Jet Studies in MC

Andy Haas

Columbia U. / Nevis Labs

JERG Meeting

Nov. 7, 2007

Samples

QCD 20-40 (also have 40,80,160,320)

Z->bb, qq

p17 MC

Particles jets (JCCA being used, but have JCCB too)

JCCA jets (JES+JSSR)

JCCB jets (JES+JSSR)

CAF files on /rooms/beam/haas/cabsrv1

Macro for analysis (loop3.C)
publicly available

Match leading two particle jets to leading two reco A and B jets within dR<0.5

Jet Width

Compare (JCCA reco pT / JCCA particle pT) vs. JCCA width

Bin in 5 GeV bins of JCCA particle pT

Here's QCD 20-40

sample for

20<pt<25

There is some

dependence...

Jet Width

But the average correction is very small (~1%)...

And thus the corrected jet resolution is also just a little bit better (~1%)

Jet Width

Note that it's easy to create false resolution improvements

pT/1.2 + 3.8 does very well

(on this jet pt spectrum)

A 16% resolution improvement!

Of course, this correction fails on a different pt spectrum, like Z->bb

Jet Width

Actually, I think jet width will be more useful as a way to tell b-jets from light quark and gluon jets

Gluons are wider, and light quarks are thinner than b-jets...

QCD 20 MC

<0.28>

Z->qq MC

<0.23>

Z->bb MC

<0.25>

Jet Width

Width of leading pt jet in Z->mumubb analysis

A lot of the b-tagged background is g->bb, which is wider!

Using JCCB as well

I happened to make this plot:

You can use a measurement of JCCB pT to correct the JCCA pT!

JCCA – JCCB pT (GeV)

PJ pT – JCCA pT (GeV)

(JCCA+JCCB)/2

Can simply average the JCCA and JCCB jets' 4-vectors

~10% improvement

Works even a little better in Z->bb

~12 % improvement

Of course, there are more optimal ways of using the info than just averaging... training a NN...

Andy Haas

2004-07-07T15:59:13