arXiv subjects

T. Aaltonen

Publications and source records attributed to T. Aaltonen.

At least 127 records · Page 7Linked to original sources

arXiv2011

Search for the Rare Radiative Decay: $W\rightarrowπγ$ in \ppbar\ Collisions at $\sqrt{s} = 1.96$ TeV

We present a search for the rare radiative decay \wpigamma\ using data corresponding to an integrated luminosity of 4.3 \invfb\ of proton-antiproton collisions at a center of mass energy of 1.96 TeV collected by the CDF experiment at Fermilab. As no statistically significant signal is observed, we set a 95% confidence level upper limit on the relative branching fraction \bratio\ at $6.4\times 10^{-5}$, a factor of 10 improvement over the previous limit.

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arXiv2011

Measurement of the Top Quark Mass in the Lepton+Jets Channel Using the Lepton Transverse Momentum

This letter reports a measurement of the top quark mass, M_{top}, in data from p-pbar collisions at sqrt{s} = 1.96 TeV corresponding to 2.7 fb^{-1} of integrated luminosity at the Fermilab Tevatron using the CDF II detector. Events with the lepton+jets topology are selected. An unbinned likelihood is constructed based on the dependence of the lepton transverse momentum, P_T, on M_{top}. A maximum likelihood fit to the data yields a measured mass M_{top} = (176.9 +/- 8.0 stat +/- 2.7 syst) GeV/c^2. In this measurement, the contribution by the jet energy scale uncertainty to the systematic error is negligible. The result provides an important consistency test for other M_{top} measurements where explicit use of the jet energy is made for deriving the top quark mass.

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arXiv2011

Measurements of Direct CP Violating Asymmetries in Charmless Decays of Strange Bottom Mesons and Bottom Baryons

We report measurements of direct CP-violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using a data sample corresponding to 1 fb-1 of integrated luminosity, we obtain the first measurements of direct CP violation in bottom strange mesons, A_CP(BsKpi) = +0.39 +- 0.15 stat +- 0.08 syst, and bottom baryons, A_CP(Lb->ppi) = +0.03 +- 0.17 stat +- 0.05 syst and A_CP(Lb->pK) = +0.37 +- 0.17 +- 0.03 syst. In addition, we measure CP violation in Bd-->Kpi decays with 3.5sigma significance, A_CP(B->Kpi) = -0.086 +- 0.023 stat +- 0.009 syst, in agreement with the current world average. Measurements of branching fractions of Bs-->K+K- and B0-->pi+pi- decays are also updated.

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arXiv2011

Measurement of Event Shapes in Proton-Antiproton Collisions at Center-of-Mass Energy 1.96 TeV

A study of event shape observables in proton-antiproton collisions at 1.96 TeV is presented. The data for this analysis were recorded by the CDF II detector at the Tevatron collider. The variables studied are the transverse thrust and thrust minor, both defined in the plane perpendicular to the beam direction. The observables are measured using energies from unclustered calorimeter cells. In addition to studies of the differential distributions, we present the dependence of event shape mean values on the leading jet transverse energy. Data are compared with pythia Tune A and to resummed parton level predictions that were matched to fixed order results at NLO accuracy (NLO+NLL). Predictions from pythia Tune A agree fairly well with the data. However, the underlying event contributes significantly to these observables, making it difficult to make direct comparisons to the NLO+NLL predictions, which do not account for the underlying event. To overcome this difficulty, we introduce a new observable, a weighted difference of the mean values of the thrust and thrust minor, which is less sensitive to the underlying event, allowing for a comparison with NLO+NLL. Both pythia Tune A and the NLO+NLL calculations agree well within the 20% theoretical uncertainty with the data for this observable, indicating that perturbative QCD successfully describes shapes of the hadronic final states.

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arXiv2011

Measurement of the mass difference between $t$ and $\bar{t}$ quarks

We present a direct measurement of the mass difference between $t$ and $\bar{t}$ quarks using $\ttbar$ candidate events in the lepton+jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron \ppbar Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of \invfb{5.6}, we measure a mass difference, $\dmt = \mathrm{M}_{t} - \mathrm{M}_{\bar{t}} = -3.3 \pm 1.4(stat) \pm 1.0(syst)}$, approximately two standard deviations away from the CPT hypothesis of zero mass difference. This is the most precise measurement of a mass difference between $t$ and its $\bar{t}$ partner to date.

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arXiv2011

Measurement of the $B^-$ lifetime using a simulation free approach for trigger bias correction

The collection of a large number of $B$ hadron decays to hadronic final states at the CDF II detector is possible due to the presence of a trigger that selects events based on track impact parameters. However, the nature of the selection requirements of the trigger introduces a large bias in the observed proper decay time distribution. A lifetime measurement must correct for this bias and the conventional approach has been to use a Monte Carlo simulation. The leading sources of systematic uncertainty in the conventional approach are due to differences between the data and the Monte Carlo simulation. In this paper we present an analytic method for bias correction without using simulation, thereby removing any uncertainty between data and simulation. This method is presented in the form of a measurement of the lifetime of the $B^{-}$ using the mode B -> D0 pi. The $B^-$ lifetime is measured as $τ_{B^-}$ = 1.663 $\pm$ 0.023 $\pm$ 0.015 ps, where the first uncertainty is statistical and the second systematic. This new method results in a smaller systematic uncertainty in comparison to methods that use simulation to correct for the trigger bias.

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arXiv2011

Observation of B0_s -> J/psi K*(892)0 and B0_s -> J/psi K0_S Decays

We report the first observation of two Cabibbo-suppressed decay modes of the B0_s meson. Using a sample of p-pbar collisions at sqrt{s}=1.96 TeV corresponding to 5.9 fb-1 of integrated luminosity collected with the CDFII detector at the Fermilab Tevatron, we search for new B0_s decay modes in a sample of events containing J/psi to mu+ mu- decays. We reconstruct a B0_s to J/psi K*(892)0 signal with K^*(892)0 to K+ pi-, observing a yield of 151 +/- 25 events with a statistical significance of 8.0 sigma. We also reconstruct a B0_s to J/psi K0_S signal with K0_S to pi+ pi-, observing a yield of 64 +/- 14 events with a statistical significance of 7.2 sigma. From these yields, we extract the branching ratios B(B0_s -> J/psi K*(892)0)= (8.3 +/- 3.8) x 10{-5} and B(B0_s -> J/psi K0)= (3.5 +/- 0.8) x 10{-5}, where statistical, systematic and fragmentation fraction uncertainties are included in the combined uncertainty.

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arXiv2011

Diffractive W and Z Production at the Fermilab Tevatron

We report on a measurement of the fraction of events with a W or Z boson which are produced diffractively in antiproton-proton collisions at a center of mass energy of 1.96 TeV, using data from 0.6 inverse femtobarns of integrated luminosity collected with the CDF-II detector equipped with a Roman-pot spectrometer that detects the antiproton (pbar) from pbar+p --> pbar+[X+W/Z]. We find that (1.00+/- 0.11)% of Ws and (0.88+/-0.22)% of Zs are produced diffractively in a region of antiproton or proton fractional momentum loss (ξ) of 0.03<ξ<0.10 and 4-momentum transferred squared t of -1 [X+W/Z]+p, by doubling the measured proton dissociation fraction. We also report on searches for W and Z production in double Pomeron exchange, p+pbar --> p+[X+W/Z]+pbar, and on exclusive Z production, pbar+p --> pbar+Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.

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arXiv2010

Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production

We present a new measurement of the inclusive forward-backward t-tbar production asymmetry and its rapidity and mass dependence. The measurements are performed with 5.3 fb^{-1} of p-pbar collisions at \sqrt{s} = 1.96 TeV, recorded with CDF II at the Fermilab Tevatron. Significant inclusive asymmetries are observed in the laboratory and t-tbar rest frame, and are consistent with CP conservation under interchange of t and tbar. In the t-tbar rest frame, the asymmetry increases with the t-tbar rapidity difference, Δ(y), and with the invariant mass M_{t-tbar} of the t-tbar system. Parton-level asymmetries are derived in two regions of each variable, and the asymmetry is found to be most significant at large Δ(y) and M_{t-tbar}. For M_{t-tbar} > 450 GeV/c^2, the parton-level asymmetry in the t-tbar rest frame is A^{t-tbar} = 0.475\pm 0.114 compared to a next-to-leading order QCD prediction of 0.088\pm 0.013.

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arXiv2010

Search for a New Heavy Gauge Boson Wprime with Electron + missing ET Event Signature in ppbar collisions at sqrt(s)=1.96 TeV

We present a search for a new heavy charged vector boson $W^\prime$ decaying to an electron-neutrino pair in $p\bar{p}$ collisions at a center-of-mass energy of $1.96\unit{TeV}$. The data were collected with the CDF II detector and correspond to an integrated luminosity of $5.3\unit{fb}^{-1}$. No significant excess above the standard model expectation is observed and we set upper limits on $σ\cdot{\cal B}(W^\prime\to eν)$. Assuming standard model couplings to fermions and the neutrino from the $W^\prime$ boson decay to be light, we exclude a $W^\prime$ boson with mass less than $1.12\unit{TeV/}c^2$ at the $95\unit{%}$ confidence level.

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arXiv2010

Search for Randall-Sundrum Gravitons in the Diphoton Channel at CDF

We report on a search for new particles in the diphoton channel using a data sample of $p\bar p$ collisions at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 5.4 fb$^{-1}$. The diphoton invariant mass spectrum of the data agrees well with the standard model expectation. We set upper limits on the production cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits on the graviton mass of 459 GeV$/c^{2}$ and 963 GeV$/c^{2}$, at the 95% confidence level, for coupling parameters ($k/\bar{M}_{Pl}$) of 0.01 and 0.1 respectively.

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arXiv2010

Observation of Single Top Quark Production and Measurement of |Vtb| with CDF

We report the observation of electroweak single top quark production in 3.2 fb-1 of ppbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3+0.6-0.5(stat+sys) pb, extract the CKM matrix element value |Vtb|=0.91+0.11-0.11 (stat+sys)+-0.07(theory), and set a lower limit |Vtb|>0.71 at the 95% confidence level, assuming m_t=175 GeVc^2.

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arXiv2010

Direct Top-Quark Width Measurement CDF

We present a measurement of the top-quark width using $t\bar{t}$ events produced in $p\bar{p}$ collisions at Fermilab's Tevatron collider and collected by the CDF II detector. In the mode where the top quark decays to a $W$ boson and a bottom quark, we select events in which one $W$ decays leptonically and the other hadronically~(lepton + jets channel) . From a data sample corresponding to 4.3~fb$^{-1}$ of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of $W$ boson that decays hadronically are reconstructed for each event and compared with templates of different top-quark widths~($Γ_t$) and deviations from nominal jet energy scale~($Δ_{JES}$) to perform a simultaneous fit for both parameters, where $Δ_{JES}$ is used for the {\it in situ} calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95$\%$ confidence level~(CL) of $Γ_t <$ 7.6 GeV and a two-sided 68$\%$ CL interval of 0.3 GeV $< Γ_t <$ 4.4 GeV for a top-quark mass of 172.5 GeV$/c^2$, which are consistant with the standard model prediction. This is the first direct measurement of $Γ_t$ to set a lower limit with 68$\%$ CL.

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arXiv2010

Measurement of the Top Pair Production Cross Section in the Dilepton Decay Channel in ppbar Collisions at sqrt s = 1.96 TeV

A measurement of the $\ttbar$ production cross section in $\ppbar$ collisions at $\sqrt{\rm s}$ = 1.96 TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II Detector. The result in a data sample corresponding to an integrated luminosity 2.8 fb$^{-1}$ is: $σ_{\ttbar}$ = 6.27 $\pm$ 0.73(stat) $\pm$ 0.63(syst) $\pm$ 0.39(lum) pb. for an assumed top mass of 175 GeV/$c^{2}$.

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arXiv2010

Improved Search for a Higgs Boson Produced in Association with Z->l+l- in proton antiproton Collisions at sqrt(s) = 1.96 TeV

We present a search for the standard model Higgs boson produced with a Z boson in 4.1 fb^-1 of data 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 times the H -> b bbar branching ratio. Improved analysis methods enhance signal sensitivity by 20% relative to previous searches beyond the gain due to the larger data sample. At a Higgs boson mass of 115 GeV/c^2 we set a limit of 5.9 times the standard model value.

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arXiv2010

Updated Search for the Flavor-Changing Neutral-Current Decay D^0 \to μ + μ-

We report on a search for the flavor-changing neutral-current decay D0 \to μ+ μ- in pp collisions at \surd s = 1.96 TeV using 360 pb-1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. A displaced vertex trigger selects long-lived D0 candidates in the μ+ μ-, π+π-, and K-π+ decay modes. We use the Cabibbo-favored D0 \to K-π+ channel to optimize the selection criteria in an unbiased manner, and the kinematically similar D0 \toπ+ π- channel for normalization. We set an upper limit on the branching fraction (D0 --> μ+ μ-) < 2.1 E-7 (3.0 E-7) at the 90% (95%) confidence level.

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arXiv2010

Measurement of the WW+WZ Production Cross Section Using a Matrix Element Technique in Lepton + Jets Events

We present a measurement of the $WW+WZ$ production cross section observed in a final state consisting of an identified electron or muon, two jets, and missing transverse energy. The measurement is carried out in a data sample corresponding to up to 4.6~fb$^{-1}$ of integrated luminosity at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector. Matrix element calculations are used to separate the diboson signal from the large backgrounds. The $WW+WZ$ cross section is measured to be $17.4\pm3.3$~pb, in agreement with standard model predictions. A fit to the dijet invariant mass spectrum yields a compatible cross section measurement.

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arXiv2010

First Measurement of the Ratio sigma_(t-tbar) / sigma_(Z/γ*->ll) and Precise Extraction of the t-tbar Cross Section

We report a measurement of the ratio of the top-antitop to Z/gamma* production cross sections in sqrt(s) = 1.96 TeV proton-antiproton collisions using data corresponding to an integrated luminosity of up to 4.6 fb-1, collected by the CDF II detector. The top-antitop cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma*->ll cross section, the extracted top-antitop cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result sigma_(top-antitop) = 7.70 +/- 0.52 pb, for a top-quark mass of 172.5 GeV/c^2.

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