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Pierre Auger Collaboration(Abraham, J. et al), & Pastor, S. (2010). Measurement of the Depth of Maximum of Extensive Air Showers above 10(18) eV. Phys. Rev. Lett., 104(9), 091101–7pp.
Abstract: We describe the measurement of the depth of maximum, X-max, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10(18) eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +/- 35-21) g/cm(2)/decade below 10(18.24) +/- (0.05) eV, and d24 +/- 3 g/cm(2)/ecade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm(2). The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Hansen, C., Monfregola, L., et al. (2011). Indication of Electron Neutrino Appearance from an Accelerator-Produced Off-Axis Muon Neutrino Beam. Phys. Rev. Lett., 107(4), 041801–8pp.
Abstract: The T2K experiment observes indications of nu(mu) -> nu(mu) e appearance in data accumulated with 1.43 x 10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Delta m(23)(2)| = 2.4 x 10(-3) eV(2), sin(2)2 theta(23) = 1 and sin(2)2 theta(13) = 0, the expected number of such events is 1.5 +/- 0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7 x 10(-3), equivalent to 2.5 sigma significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2 theta(13) < 0.28(0.34) for delta(CP) = 0 and a normal (inverted) hierarchy.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2011). Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda(0)(b) -> Lambda mu(+)mu(-). Phys. Rev. Lett., 107(20), 201802–8pp.
Abstract: We report the first observation of the baryonic flavor-changing neutral current decay Lambda(0)(b) -> Lambda mu(+)mu(-) with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses a p (p) over bar collisions data sample corresponding to 6.8 fb(-1) at root s = 1.96 TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Lambda(0)(b) -> Lambda mu(+)mu(-) are measured. We find B(Lambda(0)(b) -> Lambda mu(+)mu(-)) = [1.73 +/- 0.42(stat) +/- (syst)] x 10(-6). We also report the first measurement of the differential branching ratio of B(s)(0) -> phi mu(+)mu(-), using 49 signal events. In addition, we report branching ratios for B(+) -> K(+)mu(+)mu(-), B(0) -> K(0)mu(+)mu(-), and B -> K*(892)mu(+)mu(-) decays.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2011). Search for a Very Light CP-Odd Higgs Boson in Top Quark Decays from p p-bar Collisions at sqrt(s)=1.96 TeV. Phys. Rev. Lett., 107(3), 031801–8pp.
Abstract: We present the results of a search for a very light CP-odd Higgs boson a(1)(0) originating from top quark decays t -> H(+/-)b -> W(+/-(*)) a(1)(0)b, and subsequently decaying into tau(+)tau(-). Using a data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected by the CDF II detector in p (p) over bar collisions at 1.96 TeV, we perform a search for events containing a lepton, three or more jets, and an additional isolated track with transverse momentum in the range 3 to 20 GeV/c. Observed events are consistent with background sources, and 95% C.L. limits are set on the branching ratio of t -> H(+/-)b for various masses of H(+/-) and a(1)(0).
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for New Physics with a Dijet Plus Missing E-T Signature in p(p)over-bar Collisions at root s=1.96 TeV. Phys. Rev. Lett., 105(13), 131801–8pp.
Abstract: We present results of a signature-based search for new physics using a dijet plus missing transverse energy (E-T) data sample collected in 2 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV with the CDF II detector at the Fermilab Tevatron. We observe no significant event excess with respect to the standard model prediction and extract a 95% C. L. upper limit on the cross section times acceptance for a potential contribution from a nonstandard model process. The search is made by using novel, data-driven techniques for estimating backgrounds that are applicable to first searches at the LHC.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Exclusion of an Exotic Top Quark with-4/3 Electric Charge Using Soft Lepton Tagging. Phys. Rev. Lett., 105(10), 101801–7pp.
Abstract: We present a measurement of the electric charge of the top quark using p (p) over bar collisions corresponding to an integrated luminosity of 2: 7 fb(-1) at the CDF II detector. We reconstruct t (t) over bar events in the lepton + jets final state. We use soft lepton taggers to determine the flavor of the b jets, which we use to reconstruct the top quark's electric charge and exclude an exotic top quark with -4/3 charge at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Measurement of the W+W- Production Cross Section and Search for Anomalous WW gamma and WWZ Couplings in p(p)over-bar Collisions at root s 1.96 TeV. Phys. Rev. Lett., 104(20), 201801–8pp.
Abstract: This Letter describes the current most precise measurement of the W boson pair production cross section and most sensitive test of anomalous WW gamma and WWZ couplings in p (p) over bar collisions at a center-of-mass energy of 1.96 TeV. The WW candidates are reconstructed from decays containing two charged leptons and two neutrinos. Using data collected by the CDF II detector from 3: 6 fb(-1) of integrated luminosity, a total of 654 candidate events are observed with an expected background of 320 +/- 47 events. The measured cross section is sigma(p (p) over bar -> W+W- +X) = 12.1 +/- 0.9(stat)(-1.4)(+1.6)(syst) pb, which is in good agreement with the standard model prediction. The same data sample is used to place constraints on anomalous WW gamma and WWZ couplings.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Measurement of the WW plus WZ Production Cross Section Using the lepton plus jets Final State at CDF II. Phys. Rev. Lett., 104(10), 101801–8pp.
Abstract: We report two complementary measurements of the WW + WZ cross section in the final state consisting of an electron or muon, missing transverse energy, and jets, performed using p (p) over bar collision data at root s = 1.96 TeV collected by the CDF II detector. The first method uses the dijet invariant mass distribution while the second more sensitive method uses matrix-element calculations. The result from the second method has a signal significance of 5.4 sigma and is the first observation of WW + WZ production using this signature. Combining the results gives sigma(WW+WZ) = 16.0 +/- 3.3 pb, in agreement with the standard model prediction.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for Supersymmetry with Gauge-Mediated Breaking in Diphoton Events with Missing Transverse Energy at CDF II. Phys. Rev. Lett., 104(1), 011801–8pp.
Abstract: We present the results of a search for supersymmetry with gauge-mediated breaking and (chi) over tilde (1)(0) -> gamma(G) over tilde in the gamma gamma + missing transverse energy final state. In 2.6 +/- 0.2 fb(-1) of p (p) over bar collisions at root s 1.96 TeV recorded by the CDF II detector we observe no candidate events, consistent with a standard model background expectation of 1.4 +/- 0.4 events. We set limits on the cross section at the 95% C.L. and place the world's best limit of 149 GeV/c(2) on the (chi) over tilde (1)(0) mass at tau((chi) over tilde 01) << 1 ns. We also exclude regions in the (chi) over tilde (1)(0) mass-lifetime plane for tau((chi) over tilde 01) less than or similar to 2 ns.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for R-Parity Violating Decays of Sneutrinos to e mu, μtau, and e tau Pairs in p(p)over-bar Collisions at root s=1.96 TeV. Phys. Rev. Lett., 105(19), 191801–7pp.
Abstract: We present a search for supersymmetric neutrino (nu) over tilde production using the Tevatron p (p) over bar collision data collected with the CDF II detector and corresponding to an integrated luminosity of 1 fb(-1). We focus on the scenarios predicted by the R-parity violating (RPV) supersymmetric models in which sneutrinos decay to two charged leptons of different flavor. With the data consistent with the standard model expectations, we set upper limits on sigma(p (p) over bar -> (nu) over tilde) BR((nu) over tilde -> e mu, μtau, e tau) and use these results to constrain the RPV couplings as a function of the sneutrino mass.
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