Talk @ Pheno 2012, 2012.05.07

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 SelecDon &

ReconstrucDon

May 7, 2012 PHENO 2012: Yoshitaro Takesu 3

Event generaDon


• 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

Event SelecDon


ReconstrucDon of top & anDtop


Results


distribuDon


distribuDon


MadGraph + PYTHIA

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.


Back up slides

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


ReconstrucDon of top & anDtop


+�

i=l,jets

�pi,meas

T � piT

�2i

�2

+�

j=x,y

�pUE,meas

j � pUEl

�2j

�2

Mass distribuDon of top (lep)


Talk @ Pheno 2012, 2012.05.07

Science

Transcript of Talk @ Pheno 2012, 2012.05.07