We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs sigma(ppbar -> Z + X) Br(Z -> tau+ tau-) in proton-antiproton collisions at center of mass energy 1.96 TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos, and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 inverse fb collected with the D0 detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain sigma Br = 240 +/- 8 (stat) +/- 12 (sys) +/- 15 (lum) pb, which is consistent with the standard model prediction.
Measured cross section times branching ratio to TAU+ TAU-.
First measurements of the differential cross sections for the inclusive production of a photon in association with a heavy quark (c, b) jet are presented, covering photon transverse momenta 30-150 GeV, photon rapidities | y_gamma| < 1.0, jet rapidities |y_jet| < 0.8, and jet transverse momenta pT_jet > 15 GeV. The results are based on an integrated luminosity of 1 fb^-1 in ppbar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.
Differential cross section for (GAMMA BJET X) production in the region YRAP(GAMMA)*YRAP(JET) > 0.
Differential cross section for (GAMMA BJET X) production in the region YRAP(GAMMA)*YRAP(JET) < 0.
Differential cross section for (GAMMA CJET X) production in the region YRAP(GAMMA)*YRAP(JET) > 0.
We present a measurement of the shape of the boson rapidity distribution for $p\bar{p}\to Z / \gamma^* \to e^+e^- + X$ events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M_ee < 111 GeV and uses 0.4 $fb^{-1}$ of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of NNLO QCD are found to agree well with the data over the full rapidity range.
Normalized rapidity distribution.
Details of systematic errors.
We present a measurement of the fraction of inclusive $W$+jets events produced with net charm quantum number $\pm1$, denoted $W$+$c$-jet, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using approximately 1~fb$^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron Collider. We identify the $W$+jets events via the leptonic $W$ boson decays. Candidate $W$+$c$-jet events are selected by requiring a jet containing a muon in association with a reconstructed $W$ boson and exploiting the charge correlation between this muon and $W$ boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of $W$+$c$-jet events in the inclusive $W$+jets sample for jet $p_{T}>20$ GeV and pseudorapidity $|\eta|<2.5$ to be 0.074$\pm0.019$(stat.)$\pm^{0.012}_{0.014}$(syst.), in agreement with theoretical predictions. The probability that background fluctuations could produce the observed fraction of $W$+$c$-jet events is estimated to be $2.5\times 10^{-4}$, which corresponds to a 3.5 $\sigma$ statistical significance.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (E NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (MU NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (LEPTON NU) channel for various jet PT ranges.
We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.
Folded electron charged asymmetry.
We present measurements of the process $p\bar{p} \to WZ+X \to \ell^{\prime} \nu_{\ell^{\prime}} \ell \bar{\ell}$ at $\sqrt{s}=1.96$ TeV, where $\ell$ and $\ell^{\prime}$ are electrons or muons. Using 1 fb$^{-1}$ of data from the D0 experiment, we observe 13 candidates with an expected background of $4.5\pm0.6$ events and measure a cross section $\sigma(WZ)=2.7^{+1.7}_{-1.3}$ pb. From the number of observed events and the $Z$ boson transverse momentum distribution, we limit the trilinear $WWZ$ gauge couplings to $-0.17 \le \lambda_Z \le 0.21$ $(\Delta \kappa_Z = 0)$ at the 95% C.L. for a form factor scale $\Lambda=2$ TeV. Further, assuming that $\Delta g^Z_1 = \Delta\kappa_Z$, we find $-0.12 \le \Delta\kappa_Z \le 0.29$ $(\lambda_Z=0)$ at the 95% C.L. These are the most restrictive limits on the $WWZ$ couplings available to date.
Measured WZ cross section.
The cross section for the inclusive production of isolated photons has been measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV and have pseudorapidity |eta|<0.9. The cross section is compared with the results from two next-to-leading order perturbative QCD calculations. The theoretical predictions agree with the measurement within uncertainties.
Measured differential cross section for the production of isolated photons.
We study the process of associated photon and jet production, p+pbar --> photon + jet + X, using 8.7 fb^-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy sqrt{s}=1.96 TeV. Photons are reconstructed with rapidity |y^gamma| <1.0 or 1.5<|y^{gamma}| < 2.5 and transverse momentum pT^gamma GeV. The highest-p_T jet is required to be in one of four rapidity regions up to |y^{jet}|< 3.2. For each rapidity configuration we measure the differential cross sections in pT_gamma separately for events with the same sign (y^{gamma} y^{jet}}>0) and opposite sign (y^{gamma} y^{jet}<=0) of photon and jet rapidities. We compare the measured triple differential cross sections, d^3 sigma / d pT_gamma y^{gamma} y^{jet}, to next-to-leading order (NLO) perturbative QCD calculations using different sets of parton distribution functions and to predictions from the SHERPA and PYTHIA Monte Carlo event generators. The NLO calculations are found to be in general agreement with the data, but do not describe all kinematic regions.
The triple differential GAMMA+JET cross section for |y_gamma| < 1.0, |y_jet| <= 0.8 and y_gamma*y_jet > 0 A common 6.8% nomalization is included in the (sys) error.
The triple differential GAMMA+JET cross section for |y_gamma| < 1.0, |y_jet| 0.8 TO 1.6 and y_gamma*y_jet > 0 A common 6.8% nomalization is included in the (sys) error.
The triple differential GAMMA+JET cross section for |y_gamma| < 1.0, |y_jet| 1.6 TO 2.4 and y_gamma*y_jet > 0 A common 6.8% nomalization is included in the (sys) error.
We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb$^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle $\theta^*$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0 = 0.425 \pm 0.166 \hbox{(stat.)} \pm 0.102 \hbox{(syst.)}$ and the fraction of right-handed $W$ bosons $f_+ = 0.119 \pm 0.090 \hbox{(stat.)} \pm 0.053 \hbox{(syst.)}$, which is consistent at the 30% C.L. with the standard model.
COS(THETA*) distribution for leptonic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for hadronic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for W decay in dilepton events.. Data are read from plots and errors are statistcial (sqrt(N)).
Using 7.3 pb-1 of ppbar collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable \phistar, which probes the same physical effects as the Z/gamma* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the \phistar distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.
The measured PHI* distributions for the dielectron events corrected back to the particle level. The distributions are normalised to unity inidividually for each abs(yrap) bin and channel.
The measured PHI* distributions for the dimuon events corrected back to the particle level. The distributions are normalised to unity inidividually for each abs(yrap) bin and channel.