CDF Detector Research Articles

Higgs Boson Studies at the Tevatron

We present the combination of searches for the Standard Model Higgs boson at a center-of-mass energy of s=1.96 TeV, using the full Run 2 dataset collected with the CDF and D0 detectors at the Fermilab Tevatron collider. We also present combined measurements of Higgs Boson production cross sections, branching ratios, and couplings to fermions and bosons. Finally, we present tests of different spin and parity hypotheses for a particle H of mass 125 GeV produced in association with a vector boson and decaying into a pair of b quarks, and place constraints on such hypotheses using the D0 data.

Formula omitted] and MW(indirect) extracted from 9 fb−1μ+μ− event sample at CDF

We report on the extraction of sin2⁡θefflept and indirect measurement of the mass of the W boson from the forward-backward asymmetry of μ+μ− events in the Z boson mass region. The data sample collected by the CDF detector corresponds to the full 9 fb−1 run II sample. We measure sin2⁡θefflept=0.2315±0.0010, sin2θW=0.2233±0.0009 and MW(indirect)=80.365±0.047 GeV/c2, where each uncertainty includes both statistical and systematic contributions.

Combination of measurements of the top-quark pair production cross section from the Tevatron Collider

We combine six measurements of the inclusive top-quark pair (ttbar) production cross section (sigma_ttbar) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton anti-proton collisions at sqrt{s} = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb^{-1}. We obtain a value of sigma_ttbar = 7.60 \pm 0.41 pb for a top-quark mass of m_t=172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35^{+0.28}_{-0.33} pb at NNLO+NNLL in pertubative QCD.

Electroweak measurements from W, Z and photon final states

We present the most recent precision electroweak measurements of single W and Z boson cross section and properties from the LHC and Tevatron colliders, analyzing data collected by ATLAS, CDF, CMS, D0, and LHCb detectors. The results include the measurement of the single W and Z boson cross section at LHC, the differential cross section measurements, the measurement of W boson mass, the measurement of W and Z charge asymmetry. These measurements provide precision tests on the electroweak theory, high order predictions and the information can be used to constraint parton distribution functions.

Search forBs0→μ+μ−andB0→μ+μ−decays with the full CDF Run II data set

We report on a search for \bsmm\ and \bdmm\ decays using proton-antiproton collision data at $\sqrt{s}=1.96$ TeV corresponding to $10 \fb$ of integrated luminosity collected by the CDF detector at the Fermilab Tevatron collider. The observed number of \bd\ candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of $\brbdmm < 4.6\times 10^{-9}$ at 95% confidence level. We observe an excess of \bs\ 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 \bsmm\ could produce such an excess or larger is 6.8%. These data are used to determine a branching fraction $\brbsmm = (1.3^{+0.9}_{-0.7}) \times 10^{-8} $ and provide an upper limit of $\brbsmm < 3.1\times 10^{-8}$ at 95% confidence level.

Leptonic asymmetry in ${\rm{t\bar t}}$ production at CDF

The leptonic asymmetry in semileptonic ttbar decays is measured with the CDF detector using the full Tevatron Run II dataset, which corresponds to 9.4 fb^-1 of integrated luminosity. The measured asymmetry is extrapolated to the full kinematic range and the measured value of A_FB^lep = 0.094^+0.032_-0.029 is compared to the NLO prediction A_FB^lep = 0.038 +/- 0.003.

Top mass and properties at the LHC and Tevatron

An overview of the properties of the top quark measured with the ATLAS and CMS detectors at the LHC and with the CDF and D0 detectors at the Tevatron is presented. The latest and most precise measurements are shown, giving special emphasis to the top quark mass determinations. Measurements of the b -jet content in the top quark decay products and the W polarisation, as well as a search for flavour changing neutral current processes in top quark decays are also reviewed.

Tests of the standard electroweak model at the energy frontier

In this review, tests of standard electroweak (EW) theory at the highest available energies as a precursor to the Large Hadron Collider (LHC) era are summarized. The primary focus is on the published results (as of March 2010) from proton-antiproton collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ at the Fermilab Tevatron collected using the CDF and D0 detectors. After presenting an overview of the EW sector of the standard model, a summary of experimental tests of EW theory as of March 2010 is provided. These include gauge boson properties and self-couplings, tests of EW physics from the top-quark sector, and searches for the Higgs boson.

Search for the standard model Higgs boson produced in association with aW±boson with7.5 fb−1integrated luminosity at CDF

We present a search for the standard model Higgs boson produced in association with a $W^{\pm}$ boson. This search uses data corresponding to an integrated luminosity of 7.5 fb$^{-1}$ collected by the CDF detector at the Tevatron. We select $WH \to \ell\nu b \bar{b}$ candidate events with two jets, large missing transverse energy, and exactly one charged lepton. We further require that at least one jet be identified to originate from a bottom quark. Discrimination between the signal and the large background is achieved through the use of a Bayesian artificial neural network. The number of tagged events and their distributions are consistent with the standard model expectations. We observe no evidence for a Higgs boson signal and set 95% C.L. upper limits on the $WH$ production cross section times the branching ratio to decay to $b\bar b$ pairs, $\sigma(p\bar p \rightarrow W^{\pm} H) \times {\cal B}(H\rightarrow b\bar b)$, relative to the rate predicted by the standard model. For the Higgs boson mass range of 100 GeV/c$^2$ to 150 GeV/c$^2$ we set observed (expected) upper limits from 1.34 (1.83) to 38.8 (23.4). For 115 GeV/c$^2$ the upper limit is 3.64 (2.78). The combination of the present search with an independent analysis that selects events with three jets yields more stringent limits ranging from 1.12 (1.79) to 34.4 (21.6) in the same mass range. For 115 GeV/c$^2$ the upper limit is 2.65 (2.60).

The loss of light yield with time in the CDF II scintillation counters

The CDF II Muon System has an important role in the CDF detector (FNAL, USA), particularly with regard to the investigations of processes involving heavy quarks. JINR and INFN physicists ensured the efficient functioning of the scintillation counters of this system.In course of several years we carried out the light yield measurements, at the ends farthest from photomultiplier, of the various types of scintillation counters installed at CDF. On the basis of the results obtained, conclusions about the aging rate of the counters and the long-range projection of their efficiency during physics data taking at CDF RUN II were made.The observation period was up to 10 years.

Some top-quark properties measured in $$p\bar p$$ collisions using CDF detector at √s = 1.96 TeV (Review)

This review considers important properties of the top-quark. The top-quark decays before hadronization, and the spin information is directly transferred to the decay products. Therefore the structure of the weak interaction is investigated by measuring the helicity fractions, f, of the W boson—the top-quark decay product. Other investigations: search for the presence of V+A interaction, search for exotic top-quark charge — 4/3 and for $$t\bar t$$ — resonances—all of them, so far, were not found in the experiments — testifies against of going out of the Standard Model.

High Mass Standard Model Higgs searches at the Tevatron

We present the results of searches for the Standard Model Higgs boson decaying predominantly to WW pairs, at a center-of-mass energy of sqrt(s)=1.96 TeV, using up to 8.2 fb^{-1} of data collected with the CDF and D0 detectors at the Fermilab Tevatron collider. The analysis techniques and the various channels considered are discussed. These searches result in exclusions across the Higgs mass range of 156.5<mH<173.7 GeV for CDF and 161<mH<170 GeV for D0.

Effective axial-vector coupling of gluon as an explanation to the top quark asymmetry

We explore the possibility that the large $t\overline{t}$ forward-backward asymmetry measured by the CDF detector at Tevatron could be due to a universal effective axial-vector coupling of gluon. Using an effective field theory approach we show model independently how such a log-enhanced coupling occurs at 1-loop level. The interference with QCD gluon vector coupling naturally induces the observed positive forward-backward $t\overline{t}$ asymmetry that grows with $t\overline{t}$ invariant mass and is consistent with the cross section measurements. This scenario does not involve new flavor changing couplings nor operators that interfere with QCD, and, therefore, is not constrained by the LHC searches for 4-quark contact interactions. We predict top quark polarization effects that grow with energy and allow to test this scenario at the LHC. Our proposal offers a viable alternative to new physics scenarios that explain the $t\overline{t}$ forward-backward asymmetry anomaly with the interference between QCD and tree level new physics amplitudes.

Improved determination of the sample composition of dimuon events produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

We use a new method to estimate with 5% accuracy the contribution of pion and kaon in-flight-decays to the dimuon data set acquired with the CDF detector. Based on this improved estimate, we show that the total number and the properties of the collected dimuon events are not yet accounted for by ordinary sources of dimuons which also include the contributions, as measured in the data, of heavy flavor, $\Upsilon$, and Drell-Yan production in addition to muons mimicked by hadronic punchthrough.

Tevatron beam halo collimation system: design, operational experience and new methods11Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the US Department of Energy.

Collimation of proton and antiproton beams in the Tevatron collider is required to protect CDF and D0 detectors and minimize their background rates, to keep irradiation of superconducting magnets under control, to maintain long-term operational reliability, and to reduce the impact of beam-induced radiation on the environment. In this article we briefly describe the design, practical implementation and performance of the collider collimation system, methods to control transverse and longitudinal beam halo and two novel collimation techniques tested in theTevatron.

Limits on Anomalous Trilinear Gauge Couplings inZγEvents frompp¯Collisions ats=1.96 TeV

Using \Zg\ candidate events collected by the CDF detector at the Tevatron Colli\der, we search for potential anomalous (non-standard-model) couplings between t\he $Z$ boson and the photon. \Zg\ couplings vanish at tree level and are heavil\y suppressed at higher orders; hence any evidence of couplings indicates new ph\ysics. Measurements are performed using data corresponding to an integrated lum\inosity of 4.9 \invfb\ in the $Z \rightarrow \nu\bar{\nu}$ decay channel and 5.\1 \invfb\ in the \Zll\ ($l=\mu, e$) decay channels. The combination of these me\asurements provides the most stringent limits to date on \Zg\ trilinear gauge c\ouplings. Using an energy scale of $\Lambda = 1.5$\ TeV to allow for a direct c\omparison with previous measurements, we find limits on the CP-conserving param\eters that describe \Zg\ couplings to be $|h_3^{\gamma,Z}| < 0.022 $ and $|h_4^\{\gamma,Z}| < 0.0009$. These results are consistent with standard model predict\ions.

Invariant Mass Distribution of Jet Pairs Produced in Association with aWBoson inpp¯Collisions ats=1.96 TeV

We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb^-1. The observed distribution has an excess in the 120-160 GeV/c^2 mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this letter we report studies of the properties of this excess.

Search for High Mass Resonances Decaying to Muon Pairs ins=1.96 TeVpp¯Collisions

We present a search for a new narrow, spin-1, high mass resonance decaying to μ(+)μ⁻+X, using a matrix-element-based likelihood and a simultaneous measurement of the resonance mass and production rate. In data with 4.6 fb⁻¹ of integrated luminosity collected by the CDF detector in pp collisions at √s=1960 GeV, the most likely signal cross section is consistent with zero at 16% confidence level. We therefore do not observe evidence for a high mass resonance and place limits on models predicting spin-1 resonances, including M>1071 GeV/c² at 95% confidence level for a Z' boson with the same couplings to fermions as the Z boson.

Search for new color-octet vector particle decaying to [formula omitted] in [formula omitted] collisions at [formula omitted

We present the result of a search for a massive color-octet vector particle, (e.g. a massive gluon) decaying to a pair of top quarks in proton–antiproton collisions with a center-of-mass energy of 1.96 TeV. This search is based on 1.9 fb−1 of data collected using the CDF detector during Run II of the Tevatron at Fermilab. We study tt¯ events in the lepton+jets channel with at least one b-tagged jet. A massive gluon is characterized by its mass, decay width, and the strength of its coupling to quarks. These parameters are determined according to the observed invariant mass distribution of top quark pairs. We set limits on the massive gluon coupling strength for masses between 400 and 800 GeV/c2 and width-to-mass ratios between 0.05 and 0.50. The coupling strength of the hypothetical massive gluon to quarks is consistent with zero within the explored parameter space.

Measurement of the top quark mass in the dilepton channel usingmT2at CDF

We present measurements of the top quark mass using the \mT2, a variable related to the transverse mass in events with two missing particles. We use the template method applied to t\tbar dilepton events produced in p\pbar collisions at Fermilab's Tevatron and collected by the CDF detector. From a data sample corresponding to an integrated luminosity of 3.4 \invfb, we select 236 t\tbar candidate events. Using the \mT2 distribution, we measure the top quark mass to be M_{Top} = 168.0^{+4.8}_{-4.0} $\pm$ {2.9} GeV/c^{2}. By combining the \mT2 with the reconstructed top mass distributions based on a neutrino weighting method, we measure M_{top}=169.3 $\pm$ 2.7 $\pm$ 3.2 GeV/c^{2}. This is the first application of the \mT2 variable in a mass measurement at a hadron collider.