Last updated: 01/07/08
Tuesday, April 3rd, 10:30am, ISB 310

Paul Kunz (SLAC)

HippoDraw: interactive and Python scriptable data analysis package

Python is a dynamic object-oriented programming language that can be used for many kinds of software development. It offers strong support for integration with other languages and tools, comes with extensive standard libraries, and can be learned in a few days. Many Python programmers report substantial productivity gains and feel the language encourages the development of higher quality, more maintainable code. Increasingly, scientists from all fields are using Python in their data analysis. Combined with numerical packages such as numarray, one has array manipulation and computational capabliities similar to those found in IDL, Matlab or Octave, and one can write many efficient numerical data processing applicationss directly in Python. HippoDraw can be used as a stand-a-lone application for highly interactive data visusalization of tabular data in files. Moreover it can be integrated into a Pyhton application including support for numerical arrays. The talk will include a demonstration of Hippodraw/python's capabilities.

Monday, April 9th, 10:30am, ISB 310

Chris Hays (University of Oxford)

First Run II Measurement of the W Boson Mass with CDF

I present a new measurement of the W boson mass from the CDF Collaboration. With a total uncertainty of 48 MeV/c^2, this is the single most precise W mass measurement to date. The world uncertainty on the W mass has been reduced from 29 MeV/c^2 to 25 MeV/c^2, further constraining the mass of the Higgs boson in the context of the Standard Model.

Tuesday, April 10th, 10:30am, ISB 102

Juerg Diemand (UCSC Astronomy Dept.)

Formation and evolution of CDM halos and their substructure

Massive supercomputer simulations now allow to follow the formation and evolution of CDM halos and their subhalo population in detail. We have recently completed the "Via Lactea" run: It resolves a Milky Way scale halo with over 200 million particles, over ten times more than the previous largest run. It resolves over 10'000 subhalos, some inside the solar circle, many sub-subhalos and the mass in substructure has still not converged, i.e. it is growing with better numerical resolution. This wealth of small scale structure has implications for direct and indirect dark matter detection, stellar streams, disk heating, gravitational lensing and the Local Group dwarf galaxy population (the "missing satellites problem").

Tuesday, April 17th, 10:30am, ISB 310

Ken-Ichi Nishikawa (National Space Science and Technology Center, NASA)

Particle acceleration, magnetic field generation, and associated emission in relativistic jets

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

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Wednesday, 18th April, 12:30pm, ISB102

Tesla Jeltema ( The Observatories of the Carnegie Institution of Washington (OCIW))

The Evolution of Structure in Cluster of Galaxies

Large-scale structure has long been known to encode basic information about our universe. One often used cosmological probe are clusters of galaxies; however, many clusters are not relaxed objects. Clusters are built through the accretion of smaller groups of galaxies and through mergers with neighboring clusters. The frequency of mergers and the amount of time since the peak of cluster formation depend on cosmology. I will describe a study of the frequency of cluster mergers through time by quantifying the amount of substructure in clusters versus redshift. Based on Chandra observations, we find that, as expected qualitatively in hierarchical models of structure formation, the amount of substructure in clusters increases with redshift. This systematic trend of cluster dynamical state with time has important implications for cosmological studies with clusters, the detection of clusters in surveys, and studies of the physics of the cluster gas. On the theoretical side, I will describe an ongoing study of cluster structure in hydrodynamic simulations.

Tuesday, 24th April, 10:30am, ISB 310

Jeff Scargle (Space Science Division, NASA Ames Research Center)

Quantum Gravity based Photon Dispersion: Theory and GLAST Observations

It has long been known that the properties of gamma-ray bursts may allow detection of quantum-gravity-based photon dispersion. The timing properties (narrow pulse structures vs. cosmological light travel times --> dt / T ~ 10**18) may make up for the fact that the relevant photon energies are small on the Planck scale ( E/E_planck ~ 10**-18 ). But how likely is it that such effects exist, and will GLAST be able to detect them?

I will discuss two topics:

(1) What the many existing flavors of QG theory have to say about a
possible dependence of the speed of light on photon energy (or
violation of Lorentz invariance).

(2) A new data analysis technique for detecting energy-dependent lags
with GLAST data. This completely bin-free technique is
discussed in http://arxiv.org/abs/astro-ph/0610571

Monday, 30th April, 10:00am, ISB 310

Peter wagner (Texas A&M)

Search for Heavy, Neutral, Long-Lived Particles that Decay to Photons at CDF

Searches for events with final state photons and missing transverse energy (MET) at collider experiments are sensitive to new physics from a wide variety of models including gauge mediated supersymmetry breaking (GMSB). In these models the lightest neutralino (chi_10) decays into a photon and a weakly interacting, stable gravitino that gives rise to MET by leaving the detector without depositing any energy. The observation of an eegammagamma+MET candidate event by the CDF experiment during Run I at the Fermilab Tevatron has increased the interest in experimental tests of this class of theories. Most subsequent searches have focused on promptly produced photons, however the chi_10 can have a lifetime on the order of nanoseconds or more. In this talk I present the results of the first search for heavy, long-lived particles that decay to photons at a hadron collider using the newly installed EMTiming system at CDF to identify chi_10 candidates by virtue of their producing photons with a "delayed" arrival time.

Tuesday, 1st May, 10:30am, ISB 310

Bill Lockman (SCIPP)

Evidence for D0-D0bar mixing

A neutral meson which is not self-conjugate may undergo quantum mechanical mixing with its corresponding anti-particle through the weak interaction. This process has been observed for mesons containing down-type quarks, e.g., the neutral strange (K0) and bottom mesons (B0-d, B0-s). On the other hand, mixing of the lowest-lying neutral meson containing up-type quarks, the D0, is highly suppressed in the Standard Model, I will present the first experiment results showing evidence for D0-D0bar mixing in a study of D0->Kpi decays from the BaBar experiment. These measurements provide a new prole of the Standard Model of particle physics.

Tuesday, 8th May, 10:30am, ISB 310

Don Coyne (SCIPP)

A Scenario for Strong Gravity without Extra Dimensions

This talk first reviews why many physicists think strong gravity, extra dimensions and black holes may be discovered at LHC. Then I offer a different possible reason for the apparent weakness of the gravitational interaction, and explore a simple model showing quantitative results of surprising richness resulting from this assumption.

The consequences for Hawking evaporation of a Schwarzschild black hole show the hole will undergo a type of phase transition resulting in variously long-lived objects of reasonable sizes, with normal thermodynamic properties and inherent duality characteristics.

In particular, this scenario predicts a completely different pattern and behavior for black hole production at LHC, and makes a connection between these objects and basic elements of low-energy theories.

(No audience pre-knowledge of the intricacies of black hole thermodynamics or other arcane theory is assumed for this talk!)

Tuesday, 22nd May, 10:30am, ISB 310

Andreas Zoglauer (Space Sciences Lab, UC Berkeley)

The Advanced Compton Telescope - Goals, Design Options, and Data Analysis

The Advanced Compton Telescope (ACT) is the next major step in medium-energy gamma-ray astronomy and will enable high sensitivity spectroscopy, imaging, and polarization measurements. Its key science objectives include high resolution spectroscopy of nuclear emission from supernova explosions, all-sky monitoring for transients and rapid localizations, high sensitivity to positron annihilation emission, etc. During ACT's Vision Mission concept study several design options based on different detector concepts and slightly varying measurement principles were analyzed. The most important concepts will be presented. The large amount of measured parameters, the high background in the nuclear line regime, and the complex response of a Compton telescope ("event cones") make the data analysis a real challenge. I will give a short introduction into the two main steps, event and image reconstruction.

Tuesday, 29th May, 10:30am, ISB 310

John Rice (Department of Statistics, UC Berkeley)

Event Weighted Tests for Detecting Periodicity in Photon Arrival Times

I will discuss the statistical problem of detecting periodicity in a sequence of photon arrival times. This occurs, for example, in attempting to detect gamma-ray pulsars. A particular focus is on how auxiliary information, typically source intensity, background intensity, and incidence angles and energies associated with each photon arrival should be used to maximize the detection power. I will present a class of likelihood-based tests, score tests, which give rise to event weighting in a principled and natural way, and derive expressions quantifying the power of the tests.

Tuesday, 5th June, 10:30am, ISB 310

Antonello Polosa (CERN)

The PVLAS anomaly

The PVLAS experiment at LNL (Italy) reports the experimental observation of vacuum magnetic dichroism (and birefringence). If this result is confirmed --many alternative experiments have been proposed to test it-- theory will have to explain an intriguing new physics phenomenon. I will describe the experimental set-up and the effect observed. Then I will review the models suggested to explain the PVLAS anomaly including axion-like particles and `millicharges`. Cosmological implications and constraints will also be discussed.