H → ZZ(*) → 4e Signal and Background Study at Generator Level

The following study was done in CMSSW_1_6_7 using mostly Pythia to generate the events. The one exception is CompHep was used for the pp → Zbb(bar) → 4e samples. All of these plots have corresponding plots for the H → ZZ → 4μ and H → ZZ → 2e2μ channels (attached).

Higgs Generation

The Higgs signal was generated at a mass of 150 GeV/c² (unless specified) and was generated with the gluon fusion (MSUB(102)) and vector boson channels (MSUB(123) and MSUB(123)):

• Lowest order Higgs Production from Gluon Fusion (left) and Vector Boson Fusion (right):
  

Higg's Kinematical Variables

Here are some plots of the kinematical variables of the higgs (M_H = 150 Gev/c²). Also, plotted are the contributions due to gluon fusion (hg) and vector boson fusion (hv).

Process I.D. 102 = Gluon Fusion
Process I.D. 123 = Z Boson Fusion
Process I.D. 124 = W Boson Fusion

Mass of the Higgs

• Mass of Higgs (M_H = 150 GeV/c²): This was fit to a Breit-Wigner of Γ ≅ 0.015 and M_H ≅ 150.0 GeV/c²
  
• This is consistent with the Γ(M_H) calculated by HDecay (see HiggsDecay).

P_T of the Higgs

• P_T of Higgs (M_H = 150 GeV/c²):
  

• Vector Boson Fusion is lower by a factor of about 8 (here it appears to be 4 since I've included both channels WW->H and ZZ->H) so let's look at the normalized P_T of Higgs (M_H = 150 GeV/c²):
  

P_z of the Higgs

• P_z of Higgs (M_H = 150 GeV/c²):
  
• Normalized P_z of Higgs (M_H = 150 GeV/c²):
  

η of the Higgs

• η of Higgs (M_H = 150 GeV/c²):
  
• Normalized η of Higgs (M_H = 150 GeV/c²):
  

φ of the Higgs

• φ of the Higgs (M_H = 150 GeV/c²):
  

Energy of the Higgs

• Energy of the Higgs (M_H = 150 GeV/c²):
  

• Normalized Energy of the Higgs (M_H = 150 GeV/c²):
  

Rapidity of the Higgs

• Rapidity of the Higgs (M_H = 150 GeV/c²):
  

• Normalized Rapidity of the Higgs (M_H = 150 GeV/c²):
  

H → ZZ(*) → 4e Signal

The Z candidates.

Here we plot the invariant mass from the various combination of leptons in the finals state:
L1 is the e+ from the Z with the lowest ΔM = | MZ - MZPDG | (called Z1)
L2 is the e- from Z1
L3 is the e+ from the Z with the higher ΔM (Z2)
L4 is the e- from the Z2

• Z Candidates:
  

The Number of Signal Events Expected.

So far we have looked at the distributions with no cuts. Here we look at a series of cuts to see how many of the raw events have a shot at passing the detector's geometry and thresholds and thus have a chance of being reconstructed. On the right will be the invariant mass of the 4-vectors of the four e's that decayed from the higgs via the Z's. The plots for the four μ's and two μ/two e cases are attached but not linked in (unless there was something different to report).

p_T of the 4 Electrons (no cuts)

• P_T of the 4 Electrons (M_H = 150 GeV/c², no cuts):
  

p_T of the 4 Electrons ( |η| < 2.5 cut)

• P_T of the 4 Electrons (M_H = 150 GeV/c², fiducial η cuts):
  

p_T of the 4 Electrons ( |η| < 2.5 cut, p_T > 5 cut)

• P_T of the 4 Electrons (M_H = 150 GeV/c², p_T > 5 cut):
  

p_T of the 4 Electrons ( |η| < 2.5 cut, p_T > 5 cut, Trigger cut) The following plot has the following cuts:

• |η| < 2.5 cut
• p_T > 5 GeV
• Trigger cut:
  • Single E: At least one electron has a p_T > 26.0 GeV
  • Double E: At least two (isolated) electrons have a p_T > 14.5 GeV
  • Relaxed Double E: At least two (not necessarily isolated) electrons have a p_T > 21.8 GeV

• These last two cuts are a bit artificial since we cannot simulate isolation with this study (the double relaxed e cut does nothing).

• P_T of the 4 Electrons (M_H = 150 GeV/c², η cut, p_T > 5 cut , trigger cut):
  

Δφ of the Oppositely Charged Electron Combinations (|η| < 2.5 cut; p_T > 5 cut; trigger cut)

• L1 is the e⁺ from the Z with the lowest ΔM = | M_Z - M_Z^PDG | (called Z1)
• L2 is the e^- from Z1
• L3 is the e⁺ from the Z with the higher ΔM (Z2)
• L4 is the e^- from the Z2
  

• Δφ of the Oppositely charged Electrons (M_H = 150 GeV/c², Trigger cuts):
  

Δη of the Oppositely Charged Electron Combinations (|η| < 2.5 cut; p_T > 5 cut; trigger cut)

• Δη of the Oppositely charged Electrons (M_H = 150 GeV/c², Trigger cuts):
  

pp → ZZ(*) → 4e Background

The Z candidates.

Here we plot the invariant mass from the various combination of leptons in the finals state:
L1 is the e+ from the Z with the lowest ΔM = | MZ - MZPDG | (called Z1)
L2 is the e- from Z1
L3 is the e+ from the Z with the higher ΔM (Z2)
L4 is the e- from the Z2

• Z Candidates:
  

The Number of Background Events Expected from pp → ZZ(*) → 4e.

We perform the same exercise for the pp → ZZ(*) → 4e to see how many of these events will pass through the cuts as well. On the right will be the invariant mass of the 4-vectors of the four e's that decayed from the two Z's. The plots for the four μ's or two μ/two e case are attached but not linked in (unless there was something different to report).

p_T of the 4 Electrons (pp → ZZ(*) → 4e, no cuts)

• P_T of the 4 Electrons (pp → ZZ → 4e, no cuts):
  

p_T of the 4 Electrons (pp → ZZ(*) → 4e, |η| < 2.5 cut)

• |η| < 2.5 cut
• P_T of the 4 Electrons (pp → ZZ → 4e, η cuts):
  

p_T of the 4 Electrons (pp → ZZ(*) → 4e, |η| < 2.5 cut, p_T > 5 cut)

• |η| < 2.5 cut
• p_T > 5 GeV
• P_T of the 4 Electrons (pp → ZZ → 4e, η cuts):
  

p_T of the 4 Electrons (pp → ZZ(*) → 4e, |η| < 2.5 cut, p_T > 5 cut, Trigger cut) The following plot has the following cuts:

• |η| < 2.5 cut
• p_T > 5 GeV
• Trigger cut:
  • Single E: At least one electron has a p_T > 26.0 GeV
  • Double E: At least two (isolated) electrons have a p_T > 14.5 GeV
  • Relaxed Double E: At least two (not necessarily isolated) electrons have a p_T > 21.8 GeV
• P_T of the 4 Electrons (pp → ZZ → 4e, trigger cuts):
  

• These last two cuts are a bit artificial since we cannot simulate isolation with this study (here the relaxed double e cut is useless).

Δφ of the Oppositely Charged Electron Combinations (pp → ZZ(*) → 4e, |η| < 2.5 cut; p_T > 5 cut; trigger cut)

• L1 is the e⁺ from the Z with the lowest ΔM = | M_Z - M_Z^PDG | (called Z1)
• L2 is the e^- from Z1
• L3 is the e⁺ from the Z with the higher ΔM (Z2)
• L4 is the e^- from the Z2
  
• Δφ of the Oppositely charged Electrons (pp->ZZ, M_H = 150 GeV/c², Trigger cuts):
  

Δη of the Oppositely Charged Electron Combinations (pp → ZZ(*) → 4e, |η| < 2.5 cut; p_T > 5 cut; trigger cut)

• Δη of the Oppositely charged Electrons (pp->ZZ, M_H = 150 GeV/c², Trigger cuts):
  

pp → tt(bar) → 4e Background

The tt(bar) background can look like the H → ZZ(*) → 4l signal whenever the W's from the t's decay leptonically as well as the b jets. One surprise (well it should n't have been a surprise) was that the b quarks will hadronize well before it decays leptonically (if it does at all). It took more thought (algorithmically) than the previous two samples to extract to appropriate lepton from the event. Note: it took about 600,000 events to produce ~5000 tt(bar) → 4e events.

The possible Z Candidate combinations

Here are the invariant masses of all the combinations of leptons (one through four).
L1 is positive lepton from the W+
L2 is negative lepton from the W-
L3 is positive lepton from the B or C hadron
L4 is negative lepton from the B or C hadron

• Z Candidates:
  

Here we plot these individually to see more detail:

• Z Candidate with l₁ and l₂:
  
• Z Candidate with l₁ and l₃:
  
• Z Candidate with l₁ and l₃ (zoom):
  
• Z Candidate with l₁ and l₄:
  
• Z Candidate with l₁ and l₄ (zoom):
  
• Z Candidate with l₂ and l₃:
  
• Z Candidate with l₂ and l₃ (zoom):
  
• Z Candidate with l₂ and l₄:
  
• Z Candidate with l₂ and l₄ (zoom):
  
• Z Candidate with l₃ and l₄ (zoom):
  
• Z Candidate with l₃ and l₄ (zoom):
  

The Number of Background Events Expected from pp → tt(bar) → 4e.

We perform the same exercise for the pp → tt(bar) → 4e to see how many of these events will pass through the cuts as well. On the right will be the invariant mass of the 4-vectors of the four e's that decayed from the two Z's. The plots for the four μ's or two μ/two e case are attached but not linked in (unless there was something different to report).

p_T of the 4 Electrons (pp → tt(bar) → 4e, no cuts)

• P_T of the 4 Electrons (pp → tt(bar) → 4e, no cuts):
  

p_T of the 4 Electrons (pp → tt(bar) → 4e, |η| < 2.5 cut)

• |η| < 2.5 cut
• P_T of the 4 Electrons (pp → tt(bar) → 4e, η cuts):
  

p_T of the 4 Electrons (pp → tt(bar) → 4e, |η| < 2.5 cut, p_T > 5 cut)

• |η| < 2.5 cut
• p_T > 5 GeV
• P_T of the 4 Electrons (pp → tt(bar) → 4e, η and p_T cuts):
  

p_T of the 4 Electrons (pp → tt(bar) → 4e, |η| < 2.5 cut, p_T > 5 cut, Trigger cut) The following plot has the following cuts:

• |η| < 2.5 cut
• p_T > 5 GeV
• Trigger cut:
  • Single E: At least one electron has a p_T > 26.0 GeV
  • Double E: At least two (isolated) electrons have a p_T > 14.5 GeV
  • Relaxed Double E: At least two (not necessarily isolated) electrons have a p_T > 21.8 GeV
• P_T of the 4 Electrons (pp → tt(bar) → 4e, trigger cuts):
  

• These last two cuts are a bit artificial since we cannot simulate isolation with this study (here the relaxed double e cut is useless).

Δφ of the Oppositely Charged Electron Combinations (pp → tt(bar) → 4e, |η| < 2.5 cut; p_T > 5 cut; trigger cut)

• L1 is the e⁺ from the W⁺
• L2 is the e^- from the W^-
• L3 is the e⁺ from the positive B or C hadron
• L4 is the e^- from the negative B or C hadron
  
• Δφ of the Oppositely charged Electrons (pp->tt(bar), Trigger cuts):
  

Δη of the Oppositely Charged Electron Combinations (pp → ZZ(*) → 4e, |η| < 2.5 cut; p_T > 5 cut; trigger cut)

• Δη of the Oppositely charged Electrons (pp->tt(bar), Trigger cuts):
  

pp → ZBB(bar) → 2e2μ Background

I had to use pp → ZBB(bar) → 2e2mu instead of pp → ZBB(bar) → 4e because I was having problems creating a large ZBB(bar) sample. I should have this fixed soon.

The possible Z Candidate combinations

Here are the invariant masses of all the combinations of leptons (one through four).
L1 is positive lepton from the Z
L2 is negative lepton from the Z
L3 is positive lepton from the B or C hadron
L4 is negative lepton from the B or C hadron

• Z Candidates:
  

The Number of Background Events Expected from pp → ZBB(bar) → 2e2μ.

We perform the same exercise for the pp → ZBB(bar) → 4e to see how many of these events will pass through the cuts as well. On the right will be the invariant mass of the 4-vectors of the four e's that decayed from the two Z's. The plots for the four μ's or two μ/two e case are attached but not linked in (unless there was something different to report).

p_T of the 4 Electrons (pp → ZBB(bar) → 2e2μ, no cuts)

• P_T of the 4 Leptons (pp → ZBB(bar) → 2e2μ, no cuts):
  

p_T of the 4 Electrons (pp → ZBB(bar) → 2e2μ, |η| < 2.5 cut)

• |η| < 2.5 cut
• P_T of the 4 Leptons (pp → ZBB(bar) → 2e2μ, η cuts):
  

p_T of the 4 Electrons (pp → ZBB(bar) → 2e2μ, |η| < 2.5 cut, p_T > 5 cut)

• |η| < 2.5 cut
• p_T > 5 GeV
• P_T of the 4 Leptons (pp → ZBB(bar) → 2e2μ, η and P_T cuts):
  

p_T of the 4 Electrons (pp → ZBB(bar) → 4e, |η| < 2.5 cut, p_T > 5 cut, Trigger cut) The following plot has the following cuts:

• |η| < 2.5 cut
• p_T > 5 GeV
• Trigger cut:
  • Single E: At least one electron has a p_T > 26.0 GeV
  • Double E: At least two (isolated) electrons have a p_T > 14.5 GeV
  • Relaxed Double E: At least two (not necessarily isolated) electrons have a p_T > 21.8 GeV
• P_T of the 4 Leptons (pp → ZBB(bar) → 2e2μ, trigger cuts):
  

• The trigger cut didn't do anything on this sample but the statistics are too low so I'll look at this again when I get more statistics.
• These last two cuts are a bit artificial since we cannot simulate isolation with this study (here the relaxed double e cut is useless).

Δφ of the Oppositely Charged Electron Combinations (pp → ZBB(bar) → 4e, |η| < 2.5 cut; p_T > 5 cut; no cuts)
L1 is positive lepton from the Z
L2 is negative lepton from the Z
L3 is positive lepton from the B or C hadron
L4 is negative lepton from the B or C hadron

• Δφ of the Oppositely charged Electrons (pp->ZBB(bar), no cuts):
  
• Δφ of the Oppositely charged Electrons (pp->ZBB(bar), trigger cuts):
  

Δη of the Oppositely Charged Electron Combinations (pp → ZBB(bar) → 4e, |η| < 2.5 cut; p_T > 5 cut; no cuts)

• δη of the Oppositely charged Electrons (pp->ZBB(bar), no cuts):
  
• δη of the Oppositely charged Electrons (pp->ZBB(bar), trigger cuts):
  

Stacked Plot of M_4l

• Stacked Plot of M_4l of all the samples:
  

-- RyanKelley - 24 Jan 2008