Nuclear and Particle Theory Seminar

Mondays, 2:00pm
MIT Center for Theoretical Physics
Organizers: Joshua Foster, Govert Nijs, Fernando Romero Lopez, Phiala Shanahan, Jesse Thaler

Monday, September 12
Sokratis Trifinopoulos, MIT, IAIFI

Title: New Physics in b →s μμ: FCC-hh or a Muon Collider?​

Abstract: Rare flavour-changing neutral-current transitions b→sμ⁺μ⁻ probe higher energy scales than what is directly accessible at the LHC. Therefore, the presence of new physics in such transitions, as suggested by the present-day LHCb anomalies, would have a major impact on the motivation and planning of future high-energy colliders. The two most prominent options currently debated are a proton-proton collider at 100 TeV (FCC-hh) and a multi-TeV muon collider (MuC). In this work, we compare the discovery prospects at these colliders on benchmark new physics models indirectly detectable in b→sμ⁺μ⁻ decays but beyond the reach of the high-pT  searches at the HL-LHC. We consider a comprehensive set of scenarios: semileptonic contact interactions, Z′ from a gauged U(1)_{B 3 − L μ} and U(1)_{L μ − L τ}, the scalar leptoquark S₃, and the vector leptoquark U₁. We find that a 3 TeV MuC has a sensitivity reach comparable to the one of the FCC-hh. However, for a heavy enough mediator, the new physics effects at a 3 TeV MuC are only observed indirectly via deviations in the highest energy bin, while the FCC-hh has a greater potential for the discovery of a resonance. Finally, to completely cover the parameter space suggested by the bsμμ anomalies, among the proposed future colliders, only a MuC of 10 TeV (or higher) can meet the challenge.​


Monday, September 19
Kyle Lee, MIT, CTP

Title: Conformal Colliders Meet the LHC

Abstract: Reframing jet substructures in terms of multipoint correlation functions of energy flow light-ray operators offers new means to study the dynamics of QCD jets, providing many interesting phenomenological applications (including QCD fragmentation, track functions, precision measurements, and more) and allowing applications of theoretical developments in the study of conformal field theories.
 
In order to fully benefit from such a reframing based on energy correlators, it is imperative to develop a theoretical framework to incorporate the complicated initial state of the LHC, which goes beyond what has previously been considered in theoretical studies of energy correlators. 
 
In this talk, I will present a theoretical framework developed using SCET to study energy correlators at the LHC, allowing recent calculations of energy correlators to be seamlessly embedded in the complicated LHC environment.
 
Using this approach, I will present results for the scaling behavior of multipoint energy correlators and compare with CMS Open Data, opening the door to the quantitative study of energy correlators at the LHC.
 
Additionally, we extend existing factorization theorems to include the mass of heavy quarks. Using this framework, we then observe a clear transition from the scaling region to the region corresponding to the heavy quark mass scale, manifesting the long-sought-after dead-cone effect and illustrating fundamental effects and illustrating fundamental effects coming from the intrinsic mass of beauty and charm quarks before they are confined inside hadrons.


Monday, September 26
Masaaki Tomii, University of Connecticut

Title: $K \to \pi\pi$ decay on the lattice with periodic boundary conditions

Abstract: Since RBC/UKQCD’s latest publication of lattice result for direct CP violation and the Delta I = 1/2 rule in $K \to \pi\pi$ decay, which was made with G-parity boundary conditions in 2020, we have been revisiting this problem with a different lattice setup with periodic boundary conditions and multiple lattice spacings to see the consistency with our previous result and to improve the precision.  While there was an expectation that it could be difficult to extract physical kinematics of K to pipi decay with periodic boundary conditions, we overcome it through the variational method.  Also periodic boundary conditions provide a relatively easy way to introduce electromagnetic and isospin breaking corrections, which is desired to be implemented in near future.  In this talk, we show our preliminary result and discuss prospect of high-precision calculation of $K \to \pi\pi$ decay with periodic boundary conditions.


Monday, October 3
Fernando Romero Lopez MIT, CTP
Title: Hadronic resonances from lattice QCD

Abstract: Most of the known hadrons in the low-energy QCD spectrum correspond to resonances that are found in multi-particle scattering processes. Indeed, lattice QCD can be used to perform first-principles calculations of scattering amplitudes, and so, the properties such as the mass and width of hadronic resonances can be computed. In this talk, I will review recent progress on the study of some resonances from lattice QCD. In particular, I will focus on meson-baryon resonances, such as the Delta(1232) resonance, and the study of a three-body resonance in a toy model.

Monday, October 10
Indigenous People’s Day (No Seminar)

Monday, October 17
Lena Funcke, MIT, CTP
Title: Quantum Algorithms for Particle Physics

Abstract: In this talk, I will review recent advances in applying quantum computing to particle physics. Quantum technology offers the prospect to efficiently simulate sign-problem afflicted regimes in lattice field theory, such as the presence of topological terms, chemical potentials, and out-of-equilibrium dynamics. Moreover, quantum computing can be applied to quadratic unconstrained binary optimization (QUBO) problems in collider physics. The path towards quantum simulations of (3+1)D particle physics requires many incremental steps, including algorithmic development, hardware improvement, methods for circuit design, as well as error mitigation and correction techniques. After reviewing these requirements and recent developments, I will discuss the main challenges and future directions.

Monday, October 24
Seth Koren, University of Chicago
Title: Discrete Gauged B-L and the Cosmological Lithium Problem

Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.

The cosmological lithium problem—that theory predicts a primordial abundance far higher than that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

Monday, October 31
Harikrishnan Ramani, Stanford University

Title: Dark matter detection with trapped ions

Abstract: Axion Dark Matter, Dark Photon Dark matter and Millicharged particle dark matter are some of the simplest and popular models of dark matter and are looked for in various experiments. Yet, there continue to exist inaccessible regions in interaction and mass parameter space for these models. In this talk I propose a new way to detect the tiny electric fields produced by these dark matter candidates: the remarkably stable trapped ions, tools developed in the context of quantum metrology and quantum computing. I present preliminary data from pilot experiments as well as steps to improve sensitivity in the future.

Based on: https://arxiv.org/abs/2208.06519, https://arxiv.org/abs/2108.05283. 

Monday, November 7
No seminar this week.

Monday, November 14
Christina Gao, University of Illinois, Champaigne-Urbana
Title: Axion wind detection with the homogeneous precession domain of superfluid helium-3

Abstract: Axions and axion-like particles may couple to nuclear spins like a weak oscillating effective magnetic field. Existing proposals for detecting this “axion wind” sourced by dark matter exploit analogies to nuclear magnetic resonance (NMR) and aim to detect the small transverse field generated when the axion wind resonantly tips the precessing spins in a polarized sample of material. We describe a new proposal using the homogeneous precession domain (HPD) of superfluid 3He as the detection medium, where the effect of the axion wind is a small shift in the precession frequency of a large-amplitude NMR signal. We argue that this setup can provide broadband detection of multiple axion masses simultaneously, and has competitive sensitivity to other axion wind experiments such as CASPEr-Wind at masses below 10−7 eV by exploiting precision frequency metrology in the readout stage.


Monday, November 21
Jean-Francois Paquet, Vanderbilt University

Title: Nuclear collisions as seen through photons

Abstract: The energy spectrum of photons is understood well in ultrarelativistic collisions of protons or of nuclei, as long as the photons’ energy reaches the 10+ GeV range. For lower energy photons, however, considerable differences appear between the collisions of protons and of nuclei. In the heavy ion case, the production of GeV-energy photons appears to be dominated by electromagnetic radiation from the plasma of deconfined nuclear matter produced in the collisions. I will discuss the status of theoretical calculations of the photon energy spectrum in proton-proton and heavy-ion collisions, reviewing the current agreement with experimental data, as well as recent developments.

Monday, November 28
Wilke van der Schee, CERN

Title: Heavy ion collisions and the shape of nucleons and nuclei

Abstract: In this seminar I will give a brief introduction to the formation of quark-gluon plasma (QGP) in heavy ion collisions. This consists of an initial colliding stage, a hydrodynamic stage and a hadronic gas phase after which particles can finally be observed. While there is nowadays a wealth of experimental data, it is challenging to infer conclusions on specific aspects and I will highlight a recent effort that in particular constrains the nucleon width inside a nucleus. Finally, given the current precision of heavy ion experiments I will give examples of how these are sensitive to the shape of nuclei.



Monday, December 5
Carolyn Raithel, IAS

Title: Probing Dense Matter with Gravitational Waves
 
Abstract: Neutron star mergers provide a unique probe of the dense matter equation of state (EOS) across a wide range of parameter space, from the cold and equilibrated matter of the inspiral, to the shock-heated and higher-density conditions that govern the post-merger evolution. In this talk, I will start with an overview of what we have learned about the EOS so far from the first LIGO-Virgo observations of binary neutron star inspirals. I will then introduce a new category of “doppelgänger” EOS models, which produce the same gravitational wave signatures despite significant differences in the underlying EOS, and I will discuss the prospects for resolving this new observational degeneracy. In the second part of the talk, I will present a series of neutron star merger simulations that employ a phenomenological framework for studying new parts of the EOS parameter space. I will use these simulations to discuss what additional constraints we may be able to extract from a future detection of gravitational waves emitted the remnant neutron star that forms after a merger.