Measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using lepton plus jets events with semileptonic $B$ decays to muons

We present a measurement of the $t\overline{t}$ production cross section using $194{\mathrm{pb}}^{-1}$ of CDF II data using events with a high transverse momentum electron or muon, three or more jets, and missing transverse energy. The measurement assumes 100% $t\to Wb$ branching fraction. Events consistent with $t\overline{t}$ decay are found by identifying jets containing heavy-flavor semileptonic decays to muons. The dominant backgrounds are evaluated directly from the data. Based on 20 candidate events and an expected background of $9.5\pm 1.1$ events, we measure a production cross section of $5.3\pm {3.3}_{-1.0}^{+1.3}\mathrm{pb}$, in agreement with the standard model.

Figure 1

Elevation view of the CDF II detector.

Figure 2

$H_{\mathrm{T}}$ distributions, normalized to unity, for $t\overline{t}$ (solid line) and $W+\mathrm{\text{jets}}$ (dotted line) PYTHIA Monte Carlo events with three or more jets after the event selection described in the text.

Figure 3

Examples of muon matching distributions for the CMU in (left to right) drift direction, $x$, the longitudinal coordinate, $z$, and angle, ${\varphi }_L$. For each variable we show two $P_{\mathrm{T}}$ ranges, $2.5\le P_{\mathrm{T}}\le 3\mathrm{GeV}/c$ (wide distribution) and $5\le P_{\mathrm{T}}\le 6\mathrm{GeV}/c$ (narrow distribution). For the longitudinal coordinate $z$, we plot the product of $\mathrm{d}z$ by $\sin \theta$, which is the projection orthogonal to the direction of flight.

Figure 4

Width of the matching variable distributions ($\mathrm{d}x,\mathrm{d}z\sin \theta ,\mathrm{d}{\varphi }_L$) vs $P_{\mathrm{T}}$ for each of the muon chambers. The data points, from $J/\psi$, $W$ and $Z$ decays, are fit to the parametrizations described in the text.

Figure 5

Left: distribution of $L$ from $J/\psi$ decays. Right: the SLT efficiency as a function of the $|L|$ cut, as measured from $J/\psi$ decay.

Figure 6

$P_{\mathrm{T}}$ distribution of muons from $b$ hadron decays in PYTHIA Monte Carlo top events. The circles are all muons from $b$ hadron decays. The triangles are direct $B\to \mu \nu X$ decays and the squares are sequential $B\to D\to \mu \nu X$ (where “$B$” indicates a $b$ hadron).

Figure 7

Tag rates in the photon plus jets sample as a function of each of the tag-rate matrix parameters. Each plot is integrated over the two parameters not shown. The bottom right plot shows the tag rate as the function of the $|L|$ cut for each of the muon categories.

Figure 8

The percent difference between the number of predicted and measured tags in a variety of samples for different jet multiplicities, as marked. Jet multiplicities do not include the trigger object (photon or jet). The three photon points contain the events that make up the tag matrix. Their average is zero by definition and is shown by the line centered at zero. The dashed lines at $\pm 10\%$ indicate the systematic uncertainty as determined from these data.

Figure 9

Distribution of events with $\ge 1$ jet in ${\mathrm{E̸}}_T$ vs $I$. Regions A,B,C are defined in the text and are used to calculate the fraction of QCD events in region D (the signal region) according to Eq. (5).

Figure 10

The ratio of the number of observed tags to tags predicted using the tag matrix, as a function of ${\mathrm{E̸}}_T$, in events with at least one jet with measured energy above 20 GeV.

Figure 11

The ratio of the observed rate of tags to that predicted, as a function of $H_{\mathrm{T}}$ in region C for events with one or more jets. The arrow at 200 GeV shows where the selection cut for the $t\overline{t}$ signal sample is placed.

Figure 12

$F_{\mathrm{QCD}}$ measured according to Eq. (5) as a function of $H_{\mathrm{T}}$ in electron events (top) and muon events (bottom) with (left to right) 1, 2 or $\ge 3$ jets.

Figure 13

The SLT efficiency for $|\eta |<0.6$ (left) and $|\eta |\ge 0.6$ (right) as a function of $P_{\mathrm{T}}$, measured from $J/\psi$ and $Z$ data for $|L|<3.5$. The dotted lines are the $\pm 1\sigma$ statistical uncertainty on the fit which is used in the evaluation of the systematic uncertainty.

Figure 14

The expected background and observed tags in $W+1$, 2, 3 and 4 or more jet events. The background is corrected for the $t\overline{t}$ content of the pretag sample.

Figure 15

Comparison of the jet $E_{\mathrm{T}}$ distributions for tagged events and for expectations from fakes, QCD and $t\overline{t}$ events. The upper plot is for $W+1$ and 2 jet events and the lower plot for $W+\ge 3$ jet events.

Figure 16

$P_{\mathrm{T}}$ of the SLT tags. The upper plot is for $W+1$ and 2 jet events and the lower plot for $W+\ge 3$ jet events.

Figure 17

The impact parameter (d0) significance for tagged events, compared with expectations from backgrounds plus $t\overline{t}$. The upper plot is for $W+1$ and 2 jet events and the lower plot for $W+\ge 3$ jet events.