Department of Physics & Astronomy
University of Pennsylvania

Particle Physics

Fall 2015 and Spring 2016

Tuesdays or Thursday at 1:30pm

Contact: Associate Professor Evelyn Thomson

See also previous years, theory seminars and department colloquia

Tuesday October 4 2016 in 3W2
Alessandro Tricoli, Brookhaven National Laboratory

Colloquium: Primakoff lecture, postponed to October TBC 4:00pm in A8
Rolf Heuer, CERN

Tuesday May 24 1:30pm in 3c4
Alexis Popkow, UCLA
Galactic Very High Energy Astrophysics
Despite being discovered over a hundred years ago, the origin of cosmic rays has remained a mystery. Recent clues suggest that a large number are accelerated in supernova remnants in our Galaxy. The Cygnus region is a very active region of our Galaxy, with many sources of GeV and TeV gamma-ray emission, such as supernova remnants, pulsar wind nebulae, and massive star clusters. A detailed study of the Cygnus region can give insight into the processes of particle acceleration in astrophysical sources, and the nature of cosmic rays. VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of four 12 meter diameter imaging atmospheric Cherenkov telescopes located at Mt Hopkins, AZ, USA. From 2007 through 2012 it gathered nearly 300 hours of data in the Cygnus region from 67 to 82 degrees Galactic longitude and from -1 to 4 degrees in Galactic latitude. We are reanalyzing the VERITAS data with updated analysis techniques, and will be cross correlating that data with the results of an analysis of over five years of Fermi-LAT data in the region. Using a cross correlation of these results we can motivate continued observations in this active region of the Galaxy.

Monday May 16 3:30pm in **3N6**
Jordan Myslik, University of Victoria
Muon antineutrino oscillations at T2K
The T2K ("Tokai to Kamioka") experiment is a long-baseline neutrino oscillation experiment in Japan. A beam of muon neutrinos or muon antineutrinos is produced at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai. The unoscillated neutrino flux is measured by the near detector complex 280 m from the proton target, and the oscillated neutrino flux is measured by the far detector, Super-Kamiokande, 295 km away. Using a beam of muon neutrinos, T2K has performed precise measurements of muon neutrino disappearance, and discovered muon neutrino to electron neutrino oscillation by measuring electron neutrino appearance. Since the summer of 2014, T2K has been taking data using a beam of muon antineutrinos, and has released the results of both a muon antineutrino disappearance analysis and an electron antineutrino appearance analysis, both using antineutrino beam data up to the summer of 2015. This talk will discuss these analyses, going into detail about the role played by the near detector, and looking at future directions.

Wednesday May 4 1:00pm note time in 4N12 note place
David Nygren, University of Texas Arlington
Searches for Neutrino-less Double Beta-Decay: a Decade of Discovery Ahead at the ton-scale?
Observation of neutrino-less double beta-decay would demonstrate that the neutrino and anti-neutrino are identical. This decay mode would be prohibited if the neutrino has zero mass but the discovery of neutrino oscillations, demonstrating a non-zero mass, has strongly motivated new experimental searches. While knowledge of mass and phases is incomplete, oscillation results have provided a target range of desired search sensitivity, about a factor of about 100 greater than the current experimental limits. I will present a personal perspective on current experimental aspirations in the international context. A 'discovery class' experiment requires a ton-scale active mass and background levels reduced by more than two orders of magnitude. Is this technically possible? For the US, an opportunity appears to exist in the use of gas-phase xenon with development of new methods for background reduction, as pursued within the NEXT collaboration. The elusive neutrino may yet provide more surprises, even insight as to why there is something, rather than nothing.

Thursday April 28 11:00am in 3W2
Keisuke Yoshihara, Penn
Recent results on SUSY searches in LHC-ATLAS
Despite the absence of experimental evidence, weak scale supersymmetry (SUSY) remains one of the best motivated and studied SM extensions as a solution for hierarchy problem. This talk summarizes the recent ATLAS results on SUSY searches using ~3/fb of 13TeV proton-proton collisions in 2015 and discusses what to do next in the coming years.

Tuesday April 5 1:30pm in 3W2
Chris Hays, Oxford University
Effective field theory and the LHC: New physics through precision measurement

Tuesday March 29 1:30pm in 3W2
Jeff Dandoy, University of Chicago
Search for new phenomena in the dijet channel with the ATLAS detector at 13 TeV
With the beginning of Run II at the LHC, proton-proton collisions at a center of mass energy of 13 TeV have introduced new potential for observing physics beyond the Standard Model. The increase in center of mass energy greatly enhances the reach of searches for any new exotic particles, particularly with decay modes involving a dijet system. With 3.6 fb^{-1} collected so far in Run II, the sensitivity to new resonant particles has already surpassed the limits set with the full Run I dataset. The ability to observe non-resonant deviations from the SM such as structure within quarks themselves has also been greatly enhanced from the new operating conditions of the LHC. I will present the first results of searches for both resonant and non-resonant new physics in dijet events.

Tuesday March 22 1:30pm in 3W2
Joe Taenzer, University of Toronto
Studying V(H → WW*) with the ATLAS detector and Global sequential corrections for ATLAS jets

Tuesday March 15 1:30pm in 3W2
Philip Chang, University of Illinois
Searches for new physics in the Higgs sector
The discovery of the Higgs boson opened up a new frontier for new physics searches. One example is the study of the Higgs couplings. Precise measurement of the Higgs couplings can put constraints on new physics. I will discuss the couplings measurement in H->WW decay channel that provides the best single channel measurement. I will also then briefly discuss other ways of searching for new physics in the Higgs sector for the future.

Tuesday March 1 2016 in 3W2 at 1:30pm
Sadia Khalil, Kansas State University
Searches for Vector-like quarks at CMS experiment, at the LHC.
I will present results of searches for massive top and bottom quark partners using proton-proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 8 TeV. These fourth-generation vector-like quarks are postulated to solve the Hierarchy problem and stabilize the Higgs mass, while escaping constraints on the Higgs cross section measurement. The vector-like quark decays result in a variety of final states, containing top and bottom quarks, gauge and Higgs bosons. I will present searches using several categories of reconstructed objects, from multi-leptonic to fully hadronic final states. At 8 TeV, we set exclusion limits on both the vector-like quark mass and pair-production cross sections, for combinations of the vector-like quark branching ratios. I will also present these searches using 13 TeV collision data.

Tuesday February 23 2016 in 3W2 at 1:30pm
David Shih, Rutgers University
Natural Supersymmetry Today
I'll give a broad overview and survey of my work and others on the challenges confronting naturalness and supersymmetry after Run I of the LHC.

Colloquium: Wednesday February 17 4:15pm in A8
Lian Tao Wang, University of Chicago
Physics opportunities at future circular colliders

Tuesday February 9 2016 in 3W2 at 1:30pm
Russell Neilson, Drexel University
PICO: Searching for Dark Matter with Bubble Chambers
The PICO collaboration uses bubble chambers to search for WIMP dark matter particles. The bubble chambers are operated in a moderately superheated state providing superb rejection of the dominant gamma background at better than the 10^-10 level, and are filled with fluorinated target fluids ideally suited for investigating spin-dependent WIMP-proton interactions. PICO is currently running two experiments at the deep underground SNOLAB site: PICO-60 (previously called COUPP-60) and PICO-2L. I will present results from recent dark matter searches in both of those experiments. I will also discuss studies of unexpected backgrounds that have impacted those dark matter searches and future plans for the two experiments.

Tuesday December 1 2015 in 3W2 at 1:30pm
Yangyang Cheng, University of Chicago
Tracking to the Dark Side at ATLAS: the Present and the Potential

Tuesday November 17 2015 in 3W2 at 1:30pm
Michelle Dolinski, Drexel University
Searching for neutrinoless double beta decay with cryogenic xenon detectors

Thursday November 12 2015 in 3W2 at 1:30pm
Sinead Farrington, Warwick University
Results on the Standard-Model-like Higgs boson at LHC Run 1

Tuesday September 22 2015 in 3W2 at 1:30pm
Nick Ryder, University of Oxford
The SoLid Experiment: searching for neutrino oscillations within 10 m of a nuclear reactor

Tuesday June 2 2015 in 3W2 at 1:30pm
Kristin Lohwasser, DESY-Zeuthen
The WW puzzle: Measurement of diboson production at the LHC
The measurements of the production of W boson pairs in pp collisions at 7 and 8 TeV have shown a small but consistent excess of 1-2- sigma over the theoretical predictions, causing a bit of a stir amongst theorists and experimentalists alike. The recent results from the updated ATLAS measurements for the total and fiducial cross sections are presented together with a study of differential distributions as well as limits on anomalous triple gauge couplings.

Thursday April 30 2015 in 2C4 at 1:30pm
Mike Hance, LBNL
Searching for Exotic Heavy Leptons and Diboson Resonances at the LHC

Tuesday April 28 2015 in 3W2 at 1:30pm
John Paul Chou, Rutgers
Recent CMS Searches from Run 1 and Prospects for Run 2

Thursday April 23 2015 in 2C4 at 1:30pm
Andrew Brinkerhoff, Notre Dame
A new measurement of ttW and ttZ at CMS
For the first time at the LHC, we are able to measure the associated production of W or Z bosons with top quark pairs. These processes allow us to directly measure the top-Z coupling, and place limits on effective couplings between the top quark and the Higgs, W, and Z bosons. In addition, ttW and ttZ are important backgrounds in searches for ttH and new physics processes in the top sector, especially SUSY models. I will present recent results from ATLAS and CMS, and describe a new technique to reconstruct the ttW and ttZ systems, allowing for more precise measurements with existing data.

Tuesday April 21 2015 in 3W2 at 1:30pm
Justin Khoury, Penn
Dark matter superfluidity

Thursday April 16 2015 in 2C4 at 1:30pm
Ben Carlson, University of Pittsburgh
Search for stealth supersymmetry at the LHCslides
Supersymmetry (SUSY) can simultaneously solve the hierarchy problem, allow unification of the fundamental interactions, and provide a candidate for dark matter. Most searches for SUSY focus on the presence of large missing transverse energy (MET) carried away by the lightest SUSY particle. Recent high-MET searches at the CERN LHC have not yet found evidence for SUSY. Therefore, it is important to study well-motivated alternatives with low-MET, such as models characterized by R-parity violation, compressed spectra, and hidden valleys. In particular, the "stealth SUSY" model yields a low-MET signature while conserving R-parity by means of a new hidden sector in which SUSY is approximately conserved. I will present recent LHC searches for stealth SUSY, and discuss interesting areas for study at 13 TeV.

Tuesday April 14 2015 in 3W2 at 1:30pm
Brian Hamilton, University of Maryland
New results from LHCb
I will present several new results based on the full dataset collected by the LHCb detector during the 2011 and 2012 running periods. In particular, the first measurement from LHCb of the magnitude of the CKM matrix element Vub via semileptonic decays of the $\Lambda_{b}$ baryon and its impact on contributions of right handed currents will be discussed. I will also present new results on the electroweak penguin decay $B \to K^{*} \mu\mu$ and the status of anomalies in this channel observed in the previous analysis which used a subset of the full data. Plans for the LHCb experiment during Run 2 of the LHC and beyond will also be discussed.

Thursday April 2 2015 in 2C4 at 1:30pm
Alex Tuna, University of Pennsylvania
Higgs boson decay to tau+ tau-

Tuesday March 31 2015 in 3W2 at 1:30pm
Ben Hooberman, University of Illinois
Recent results from LHC dilepton+jets+missing transverse momentum Searches
The discovery of a Higgs boson at the LHC has answered critical open questions in the standard model. Despite strong evidence that the standard model is incomplete, no compelling evidence for beyond-the-standard model physics has been observed. However, two recent searches from CMS and ATLAS in the dilepton + jets + ETmiss final state have uncovered moderate excesses with respect to standard model predictions, at the level of ~2.5-3.0sigma. This talk will discuss the strategy, background estimation, and results of these searches, as well as possible signal interpretations in supersymmetric models.

Thursday March 26 2015 in 2C4 at 1:30pm
John Alison, University of Chicago
Fast Track Finding at the LHC

Tuesday March 24 2015 in 3W2 at 1:30pm
Chase Shimmin, University of California at Irvine
Observing Ultra-High Energy Cosmic Rays with Smartphones
In this talk I discuss the possibility of using a network smartphones and similar devices to search for ultra-high energy ($>10^{18}$ eV) cosmic rays via a community-sourced scientific platform. Muons and energetic photons produced in UHECR events leave a signature of bright pixels in images from on-board CMOS cameras, while GPS location data allows for the reconstruction of extensive air showers observed by multiple devices. The ubiquity of these consumer devices around the globe enables instrumenting a far greater area than conventional observatories, enhancing sensitivity to the very rarest events. Given certain levels of participation, it is even possible to match the observational power of state-of-the-art facilities such as the Pierre Auger observatory, at the highest energies.

Tuesday March 17 2015 in 3W2 at 1:30pm
John Campbell, Fermi National Accelerator Lab
Monte Carlo for FeMtobarn processes (MCFM) and related topics

Wednesday March 4 2015 at 2:00pm in 2C4 at 2:00pm
Alberto Belloni, University of Maryland
Looking towards 2025 - Preparing the CMS hadronic calorimeter for the High-Luminosity LHC runs

Tuesday Mar 3 2015 at 1:30pm in Room 3W2
Reserved for search

Tuesday Feb 24 2015 at 1:30pm in Room 3W2
Holger Muller, University of California, Berkeley
Atom interferometry measurements in fundamental physics
Chameleons are flexible models for dark energy that avoid conflict with laboratory experiments by becoming short-ranged in the presence of dense objects. Probing the chameleon field with atoms rather than bulk matter strongly reduces this "screening." We developed an atom interferometer inside an optical cavity [1] to reach high reproducibility in tight spaces. Our experiment is the first to rule out a range of chameleon and other dark energy candidates that would reproduce the observed cosmic acceleration [2].
We will also comment on our measurement of the fine structure constant, for which we have boosted atom interferometry into the 10^-10 range by suppressing the effects of so-called diffraction phases [3]. After six data taking campaigns we are close to reporting a new measurement with an anticipated accuracy of about 0.25 parts per billion. This would be similar to the one of the electron's gyromagnetic anomaly g-2, allowing for new precise tests of quantum electrodynamics.
[1] arxiv:1409.7130. Phys. Rev. Lett., in press.
[2] arXiv:1502.03888.
[3] arXiv:1410.8486.

Tuesday Feb 17 2015 Room 3W2
Reserved for search

Thursday Feb 12 2015 Room 2C4
Reserved for search

Tuesday Feb 10 2015 Room 3W2
Reserved for search

Thursday Jan 29 2015 Room 2C4
Reserved for search

Tuesday Jan 20 2015 Room 3W2
Reserved for search

October 28 2014
Naoko Kurahashi Neilson, Drexel
Detecting Cosmic Neutrinos with IceCube at the Earth's South Pole
The IceCube Neutrino Observatory has recently discovered a diffuse flux of astrophysical neutrinos, neutrinos from beyond the solar system. But how does one collect neutrinos at the South Pole? Why study neutrinos for astronomy? In this talk, I will try to answer such questions and show nice pictures from Antarctica. I will also discuss the multiple diffuse flux analyses in IceCube that observe the astrophysical flux, and what each can tell us. Spatial analyses that aim to identify the sources of such astrophysical neutrinos will also be discussed, followed by an attempt to reconcile all results, to draw a coherent picture that is the state of neutrino astronomy.

September 30 2014
Chunhui Chen, Iowa State University
Production of high transverse momentum vector bosons reconstructed as single jets and its application to search for NP at the LHC (slides)
Highly boosted hadronically decaying particles have been widely used as a unique signature to search for NP at the LHC. In this talk, we present a measurement of the cross-section for high transverse momentum W and Z bosons produced in *pp* collisions and decaying to all-hadronic final states by ATLAS experiment. The measurement is performed by reconstructing boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet center-of-mass frame is used to suppress the large multi-jet background. In this talk, we will also discuss potential applications of the jet substructure in the jet rest frame in searches for NP at the LHC.

September 16 2014
Joana Miguens, LIP,Portugal
Higgs boson measurements in the H->WW*->lvlv channel with ATLAS (slides)
After the discovery at the LHC, precision measurements of the Higgs boson are essential to determine its nature. The H->WW*->lvlv decay channel offers a sensitive experimental signature. The Higgs resonance mass cannot be reconstructed because of the two neutrinos in the final state. Nonetheless, once the backgrounds are under control, the large H->WW* branching fraction and good signal-to-background ratio provide powerful measurements of the Higgs production and couplings. I will present the analysis and discuss the results from ATLAS on the H->WW*->lvlv channel, based on the full dataset collected during Run-I of the LHC, where an excess of events is observed, providing evidence for the Higgs boson at mH=125GeV.