Post on 12-Jan-2017
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
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
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)
pp̄� tt̄� bW+b̄W� � bl+�l + b̄jj
pp̄�W+bb̄jjpp̄�W+jjjj
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
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
ReconstrucDon of top & anDtop
May 7, 2012 PHENO 2012: Yoshitaro Takesu 15
+�
i=l,jets
�pi,meas
T � piT
�2i
�2
+�
j=x,y
�pUE,meas
j � pUEl
�2j
�2