arXiv subjects

T. Aaltonen

Publications and source records attributed to T. Aaltonen.

At least 109 records · Page 6Linked to original sources

arXiv2011

Measurement of the Cross Section for Prompt Isolated Diphoton Production in p\bar p Collisions at \sqrt{s} = 1.96 TeV

This article reports a measurement of the production cross section of prompt isolated photon pairs in proton-antiproton collisions at \sqrt{s} = 1.96 TeV using the CDF II detector at the Fermilab Tevatron collider. The data correspond to an integrated luminosity of 5.36/fb. The cross section is presented as a function of kinematic variables sensitive to the reaction mechanisms. The results are compared with three perturbative QCD calculations: (1) a leading order parton shower Monte Carlo, (2) a fixed next-to-leading order calculation and (3) a next-to-leading order/next-to-next-to-leading-log resummed calculation. The comparisons show that, within their known limitations, all calculations predict the main features of the data, but no calculation adequately describes all aspects of the data.

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arXiv2011

Measurement of the Cross Section for Prompt Isolated Diphoton Production in p\bar p Collisions at \sqrt{s} = 1.96 TeV

This letter reports a measurement of the cross section of prompt isolated photon pair production in p\bar p collisions at a total energy \sqrt{s} = 1.96 TeV using data of 5.36/fb integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured cross section, differential in basic kinematic variables, is compared with three perturbative QCD predictions, a Leading Order (LO) parton shower calculation and two Next-to-Leading Order (NLO) calculations. The NLO calculations reproduce most aspects of the data. By including photon radiation from quarks before and after hard scattering, the parton shower prediction becomes competitive with the NLO predictions.

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arXiv2011

Measurement of the top-quark mass in the lepton+jets channel using a matrix element technique with the CDF II detector

A measurement of the top-quark mass is presented using Tevatron data from proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96$ TeV collected with the CDF II detector. Events are selected from a sample of candidates for production of $t\bar t$ pairs that decay into the lepton+jets channel. The top-quark mass is measured with an unbinned maximum likelihood method where the event probability density functions are calculated using signal and background matrix elements, as well as a set of parameterized jet-to-parton transfer functions. The likelihood function is maximized with respect to the top-quark mass, the signal fraction in the sample, and a correction to the jet energy scale (JES) calibration of the calorimeter jets. The simultaneous measurement of the JES correction ($\JES$) amounts to an additional \textit{in situ} jet energy calibration based on the known mass of the hadronically decaying $W$ boson. Using the data sample of 578 lepton+jets candidate events, corresponding to 3.2 $fb^{-1}$ of integrated luminosity, the top-quark mass is measured to be $m_t = \rm 172.4 \pm 1.4\:(stat+\JES) \pm 1.3\:(syst) GeV/{\it c}^2$.

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arXiv2011

Measurement of the Top Pair Production Cross Section in the Lepton + Jets Channel Using a Jet Flavor Discriminant

We present a new method to measure the top quark pair production cross section and the background rates with 2.7 fb$^{-1}$ of data from $p\bar{p}$ collisions at $\sqrt{s} =1.96$ TeV collected with the CDF II Detector. The size of the dataset was chosen to directly show the improvements of this new method. We select events with a single electron or muon, missing transverse energy, and at least one b-tagged jet. We perform a simultaneous fit to a jet flavor discriminant across nine samples defined by the number of jets and b-tags. We measure a top cross section of $σ_{t\bar{t}} = 7.64 \pm 0.57 \mathrm{(stat + syst)} \pm 0.45 \mathrm{(luminosity)}$ pb. An advantage of this approach is that many systematic uncertainties are measured in situ and inversely scale with integrated luminosity.

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arXiv2011

Measurement of branching ratio and Bs0 lifetime in the decay Bs0 -> J/psi f0(980) at CDF

We present a study of Bs0 decays to the CP-odd final state J/psi f0(980) with J/psi -> mu+ mu- and f0(980) -> pi+ pi-. Using ppbar collision data with an integrated luminosity of 3.8/fb collected by the CDF II detector at the Tevatron we measure a Bs0 lifetime of tau(Bs0 -> J/psi f0(980)) = 1.70 -0.11+0.12(stat) +-0.03(syst) ps. This is the first measurement of the Bs0 lifetime in a decay to a CP eigenstate and corresponds in the standard model to the lifetime of the heavy Bs0 eigenstate. We also measure the product of branching fractions of Bs0 -> J/psi f0(980) and f0(980) -> pi+ pi- relative to the product of branching fractions of Bs0 -> J/psi phi and phi -> K+ K- to be R_f0/phi = 0.257 +_0.020(stat) +-0.014(syst), which is the most precise determination of this quantity to date.

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arXiv2011

Measurements of the Angular Distributions in the Decays B -> K(*) mu+ mu- at CDF

We reconstruct the decays B -> K(*) mu+ mu- and measure their angular distributions in ppbar collisions at sqrt{s}=1.96TeV using a data sample corresponding to an integrated luminosity of 6.8fb-1. The transverse polarization asymmetry AT(2) and the time-reversal-odd charge-and-parity asymmetry Aim are measured for the first time, together with the K* longitudinal polarization fraction FL and the muon forward-backward asymmetry AFB, for the decays B0 -> K*0 mu+ mu- and B+ -> K*+ mu+ mu-. Our results are among the most accurate to date and consistent with those from other experiments.

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arXiv2011

Evidence for t\bar{t}γProduction and Measurement of σ_t\bar{t}γ/ σ_t\bar{t}

Using data corresponding to 6.0/fb of ppbar collisions at sqrt(s) = 1.96 TeV collected by the CDF II detector, we present a cross section measurement of top-quark pair production with an additional radiated photon. The events are selected by looking for a lepton, a photon, significant transverse momentum imbalance, large total transverse energy, and three or more jets, with at least one identified as containing a b quark. The ttbar+photon sample requires the photon to have 10 GeV or more of transverse energy, and to be in the central region. Using an event selection optimized for the ttbar+photon candidate sample we measure the production cross section of, and the ratio of cross sections of the two samples. Control samples in the dilepton+photon and lepton+photon+$\met$, channels are constructed to aid in decay product identification and background measurements. We observe 30 ttbar+photon candidate events compared to the standard model expectation of 26.9 +/- 3.4 events. We measure the ttbar+photon cross section to be 0.18+0.08 pb, and the ratio of the cross section of ttbar+photon to ttbar to be 0.024 +/- 0.009. Assuming no ttbar+photon production, we observe a probability of 0.0015 of the background events alone producing 30 events or more, corresponding to 3.0 standard deviations.

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arXiv2011

Observation of the Xi_b^0 Baryon

The observation of the bottom, strange baryon $Ξ^0_b$ through the decay chain $Ξ^0_b \rightarrow Ξ_c^+ \, π^-$, where $Ξ_c^+ \rightarrow Ξ^- \, π^+ \, π^+$, $Ξ^- \rightarrow Λ\, π^-$, and $Λ\rightarrow p \, π^-$, is reported using data corresponding to an integrated luminosity of 4.2 fb$^{-1}$ from $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV recorded with the Collider Detector at Fermilab. A signal of $25.3^{+5.6}_{-5.4}$ candidates is observed whose probability of arising from a background fluctuation is $3.6 \times 10^{-12}$, corresponding to 6.8 Gaussian standard deviations. The $Ξ^0_b$ mass is measured to be $5787.8\pm5.0(\textrm{stat})\pm1.3(\textrm{syst})$ MeV/$c^2$. In addition, the $Ξ^-_b$ baryon is observed through the process $Ξ^-_b \rightarrow Ξ_c^0 \, π^-$, where $Ξ_c^0 \rightarrow Ξ^-\, π^+$, $Ξ^- \rightarrow Λ\, π^-$, and $Λ\rightarrow p \, π^-$.

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arXiv2011

Improved $b$-jet Energy Correction for $H \to b\bar{b}$ Searches at CDF

We present a method for improving the $b$-jet energy resolution in order to improve the signal sensitivity in searches for particles decaying to a $b$ quark and anti-$b$ quark. A correction function is computed for individual jets, which combines information from the secondary vertex tagger, the offline tracking and standard calorimeter-based jet-energy reconstruction algorithm in order to provide a more accurate measurement of the true $b$-quark energy. We apply the correction to Monte-Carlo-simulated jets in the process $WH \rightarrow \ell νb\bar b$ and find an improvement in both the mean and the resolution of the $b$-jet energy with respect to the $b$-quark energy. The correction improves the measured Higgs dijet invariant mass resolution from $\sim$ 15%(standard jet corrections) to $\sim$ 11%(improved jet corrections) in the Higgs mass range from 100 GeV/$c^2$ - 150 GeV/$c^2$. Using the corrected $b$-jet energies instead of the standard calorimeter-based $b$-jet energies results in a $\sim$ 9% improvement in the expected sensitivity for Higgs boson production cross section in the most sensitive search region of the $WH \rightarrow \ell νb\bar b$ analysis, which is two tagged jets and one charged central lepton.

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arXiv2011

Limits on Anomalous Trilinear Gauge Couplings in Zgamma Events from ppbar Collisions at sqrt{s} = 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 $Z \rightarrow ν\barν$ decay channel and 5.\1 \invfb\ in the \Zll\ ($l=μ, e$) 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 $Λ= 1.5$\ 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^{γ,Z}| < 0.022 $ and $|h_4^\{γ,Z}| < 0.0009$. These results are consistent with standard model predict\ions.

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arXiv2011

Measurement of the ttbar production cross section in ppbar collisions at sqrt(s)=1.96 TeV using events with large missing transverse energy and jets

In this paper we report a measurement of the ttbar production cross section in ppbar collisions at sqrt(s)=1.96 TeV using data corresponding to an integrated luminosity of 2.2fb-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 ttbar 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 ttbar production cross section of 7.99 +/- 0.55(stat) +/- 0.76(syst) +/- 0.46(lumi) pb, assuming a top mass m_top = 172.5 GeV/c^2, in agreement with previous measurements and standard model predictions.

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arXiv2011

First Search for Multijet Resonances in $\sqrt{s} = 1.96$ TeV $ p\bar{p}$ Collisions

We present the first model independent search for three-jet hadronic resonances within multijet events in $\sqrt{s} = 1.96$ TeV $p\bar{p}$ collisions at the Fermilab Tevatron using the CDF II detector. Pair production of supersymmetric gluinos and squarks with hadronic R-parity violating decays is employed as an example of a new physics benchmark for this signature. Selection criteria based on the kinematic properties of an ensemble of jet combinations within each event help to extract signal from copious QCD background. Our background estimates include all-hadronic $t\bar{t}$ decays that have a signature similar to the signal. No significant excess outside the top quark mass window is observed in data with an integrated luminosity of 3.2 fb$^{-1}$. We place 95% confidence level limits on the production cross section $σ(p \bar{p} \rightarrow XX^{'}) \times \rm{BR}$($\widetilde{g}\widetilde{g}$$ \rightarrow 3 {\rm jet}+3 {\rm jet})$ where $X, X' = \widetilde{g}, \widetilde{q}$, or $\widetilde{\bar{q}}$, with $\widetilde{q}$, $\widetilde{\bar{q}} \rightarrow \widetilde{g}$ + jet, as a function of gluino mass, in the range of 77 GeV/$c^2$ to 240 GeV/$c^2$.

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arXiv2011

Search for New Dielectron Resonances and Randall-Sundrum Gravitons at the Collider Detector at Fermilab

A search for new dielectron mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7/fb is presented. No significant excess over the expected standard model prediction is observed. In this dataset, an event with the highest dielectron mass ever observed (960 GeV/c^2) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4/fb diphoton analysis, the RS-graviton lower mass limit for the coupling k/\bar{M}_{Pl}=0.1 is 1058 GeV/c^2, making it the strongest limit to date.

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arXiv2011

Search for New Heavy Particles Decaying to Z0 Z0 to llll, lljj in p pbar Collisions at Sqrt(s) = 1.96 TeV

We report on a search for anomalous production of Z boson pairs through a massive resonance decay in data corresponding to 2.5-2.9 fb^-1 of integrated luminosity in p pbar collisions at 1.96 TeV using the CDF II detector at the Fermilab Tevatron. This analysis, with more data and channels where the Z bosons decay to muons or jets, supersedes the 1.1 fb^-1 four-electron channel result previously published by CDF. In order to maintain high efficiency for muons, we use a new forward tracking algorithm and muon identification requirements optimized for these high signal-to-background channels. Predicting the dominant backgrounds in each channel entirely from sideband data samples, we observe four-body invariant mass spectra above 300 GeV/c^2 that are consistent with background. We set limits using the acceptance for a massive graviton resonance that are 7-20 times stronger than the previously published direct limits on resonant ZZ production.

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arXiv2011

Top quark mass measurement using the template method at CDF

We present a measurement of the top quark mass in the lepton+jets and dilepton channels of $t\bar{t}$ decays using the template method. The data sample corresponds to an integrated luminosity of 5.6 fb$^{-1}$ of $p\bar{p}$ collisions at Tevatron with $\sqrt{s}=1.96$ TeV, collected with the CDF II detector. The measurement is performed by constructing templates of three kinematic variables in the lepton+jets and two kinematic variables in the dilepton channel. The variables are two reconstructed top quark masses from different jets-to-quarks combinations and the invariant mass of two jets from the $W$ decay in the lepton+jets channel, and a reconstructed top quark mass and $m_{T2}$, a variable related to the transverse mass in events with two missing particles, in the dilepton channel. The simultaneous fit of the templates from signal and background events in the lepton+jets and dilepton channels to the data yields a measured top quark mass of $M_{top} = 172.1 \pm 1.1(stat) \pm 0.9(syst).$

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arXiv2011

First Measurement of the Angular Coefficients of Drell-Yan $e^{+}e^{-}$ pairs in the Z Mass Region from $p\bar{p}$ Collisions at $\sqrt{s}$ = 1.96 TeV

We report on the first measurement of the angular distributions of final state electrons in $p\bar{p}\to γ^{*}/Z\to e^{+}e^{-}+X$ events produced in the $Z$ boson mass region at $\sqrt{s}=1.96$ TeV. The data sample collected by the CDF II detector for this result corresponds to 2.1 fb$^{-1}$ of integrated luminosity. The angular distributions are studied as a function of the transverse momentum of the electron-positron pair and show good agreement with the Lam-Tung relation, consistent with a spin-1 description of the gluon, and demonstrate that at high values of the transverse momentum, $Z$ bosons are produced via quark anti-quark annihilation and quark-gluon Compton processes.

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arXiv2011

Measurement of the Forward-Backward Asymmetry in the B -> K(*) mu+ mu- Decay and First Observation of the Bs -> phi mu+ mu- Decay

We reconstruct the rare decays $B^+ \to K^+μ^+μ^-$, $B^0 \to K^{*}(892)^0μ^+μ^-$, and $B^0_s \to ϕ(1020)μ^+μ^-$ in a data sample corresponding to $4.4 {\rm fb^{-1}}$ collected in $p\bar{p}$ collisions at $\sqrt{s}=1.96 {\rm TeV}$ by the CDF II detector at the Fermilab Tevatron Collider. Using $121 \pm 16$ $B^+ \to K^+μ^+μ^-$ and $101 \pm 12$ $B^0 \to K^{*0}μ^+μ^-$ decays we report the branching ratios. In addition, we report the measurement of the differential branching ratio and the muon forward-backward asymmetry in the $B^+$ and $B^0$ decay modes, and the $K^{*0}$ longitudinal polarization in the $B^0$ decay mode with respect to the squared dimuon mass. These are consistent with the theoretical prediction from the standard model, and most recent determinations from other experiments and of comparable accuracy. We also report the first observation of the $B^0_s \to ϕμ^+μ^- decay and measure its branching ratio ${\mathcal{B}}(B^0_s \to ϕμ^+μ^-) = [1.44 \pm 0.33 \pm 0.46] \times 10^{-6}$ using $27 \pm 6$ signal events. This is currently the most rare $B^0_s$ decay observed.

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arXiv2011

Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in ppbar Collisions at sqrt(s) = 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.

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