SCIPP Seminar Archive


SCIPP Seminar Home

Winter Quarter 2012 Archive

Last updated: March 15, 2012

PLEASE NOTE SPECIAL DAY & LOCATION: Wednesday, March 14, 10:30am
Wednesday, March 14: 10:30am
Location: ISB 310
Ning Zhou (UC Irvine)
Title: Search for same-sign top-quark production and fourth-generation down-type quarks


A search is presented for same-sign top-quark production and down-type heavy quarks of charge -1/3 in events with two isolated leptons (electron or muon) that have the same electric charge, at least two jets and large missing transverse momentum. The data are selected from pp collisions at sqrt(s)=7TeV recorded by the ATLAS detector and correspond to an integrated luminosity of 1.04fb-1. The observed data are consistent with expectations from Standard Model processes. Upper limits are set at 95% confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0pb depending on the assumed mediator mass. Upper limits are also set on the pair-production cross-section for new heavy down-type quarks; a lower limit of 450GeV is set at 95% confidence level on the mass of heavy down-type quarks under the assumption that they decay 100% of the time to W+top.

Friday March 9: 12:30pm
Location: ISB 310
Toru Tanimori (Department of Physics, Faculty of Science, Kyoto University, Kyoto, Japan)
Title: Electron Tracking Compton Camera with Balloon Experiment for celestial and terrestrial MeV gamma-rays in the North Pole and its application to Medical Imaging.


To explore MeV gamma-ray astronomy, we have developed Electron Tracking Compton Camera (ETCC) consisting of a gaseous Time projection Chamber (TPC) based on the micro pixel gas counter and Scintillator pixels. By measuring the 3D-track of a recoil electron in TPC, ETCC can measure the direction of gamma-rays photon by photon with a 3str wide field of view, and provides both a good background rejection and an angular resolution of ~1degree at 1MeV (FWHM). Our final goal using a 1x1x0.5m size satellite ETCC is the all-sly survey with several ten times better sensitivities of COMPTEL. We already carried out the observation of celestial sub-MeV gamma rays using with a small ETCC with a balloon (Sub-MeV gamma ray Imaging Loaded-on-balloon Experiment: SMILE-I) in 2006, and successfully obtained diffuse cosmic and atmosphere gamma ray. Now we are constructing a medium ETCC with a 30 cm cubic for the next balloon experiment to catch gamma-rays from the Crab and terrestrial gamma-ray burst occurred in North Pole in 2013. Also ETCC has a capability to find a high-z Gamma-Ray Bursts beyond z>10 by detecting MeV gamma rays from long duration GRBs of Population-III stars.

In addition, I would like to mention on the application for both molecular imaging and medical imaging using a new type of RI emitting higher energy gamma rays than 500kev, and proton therapy beam.

Tuesday, March 6: 10:30am
Location: NS2 307
Kevork Abazajian (UC Irvine)
Title: Deviant Dark Matter: Indirect Indicators of and Constraints on the Nature of Dark Matter


Unexpected cosmic-ray and gamma-ray signals have recently been claimed as sourced by dark matter annihilation. Cosmic-ray signals are constrained by higher-energy gamma-ray observations, and gamma-ray signals prove to be consistent with stellar remnants as well as dark matter. In another regime, small-scale cosmological structure, at the sub-Galactic scale, has indicated potential deviations from the canonical weakly-interacting cold dark matter paradigm. I will review the status of dark matter candidates' potential solutions of these "deviant" signals.

SPECIAL SCIPP THEORY SEMINAR: Tuesday, February 28, 12:15pm, ISB 231
Tuesday, February 28: 12:15pm
Location: ISB 231
Chris Kelso (University of Chicago)
Title: Toward A Consistent Picture For CRESST, CoGeNT and DAMA


Three dark matter direct detection experiments (DAMA/LIBRA, CoGeNT, and CRESST-II) have each reported signals which resemble that predicted for a dark matter particle with a mass of roughly 10 GeV. I will compare the signals of these experiments and discuss whether they can be explained by a single species of dark matter particle, without conflicting with the constraints of other experiments. I will show that the spectrum of events reported by CoGeNT and CRESST-II are consistent with each other and with the constraints from CDMS- II, although some tension with xenon-based experiments remains. Similarly, the modulation signals reported by DAMA/LIBRA and CoGeNT appear to be compatible, although the corresponding amplitude of the observed modulations are a factor of at least a few higher than would be naively expected, based on the event spectra reported by CoGeNT and CRESST-II. I will also discuss some ways that this apparent discrepancy could potentially be resolved.

Tuesday, February 28: 10:30am
Location: ISB 102
Patrick Draper
Title: Basic Consequences of mh=125 GeV for the MSSM and Gauge Mediation


Recently, the ATLAS and CMS collaborations have found evidence for a Standard Model-like Higgs boson at a mass near 125 GeV. In the parameter space of the MSSM, a 125 GeV Higgs implies either extremely heavy stops or large stop mixing. In gauge-mediated models of SUSY-breaking, the mixing parameter is small at the messenger scale. Such models can realize large mixing at the electroweak scale only if a gaugino is very heavy, likely beyond the reach of the LHC. In such cases the NLSP is typically long-lived, stop masses become tachyonic at high scales, and the level of fine-tuning is part per mil. Viable models of gauge mediation are therefore quite restricted or must incorporate new Higgs-sector physics.

Tuesday, February 21: 10:30am
Location: ISB 102
Leonardo Senatore (Stanford)
Title: On Loops in Single Field Inflation
Abstract: TBA
Tuesday, February 14: 10:30am
Location: ISB 102
Shih-Chieh Hsu (LBNL)
Title: Measurements of dibosons with the ATLAS detector and associated constraints on new physics


The production of pairs of bosons at the highest available energies delivered by Large Hadron Collider (LHC) is of great interest since it provides a unique opportunity to test the predictions of the electroweak sector of the Standard Model at the TeV energy scale, and it is the irreducible background to the search for the Higgs boson and new physics signatures.

Diboson cross sections have been measure for all combinations of W,Z and isolated photons. The cross sections are measured in kinematic regions defined by the decay kinematics, in some cases including vetoes on additional jets. The measurements are also exptrapolated to the full phase space using theoretical calculations of the acceptance, and are additionally used to place the most stringent or competitive contraints on triple-gauge boson couplings. The prospects of diboson production studies in the future LHC run will also be discussed.

Tuesday, February 7: 10:30am
Location: ISB 102
Brenda Dingus (LANL)
Title: The HAWC Observatory: A new view of the TeV Sky


The High Altitude Water Cherenkov (HAWC) observatory is being built at 13400' elevation in Mexico. This observatory will have a wide field of view and high duty factor to search the TeV sky for the highest energy, as well as transient, gamma-ray sources. I will describe the capabilities of HAWC and summarize the discoveries of Milagro, the predecessor of HAWC.

Tuesday, January 31: 12:00pm
Location: ISB 310
Yasunori Nomura (UCB)
Title: Quantum Mechanics, Gravity, and the Multiverse


The discovery of the accelerating universe has led to the dramatic new view that our universe may be one of the many universes in which low energy physical laws take different forms: the multiverse. I explain why/how this view is supported both observationally and theoretically, especially by string theory and eternal inflation. I then describe how quantum mechanics plays a crucial role in understanding the multiverse, even at the largest distance scales. The resulting picture leads to a revolutionary change of our view on spacetime and gravity, and provides complete unification of the eternally inflating multiverse and many worlds in quantum mechanics. The talk is based mainly on the work presented in arXiv:1104.2324 and arXiv:1110.4630.

Tuesday, January 24: 10:30am
Location: ISB 102
Joseph Perl (SLAC)
Title: Targeting Cancer: Simulation Tools to Improve Radiation Therapy


Radiation therapy treats cancer with precisely shaped beams of subatomic particles. Advances in medical imaging encourage us to target these beams more precisely than ever, delivering dose to a tumor while avoiding sensitive structures, and doing all of this in 3D or even 4D (with time/motion being the fourth dimension).

We will show how simulation tools originally developed for High Energy Physics are applied to Radiation Therapy, and how an NIH-funded collaboration between SLAC, the University of California San Francisco and the Massachusetts General Hospital are making accurate simulation easier to use for medical physicists worldwide.

Tuesday, January 17: 10:30am
Location: ISB 102
Peter Nugent (LBL)
Title: The Future of Supercomputing and Astrophysics


Computing has played a pivotal role in theoretical astrophysics since the 1950's. However, in the past few years computing resources have been stressed by both observational surveys and computational simulations. Several of the next generation surveys proposed for in the coming decade (Palomar Transient Factory II, Dark Energy Survey, BigBOSS, LSST, etc.) will exacerbate this problem both by the sheer data volume they will produce and the flops required to analyze/simulate this data. Here I will review the current status of some of the present programs (their successes and failures), the demands of future surveys, and the capabilities and limitations that next-generation supercomputing architectures will impose on these efforts. In particular, I will highlight the problems that hybrid architectures, massive data sets and energy requirements/limitations will play over the coming years in this field.