Search

We report on a search for $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ decays using proton-antiproton collision data at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $10{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of $B^0$ candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<4.6\times {10}^{-9}$ at 95% confidence level. We observe an excess of $B_s^0$ candidates. The probability that the background processes alone could produce such an excess or larger is 0.94%. The probability that the combination of background and the expected standard model rate of $B_s^0\to {\mu }^{+}{\mu }^{-}$ could produce such an excess or larger is 6.8%. These data are used to determine a branching fraction $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})=({1.3}_{-0.7}^{+0.9})\times {10}^{-8}$ and provide an upper limit of $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})<3.1\times {10}^{-8}$ at 95% confidence level.

This article presents a measurement of the top quark mass using the CDF II detector at Fermilab. Colliding beams of protons and antiprotons at Fermilab’s Tevatron ($\sqrt{s}=1.96\mathrm{TeV}$) produce top/antitop pairs, which decay to $W^{+}{W}^{-}b\overline{b}$; events are selected where one $W$ decays to hadrons and the other $W$ decays to either $e$ or $\mu$ plus a neutrino. The data sample corresponds to an integrated luminosity of approximately $318{\mathrm{pb}}^{-1}$. A total of 165 $t\overline{t}$ events are separated into four subsamples based on jet transverse energy thresholds and the number of $b$ jets identified by reconstructing a displaced vertex. In each event, the reconstructed top quark invariant mass is determined by minimizing a ${\chi }^2$ for the overconstrained kinematic system. At the same time, the mass of the hadronically decaying $W$ boson is measured in the same event sample. The observed $W$ boson mass provides an in situ improvement in the determination of the hadronic jet energy scale. A simultaneous likelihood fit of the reconstructed top quark masses and the $W$ boson invariant masses in the data sample to distributions from simulated signal and background events gives a top quark mass of ${173.5}_{-3.8}^{+3.9}\mathrm{GeV}/c^2$.

We present an improved measurement of $\mathrm{CP}$-violating asymmetries in $B^0\to {\pi }^{+}{\pi }^{-}$ decays based on a $78{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We reconstruct one neutral B meson as a $B^0\to {\pi }^{+}{\pi }^{-}$ $\mathrm{CP}$ eigenstate and identify the flavor of the accompanying B meson from inclusive properties of its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the $\mathrm{CP}$-violating asymmetry amplitudes ${\mathcal{A}}_{\pi \pi }=+0.77\mathrm{}\pm 0.27\left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)$ and ${\mathcal{S}}_{\pi \pi }=-1.23\pm 0.41\left(\mathrm{stat}\right){}_{-0.07}^{+0.08\mathrm{}}\left(\mathrm{syst}\right),$ where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for $\mathrm{CP}$-violating asymmetry parameters ${\mathcal{A}}_{\pi \pi }$ and ${\mathcal{S}}_{\pi \pi }$ based on a frequentist approach. We rule out the $\mathrm{CP}$-conserving case, ${\mathcal{A}}_{\pi \pi }={\mathcal{S}}_{\pi \pi }=0,$ at the $99.93\%$ confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle ${\phi }_2.$

We present the first observation and cross section measurement of exclusive dijet production in $\overline{p}p$ interactions, $\overline{p}p\to \overline{p}+\mathrm{dijet}+p$. Using a data sample of $310{\mathrm{pb}}^{-1}$ collected by the Run II Collider Detector at Fermilab at $\sqrt{s}=1.96\mathrm{TeV}$, exclusive cross sections for events with two jets of transverse energy $E_T^{\mathrm{jet}}\ge 10\mathrm{GeV}$ have been measured as a function of minimum $E_T^{\mathrm{jet}}$. The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of $200{\mathrm{pb}}^{-1}$ of $b$-tagged jet events, where exclusive dijet production is expected to be suppressed by the $J_z=0$ total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the $pp$ Large Hadron Collider at $\sqrt{s}=14\mathrm{TeV}$ are discussed.

We report on a search for the flavor-changing neutral-current decay $D^0\to {\mu }^{+}{\mu }^{-}$ in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using $360{\mathrm{pb}}^{-1}$ of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. A displaced vertex trigger selects long-lived $D^0$ candidates in the ${\mu }^{+}{\mu }^{-}$, ${\pi }^{+}{\pi }^{-}$, and $K^{-}{\pi }^{+}$ decay modes. We use the Cabibbo-favored $D^0\to K^{-}{\pi }^{+}$ channel to optimize the selection criteria in an unbiased manner, and the kinematically similar $D^0\to {\pi }^{+}{\pi }^{-}$ channel for normalization. We set an upper limit on the branching fraction $\mathcal{B}(D^0\to {\mu }^{+}{\mu }^{-})<2.1\times {10}^{-7}(3.0\times {10}^{-7})$ at the 90% (95%) confidence level.

We present a measurement of the ratio of the top-quark branching fractions $R=\mathcal{B}(t\to Wb)/\mathcal{B}(t\to Wq)$, where $q$ represents quarks of type $b$, $s$, or $d$, in the final state with a lepton and hadronic jets. The measurement uses $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collision data from $8.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the Collider Detector at Fermilab during Run II of the Tevatron. We simultaneously measure $R=0.94\pm 0.09$ ($\mathrm{stat}+\mathrm{syst}$) and the $t\overline{t}$ production cross section ${\sigma }_{t\overline{t}}=7.5\pm 1.0(\mathrm{stat}+\mathrm{syst})\mathrm{pb}$. The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element, $|V_{\mathrm{tb}}|=0.97\pm 0.05$ ($\mathrm{stat}+\mathrm{syst}$) is extracted assuming three generations of quarks, and a lower limit of $|V_{\mathrm{tb}}|>0.89$ at 95% credibility level is set.

The cross section for jets from $b$ quarks produced with a $W$ boson has been measured in $p\overline{p}$ collision data from $1.9{\mathrm{fb}}^{-1}$ of integrated luminosity recorded by the CDF II detector at the Tevatron. The $W+b$-jets process poses a significant background in measurements of top quark production and prominent searches for the Higgs boson. We measure a $b$-jet cross section of $2.74\pm 0.27(\mathrm{stat})\pm 0.42(\mathrm{syst})\mathrm{pb}$ in association with a single flavor of leptonic $W$ boson decay over a limited kinematic phase space. This measured result cannot be accommodated in several available theoretical predictions.

We present a search for the associated production of charginos and neutralinos in $\mathrm{p}\overline{\mathrm{p}}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The data were collected at the Collider Detector at Fermilab (CDF II) and correspond to integrated luminosities between 0.7 and $1.0{\mathrm{fb}}^{-1}$. We look for final states with one high-$p_{\mathrm{T}}$ electron or muon, and two additional leptons. Our results are consistent with the standard model expectations, and we set limits on the cross section as a function of the chargino mass in three different supersymmetric scenarios. For a specific minimal supersymmetric standard model scenario with no slepton mixing, we set a 95% C.L. limit at $151\mathrm{GeV}/c^2$.

We report on a search for the process $p\overline{p}\to \gamma +W/Z$ with $W/Z\to q\overline{q}$ in events containing two jets and a photon at the center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$, using $184{\mathrm{pb}}^{-1}$ of data collected by the CDF II detector. A neural network event selection has been developed to optimize the rejection of the large QCD production background; it is shown that this method gives a significant improvement in both signal-to-noise ratio and signal sensitivity, as compared with an event selection based on conventional cuts. An upper limit is presented for the $\gamma +W/Z$ production cross section with the $W$ and $Z$ decaying hadronically.

We report on the results of a search for standard model Higgs bosons produced in association with $W$ bosons from $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The search uses a data sample corresponding to approximately $1{\mathrm{fb}}^{-1}$ of integrated luminosity. Events consistent with the $W\to \ell \nu$ and $H\to b\overline{b}$ signature are selected by triggering on a high-$p_T$ electron or muon candidate and tagging one or two of the jet candidates as having originated from $b$ quarks. A neural network filter rejects a fraction of tagged charm and light-flavor jets, increasing the $b$-jet purity in the sample. We observe no excess $\ell \nu b\overline{b}$ production beyond the background expectation, and we set 95% confidence level upper limits on the production cross section times branching fraction $\sigma (p\overline{p}\to WH)\mathrm{Br}(H\to b\overline{b})$ ranging from 3.9 to 1.3 pb, for specific Higgs boson mass hypotheses in the range 110 to $150\mathrm{GeV}/c^2$, respectively.

We search for the standard model Higgs boson produced with a $Z$ boson in $4.1{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the CDF II detector at the Tevatron. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the $Z$ boson to electrons or muons, we set 95% credibility level upper limits on the $ZH$ production cross section multiplied by the $H\to b\overline{b}$ branching ratio. Improved analysis methods enhance signal sensitivity by 20% relative to previous searches. At a Higgs boson mass of $115\mathrm{GeV}/c^2$ we set a limit of 5.9 times the standard model cross section.

We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from $2.5{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the Collider Detector at Fermilab at $\sqrt{s}=1.96\mathrm{TeV}$. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a $b$ quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to bottom squarks. This result constrains the gluino-pair-production cross section to be less than 40 fb at 95% credibility level for a gluino mass of $350\mathrm{GeV}/c^2$.

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a $b$ quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and $150\mathrm{GeV}/c^2$. For a Higgs boson mass of $125\mathrm{GeV}/c^2$, the observed (expected) limit is 6.7 (3.6) times the standard model prediction.

In this paper we report a measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using data corresponding to an integrated luminosity of $2.2{\mathrm{fb}}^{-1}$ collected with the CDF II detector at the Tevatron accelerator. We select events with significant missing transverse energy and high jet multiplicity. This measurement vetoes the presence of explicitly identified electrons and muons, thus enhancing the tau contribution of $t\overline{t}$ decays. Signal events are discriminated from the background using a neural network, and heavy flavor jets are identified by a secondary-vertex tagging algorithm. We measure a $t\overline{t}$ production cross section of $7.99\pm 0.55(\mathrm{stat})\pm 0.76(\mathrm{syst})\pm 0.46(\mathrm{lumi})$ pb, assuming a top mass $m_{\mathrm{top}}=172.5\mathrm{GeV}/c^2$, in agreement with previous measurements and standard model predictions.

We present a measurement of $CP$-violating asymmetries in $B^0\to {\pi }^{+}{\pi }^{-}$ decays based on a $41.8{\mathrm{f}\mathrm{b}}^{-1}$ data sample collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We fully reconstruct one neutral $B$ meson as a $B^0\to {\pi }^{+}{\pi }^{-}$ $CP$ eigenstate and identify the flavor of the accompanying $B$ meson from its decay products. From the asymmetry in the distribution of the time intervals between the two $B$ meson decay points, we obtain the $CP$-violating asymmetry parameters ${\mathcal{S}}_{\pi \pi }=-{1.21}_{-0.27}^{+0.38}(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}{)}_{-0.13}^{+0.16}(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$ and ${\mathcal{A}}_{\pi \pi }=+{0.94}_{-0.31}^{+0.25}(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.09(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$.

We report the results of a study of two-body B meson decays to the complete set of $K\pi ,$ $\pi \pi ,$ and $K\overline{K}$ final states. The study is performed on a data sample of $31.7\pm 0.3$ million $B\overline{B}$ events recorded on the ${\rm Y}\left(4\mathrm{}\mathrm{S}\right)$ resonance by the Belle experiment at KEKB. We observe significant signals in all $K\pi$ final states and in the ${\pi }^{+}{\pi }^{-}$ and ${\pi }^{+}{\pi }^0$ final states. We set limits on the ${\pi }^0{\pi }^0$ and $K\overline{K}$ final states. A search is performed for partial-rate asymmetries between conjugate states for flavor-specific final states.

We report a measurement of the $t\overline{t}$ production cross section using the CDF II detector at the Fermilab Tevatron. The data consist of events with an energetic electron or muon, missing transverse energy, and three or more hadronic jets, at least one of which is identified as a $b$-quark jet by reconstructing a secondary vertex. The background fraction is determined from a fit of the transverse energy of the leading jet. Using $162\pm 10{\mathrm{pb}}^{-1}$ of data, the total cross section is found to be $6.0\pm 1.6(\mathrm{stat}.)\pm 1.2(\mathrm{syst}.)\mathrm{pb}$, which is consistent with the standard model prediction.