Search for Higgs in the dilepton dineutrino final state with CMS
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Transcript of Search for Higgs in the dilepton dineutrino final state with CMS
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04/22/23 1
Search for Higgs in the dilepton dineutrino final state
with CMS
Frank Würthwein
UCSD
GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 2GGI 2011
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Higgs Production
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Dominant Process
Subdominant Process
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Higgs Production x Decay
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event yields/fb In this talk, I will focus ondilepton + MET .
WW -> lν lν
ZZ -> ll νν
There are crudely speaking3 experimental regimes.
“250”
Easy WW Easy ZZHard WW
GGI 2011
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SM backgrounds• No striking signature to
distinguish higgs from bkg’s.– Counts & multi-dim. shapes
• Key selections:– Lepton pT > 20/10GeV with
tight Id & Isolation• Wjets, QCD
– Large MET, MT, and Z veto• Drell-Yan
– # of jet classification (pT>30GeV) and top veto
• Top
– Kinematics (mll, ΔΦ)
• WW
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Higgs 130
In addition: WZ,ZZ,Wγ(*)
GGI 2011
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H -> WW for low vs medium mass
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Bkg from Wjets grows as lepton pT decreases.
Lepton pT decreases as W* becomes more virtual.
Plots from CDF out of S.-C. Hsu thesis
Bkg from DY grows for very small dilepton mass.
Dilepton mass is small forlow higgs mass.
GGI 2011
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WW vs ZZ for high mass
• As higgs mass increases the boost of the Z in higgs to ZZ leads to significant MET and significant transverse mass of the ll+MET system.
• This makes H -> ZZ -> ll + MET an interesting channel in the mH ~ 300 – 500 GeV range already this year.
04/22/23 7GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 8GGI 2011
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Summary of bkg estimation
• Bkg estimated from data– Evaluated at HWW selection
• WW (for mH < 200GeV)• Wjets• Drell-Yan
– Evaluated at WW level• Top
– rely on MC to extrapolate to HWW
• Bkg estimated from MC– Dibosons (WZ,ZZ,Wγ)– Z to ττ
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0-jet
1-jet
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Cut based analysis
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H160H130
WW selection WW selection
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Missing Energy and pile-up
04/22/23 11GGI 2011
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Drell-Yan Estimation
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• DY (mostly) in ee,μμ– Fake MET due to tails of detector
resolution => difficult to simulate
• Predict “out” from “in”– Measure same flavor “in”– Subtract non-res contribution via eμ– Subtract VZ based on MC– Multiply result by R
• Measured in MC and at higher MET in data.
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Wjets Estimation• Measure “FR” with QCD events
– FR = prob. for “fake” lepton that passes loose selection to also pass tight lepton selection.
– FR = function of (pT,η)
• Extrapolate Wjets applying FR onto 1 loose 1 tight after higgs selection
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Validation of Method in same sign at WW selection:
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Top background
• Jet veto kills top• Remaining top can be tagged
– Soft b-jets
– Soft muons
• Top tagging eff. ~50% in 0-jet• Residual top estimated via:
• Measure ε in 1 b-jet events– There must be another b-quark
• Systematics ~20-30%
04/22/23 14GGI 2011
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Yields at WW selection
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Summary of yields for 1.6/fb in the 0-, 1-, 2-jet bins.
Yields agree with expectations.Measure WW cross section as a crosscheck
GGI 2011
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WW background
• Irreducible background with no single striking discriminator• Kinematic shapes in multidimensional space
– low mass, ΔΦll , lepton momenta, transverse mass of higgs
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Example: mH=130 GeV
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Cut based Higgs selection
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Spin-0 physics
Example: mH=160 GeVGGI 2011
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WW bkg estimate from data
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• For mH < 200GeV there is very little higgs contribution above 100GeV in dilepton mass.
• We thus can use that region to determine the normalization of WW bkg, and extrapolate into the higgs selection region using MC.
GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 19GGI 2011
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Yields after Higgs selection
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Example: mH=140GeV
Good agreement between observed and expectedNo sign of Higgs
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Yields after Higgs selection
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Example: mH=140GeV
Good agreement between observed and expectedNo sign of Higgs
0-jet has most of the sensitivity
GGI 2011
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Limits for cut based analysis
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Observed: exclude higgs in range [147,194] GeVExpected: exclude higgs in range [132, 201] GeV
GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 23GGI 2011
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H to ZZ to ll νν
• MET resolution and its non-gaussian tails – Zjets• Estimating WW & top via eμ • MC used to estimate WZ/ZZ bkg
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Key Issues:
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Analysis Strategy
• Two high pT isolated same flavor leptons (ee, μμ).• Tight dilepton mass window (+- 15GeV) around Z
mass.• Large MET to suppress Zjets• Veto events with:
– small Δϕ between MET and nearest jet• Suppress Zjets with MET from large undermeasurements of jets
– b-tagged jets => suppress top– third lepton => suppress WZ/ZZ
04/22/23 25GGI 2011
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Selections
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Bkg Estimation
• Data Driven:– MET tails measured in γ+jets to estimate Zjets.– Top, WW using eμ events
• From MC:– WZ, ZZ
04/22/23 27GGI 2011
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MET from γ+jets reweighting
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μμ eeGGI 2011
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Higgs transverse mass
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Transverse mass of Higgs larger than all backgroundsonly for very large higgs masses.
GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 30GGI 2011
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Final Yields
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Observed and predicted agree well.No sign of higgs.
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Final Yields
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Bkg decreases tenfold from low to high mass.Sensitivity to higgs largely a matter of luminosity.
GGI 2011
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Final Yields
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ZZ dominates except for low mass.Zjets remains second largest bkg even at high mass.WZ bkg with lost 3rd lepton significant at all masses.
GGI 2011
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Limits on H to ZZ to ll νν
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Higgs excluded in range 340-375 GeV GGI 2011
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Outline
• Introduction• H to WW to lν lν
– Background Suppression & Estimation– Results
• H to ZZ to ll νν– Background Suppression & Estimation– Results
• Outlook
04/22/23 35GGI 2011
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Necessary Improvements
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For higgs mass of 120 GeV the systematic error on Wjets is roughly the same as the expected higgs signal.
Progress requires innovation in addition to luminosity !!!
GGI 2011
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Desirable Improvement
• There is information left inside the cuts• There is information in correlations of the kinematic
variables that is not fully exploited by square cuts.04/22/23 37
MVA output for eμ 0-jet and 130,140,160GeV higgs
GGI 2011
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Conclusions
• No higgs found– H to WW to lν lν excludes mH from 147 – 194 GeV– H to ZZ to ll νν excludes mH from 340 – 375 GeV
• Pushing the sensitivity towards lower mass higgs requires innovation and luminosity.
• Pushing the sensitivity towards higher mass higgs requires mostly luminosity.
04/22/23 38GGI 2011