- The document examines the W+4 jets background to the top quark asymmetry observed at the Tevatron. - Event generation is performed with MadGraph 5 using CTEQ6L1 PDFs and a factorization scale of 20 GeV. - Kinematic distributions of the W+4 jets process are studied after event selection and reconstruction of top quarks. - A large forward-backward asymmetry is seen in the W+4 jets background, suggesting background contaminations may be higher than expected and contributing to the observed anomaly.

1. On
the
W+4
jets
background
to
the
top-­‐
quark
asymmetry
at
the
Tevatron
Yoshitaro
Takaesu
KEK,
Japan
In
collaboraDon
with
K.
Hagiwara
(KEK)
and
J.
Kanzaki
(KEK),
in
preparaDon

2. IntroducDon
• Large
top
forward-­‐backward
asymmetry
(
)
has
been
observed
at
the
Tevatron.
• Contribu>ons
of
NNLL
QCD,
EW
correc>ons,
NLO
of
,
etc.
have
been
discussed,
but
we
do
not
know
the
sa>sfactory
answer
yet.
• We
focus
on
W+4
jets
background
for
this
anomalous
.
May
7,
2012
2
PHENO
2012:
Yoshitaro
Takesu

3. Event
SelecDon
&
ReconstrucDon
May
7,
2012
PHENO
2012:
Yoshitaro
Takesu
3

4. Event
generaDon
May
7,
2012
4
PHENO
2012:
Yoshitaro
Takesu
•
PDF:
CTEQ
6L1
•
Fact_scale
=
(
)
20
GeV
(W+4
jets)
matrix-­‐element
level
(MadGraph
5)
p¯p t¯t bW+¯bW bl+
l + ¯bjj
p¯p W+
b¯bjj
p¯p W+
jjjj

5. Event
SelecDon
May
7,
2012
5
PHENO
2012:
Yoshitaro
Takesu

6. ReconstrucDon
of
top
&
anDtop
May
7,
2012
PHENO
2012:
Yoshitaro
Takesu
6

7. Results
May
7,
2012
PHENO
2012:
Yoshitaro
Takesu
7

8.
distribuDon
May
7,
2012
8
PHENO
2012:
Yoshitaro
Takesu

9.
distribuDon
May
7,
2012
9
PHENO
2012:
Yoshitaro
Takesu

10.
distribuDon
May
7,
2012
10
PHENO
2012:
Yoshitaro
Takesu
MadGraph
+
PYTHIA

11. Summary
• We
inves>gated
W+4
jets
background
in
detail
on
,
and
distribu>ons.
• Large
is
seen
in
W+4
jets
background.
• Anomaly
in
by
D0
may
suggests
BG
contamina>ons
in
signal
than
expected.
• We
suggest
to
re-­‐evaluate
W+4
jets
BG
at
the
Tevatron,
comparing
with
distribu>ons
we
discussed.
May
7,
2012
11
PHENO
2012:
Yoshitaro
Takesu

12. May
7,
2012
12
PHENO
2012:
Yoshitaro
Takesu

13. Back
up
slides

14. Reconstruc>on
of
top
For
the
other
W
Select
W
candidates
(j1,j2)
b1
=
b-­‐tagged
jet
b2
=
b-­‐tagged
jet
(
if
#
b
=2
)
the
remained
jet
(
if
#
b
=1
)
use
4
leading
jets
(including
b-­‐tagged
jet)
for
reconstruc>ons
If
no
candidate,
throw
away
the
event
May
7,
2012
14
PHENO
2012:
Yoshitaro
Takesu

15. ReconstrucDon
of
top
&
anDtop
May
7,
2012
PHENO
2012:
Yoshitaro
Takesu
15
+
i=l,jets
pi,meas
T pi
T
2
i
2
+
j=x,y
pUE,meas
j pUE
l
2
j
2

16. Mass
distribuDon
of
top
(lep)
May
7,
2012
PHENO
2012:
Yoshitaro
Takesu
16