40642633
Level-3 calorimeter resolution available for the Level-1 and Level-2 CDF triggers
As the Tevatron luminosity increases more sophisticated selections are required to be efficient in selecting rare events from a very huge background. To cope with this problem, CDF has pushed the Level-3 calorimeter algorithm resolutions up to Level-2 and, when possible, at Level-1, increasing efficiency and, at the same time, keeping under control the rates. This strategy increases the purity of the Level-2 and Level-1 samples, produces free-bandwidth that allows to reduce the thresholds. The global effect is an increase of the signal efficiency of important Tevatron Standard Model Higgs search channels (H → WW, ZH, WH). The L2 upgrade improves the cluster finding algorithm, the resolution of the Missing Transverse Energy (MET) and the SUM Transverse Energy (SUMET) calculations. The same Level-2 MET and SUMET improved resolution has been made available to the Level-1 system, exploiting the same hardware used for the Level-2 upgrade. The upgrade is based on the Pulsar board, a general purpose VME board developed at CDF and already used for upgrading both the Level-2 tracking and the Level-2 global decision crate. The Level-2 upgrade has been designed, built, tested and commissioned in six months. It was accepted as the default system for CDF in August 2007. The same Level-2 hardware can be used in such a way to provide the Level-1 calorimeter system of the same MET, SUMET resolution provided to Level-2. While in the upgraded Level-2 system the algorithms are executed in a commercial CPU within the typical Level-2 processing timing of 20 μs, in the upgraded Level-1 system, MET and SUMET are calculated by powerful FPGAs within 5 μs. The Level-1 upgrade is currently ongoing and in commissioning phase.We describe the CDF Level-2 and the new Level-1 calorimeter upgrades, the architecture and the trigger performances, with particular emphasis on a new calorimeter MET_JET-based trigger performances used for CDF Higgs search.
122797867
Search for third generation squarks in the missing transverse energy plus jet sample at CDF Run II
The twentieth century leaves behind one of the most impressive legacies, in terms of human knowledge, ever achieved. In particular the StandardModel (SM) of particle physics has proven to be one of the most accurate descriptions of Nature. The level of accuracy of some theoretical predictions has never been attained before. It includes the electromagnetic interaction, and the weak and strong force, developing the Lagrangian from symmetry principles. There are two different types of fundamental constituents of Nature, in the framework of the Standard Model: bosons and fermions. Bosons are those particles responsible for carrying the interactions among the fermions, which constitute matter. Fermions are divide into six quarks and six leptons, forming a three-folded structure. All these fermions and bosons have an antimatter partner. However, several difficulties point along with the idea that the Standard Model is only an effective low energy theory. These limitations include the difficulty to incorporate gravity and the lack of justification to fine tuning of some perturbative corrections. Moreover, some regions of the theory are not understood, like the mass spectrum of the Standard Model or the mechanism for electroweak symmetry breaking. Supersymmetry is a newer theoretical framework, thought to adress the problems foundmore » in the Standard Model, while preserving all its predictive power. It introduces a new symmetry that relates a new boson to each SM fermion and a new fermion to each SM boson. In this way, for every existing boson in the SM it must exist a fermionic super-partner (named with a sufix ino), and likewise, for every fermion a bosonic super-partner (named with a prefix s) must also exist. Moreover, another symmetry called R-parity is introduced to prevent baryon and lepton number violating interactions. If R-parity is conserved, super-particles can only be pair-produced and they cannot decay completely in SM particles. This implies the existence of a lightest SUSY particle (LSP) which would provide a candidate for cold dark matter, that account for 23% of the universe content, as strongly suggested by recent astrophysical data [1]. The Tevatron is a hadron collider operating at Fermilab, USA. This accelerator provides proton-antiproton (p{bar p}) collisions with a center of mass energy of {radical}s = 1.96 TeV. CDF and D0 are the detectors built to analyse the products of the collisions provided by the Tevatron. Both experiments have produced a very significant scientific output in the last few years, like the discovery of the top quark or the measurement of the B{sub s} mixing. The Tevatron experiments are also reaching sensitivity to the SM Higgs boson. The scientific program of CDF includes a broad spectrum on searches for physics signatures beyond the Standard Model. Tevatron is still the energy frontier, what means an unique opportunity to produce a discovery in physic beyond the Standard Model. The analyses presented in this thesis focus on the search for third generation squarks in the missing transverse energy plus jets final state. The production of sbottom ({tilde b}) and stop ({tilde t}) quarks could be highly enhanced at the Tevatron, giving the possibility of discovering new physics or limiting the parameter space available in the theory. No signal is found over the predicted Standard Model background in both searches. Instead, 95% confidence level limits are set on the production cross section, and then translated into the mass plane of the hypothetical particles. This thesis sketches the basic theory concepts of the Standard Model and the Minimal Supersymmetric Extension in Chapter 2. Chapter 3, describes the Tevatron and CDF. Based on the CDF subsystems information, Chapter 4 and 5 describe the analysis objet reconstruction and the heavy flavor tagging tools. The development of the analyses is shown in Chapter 6 and Chapter 7. Finally, Chapter 8 is devoted to discuss the results and conclusions of this work, and future prospects.« less
3159956
Galaxy Clusters in the Line of Sight to Background Quasars. I. Survey Design and Incidence of Mg II Absorbers at Cluster Redshifts
We describe the first optical survey of absorption systems associated with cluster galaxies at z = 0.3–0.9. We have cross-correlated quasars from the third data release of the SDSS with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We have found 442 quasar-cluster pairs for which the Mg II λλ2796, 2803 doublet might be detected at a transverse (physical) distance d 2.0 A ) near cluster redshifts shows a significant (>3 σ) overabundance (up to a factor of 15) when compared with the "field" population; (2) the overabundance is more evident at d < 1 h71−1 Mpc than at d < 2 h71−1 Mpc , and more evident in a subsample of the most massive clusters; and (3) the population of weak Mg II systems (W02796 < 0.3 A ) near cluster redshifts conforms to the field statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear flat and well fitted by a power law in the entire W range. Since either the absorber number density or the filling factor/cross section affects the absorber statistics, an interesting possibility is that we have detected the signature of truncated halos due to environmental effects. Thus, the excess of strong systems is due to a population of absorbers in an overdense galaxy region, and the lack of weak systems to a different population, that got destroyed in the cluster environment.