Showing papers by "M. J. Shochet published in 2010"

The ATLAS Simulation Infrastructure

Abstract: The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for large-scale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.

Observation of a centrality-dependent dijet asymmetry in lead-lead collisions at √sNN=2.76 Tev with the ATLAS detector at the LHC

Abstract: By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

Readiness of the ATLAS Tile Calorimeter for LHC collisions.

Abstract: The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector has successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems’ precision is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.

The ATLAS Inner Detector commissioning and calibration

Abstract: The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 +/- 0.9 mu m and a relative momentum resolution sigma (p) /p=(4.83 +/- 0.16)x10(-4) GeV(-1)xp (T) have been measured for high momentum tracks.

Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the ATLAS Detector at the LHC

Abstract: A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated luminosity of 315 nb(-1) collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% C. L. the q* mass interval 0: 30< m(q)*< 1:26 TeV, extending the reach of previous experiments.

Measurement of the W → ℓν and Z/γ* → ℓℓ production cross sections in proton-proton collisions at √ s = 7 TeV with the ATLAS detector

Abstract: First measurements of the W -> lnu and Z/gamma* -> ll (l = e, mu) production cross sections in proton-proton collisions at sqrt(s) = 7 TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W -> lnu and 179 Z/gamma* -> ll candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb-1. The measured total W and Z/gamma*-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are $\stotW$ * BR(W -> lnu) = 9.96 +- 0.23(stat) +- 0.50(syst) +- 1.10(lumi) nb and $\stotZg$ * BR(Z/gamma* -> ll) = 0.82 +- 0.06(stat) +- 0.05(syst) +- 0.09(lumi) nb (within the invariant mass window 66 < m_ll < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 +- 0.9(stat) +- 0.4(syst). In addition, measurements of the W+ and W- production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.

Readiness of the ATLAS liquid argon calorimeter for LHC collisions

Abstract: The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing performance, electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events allow to check the intrinsic constant term of the energy resolution. The uniformity of the electromagnetic barrel calorimeter response along eta (averaged over phi) is measured at the percent level using minimum ionizing cosmic muons. Finally, studies of electromagnetic showers from radiative muons have been used to cross-check the Monte Carlo simulation. The performance results obtained using the ATLAS readout, data acquisition, and reconstruction software indicate that the liquid argon calorimeter is well-prepared for collisions at the dawn of the LHC era.

Observation of single top quark production and measurement of |V tb| with CDF

Abstract: We report the observation of electroweak single top quark production in 3.2 fb{sup -1} of p{bar p} collision data collected by the Collider Detector at Fermilab at {radical}s = 1.96 TeV. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3{sub -0.5}{sup +0.6}(stat + sys) pb, extract the CKM matrix element value |V{sub tb}| = 0.91{sub -0.11}{sup +0.11}(stat + sys) {+-} 0.07(theory), and set a lower limit |V{sub tb}| > 0.71 at the 95% confidence level, assuming m{sub t} = 175 GeV/c{sup 2}.

Studying the underlying event in Drell-Yan and high transverse momentum jet production at the Tevatron

Abstract: 21 paginas, 15 figuras, 3 tablas.-- PACS numbers: 13.87.Ce, 14.60.Cd, 14.60.-- CDF Collaboration: et al.

Performance of the ATLAS detector using first collision data

Abstract: More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track- and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies.

Commissioning of the ATLAS Muon Spectrometer with Cosmic Rays

Abstract: The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer is ready to detect muons produced in high energy proton-proton collisions.

Measurement of pion and proton response and longitudinal shower profiles up to 20 nuclear interaction lengths with the ATLAS tile calorimeter

Abstract: The response of pions and protons in the energy range of 20–180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron–scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal shower development for pions and protons up to 20 nuclear interaction lengths. It was found that pions penetrate deeper in the calorimeter than protons. However, protons induce showers that are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal shower profiles are described by an analytical shower parametrization within an accuracy of 5–10%. The amount of energy leaking out behind the calorimeter is determined and parametrized as a function of the beam energy and the calorimeter depth. This allows for a leakage correction of test-beam results in the standard projective geometry.

Search for new bottomlike quark pair decays QQ̄→(tW) (t̄W ± ) in same-charge dilepton events

Abstract: We report the most restrictive direct limits on masses of fourth-generation down-type quarks b{sup '}, and quarklike composite fermions (B or T{sub 5/3}), decaying promptly to tW{sup +}-. We search for a significant excess of events with two same-charge leptons (e, mu), several hadronic jets, and missing transverse energy. An analysis of data from pp collisions with an integrated luminosity of 2.7 fb{sup -1} collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits m{sub b}{sup '}, m{sub B}>338 GeV/c{sup 2} and m{sub T{sub 5{sub /{sub 3}}}}>365 GeV/c{sup 2} at 95% confidence level.

The FastTracker Real Time Processor and Its Impact on Muon Isolation, Tau and b-Jet Online Selections at ATLAS

Abstract: As the LHC luminosity is ramped up to 3 × 1034 cm2 s1 and beyond, the high rates, multiplicities, and energies of particles seen by the detectors will pose a unique challenge. Only a tiny fraction of the produced collisions can be stored offline and immense real-time data reduction is needed. An effective trigger system must maintain high trigger efficiencies for the physics we are most interested in while suppressing the enormous QCD backgrounds. This requires massive computing power to minimize the online execution time of complex algorithms. A multi-level trigger is an effective solution to meet this challenge. The Fast Tracker (FTK) is an upgrade to the current ATLAS trigger system that will operate at full Level-1 output rates and provide high-quality tracks reconstructed over the entire inner detector by the start of processing in the Level-2 Trigger. FTK solves the combinatorial challenge inherent to tracking by exploiting the massive parallelism of associative memories that can compare inner detector hits to millions of pre-calculated patterns simultaneously. The tracking problem within matched patterns is further simplified by using pre-computed linearized fitting constants and relying on fast DSPs in modern commercial FPGAs. Overall, FTK is able to compute the helix parameters for all tracks in an event and apply quality cuts in less than 100 μs. The system design is defined and the performance presented with respect to high transverse momentum (high-pT) Level-2 objects: b jets, tau jets, and isolated leptons. We test FTK algorithms using the full ATLAS simulation with WH events up to 3 × 1034 cm2s1 luminosity and compare the FTK results with the offline tracking capability. We present the architecture and the reconstruction performance for the mentioned high-pT Level-2 objects.

Measurement of the W+w- production cross section and search for anomalous WWγ and WWZ couplings in pp̄ collisions at √s=1.96TeV

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.

Top quark mass measurement in the lepton+jets channel using a matrix element method and in situ jet energy calibration

Abstract: Aaltonen, T., Alvarez Gonzalez, B., Amerio, S., Amidei, D., Anastassov, A., Annovi, A., Antos, J., Apollinari, G., Appel, J.A., Apresyan, A., Arisawa, T., Artikov, A., Asaadi, J., Ashmanskas, W., Auerbach, B., Aurisano, A., Azfar, F., Badgett, W., Barbaro-Galtieri, A., Barnes, V.E., Barnett, B.A., Barria, P., Bartos, P., Bauce, M., Bauer, G., Bedeschi, F., Beecher, D., Behari, S., Bellettini, G., Bellinger, J., Benjamin, D., Beretvas, A., Bhatti, A., Binkley, M., Bisello, D., Bizjak, I., Bland, K.R., Blumenfeld, B., Bocci, A., Bodek, A., Bortoletto, D., Boudreau, J., Boveia, A., Brau, B., Brigliadori, L., Brisuda, A., Bromberg, C., Brucken, E., Bucciantonio, M., Budagov, J., Budd, H.S., Budd, S., Burkett, K., Busetto, G., Bussey, P., Buzatu, A., Calancha, C., Camarda, S., Campanelli, M., Campbell, M., Canelli, F., Canepa, A., Carls, B., Carlsmith, D., Carosi, R., Carrillo, S., Carron, S., Casal, B., Casarsa, M., Castro, A., Catastini, P., Cauz, D., Cavaliere, V., Cavalli-Sforza, M., Cerri, A., Cerrito, L., Chen, Y.C., Chertok, M., Chiarelli, G., Chlachidze, G., Chlebana, F., Cho, K., Chokheli, D., Chou, J.P., Chung, W.H., Chung, Y.S., Ciobanu, C.I., Ciocci, M.A., Clark, A., Compostella, G., Convery, M.E., Conway, J., Corbo, M., Cordelli, M., Cox, C.A., Cox, D.J., Crescioli, F., Cuenca Almenar, C., Cuevas, J., Culbertson, R., Dagenhart, D., D'Ascenzo, N., Datta, M., De Barbaro, P., De Cecco, S., De Lorenzo, G., Dell'Orso, M., Deluca, C., Demortier, L., Deng, J., Deninno, M., Devoto, F., D'Errico, M., Di Canto, A., Di Ruzza, B., Dittmann, J.R., D'Onofrio, M., Donati, S., Dong, P., Dorigo, T., Ebina, K., Elagin, A., Eppig, A., Erbacher, R., Errede, D., Errede, S., Ershaidat, N., Eusebi, R., Fang, H.C., Farrington, S., Feindt, M., Fernandez, J.P., Ferrazza, C., Field, R., Flanagan, G., Forrest, R., Frank, M.J., Franklin, M., Freeman, J.C., Furic, I., Gallinaro, M., Galyardt, J., Garcia, J.E., Garfinkel, A.F., Garosi, P., Gerberich, H., Gerchtein, E., Giagu, S., Giakoumopoulou, V., Giannetti, P., Gibson, K., Ginsburg, C.M., Giokaris, N., Giromini, P., Giunta, M., Giurgiu, G., Glagolev, V., Glenzinski, D., Gold, M., Goldin, D., Goldschmidt, N., Golossanov, A., Gomez, G., Gomez-Ceballos, G., Goncharov, M., Gonzalez, O., Gorelov, I., Goshaw, A.T., Goulianos, K., Gresele, A., Grinstein, S., Grosso-Pilcher, C., Group, R.C., Guimaraes Da Costa, J., Gunay-Unalan, Z., Haber, C., Hahn, S.R., Halkiadakis, E., Hamaguchi, A., Han, J.Y., Happacher, F., Hara, K., Hare, D., Hare, M., Harr, R.F., Hatakeyama, K., Hays, C., Heck, M., Heinrich, J., Herndon, M., Hewamanage, S., Hidas, D., Hocker, A., Hopkins, W., Horn, D., Hou, S., Hughes, R.E., Hurwitz, M., Husemann, U., Hussain, N., Hussein, M., Huston, J., Introzzi, G., Iori, M., Ivanov, A., James, E., Jang, D., Jayatilaka, B., Jeon, E.J., Jha, M.K., Jindariani, S., Johnson, W., Jones, M., Joo, K.K., Jun, S.Y., Junk, T.R., Kamon, T., Karchin, P.E., Kato, Y., Ketchum, W., Keung, J., Khotilovich, V., Kilminster, B., Kim, D.H., Kim, H.S., Kim, H.W., Kim, J.E., Kim, M.J., Kim, S.B., Kim, S.H., Kim, Y.K., Kimura, N., Kirby, M., Klimenko, S., Kondo, K., Kong, D.J., Konigsberg, J., Kotwal, A.V., Kreps, M., Kroll, J., Krop, D., Krumnack, N., Kruse, M., Krutelyov, V., Kuhr, T., Kurata, M., Kwang, S., Laasanen, A.T., Lami, S., Lammel, S., Lancaster, M., Lander, R.L., Lannon, K., Lath, A., Latino, G., Lazzizzera, I., Lecompte, T., Lee, E., Lee, H.S., Lee, J.S., Lee, S.W., Leo, S., Leone, S., Lewis, J.D., Lin, C.-J., Linacre, J., Lindgren, M., Lipeles, E., Lister, A., Litvintsev, D.O., Liu, C., Liu, Q., Liu, T., Lockwitz, S., Lockyer, N.S., Loginov, A., Lucchesi, D., Lueck, J., Lujan, P., Lukens, P., Lungu, G., Lys, J., Lysak, R., Madrak, R., Maeshima, K., Makhoul, K., Maksimovic, P., Malik, S., Manca, G., Manousakis-Katsikakis, A., Margaroli, F., Marino, C., Martinez, M., Martinez-Ballarin, R., Mastrandrea, P., Mathis, M., Mattson, M.E., Mazzanti, P., McFarland, K.S., McIntyre, P., McNulty, R., Mehta, A., Mehtala, P., Menzione, A., Mesropian, C., Miao, T., Mietlicki, D., Mitra, A., Miyake, H., Moed, S., Moggi, N., Mondragon, M.N., Moon, C.S., Moore, R., Morello, M.J., Morlock, J., Movilla Fernandez, P., Mukherjee, A., Muller, T., Murat, P., Mussini, M., Nachtman, J., Nagai, Y., Naganoma, J., Nakano, I., Napier, A., Nett, J., Neu, C., Neubauer, M.S., Nielsen, J., Nodulman, L., Norniella, O., Nurse, E., Oakes, L., Oh, S.H., Oh, Y.D., Oksuzian, I., Okusawa, T., Orava, R., Ortolan, L., Pagan Griso, S., Pagliarone, C., Palencia, E., Papadimitriou, V., Paramonov, A.A., Patrick, J., Pauletta, G., Paulini, M., Paus, C., Pellett, D.E., Penzo, A., Phillips, T.J., Piacentino, G., Pianori, E., Pilot, J., Pitts, K., Plager, C., Pondrom, L., Potamianos, K., Poukhov, O., Prokoshin, F., Pronko, A., Ptohos, F., Pueschel, E., Punzi, G., Pursley, J., Rahaman, A., Ramakrishnan, V., Ranjan, N., Redondo, I., Renton, P., Rescigno, M., Rimondi, F., Ristori, L., Robson, A., Rodrigo, T., Rodriguez, T., Rogers, E., Rolli, S., Roser, R., Rossi, M., Rubbo, F., Ruffini, F., Ruiz, A., Russ, J., Rusu, V., Safonov, A., Sakumoto, W.K., Santi, L., Sartori, L., Sato, K., Saveliev, V., Savoy-Navarro, A., Schlabach, P., Schmidt, A., Schmidt, E.E., Schmidt, M.P., Schmitt, M., Schwarz, T., Scodellaro, L., Scribano, A., Scuri, F., Sedov, A., Seidel, S., Seiya, Y., Semenov, A., Sforza, F., Sfyrla, A., Shalhout, S.Z., Shears, T., Shepard, P.F., Shimojima, M., Shiraishi, S., Shochet, M., Shreyber, I., Siegrist, J., Simonenko, A., Sinervo, P., Sissakian, A., Sliwa, K., Smith, J.R., Snider, F.D., Soha, A., Somalwar, S., Sorin, V., Squillacioti, P., Stanitzki, M., Denis, R.S., Stelzer, B., Stelzer-Chilton, O., Stentz, D., Strologas, J., Strycker, G.L., Sudo, Y., Sukhanov, A., Suslov, I., Takemasa, K., Takeuchi, Y., Tang, J., Tecchio, M., Teng, P.K., Thom, J., Thome, J., Thompson, G.A., Thomson, E., Ttito-Guzman, P., Tkaczyk, S., Toback, D., Tokar, S., Tollefson, K., Tomura, T., Tonelli, D., Torre, S., Torretta, D., Totaro, P., Trovato, M., Tu, Y., Turini, N., Ukegawa, F., Uozumi, S., Varganov, A., Vataga, E., Vazquez, F., Velev, G., Vellidis, C., Vidal, M., Vila, I., Vilar, R., Volobouev, I., Vogel, M., Volpi, G., Wagner, P., Wagner, R.L., Wakisaka, T., Wallny, R., Wang, S.M., Warburton, A., Waters, D., Weinberger, M., Wester, W.C., Whitehouse, B., Whiteson, D., Wicklund, A.B., Wicklund, E., Wilbur, S., Wick, F., Williams, H.H., Wilson, J.S., Wilson, P., Winer, B.L., Wittich, P., Wolbers, S., Wolfe, H., Wright, T., Wu, X., Wu, Z., Yamamoto, K., Yamaoka, J., Yang, T., Yang, U.K., Yang, Y.C., Yao, W.-M., Yeh, G.P., Yi, K., Yoh, J., Yorita, K., Yoshida, T., Yu, G.B., Yu, I., Yu, S.S., Yun, J.C., Zanetti, A., Zeng, Y., Zucchelli, S.

Combined Tevatron upper limit on gg→H→W+W- and constraints on the Higgs boson mass in fourth-generation fermion models

Abstract: We combine results from searches by the CDF and D0 collaborations for a standard model Higgs boson (H) in the process gg -> H -> W+W- in p (p) over bar collisions at the Fermilab Tevatron Collider at root s = 1.96 TeV. With 4.8 fb(-1) of integrated luminosity analyzed at CDF and 5.4 fb(-1) at D0, the 95% confidence level upper limit on sigma(gg -> H) x B(H -> W+W-) is 1.75 pb at m(H) = 120 GeV, 0.38 pb at m(H) = 165 GeV, and 0.83 pb at m(H) = 200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% confidence level a standard-model-like Higgs boson with a mass between 131 and 204 GeV.

Measurements of the top-quark mass using charged particle tracking

Abstract: We present three measurements of the top-quark mass in the lepton plus jets channel with approximately 1.9 fb{sup -1} of integrated luminosity collected with the CDF II detector using quantities with minimal dependence on the jet energy scale. One measurement exploits the transverse decay length of b-tagged jets to determine a top-quark mass of 166.9{sub -8.5}{sup +9.5} (stat) {+-} 2.9 (syst) GeV/c{sup 2}, and another the transverse momentum of electrons and muons from W-boson decays to determine a top-quark mass of 173.5{sub -8.9}{sup +8.8} (stat) {+-} 3.8 (syst) GeV/c{sup 2}. These quantities are combined in a third, simultaneous mass measurement to determine a top-quark mass of 170.7 {+-} 6.3 (stat) {+-} 2.6 (syst) GeV/c{sup 2}.

Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using Cosmic Muons

Abstract: The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons. In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated contribution to the constant term of (0.29(-0.04)(+0.05))% in the barrel and (0.54(-0.04)(+0.06))% in the endcaps. The same data are used to measure the drift velocity of ionization electrons in liquid argon, which is found to be 4.61 +/- 0.07 mm/mu s at 88.5 K and 1 kV/mm.

Measurement of the Ratio σtt̅ /σZ/γ*→ll and Precise Extraction of the tt̅ Cross Section

Abstract: We report a measurement of the ratio of the t (t) over bar to Z/gamma* production cross sections in root s = 1.96 TeV p (p) over bar collisions using data corresponding to an integrated luminosity of up to 4.6 fb(-1), collected by the CDF II detector. The t (t) over bar cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma* -> ll cross section predicted by the standard model, the extracted t (t) over bar cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result sigma(t (t) over bar) = 7.70 +/- 0.52 pb, for a top-quark mass of 172.5 GeV/c(2).

Diffractive W and Z production at the Fermilab Tevatron

Abstract: We report on a measurement of the fraction of events with a W or Z boson produced diffractively in antiproton-proton collisions at a center of mass energy of 1.96 TeV, using data from 0.6 inverse femtobarns of integrated luminosity collected with the CDF-II detector equipped with a Roman-pot spectrometer that detects the antiproton (pbar) from pbar+p --> pbar+[X+W/Z]. We find that (0.97 +/- 0.11)% of Ws and (0.85 +/- 0.22)% of Zs are produced diffractively in a region of (anti)proton fractional momentum loss (\xi) of 0.03 pbar+Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.

Measurements of branching fraction ratios and CP asymmetries in B ±→DCPK± decays in hadron collisions

Abstract: 9 paginas, 3 figuras, 2 tablas.-- PACS numbers: 13.25.Hw, 11.30.Er, 14.40.Nd.--CDF Collaboration: et al.

Direct Top-Quark Width Measurement at CDF

Abstract: We present a measurement of the top-quark width using $t\bar{t}$ events produced in $p\bar{p}$ collisions at Fermilab's Tevatron collider and collected by the CDF II detector. In the mode where the top quark decays to a $W$ boson and a bottom quark, we select events in which one $W$ decays leptonically and the other hadronically~(lepton + jets channel) . From a data sample corresponding to 4.3~fb$^{-1}$ of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of $W$ boson that decays hadronically are reconstructed for each event and compared with templates of different top-quark widths~($\Gamma_t$) and deviations from nominal jet energy scale~($\Delta_{JES}$) to perform a simultaneous fit for both parameters, where $\Delta_{JES}$ is used for the {\it in situ} calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95$\%$ confidence level~(CL) of $\Gamma_t <$ 7.6 GeV and a two-sided 68$\%$ CL interval of 0.3 GeV $< \Gamma_t <$ 4.4 GeV for a top-quark mass of 172.5 GeV$/c^2$, which are consistant with the standard model prediction. This is the first direct measurement of $\Gamma_t$ to set a lower limit with 68$\%$ CL.

Search for pair production of supersymmetric top quarks in dilepton events from pp̄ collisions at √s=1.96TeV

Abstract: We present the results of a search for pair production of the supersymmetric partner of the top quark (the top squark (t) over tilde (1)) decaying to a b quark and a chargino (chi) over tilde (+/-)(1) with a subsequent (chi) over tilde (+/-)(1) decay into a neutralino (chi) over tilde (0)(1), lepton l, and neutrino nu Using a data sample corresponding to 2.7 fb(-1) of integrated luminosity of p (p) over bar collisions at root s = 1: 96 TeV collected by the CDF II detector, we reconstruct the mass of top squark candidate events and fit the observed mass spectrum to a combination of standard model processes and (t) over tilde (1)(t) over tilde (1). We find no evidence for (t) over tilde (1)(t) over tilde (1) production and set 95% C. L. limits on the masses of the top squark and the neutralino for several values of the chargino mass and the branching ratio B((X) over tilde (+/-)(1) -> (chi) over tilde (0)(1)l(+/-)nu).

Measurement of w-boson polarization in top-quark decay in pp̄ collisions at √s=1.96TeV

Abstract: We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb(-1) of p (p) over bar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c(2), three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f(0)) and right-handed (f(0)) W bosons yields the model- independent results f(0) =0. 88 +/- 0.11(stat) +/- 0.06(syst) and f(+) = 0.15 +/- 0.07(stat) +/- 0.06(syst) with a correlation coefficient of -0.59. A measurement of f(0) [f(+)] constraining f(+) [f(0)] to its standard model value of 0.0 [0.7] yields f(0) 0.70 + 0.07(stat) +/- 0.04(syst) [f(+) - 0.01 +/- 0.02(stat) +/- 0.05(syst)]. All these results are consistent with standard model expectations. We achieve the single most precise measurements of f(0) for both the model- independent and modeldependent determinations.

Search for the supersymmetric partner of the top quark in pp̄ collisions at √s=1.96TeV

Abstract: We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy root s = 1: 96 TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb(-1) collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence level in the stop quark versus sneutrino mass plane are set. Stop quark masses up to 180 GeV/c(2) are excluded for sneutrino masses around 45 GeV/c(2), and sneutrino masses up to 116 GeV/c(2) are excluded for stop quark masses around 150 GeV/c(2).

Measurement of the Λb0 lifetime in Λb0→Λc+π - decays in pp̄ collisions at √s=1.96TeV

Abstract: We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions. This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium fur Bildung und Forschung, Germany; the World Class University Program, the National Research Foundation of Korea; the Science and Technology Facilities Council and the Royal Society, UK; the Institut National de Physique Nucleaire et Physique des Particules/CNRS; the Russian Foundation for Basic Research; the Ministerio de Ciencia e Innovacion, and Programa Consolider- Ingenio 2010, Spain; the Slovak RD and the Academy of Finland.