Search for a standard model like Higgs boson in the H → ZZ → 2ℓ2q decay channel in CMS at √s=8 TeV

This is a condensed description with plots for the analysis CMS-HIG-12-024

Responsible: OscarGonzalezLopez

Abstract

A search for a heavy Higgs boson in the H → ZZ → 2ℓ2q decay channel, where ℓ=e or μ, and q =u,d,c,s,b at a center-of-mass energy of 8 TeV is presented. 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 8 TeV, corresponding to an integrated luminosity of 19.6 fb-1. Events are classified according to probability of the jets to originate from quarks of light or heavy flavor. Angular spin correlations of the decay products are used to separate signal from background events. The existence of a heavy Higgs boson would appear as a resonance in the invariant mass m(ZZ) spectrum, so this variable is used as final discriminator. No significant excess is observed above the background expectation. The presence of a standard model-like Higgs boson with a mass in the 290600 GeV range is excluded at 95% confidence level.

Figures from PAS HIG-12-024

Angular Spin Correlations
Diagram png Diagram describing the production and decay angles in the process $\mathrm{gg \to HZZ \to llqq}$. These angles are defined in the parent particle rest frames (H or Z).
LD png Likelihood discriminant built from 5 angles in the decay $\mathrm{gg \to HZZ \to llqq}$, for events with a candidate of mass in the range 220 < mZZ(GeV/c2) < 800. Data (dots with error bars) are compared to the expected background (histograms). The bottom of each plot shows the ratio of data and simulation. The red dashed histogram indicates 20 times the expected distribution for a 300 GeV/c2 mass Higgs boson. The background is normalized by comparing the expectation to the data in the sidebands.

Distributions of the five helicity angles for events with a candidate of mass in the range 220 < mZZ(GeV/c2) < 800. Data (dots with error bars) are compared to the expected  background (histograms). The bottom of each plot shows the ratio of data and simulation. The red dashed histogram indicates 20 times the expected distribution for a 300 GeV/c2  mass Higgs boson. The background is normalized by comparing the expectation to the data in the sidebands.

cos(Θ1) png cos( Θ 2) png
cos(Θ*) png Φ png

Φ 1 png  

Control and Selection Plots
mJJ png distribution of the m(jj) variable for data and simulated events after requiring a leptonic Z and at least two jets. In addition to data (black points) and background simulation (filled histograms), we show a SM Higgs simulation (MH = 300 GeV/c2, red line), scaled by a factor 100 for better visibility.

JP discriminant png Distribution of the Jet Probability b-tagging discriminator after final selection . The bottom plot shows the ratio of data and simulation. The red dashed histogram indicates the expected distribution for a 300 GeV/c2 mass Higgs boson. Background distributions are normalized to the data.

METsig png Distribution of the MET significance estimator, after final selection except the requirement on itself. The bottom plot shows the ratio of data and simulation. The red dashed histogram indicates the expected distribution for a 300 GeV/c2 mass Higgs boson. Background distributions are normalized to the data.

Total Events png Final number of events in each of the b-tagging categories after final selection. The bottom plot shows the ratio of data and simulation. The red dashed histogram indicates the expected distribution for a 300 GeV/c2 mass Higgs boson. Background distributions are normalized to the corresponding sideband regions.

Top Background
emuVsTopMC png M(ℓℓlj) invariant mass for e-μ data compared to the prediction of tt MC plus other small backgrounds; red dots are e-μ data; white histogram, tt MC; blue histogram, other small backgrounds; grey area is the systematic error of the prediction.

emuVseemm png M(ℓℓjj) invariant mass for ee+μμ and e-μ data for events outside the leptonic Z mass window, with the requierement of 2 b-tagged jets, and MET significance >8 . Black dots are ee+μμ data, white histogram, e-μ data; grey area is the e-μ statistical error.

M(ℓℓjj) Distribution in the Sidebands
Mass distributions of the ℓℓjj system for events in the mjj sideband region in the electron (left) and muon (right) channels. From top to bottom, plots correspond to the 0-, 1- , and 2-btag categories. In the 2-btag category a variable bin size is used to aggregate the low number of events in the tail of the distributions. The dots are data (19.6 fb-1), pale green histogram corrected Z+jets simulation, light blue simulated diboson background and dark blue tt events from data (which include single top, WW, $\mathrm{Z \to \tau\tau +jets}$ ).
Mlljj_ee0bSB png Mlljj_mm0bSB png

Mlljj_ee1bSB png Mlljj_mm1bSB png
Mlljj_ee2bSB png Mlljj_mm2bSB png

M(ℓℓjj) Distribution in the Signal Region
The mZZ invariant mass distribution after final selection in three categories: 0 btag (top), 1 b-tag (middle), and 2 b-tag (bottom). The electron channel is shown on the left and the muon channel is shown on the right. The points show the data and the histograms the background contributions normalized to the data in the sideband. Also shown is a SM Higgs boson signal (MH = 300 GeV/c2) with a cross section five times the SM value. The grey band indicates the systematic uncertainty on the normalization and shape of the background.

Mlljj_ee0b png Mlljj_mm0b png
Mlljj_ee1b png Mlljj_mm1b png
Mlljj_ee2b png Mlljj_mm2b png

Limits HZZ2l2q
Limit2l2q png Observed (solid) and expected (dashed) 95% CL upper limits, obtained with the asymptotic CLs technique, on the ratio of the production cross section to the SM expectation for the Higgs boson, . The 68% and 95% ranges of expectation for the background-only model are also shown with green and yellow bands, respectively. The solid horizontal line at unity indicates the expectation for a SM-Higgs-like boson.

Limit2l2q png Observed (solid) and expected (dashed) 95% CL upper limits, obtained with the asymptotic CLs technique, on the production cross section times branching fraction of $\mathrm{H \to ZZ}$ . The 68% and 95% ranges of expectation for the background-only model are also shown with green and yellow bands, respectively.

CombLimit2l2q png Combined limit of the $\mathrm{HZZ \to llqq}$ analysis at 7TeV (4.9 fb-1) and 8TeV (19.6 fb-1 ). Observed (solid) and expected (dashed) 95% CL upper limits, obtained with the asymptotic CLs technique, on the ratio of the production cross section to the SM expectation for the Higgs boson, . The 68% and 95% ranges of expectation for the background-only model are also shown with green and yellow bands, respectively. The solid horizontal line at unity indicates the expectation for a SM-Higgs-like boson.

Limits Combination HZZ
LimitHZZ png Observed (black line) and expected (red line) 95% CL upper limit on the ratio of the product of the production cross section and branching fraction to the SM expectation for the Higgs boson decaying into two Z bosons obtained using the asymptotic CLs technique. The 68% and 95% CL ranges of expectation for the background-only model are also shown with green and yellow bands, respectively. The horizontal solid line at unity indicates the SM expectation. Result is combination of all individual channels: H to ZZ to 2ℓ2ℓl', H to ZZ to 2ℓ2v and H to ZZ to 2ℓ2q.

LimitHZZ png Observed (black line) and expected (red line) 95% CL upper limit on the ratio of the product of the production cross section and branching fraction to the SM expectation for the Higgs boson decaying into two Z bosons obtained using the asymptotic CLs technique. The 68% and 95% CL ranges of expectation for the background-only model are also shown with green and yellow bands, respectively. The horizontal solid line at unity indicates the SM expectation. Overlayed are observed 95% CL limits for all individual channels: H to ZZ to 2ℓ2ℓ' (violet line), H to ZZ to 2ℓ2v (dark green line) and H to ZZ to 2ℓ2q (gray line).

Event displays

eventDisplay7TeV.png
Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng 2thm2.png r1 manage 15.5 K 2013-07-18 - 10:01 DanielDominguezVazquez  
PNGpng HZZCombination.png r1 manage 22.7 K 2013-07-18 - 10:52 DanielDominguezVazquez  
PDFpdf HZZCombination2.pdf r1 manage 17.6 K 2013-07-18 - 10:22 DanielDominguezVazquez  
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PNGpng SB_LOG_mm_2_mH.png r1 manage 19.5 K 2013-07-18 - 10:04 DanielDominguezVazquez  
PDFpdf angles-HZZ2l2q.pdf r1 manage 13.5 K 2013-07-18 - 10:01 DanielDominguezVazquez  
PNGpng angles-HZZ2l2q.png r1 manage 21.9 K 2013-07-18 - 10:56 DanielDominguezVazquez  
PNGpng combined_limit_observed_all-btag_ll.png r1 manage 33.5 K 2013-07-18 - 11:44 DanielDominguezVazquez  
PNGpng eventDisplay7TeV.png r1 manage 1515.8 K 2013-07-18 - 12:09 DanielDominguezVazquez  
PNGpng h_ll_ct1.png r1 manage 20.2 K 2013-07-18 - 10:02 DanielDominguezVazquez  
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PNGpng lh_ll_btagTOT.png r1 manage 15.7 K 2013-07-18 - 10:09 DanielDominguezVazquez  
PNGpng lh_ll_metCorrected.png r1 manage 16.6 K 2013-07-18 - 10:09 DanielDominguezVazquez  
PDFpdf limit_observed_all-btag_ll_600.pdf r1 manage 18.2 K 2013-07-18 - 10:31 DanielDominguezVazquez  
PNGpng limit_observed_all-btag_ll_600.png r1 manage 33.5 K 2013-07-18 - 10:45 DanielDominguezVazquez  
PNGpng xs_limit_observed_all-btag_ll_600.png r1 manage 35.6 K 2013-07-18 - 10:45 DanielDominguezVazquez  
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Topic revision: r5 - 2014-01-26 - OscarGonzalezLopez
 
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