arXiv subjects

T. Aaltonen

Publications and source records attributed to T. Aaltonen.

At least 91 records · Page 5Linked to original sources

arXiv2012

A search for dark matter in events with one jet and missing transverse energy in pp-bar collisions at sqrt(s) = 1.96 TeV

We present the results of a search for dark matter production in the monojet signature. We analyze a sample of Tevatron pp-bar collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7/fb recorded by the CDF II detector. In events with large missing transverse energy and one energetic jet, we find good agreement between the standard model prediction and the observed data. We set 90% confidence level upper limits on the dark matter production rate. The limits are translated into bounds on nucleon-dark matter scattering rates which are competitive with current direct detection bounds on spin-independent interaction below a dark matter candidate mass of 5 GeV/c^2, and on spin-dependent interactions up to masses of 200 GeV/c^2.

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arXiv2012

Precise measurement of the W-boson mass with the CDF II detector

We have measured the W-boson mass MW using data corresponding to 2.2/fb of integrated luminosity collected in proton-antiproton collisions at 1.96 TeV with the CDF II detector at the Fermilab Tevatron collider. Samples consisting of 470126 W->enu candidates and 624708 W->munu candidates yield the measurement MW = 80387 +- 12 (stat) +- 15 (syst) = 80387 +- 19 MeV. This is the most precise measurement of the W-boson mass to date and significantly exceeds the precision of all previous measurements combined.

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arXiv2012

Combination of CDF and D0 measurements of the W boson helicity in top quark decays

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7 - 5.4 fb^-1 of ppbar collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0 = 0.722 \pm 0.081 [\pm 0.062 (stat.) \pm 0.052 (syst.)] and f+ = -0.033 \pm 0.046 [\pm 0.034 (stat.) \pm 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 \pm 0.057 [\pm 0.035 (stat.) \pm 0.046 (syst.)] and f+ = -0.015\pm0.035 [\pm 0.018 (stat.) \pm 0.030 (syst.)]. The results are consistent with standard model expectations.

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arXiv2012

Observation of Exclusive Gamma Gamma Production in p pbar Collisions at sqrt{s}=1.96 TeV

We have observed exclusive γγproduction in proton-antiproton collisions at \sqrt{s}=1.96 TeV, using data from 1.11 \pm 0.07 fb^{-1} integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E_T > 2.5 GeV and pseudorapidity |η| < 1.0, with no other particles detected in -7.4 < η< +7.4. The two showers have similar E_T and azimuthal angle separation Δϕ\sim π; 34 events have two charged particle tracks, consistent with the QED process p \bar{p} to p + e^+e^- + \bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive π^0π^0 is consistent with zero and is < 15 at 95% C.L. The cross section for p\bar{p} to p+γγ+\bar{p} with |η(γ)| < 1.0 and E_T(γ) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.

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arXiv2012

Measurements of Angular Distributions of Muons From Upsilon Meson Decays in p p-bar Collisions at sqrt(s)=1.96 TeV

The angular distributions of muons from Upsilon(1S,2S,3S) to mu+mu- decays are measured using data from proton anti-proton collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7 /fb and collected with the CDF II detector at the Fermilab Tevatron. This analysis is the first to report the full angular distributions as functions of transverse momentum pT for the Upsilon mesons in both the Collins-Soper and s-channel helicity frames. This is also the first measurement of spin alignment of Upsilon(3S) mesons. Within the kinematic range of Upsilon rapidity |y|<0.6 and pT up to 40 GeV/c, the angular distributions are found to be nearly isotropic.

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arXiv2012

Search for a low mass Standard Model Higgs boson in the tau-tau decay channel in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV

We report on a search for the standard model Higgs boson decaying into pairs of tau leptons in $p\bar{p}$ collisions produced by the Tevatron at $\sqrt{s}$ = 1.96 TeV. The analyzed data sample was recorded by the CDFII detector and corresponds to an integrated luminosity of 6.0 fb$^{-1}$. The search is performed in the final state with one tau decaying leptonically and the second one identified through its semi-hadronic decay.Since no significant excess is observed, a 95% credibility level upper limit on the production cross section times branching ratio to the tau-tau final state is set for hypothetical Higgs boson masses between 100 and 150 GeV/$c^2$. For a Higgs boson of 120 GeV/$c^2$ the observed (expected) limit is 14.6 (15.3) the predicted value.

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arXiv2012

Search for WZ+ZZ production with MET + jets with b enhancement at sqrt(s) = 1.96 TeV

Diboson production ($WW+WZ+ZZ$) has been observed at the Tevatron in hadronic decay modes dominated by the $WW$ process. This paper describes the measurement of the cross section of $WZ$ and $ZZ$ events in final states with large $\mett$ and using $b$-jet identification as a tool to suppress $WW$ contributions. Due to the limited energy resolution, we cannot distinguish between partially hadronic decays of $WZ$ and $ZZ$, and we measure the sum of these processes. The number of signal events is extracted using a simultaneous fit to the invariant mass distribution of the two jets for events with two $b$-jet candidates and events without two $b$-jet candidates. We measure a cross section $σ(p\bar{p}\to WZ,ZZ) = 5.8^{+3.6}_{-3.0}$ pb, in agreement with the standard model.

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arXiv2011

Search for a Higgs Boson in the Diphoton Final State in p-pbar Collisions at sqrt(s) = 1.96 TeV

A search for a narrow Higgs boson resonance in the diphoton mass spectrum is presented based on data corresponding to 7.0 fb^-1 of integrated luminosity from p-pbar collisions at sqrt(s) = 1.96 TeV collected by the CDF experiment. No evidence of such a resonance is observed, and upper limits are set on the cross section times branching ratio of the resonant state as a function of Higgs boson mass. The limits are interpreted in the context of the standard model and one fermiophobic benchmark model where the data exclude fermiophobic Higgs bosons with masses below 114 GeV/c^2 at a 95% Bayesian credibility level.

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arXiv2011

Measurement of the branching fraction ${\mathcal{B}}(Λ^0_b\rightarrow Λ^+_cπ^-π^+π^-)$ at CDF

We report an analysis of the $Λ^0_b\rightarrowΛ^+_cπ^-π^+π^-$ decay in a data sample collected by the CDF II detector at the Fermilab Tevatron corresponding to 2.4 fb$^{-1}$ of integrated luminosity. We reconstruct the currently largest samples of the decay modes $Λ^0_b\rightarrow Λ_c(2595)^+π^-$ (with $Λ_c(2595)^+\rightarrowΛ^+_cπ^+π^-$), $Λ^0_b\rightarrow Λ_c(2625)^+π^-$ (with $Λ_c(2625)^+\rightarrowΛ^+_cπ^+π^-$), $Λ^0_b\rightarrow Σ_c(2455)^{++}π^-π^-$ (with $Σ_c(2455)^{++}\rightarrowΛ^+_cπ^+$), and $Λ^0_b\rightarrow Σ_c(2455)^0π^+π^-$ (with $Σ_c(2455)^0\rightarrowΛ^+_c π^-$) and measure the branching fractions relative to the $Λ^0_b\rightarrowΛ^+_cπ^-$ branching fraction. We measure the ratio $\BR(Λ^0_b\rightarrow Λ^+_cπ^-π^+π^-) /\BR(Λ^0_b\rightarrow Λ^+_c π^-) = 3.04 \pm 0.33(\text{stat})^{+0.70}_{-0.55}(\text{syst})$ which is used to derive $\BR(Λ^0_b\rightarrow Λ^+_cπ^-π^+π^-)= (26.8^{+11.9}_{-11.2})\times10^{-3}$.

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arXiv2011

Measurement of ZZ production in leptonic final states at {\surd}s of 1.96 TeV at CDF

In this paper we present a precise measurement of the total ZZ production cross section in pp collisions at {\surd}s= 1.96 TeV, using data collected with the CDF II detector corresponding to an integrated luminosity of approximately 6 fb-1. The result is obtained by combining separate measurements in the four-charged (lll'l'), and two-charged-lepton and two-neutral-lepton (llvv) decay modes of the Z. The combined measured cross section for pp {\to} ZZ is 1.64^(+0.44)_(-0.38) pb. This is the most precise measurement of the ZZ production cross section in 1.96 TeV pp collisions to date.

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arXiv2011

Search for Standard Model Higgs Boson Production in Association with a W Boson at CDF

We present a search for the standard model Higgs boson production in association with a $W$ boson in proton-antiproton collisions ($p\bar{p}\rightarrow W^\pm H \rightarrow \ellνb\bar{b}$) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 2.7 fb$^{-1}$. We recorded this data with two kinds of triggers. The first kind required high-p$_T$ charged leptons and the second required both missing transverse energy and jets. The search selects events consistent with a signature of a single lepton ($e^\pm/μ^\pm$), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a jet probability tagging method. Kinematic information is fed in an artificial neural network to improve discrimination between signal and background. The search finds that both the observed number of events and the neural network output distributions are consistent with the standard model background expectations, and sets 95% confidence level upper limits on the production cross section times branching ratio. The limits are expressed as a ratio to the standard model production rate. The limits range from 3.6 (4.3 expected) to 61.1 (43.2 expected) for Higgs masses from 100 to 150 GeV/$c^{2}$, respectively.

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arXiv2011

Search for new phenomena in events with two $Z$ bosons and missing transverse momentum in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

We present a search for new phenomena in events with two reconstructed $Z$ bosons and large missing transverse momentum, sensitive to processes $p\bar{p}\rightarrow X_2X_2 \rightarrow Z Z X_1 X_1$, where $X_2$ is an unstable particle decaying as $X_2\rightarrow ZX_1$ and $X_1$ is undetected. The particles $X_1$ and $X_2$ may be, among other possibilities, fourth generation neutrinos or supersymmetric particles. We study the final state in which one $Z$ boson decays to two charged leptons and the second decays hadronically. In data corresponding to an integrated luminosity of 4.2 fb$^{-1}$ from proton-antiproton collisions recorded by the CDF II detector at the Tevatron, with center-of-mass energy of 1.96 TeV, we find agreement between data and standard-model backgrounds. We calculate 95% confidence level upper limits on the cross section of the process $p\bar{p}\rightarrow X_2X_2 \rightarrow Z Z X_1 X_1$ ranging from 50 fb to 1 pb, depending on the masses of $X_1$ and $X_2$.

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arXiv2011

Measurement of the CP-Violating Phase beta_s in B0s -> J/Psi Phi Decays with the CDF II Detector

We present a measurement of the \CP-violating parameter \betas using approximately 6500 $\BsJpsiPhi$ decays reconstructed with the CDF\,II detector in a sample of $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV corresponding to 5.2 fb$^{-1}$ integrated luminosity produced by the Tevatron Collider at Fermilab. We find the \CP-violating phase to be within the range $\betas \in [0.02, 0.52] \cup [1.08, 1.55]$ at 68% confidence level where the coverage property of the quoted interval is guaranteed using a frequentist statistical analysis. This result is in agreement with the standard model expectation at the level of about one Gaussian standard deviation. We consider the inclusion of a potential $S$-wave contribution to the $\Bs\to J/ψK^+K^-$ final state which is found to be negligible over the mass interval $1.009 < m(K^+K^-)<1.028 \gevcc$. Assuming the standard model prediction for the \CP-violating phase \betas, we find the \Bs decay width difference to be $\deltaG = 0.075 \pm 0.035\,\textrm{(stat)} \pm 0.006\,\textrm{(syst)} \ps$. We also present the most precise measurements of the \Bs mean lifetime $τ(\Bs) = 1.529 \pm 0.025\,\textrm{(stat)} \pm 0.012\,\textrm{(syst)}$ ps, the polarization fractions $|A_0(0)|^2 = 0.524 \pm 0.013\,\textrm{(stat)} \pm 0.015\,\textrm{(syst)}$ and $|A_{\parallel}(0)|^2 = 0.231 \pm 0.014\,\textrm{(stat)} \pm 0.015\,\textrm{(syst)}$, as well as the strong phase $δ_{\perp}= 2.95 \pm 0.64\,\textrm{(stat)} \pm 0.07\,\textrm{(syst)} \textrm{rad}$. In addition, we report an alternative Bayesian analysis that gives results consistent with the frequentist approach.

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arXiv2011

Measurement of CP--violating asymmetries in D0 --> pi+ pi- and D0 --> K+K- decays at CDF

We report on a measurement of CP-violating asymmetries (Acp) in the Cabibbo-suppressed D0 --> pi+ pi- and D0 --> K+K- decays reconstructed in a data sample corresponding to 5.9 fb-1 of integrated luminosity collected by the upgraded Collider Detector at Fermilab. We use the strong decay D*+ --> D0 pi+ to identify the flavor of the charmed meson at production and exploit CP-conserving strong c-cbar pair-production in p-pbar collisions. High-statistics samples of Cabibbo-favored D0 --> K- p+ decays with and without a D* tag are used to correct for instrumental effects and significantly reduce systematic uncertainties. We measure Acp(D0 --> pi+ pi-) = (+0.22 +- 0.24 (stat) +- 0.11 (syst))% and Acp(D 0 --> K+ K-) = (-0.24 +- 0.22 (stat) +- 0.09 (syst))%, in agreement with CP conservation. These are the most precise determinations from a single experiment to date. Under the assumption of negligible direct CP violation in D0 --> pi+ pi- and D0 --> K+K- decays, the results provide an upper limit to the CP-violating asymmetry in D0 mixing, |Acp^{ind}(D0)|< 0.13% at the 90% confidence level.

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arXiv2011

Search for New $T^\prime$ Particles in Final States with Large Jet Multiplicities and Missing Transverse Energy in ppbar Collisions at sqrt(s) = 1.96 TeV

We present a search for a new particle T' decaying to a top quark via T' -> t + X, where X goes undetected. We use a data sample corresponding to 5.7 fb-1 of integrated luminosity of ppbar collisions with sqrt{s} = 1.96 TeV, collected at Fermilab by the CDF II detector. Our search for pair production of T' is focused on the hadronic decay channel, ppbar -> T'T' -> tt +XX -> bbqqqq + XX. We interpret our results in terms of a model where T' is an exotic fourth generation quark and X is a dark matter candidate. The data are consistent with standard model expectations. We set a limit on the generic production of T'T'->tt+XX, excluding the fourth generation exotic quarks T' at 95% confidence level up to m_T' = 400 GeV/c2 for m_X < 70 GeV/c2.

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arXiv2011

Search for high-mass resonances decaying into ZZ in p$\bar{p}$ collisions at $\sqrt{s}=1.96$\,TeV

We search for high-mass resonances decaying into Z boson pairs using data corresponding to 6 fb^-1 collected by the CDF experiment in p\bar{p} collisions at sqrt{s}=1.96 TeV. The search is performed in three distinct final states: ZZ --> l^+l^-l^+l^-, ZZ --> l^+l^-νν, and ZZ --> l^+l^-jj. For a Randall-Sundrum graviton G*, the 95% CL upper limits on the production cross section times branching ratio to ZZ, sigma(p\bar{p} --> G^* --> ZZ), vary between 0.26 pb and 0.045 pb in the mass range 300 < M_{G*} < 1000 GeV/c^2.

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arXiv2011

Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-

We report the first observation of the baryonic flavor-changing neutral current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}. We also report the first measurement of the differential branching ratio of B_s -> phi mu+ mu- using 49 signal events. In addition, we report branching ratios for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.

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arXiv2011

Search for a Heavy Top-Like Quark in p\bar{p} Collisions at {\surd}s = 1.96 TeV

We present the results of a search for pair production of a heavy top-like (t') quark decaying to Wq final states using data corresponding to an integrated luminosity of 5.6 fb-1 collected by the CDF II detector in pp collisions at {\surd}s = 1.96 TeV. We perform parallel searches for t' \to Wb and t' \to Wq (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t quark mass, we set upper limits on the t \bar{t} production cross section and exclude a standard model fourth-generation t' quark decaying to W b (W q) with mass below 358 (340) GeV/c2 at 95% CL.

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