March 2006

Monday, March 13th, 2006, 4:00 PM
ISB 102
Note: Unusual time and location!

Top Quark Production at Hadron Colliders

Joao Guimaraes da Costa (Harvard/Fermilab)

The top quark has been discovered ten years ago at the Tevatron Collider at Fermilab. The small data samples collected until recently did not permit precise measurements of the top quark properties. However, a new era of high-statistics top quark physics is just starting and full reconstruction of top decays will be pivotal. In this talk, I will describe how top quarks are produced and identified at hadron colliders. I will focus on the latest measurements of the top quark pair-production cross section and the top mass at the CDF experiment, which benefited from recent improvements in b-quark identification. These measurements have reached a new level of precision and provide a window into the physics at the Large Hadron Collider.


Friday, March 10th, 4:00 PM
ISB 102
Note: Unusual time and location!

Top Quark Physics at Hadron Colliders

Arnulf Quadt (Bonn/Rochester/Fermilab)

The top quark with a mass of about 175 GeV is by far the heaviest amongst the six quarks. It was discovered only recently, in 1995, by the CDF and D0 experiments at the proton-antiproton collider Tevatron, at sqrt(s) = 1.8 TeV. Consequently, relatively little is known about the top quark. For example, its electric charge has so far not been measured directly. The precise knowledge of the mass of the top quark is crucial for the quantitative understanding of radiative corrections in the Standard Model. Due to its large mass, the top quark is special in several respects and behaves differently from the other quarks. Its weak interactions, for example in its dominant decay to a b-quark and a W-boson, is stronger than the formation of bound states due to the strong force. Therefore, its production and decay properties such as spin correlations and helicity information are propagated to its decay products before they can be diluted by chromomagnetic interactions. Hence, the top quark serves as a unique laboratory for tests of weak and strong interactions in the Standard Model and searches for new physics. In this seminar, the latest measurements and studies of top quark properties, obtained at the Tevatron RunII, are summarized and an outlook for the physics potential of the Large Hadron Collider in the top quark sector is given.


Wednesday, March 8th, 4:00 PM
ISB 102
Note: Unusual time and location!

Tracking challenges at LHC and ILC

Ariane Frey (Max Planck Institute)

The Large Hadron Collider (LHC), scheduled to start data taking in 2007, and the possible future International Linear Collider (ILC) will provide exciting opportunities to study particle interactions at the TeV scale where new phenomena are expected to manifest themselves. The tracking components of the large detectors at these accelerators play a crucial role in exploiting the rich physics potential. The tracking devices will live in challenging, albeit very different environments. In this seminar I will focus on the solution chosen by CMS at LHC of a full Silicon tracker and on a candidate vertex detector for an experiment at the ILC based on the DEPFET (DEpleted P-channel Field Effect Transistor) technology.


Friday, March 3rd, 4:00 PM
ISB 310
Note: Unusual time!

An Improved Measurement of the Top Quark Mass from DZero

Ariel Schwartzman (Princeton/Fermilab)

The top quark mass is a fundamentally important parameter of the Standard Model. The fact that the top quark is much more massive than the other fermions has led to speculation that it has a special role within the Standard Model, and that its interactions may be sensitive to new physics. A precise measurement of the top quark mass, in conjunction with further improvements in the W mass measurement, will allow us to place stringent constraints on the Standard Model Higgs boson mass and set the stage for a final confrontation of the Standard Model at the Large Hadron Collider.
I will present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state, using data collected with the DZero experiment at the Fermilab Tevatron collider.
The Matrix element method makes extensive use of the available statistical information and has been extended for the first time to include b-quark jet tagging using secondary vertex reconstruction to further improve the precision of the measurement.



Monday, February 27th, 4:00 PM
ISB 310
Note: Unusual time!

The Rarest B Decay: The Electroweak Penguin Process b -> s l+ l- at the BaBar Experiment

Jeffrey Berryhill (UCSB/SLAC)

The BaBar experiment currently underway at the Stanford Linear Accelerator Center has recorded roughly half a billion B meson decays. These unprecedentedly large samples allow for the measurement of the rare flavor-changing neutral current B decays, which in the Standard Model can only proceed through electroweak loop "penguin" diagrams. The decay rates and distributions of penguin decays can be dramatically modified by new physics at the electroweak scale, with a sensitivity comparable to the highest-energy colliding beam experiments. The electromagnetic penguin decay b -> s gamma has been known about experimentally for over a decade and is now a high-precision test of the Standard Model. The more rare electroweak penguin decay b -> s l+ l-, however, has only recently been uncovered experimentally and provides entirely new tests of flavor physics at the electroweak scale. I will describe the experimental techniques for successfully measuring these decays, which occur less than once per million mesons produced, as well as presenting measurements of the many observables in this process which unambiguously test the electroweak theory.

Wednesday, February 22nd, 4:00 PM
ISB 102
Note: Unusual time and location!

Searches for the Standard Model Higgs Boson at CDF

Jason Neilsen (LBL)

The Higgs boson, which plays a central role in electroweak symmetry breaking as described by the standard model, has not yet been observed experimentally. Final search results from the four LEP experiments indicate that the mass of the Higgs boson must be greater than 114 GeV/c2. Experiments at the Tevatron, currently the world's highest-energy particle accelerator, have taken up the hunt and seek to pin down the standard model Higgs boson mass through both direct searches and precision electroweak measurements. The direct search for Higgs boson production and decay requires detailed knowledge of the data sample composition which pushes experimental technique and collider phenomenology to the bleeding edge. Results from the search for the Higgs boson using data from the Collider Detector at Fermilab highlight the challenges of new particle searches at present and future hadron colliders.

Tuesday, February 14th, 10:30 AM
ISB 310

The Spectrum of Markarian 421 Above 100 GeV with STACEE

Jennifer Carson (SLAC)

Markarian 421 was the first blazar detected above 300 GeV, and it remains one of only ten known TeV blazars. TeV measurements of its flaring activity and spectral variability have placed some of the best constraints to date on models of the high-energy emission from blazars. However, observations between about 50 and 300 GeV are rare, and the high-energy peak of the spectral energy distribution (SED), predicted to be in this range, has never been directly detected. We present the spectrum of Markarian 421 above 100 GeV as measured by the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE). STACEE is a ground-based Cherenkov telescope using the wavefront sampling technique to detect gamma rays at lower energies than achieved by imaging telescopes. We discuss the STACEE observations of Markarian 421 in the context of coincident multiwavelength observations and show that the results suggest that we may be! detecting the high-energy peak of the SED for the first time.


Friday, February 10th, 4:00 PM
ISB 102
Note: Unusual time and location!

Single Top Quark Physics

Reinhard Schwienhorst (Michigan State/Fermilab)

Even though it has been over ten years since the top quark discovery, still only very little is known experimentally about this elusive particle. We are currently investigating the top quark and its interactions at the Fermilab Tevatron proton-antiproton collider. Of particular interest is the electroweak interaction of the top quark because of its link to electroweak symmetry breaking. At the Tevatron, this interaction produces a unique final state signature of only a single top quark. I will present the status of searches for electroweak production of single top quarks.


Monday, February 6th, 4:00 PM
ISB 310
Note: Unusual time!

Measurement of the ttbar cross section and search for anomalous semi-leptonic decays at CDF

Anyes Taffard (UIUC/Fermilab)

Ten years have passed since the top quark discovery and still very little is known experimentally about the heaviest of the quarks. In this talk, I will review the production and decay mechanisms of the top quark, discuss the techniques used to identify b-jets from top decay and report on the measurement of the top production cross section. I will then follow up on the Run I CDF excess of jets in W+jets events with both a secondary vertex and a semileptonic decay, which indicated a possible anomalous rate of semileptonic decay from heavy flavor hadrons.


Wednesday, February 1st, 4:00 PM
ISB 102
Note: Unusual time and location!

Bump Hunting and Hadron Spectroscopy at the B Factories

David C. Williams (SCIPP & SLAC)

One of the byproducts of the B factory experiments is an enormous sample of charm flavor data. The analysis of this charm data has resulted in the discover of a plethora of new particles, including several types of new specifies of charmonium, charm mesons, and charm baryons. In this talk I review the status of hadron spectroscopy at the B factories, explore some of the theoretical and experimental challenges poised by some of the more controversial discoveries, and present one of the latest discoveries by BaBar.


Wednesday, January 11th, 2:00 PM
ISB 310
Note: Unusual time!

How to Use Nuclear and Particle Physics to Solve Real Life Problems

Ivan Novikov (Purdue)

I show how methods of nuclear and particle physics can be used to detect, identify and locate various hidden substances.  We focus on developed at Purdue neutron interrogation systems for elemental analysis of special materials in sealed containers.


Tuesday, January 10th, 10:30 AM
ISB 102
Note: Unusual location!

X-ray Observations of Cataclysmic Variable Stars

Dirk Pandel (UC Santa Barbara)

For the past 6 years, XMM-Newton and Chandra have been providing us with X-ray data of excellent sensitivity and spectral resolution and have greatly improved our understanding of the high-energy processe in many astronomical objects. I will discuss what we have learned about the physics of accretion in magnetic and nonmagnetic Cataclysmic Variable Stars.


Friday, January 6th, 2:00 PM
ISB 310
Note: Unusual time!

Qinglin Zeng (Colorado State)

Please click here to view title and abstract