## Nuclear and Particle Physics Colloquium (NPPC)

#### Spring 2021

hosted by: Or Hen

#### Via Zoom:   https://mit.zoom.us/j/484157606

Francesca Cavanna, INFN Sezione di Torino

LUNA Results on Deuterium Burning and Implications for Cosmology

Abstract:
Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN).

Although astronomical observations of primordial deuterium abundance have reached percent accuracy, theoretical predictions based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)3He reaction.

I will report on a new measurement of the D(p,γ)3He cross section performed by the LUNA collaboration to an unprecedented precision of better than 3%. This result settles the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances as probes of the physics of the early Universe.

hosted by: Gunther Roland

#### Via Zoom:   https://mit.zoom.us/j/484157606

Jing Wang, MIT

Evidence of X(3872) Production in Heavy-Ion Collisions with CMS Experiment

Abstract:
The structure of the exotic meson X(3872) is still under debate. The similarity of the X(3872) mass and the D-D̄* mass threshold inspired the interpretation that X(3872) is a D-D̄* “molecule” with small binding energy. Another explanation is that this meson is a tetra-quark, consisting of a di-quark and di-antiquark. Relativistic heavy-ion collisions produce an extremely hot and strongly interacting medium, which provides a new environment to study the nature of multi-quark states. Because of the different radii of a D-D̄* “molecule” and a tetra-quark, these two proposed states are expected to interact differently with the medium. Therefore, the yield of X(3872) in heavy-ion collisions can provide insight into its structure. The ratios of production cross-section of fully reconstructed X(3872) over ψ(2S) in PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS detector are presented.

Please Note: This is Tuesday at 4:50PM

hosted by: Philip Harris

#### Via Zoom:   https://mit.zoom.us/j/484157606

Mihoko Nojiri, KEK Theory Center

Morphology for Jet Classification

Abstract:
Minkowski Functionals (MFs) defined in integral geometry is a mathematical tool to describe complex spatial structure. It has been applied on various systems such as cosmological structure and material science. In this talk, We introduce a morphological analysis of jet image (of particle physics ) utilizing MFs together with machine learning.

The MFs provide geometric information of the jet constituents, and they are independent of the IRC safe observables commonly used in jet physics. We introduce a new ML jet classifier utilizing MFs. It is computationally cheap, and stable by aggregating soft activities using MFs with tagging performance to comparable to that of the convolutional neural network (CNN) trained on jet images. The result suggests that the MFs can be an efficient parameterization of the feature space of jets.

hosted by: Daniel Harlow

#### Via Zoom:   https://mit.zoom.us/j/484157606

Johannes Michel, MIT

QED Effects in Drell-Yan Angular Distributions at the LHC

Abstract:
Measuring the angular distribution of Drell-Yan lepton pairs at the LHC gives access to the 3D structure of the proton encoded in TMD distributions, and enables precise consistency checks of the Standard Model. I review the factorization properties of the underlying hadronic structure functions in QCD and show how they enter in state-of-the-art theory predictions for Drell-Yan and related color-singlet processes like gluon-fusion Higgs production.

I then ask how robust these results are against QED radiative corrections that can in particular be enhanced by large logarithms. I first focus on the effect of final-state photon radiation that requires a careful experimental definition of "leptons" (similar to QCD jets), and show why on theory grounds, a particular lepton definition is especially suited to study angular distributions.

These results hold in an often-employed approximation where the production and decay of the vector boson are factorized. In the last part of my talk, I sketch ongoing work on an effective field theory setup allowing us to quantify how good that approximation is for resonant Z or W production and decay, in particular in the TMD limit of small transverse momentum.

hosted by: Or Hen

#### Via Zoom:   https://mit.zoom.us/j/484157606

Sharona Gordon, University of Washington

Science, Power, and Activism: The Meaning of Inclusion in Academic Sciences

Abstract:
Sexual harassment is more prevalent in academic sciences, engineering, and medicine than in any other public sector, private sector, or government workplace except for the military. Women’s physical health, mental health, and careers continue to suffer as four decades of combating sexual harassment in the academy have yielded little progress. The #MeToo movement is raising awareness of sexual harassment as a major contributor to the so-called “leaky pipeline” that drives women out of academic sciences. In this talk, Professor Gordon will share the narrative of her career path and how her experiences lead to her current activism and founding of Below the Waterline, an organization devoted to supporting targets of gender harassment in academia. Below the Waterline now works with people of all genders to understand how personal, collective, and institutional power can be leveraged to create an academic culture that respects and values individuals.

hosted by: Aram Harrow

#### Via Zoom:   https://mit.zoom.us/j/484157606

Anand Natarajan, MIT

Quantum Correlations, Complexity Theory, and the Connes Embedding Problem

Abstract:
Nonlocal correlations were introduced by John Bell in 1964 as a way to operationally distinguish quantum mechanics from classical models of the world. Since then, they have become an important tool in probing the structure of quantum mechanics. An open problem in this area, arising from the work of Boris Tsirelson, was to determine whether the set of correlations arising from the so-called "commuting operator" model of quantum nonlocality is strictly larger than the set arising from the "tensor product" model. This question, in addition to its intrinsic interest, is also surprisingly connected to the Connes embedding problem, an open problem in operator algebras: a positive answer to the Connes problem implies that the two correlation sets in Tsirelson's problem are equal. In this talk I will present work resolving these problems using computational complexity theory.

Based on joint work with Zhengfeng Ji, Thomas Vidick, John Wright, and Henry Yuen (https://arxiv.org/abs/2001.04383).

hosted by: Phil Harris

#### Via Zoom:   https://mit.zoom.us/j/484157606

David Miller, University of Chicago - ATLAS, ML

Black Boxes or Interpretable Models? Applications of Machine Learning, Symmetries, and Domain Knowledge to High-Dimensional Problems in Particle Physics

Abstract:
The world of artificial intelligence (AI) and machine learning (ML) has undergone what Brian Nord referred to as the "3rd Age of AI” due to the confluence of developments in Algorithms, Computing Resources, and Big Data. Particle Physics has benefitted from, and in many ways strengthened and advanced, progress in AI/ML for decades due to its proliferation of enormous data sets, complex instrumentation, and computing infrastructure. However, there exist both known and unknown deficiencies in our ability to explain “why” some AI/ML models yield a certain result. From my very novice perspective, I will discuss some of the context and common applications of AI/ML in experimental particle physics. I will then focus on three projects ongoing in my group that we believe target important problems relevant to the use of machine learning, symmetries, and domain knowledge in particle physics.

hosted by:

#### Via Zoom:   https://mit.zoom.us/j/484157606

Federico Sanchez Nieto, University of Geneva

The Pursuit of Neutrino CP Violation with the T2K Experiment: Challenges and Prospects

Abstract:
After a decade of operation, the T2K Collaboration published in 2020 in Nature very exciting results showing the strongest constraint yet on the parameter that governs the breaking of the symmetry between matter and antimatter using neutrino oscillations. T2K has studied how beams of muon neutrinos and antineutrinos transition into electron neutrinos and electron antineutrinos, respectively. The parameter governing the matter/antimatter symmetry breaking in neutrino oscillation, called δcp phase, can take a value from -180º to 180º. For the first time, T2K has disfavored almost half of the possible values at the 99.7% confidence level. This outstanding result is starting to reveal a basic property of neutrinos that have not been measured until now. This is an important step on the way to knowing whether or not neutrinos and antineutrinos behave differently. In the quest of CP violation, many challenges compromise the performance of the T2K experiment. I will discuss the challenges and describe the possible solutions selected by the experiment to overcome these limitations.

hosted by: Or Hen

#### Via Zoom:   https://mit.zoom.us/j/484157606

Igor Korover, MIT

Nucleon structure from 1D to 3D

Abstract:
Understanding the microscopic structure of matter is an endeavor that is ongoing for more than half a century. From the first electron beam at SLAC, we have learned much about nucleon structure, although most of our understanding is based on measurements along one longitudinal direction. In last two decades, a new experimental approach to study nucleon structure through deeply virtual exclusive processes has been developed. In these processes, additional information from the transverse direction is combined with longitudinal measurements to create a 3D image of the nucleon. In my talk, I will briefly present the underlying physics that allows us to access this structural information and focus on the ongoing analysis of the experimental data taken at Jefferson Laboratory. Then, I will discuss the impact of the future EIC to significantly advance our understanding of nucleon structure.

hosted by: Philip Harris / Tracy Slatyer

#### Via Zoom:   https://mit.zoom.us/j/484157606

Francesca Calore, LAPTh - CNRS

Unveiling the Nature of Dark Matter: A Multi-Faceted Search Program

Abstract:
Unveiling the nature of dark matter is one of the major endeavors of our century. The search for dark matter is developed across multiple channels and with different techniques. I will review the main candidate for particle dark matter and introduce how we tackle the challenge of discovering them. I will focus especially on indirect dark matter searches with gamma rays, which aims to identify the nature of dark matter and narrow down the parameter space of different dark matter candidates by using data from gamma-ray instruments on ground and in space. I will finally provide some prospects for future observations.

hosted by:

#### Via Zoom:   https://mit.zoom.us/j/484157606

Laurent Lellouch, CNRS & Aix-Marseille U.

Leading Hadronic Contribution to the Muon Magnetic Moment from Lattice Quantum Chromodynamics

Abstract:
Twenty years ago in an experiment at Brookhaven National Laboratory, physicists measured the muon's anomalous magnetic moment, $a_\mu=(g_\mu-2)/2$, with a remarkable precision of 0.54 parts per million. Since then, the standard model prediction for $a_\mu$ has exhibited a discrepancy with experiment of over 3 standard deviations. On April 7 a new Fermilab experiment presented its first results, brilliantly confirming Brookhaven's measurement and bringing the discrepancy with the standard model to a near discovery level of 4.2 sigmas. To fully leverage this and future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the standard model prediction with independent methods, and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of $a_\mu$, I will present a precise lattice QCD calculation, by the BMW collaboration, of the contribution to this quantity that most limits the precision of the standard model prediction. The result of this calculation significantly reduces the gap between the standard model and experiment, and suggests that new physics may not be needed to explain the current experimental world average of $a_\mu$.