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Lunchtime Seminars

Tuesdays ~ 12pm ~ Kolker Room, 26-414

 

Committee:
Gunther Roland, Chair ~ Doug Hasell~ Paolo Zuccon



September 19, 2017

 

Ran Bi, MIT

Boson-jet correlations and boson-tagged jet fragmentation functions in heavy ion collisions with CMS

A typical approach to study the quark gluon plasma produced in heavy ion collisions is to understand the passage of elementary particles through it. As electroweak bosons such as photons and Z bosons do not participate in the strong interaction, their correlation with jets within the same event is a clean probe of the medium-induced energy loss of jets. With high statistics PbPb and pp collision data taken at a center-of-mass energy of 5.02 TeV with the CMS detector, boson-jet correlations and, for the first time in PbPb collisions, photon-tagged jet fragmentation functions have been measured. These measurements provide strong evidence for medium-induced jet energy loss and offer a first look at jet substructure in photon-jet events.

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



September 26, 2017

 

Ivan Kozyryev, Harvard University

PeV-scale particle physics with microkelvin polyatomic molecules

 

Striking prevalence of matter over anti-matter in our Universe still remains a challenging puzzle to cosmology and particle physics. New theoretical models like supersymmetry propose to solve this paramount mystery by postulating additional fundamental particles beyond the reach of modern accelerators. However, such theories also predict enhanced violations of time-reversal symmetry (T) and, therefore, can be experimentally tested by ultra-precise spectroscopic measurements. In this talk, I will describe an experimentally feasible approach to precisely probe T-violation using spectroscopy of laser-cooled heavy polyatomic molecules. While relying on presently accessible techniques, we provide a new paradigm for testing fundamental particle physics leading to permanent electric dipole moments at the level previously considered impossible. I will describe our experimental progress on laser cooling and trapping of complex polyatomic molecules that can be used to unlock the mysteries of cosmos.


 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)

 


 


October 3, 2017

TIME ALTERED DUE TO NOBEL EVENT

 

Livia Soffi, Cornell University

Since the discovery of the Higgs boson in 2012, the experimental program at the LHC has started to explore previously unreachable kinematical regimes, where potentially new heavy particles can be produced. The ATLAS and CMS experiments can search for new physics in a wide range of final states with the highest sensitivity to date. Among all the possible signatures, final states involving photons, despite the relatively small cross section compared to hadronic signatures, provide a powerful handle in the signal over background discrimination. Such searches find their motivation in a wide panorama of theoretical models such as minimal extensions of the standard model, extradimensions and dark matter. Over the past few years a set of photon reconstruction and identification techniques have been developed and optimized in order to reach the detectors design performance. In this talk the most recent and promising results on searches for new physics with photons in the final state obtained with the CMS experiment at the LHC are presented. One of the most exciting results of LHC Run 2, concerning searches for high mass diphoton resonances, is largely discussed. Complementary analyses involving photons are also shown, such as searches for long-lived particles decaying to photons exploiting a novel technique for delayed photon identification and searches for dark matter produced in association with photons. Possible extensions to these analyses and long term plans in preparation for the high-luminosity phase of the LHC are finally described.


 

 

time:    3 pm
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



October 10, 2017

 

Melanie Heil, MIT

Cosmic rays are typically divided into two categories: primary cosmic rays, which are produced directly in the cosmic ray sources, and secondary cosmic rays, which are produced by interaction processes of primary cosmic rays with the interstellar medium. The Alpha Magnetic Spectrometer is a multi-purpose particle physics experiment installed on the International Space Station in 2011 measuring all individual charged components of cosmic rays up to multi-TeV energies. AMS is an LNS led experiment. The science objectives of AMS are the measurement of individual cosmic ray particle fluxes with %-level precision to e.g. study dark matter signatures in cosmic rays and search for primordial antimatter in our Galaxy. In its first six years on orbit AMS has already collected over 100 billion cosmic ray events and these large statistics demand for in-depth systematic error studies.  An overview of the experiment and the details of the latest AMS results on the spectra of primary (He, C, O) and secondary (Li, Be, B) cosmic ray nuclei will be presented. Unexpectedly, we observe that primary nuclei in cosmic rays at high rigidities (> 60 GV) have identical spectra. At the same time we observe that also secondary nuclei have an identical rigidity dependence above 60 GV, which is different from the rigidity dependence of the primaries. For all measured nuclei fluxes we observe an unexpected hardening of the spectra above > 200 GV, which cannot be explained by the current standard model of cosmic rays.

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



October 17, 2017

 

Brian Lenardo, UC Davis

A promising solution to the dark matter problem is the Weakly Interacting Massive Particle (WIMP), a proposed beyond-the-standard-model particle that would permeate the galaxy and interact extremely weakly with baryonic matter. WIMPs in the vicinity of Earth would produce rare low energy (1's - 10's of keV) nuclear recoils that could be observed in a low-background detector. Currently, the leading experiments searching for WIMP interactions use liquid xenon as a scattering target. These experiments measure both scintillation light and ionization to reconstruct the energy, position, and particle type of the interaction to discriminate signal from background. In this talk, I will describe the search for dark matter with the LUX experiment, a dual-phase xenon TPC operated underground in Lead, South Dakota. I will then discuss how a deeper understanding of charge production and scintillation emission in liquid xenon can allow experiments like LUX to explore new parameter space. To this end, we have performed several measurements to calibrate the scintillation and ionization response of liquid xenon to nuclear recoils. I will describe these measurements and show how they allow LUX and other liquid xenon experiments to robustly extend their search windows to either constrain or discover a wider array of WIMP dark matter models. 

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



October 24, 2017

 

Gerry Miller, University of Washington

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



October 31, 2017

 

Yotam Soreq- MIT

Gamma ray constraints on Decaying dark matter and implications for IceCube

Utilizing the Fermi measurement of the gamma-ray spectrum toward the Galactic Center, we derive some of the strongest constraints to date on the dark matter (DM) lifetime in the mass range from hundreds of MeV to above an EeV.  We model Galactic and extragalactic DM decay and include contributions to the DM-induced gamma-ray flux resulting from both primary emission and inverse-Compton scattering of primary electrons and positrons. For the extragalactic flux, we also calculate the spectrum associated with cascades of high-energy gamma-rays scattering off of the cosmic background radiation. We argue that a decaying DM interpretation for the 10 TeV - 1 PeV neutrino flux observed by IceCube is disfavored by our constraints. Our results also challenge a decaying DM explanation of the AMS-02 positron flux. We interpret the results in terms of individual final states and in the context of simplified scenarios such as a hidden-sector glueball model. 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



November 7, 2017

 

Carlos Arguelles-Delgado, MIT

New Physics Searches with the >TeV Neutrinos

IceCube observation of high-energy astrophysical neutrinos has opened the astrophysical neutrino window. As we accumulate statistics IceCube not only starts characterizing the astrophysical neutrino component, but also makes improved measurements of the highest energy atmospheric neutrinos. In this talk I will discuss how we can use both high-energy atmospheric neutrinos as well as astrophysical neutrinos as a probe of new physics.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)



November 14, 2017

 

Matthew Musgrave, MIT

Polarized 3He++ Ion Source for RHIC and an EIC

The capability of accelerating a polarized 3He ion beam in RHIC would provide an effective polarized neutron beam for the study of new high-energy QCD studies of nucleon structure. This development would be particularly beneficial for the future plans of an Electron Ion Collider, which could use a polarized 3He ion beam to probe the spin structure of the neutron. The proposed polarized 3He ion source is based on the Electron Beam Ion Source (EBIS) currently in operation at Brookhaven National Laboratory (BNL). 3He gas would be polarized within the 5 T field of the EBIS solenoid via Metastability Exchange Optical Pumping (MEOP) and then pulsed into the EBIS vacuum and drift tube system where the 3He will be ionized by the 10 Amp electron beam. The goal of the polarized 3He ion source is to achieve 2.5 x 1011 3He++/pulse at 70% polarization. An upgrade of the EBIS is currently underway at BNL in two phases. Phase one will increase the ion production capability by lengthening the trap volume and allow gas injection into the ionization region. Phase two will enable polarized 3He ion production. The source is being developed through collaboration between BNL and MIT.

 

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)


November 21, 2017

 

Luisa Kenausis, MIT

Nuclear Weapons Education Project

Educating students about the dangers of nuclear weapons is critical to our survival because students are tomorrow’s technical and professional leaders. Well-informed leaders are the key to well-informed citizens, and both are necessary to lay the groundwork for a rational nuclear weapons policy. The specific goal of this project is to introduce the dangers of nuclear weapons into the early undergraduate curriculum, in order to produce graduates who are cognizant of nuclear weapons and the issues and dangers surrounding them.

For the past few years, Prof. Aron Bernstein has worked intensively with a volunteer group primarily at MIT on developing this project through its early stages. In September, the project was able to hire Luisa Kenausis as a full-time coordinator for the project. Thus far this semester, we have focused on three main tasks: working to raise additional funds for the project; developing general educational materials for the project website, http://nuclearweaponsedproj.mit.edu; and reaching out to a network of interested faculty members (approximately two dozen faculty members in a dozen universities) to help facilitate the introduction of nuclear weapons material into their curricula.

 

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)


 

November 28, 2017

 

NO TALK THIS WEEK


December 5, 2017

 

Laura Havener, Columbia University

TBA

TBA

 

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)


December 12, 2017

 

Roxanne Guenette, Harvard University

TBA

TBA

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)

 



December 19, 2017

 

Julieta Gruszko, MIT

TBA

TBA

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served at 11:50.)