High Energy and Nuclear Seminar (Fall 05)

The group has a weekly Friday seminar as well as Tuesday brown bag lunch meeting. The later generally involves a talk by students or other members of the group, and offers an informal settings for discussion of current issues.

Friday Seminar

The origin of the highest energy cosmic rays has remained a profound mystery for decades. Physicists are generally interested in cosmic ray sources as potential "beam generators", providing a source of particles (including, perhaps, neutrinos) with energies far beyond that which could ever be achieved by particle accelerators on Earth. But arguably even more compelling is the underlying astrophysical mystery as to the nature of the accelerating engines for cosmic rays. Are ultra-high energy cosmic rays accelerated in jets of accreting black holes? Do they derive from relativistic shocks in intergalactic space? Are cosmic rays generated during gamma-rays burst events? Or do cosmic rays result from the decay of semi-stable super-massive particles left over from the Big Bang? In this talk, I will look at how the data from cosmic rays can be used to address these questions. I will emphasize in particular new first results from the Pierre Auger Cosmic Ray Observatory, including the spectrum, searches for anisotropy, and constraints on gamma-rays fraction, which already place important constraints on many models for cosmic ray origin.

Tuesday Baglunch

PRIMEX is an ambitious experiment that plans to make a measurement of the neutral pion lifetime with a precision of 1-2%. The first phase of data taking was completed Nov. 2004. I will give an update on the data analysis so far, and what we hope to accomplish in 2006.

Departmental Colloquium

When a high-energy particle such as a gamma-ray, neutron or cosmic-ray muon is incident on an ultra-low temperature system such as superfluid 3-He, it may heat a small region of the liquid to temperatures of the order of a thousand times the ambient one. The recovery from this very unusual situation, and its possible consequences for the nucleation of first-order phase transitions, topological singularities, etc., provide a fascinating challenge to theory. I will discuss some of these problems in the context of the Stanford experiments on nucleation of the 3-He B phase by radiation and the recent neutron experiments on 3-He which are designed to mimic the behavior of the early Universe.

Tuesday Baglunch

In gravitational physics, the notion of mass-energy turns out to be complicated to define. In part, this is because the usual notion of a conserved energy depends on an underlying time translation invariance of the theory, but also because "everything gravitates", including the gravitational field itself. On the other hand quantum field theory poses its own challenges to defining the mass of a particle, especially when the particle is in a thermal bath or interacts with an external field. On the thrid hand, particle experimentalists will happily explain what it is they measure! Come for a discussion, and presentations of some approaches to these issues.

Tuesday Baglunch

One of the most compelling mechanisms to explain the the matter-antimatter asymmetry in the Universe is leptogenesis because it is tightly connected to neutrino phenomenology. I will introduce the seesaw mechanism for neutrino masses, show how leptogenesis works and explain how constraints for neutrino masses arise from leptogenesis.

Friday Seminar

The considerable center-of-mass energy and luminosity at the LHC will ensure a discovery reach for new particles which extends well into the multi-TeV region. ATLAS has carried out many studies of the implications of this capability for Beyond the Standard Model Physics. In this talk, I will focus on studies involving extra-dimensions, little higgs, strong symmetry breaking, compositeness and new gauge bosons. I will also discuss the impact of possible LHC upgrades on these physics capabilities of the ATLAS detector.

To view the transparencies of this talk, click at these links: pdf and ppt.

Friday Seminar

Dark matter has been around for a long time. Originally, it was needed to explain galactic dynamics and more recently, evidence has come from microwave background and supernova measurements. However, we still do not know what dark matter is. One general idea is that dark matter is composed of fundamental particles and I will discuss some aspects of the three main ways of looking for particle dark matter: direct searches and two type so indirect searches. Each tells us something a different about dark matter in our galaxy. I will talk about new interpretations of recent results and some new experimental ideas.

To view the transparencies of this talk, click at these links pdf and ppt.

Tuesday baglunch

The effective theory of an initial state is a method for encoding the effects of new physics in the short distance properties of a state. This talk describes the construction of an effective state and its renormalization and discussed how it is applied in the trans-Planckian problem of inflation. The effective state idea then provides a general, model-independent, parameterization of the trans-Planckian signal in the cosmic microwave background. The talk concludes with an overview of the prospects for observing this signal.

To view the transparencies of this talk, click at these links: pdf and pdf

Friday Seminar

I will review the latest evidence for neutrino oscillations and show that we now know that neutrinos are massive particles. With this evidence in the bag I will then move on and describe how we are planning to measure the neutrino mass scale in a not-too-far future. Along the way I will also discuss some of the first glimpses of an "applied neutrino physics", a new field in science. This trip will take us into the land of astrophysics, particle, nuclear, atomic, condensed matter physics as well as geophysics.

To view the transparencies of this talk, click at this link: pdf.

Friday Seminar

A new resonant method of studying nuclear Electric Dipole Moments (EDM) in storage rings will be presented. A deuteron EDM at 10^-29 e cm, and a proton EDM at 10^-28 e cm will have the best sensitivity of current or planned experiments on theta_qcd, quark-color EDMs.

To view the transparencies of this talk, click at this link: ppt.

Departmental Colloquium

Einstein's theory of general relativity provides us with our modern understanding of gravitation, incorporating the principles of relativity into gravity. A consequence of this incorporation is that gravity must radiate: accelerating masses generate gravitational waves in the same way that accelerating charges generate electromagnetic waves. Gravity's relative weakness means that this radiation couples very weakly to matter; the effects of these waves are thus subtle and difficult to measure. A newly developed network of detectors is now on the cusp of being able to measure these waves from violent astrophysical processes; future improvements and the development of space-based detectors promise to make such measurements routine. Presented in this talk will be the basics of gravitational-wave physics, describing the properties of the radiation, how it is generated by accelerating masses, and how it may be measured by its tidal imprint. Mention will be made of the detectors currently operating, as well as plans for future upgrades and for space-based detectors. Finally, the science reach of these measurements will be discussed. Gravitational waves' greatest impact will be as a tool for astronomy, opening a direct window onto phenomena that cannot be easily probed otherwise.

Tuesday Baglunch

Our very existence is a direct evidence of the fact that the Universe has a nonzero baryon number. The Standard Model does not have the ingredients that are necessary to produce the observed baryon asymmetry. Therefore, the presence of such an asymmetry is the most direct evidence of the existence of some new Physics beyond the Standard Model. In this presentation, I will review the criteria needed for the generation of a baryon asymmetry, and discuss some of the most popular mechanisms to achieve it. In particular, I will focus on a mechanism based on supersymmetry ("Affleck-Dine baryogenesis"), and I will provide a rapid discussion of leptogenesis, a mechanism naturally present in Grand Unified Theories.

Friday Seminar

A variety of new experiments are planned in the next few years to search for dark matter in the forms of WIMPs, or Weakly Interacting Massive Particles. A critical challenge is the development of new detector technologies that are sensitive to small energy depositions, scalable to large masses, and suffer little from radioactive background. In particular, I will discuss the CLEAN and XENON experiments, which will use liquid neon and liquid xenon as detection media.

To view the transparencies of this talk, click at this link: pdf.

Departmental Colloquium

All observational evidence strongly suggest that our universe is essentially devoid of antimatter. The origin of this cosmological matter-antimatter asymmetry is recognized as one of the fundamental questions of modern physics. Interestingly enough, the ingredients for its explanation are contained in the microscopic laws of elementary particle physics. Since 1999, experiments running at particle accelerators in Japan and California have been probing this issued by measuring fundamental disparities in the behavior of particles and antiparticles, via the mechanism of CP (Charge Parity) violation. This talk will describe the experimental program of these experients, known as B-Factories, and present the most recent results, including tantalizing discrepancies with the theoretical predictions of the Standard Model of particle physics that may soon provide insight into "new physics".

DISTINGUISHED FACULTY LECTURE SERIES

In "Candide" Voltaire mocks Pangloss for accepting Leibniz's thesis that this is the best of all possible worlds. But physics may uphold the unfortunate character's view by showing that in most other possible domains life simply could not exist. Physicists are now considering theories of the "multiverse," in which different parts of the universe are physically different by having different properties and values for the constants of nature. Professor Donoghue will explain why we're looking at physical theories of the multiverse, how they change the search for the fundamental theory, and how difficult it will be - philosophically and practically - to test those ideas. Massachusetts Room, Mullins Center

Tuesday Baglunch

This year's big summer conference was the 2005 Lepton-Photon Conference (LP2005). Although no spectacular new results were announced, there were a number of fine talks. Especially interesting were plans for future experimental activities. We consider the flavor physics, neutrino physics, astrophysics and briefly the forthcoming operation of the LHC.

To view the transparencies of this talk, click at these links: pdf and ppt