arXiv subjects

T. Aaltonen

Publications and source records attributed to T. Aaltonen.

At least 217 records · Page 12Linked to original sources

arXiv2008

Search for the Flavor Changing Neutral Current Decay t $\to Zq$ in $p \bar{p}$ Collisions at $\sqrt{s}=1.96$

We report a search for the flavor changing neutral current (FCNC) decay of the top quark \tZq ($q=u,c$) in \ppbar collisions at $\sqrt{s} = 1.96\tev$ using a data sample corresponding to an integrated luminosity of 1.9\invfb collected by the CDF II detector. This decay is strongly suppressed in the standard model (SM) and an observation of a signal at the Tevatron would be an indication of physics beyond the SM. Using $Z+\ge4$ jet final state candidate events, both with and without an identified bottom quark jet, we discriminate signal from background by exploiting kinematic constraints present in FCNC events and obtain an upper limit of $\btZq < 3.7%$ at 95% C.L.

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arXiv2008

Search for large extra dimensions in final states containing one photon or jet and large missing transverse energy produced in p-pbar collisions at sqrt(s) = 1.96 TeV

We present the results of searches for large extra dimensions in samples of events with large missing transverse energy and either a photon or a jet produced in p-pbar collisions at sqrt(s) = 1.96 TeV collected with the CDF II detector. For gamma + missing Et and jet + missing Et candidate samples corresponding to 2.0 fb^-1 and 1.1 fb^-1 of integrated luminosity respectively, we observe good agreement with standard model expectations and obtain a combined lower limit on the fundamental parameter of the large extra dimensions model, Md, as a function of the number of extra dimensions in the model.

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arXiv2008

Search for the Rare Decays B^+ -> mu^+ mu^- K^+, B^0 -> mu^+ mu^- K^*0(892), and B^0_s -> mu^+ mu^- phi at CDF

We search for b to sμ^+μ^- transitions in B meson (B^+, B^0, or B^0_s) decays with 924pb^{-1} of p pbar collisions at sqrt(s)=1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We find excesses with significances of 4.5, 2.9, and 2.4 standard deviations in the B^+ to μ^+μ^-K^+, B^0 to μ^+μ^-K^*(892)^0, and B_s^0 to μ^+μ^-ϕdecay modes, respectively. Using B to J/psi h (h = K^+, K^*(892)^0, phi) decays as normalization channels, we report branching fractions for the previously observed B^+ and B^0 decays, BR(B^+ to μ^+μ^-K^+)=(0.59\pm0.15\pm0.04) x 10^{-6}, and BR(B^0 to μ^+μ^-K^*(892)^0)=(0.81\pm0.30\pm0.10) x 10^{-6}, where the first uncertainty is statistical, and the second is systematic. These measurements are consistent with the world average results, and are competitive with the best available measurements. We set an upper limit on the relative branching fraction BR(B_s^0 to μ^+μ^-ϕ)/BR(B_s^0 to J/ψϕ) <2.6(2.3)\times10^{-3} at the 95(90)% confidence level, which is the most stringent to date.

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arXiv2008

First Measurement of the Fraction of Top Quark Pair Production Through Gluon-Gluon Fusion

We present the first measurement of the fraction of top quark pair production through gluon-gluon fusion. We use 0.96/fb of s**(1/2)=1.96 TeV p-pbar collision data recorded with the CDF II detector at Fermilab. We identify the candidate t-tbar events with a high-energy charged lepton, a neutrino candidate, and four or more jets. Using charged particles with low transverse momentum in t-tbar events, we find the fraction of top quark pair production through gluon-gluon fusion to be 0.07+/-0.14(stat)+/-0.07(syst), corresponding to a 95% confidence level upper limit of 0.33, in agreement with the standard model NLO prediction of 0.15+/-0.05.

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arXiv2008

Two-Particle Momentum Correlations in Jets Produced in ppbar Collisions at s**(1/2) = 1.96-TeV

We present the first measurement of two-particle momentum correlations in jets produced in $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV. Results are obtained for charged particles within a restricted cone with an opening angle of 0.5 radians around the jet axis and for events with dijet masses between 66 and 563 GeV/c$^{2}$. A comparison of the experimental data to theoretical predictions obtained for partons within the framework of resummed perturbative QCD in the next-to-leading log approximation (NLLA) shows that the parton momentum correlations survive the hadronization stage of jet fragmentation, giving further support to the hypothesis of local parton-hadron duality. The extracted value of the NLLA parton shower cutoff scale $Q_\mathit{eff}$ set equal to $Λ_\mathit{QCD}$ is found to be $(1.4^{+0.9}_{-0.7})\times 100$ MeV.

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arXiv2008

Measurement of Lifetime and Decay-Width Difference in B0s -> J/psi phi Decays

We measure the mean lifetime, tau=2/(Gamma_L+Gamma_H), and the width difference, DeltaGamma=Gamma_L-Gamma_H, of the light and heavy mass eigenstates of the B0s meson, B0sL and B0sH, in B0s -> J/psi phi decays using 1.7 fb^-1 of data collected with the CDF II detector at the Fermilab Tevatron ppbar collider. Assuming CP conservation, a good approximation for the B0s system in the Standard Model, we obtain DeltaGamma = 0.076^+0.059_-0.063 (stat.) +- 0.006 (syst.) ps^-1 and tau = 1.52 +- 0.04 (stat.) +- 0.02 (syst.) ps, the most precise measurements to date. Our constraints on the weak phase and DeltaGamma are consistent with CP conservation. Dedicated to the memory of our dear friend and colleague, Michael P. Schmidt

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arXiv2008

Search for Hadronic Decays of W and Z Bosons in Photon Events in ppbar Collisions at s**(1/2)=1.96 GeV

We report on a search for the process $p\bar{p}\to γ+W/Z$ with $W/Z\to q\bar{q}$ in events containing two jets and a photon at the center-of-mass energy $\sqrt{s}=1.96$ TeV, using 184 pb$^{-1}$ of data collected by the CDF II detector. A neural network event selection has been developed to optimize the rejection of the large QCD production background; it is shown that this method gives a significant improvement in both signal-to-noise ratio and signal sensitivity, as compared with an event selection based on conventional cuts. An upper limit is presented for the $γ+W/Z$ production cross section with the $W$ and $Z$ decaying hadronically.

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arXiv2008

Search for Bs --> mu+mu- and Bd --> mu+mu- Decays with 2fb-1 of ppbar Collisions

We have performed a search for Bs-->mu+mu- and Bd-->mu+mu- decays in ppbar collisions at sqrt(s) = 1.96TeV using 2fb-1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron Collider. The observed number of Bs and Bd candidates is consistent with background expectations. The resulting upper limits on the branching fractions are B(Bs-->mu+mu-) < 5.8X10^-8 and B(Bd-->mu+mu-) < 1.8X10^-8 at 95% C.L.

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arXiv2008

First Measurement of the Production of a W Boson in Association with a Single Charm Quark in Proton Anti-proton Collisions at sqrt(s)=1.96 TeV

We present the first measurement of the production cross section of a W boson with a single charm quark (c) in p-pbar collisions at sqrt(s)=1.96 TeV, using soft muon tagging of c jets. In a data sample of ~1.8 fb-1, recorded with the CDF II detector at the Fermilab Tevatron, we select events with W+1 or 2 jets. We use the charge correlation between the W and the muon from the semileptonic decay of a charm hadron to extract the Wc signal. We measure sigma_{Wc}(p_{Tc}>20 GeV/c, |η_c|<1.5)\times BR(W->\ellν) = 9.8+/-3.2 pb, in agreement with theoretical expectations.

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arXiv2008

Observation of Orbitally Excited B_s Mesons

We report the first observation of two narrow resonances consistent with states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed as B^+ \to J/ψK^+, J/ψ\to μ^+ μ^- or B^+ \to \bar{D}^0 π^+, \bar{D}^0 \to K^+ π^-. We deduce the masses of the two states to be m(B_{s1}) = 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.

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arXiv2008

Measurement of the cross section for W-boson production in association with jets in ppbar collisions at sqrt(s)=1.96 TeV

We present a measurement of the cross section for W-boson production in association with jets in pbar-p collisions at sqrt(s)=1.96 TeV. The analysis uses a data sample corresponding to an integrated luminosity of 320 pb^-1 collected with the CDF II detector. W bosons are identified in their electron decay channel and jets are reconstructed using a cone algorithm. For each W+>= n-jet sample (n= 1 - 4) we measure dsigma(ppbar =>W+>=n-jet)/dE_T^(nth-jet) x BR(W => e nu) with respect to the transverse energy E_T of the n^th-highest E_T jet above 20 GeV, and the total cross section sigma(ppbar =>W+>=n-jet; E_T^(nth-jet)>25 GeV) x BR(W => e nu), for a restricted W => e nu decay phase space. The cross sections, corrected for all detector effects, can be directly compared to particle level W+ jet(s) predictions. We present here comparisons to leading order and next-to-leading order predictions.

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arXiv2008

Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1 integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV recorded by the CDF II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are expected from standard model background processes. We place 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115 GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model prediction.

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arXiv2008

First Measurement of ZZ Production in ppbar Collisions at sqrt(s)=1.96 TeV

We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of llll and llnunu channels, we observe an excess of events with a probability of $5.1\times 10^{-6}$ to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation.

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arXiv2008

Search for Heavy Top-like Quarks t' -> Wq Using Lepton Plus Jets Events in 1.96 TeV Proton-Antiproton Collisions

We present the results of a search for pair production of a new heavy top-like quark t' decaying to a W boson and another quark using the CDF II detector in Run II of the Tevatron proton-antiproton collider. Using a data sample corresponding to 760 pb^-1 of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t' quark mass to a combination of standard model processes and t' pair production. We see no evidence for t' pair production, and we infer a lower limit of 256 GeV/c^2 on the mass of the t' at 95% C.L. assuming standard strong couplings for the t'.

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arXiv2008

Observation of Exclusive Dijet Production at the Fermilab Tevatron p-pbar Collider

We present the first observation and cross section measurement of exclusive dijet production in pbar-p interactions, pbar + p --> pbar + dijet + p. Using a data sample of 310 pb-1 collected by the Run II Collider Detector at Fermilab at sqrt{s}=1.96 TeV, exclusive cross sections for events with two jets of transverse energy ET >= 10 GeV have been measured as a function of minimum ET(jet). The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200 pb-1 of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the Jz=0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at sqrt{s}=14 TeV are discussed.

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arXiv2008

Search for chargino-neutralino production in p-pbar collisions at 1.96 TeV with high pT leptons

We present a search for the associated production of charginos and neutralinos in p-pbar collisions at 1.96 TeV. The data were collected at the Collider Detector at Fermilab (CDF II) and correspond to integrated luminosities between 0.7 and 1.0 fb-1. We look for final states with one high pT electron or muon, and two additional leptons. Our results are consistent with the standard model expectations, and we set limits on the cross section as a function of the chargino mass in three different supersymmetric scenarios. For a specific MSSM scenario with no slepton mixing we set a 95 % C.L. limit at 151 GeV/c^2.

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arXiv2007

A direct Measurement of the W Boson Width in ppbar Collisions at sqrt(s) = 1.96 TeV

A direct measurement of the total decay width of the W boson G_W is presented using 350 pb-1 of data from ppbar collisions at sqrt(s) = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. The width is determined by normalizing predicted signal and background distributions to 230185 W candidates decaying to enu and munu in the transverse-mass region 50 < M_T < 90 GeV and then fitting the predicted shape to 6055 events in the high-M_T region, 90 < M_T < 200 GeV. The result is G_W = 2032 +/- 45 (stat.) +/- 57 (syst.) MeV, consistent with the standard model expectation.

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arXiv2007

First Flavor-Tagged Determination of Bounds on Mixing-Induced CP Violation in Bs -> J/psi phi Decays

This Letter describes the first determination of bounds on the CP-violation parameter 2*beta_s using Bs decays in which the flavor of the bottom meson at production is identified. The result is based on approximately 2,000 Bs -> J/psi phi decays reconstructed in a 1.35 fb-1 data sample collected with the CDF II detector using p-bar p collisions produced at the Fermilab Tevatron. We report confidence regions in the two-dimensional space of 2*beta_s and the decay-width difference Delta-Gamma. Assuming the standard model predictions of 2*beta_s and Delta-Gamma, the probability of a deviation as large as the level of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations. Dedicated to the memory of our dear friend and colleague, Michael P. Schmidt.

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