David Hedin

We present a measurement of the fundamental parameter of the standard model, the weak mixing angle ${\sin }^2{\theta }_{\text{eff}}^{\ell }$ which determines the relative strength of weak and electromagnetic interactions, in $p\overline{p}\to Z/{\gamma }^{*}\to e^{+}{e}^{-}$ events at a center of mass energy of 1.96 TeV, using data corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron. The effective weak mixing angle is extracted from the forward-backward charge asymmetry as a function of the invariant mass around the $Z$ boson pole. The measured value of ${\sin }^2{\theta }_{\text{eff}}^{\ell }=0.23147\pm 0.00047$ is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.

We measure the mass of the top quark in $\text{lepton}+\text{jets}$ final states using the full sample of $p\overline{p}$ collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at $\sqrt{s}=1.96\mathrm{TeV}$, corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from $t\overline{t}$ production or background. The overall jet energy scale is constrained in situ by the mass of the $W$ boson. We measure $m_t=174.98\pm 0.76\mathrm{GeV}$. This constitutes the most precise single measurement of the top-quark mass.

Combined constraints from the CDF and D0 Collaborations on models of the Higgs boson with exotic spin $J$ and parity $P$ are presented and compared with results obtained assuming the standard model value $J^P=0^{+}$. Both collaborations analyzed approximately $10{\mathrm{fb}}^{-1}$ of proton-antiproton collisions with a center-of-mass energy of 1.96 TeV collected at the Fermilab Tevatron. Two models predicting exotic Higgs bosons with $J^P=0^{-}$ and $J^P=2^{+}$ are tested. The kinematic properties of exotic Higgs boson production in association with a vector boson differ from those predicted for the standard model Higgs boson. Upper limits at the 95% credibility level on the production rates of the exotic Higgs bosons, expressed as fractions of the standard model Higgs boson production rate, are set at 0.36 for both the $J^P=0^{-}$ hypothesis and the $J^P=2^{+}$ hypothesis. If the production rate times the branching ratio to a bottom-antibottom pair is the same as that predicted for the standard model Higgs boson, then the exotic bosons are excluded with significances of 5.0 standard deviations and 4.9 standard deviations for the $J^P=0^{-}$ and $J^P=2^{+}$ hypotheses, respectively.

We present a measurement of the distribution of the variable ${\varphi }_{\eta }^{*}$ for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of $10.4{\mathrm{fb}}^{-1}$ at $\sqrt{s}=1.96\mathrm{TeV}$. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ${\varphi }_{\eta }^{*}$ probes the same physical effects as the $Z/{\gamma }^{*}$ boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the ${\varphi }_{\eta }^{*}$ distributions for dilepton masses away from the $Z\to {\ell }^{+}{\ell }^{-}$ boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.

We measure the ratio of cross sections, $\sigma (p\overline{p}\to Z+2b\text{jets})/\sigma (p\overline{p}\to Z+2\text{jets})$, for associated production of a $Z$ boson with at least two jets with transverse momentum $p_T^{\text{jet}}>20\mathrm{GeV}$ and pseudorapidity $|{\eta }^{\text{jet}}|<2.5$. This measurement uses data corresponding to an integrated luminosity of $9.7{\mathrm{fb}}^{-1}$ collected by the D0 experiment in Run II of Fermilab’s Tevatron $p\overline{p}$ Collider at a center-of-mass energy of 1.96 TeV. The measured integrated ratio of $0.0236\pm 0.0032(\text{stat})\pm 0.0035(\text{syst})$ is in agreement with predictions from next-to-leading-order perturbative QCD and the Monte Carlo event generators pythia and alpgen.

We present a measurement of the electron charge asymmetry in $p\overline{p}\to W+X\to e\nu +X$ events at a center-of-mass energy of 1.96 TeV, using data corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron pseudorapidity and is presented in five kinematic bins based on the electron transverse energy and the missing transverse energy in the event. The measured asymmetry is compared with next-to-leading-order predictions in perturbative quantum chromodynamics and provides accurate information for the determination of parton distribution functions of the proton. This is the most precise lepton charge asymmetry measurement to date.

We present an updated measurement of the $B_s^0$ lifetime using the semileptonic decays $B_s^0\to D_s^{-}{\mu }^{+}\nu X$, with $D_s^{-}\to \varphi {\pi }^{-}$ and $\varphi \to K^{+}{K}^{-}$ (and the charge conjugate process). This measurement uses the full Tevatron Run II sample of proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$, comprising an integrated luminosity of $10.4{\mathrm{fb}}^{-1}$. We find a flavor-specific lifetime ${\tau }_{\mathrm{fs}}(B_s^0)=1.479\pm 0.010(\text{stat})\pm 0.021(\text{syst})\mathrm{ps}$. This technique is also used to determine the $B^0$ lifetime using the analogous $B^0\to D^{-}{\mu }^{+}\nu X$ decay with $D^{-}\to \varphi {\pi }^{-}$ and $\varphi \to K^{+}{K}^{-}$, yielding $\tau (B^0)=1.534\pm 0.019(\text{stat})\pm 0.021(\text{syst})\mathrm{ps}$. Both measurements are consistent with the current world averages, and the $B_s^0$ lifetime measurement is one of the most precise to date. Taking advantage of the cancellation of systematic uncertainties, we determine the lifetime ratio ${\tau }_{\mathrm{fs}}(B_s^0)/\tau (B^0)=0.964\pm 0.013(\text{stat})\pm 0.007(\text{syst})$.

We present a measurement of the forward-backward asymmetry in the production of $B^{\pm }$ mesons, $A_{\mathrm{FB}}(B^{\pm })$, using $B^{\pm }\to J/\psi K^{\pm }$ decays in $10.4{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., $b$ quark or $\overline{b}$ antiquark, to be produced in the direction of the proton beam. We extract $A_{\mathrm{FB}}(B^{\pm })$ from a maximum likelihood fit to the difference between the numbers of forward- and backward-produced $B^{\pm }$ mesons. We measure an asymmetry consistent with zero: $A_{\mathrm{FB}}(B^{\pm })=[-0.24\pm 0.41(\mathrm{stat})\pm 0.19(\mathrm{syst})]\%$.

We measure the direct $CP$-violating parameter $A_{CP}$ for the decay of the charged charm meson, $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ (and charge conjugate), using the full $10.4{\mathrm{fb}}^{-1}$ sample of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the D0 detector at the Fermilab Tevatron collider. We extract the raw reconstructed charge asymmetry by fitting the invariant mass distributions for the sum and difference of charge-specific samples. This quantity is then corrected for detector-related asymmetries using data-driven methods and for possible physics asymmetries (from $B\to D$ processes) using input from Monte Carlo simulation. We measure $A_{CP}=[-0.16\pm 0.15(\text{stat})\pm 0.09(\text{syst})]\%$, which is consistent with zero, as expected from the standard model prediction of $CP$ conservation, and is the most precise measurement of this quantity to date.