D0 Measurement Research Articles

Combined D0 measurements constraining theCP-violating phase and width difference in theBs0system

We combine the D0 measurement of the width difference between the light and heavy B-s(0) mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B-s(0)-> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B-s(0) lifetime, we obtain Delta Gamma(s)equivalent to(Gamma(L)-Gamma(H))=0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=0.70(-0.47)(+0.39) or Delta Gamma(s)=-0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=2.44(-0.39)(+0.47). The data sample corresponds to an integrated luminosity of 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron Collider.

Measurement of thett¯production cross section inpp¯collisions ats=1.96 TeVusing secondary vertexbtagging

We report a new measurement of the t{bar t} production cross section in p{bar p} collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using 425 pb{sup -1} of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the t{bar t} content of the sample by tagging b jets with a secondary vertex tagging algorithm, the t{bar t} production cross section is measured to be: {sigma}{sub p{bar p} {yields} t{bar t}+X} = 6.6 {+-} 0.9(stat + syst) {+-} 0.4(lum) pb. This cross section is the most precise D0 measurement to date for t{bar t} production and is in good agreement with standard model expectations.

Constraining the Phase ofBs−B¯sMixing

New physics contributions to B_s-\bar{B}_s mixing can be parametrized by the size (r_s^2) and the phase (2\theta_s) of the total mixing amplitude relative to the Standard Model amplitude. The phase has so far been unconstrained. We first use the D0 measurement of the semileptonic CP asymmetry A_SL to obtain the first constraint on the semileptonic CP asymmetry in B_s decays, A_SL^s=-0.008 \pm 0.011. Then we combine recent measurements by the CDF and D0 collaborations - the mass difference (\Delta M_s), the width difference (\Delta\Gamma_s) and A_SL^s - to constrain 2\theta_s. The errors on \Delta\Gamma_s and A_SL^s should still be reduced to have a sensitive probe of the phase, yet the central values are such that the regions around 2\theta_s ~ 3\pi/2 and, in particular, 2\theta_s ~ \pi/2, are disfavored.

Open charm production at STAR

We present the open charm spectra at mid-rapidity from direct reconstruction of D0, D* and D± in d+Au collisions at using the STAR detector at RHIC. The indirect electron/positron measurements via charm semileptonic decays in p+p and d+Au collisions are also reported. The total cross section per nucleon–nucleon collision is extracted from both direct and indirect measurements and are consistent with each other. By combining the D0 and semileptonic measurements together, the cross section of 1.4 ± 0.2 ± 0.4 mb is higher than expectations from PYTHIA and other pQCD calculations. The open charm pT distribution from direct measurements covers the pT range up to ∼10 GeV/c and follows a power-law distribution.

Combined fits to the supersymmetric explanation of anomalous lepton-γ-missing ET events

The CDF experiment reported a lepton–photon missing transverse energy (E/T) signal 3σ in excess of the Standard Model prediction in Tevatron Run I data. The excess can be explained by the resonant production of a smuon, which subsequently decays to a muon, a photon and a gravitino. Here, we perform combined fits of this model to the CDF γlE/T excess, the D0 measurement of the same channel and the CDF γE/T channel. Although the rates of the latter two analyses are in agreement with the Standard Model prediction, our model is in good agreement with these data because their signal to background efficiency is low at the best-fit point. However, they help to constrain the model away from the best-fit point.