Department of Physics & Astronomy
University of Pennsylvania

Particle Physics

Spring 2017

Tuesdays at 1:30pm in ***2C8***

Contact: Associate Professor Evelyn Thomson

See also previous years, theory seminars and department colloquia

Possible dates in Fall 2017
Tuesday September 19 2017 at 1:30pm
Shih-Chieh Hsu, University of Washington
Hunting for Dark Matter with Boosted Higgs Bosons in ATLAS
Although dark matter (DM) contributes a large component of the mass-energy of the universe, its properties and interactions with known particles remain unknown. In light of this unsolved puzzle, searches for DM pair-produced at Large Hadron Collider (LHC) provide important information complementary to direct and indirect searches in order to determine whether a signal observed experimentally indeed stems from DM. In this presentation, I will report the latest search results of DM pair production in association with a Higgs boson using the LHC Run2 data (sqrt(s)=13 TeV) collected by the ATLAS detector. I'll demonstrate the improvement of the analysis using the state-of-the-art boosted Higgs boson techniques. Because the observed data are found to be consistent with the expected Standard Model backgrounds, I'll show results interpreted using Z'-2HDM simplified models with the most stringent limits. Finally, I will discuss the prospects of this search in the coming LHC Run2 and new ideas of the boosted Higgs tagging.

Tuesday February 21 2017 at 1:30pm in 2C8
Jorge Chaves, Cornell
Search for right-handed W and heavy neutrinos in the 2l+2j final state at CMS
Despite the discovery of the standard model (SM) Higgs boson, there are still unanswered questions that are not explained by the SM, such as the nature of the chiral structure of weak interactions. During Run-1 at the LHC, no clear signs for physics beyond the SM were seen, but there were a few hints of possible new physics. One particular hint was a 2.8\sigma excess seen at the CMS experiment in the search for a heavy right-handed W and heavy neutrino. These particles arise when a left-right symmetry is added to the electroweak sector. In this seminar, I will discuss the Run-1 excess and show preliminary results from the current search with CMS at 13 TeV for a right-handed W in the two leptons plus two jets final state. Additionally, I will discuss the high-luminosity upgrade of the CMS tracker focusing on a proposed track-trigger system to be realized using FPGA technology.

Tuesday December 20 2016 at 1:30pm in 4C8
Shion Chen, University of Tokyo
Quest for gauginos in LHC-Run2 / ATLAS
Despite no significant beyond-the-standard model signatures has been observed in LHC Run1, the discovery of standard model higgs brought a substantial impact on supersymmetry search. As typical minimal models naively need O(10TeV) light flavor sfermions to reconcile with the 125 GeV higgs, there is a grown motivation in searching gauginos which are almost free from the higgs mass constraint. Gluino is in particular an interesting target in early Run2 as the production cross-section greatly enhanced by the doubled center-of-mass energy, and the status is quickly evolving along luminosity. Searching EWKinos, especially for realistic scenarios where the mass spectra is compressed, has more challenges due to their low production cross-section, poor S/N and trigger issue etc., however these are starting to be overcome by recent effort and emerging large data statistics of Run2 and later. This talk will cover the status-quo and prospect of both searches in the ATLAS experiment, with particular focus on (1) up-to-date analysis of gluino search in 1-lepton final state, and (2) R&D studies on multi-variate techniques for the compressed spectra analysis of EWKino search.

Tuesday December 13 2016 at 1:30pm in 4C8
Alessandro Tricoli, Brookhaven National Laboratory
A new era of precision physics with di-bosons at the LHC
The Run-2 of the LHC has opened up a new window on precision physics measurements. Thanks to higher cross sections of physics processes at 13 TeV compared to 7 and 8 TeV centre-of-mass energies, the increasing amount of data being collected and sophisticated experimental techniques, we can reach high precisions on measurements of properties of rare processes such as the production cross sections of two massive electroweak gauge bosons, for example two W bosons. LHC results on di-boson production cross sections at different centre-of-mass energies constitute stringent tests of both the strong and the electroweak sectors of the Standard Model and provide a model-independent mean to search for new physics at high energy scales. The high experimental precision recently achieved in several Run-1 measurements at the LHC together with hints of discrepancies observed between some di-boson measurements and Standard Model predictions have prompted significant progress in calculations at high orders in perturbation theory. This global effort has led in the past months to the so-called "next-to-next-to-leading order revolution", i.e. and explosion of new calculations that can reach percent level precision in the calculation of several processes including di-boson production cross sections. We are indeed on the threshold of a new era of precision physics for di-boson production at the multi-TeV energy scales. This seminar will focus on recent measurements of inclusive and differential cross sections for WW production at centre of mass energies of 13 TeV and 8 TeV by the ATLAS Collaboration at the LHC.

Tuesday December 6 2016 at 1:30pm in 4C8
Allison McCarn, University of Michigan
Searches for New Physics Through Third Generation Particles at the ATLAS Detector
The Standard Model (SM) has been central to particle physics for decades, and its success in predicting observational results has culminated in the 2012 discovery of a Higgs boson at the Large Hadron Collider. However, the theory is considered ‘not natural’, requiring finely-tuned parameters to allow for the precise cancellation of large radiative corrections to the Higgs boson mass. In pursuit of a more natural theory, extensions to the SM have been proposed that would stabilize the Higgs boson mass and resolve the hierarchy problem (supersymmetry, extended Higgs sectors, models with vector-like quarks). This presentation will focus on several ATLAS searches for new physics involving third generation particles, both targeting extended Higgs sectors and vector-like quarks.

Tuesday November 15 2016 at 1:30pm in 4C8
Matthew Klein, Columbia University
Search for supersymmetry in events with four or more leptons at ATLAS

Tuesday November 1 2016 at 1:30pm in 4C8
John Alison, University of Chicago
Di-Higgs at the LHC: Current Status and Future Prospects
I will discuss motivations for searching for di-Higgs production at the LHC. Recent results and projected sensitivities will be presented with particular emphasis on the dominant hh->4b channel.

Thursday October 27 2016 at 3pm in room DRL A6
Andrew Missert, University of Colorado, Boulder
Improving T2K Oscillation Results with a Maximum Likelihood Event Reconstruction
The Tokai-to-Kamioka (T2K) experiment is an accelerator-based long-baseline neutrino oscillation experiment that uses a unique off-axis neutrino beam to precisely measure the parameters that govern neutrino flavor oscillations. This talk will outline the experiment and the current results, which offer tantalizing hints regarding the existence of CP violation in the neutrino sector. It will also cover future improvements to the T2K analysis, most notably the development of a new maximum-likelihood event reconstruction algorithm for Super Kamiokande, which could be used to squeeze even more information about the oscillation parameters from the existing data.

Friday October 14 2016 at 1:30 pm in room 4C6
Adi Bornheim, Caltech
Precision Timing Detectors for Particle Physics
High energy particle collider experiments are facing ever more challenging conditions, operating at todays accelerators which are providing instantaneous luminosity of 1034 cm-2s-1 and above. The high center of mass energy, the large number of simultaneous collisions of beam particles and the very high repetition rates of the collision events pose huge challenges. This results in extremely high particle fluxes, causing very high occupancy in the detectors operating at these machines. Detectors which can provide timing measurements with a precision of a few 10 ps and below can be a major aid in the reconstruction of the physics events under such challenging conditions. In this talk I will present a broad range of R&D activities on precision timing detectors with a focus on calorimeter based measurements. I will discuss possible implementations of precision timing detectors for the upgrades of the LHC detectors to cope with the conditions expected at the high luminosity upgrade of the accelerator as well as for future colliders.

Colloquium: Primakoff lecture, October 13
Rolf Heuer, CERN (former director general)

Tuesday September 20 2016 at 3pm in room 2C8
Jonathan Insler, Drexel University
Results from the DUNE 35-ton Prototype Detector
The 35 ton prototype for the Deep Underground Neutrino Experiment (DUNE) far detector was a single phase liquid argon time projection chamber (LAr-TPC) integrated detector that took cosmics data for a six week run from February to the middle of March 2016. The 35 ton was built to test the liquid argon technologies to be used by the full size DUNE far detector in a fully integrated system. The 35 ton had two drift volumes of lengths 2.23 m and 0.23 m on either side of its anode plane assembly (APA) and made use of wire planes with wrapped wires and a photon detection system (PDS) utilizing photon detection panels read out by silicon photomultipliers (SiPMs). We present an analysis of 35 ton detector cosmics data with a focus on the performance of the PDS.

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.