arXiv subjects

T. Aaltonen

Publications and source records attributed to T. Aaltonen.

At least 73 records · Page 4Linked to original sources

arXiv2013

Search for Supersymmetry with Like-Sign Lepton-Tau Events at CDF

We present a search for chargino-neutralino associated production using like electric charge dilepton events collected by the CDF II detector at the Fermilab Tevatron in proton-antiproton collisions at $\sqrt{s} = 1.96$ TeV. One lepton is identified as the hadronic decay of a tau lepton, while the other is an electron or muon. In data corresponding to 6.0 fb$^{-1}$ of integrated luminosity, we obtain good agreement with standard model predictions, and set limits on the chargino-neutralino production cross section for simplified gravity- and gauge-mediated models. As an example, assuming that the chargino and neutralino decays to taus dominate, in the simplified gauge-mediated model we exclude cross sections greater than 300 fb at 95% credibility level for chargino and neutralino masses of 225 \gevcc. This analysis is the first to extend the LHC searches for electroweak supersymmetric production of gauginos to high $\tanβ$ and slepton next-to-lightest supersymmetric particle scenarios.

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arXiv2013

Combination of searches for the Higgs boson using the full CDF data set

We present a combination of searches for the standard model Higgs boson using the full CDF Run II data set, which corresponds to an integrated luminosity of 9.45--10.0 fb$^{-1}$ collected from $\sqrt{s}=1.96$ TeV $p{\bar{p}}$ collisions at the Fermilab Tevatron. The searches consider Higgs boson production from gluon-gluon fusion, vector-boson fusion, and associated production with either a $W$ or $Z$ boson or a $t{\bar{t}}$ pair. Depending on the production mode, Higgs boson decays to $W^+W^-$, $ZZ$, $b{\bar{b}}$, $τ^+τ^-$, and $γγ$ are examined. We search for a Higgs boson with masses ($m_H$) in the range 90--200 GeV/$c^2$. In the absence of a signal, we expect based on combined search sensitivity to exclude at the 95% credibility level the mass regions $90<m_H<94$ GeV/$c^2$, $96<m_H<106$ GeV/$c^2$, and $153<m_H<175$ GeV/$c^2$. The observed exclusion regions are $90<m_H<102$ GeV/$c^2$ and $149<m_H<172$ GeV/$c^2$. A moderate excess of signal-like events relative to the background expectation at the level of 2.0 standard deviations is present in the data for the $m_H=125$ GeV/$c^2$ search hypothesis. We also present interpretations of the data within the context of a fermiophobic model and an alternative standard model incorporating a fourth generation of fermions. Finally, for the hypothesis of a new particle with mass 125 GeV/$c^2$, we constrain the coupling strengths of the new particle to $W^\pm$ bosons, $Z$ bosons, and fermions.

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arXiv2013

Measurement of the top quark forward-backward production asymmetry and its dependence on event kinematic properties

We present new measurements of the inclusive forward-backward ttbar production asymmetry, AFB, and its dependence on several properties of the ttbar system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during ppbar collisions at sqrt(s) = 1.96 TeV, corresponding to an integrated luminosity of 9.4 fb^(-1). We measure the asymmetry using the rapidity difference Delta-y=y_(t)-y_(tbar). Parton-level results are derived, yielding an inclusive asymmetry of 0.164+/-0.047 (stat + syst). We observe a linear dependence of AFB on the top-quark pair mass M(ttbar) and the rapidity difference |Delta-y| at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are 7.4*10^(-3) and 2.2*10^(-3) for M(ttbar) and |Delta-y| respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the ttbar system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.

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arXiv2013

Measurement of the Mass Difference Between Top and Anti-top Quarks at CDF

We present a measurement of the mass difference between top ($t$) and anti-top ($\bar{t}$) quarks using $t\bar{t}$ candidate events reconstructed in the final state with one lepton and multiple jets. We use the full data set of Tevatron $\sqrt{s} = 1.96$ TeV proton-antiproton collisions recorded by the CDF II detector, corresponding to an integrated luminosity of 8.7 fb$^{-1}$. We estimate event-by-event the mass difference to construct templates for top-quark signal events and background events. The resulting mass difference distribution of data compared to signal and background templates using a likelihood fit yields $ΔM_{top} = {M}_{t} - {M}_{\bar{t}} = -1.95 $pm$ 1.11 (stat) $pm$ 0.59 (syst)$ and is in agreement with the standard model prediction of no mass difference.

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arXiv2013

Updated search for the standard model Higgs boson in events with jets and missing transverse energy using the full CDF data set

We present an updated search for the Higgs boson produced in association with a vector boson in the final state with missing transverse energy and two jets. We use the full CDF data set corresponding to an integrated luminosity of 9.45 fb${}^{-1}$ at a proton-antiproton center-of-mass energy of $\sqrt{s}=1.96$ TeV. New to this analysis is the inclusion of a $b$-jet identification algorithm specifically optimized for $H\to b\bar{b}$ searches. Across the Higgs boson mass range $90 \le m_H \le 150$ GeV$/c^2$, the expected 95% credibility level upper limits on the $V H$ production cross section times the $H\to b\bar{b}$ branching fraction are improved by an average of 14% relative to the previous analysis. At a Higgs boson mass of 125 GeV$/c^2$, the observed (expected) limit is 3.06 (3.33) times the standard model prediction, corresponding to one of the most sensitive searches to date in this final state.

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arXiv2012

Search for the Higgs boson in the all-hadronic final state using the full CDF data set

This paper reports the result of a search for the standard model Higgs boson in events containing four reconstructed jets associated with quarks. For masses below 135GeV/c2, Higgs boson decays to bottom-antibottom quark pairs are dominant and result primarily in two hadronic jets. An additional two jets can be produced in the hadronic decay of a W or Z boson produced in association with the Higgs boson, or from the incoming quarks that produced the Higgs boson through the vector-boson fusion process. The search is performed using a sample of \sqrt{s} = 1.96 TeV proton-antiproton collisions corresponding to an integrated luminosity of 9.45 fb-1 recorded by the CDF II detector. The data are in agreement with the background model and 95% credibility level upper limits on Higgs boson production are set as a function of the Higgs boson mass. The median expected (observed) limit for a 125GeV/c2 Higgs boson is 11.0 (9.0) times the predicted standard model rate.

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arXiv2012

Combination of the top-quark mass measurements from the Tevatron collider

The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the mass of its isospin partner, the bottom quark. It decays almost 100% of the time to a $W$ boson and a bottom quark. Using top-antitop pairs at the Tevatron proton-antiproton collider, the CDF and {\dzero} collaborations have measured the top quark's mass in different final states for integrated luminosities of up to 5.8 fb$^{-1}$. This paper reports on a combination of these measurements that results in a more precise value of the mass than any individual decay channel can provide. It describes the treatment of the systematic uncertainties and their correlations. The mass value determined is $173.18 \pm 0.56 \thinspace ({\rm stat}) \pm 0.75 \thinspace ({\rm syst})$ GeV or $173.18 \pm 0.94$ GeV, which has a precision of $\pm 0.54%$, making this the most precise determination of the top quark mass.

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arXiv2012

Search for Scalar Top Quark Production in p-pbar Collisions at sqrt(s)=1.96 TeV

We report on a search for the supersymmetric partner of the top quark (scalar top) decaying into a charm quark and a neutralino in p-pbar collisions at sqrt(s)=1.96 TeV. The data sample, collected by the CDFII detector at the Fermilab Tevatron, corresponds to an integrated luminosity of 2.6 fb-1. Candidate events are selected by requiring two or more jets and a large imbalance in the transverse momentum. To enhance the analysis sensitivity, at least one of the jets is required to be identified as originating from a charm quark using an algorithm specifically designed for this analysis. The selected events are in good agreement with standard model predictions. In the case of large mass splitting between the scalar top quark and the neutralino we exclude a scalar top quark mass below 180 GeV at 95% confidence level.

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arXiv2012

Measurement of CP-violation asymmetries in D0 to Ks pi+ pi-

We report a measurement of time-integrated CP-violation asymmetries in the resonant substructure of the three-body decay D0 to Ks pi+ pi- using CDF II data corresponding to 6.0 invfb of integrated luminosity from Tevatron ppbar collisions at sqrt(s) = 1.96 TeV. The charm mesons used in this analysis come from D*+(2010) to D0 pi+ and D*-(2010) to D0bar pi-, where the production flavor of the charm meson is determined by the charge of the accompanying pion. We apply a Dalitz-amplitude analysis for the description of the dynamic decay structure and use two complementary approaches, namely a full Dalitz-plot fit employing the isobar model for the contributing resonances and a model-independent bin-by-bin comparison of the D0 and D0bar Dalitz plots. We find no CP-violation effects and measure an asymmetry of ACP = (-0.05 +- 0.57 (stat) +- 0.54 (syst))% for the overall integrated CP-violation asymmetry, consistent with the standard model prediction.

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arXiv2012

Measurement of the Top Quark Mass in the All-Hadronic Mode at CDF

We present a measurement of the top quark mass (Mtop) in the all-hadronic decay channel using 5.8 fb^{-1} of proton-antiproton data collected with the CDF II detector at the Fermilab Tevatron Collider. Events with 6 to 8 jets are selected by a neural network algorithm and by the requirement that at least one of the jets is tagged as a b quark jet. The measurement is performed by a likelihood fit technique, which determines simultaneously Mtop and the jet energy scale (JES) calibration. The fit yields a value of 172.5 +- 1.4(stat) +-1.0(JES) +-1.1(syst) GeV/c^2.

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arXiv2012

Precision Top-Quark Mass Measurements at CDF

We present a precision measurement of the top-quark mass using the full sample of Tevatron $\sqrt{s}=1.96$ TeV proton-antiproton collisions collected by the CDF II detector, corresponding to an integrated luminosity of 8.7 $fb^{-1}$. Using a sample of $t\bar{t}$ candidate events decaying into the lepton+jets channel, we obtain distributions of the top-quark masses and the invariant mass of two jets from the $W$ boson decays from data. We then compare these distributions to templates derived from signal and background samples to extract the top-quark mass and the energy scale of the calorimeter jets with {\it in situ} calibration. The likelihood fit of the templates from signal and background events to the data yields the single most-precise measurement of the top-quark mass, $\mtop = 172.85 $\pm$ 0.71 (stat) $\pm$ 0.85 (syst) GeV/c^{2}.$

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arXiv2012

Measurement of the $WZ$ Cross Section and Triple Gauge Couplings in $p \bar p$ Collisions at $\sqrt{s} = 1.96$ TeV

This Letter describes the current most precise measurement of the $WZ$ production cross section as well as limits on anomalous $WWZ$ couplings at a center-of-mass energy of 1.96 TeV in proton-antiproton collisions for the Collider Detector at Fermilab (CDF). $WZ$ candidates are reconstructed from decays containing three charged leptons and missing energy from a neutrino, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector (7.1 fb$^{-1}$ of integrated luminosity), 63 candidate events are observed with the expected background contributing $8 \pm 1$ events. The measured total cross section $σ(p \bar p \to WZ) = 3.93_{-0.53}^{+0.60}(\text{stat})_{-0.46}^{+0.59}(\text{syst}) $ pb is in good agreement with the standard model prediction of $3.50\pm 0.21$. The same sample is used to set limits on anomalous $WWZ$ couplings.

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arXiv2012

An inclusive search for the Higgs boson in the four-lepton final state at CDF

An inclusive search for the standard model Higgs boson using the four-lepton final state in proton-antiproton collisions produced by the Tevatron at sqrt(s) = 1.96 TeV is conducted. The data are recorded by the CDF II detector and correspond to an integrated luminosity of 9.7 /fb. Three distinct Higgs decay modes, namely ZZ, WW, and tau-tau, are simultaneously probed. Nine potential signal events are selected and found to be consistent with the background expectation. We set a 95% credibility limit on the production cross section times the branching ratio and subsequent decay to the four lepton final state for hypothetical Higgs boson masses between 120 GeV/c^2 and 300 GeV/c^2.

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arXiv2012

Search for Standard Model Higgs Boson Production in Association with a W Boson Using a Matrix Element Technique at CDF in p-bar{p} Collisions at sqrt{s} = 1.96 TeV

This paper presents a search for standard model Higgs boson production in association with a $W$ boson using events recorded by the CDF experiment in a dataset corresponding to an integrated luminosity of 5.6 fb-1. The search is performed using a matrix element technique in which the signal and background hypotheses are used to create a powerful discriminator. The discriminant output distributions for signal and background are fit to the observed events using a binned likelihood approach to search for the Higgs boson signal. We find no evidence for a Higgs boson, and 95% confidence level (C.L.) upper limits are set on the Higgs boson production rate. The observed limits range from 3.5 to 37.6 relative to the standard model expectation for Higgs boson masses between 100 and 150 GeV. The 95% C.L. expected limit is estimated from the median of an ensemble of simulated experiments and varies between 2.9 and 32.7 relative to the production rate predicted by the standard model over the Higgs boson mass range studied.

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arXiv2012

Measurement of the masses and widths of the bottom baryons Sigma_b+- and Sigma_b*+-

Using data from proton - anti-proton collisions at the energy Ecm = 1.96 TeV recorded by the CDF II detector at the Fermilab Tevatron, we present improved measurements of the masses and first measurements of natural widths of the four bottom baryon resonance states Sigma_b+, Sigma_b*+ and Sigma_b-, Sigma_b*-. These states are fully reconstructed in their decay modes to Lambda_b pi+-, where Lambda_b -->Lambda_c+ pi- with Lambda_c+ -->prot K- pi+. The analysis is based on a data sample corresponding to an integrated luminosity of 6.0/fb collected by an online event selection based on tracks displaced from the proton - anti-proton interaction point.

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arXiv2012

Measurement of Bs0 --> Ds()+ Ds()- Branching Ratios

The decays Bs0 --> Ds(*)+ Ds(*)- are reconstructed in a data sample corresponding to an integrated luminosity of 6.8 fb-1 collected by the CDF II detector at the Tevatron p\bar{p} collider. All decay modes are observed with a significance of more than 10 sigma, and we measure the Bs0 production rate times Bs0 --> Ds(*)+ Ds(*)- branching ratios relative to the normalization mode B0 --> Ds+ D- to be $0.183 \pm 0.021 \pm 0.017$ for Bs0 --> Ds+ Ds-, $0.424 \pm 0.046 \pm 0.035$ for Bs0 --> Ds*+- Ds-+, $0.654 \pm 0.072 \pm 0.065$ for Bs0 --> Ds*+ Ds*-, and $1.261 \pm 0.095 \pm 0.112$ for the inclusive decay Bs0 --> Ds(*)+ Ds(*)-, where the uncertainties are statistical and systematic. These results are the most precise single measurements to date and provide important constraints for indirect searches for non-standard model physics in Bs0 mixing.

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arXiv2012

Search for anomalous production of multiple leptons in association with W and Z bosons at CDF

This paper presents a search for anomalous production of multiple low-energy leptons in association with a W or Z boson using events collected at the CDF experiment corresponding to 5.1 fb$^{-1}$ of integrated luminosity. This search is sensitive to a wide range of topologies with low-momentum leptons, including those with the leptons near one another. The observed rates of production of additional electrons and muons are compared with the standard model predictions. No indications of phenomena beyond the standard model are found. A 95% confidence level limit is presented on the production cross section for a benchmark model of supersymmetric hidden-valley Higgs production. Particle identification efficiencies are also provided to enable the calculation of limits on additional models.

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arXiv2012

Search for the Standard Model Higgs Boson Produced in Association with a $Z$ Boson in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV

We present a search for the standard model Higgs boson produced in association with a $Z$ boson, using up to 7.9 fb$^{-1}$ of integrated luminosity from $p\bar{p}$ collisions collected with the CDF II detector. We utilize several novel techniques, including multivariate lepton selection, multivariate trigger parametrization, and a multi-stage signal discriminant consisting of specialized functions trained to distinguish individual backgrounds. By increasing acceptance and enhancing signal discrimination, these techniques have significantly improved the sensitivity of the analysis above what was expected from a larger dataset alone. We observe no significant evidence for a signal, and we set limits on the $ZH$ production cross section. For a Higgs boson with mass 115 GeV/$c^2$, we expect (observe) a limit of 3.9 (4.8) times the standard model predicted value, at the 95% credibility level.

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