Committee: William Detmold, Chair ~ Daniel Harlow ~ Philip Harris ~ Or Hen
hosted by: Daniel Harlow
Zohar Komargodski, SCGP, Stony Brook University
Weakly Coupled Limits of Quantum Field Theory
Abstract: In the 70’s it was understood that QCD becomes weakly coupled in the high-energy/short-distance limit. There are, however, many quantum systems where the short distance limit does not lead to such dramatic simplifications.
We argue that, by contrast, the small angle limit is always weakly coupled. We show how computations can be done in this limit and compare with some experiments and numerical simulations.
Similarly, we discuss the limit of large global quantum numbers. This also sometimes leads to surprising simplifications. We discuss two examples where the large charge limit leads to a new weak coupling expansion and in one instance we also provide a dual random matrix theory description for the large charge limit.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Daniel Harlow
Sašo Grozdanov, MIT
Holographic View on Transport in Quark-Gluon Plasma
Abstract: Quark-gluon plasma (QGP) is a state of deconfined nuclear matter controlled by the dynamics of Quantum Chromodynamics (QCD). In the experimentally accessible regimes of QGP, the fact that QCD is strongly coupled prevents the use of perturbative quantum field theory method in its analysis. However, recent advances in string theory gave rise to the holographic duality that relates certain strongly coupled gauge theories similar to QCD to a dual, weakly interacting gravitational description. While very successful in describing aspects of infinitely strongly coupled theories (the simplest limit of holography), coupling-dependent studies that require the analysis of higher-derivative theories of gravity have only recently started being extensively utilised.
In my talk, I will present a series of new results, describing near- and far-from-equilibrium transport in holographic plasmas as a function of the coupling constant from infinitely strong towards weak coupling. Firstly, I will focus on aspects of relativistic all-order hydrodynamics, that is, its convergence and higher-order transport coefficients. Then, I will discuss the interplay between the hydrodynamic and the non-hydrodynamic modes that control relaxation and thermalisation in plasmas. In particular, I will connect holographic predictions with those expected from kinetic theory, perturbative quantum field theory and lattice calculations. Finally, the last part of the talk will focus on our first coupling-dependent predictions for the far-from-equilibrium dynamics of a holographic model of QGP.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Will Detmold
Ian Moult, SLAC
The Substructure of Jets at the Large Hadron Collider
Abstract: Collimated sprays of hadrons, called jets, are an emergent phenomenon of Quantum Chromodynamics at high energies. In this talk, I will explain how understanding the detailed energy flow, or substructure, of jets has come to play a central role at the Large Hadron Collider (LHC). I will present several recent advances in our theoretical understanding of the substructure of jets, highlighting in particular the remarkably simple theoretical structure and universal scaling laws that emerge at small angular scales. I will then describe the important role these theoretical advances have played at the LHC, where they have enabled innovative probes of the Standard Model and novel searches for new physics.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Markus Klute
Benjamin Nachman, SITC, Lawrence Berkeley National Laboratory
Deep Learning, Quantum Information, and the LHC as a Gluon Factory
Abstract: Jets produced from high-energy quarks and gluons are ubiquitous at the Large Hadron Collider (LHC). These objects can be used to study emergent quantum properties of the strong force as well as search for new particles and forces beyond the Standard Model. As a jet can have O(100) particles, analyzing jets is inherently a high-dimensional problem. Therefore, jet physics has been leading the integration and development of modern machine learning tools for high-energy physics. This high dimensionality also is a challenge for classical techniques to account for all quantum effects in the evolution of jet formation. I will start by discussing the exciting new field of precision jet substructure, with the latest results from the ATLAS experiment and interpreted in the context of new theory calculations. This sets the stage for two exciting parallel developments where quantum computers and machine learning may lead to fundamentally new insights. After briefly mentioning the potential of quantum algorithms, I will illustrate the power of deep learning with a new class of algorithms called weak supervision that can learn directly from (unlabeled) data and potentially uncover high dimensional structures hidden from our ordinary three-dimensional view. In this way, machine learning can help us learn something new and fundamental about nature.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Will Detmold
Andrea Pocar, UMass Amherst
Why Do Neutrinos Have Mass?
A Puzzle That Links Cosmology to Particle Physics and Some of the Rarest Events in Nature
Abstract: Understanding why neutrinos have mass and through what fundamental processes their mass is so tiny are open questions in particle and nuclear physics, and in cosmology. Neutrino-less double beta (0νββ) decay (0νββ), a nuclear disintegration in which two neutrons decay into protons with the emission of just two electrons, is a lepton number violating process that could help to address these questions. The detection of 0νββ decay would require that neutrinos are massive Majorana particles, with no distinction between neutrinos and antineutrinos, a compelling property that could be a portal into understanding the matter-antimatter imbalance observed in the universe today.
This talk introduces 0νββ decay in the broader context of understanding neutrino properties, and introduces the current state of art efforts to search for it, with a focus on the nEXO experiment, a large time projection chamber under design to operate with five-tonnes of mass-136-enriched xenon. Experimental challenges and theoretical hurdles to address to fully interpret the data will be addressed.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
No Talk this Week
hosted by: Janet Conrad
Dorothea vom Bruch, Sorbonne University, Paris Diderot University
Winner of the 2019 Grodzins Postdoctoral Award
Allen: A High Level Trigger on GPUs for LHCb
Abstract:The upgraded LHCb experiment at CERN will run without a hardware level trigger in 2021, resulting in the complete detector being read out at the full bunch-crossing rate of 30 MHz and a maximum data rate of 40 Tbit/s. Events of interest are selected with a software-only trigger in two stages. This allows unprecedented flexibility for trigger selections but at the same time poses a significant computing challenge.
I present the “Allen” project, capable of processing the full first trigger stage, High Level Trigger 1 (HLT1), on about 500 state of the art consumer, professional or scientific graphics processing units (GPUs). Allen enables the exploitation of LHCb’s broad physics program in Run 3. As the first complete high-rate GPU trigger, it has the potential to significantly impact the trigger systems of other HL-LHC experiments, as well as experiments at future facilities and colliders.
During HLT1, a sub-set of the full offline track reconstruction for charged particles is run to select particles of interest based on single or two-track selections. After this first stage, the event rate is reduced by a factor 30 and selected events are passed on to the second trigger stage. The HLT1 tasks include decoding the raw data, clustering of hits, pattern recognition, as well as track fitting, vertex reconstruction and the selection of interesting events.
I will discuss the concept, advantages and challenges of performing a full event selection on GPUs and introduce the framework we have developed for this task, including a custom sequencer and memory manager. In addition, I will present the core algorithms optimized for many-core architectures.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Or Hen
Karl van Bibber, UC Berkeley
The HAYSTAC Experiment
Abstract:Recent years have seen a crescendo of attention to ultralight bosons, and the axion in particular, as promising dark matter candidates. Owing to their large occupation number, the search strategy favors treating ultralight dark matter as wavelike; the most sensitive searches for the axions relying on their resonant conversion to photons in a microwave cavity permeated by a strong magnetic field. The expected signal however is extraordinarily weak, on the order of yoctowatts, and thus the microwave cavity experiment has been both a driver and beneficiary of the ongoing revolution in quantum sensing. The Yale-Berkeley-Colorado HAYSTAC experiment has been both a data pathfinder and an innovation testbed for new microwave cavity concepts and quantum-limited detection schemes for the axion search at the highest frequencies explored to date. The experiment is currently operating with a squeezed-vacuum state receiver, joining LIGO as one of the first, if not the first, data-production experiments to do so.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Phil Harris
Matthew Rudolph, Syracuse University
Lepton Flavor Universality and Violation at LHCb
Abstract: Recent hints of lepton flavor non-universality in B hadron decays at the LHCb, BaBar, and Belle experiments are currently some of the most promising signs for new physics beyond the Standard Model. I will review the experimental situation of these “b-anomalies”, including recent developments. LHCb has a large ongoing program designed to update and expand our measurements, both with current data and after the LHCb upgrade. This includes many searches for direct lepton flavor violation, which is often predicted by theoretical models seeking to explain the anomalies.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.
Veterans Day - No Talk this Week
hosted by: Or Hen
Spencer Axani, MIT
New results from the eight-year sterile neutrino search with IceCube
Abstract: Recent global fit results to the 3+1 sterile neutrino model indicate a preference for an eV-scale sterile state. The IceCube Neutrino Observatory is uniquely positioned to search for the signature of this state using matter enhanced oscillations of atmospheric muon neutrinos passing through the core of the Earth. We present the results from two new searches using eight years of IceCube data. The first result is from a sensitive search for a matter enhanced resonance at TeV neutrino energies. The second seeks to explore a higher mass sterile hypothesis, where the oscillations become averaged out within the detector.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.
No Talk this Week
hosted by: Will Detmold
Rainer Sommer, Humboldt University of Berlin
How strong are the strong interactions?
Abstract: The ALPHA Collaboration has computed one of the most elusive fundamental parameters of Nature: the strong coupling.
It governs the interactions of quarks and gluons. At high energies, such as the ones reached at the Large Hadron Collider (LHC) at CERN, many processes can be computed in terms of a Taylor series in this coupling. A precise input value for these series is thus essential to make full use of this accelerator.
We have simulated the fundamental theory of strong interactions called Quantum Chromodynamics (QCD) over a large range of energy scales in order to extract the coupling at LHC energies. We briefly discuss also a new strategy to get even higher precision which makes use of a modified theory with artificial very massive quarks.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Or Hen
Paul Reimer, Argonne National Laboratory
Measurement of the Flavor Asymmetry in the Proton’s Sea Quarks
Abstract: For over 40 years we have understood protons as bound states of quarks and gluons interacting through the strong force, described by Quantum Chromodynamics (QCD). At large energy scales, perturbative QCD successfully describes the strong interaction, but yet our understanding of the dynamics that form a physical proton from quarks and gluons is, at best, poor. Both experiment and theory fail to explain basic properties including the proton spin, mass, or the flavor composition of the antiquark sea. Contrary to naïve assumptions, there is a remarkable asymmetry between the anti-down anti-down d ̅ and anti-up (u ̅) quarks has been observed. This asymmetry cannot be generated through perturbative QCD and demonstrates that at any energy scale, there is a fundamental anti-quark component in the proton. The Drell-Yan reaction is uniquely sensitive to antiquark distributions of the interacting hadrons because the reaction requires an anti-quark in one of the initial state hadrons. With the kinematics of the SeaQuest spectrometer, it is particularly sensitive to the anti-quarks of the target nuclei. The E906/SeaQuest collaboration has measured the ratio of deuterium to hydrogen Drell-Yan cross sections. From these data, we have extracted the ratio of d ̅/u ̅. These data extend the range of previous measurements to larger xBj and improve the statistical significance at lower xBj. This talk will present these measurements and the extracted ratio. It will also highlight other continuing analyses future Drell-Yan measurements at Fermilab.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
