Hgg with different generators

1
H?gg with different generators

• Y.Fang, B.Mellado, Sau Lan Wu
• (University of Wisconsin)

2
Outline

• Comparison of variables for gg Fusion, and vbf
  H?gg.
• cut efficiency for H1jet.
• cut efficiency for H2jets

3
Samples for MH130GeV

• gg Fusion H?gg
• Alpgen 2.06(interfaced with herwig) H0-4jets
  
• MC_at_NLO NLO
• MCFM H2jets (parton level generator with Matrix
  Element (ME) calculation for this process)
• VBF H?gg
• Alpgen 2.0.6 H2,3jets.
• Herwig
• Pythia 6.2

4
Cross section
Alpgen PTJgt20GeV, ?Rlt0.7

• MC_at_NLO has some NLO calculation, so it is
  reasonable its cross section has one factor
  larger.
• For alpgen, the cross sections are affected by
  Generator cut (e.g. pt Gen cut for the jet).
• For the H2jets comparison study, we apply some
  pre-selection cuts to make samples generated by
  different generators have similar phase space.

5
gg Fusion H?gg
The difference of PTgg distribution needs to be
understood.
6
gg Fusion H?gg

• Similar difference can be seen for leading jet
  distribution.
• For sub-leading jet, Alpgen has harder jet due to
  its ME calculation.

7
gg Fusion H?gg

• The third and fourth jets from Alpgen J0-J1 are
  basically from parton shower
• which is consistent with MC_at_NLO.
• Alpgen J0-J4 has jets from ME, which makes its
  3rd and 4th jets harder.

8
gg Fusion H?gg

• MCFM generates parton level gg ?H2jets with ME
  calculation which
• is statistically comparable with Alpgen
  J0-J4.
• For MC_at_NLO, Alpgen J0-J1, deviation has been
  seen.

9
VBF H?gg
Preselection cuts PTg1,Tg2gt20GeV,PTJ1,J2gt20GeV
10
VBF H?gg
As expected, the distribution for leading and
subleading jets are consistent.
11
VBF H?gg
Alpgens third jet has matrix element matched
parton shower, it is hardest. Herwigs pt
distribution of third jet is somehow close to
alpgen.
12
VBF ??1j2j

• For PYTHIA and Herwig, the peak
• at low ?? is partly due to one
• of leading/sub-leading jet from FSR
• radiation( angularly close to
• hardest quark jet it radiates from).
• For Alpgen, hard radiated jets
• from ME can go to leading
• or sub-leading jets, these hard jets
• dont have co-linear behavior.

?? distribution in the range ??lt1.5
13
Cut efficiency with H1jet analysis for VBF and
ggFusion samples

• Pg1gt45GeV, Pg2gt25GeV
• photon efficiency (fixed rejection scenario
  in this talk).
• b. PTjgt20GeV.
• Mggjgt331GeV.
• Mass win 127.34ltMHlt132.66GeV

14
Cuts description for H2jets
Pre-selection cut PT?1gt20 GeV, PT?2gt20 GeV,
?glt2.5 Njetgt1,
PTj1gt20GeV,PTj2gt20GeV
15
Cut efficiency for H2jet analysis
The final cross-sections Pythia 0.647fb, alpgen
0.661fb, Herwig 0.640fb

• For Alpgen H3j, the 3rd jet from ME is more
  likely
• to be chosen as tagged jet than the other
• samples. This jet has different
  pseudorapidity
• activity from traditional tagging jets.
• This explains why alpgen H3j(inclu) has low
• efficiency at cut b.
• At cut e, Alpgen H2j(exclu) and Pythia,Herwig
  run
• out of third jet Ptgt20GeV, so they have high
• efficiency (see backup slide).

16
Cut efficiency for H2jet analysis for gg Fusion
samples

• Alpgen H0,1jet alpgen can not pass cut b (lack
  2nd hard tagging jet).
• MC_at_NLO with more high ??j1j2(see plot on page 8)
  helps explain higher efficiency for cut b.
• For cut e, MC_at_NLO has a relative higher survival
  possibility due to the fact
• it doesnt have many third jets in center
  (also see Junichis talk).
• Same reason explains why Alpgen H2j(exclu) has
  high efficiency for cut e.

17
Conclusion

• variables from gg Fusion and VBF H?gg are
  compared.
• For H1jet analysis, results from different
  samples are consistent.
• For H2jets analysis
• Different VBF generators provides comparable
  results.
• For gg Fusion, discrepancy between MC_at_NLO and can
  be seen.
• The difference has been studied a little bit.
• Uncertainty study for Alpgen samples need to be
  done.
• Plan to use SHERPA.

18
backup slides
19
Variables for vbf H?gg after cut c