Measurement of color flow in $t\overline{t}$ events from $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present the first measurement of the color representation of the hadronically decaying $W$ boson in $t\overline{t}$ events, from $5.3{\mathrm{fb}}^{-1}$ 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 $0.56\pm 0.42(\mathrm{stat}+\mathrm{syst})$, in agreement with the standard model.

Figure 1

Diagram showing two jets in the $\eta$-$\varphi$ plane, and the reconstruction of the jet pull vectors ($\overrightarrow{t}$), jet pull angles (${\theta }^{\mathrm{pull}}$), and relative jet pull angles (${\theta }_{\mathrm{rel}}^{\mathrm{pull}}$).

Figure 2

The average of the two jet ${\theta }_{\mathrm{rel}}^{\mathrm{pull}}$ 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 ${\chi }^2$/number of degrees of freedom (ndf) compares the data to the total MC distribution.

Figure 3

(a) Leading-$p_T$ and (b) second-leading-$p_T$ jet ${\theta }_{\mathrm{rel}}^{\mathrm{pull}}$ distributions for $w$-pair jets, in events with two jets and no $b$-tagged jets. The ${\chi }^2/\mathrm{ndf}$ compares the data to the total MC distribution.

Figure 4

The discriminating color-flow variable, the minimum ${\theta }_{\mathrm{rel}}^{\mathrm{pull}}$ 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 $t\overline{t}$ MC shape is obtained using the measured value of $f_{\mathrm{Singlet}}$.

Figure 5

Expected C.L. bands for $f_{\mathrm{Singlet}}$. 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 $f_{\mathrm{Singlet}}$.