b/c/tau Tagging at the Tevatron
- State of the Art

Andy Haas*

Columbia U. / Nevis Labs

ALCPG 2007

Fermilab

October 24, 2007

*Lots of slides stolen from:

B-Tagging is critical to physics at the Tevatron

Top (t->Wb, single-top)

SUSY (stop, sbottom, ...)

Higgs (h->bb)

We've learned a lot...

Smart (multivariate) b/c reconstruction

Accurate measurement of efficiency / fake rate

Optimal use of info in analyses

Disclaimers and Qualifications

I'm on D0

Biased towards our methods

But CDF is similar, and we do share techniques

b-ID convener, for past 2 years

Now Higgs convener

Single-top has slightly different needs...

I like searches!

Other issues may dominate for precision measurements
(top cross-section, etc.)

Tevatron (p-pbar) is an extremely difficult environment

QCD background!
sigma(Z->bb)/sigma(bb)=~0.05 (under peak)!

Personpower-limited
~150 FTE / experiment!

b/c Tagging Techniques

Start loose

Measuring b/c Tagging

Efficiencies in data

Performance

Use of b-tagging

in physics analyses

Single-tight / Double-loose

WH(->bb) as an example

Note: 2 b's in most final states!

Base:

Find optimal double b-tag working point (usually very loose)

Single-tight / Double-loose

WH(->bb) as an example

Note: 2 b's in most final states!

Base:

Find optimal double b-tag working point (usually very loose)

Better:

Add optimal (orthogonal) single b-tag working point

Usually much tighter

Careful: adding single tag can change the optimal double tag working point!

Gain in performance:

~10% in sensitivity compared to one working point

Two Working Points

Better still:

Add double-tight working point

And single-loose working point

(Keep selections orthogonal!)

Gain in performance:

~2% in sensitivity compared to two working points

Double
Tight

Double
Loose

Single

Tight

Single
Loose

Sensitivity

Many Working Points

Even Better Still:

Use 3,4,... 12 working points

Including untagged there are 169 boxes (1 and 2 tags)

Order in terms of sensitivity

(and keep orthogonal)

Gain in performance:

~10% in sensitivity compared to two working points

Infinite Working Points

Use the output of the NN tagger

Danger: how to account for data/MC scale factors?

Under development

Gain in performance:

~0% in sensitivity compared to 12 working points

But can be added much more simply as an input to another NN...

Soft-lepton Tagging

Muon-only

so far!

tau Tagging

Use a tau NN

Input track ip as a variable?

No use of tracking for tau identification at Tevatron, so far

(at D0, and I'm pretty sure at CDF)

Issues:

Short tau lifetime

Small tau mass

Backgrounds from b/c jets

Data/MC disagreements

Could be used if there were excellent tracking and different backgrounds

ILC?

NN output

same sign /

opposite sign

Conclusions / Summary

Good b/c tagging starts with good tracking!

Combine jet lifetime / vertex info into NN's trained on MC to separate b/c/light jets

Measure performance in data using muon-tags / away tags / negative tags -> TRF's

Use multiple operating points simultaneously to take advantage of all information from tagging

Soft-lepton tagging
(muons, electrons?)

tau-tagging -> for the ILC!

Evidence for

single-top!

Backup

Andy Haas

2004-07-07T15:59:13