122060237
Higgs Physics at CMS
Searches for the Higgs boson at CMS, based on the data collected in 2011 and 2012 at 7 and 8 TeV centre-of-mass energy, corresponding to integrated luminosities of 5 and 20 fb −1 , are presented. The observed new boson is found to be consistent with the Standard Model Higgs boson in all investigated properties such as the spin and couplings to bosons and fermions. The measured mass of this new particle is 125.7 ± 0.3 (stat.) ± 0.3 (syst.) GeV.
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
121659740
The CDF level 2 calorimetric trigger upgrade
Abstract CDF II upgraded the calorimeter trigger to cope with the higher detector occupancy due to the increased Tevatron instantaneous luminosity ( ∼ 2.8 × 10 32 cm - 2 s - 1 ) . While the original system was implemented in custom hardware and provided to the L2 trigger a limited-quality jet clustering performed using a reduced resolution measurement of the transverse energy in the calorimeter trigger towers, the upgraded system provides offline-quality jet reconstruction of the full resolution calorimeter data. This allows to keep better under control the dependence of the trigger rates on the instantaneous luminosity and to improve the efficiency and purity of the trigger selections. The upgraded calorimeter trigger uses the general purpose VME board Pulsar, developed at CDF II and already widely used to upgrade the L2 tracking and L2 decision systems. A battery of Pulsars is used to merge and send the calorimeter data to the L2 CPUs, where software-implemented algorithms perform offline-like clustering. In this paper we review the design and the performance of the upgraded system.
126715
Searches for third generation squarks at the Tevatron
In the Minimal Supersymmetric Standard Model (MSSM), the large mixing between the chiral states of the scalar partner particles of the standard model fermions might lead to small masses for sbottom and stop quarks. Dedicated searches are carried out in final states with large missing transverse energy and at least two jets, where at least one of the jets is required to be b-tagged (sbottom searches) or c-tagged (stop searches). Most recent results from several analysis performed by the CDF and D0 collaborations are presented.
122989916
Search for charmed particles with the heavy liquid bubble chamber BIBC
Abstract In a search for short lived particles with a high resolution C 3 F 8 bubble chamber and a streamer chamber, 21 charmed meson candidates produced by 340 GeV cπ − have been identified. The cross section for associated charm production is (28±11) μb per nucleon assuming a linear A -dependence. The mean lifetimes of the D mesons in units of 10 −13 s are τ( D 0 , D 0 ) = 4.1 −1.3 +2.6 ± 0.5, τ( D ± ) = 6.3 −2.3 4.8 ± 1.5 .