# 2012/2013

Organizers: Ashutosh Kotwal, Tom Mehen and Kate Scholberg

Held in Duke Physics Room 278 (old Room 246) (Unless otherwise noted)

Regular time for Spring '13 semester: Mondays 1 pm, with alternate times Mon 11 am and Wed 10 am. Currently all dates not listed are open.

October 25: Fany Dudziak, Iowa State University

From the electron performances to the new boson discovery in the H->ZZ*->4l channel in the ATLAS experiment

On July 4th, CERN has announced the discovery in ATLAS and CMS of a Higgs-like boson, pinnacle of 50 years of hunt. One of the two golden channels for the Higgs discovery is the H->ZZ*->4l channel. In this analysis, lepton performances are paramount. Thus, in ATLAS, huge efforts have been done in the last years towards the improvement of the electron performances, especially at low energy. I will describe in detail the H->ZZ*->4l analysis focusing on the electron performances.

November 1: Tina Lund, NCSU

Neutrino propagation through turbulent supernova matter

The flavor evolution of neutrinos propagating through a turbulent medium is a highly interesting and complicated problem. Depending upon the hierarchy and the properties of the turbulence, the neutrino spectral signatures of collective effects and/or shock waves in the supernova may be smothered to the point where they are unobservable in the “golden” channels (νe → νμ transitions) of the next Galactic Supernova Neutrino Burst. However, at the same time, turbulence can also generate effects in mixing channels where none previously existed. We investigate the effects of neutrino self-interactions, MSW conversions as well as the impact of turbulence on the neutrino flavor evolution along single radial directions in turbulent dense matter, paying special attention to the combined impact of these three effects. We find that adding up to 10% turbulence leads to only minor differences in the emerging neutrino spectra, while overall features of the collective and MSW interactions remain.

January 4: Shu Li, USTC (China) and CPPM (Marseille, France), 1 pm

Measurement of W+W- production in Proton-Proton Collisions at sqrt(s) = 7 TeV with the ATLAS Detector at LHC

I present the measurement of the Standard Model (SM) W+W- production cross sections in the purely leptonic decay channels with final states of ee, emu and mumu using the 4.6/fb of 7 TeV pp collisions data set collected in 2011. The measurements allow for a stringent test of the non-Abelian SU(2)xU(1) SM electroweak sector; give an opportunity to probe new physics via anomalous TGCs (aTGCs) that may be observed in the distri- bution of the kinematic variables of the produced W+W-, or their decayed final states in their highly energetic region; and provide a good understanding of the irreducible background for the searches of the Higgs boson through the H->WW decay channel and current Higgs property measurement. The precision of the measured total cross section and aTGC limits have already surpassed Tevatron results and laid a solid foundation for further precision improvements and possible implications of new physics beyond SM with the 20/fb 8 TeV collision data taken by the end of 2012 recorded by ATLAS.

January 7: Ludovica Aperio Bella, LAPP, 1 pm

Search for Technihadrons in Dilepton Channel and Timing Alignment of the ATLAS Liquid Argon Electromagnetic Calorimeters

The LHC campaign in the first three years of data taking was very successful. The 2011 run has allowed to record more than $5~\ifb$ of data at $\sqrt{s} = 7$~TeV with the ATLAS experiment. In this presentation the whole 2011 data set is used to performed different studies. The results of the analysis performed to ensure a good timing alignment for the whole Liquid Argon (LAr) Calorimeter are presented. An accurate timing alignment of the ATLAS LAr Calorimeter is essential to guarantee the optimal energy reconstruction and also to synchronize the detector readout system with the LHC bunch crossing. In the second part of the presentation, a Beyond the Standard Model search on simple final state topologies as the isolated and high energy di-leptons final states is described. These topologies are characterized by a clear signature and can constrain several extensions of the Standard Model (SM) e.g. the Technicolor (TC) models which predict the existence of new heavy neutral particles decaying in high energy leptons. No evidence for a TC signal is observed and limits are set on the cross-section times the branching fraction vs technicolor mass in two dierent Technicolor scenarios Low-scale Technicolor (LSTC) and the MinimalWalking Technicolor (MWT). Exclusion regions in the parameters phase space are also evaluated.

January 11: Advait Nagarkar, Ohio State University, 1 pm NON-STANDARD DAY

Measurement of the total ZZ production cross section in the four-lepton channel using 5.8/fb of ATLAS data at √s = 8 TeV
The ZZ production cross section has been measured by the ATLAS experiment using the four-lepton decay channel, where the term lepton implies electrons and muons. A data sample of 5.8/fb collected in pp collisions at √s = 8 TeV at the LHC in 2012 is used. Events are selected by requiring four leptons with p_T > 15 GeV, forming two opposite-sign same-flavour lepton pairs with mass between 66 and 116 GeV, with the leading lepton required to have p_T > 25 GeV. We observe 85 candidate events in the acceptance region |η| < 2.5 for muons (|η| < 2.47 for electrons) with a background expectation of 1.3±1.2(stat.)±0.5(syst.). The ZZ→4ℓ production cross section, measured in a fiducial phase-space corresponding closely to the acceptance defined above, is 21.0^+2.4_-2.2(stat.)^+0.6_-0.5(syst.)±0.8(lumi.) fb. After correcting for the ZZ→4ℓ branching fraction and the fiducial acceptance, this extrapolates to a total ZZ production cross section of 9.3^+1.1_-1.0(stat.)^+0.4_-0.3(syst.)±0.3(lumi.) pb, where the total cross section is defined with both Z-bosons with mass between 66 and 116 GeV. This is consistent with the Standard Model expectation of 7.4±0.4 pb.

January 14: Yong Yang, Caltech, 1 pm

CMS ECAL calibration and search for the Standard Model Higgs boson in the di-photon decays

The search for the Standard Model Higgs boson in the di-photon decays in CMS makes use of the excellent photon energy resolution of the crystal electromagnetic calorimeter (ECAL) which consists of approximately 76,000 crystals. The energy resolution, for unconverted photons at high energies, is approaching to a constant term which is dominated by the channel-by-channel nonuniformity of the energy responses. The energy intercalibration of all crystals in ECAL has therefore been a challenging task for the CMS experiment. At the LHC, radiation damage to crystals causes dose-rate dependent transparency variations, and this fact imposes an additional challenge for a crystal calorimeter at the LHC. In this talk I will focus on the intercalibration of CMS ECAL using photon pairs from neutral pion and eta decays and the laser monitoring based energy correction for the transparency variations, as well as their impact on the search sensitivity of the analysis. The final energy resolution performance is further improved by a multivariate-based regression energy correction using simulated events. A few other aspects of this analysis, including resolution smearing in simulation, signal and background modeling, etc., will also be discussed.

January 28: Kanishka Rao, UC Irvine, 1 pm

Top-quarks, dark matter, and BSM Higgs at CDF and ATLAS

We present searches in the top-quark, dark matter and BSM Higgs sectors at the CDF and ATLAS experiments. We present a search for fourth generation quarks at the ATLAS detector using a novel W identification method. We search for a new particle resonance that might explain the CDF observed top-quark asymmetry at CDF and ATLAS. We also describe a new method, 'basis-limits', which allows for powerful reinterpretation of experimental results without the need for experiment-specific tools, which are usually not available publicly. Finally, we discuss BSM scenarios for the newly discovered boson at the LHC, specifically in the 2 Higgs Doublet Model framework. We present a search for such a model at CDF and prospects at the LHC.

January 30: Katie Mack, U. of Melbourne, 10 am

Dark Matter Particle Physics and Cosmological Evolution

I will present a summary of current prospects for constraining dark matter models in high-redshift astronomy and discuss new avenues of investigation (and work in progress), including a self-consistent treatment of dark matter particle physics in cosmological simulations. Dark matter annihilation or decay in the era of galaxy formation has the potential to alter the evolution of early structures and the intergalactic medium, which may be detectable in the high-redshift 21cm signal of neutral hydrogen. I will discuss how feedback effects between different regimes of dark matter energy injection can alter the formation and evolution of the first stars and galaxies in previously unexplored ways.

February 25: Jorge Diaz, Indiana U., 1 pm

Testing Lorentz invariance with neutrinos

In the past, neutrinos played a fundamental role in the development of our understanding of the nuclear forces, when neutrinos served as probes to study the interior of hadrons. Today, neutrino-oscillation experiments can be viewed as natural interferometers sensitive to possible new physics. In particular, neutrinos can be used to test Lorentz invariance, a cornerstone of modern physics. In this talk, I will introduce a general formalism to study Lorentz violation and describe how we can search for possible deviations from exact Lorentz invariance using neutrino oscillations. I will also show how the breaking of Lorentz symmetry in neutrinos could explain some anomalous results that different experiments have observed in recent years. Additionally, I will describe the effects of Lorentz violation in tritium decay, polarized-neutron decay, and double beta decay and how we can use current and future experiments to search for the key signals of the violation of Lorentz invariance.

April 1: Chris Neu, U. of Virginia, 1 pm

The Interplay Between the Top Quark and the Higgs Boson: How a discovery from a generation ago can help us understand the latest breakthrough in particle physics

The recent discovery at the LHC of a new fundamental particle has generated a significant amount of excitement around the globe -- an excitement unmatched in particle physics since the discovery of the top quark in 1995. Given its observed decay channels, its mass and a handful of its properties, indications are that this new particle could be the long-sought Higgs boson, purported to be the linchpin in understanding the imposition of mass to the fundamental particles. But much remains to be known about this new particle -- it could be the Higgs boson predicted by the standard model or it could be something more exotic. Characterization of this new particle must be done in many different channels; its interactions with the top quark will play a vital role in this endeavor. Herein I describe the importance the top quark will play in studies of this new particle, and describe in detail one particularly important channel in the characterization effort: the search for production of the Higgs in association with top-quark pairs at CMS.

April 15: Max Chertok, UC Davis, 1 pm

Searches for Beyond the Standard Model Higgs at CMS

The 2012 discovery of a Higgs-like particle at the Large Hadron Collider, at CERN, in Geneva, Switzerland, has captured the world's attention. This may indeed be the long-sought Higgs boson, first predicted in the 1960's to explain how SM particles acquire their masses. This brand-new particle, however, may be accompanied by other new states predicted in theories with more complex Higgs structures. In this talk, I will present the status of searches for BSM Higgs at CMS, including those for doubly-charged states as well as scalar and pseudoscalar Higgs predicted by NMSSM models.