p17 ZH -> mumu bb
w/ Neural Net Event Selection

Andy Haas
Columbia University

Higgs Workshop

April 12, 2007

Analysis Updates

Now using all available MC samples
(mostly backgrounds)

Keeping track of all these numbers and typing them into a table has been lots of fun :)

Use ALPGEN as main MC source for Z+jets, but have Pythia as a cross-check

New QCD Fit

Use QCD shape from non-isolated data

Smear muons properly in MC to describe Z shape better

-> Add “ApplyMuonSmear” processor

Consider tt contribution while fitting

Apply re-weighting for ALPGEN bugs in 0,1 lp samples for mZ distributions

ALPGEN

Pythia

0 btags

0 btags

tt

I like the Pythia shape a little better,

but it makes hardly any difference
for the QCD background fit...

ALPGEN

Pythia

1 btags

1 btags

tt

New QCD Fit

ALPGEN

Pythia

2 btags

2 btags

tt

New QCD Fit

Result is that QCD remains an almost negligible background inside

Z mass window (70-110 GeV)

Mjj / 2L and 1T

Separate data into two orthogonal samples:

“2Loose”: >=2 L4 b-tagged jets

“1Tight”: >=1 VERYTIGHT b-tagged jets && !>=2 L4 b-tagged jets

Using TRFs for b-tagging in MC, so it was some exercise in probability theory to calculate the probability for an event to have 1 VT tag given that it does not have >=2 L4 tags

2L

1T

Mjj Limits

2L

1T

Train Neural Networks

NN Inputs

M_bb is

nonsense in the

data before tagging

M_bb is set

to M_jj for

single-tag

channel

1T

2L

Pre-tag

Post-tag

NN Inputs

M_jj is not used in the (2L) NNs – M_bb performs significantly better!

1T

2L

Pre-tag

Post-tag

NN Inputs

1T

2L

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Post-tag

NN Inputs

1T

2L

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Post-tag

NN Inputs

1T

2L

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NN Inputs

1T

2L

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NN Inputs

1T

2L

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NN Inputs

1T

2L

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NN Inputs

1T

2L

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NN Inputs

1T

2L

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NN Inputs

1T

2L

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Post-tag

NN Output: ZZ

1T

2L

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Post-tag

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Post-tag

NN Output: ZZ

1T

2L

Pre-tag

Post-tag

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NN Output: mH=125

1T

2L

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NN Output: mH=125

1T

2L

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NN Output: tt Cross-check

Train NN against tt as the signal.

Some evidence for tt, consistent with expectations (I input xs=7.0pb).

1T

2L

Post-tag

Post-tag

tt Cross-check w/ Wider Acceptance

Widen Z mass window, 70-110 -> 40-500, accept more tt signal.

Good evidence for tt, consistent with expectations (I input xs=7.0pb).

1T

2L

Post-tag

Post-tag

Wade's LLR's

1.1

mm

Discovery!!!

NN Output: mH=145

B~10^-2

S/B~1/10

1T

2L

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Limit / SM from Wade

1.1

mm

Conclusions

Results using combination of full 1.1/fb, single/double b-tags, and NN are equivalent to ~4x the luminosity of last summer's conference result

Need more work on systematics, now that a NN is involved

Use agreement of un-tagged data/MC NN outputs in signal region?

Have updated the analysis note

About 90 pages long
(mostly plots)! :)

Analysis: Limit/SM (mh=115)

-------------------------

Nominal Mjj (ICHEP'06): 42

Updated P17 Mjj: 36

p17 NN 2Tag: 27

p17 NN 1Tag: 35

p17 NN 1+2Tags: 20

p17 NN 1+2Tags:
e+mu combined: 14 (estimated)

CDF (1/fb – Moriond'07)

e+mu combined, MET filter: 16

We'll be ahead of CDF
in ZH->llbb!

Andy Haas

2004-07-07T15:59:13