Transcript Document

Early History of the Dzero tt dilepton Analyses (with an em bias)
Before the Beginning …
V. Balamurali, J. Bantly, V. Bhatnagar, J. Cochran, K. Genser, R. Hall, R. Kehoe, M. Narain, H. Singh, S. Wimpenny
mt > 91 GeV/c2
We’re busy readying the detector &
designing our analyses
What Background levels did we expect ?
In mid 1994, All Analyses are Reoptimized to Search for High Mass Top
Dilepton Channels Adopt the use of HT
We begin as a group under the leadership of
Steve Wimpenny
HT  ET (electron)   ET (jets)
(for ee & em)
HT   ET ( jets)
1st order of business – develop e/m id
em “physics”
(working with id groups of course!)
(for mm)
Significant Improvement in Signal/Background for High Mass Top !
Hand Scanning of thousands of single m events !
tt (mt = 200 GeV/c2)
Background
Do we understand muon bremsstrahlung ?
Data and MC discrepancy!
Solved in GEANT 3.16!
But is this a problem ?
m+g can look like m+e
(if g is matched to m track)
g
em “fakes”
m
HT (GeV)
Introduce DR(e,m) cut for em analysis
Applying the New Analysis to the Run 1A & available Run 1B data,
we find more candidates!
Having decided on our analyses, we cautiously begin looking at the data …
ee
January 1993: em Event 417 is found by Boaz Klima
This event was not found by our initial search!
With new muon reconstruction 417 easily passes our selection
What do we see in run 1A ?
And what did we see when we looked at the data ?
em: 2 candidates
em: 1 candidate
(event 417)
PNUT2: Calorimeter only ETmiss
PNUT3: Full ETmiss
However, for loose cuts, background expectations don’t agree with data
– why not ?
mm: 1 candidate
We know that making cut on ETmiss(calorimeter) brings data into
agreement, but why ?
The answer: We had not yet considered e mis-id background
from W(mn)+jets(e)
em
ee
mm
2
0
1
# of tt (170)
0.76  0.10
0.55  0.09
0.27  0.06
Background
0.12  0.03
0.28  0.14
0.25  0.04
Luminosity (pb-1)
47.9  5.7
55.7  6.7
44.2  5.3
ee: 0 candidates
# of Candidates
ETmiss(calorimeter) cuts on the W pT in W(mn)+jets events
These results were included in the top discovery paper:
And how good are our variables at rejecting “physics” backgrounds ?
mm: 0 candidates
Top Turns Ten Symposium: Fermilab 10/21/05
Jim Cochran Iowa State University (formerly SUNY Stony Brook & UC Riverside)