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Trilepton searches for chargino-neutralino production at the Tevatron

Description: The Tevatron Collider experiments, CDF and D0, have collected substantial data sets with which to probe for physics beyond the Standard Model. Two recent searches for trilepton events arising from supersymmetric {tilde {chi}}{sub 1}{sup {+-}} {tilde {chi}}{sub 2}{sup 0} production are presented.
Date: April 1, 2008
Creator: Chertok, Maxwell & /UC, Davis
Partner: UNT Libraries Government Documents Department

A search for double-charged Higgs bosons at the Tevatron

Description: We search for the pair production of doubly charged Higgs particles followed by the lepton-flavor violating decay of each Higgs into electron-and-tau and muon-and-tau pairs using 350 pb{sup -1} of data collected by the CDF II experiment at the Fermilab Tevatron. Separate searches investigate cases where three or four final state leptons are detected, and the limits for each exclusive decay mode reflect the combined results of both searches. Assuming the H{sup {+-}{+-}}{sub L} decays exclusively into like sign electron-and-tau pairs, we set a lower limit on its mass of 114 GeV/c2 at the 95 % confidence level. In the case of exclusive muon-and-tau decays, we set a lower mass limit of 112 GeV/c2 also at the 95% confidence level.
Date: January 1, 2006
Creator: Baraoiant, Sasha & /UC, Davis
Partner: UNT Libraries Government Documents Department

Search for leptoquarks and 4th generation quarks at CDF

Description: At Run II of the Fermilab Tevatron, the CDF experiment provides good sensitivity for either discovery or setting limits on 1st and 2nd generation scalar, or 3rd generation vector, leptoquark pair-production, where each leptoquark decays to a charged lepton and a quark with variable branching ratio {beta}, or decays to a neutrino and quark with branching ratio (1 - {beta}). By comparison with the theoretical expectations, we set mass limits, in some cases as a function of {beta}. New quark generations are predicted in various scenarios for physics beyond the Standard Model. Here we include results from searches for t' and for b' production. The t' is searched for in decays to W{sub q} and the b' in decays to Z{sup 0}b. All of these measurements are based on an integrated luminosity of 200-350 pb{sup -1}, taken at {radical}s = 1.96 TeV.
Date: January 1, 2005
Creator: Soha, A. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Top quark physics

Description: While the top quark was discovered in 1995 at the Fermilab Tevatron, a decade later they still have very little information about the top. As the heaviest particle yet discovered, the top quark is interesting in and of itself, but some speculate that it may play a special role in physics beyond the Standard Model. With Run 2 of the Tevatron well underway, they have the opportunity to study top quark properties with much better sensitivity, and to test whether top quarks behave as predicted by current theories. This article focuses on the basics of top quark physics at the Tevatron, highlighting only a sample of the many recent measurements, as new results are being released monthly, and constantly changing the landscape of our knowledge of top.
Date: October 1, 2005
Creator: Erbacher, Robin D. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Top Quark Properties from Top Pair Events and Decays

Description: Over a decade since the discovery of the top quark we are still trying to unravel mysteries of the heaviest observed particle and learn more about its nature. The continuously accumulating statistics of CDF and DO data provide the means for measuring top quark properties with ever greater precision and the opportunity to search for signs of new physics that could be manifested through subtle deviations from the standard model in the production and decays of top quarks. In the following we present a slice of the rich program in top quark physics at the Fermilab Tevatron: measurements of the properties of top quark decays and searches for unusual phenomena in events with pair produced tops. In particular, we discuss the most recent and precise CDF and DO measurements of the transverse polarization of W bosons from top decays, branching ratios and searches for flavor-changing neutral current decays, decays into charged Higgs and invisible decays. These analyses correspond to integrated luminosities ranging from 0.9 to 2.7 fb{sup -1}.
Date: November 1, 2008
Creator: Ivanov, A. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Top Quark Pair Production Cross Section and Forward-Backward Asymmetry at the Tevatron

Description: We present recent results on top quark pair production cross section and forward-backward asymmetry at the Tevatron. Three new cross section measurements from CDF and one new measurement from DO are presented that utilize the full dataset available. A new DO top cross section combination gives a ttbar production cross section of sigma ttbar = 7.83 + 0.46-0.45 (stat) + 0.64-0.53 (syst) +-0.48 (lumi). The new CDF cross section combination for ttbar production is found to be 7.0 +- 0.3 (stat) +- 0.4 (syst) +- 0.4 (lumi) pb giving a total uncertainty of 9%, very close to the that of the current best theoretical predictions. It is important to measure the top cross section in as many different channels as possible and investigate their compatibility. This is useful as new physics might show up differently in the different channels. Thus any significant discrepancy could be a sign of new physics. Three new measurements of the forward-backward asymmetry are also presented. The two CDF measurements unfold the observed asymmetry back to parton level in order to directly compare the values obtained with theoretical predictions. The DO measurement is not unfolded and therefore does not depend on the specific method used for unfolding.
Date: October 1, 2008
Creator: Lister, Alison & /UC, Davis
Partner: UNT Libraries Government Documents Department

Searches in photon and jet states

Description: The authors present recent results from the Collider Detector at Fermilab (CDF) and D0 experiments using data from proton-antiproton collisions with {radical}s = 1.96 TeV at Run II of the Fermilab Tevatron. New physics may appear in events with high transverse momentum objects, including photons and quark or gluon jets. The results described here are of signature-based searches and model-based searches probing supersymmetry, leptoquarks, 4th generation quarks, and large extra dimensions.
Date: June 1, 2007
Creator: Soha, A. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Top physics at CDF

Description: Recent results in top physics at CDF presented at the Lake Louise Winter Institute 2008 are discussed, including updates to the top mass, single top search, a search for flavor changing neutral currents in top decay, and W-helicity measurements. Several newer measurements are also presented including the forward-backward asymmetry, the t{bar t} differential cross-section d{sigma}/dM{sub t{bar t}}, and a search for top pair production from massive gluons. Most of the discussed measurements utilize close to 2 fb{sup -1} of data collected at CDF.
Date: July 1, 2008
Creator: Schwarz, Thomas A. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Long-term X-ray Variability of NGC 4945

Description: Though short-term X-ray variability has been studied for the active galaxy NGC 4945, long-term studies promise to contribute to our understanding of the processes involved in accretion onto supermassive black holes. In order to understand the relationship between black hole mass and breaks in the power spectral density (PSD), the long-term X-ray variability of NGC 4945 was studied over the energy range 8-30 keV. Observations occurred over the year 2006 using the Rossi X-ray Timing Explorer. The data was reduced using the package FTOOLS, most notably the scripts Rex and faxbary. Light curves were produced and a PSD was obtained using a Fast Fourier Transform algorithm. Preliminary studies of the light curve show greater X-ray variability at higher frequencies. This result complements previous studies of NGC 4945 by Martin Mueller. However, the PSD produced must go through further study before accurate results can be obtained. A way to account for the window function of the PSD must be found before the behavior at lower frequencies can be studied with accuracy and the relationship between black hole mass and the break in NGC 4945's PSD can be better understood. Further work includes exploration into ways to subtract the window function from the PSD, as well as a closer analysis of the PSD produced by averaging the data into logarithmic bins. The possibility of a better way to bin the data should be considered so that the window function would be minimized.
Date: August 29, 2007
Creator: Miller, Amara & /UC, Davis /SLAC
Partner: UNT Libraries Government Documents Department

Search for 3rd Generation Vector Leptoquarks in the Di-tau Di-jet Channel in Proton Antiproton Collisions at square root s = 1.96 TeV

Description: We search for third generation vector leptoquarks (V LQ3) produced in colliding p{bar p} beams operating at {radical}s = 1.96 TeV at the CDF experiment in Run II of the Fermilab Tevatron. We use 322 pb{sup -1} of data to search for the V LQ3 signal in the di-tau plus di-jet channel. For the first time, the full matrix element is used in the Monte Carlo simulation of this signal. With no events observed in the signal region, we set a 95% C.L. upper limit on the V LQ3 pair production cross section of {sigma} < 344fb, assuming Yang-Mills couplings and Br(V LQ3 {yields} b{tau}) = 1, and a lower limit on the V LQ3 mass of m{sub V LQ3} > 317 GeV=c{sup 2}. If theoretical uncertainties on the cross section are applied in the least favorable manner the results are {sigma} < 360fb and m{sub V LQ3} > 294 GeV=c{sup 2}. The Minimal coupling V LQ3 result is an upper limit on the cross section of {sigma} < 493fb ({sigma} < 610fb) and the lower limit on the mass is m{sub V LQ3} > 251 GeV=c{sup 2} (m{sub V LQ3} > 223 GeV=c{sup 2}) for the nominal (1{sigma} varied) theoretical expectation.
Date: December 1, 2006
Creator: Forrester, Stanley Scott & /UC, Davis
Partner: UNT Libraries Government Documents Department

Search for Supersymmetry in p anti-p Collisions at s**(1/2) =1.96-TeV Using the Trilepton Signature of Chargino-Neutralino Production

Description: The production of chargino-neutralino pairs and their subsequent leptonic decays is one of the most promising supersymmetry (SUSY) signatures at the Tevatron p{bar p} collider. We present here the most recent results on the search for the three-lepton and missing-transverse-energy SUSY signature using data collected with the CDF II detector. The results are interpreted within the minimal supergravity (mSugra) scenario.
Date: October 1, 2009
Creator: Forrest, R. & /UC, Davis
Partner: UNT Libraries Government Documents Department

New phenomena searches at CDF

Description: The authors report on recent results from the Collider Detector at Fermilab (CDF) experiment, which is accumulating data from proton-antiproton collisions with {radical}s = 1.96 TeV at Run II of the Fermilab Tevatron. The new phenomena being explored include Higgs, Supersymmetry, and large extra dimensions. They also present the latest results of searches for heavy objects, which would indicate physics beyond the Standard Model.
Date: April 1, 2006
Creator: Soha, Aron & /UC, Davis
Partner: UNT Libraries Government Documents Department

Search for Heavy Top-like Quarks t-rime ---> Wq Using Lepton Plus Jets Events in 1.96-TeV p anti-p Collisions

Description: We present the results of a search for a new heavy top-like quark, tprime, decaying to a W boson and another quark using the CDF II Detector in Run II of the Tevatron ppbar collider. New top-like quarks are predicted in a number of models of new physics. Using a data sample corresponding to 2.8 fb-1 of integrated luminosity we fit the observed spectrum of total transverse energy and reconstructed quark mass to a combination of background plus signal. We see no evidence for tprime production, so use this result to set limits on the tprime tprimebar production cross section times the branching ratio of tprime to Wq and infer a lower limit of 311 GeV/c2 on the mass of the tprime at 95% CL.
Date: October 1, 2008
Creator: Lister, Alison & /UC, Davis
Partner: UNT Libraries Government Documents Department

A Unified Dark Matter Model in sUED

Description: We propose a dark matter model with standard model singlet extension of the universal extra dimension model (sUED) to explain the recent observations of ATIC, PPB-BETS, PAMELA and DAMA. Other than the standard model fields propagating in the bulk of a 5-dimensional space, one fermion field and one scalar field are introduced and both are standard model singlets. The zero mode of the new fermion is identified as the right-handed neutrino, while its first KK mode is the lightest KK-odd particle and the dark matter candidate. The cosmic ray spectra from ATIC and PPB-BETS determine the dark matter particle mass and hence the fifth dimension compactification scale to be 1.0-1.6 TeV. The zero mode of the singlet scalar field with a mass below 1 GeV provides an attractive force between dark matter particles, which allows a Sommerfeld enhancement to boost the annihilation cross section in the Galactic halo to explain the PAMELA data. The DAMA annual modulation results are explained by coupling the same scalar field to the electron via a higher-dimensional operator. We analyze the model parameter space that can satisfy the dark matter relic abundance and accommodate all the dark matter detection experiments. We also consider constraints from the diffuse extragalactic gamma-ray background, which can be satisfied if the dark matter particle and the first KK-mode of the scalar field have highly degenerate masses.
Date: November 1, 2008
Creator: Bai, Yang; /Fermilab; Han, Zhenyu & /UC, Davis
Partner: UNT Libraries Government Documents Department

Self-accelerating Warped Braneworlds

Description: Braneworld models with induced gravity have the potential to replace dark energy as the explanation for the current accelerating expansion of the Universe. The original model of Dvali, Gabadadze and Porrati (DGP) demonstrated the existence of a ''self-accelerating'' branch of background solutions, but suffered from the presence of ghosts. We present a new large class of braneworld models which generalize the DGP model. Our models have negative curvature in the bulk, allow a second brane, and have general brane tensions and localized curvature terms. We exhibit three different kinds of ghosts, associated to the graviton zero mode, the radion, and the longitudinal components of massive graviton modes. The latter two species occur in the DGP model, for negative and positive brane tension respectively. In our models, we find that the two kinds of DGP ghosts are tightly correlated with each other, but are not always linked to the feature of self-acceleration. Our models are a promising laboratory for understanding the origins and physical meaning of braneworld ghosts, and perhaps for eliminating them altogether.
Date: November 1, 2006
Creator: Carena, Marcela; Lykken, Joseph; /Fermilab; Park, Minjoon; /UC, Davis; Santiago, Jose et al.
Partner: UNT Libraries Government Documents Department

A Silicon-Tungsten ECal with Integrated Electronics

Description: We summarize recent R&D progress for a silicon-tungsten electromagnetic calorimeter (ECal) with integrated electronics, designed to meet the ILC physics requirements. A basic physics requirement for ILC detectors is that they provide excellent reconstruction of hadronic final states. This allows access to new physics which is complementary to the LHC. One statement for a requirement on jet reconstruction is that intermediate particles which decay into jets, such as W, Z, or top, can be identified and isolated. This places unprecedented requirements on 2-jet or 3-jet mass resolution, typically at the level of 3-5% using the PFA technique, which makes challenging demands on the calorimeters. The electromagnetic energy resolution is not expected to limit jet resolution using a PFA. However, particle separation - photon-photon and charged hadron-photon - is crucial. In addition, if one provides this kind of imaging calorimeter to meet the PFA needs, these same features will also be put to good use for reconstruction of specific tau decay modes (to enable final-state polarization measurement), to 'track' photons (even if originating from a vertex displaced from the interaction point), to track MIPS, and so forth. Figure 1 and Table 1 provide some context for our ECal design within the SiD detector concept, along with some main design parameters. More detail is included in the presentation.
Date: November 10, 2011
Creator: Frey, R.; U., /Oregon; Brau, James E.; U., /Oregon; Breidenbach, Martin; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Fast Neutron Damage Studies on NdFeB Materials

Description: Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) since both accelerator and detectors will be subjected to large fluences of hadrons, leptons and {gamma}'s over the life of the facility [1]. While the linacs will be superconducting, there are still many uses for NdFeB in the damping rings, injection and extraction lines and final focus. Our understanding of the situation for rare earth, permanent magnet materials was presented at PAC03 [2]. Our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented at EPAC04 [3]. We have extended the doses, included other manufacturer's samples, and measured induced radioactivities which are discussed in detail.
Date: May 17, 2005
Creator: Anderson, S.; Spencer, J.; Wolf, Z.; /SLAC; Baldwin, A.; Pellett, D. et al.
Partner: UNT Libraries Government Documents Department

Solving Large Scale Nonlinear Eigenvalue Problem in Next-Generation Accelerator Design

Description: A number of numerical methods, including inverse iteration, method of successive linear problem and nonlinear Arnoldi algorithm, are studied in this paper to solve a large scale nonlinear eigenvalue problem arising from finite element analysis of resonant frequencies and external Q{sub e} values of a waveguide loaded cavity in the next-generation accelerator design. They present a nonlinear Rayleigh-Ritz iterative projection algorithm, NRRIT in short and demonstrate that it is the most promising approach for a model scale cavity design. The NRRIT algorithm is an extension of the nonlinear Arnoldi algorithm due to Voss. Computational challenges of solving such a nonlinear eigenvalue problem for a full scale cavity design are outlined.
Date: September 28, 2006
Creator: Liao, Ben-Shan; Bai, Zhaojun; /UC, Davis; Lee, Lie-Quan; Ko, Kwok & /SLAC
Partner: UNT Libraries Government Documents Department