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r7 - 2012-03-05 - VladimirRekovic
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    CMSPublic All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2021 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback