Measurement of the p anti-p --> t anti-t production cross section at s**(1/2) = 1.96-TeV in the fully hadronic decay channel. Page: 6 of 10
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6
TABLE I: Efficiency for selection criteria applied before b-jet
identification. Efficiencies listed include the efficiency for all
previous selection criteria. The trigger efficiency is quoted for
events that have passed the preselection. The uncertainties
are due to Monte Carlo statistics. Listed are the selection ef-
ficiencies as determined for tt in the hadronic decay channel,
the lepton+jets decay channel and the efficiency for all differ-
ent decay channels corrected for W boson branching fractions.
cut tt -> hadrons tt -> f + jets any tt
preselection 0.2706 + 0.0016 0.0311 + 0.0008 0.1385 + 0.0011
trigger 0.2527 + 0.0015 0.0268 + 0.0007 0.1284 + 0.0010
DO Run II 405 pb 600- DO Run II 405 pb1
(a: 1 SVT tag) (b: s2 SVT tag)
400
1000
200 -
500 o
0 200 400 00 1000 200 400 1000
H [GeV]
FIG. 1: The HT distribution for single-tag events (a) and
double-tag events (b). Shown are the data (points), the back-
ground (solid line) and the expected tt distribution (filled his-
togram) multiplied by 140 (60) for the single (double)-tag
analysis.
ciency for b-quark jets. Events with two or more loosely
tagged jets were called double-tag events. The sample
that did not contain two loosely tagged jets was inspected
for events with one tight tag. Events thus isolated were
labeled single-tag events. The fully exclusive samples
of single-tag and double-tag events were treated sepa-
rately because of their different signal-to-background ra-
tios. The use of the tight SVT selection for single tagged
events optimized the rejection of mistags, the main back-
ground in the single-tag analysis. When two tags were
required, the background sample started to be dominated
by direct bb production. The choice to use the loose SVT
optimized the double-tag analysis for signal efficiency in-
stead of background rejection.
Compared to light-quark QCD multijet events, tt
events on average have more jets of higher energy and
with less boost in the beam direction, resulting in events
with many central jets that all have similar and rela-
tively high energies. Moreover, the fully hadronic decay
makes it possible to reconstruct the W boson and t quark
four-momenta. To distinguish between signal and back-
ground, we used the following event characteristics [11]:
(1) HT: The scalar sum of the corrected transverse
momenta of the jets (Fig. 1).
(2) E6: The square root of the product of the trans-
verse momenta of the fifth and sixth leading jet (Fig. 2).
(3) A: The aplanarity as calculated from the normal-
ized momentum tensor (Fig. 3) [8, 9, 11].0
2010
DO Run II 405 pb1 DO Run II 405 pb
(a: 1 SVT tag) 800 (b: 2 SVT tag)
00-
600
00- 400
200
' 20 80 100 20 4 80 100
ET56FIG. 2: The E56 distribution for single-tag events (a) and
double-tag events (b). Shown are the data (points), the back-
ground (solid line) and the expected tt distribution (filled his-
togram) multiplied by 140 (60) for the single (double)-tag
analysis.
0
1000 DO Run II 405 pb1 400 DO Run II 405 pb1
(a: 1 SVT tag) (b: s2 SVT tag)
300-
500 200
100
3Ni50210.1 0.2 0. . 0.5 01 .2 0. .4 0.5
Aplanarity
FIG. 3: The A distribution for single-tag events (a) and
double-tag events (b). Shown are the data (points), the back-
ground (solid line) and the expected tt distribution (filled his-
togram) multiplied by 140 (60) for the single (double)-tag
analysis.
(4) (n2): The PT-weighted mean square of the y of the
jets in an event (Fig. 4), see also Ref. [11].
(5) M: The mass-X2 variable, which was defined as
M (Mw7 -Mw)2/ 0, +(MwZ-Mw)2/0, ,+(mt -
m/ I where the parameters Mw, am. and om
were the invariant mass and mass resolution from the jetDO Run II 405 pb
(a: 1 SVT tag)
1000500k
qI
FIG. 4: The (p2) distribution for single-tag events (a) and
double-tag events (b). Shown are the data (points), the back-
ground (solid line) and the expected tt distribution (filled his-
togram) multiplied by 140 (60) for the single (double)-tag
analysis.DO Run II 405 pb1
(b: 2 SVT tag)
400k200
1 2 4
< >1 2 - .
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Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al. Measurement of the p anti-p --> t anti-t production cross section at s**(1/2) = 1.96-TeV in the fully hadronic decay channel., article, December 1, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc881362/m1/6/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.