b-ID Status

Andy Haas - Columbia University

on behalf of the b-ID group

D0 Collaboration Meeting @MSU

July 6, 2007

New TRFs

Tim Scanlon has made new TRFs for p17 JLIP and NN

Extends to higher pT

Separate pT parameterization for each |eta| bin, so smaller systematic uncertainties

Will be added to (p17) btags_cert soon, so can be used in CAFe

Some beta-testers have already tried this out

We will eventually use the updated nn_cert for p20 certification

But want to take just one step at a time

b-tag fake rate

b-tag efficiency

TRF W/Z+bb Discrepancies

Studied TRFs for gluon-splitting samples, like W+bb, Z+bb

Observe a 5-10% overestimate of the TRF, compared to actual tagging in MC at low pT

Due to lower b-quark momentum (as a fraction of the jet momentum) in these samples

Yvonne has measured a correction for this

Will be put into BTagProcessor...

You will tell it that you're running on W/Z+bb and the TRF will be corrected

5-10%, low pT

Scale factor for W/Z+bb

Taggability Issues

Thorsten worked on the taggability processor

Checked into CVS: btags_cert_caf

BTagProcessor is able to apply parameterized taggability

We are underestimating the taggability for jets from the PV at low pT by 5-10% and 2% at high pT

Not yet fixed in new processor...

Has made progress on the flavor dependence...

Still need to study tau dependence...

In beta-testing... users are having success

Ratio of taggability for

all jets / PV jets

15

100

2.5

0

1.2

1.0

1.1

1.0

Taggability for b/c's goes up!

20% at 15 GeV

10% in ICR

To do...

A couple big holes
(in addition to the projects “underway”)

No TRF has been measured for taus!

Just using the light-jet fake rate

We know this is wrong. Taus are tagged about as often as charm (after taggability)

No light-jet data/MC scale factor!

Can not do a “direct tagging” analysis involving light jets

Muon Soft-lepton Tagger (NN)

Hwidong

Adds ~5% efficiency to b-ID / negligible extra fake rate

Have measured the tagging efficiency in data and MC!

Modified System8 method used

Now working on measuring fake-tag-rate

Using Negative Tag Rate method based on muon IP significance

Next hurdle is the data/MC scale factors for the muon efficiency and fake rate in the jet

High Luminosity Studies

Alejandro and Don (and Suneel)

b-id works fine at high luminosity, but taggability starts to suffer...

MC

Data:

p20 NN Certification

Sarah Schlobohm + Andy Haas + Dale Johnston

Have run several “certifications” so far:

Re-cert p17 data / MC (to cross-check with old p17 certification)

p20 pass1 data / p17 MC

p20 pass2 data / p17 MC

So far, using p17 NN tagger... results on p17 and p20 data are similar...

Need the “p20 NN tagger” -> Needed p20 MC, now have it!

Re-tune JLIP on p20 pass2 data and p20 MC -> DONE! (Thanks, Daniel Bloch!)

Re-train NN (with retrained JLIP) on p20 MC -> IN PROGRESS

p17 (re-cert)

p20 data/ p17 MC

SF

MC

Data

Data

JLIP problems

Problem seen in p20 JLIP inputs, compared to p17

Much weaker discrimination in p20...

Re-tuned JLIP

re-tuned JLIP appears to be working better now!

p20 JLIP

p17 JLIP

all on p20 pass2 data

p20 Trigger Issues

Dale Johnston

Important to exclude “biased” triggers when studying b-id efficiencies / fake-rates

List of biased triggers has been re-examined and fixed up...

With incomplete

list of biased

triggers

Many improvements worked on lately, will be available soon:

New TRFs with higher pT range and smaller uncertainties

A correction for W/Z+bb TRFs

A taggability processor, with corrections for b,c,tau jet flavors...

Inst. luminosity dependence studies well underway

Muon soft-lepton tagger is maturing, fake-rate being measured in data

We have preliminary p20 (pass2) NN TRFs!

But performance on p20 data is about the same as for p17 data...

Have re-tuned JLIP, will re-train NN --> Just got p20 MC!

Fixed up “unbiased” trigger list for p20 data

Can use p17 TRFs for initial p20 studies

preliminary p20-tuned b-id ready by ~ end of July

A few major “holes” still exist (no one working on them yet...) !!!

tau TRFs, light-jet data/MC scale factors (needed for “direct-tag” analyses)

Future projects:

Use of continuous NN output (many groups interested...)

b/c – jet separation (Brendan Casey, Gustavo et al.)

soft-electron tagger? b / g->bb separation?

b-ID Status

Backup / Details

“Continuous” NN Output

Several people have expressed interest in using the continuous b-ID NN output as a variable for input to a NN event selection

Not an easy thing to do right!

MC and data do not give the same NN output shape!

There are several plausible methods for correcting the shape

Alan Magerkurth has devised a way to use all 12 NN operating points

Mike Mulhearn will investigate correcting the full output distribution, using the SF's, for use in a ME analysis

Gordon and John are also interested in creating data TRF “functions” (TRFF's)

Inst. Luminosity Dependence

Suneel Dutt

Showed before that NN inputs / outputs are not sensitive to inst. lum.

Taggability on average decreases with increasing inst. lum.

But taggability for “clean” events with <4 PV does not suffer at higher inst. lum.

Can see average number of taggable jets start to fall off around ~150e30

b-ID Improvements

SVT Optimization (Yvonne)

D0Note 5265

Random grid search of taggability and secondary-vertexing parameters

Fix old feature of re-using tracks on vertices

More realistic number of secondaries

Important – input to NN tagger!

Revive the 2-pass vertexing algorithm

Look for a tight vertex first, then a loose one if no tight was found

Better vertex parameters

Input to NN tagger!

Slightly higher efficiency

current operating points

points from search

TRFs and JSSR

Fabrice pointed out that it's important to run BTagProcessor after JSSR

Otherwise pT>15 for taggability has different meaning in data vs. MC

Result is to enhance the number of taggable jets at low pT

Is now the certified procedure for p17 (and p20) publications!

https://plone4.fnal.gov/P1/D0Wiki/object-id/bid/bidjssr

Old, btagging->JSSR

New, JSSR->btagging

1 b-tags (L4)

pT of second-leading jet (GeV)

Andy Haas

2004-07-07T15:59:13