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Lunchtime Seminars

Tuesdays ~ 12pm ~ Kolker Room, 26-414

 

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



September 13, 2016

 

William Barletta, MIT/USPAS & Martin Breidenbach, SLAC

Accelerator Research in the U.S. for High Energy Physics:
A biased perspective

The U.S. could move boldly toward increasing the pace of transformational accelerator research for high-energy physics. Profound questions remain to be answered in particle physics; recent discoveries reconfirm the value of continued investments. However, going beyond the present generation of high energy accelerators will require changing the capability-cost curve of accelerators, which can only happen through an aggressive, sustained, and imaginative R&D program aimed at building the future accelerators at a dramatically lower cost. Both of us were members of Department of Energy panel that recently studied the potential structure of such a research program. We participated fully in the process and approve the report.  Nonetheless, our experience led us to continue and extend our analysis of the issues that will drive accelerator research aimed at future accelerators for high-energy physics with the aim of informing interested physicists from all disciplines, not just accelerator experts. Broadly, we will look at prospects for proton-proton colliders and electron-position colliders – all interlaced with our biases and (and perhaps not so politically correct) opinions.

The talk will be given by W. Barletta

 

 

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

(Lunch will be served at 11:50.)



September 20, 2016

 

Dr. Karoline Schäffner, INFN/GSSI

The COSINUS project: development of new NaI-based detectors for direct dark matter search

 

Dark matter remains one of the central open questions in astroparticle physics. Although modern astronomical observations and particle physics experiments are providing precision data in uncovering its true nature, experimental evidence of dark matter still today solely relies on gravitational interaction. Among a long list of hypothetical new particles WIMPs (Weakly Interacting Massive Particles) provide compelling arguments as they provide for a relic density that matches observation. Direct dark matter searches use different detector technologies, all aiming to observe dark matter particles via the process of elastic scattering off atomic nuclei in their earth-bound detectors.

 

At present the situation in the sector of direct dark matter detection is controversial. Several experiments (CDMS-Si, Cogent, DAMA) detect events above the known background level, which allows us to infer properties of a dark matter particle. In particular, the DAMA/LIBRA collaboration observes in more than 13 annual cycles a statistically robust modulation signal in their sodium-iodide (NaI) target crystals.

 

The COSINUS R&D project started in 2016 and aims to develop a cryogenic scintillating calorimeter using undoped NaI as target. Thanks to the two-channel detection approach (heat signal and light signal) possible signal events (nuclear recoils) can be discriminated from common background (electrons/gammas) by the ratio of light to heat signal. The event-by-event based particle-identification renders the detection technique of COSINUS unique among other NaI-based detectors as it offers the possibility of identifying any target-specific particle interactions and to suppress background. If the performance of the proposed NaI calorimeter can be proven to be comparable to already existing scintillating bolometers, as e.g.~used in the CRESST dark matter search, such NaI detectors have the potential, to give an answer on the particle interaction channel participating in the DAMA/LIBRA modulation signal with higher sensitivity due to the explicit lower energy threshold and within a very moderate exposure of few 10 kg-days. 

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

(Lunch will be served at 11:50.)

 


 

 


September 27, 2016

 

Rachel Carr, MIT

Data points from a year as a Congressional Science Fellow

Each year, a number of scientific organizations give scientists and engineers the opportunity to engage with the federal government as Congressional Science Fellows. The experience puts fellows directly into the offices of members of Congress or congressional committees, where they offer technical and analytical perspective and learn about the legislative process. In this talk, I will share highlights from my year working on energy and technology policy in the Senate through a fellowship sponsored by the American Institute of Physics and the Acoustical Society of America.

 

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

(Lunch will be served at 11:50.)


 


October 4, 2016

 

Alex Barbieri, MIT

Latest boson-jet results in Heavy Ion collisions at the LHC from CMS

Boson-jet studies are a "golden channel" to study the properties of the Quark Gluon Plasma, as they offer a way to cleanly measure both the initial and final states of probes which pass through the strongly interacting medium. With the higher statistics data at 5.02 TeV collected during the Fall 2015 LHC heavy ion run with the CMS detector, we are able to show quantitative measurements of Z-jet correlations in heavy ion collisions and significantly improved, highly differential photon-jet measurements as well. Jet quenching without significant deflection is observed, and can help differentiate phenomenological models of the QGP.

 

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

(Lunch will be served at 11:50.)



October 11, 2016

 

Reynier Cruz Torres, MIT

Contact interactions in nuclei

Historically, the use of effective theories has been essential in the study of the convoluted structure of the atomic nucleus. Examples of these theories range from the Fermi Gas model, Liquid Drop model, Shell model, to modern Chiral perturbation theory.

 

These theories constitute a very good description of the mean field part of the nucleon momentum distribution. However, they fail to describe the short-range, high-momentum tail, which determines the behavior of approximately 20% of all nucleons in the nucleus. Contact interaction is an effective theory developed for the study of the high-momentum behavior of dilute ultra-cold two-component atomic gases. Even though nuclei don't fully satisfy the conditions of this theory, there is experimental evidence that shows that Contact interaction can be applied to nuclear systems. Here, we present the extraction of nuclear contacts from 2-body momentum distributions at high center-of-mass and relative momentum.


Furthermore, we compare the distributions obtained from the extracted contacts to 1-body momentum distributions, 2-body momentum distributions in the region sensitive to SRC, and to experimental data.

 

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

(Lunch will be served at 11:50.)



October 18, 2016

 

Zeynep Demiragli, MIT

Shining Light On Dark Matter with the CMS Experiment

The CERN LHC provides the possibility of directly pair-producing weakly interacting massive particles in TeV-scale particle collisions. Dark matter searches done in final states with invisible particles recoiling against hadronic activity are among the most sensitive. In this talk, these hadronic topologies and the kinematic variables are explored, such as jet substructure as a means of tagging heavy bosons. The focus of the talk is the recent results obtained using data collected at the Run-II of the LHC.

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

(Lunch will be served at 11:50.)



October 25, 2016

 

Gian Michele Innocenti, MIT

Heavy flavour measurements in heavy-ion collisions with CMS

The measurement of the production of heavy flavour quarks (charm and beauty) is considered a powerful tool to study the properties of the high-density QCD medium created in heavy-ion collisions, the Quark Gluon Plasma. Heavy quarks are created in hard scatterings in the early stages of the collision and they interact with the deconfined medium via collisional and radiative processes.
Therefore, precise measurements of the production yields of mesons and jets containing these heavy quarks in heavy-ion collisions provide insights into the mechanisms of quark interactions with the medium and on the transport properties of the Quark Gluon Plasma. In this seminar, an overview on the heavy flavor measurements performed by CMS in proton-proton, proton-lead and lead-lead collisions will be presented.

 

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

(Lunch will be served at 11:50.)

 


 


November 1, 2016

 

Andrea Marini, MIT

Charged Higgs searches with the CMS experiment

The observation of a scalar boson by ATLAS and CMS experiments with a mass of about 125GeV led to a new era in physics. The discovery of an additional scalar boson (charged or neutral) would provide evidence for an extended Higgs sector. The focus of the talk is on the latest results of the searches for a Charged Higgs boson with the data collected during the Run-II of the LHC by the CMS experiment.

 

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

(Lunch will be served at 11:50.)



November 8, 2016

 

Jakob Salfeld-Nebgen, MIT

Precision measurements at the LHC: Luminosity and W/Z cross section measurements with the CMS

With the start of Run-2 of the LHC in 2015 physical processes predicted by the Standard Model are now being tested at 13 TeV centre-of-mass energy. In particular, the cross section of W and Z bosons in proton-proton collisions can be measured with high accuracy.


The inclusive and differential cross sections are compared with predictions from higher-order calculation in QCD and the electroweak sector and parton distribution functions can be experimentally evaluated. A leading systematic uncertainty in the measurements is the normalization of the dataset, the integrated luminosity. A dedicated accelerator setup, so called van-der-Meer scans, enable precise estimates of the proton beam properties. I will present the important aspects of luminosity measurements at the LHC and the current status of the W and Z boson cross section measurements with CMS.

 

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

(Lunch will be served at 11:50.)


November 15, 2016

 

Diana Gooding, MIT

Quantum Dots and Liquid Scintillators in 0νββ-decay Searches

Liquid-scintillator detectors make neutrino measurements at around 1 MeV with energy resolution of ~5% -a factor of two better than water Cherenkov detectors, and just as scalable from 1 ton to 1 kiloton. At this energy, however, the scintillation light is isotropic and cannot provide enough information to reconstruct the trajectories of outgoing particles. While most of the Cherenkov light produced is absorbed and reemitted by the scintillator, a fraction of it propagates through the detector, retaining its directional information. Separating these scintillation and Cherenkov signals requires fast photo detectors and an ability to tune the spectral response of the scintillator. Along this front, quantum dots have emerged as promising wavelength shifters, since their size and thus fluorescence properties are highly tunable. Most importantly, these quantum dots can be made of candidate isotopes for neutrino-less double beta decay, and then suspended in standard scintillators like linear alkyl benzenes. This talk outlines the optical characterization and performance of quantum-dot-doped liquid scintillator.

 

 

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

(Lunch will be served at 11:50.)


 

November 22, 2016

 

G. Hagen, ORNL and University of Tennessee, Knoxville

Coupled-cluster computations of atomic nuclei

This talk reviews recent progress in first-principles computations of atomic nuclei. An optimization of an interaction from chiral effective field theory to few-nucleon systems and oxygen isotopes yielded much improved binding energies and charge radii in light and medium-mass nuclei. The computation of the nucleus 48Ca showed that its neutron skin (difference between the radii of the neutron and proton distributions) is smaller than previously thought, and we made prediction for its dipole polarizability which has recently been measured. We predicted the 2+ state in 78Ni from a correlation with the 2+ state in 48Ca using chiral nucleon-nucleon and three-nucleon interactions. Our results confirm that 78Ni is doubly magic. It was also found that continuum effects play an important role in the level ordering of 79Ni. I will also show preliminary results for neutron deficient tin isotopes, where in particular we make predictions for the spin structure of 101Sn and the super allowed Gamow-Teller decay of 100Sn from first principles.


November 29, 2016

 

Paul Miller, Lawrence Livermore National Lab

Interplanetary Defence: It's not if, but when

This talk will provide an introduction to the impact threat of near-earth asteroids, describe some of the current efforts to prepare for what is an unlikely but inevitable event, and illustrate examples of current research challenges on the topic.

 

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

(Lunch will be served at 11:50.)


December 6, 2016

 

David DeMille, Yale University

Probing physics at the TeV scale—and above—with room-scale experiments

Remarkably, it is possible to use small experiments—with teams of a few people, in a university lab—to probe for well-motivated phenomena at very high energy scales. This talk will focus particularly on experiments searching for CP-violating electric dipole moments (EDMs) of the electron and the proton. In a very broad class of theoretical models, the expected size of these EDMs is far larger than expected in the Standard Model. Recent advances in experimental techniques are now enabling very rapid improvements in the sensitivity of these searches. For example, the latest result of our ACME experiment, which set an improved limit on the size of the electron's EDM, can be interpreted as excluding certain particles with mass below several TeV, within a range of viable models. Our newly-launched CeNTREX search for the proton EDM is projected to be sensitive to CP-violating effects at similar scales, but in the hadronic rather than the leptonic sector. Current and planned improvements to both experiments can extend the energy reach of both experiments by an order of magnitude or more, far beyond the range of energies directly accessible at colliders.

 

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

(Lunch will be served at 11:50.)


December 13, 2016

 

Sally Seidel, University of New Mexico

A Tasting Menu of Recent ATLAS Results

A selection of recent measurements by the ATLAS experiment at the Large Hadron Collider is presented. I've attempted to choose results that differ from predictions by a couple of sigma as these might be places where interesting things could happen, or at least we may need to learn more to fully understand their implications. Topics to be covered include the search for Higgs boson pair production in the γγ bb final state, measurements of top‐quark pair differential cross sections in the lepton+jets channel, the measurement of the branching ratio Γ Λ 0 b ( 0 →ψ (2S)Λ0 )/ Γ Λ 0 b ( 0 → J /ψΛ0 ), and a search for gluinos in events with an isolated lepton, jets, and missing transverse energy. The first observation of an excited Bc meson is also described.

 

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

(Lunch will be served at 11:50.)