Observation of Z Decays to B Quark Pairs at the Tevatron Collider

Observation of Z Decays to B Quark Pairs at the Tevatron Collider
Author:
Publisher:
Total Pages: 14
Release: 1998
Genre:
ISBN:

A search for Z boson decays to pairs of b-quark jets has been performed in the full dataset collected with the CDF detector at the Tevatron p{anti p} collider. After the selection of a pure sample of b {anti b} events by means of the identification of secondary vertices from b-quark decays, we have used two kinematic variables to further discriminate the electroweak b {anti b} production from QCD processes, and sought evidence for the Z decay in the dijet invariant mass distribution. An absolute background prediction allows the extraction of an excess of events inconsistent with the background predictions by 3.23? but in good agreement with the amount and characteristics of the expected signal. We then fit the mass distribution with an unbinned likelihood technique, and obtain a Z → b {anti b} signal amounting to 91 ± 30 ± 19 events.

Physics In D>=4: Tasi 2004 - Proceedings Of The Theoretical Advanced Study Institute In Elementary Particle Physics

Physics In D>=4: Tasi 2004 - Proceedings Of The Theoretical Advanced Study Institute In Elementary Particle Physics
Author: John Terning
Publisher: World Scientific
Total Pages: 873
Release: 2006-07-07
Genre: Science
ISBN: 9814477982

This book contains write-ups of lectures from a summer school for advanced graduate students in elementary particle physics. In the first lecture, Scott Willenbrock gives an overview of the standard model of particle physics. This is followed by reviews of specific areas of standard model physics: precision electroweak analysis by James Wells, quantum chromodynamics and jets by George Sterman, and heavy quark effective field by Matthias Neubert. Developments in neutrino physics are discussed by André de Gouvea and the theory behind the Higgs boson is addressed by Laura Reina. Collider phenomenology from both experimental and theoretical perspectives are highlighted by Heidi Schellman and Tao Han. A brief survey of dynamical electroweak symmetry breaking is provided by R Sekhar Chivukula and Elizabeth H Simmons. Martin Schmaltz covers the recent proposals for “little” Higgs theories. Markus Luty describes what is needed to make supersymmetric theories realistic by breaking supersymmetry. There is an entire series of lectures by Raman Sundrum, Graham Kribs, and Csaba Csáki on extra dimensions. Finally, Keith Olive completes the book with a review of astrophysics.

Search for Pair Production of a New B' Quark that Decays Into a Z Boson and a Bottom Quark with the ATLAS Detector at the LHC

Search for Pair Production of a New B' Quark that Decays Into a Z Boson and a Bottom Quark with the ATLAS Detector at the LHC
Author: Andre Milton Bach
Publisher:
Total Pages: 260
Release: 2012
Genre:
ISBN:

A search with the ATLAS detector for the pair production of a new b' quark in the Z boson plus b quark decay channel is reported. The pp collision data comprise 4.7 fb-1 of integrated luminosity at sqrt(s) = 7 TeV collected at the CERN Large Hadron Collider in 2011. This search complements recent searches for a b' decaying to a W boson and a top quark, and it is particularly important for new physics models containing vector-like quarks. From events containing both a Z boson reconstructed from electrons and a b tagged jet, any potential signal is enriched by selecting a subsample with large b' candidate pT. No evidence for a b' signal is found in this subsample; the invariant mass spectrum of the b' candidate agrees well with the Standard Model prediction. For the case of a b' that decays only to Z + b, masses mb'

Discovery of Single Top Quark Production

Discovery of Single Top Quark Production
Author: Dag Gillberg
Publisher: Springer Science & Business Media
Total Pages: 149
Release: 2011-01-22
Genre: Science
ISBN: 1441977996

The top quark is by far the heaviest known fundamental particle with a mass nearing that of a gold atom. Because of this strikingly high mass, the top quark has several unique properties and might play an important role in electroweak symmetry breaking—the mechanism that gives all elementary particles mass. Creating top quarks requires access to very high energy collisions, and at present only the Tevatron collider at Fermilab is capable of reaching these energies. Until now, top quarks have only been observed produced in pairs via the strong interaction. At hadron colliders, it should also be possible to produce single top quarks via the electroweak interaction. Studies of single top quark production provide opportunities to measure the top quark spin, how top quarks mix with other quarks, and to look for new physics beyond the standard model. Because of these interesting properties, scientists have been looking for single top quarks for more than 15 years. This thesis presents the first discovery of single top quark production. It documents one of the flagship measurements of the D0 experiment, a collaboration of more than 600 physicists from around the world. It describes first observation of a physical process known as “single top quark production”, which had been sought for more than 10 years before its eventual discovery in 2009. Further, his thesis describes, in detail, the innovative approach Dr. Gillberg took to this analysis. Through the use of Boosted Decision Trees, a machine-learning technique, he observed the tiny single top signal within an otherwise overwhelming background. This Doctoral Thesis has been accepted by Simon Fraser University, Burnaby, BC, Canada.

Physics in D >

Physics in D >
Author: John Terning
Publisher: World Scientific
Total Pages: 876
Release: 2006
Genre: Science
ISBN: 9812568093

This book contains write-ups of lectures from a summer school for advanced graduate students in elementary particle physics. In the first lecture, Scott Willenbrock gives an overview of the standard model of particle physics. This is followed by reviews of specific areas of standard model physics: precision electroweak analysis by James Wells, quantum chromodynamics and jets by George Sterman, and heavy quark effective field by Matthias Neubert. Developments in neutrino physics are discussed by Andr‚ de Gouvea and the theory behind the Higgs boson is addressed by Laura Reina. Collider phenomenology from both experimental and theoretical perspectives are highlighted by Heidi Schellman and Tao Han. A brief survey of dynamical electroweak symmetry breaking is provided by R Sekhar Chivukula and Elizabeth H Simmons. Martin Schmaltz covers the recent proposals for ?little? Higgs theories. Markus Luty describes what is needed to make supersymmetric theories realistic by breaking supersymmetry. There is an entire series of lectures by Raman Sundrum, Graham Kribs, and Csaba Cs ki on extra dimensions. Finally, Keith Olive completes the book with a review of astrophysics.

B Decays

B Decays
Author: Sheldon Stone
Publisher: World Scientific
Total Pages: 676
Release: 1994
Genre: Science
ISBN: 9789810218362

This 2nd edition is an extensive update of "B Decays?. The revisions are necessary because of the extensive amount of new data and new theoretical ideas. This book reviews what is known about b-quark decays and also looks at what can be learned in the future.The importance of this research area is increasing, as evidenced by the approval of the luminosity upgrade for CESR and the asymmetric B factories at SLAC and KEK, and the possibility of experiments at hadron colliders.The key experimental observations made thus far, measurement of the lifetimes of the different B species, B0-B0 mixing, the discovery of ?Penguin? mediated decays, and the extraction of the CKM matrix elements Vub and Vcb from semileptonic decays, as well as more mundane results, are described in great detail by the experimentalists who have been closely involved with making the measurements. Theoretical progress in understanding b-quark decays using HQET and lattice gauge techniques are described by theorists who have developed and used these techniques.Synthesizing the experimental and theoretical information, several articles discuss the implications for the ?Standard Model? and how further tests can be done using measurements of CP violation in the B system.

Observation of Top Quark Pairs Produced in Association with a Vector Boson in Pp Collisions at {u221A}(s)

Observation of Top Quark Pairs Produced in Association with a Vector Boson in Pp Collisions at {u221A}(s)
Author:
Publisher:
Total Pages: 52
Release: 2016
Genre:
ISBN:

Measurements of the cross sections for top quark pairs produced in association with a W or Z boson are presented, using 8 TeV pp collision data corresponding to an integrated luminosity of 19.5 fb-1, collected by the CMS experiment at the LHC. We found that final states are selected in which the associated W boson decays to a charged lepton and a neutrino or the Z boson decays to two charged leptons. Signal events are identified by matching reconstructed objects in the detector to specific final state particles from tt-W or tt-Z decays. The tt-W cross section is measured to be 382+117 -102 fb with a significance of 4.8 standard deviations from the background-only hypothesis. The tt-Z cross section is measured to be 242+65 -55 fb with a significance of 6.4 standard deviations from the background-only hypothesis. These measurements are used to set bounds on five anomalous dimension-six operators that would affect the tt-W and tt-Z cross sections.

A Search For The Z {u2192} B Anti-b Process at The D-Zero Experiment

A Search For The Z {u2192} B Anti-b Process at The D-Zero Experiment
Author:
Publisher:
Total Pages: 185
Release: 2006
Genre:
ISBN:

In 2001, the D0 experiment entered a new era. Run II of the Tevatron at the Fermi National Accelerator Laboratory began, and the collider became the highest energy particle accelerator in the world. Accordingly, the D0 detector had already undergone a series of upgrades in order to fully exploit the physics now within reach. These included improvements to the tracking, calorimetry, muon detection and triggering capabilities. In the Standard Model, the Higgs boson is the last piece of the puzzle that remains to be discovered. The Higgs mechanism and consequently the Higgs boson is thought to be the fundamental ingredient by which particles acquire mass, and its existence (or lack of existence) is one of the most pressing issues in particle physics today. As such, one of the main goals of the Run II physics programme at D0 is to search for it. Armed with new accelerator capabilities, D0 will be able to impose tighter constraints on the mass of the Higgs, and perhaps even detect this elusive particle. If the Higgs does exist, it will be extremely difficult to find. One of the main challenges at a hadron-hadron collider is to reduce the large QCD background that masks the relatively tiny Higgs signal. Experimental evidence indicates that the Higgs mass is relatively low, in which case it will decay predominantly to a b$ar{b}$ quark-antiquark pair. The daughter products that must be used to reconstruct the parent Higgs are therefore likely to be heavy flavour b-quark jets whose energies must be known as accurately as possible. In the first part of this thesis consideration is given to these jets, in particular to the jet energy resolution and dijet mass resolution that they could offer. One way of investigating the necessary tools for such a Higgs search is to study a very similar decay to that of a low-mass Higgs particle: a Z boson decaying to a b quark and an anti-b-quark. This signal, not previously observed at the Tevatron, offers an ideal testbed in which to explore suitable triggering and analysis techniques. It also offers us the opportunity to further our understanding of b-quark jets in a hadronic environment, an element crucial to much of the physics at D0. To this end, the first search has been performed at D0 for the Z → b$ar{b}$ decay, using the initial 300 pb-1 of data from Run II. Triggers have been specifically designed and implemented for this purpose. Here we present evidence for Z → b$ar{b}$ decays. An excess of 1260 ± 130 (stat.) ± 260 (syst.) events is observed, which is in good agreement with Monte Carlo predictions and amounts to a Z → b$ar{b}$ signal of 4.3 standard deviations.