b ID for Massive bb pairs

1
The PhysicsofGenerations Don Lincoln f
2
Four Fermion General Theory
Drell-Yan Only

• Theory consists of all terms of any chiral
  combinations

3
Tevatron Run I Limits
Drell-Yan
Units TeV
QCD
4
Topics Currently Covered

• All pp ? two particles
• pp ? mm- (p? resolution limited)
• pp ? ee- (visa problems)
• pp ? en (MET questions)
• pp ? bb (two tagging approaches)
• pp ? jet-jet (most robust)
• ds/dM ds/d(cos q)

5
Run II Projected Dijet Mass Spectrum
Dramatic increase in high pT cross sections Large
gains in statistics
6
Run II Drell-Yan
PRL 82 4769 (1999)
Constructive Interference
Projected Limits (Bayesian)
Destructive Interference
7
2VTX Tagging High P? b Jets
Isnt that two there?

• Don Lincoln
• f

8
Motivation

• High mass bb pairs can be sign of new physics
  (compositeness ?)
• Problem
• 1001 QCDbb
• Solutions
• m tagging
• 2nd VTX tagging
• Impact parameter

CDF PRL 82 (1999) 2038
Fit to CDF qQCD calculation
9
Current Work
Decay Length
Impact Parameter
DR
Question Is failure to reconstruct secondary
vertex due to tracking efficiency or vertex
algorithm?
DCA

• Many variables have been tried for 2 VTX tag
• Decay length significance (2D 3D)
• Vertex Mass
• DR
• etc.
• Only decay length and related quantities works.
• Consider other tags eventually.

Key
Calorimeter Jet
b hadron
Secondary vertex
Primary vertex
Particles of Interest
10
What if ?
Efficiency only that of finding a good
secondary vertex
We know that one can find secondary vertices by
accident in light quark initiated events
Eff(found) Eff(luck) Eff(right)
Estimate Eff(right) Eff(found) -
Eff(light) No light statistics at high
pt Reality could be worse Eyeball trends and
guess.
11
Decay Length (found and 2VTX)
Found found track 2VTX used in secondary
vertex Ptmin(track) 500 MeV Efficiency
2VTX/found Efficiency Pt and flavor-initiator
independent
12
DR (real and found)
Found correct fake Ptmin(track) 500
MeV Efficiency found/real Light quark jets
has better tracking efficiency in core.
13
Tracking Efficiency vs Pt.
14
Summary

• Several different high mass di-object searches
  underway
• In bb
• Need to understand tracking efficiency in core of
  jets
• Need to look more at muon tagging (but low mass
  reach)
• Need to better understand b quark content from
  parton showers.
• Active effort
• Need more people thinking about it.