Recent Results from Experiment D0

Brief summary of resent experimental results from experiment D0 at TEVATRON in FNAL.


B-physics
Several results in spectroscopy of hadrons from is coming from study of physics of b quark, which could be directly identified in 60% of events. We present a measurement of the semileptonic mixing asymmetry a = (Γ(Ā)−Γ(A))/(Γ(Ā)+Γ(A)) for B 0 mesons, a d sl . Using two independent decay channels: B 0 → μ + D + X, D → K + π − π − and B 0 → μ + D * + X, B 0 → μ + D * + X with D * →D 0 + π − ,D 0 → K + π − (and charge conjugate processes), we have determined the semileptonic mixing asymmetry for B 0 mesons, a d sl . We extract the charge asymmetries in these two channels as a function of the visible proper decay length (VPDL) of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal VPDL regions for each channel, yielding: a d sl = 0.68± 0.45 (stat.) ±0.14 (syst.) Combination of measurements of a d sl (D0 and existing world-average from B factories), a s sl , and the two impact-parameter-binned constraints from the same-charge dimuon asymmetry A b sl . The bands represent the ±1 standard deviation uncertainties on each measurement. The ellipses represent the 1, 2, 3, and 4 standard deviation twodimensional confidence level regions of the combination [1] in Fig.2.
We have measure the time-integrated flavor-specific semileptonic charge asymmetry in the decays of B 0 s mesons that have undergone flavor mixing, a s ls , using B 0 s (B 0 s ) → D ± s + μ + + X decays, with D ± s → φπ ± and φ → K + K − . of proton-antiproton collisions. A fit to the difference between the time-integrated D − s and D + s mass distributions of the B 0 s andB 0 s candidates yields the flavor-specific asymmetry a s ls = −1.08 ± 0.72(stat) ± 0.17(syst) which is the most precise measurement and in agreement with the standard model prediction. We have investigated the decay Fig.2.
From the study of the invariant mass and spin of the K + K − system, we find evidence for the two-body decay and measure the relative branching fraction of the decays to be [2] R f 2 /φ = 0.22 ± 0.05 (stat) ± 0.04 (syst). We measure the Λ 0 b lifetime in the fully reconstructed decay The lifetime of the topologically similar decay channel B 0 → J/ψK 0 S is also measured [4]. We obtain τ(Λ 0 b ) = 1.303 ± 0.075(stat.) ± 0.035(syst.)ps and τ(B 0 ) = 1.508 ± 0.025(stat.) ± 0.043(syst.)ps. Using these measurements, we determine the lifetime ratio of τ(Λ 0 b )/τ(B 0 ) = 0.864 ± 0.052(stat.) ± 0.033(syst.). We present a measurement of the relative branching fraction, Fig. 2. The J/ψ f 0 (980) final state corresponds to a CP-odd eigenstate of B 0 s that could be of interest in future studies of CP violation. With 8 f b −1 of data recorded with the D0 detector we find Using data corresponding to an integrated luminosity of 1.3 f b −1 , we observe a narrow mass state decaying into υ(1S ) + γ, where the υ(1S ) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551±0.014(stat.)±0.017(syst.)GeV/c 2 , which is consistent with that of the state recently observed by the ATLAS Collaboration Fig.3 [5].

Electroweek Interactions
Mass measurement of W mass combined from experiments CDF and D0 are in Fig. 4 [6].  We present a measurement of the W boson mass using data corresponding to 4.3 f b −1 of integrated luminosity collected with the D0 detector during Run II at the Fermilab Tevatron pp collider. With a sample of 1,677,394 decay W → e or μ candidate events, we measure M W = 80.367 ± 0.026GeV. This result is combined with an earlier D0 result determined using an independent Run II data sample, corresponding to 1 f b −1 of integrated luminosity, to yield M W = 80.375 ± 0.023GeV [7].
We study the processes pp → WZ → ν, + − and pp → ZZ → + − νν where = e or μ. Using 8.6 fb −1 of integrated luminosity. We measure the WZ production cross section to be 4.50 +0.63 −0.66 pb which is consistent with, but slightly above a prediction of the standard model. The ZZ cross section is measured to be 1.64 ± 0.46 pb, in agreement with a prediction of the standard model. Combination with an earlier analysis of the ZZ → + − + − channel yields a ZZ cross section of 1.44 +0.35 −0.34 pb [9]. We study WW and WZ production with lνqq (l = e, μ) final states using data corresponding to4.3 f b −1 of integrated luminosity. Assuming the ratio between the production cross sections σ(WW) and σ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to be σ(WV) = 19.6 +3.2 −3.0 pb, and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously fitting WW and WZ contributions, we measure σ(WW) = 15.9 +3.7 −3.2 pb and σ(WZ) = 3.3 +4.1 −3.3 pb, which is consistent with the standard model predictions [8]. We present a measurement of pp → Zγ → ll + γ, l = e, μ production with a data sample corresponding to an integrated luminosity of 6.2 f b −1 . The results of the electron and muon channels are combined, and we measure the total production cross section and the differential cross section dσ/dp γ T , where p γ T is the momentum of the photon in the plane transverse to the beamline Fig. 5. The results obtained are consistent with the standard model predictions from next-to-leading order calculations. We use the transverse momentum spectrum of the photon to place limits on anomalous ZZγ and Zγγ couplings [9]. We measure the cross section and the difference in rapidities between photons and charged leptons for inclusive W → lν + γ production in eγ and μγ final states. Using data corresponding to an integrated luminosity of 4.2 f b −1 , the cross section multiplied by the branching fraction for the process pp → Wγ + X → lνγ + X, measured to be 15.8 ± 0.8 (stat.) ±1.2(syst.) pb,  and the distribution of the charge-signed photon-lepton rapidity difference are found to be in agreement with the standard model. These results provide the most stringent limits on anomalous WWγ couplings for data from hadron colliders: −0.4 < Δκ γ < 0.4 and −0.08 < λ γ < 0.07 at the 95% C.L.

QCD Interactions
We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton  Figure 5. A comparison of the measured WW and WZ signals (filled histograms) to background-subtracted data (points) in the dijet mass distribution (summed over electron and muon channels) for 0, 1, and 2-tag sub-channels after the combined fit to data using the dijet mass distribution [9] (left). Unfolded dσ/dp γ p T distribution with no M llγ requirement for combined electron and muon data compared to the NLO prediction (right). distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance ΔR in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of !R and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 f b −1 . The results are well described by a perturbative QCD calculation in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50 to 400 GeV [10] Fig. 6.
We present measurements of the differential cross section dσ/dp T γ for the inclusive production of a photon in association with a b-quark jet for photons with rapidities |y γ | < 1.0 and 30 < p T γ < 300GeV, as well as for photons with 1.5 < |y γ | < 2.5 and 30 < p T γ < 200GeV, where p T γ is the photon transverse momentum Fig. 8. The b-quark jets are required to have pT > 15GeV and rapidity |y jet | < 1.5. The results are based on data corresponding to an integrated luminosity of 8.7 f b −1 . The measured cross sections are compared with next-to-leading order perturbative QCD calculations using different sets of parton distribution functions as well as to predictions based on the kT-factorization QCD approach, and those from the Sherpa and Pythia Monte Carlo event generators [11].
In special runs of D0 experiment with Proton Forward Detector we have meured elastic scattering of pp at √ (s) = 1.960T eV. Comparison with other experiments is displayed in Fig. refQCD-3ab [12]. We investigate the decay B 0 s → J/ψK + K − for invariant masses of the K + K − pair in the range 1.35 < M(K + K − ) < 2 GeV. The data sample corresponds to an integrated luminosity of 10.4 fb −1 of pp collisions at √ s = 1.96 TeV. From the study of the invariant mass and spin of the K + K − system, we find evidence for the two-body decay and measure the relative branching fraction of the decays to be R f 2 /φ = 0.22 ± 0.05 (stat) ± 0.04 (syst).

TOP quark Physics
The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the mass of its isospin partner, the bottom quark. It decays almost 100%. of the time to a W boson and a b quark. The summary of cross section production of tt is presented in Fig. 9, with final combination: σ tt = 7.65 ± 0.42pb.
We present a measurement of the top quark mass (m t ) in pp collisions at √ s = 1.96 TeV using tt events with two leptons (ee, eμ, or μμ) and accompanying jets in 4.3 f b −1 of data collected. We analyze the kinematically underconstrained dilepton events by integrating over their neutrino rapidity distributions. We reduce the dominant systematic uncertainties from the calibration of jet energy using a correction obtained from tt events with a final state of a single lepton plus jets. We also correct jets in simulated events to replicate the quark flavor dependence of the jet response in data. We measure m t = 173.7 ± 2.8 (stat) ± 1.5 (syst) GeV and combining with our analysis in 1 f b −1 of preceding data we measure m t = 174.0 ± 2.4 (stat) ± 1.4 (syst) GeV. Taking into account statistical and systematic correlations, a combination with the D0 matrix element result from both data sets yields m t = 173.9 ± 1.9 (stat) ± 1.6 (syst) GeV [13].
We measure lepton angular distributions in tt → W + b, W −b → l + νbl − . Using data corresponding to an integrated luminosity of 5.4 f b −1 , we find that the angular distributions of l − relative to antiprotons and l + relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A l FB = (11.8 ± 3.2) [14]. We present measurements of the tWb coupling form factors using information from electroweak single top quark production and from the helicity of W bosons from top quark decays in tt events Fig.  10 [15]. We set upper limits on anomalous tWb coupling.
Combining measurements that simultaneously determine the fractions of W bosons with longitudinal ( f 0 ) and right-handed ( f + ) helicities, we find   between correlated and uncorrelated top quark spin hypotheses, we define a discriminant R, which is displayed in Fig. 10 together with MC events with and without spin correlation as well as background. Data support the hypothesis with top-antitop spin correlation C = 0.85 ± 0.29 [17] which is in good agreement with the SM prediction.
The total width of top quark Γ t is extracted from the partial decay width Γ(t → Wb) and the branching fraction B(t → Wb). Γ(t → Wb) is obtained from the t-channel single top quark production cross section and B(t → Wb) is measured in tt events. For a top mass of 172.5 GeV, the resulting width is Γ t = 2.00 +0.47 −0.43 GeV. This translates to a top-quark lifetime of τ t = (3.29 +0.90 −0.63 ) × 10 −25 s [18]. We have also extract an improved direct limit on the CKM matrix element 0.81 < |V tb | ≤ 1 at 95% C.L. and a limit of |V tb | < 0.59 for a high mass fourth generation bottom quark assuming unitarity of the fourth generation quark mixing matrix. We searched for a narrow tt resonance that decays into a lepton+jets final state based on an integrated luminosity of 5.3 f b −1 of proton-antiproton collision. We set upper limits on the production cross section of such a resonance multiplied by its branching fraction to tt which we compare to predictions for a leptophobic topcolor Z boson. We exclude such a resonance at the 95% confidence level for masses below 835GeV Fig. 11 [19]. We present new direct constraints on a general Wtb interaction using data corresponding to an integrated luminosity of 5.4 f b −1 . The standard model provides a purely left-handed vector coupling at the Wtb vertex, while the most general, lowest dimension Lagrangian allows right-handed vector and left-or right-handed tensor couplings as well.
We obtain precise limits on these anomalous couplings by comparing the data to the expectations from different assumptions on the Wtb coupling [20].
We present measurements of production cross sections of single top quarks in pp collisions at √ (s) = 1.96T eV [21] in a data sample corresponding to an integrated luminosity of 5.4 f b −1 . We select events with an isolated electron or muon, an imbalance in transverse energy, and two, three, or four jets, with one or two of them containing a bottom hadron. We obtain an inclusive cross section of (pp → tb + X), σ(tqb + X) = 3.43 ± 0.73 0.74 pb and use it to extract the CKM matrix element 0.79 < |V tb | ≤ 1 at the 95% C.L. We also measure σ(pptb + X) = 0.68± 0.38 0.35 ; pb and σ(pptqb + X) = 2.86± 0.69 0.63 ; pb

HIGGS boson
We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair.
The data correspond to integrated luminosities of up to 9.7 f b −1 Fig. 12 [22]. The searches are conducted for a Higgs boson with mass in the range 100 -150 GeV. We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120and135GeV/c 2 . The largest local significance is 3.3 standard deviations, corresponding to a global significance of 3.1 standard deviations. We interpret this as evidence for the presence of a new particle consistent with the standard model Higgs boson, which is produced in association with a weak vector boson and decays to a bottom-antibottom quark pair [23].

New Phenomena
We present the first search for supersymmetry (SUSY) in Zγ final states with large missing transverse energy using data corresponding to an integrated luminosity of 6.2 f b −1 [24]. This signature is predicted in gauge-mediated SUSY-breaking models, where the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP) and is produced in pairs, possibly through decay from heavier supersymmetric particles. The NLSP can decay either to a Z boson or a photon and an associated gravitino that escapes detection. We exclude this model at the 95% C.L. for SUSY breaking scales of Λ < 87T eV, corresponding to neutralino masses of < 151GeV.
We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of 7.3 fb −1 [25]. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of R −1 > 260 GeV in a minimal UED model.  The Tevatron has finished data taking, but the analysis of data with full statistics of reconstructed events will still continue and new results will comme in the next year.