Measurement of color flow in t-tbar events from p-pbar collisions at sqrt(s)=1.96 TeV

Abstract

We present the first measurement of the color representation of the hadronically decaying W boson in t-tbar events, from 5.3 fb^-1 of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, "jet pull," is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored W bosons is 0.56 +- 0.42(stat+syst), in agreement with the standard model.

Figures (5)

• Figure 1: (Color online) Diagram showing two jets in the $\eta$-$\phi$ plane, and the reconstruction of the jet pull vectors ($\vec{t}$), jet pull angles ($\theta^{\rm pull}$), and relative jet pull angles ($\theta^{\rm pull}_{\rm rel}$).
• Figure 2: (Color online) The average of the two jet $\theta^{\rm pull}_{\rm rel}$ distributions for jets in pairing (a) $w$ and (b) $b$, in events with exactly four jets, at least two $b$-tags, and the $M_W$ requirement on the $w$-pair jets. The $\chi^2$/ndf compares the data to the total MC distribution.
• Figure 3: (Color online) (a) Leading-$p_T$ and (b) second-leading-$p_T$ jet $\theta^{\rm pull}_{\rm rel}$ distributions for $w$-pair jets, in events with two jets and no $b$-tagged jets. The $\chi^2$/ndf compares the data to the total MC distribution.
• Figure 4: (Color online) The discriminating color-flow variable, the minimum $\theta^{\rm pull}_{\rm rel}$ for the $w$-pair jets, for events passing the $M_W$ requirement, with $\Delta R<2$, and $\eta_d<1.0$ for both jets. The $t\bar{t}$ MC shape is obtained using the measured value of $f_{\rm Singlet}$.
• Figure 5: (Color online) Expected C.L. bands for $f_{\rm Singlet}$. The measured value is shown on the horizontal axis, and the input value on the vertical axis. The wide-dashed line shows the expected value and the black-white fine-dashed line indicates the measured value of $f_{\rm Singlet}$.