LNS Lunchtime Seminars | Laboratory for Nuclear Science

Seminar Details

Tuesdays 12:00 PM

All seminars are hybrid

https://mit.zoom.us/j/99963678487

Building 26, 414 (Kolker Room)

Committee: Ronald Garcia Ruiz ~ Michael Williams ~ Prajwal MohanMurthy

Fall 2024

Gerald Miller

Might Normal Nuclear Matter Be Quarkyonic?

Abstract:
The possibility that nuclear matter might be quarkyonic is considered. Quarkyonic matter is high baryon density matter that can be approximately thought of as a filled Fermi sea of quarks surrounded by a shell of nucleons. Thus, nucleon occupation probabilities are depleted for low momentum nucleons. Plausibility arguments for the existence of quarkyonic matter, based on experimental measurements of deep inelastic scattering on nucleons, are presented. Then a model of nuclear matter that includes nucleon interactions with a σ meson and a pion that to provide the necessary attraction. This model is similar the well-known Walecka model, but the necessary repulsive stabilizing forces are provided by the limit that the quark occupation probability must be less than unity. It turns out that isospin-symmetric nuclear matter binds with acceptable values of the compressibility and other parameters for nuclear matter at saturation. Quarkyonic matter predicts a strong depletion of nucleons in normal nuclear matter at low momentum. Such a depletion for nucleon momenta less than 120 MeV is shown to be consistent with quasi-elastic electron scattering data.

Kieran Flanagan

ActMol: A table top nuclear facility for fundamental science

Abstract:
Bespoke radioactive molecules constructed using octupole deformed nuclei (in particular actinide isotopes) represents a new frontier for high precision experiments. When compared to molecules containing stable (or very long-lived) nuclei, they have gains in sensitivity to parity and time-reversal violating effects that are up to 3 orders of magnitude larger. Recent advances in molecular trapping techniques also make it feasible to consider experiments that study radioactive molecules for prolonged interaction times. This would extend searches for parity- and time-reversal violations beyond the TeV energy scale, providing a complementary search domain to proposed future accelerator projects with tabletop instrumentation.

One challenge associated with utilizing radioactive molecules is a lack of existing spectroscopic data, because of their short-lived nature. Identifying the most sensitive molecular probe for new physics therefore remains an open question. Furthermore, how to produce enough radioactive molecules at a low enough temperature to perform competitive measurements has yet to be addressed.

This talk will present a new project at the University of Manchester that will develop a novel spectrometer to perform high resolution spectroscopy on actinide molecules. In doing so the project aims to identify the most sensitive systems for future experiments that search for new physics beyond the standard model of particle physics.

Jiaxiang Wang

Mechanical detection of nuclear decay

Abstract:
Measuring tiny forces and momentum transfers can enable many tests of fundamental physics. Levitated optomechanical systems in high vacuum, which have shown outstanding force and momentum sensitivity, are sensitive to the tiny momentum transfer from a single nucleus decaying within the object. This ensures sensitivity to any particles emitted in the decay, including neutral particles. In these systems, thermal noise can be eliminated and the fundamental sensitivity possible is set by constraints from quantum mechanics on the measurement process itself. By controlling the mechanical motion of a micron-sized particle precisely, and measuring its motion using light, we can detect individual alpha decays within the particle. Further development of this technique will enable new searches for sterile neutrinos, a type of dark matter candidate, by momentum reconstruction of optically trapped nano-particles doped with beta emitters.

Efrain Segarra

Next measurement of the neutron electric dipole moment: n2EDM at PSI

Abstract:
The world’s leading measurement of the neutron’s electric dipole moment (EDM) is currently ongoing at the Paul Scherrer Institute (PSI): the n2EDM experiment. n2EDM will deliver, at minimum, an order of magnitude better sensitivity as compared to current limits on the neutron EDM. This increased sensitivity on the neutron EDM will provide stringent constraints on time-reversal violating processes and deeply probe physics beyond the Standard Model (BSM), furthering our understanding on the origins of the baryon asymmetry of the universe. This talk will highlight the recent achievements and successes during commissioning – from high-voltage operation to magnetic-field uniformity. I will also introduce new techniques we have developed to characterize our apparatus, and emphasize how n2EDM will reach a ground-breaking sensitivity of 10^-27 e.cm.

No Talk

Larisa Thorne

The Role of Atomic Tritium in Future Neutrino Mass Experiments

Abstract:
Nearly 70 years since the neutrino was discovered, and 25 years since discovery of neutrino oscillations established its non-zero mass, the absolute neutrino-mass scale remains unknown. Tritium beta decay endpoint measurements currently offer the best upper limit on the neutrino mass. A next-generation experiment with greater sensitivity must overcome one of the major systematics for this kind of measurement: the molecular nature of the beta decay source. Past and current tritium beta decay experiments use a molecular tritium source in which one of the tritium atoms undergoes decay. A fraction of the decay energy excites the molecule into rotational, vibrational, or electronic excited states, which causes broadening in the molecule's final state distribution (FSD), and has a smearing effect on the beta decay spectrum. In order to achieve a reduced systematic uncertainty due to this FSD smearing, next-generation experiments must switch to an atomic tritium source. I will present an overview of the necessary steps to develop an atomic tritium source through the lens of the Project 8 experiment. This multi-institution development program includes dissociation of molecular tritium, cooling the resulting tritium atoms via a two-step process down to 10mK, and trapping them magnetically. In addition to this overview, I will focus on the multitude of tritium-compatible diagnostic tools being developed at JGU Mainz to measure atom flux, atom beam shape, and temperature; and their role in similar experiments.

Molly Park

Probing the Quark-Gluon Plasma with Photon-Tagged Jet Substructure

Abstract:
At the Large Hadron Collider, lead ions are collided at ultra-relativistic velocities to produce the quark-gluon plasma (QGP), a deconfined state of matter where quarks and gluons exhibit collective, fluid-like behavior. Jets are produced in hard scatterings prior to and independently of QGP formation, and serve as natural probes throughout the QGP's evolution. By studying how internal jet structure is modified through interaction with the QGP, we can constrain QGP properties such as its resolution length. This talk will present recent CMS measurements of photon-tagged jet substructure in proton-proton (pp) and lead-lead (PbPb) collisions with the CMS detector. The use of photon-tagged jets helps mitigate selection bias effects, offering insight into mechanisms of jet energy loss mechanisms and medium properties.iments.

Hannah Binney

Measuring the muon’s anomalous magnetic moment with the Muon g-2 experiment

Abstract:
The Fermilab Muon g-2 experiment, which measures the anomalous magnetic moment of the muon, published the results of the second and third data taking run in 2023. This result included 4 times as many statistics as the initial Run-1 result and improved the measurement precision by a factor of two. The muon anomalous magnetic moment has now been measured to an unprecedented 190 ppb, with more data currently being analyzed. This talk will primarily discuss the Run-2/3 data taking campaign and analysis, with a specific focus on the muon precession frequency analysis, including the fitting procedure and systematic uncertainty assessment. I will also discuss improvements made to the reconstruction and pileup subtraction algorithms. Finally, I will briefly discuss some experimental improvements implemented for the final data taking runs.

Anja Beck

Rare b-baryon decays at LHCb: studying penguins in the jungle

Abstract:
Rare electroweak penguin decays, such as b->s mu mu, are useful probes of the standard model (SM). Angular observables of b->s mu mu decays in the meson sector indicate tensions with SM predictions. Similar measurements of baryon decays provide complementary information to disentangle the underlying physics. Due to their non-integer spins and a rich resonance structure however, baryonic decays are much more complex. In this talk, I want to explain what makes baryons so complicated and how recent LHCb measurements try to complete the picture

Gillian Kopp

Enabling Novel Long-Lived Particle Searches through 5D Calorimetry in the CMS Experiment

Abstract:
The Compact Muon Solenoid (CMS) experiment records proton-proton collisions from the LHC to measure properties of the Standard Model and search for new physics. Recently, long-lived particles have emerged as a compelling direction in which to search for physics beyond the Standard Model. As these searches are typically limited by the event selection, implementing dedicated long-lived particle (LLP) triggers provides an excellent avenue to expand experimental coverage into this challenging parameter space. A novel hardware-level LLP trigger has been developed and implemented in the CMS experiment for Run 3 (2022-2026), exploiting the recent hadron calorimeter (HCAL) upgrade. The hardware- and firmware-based trigger algorithm identifies delayed jets, resulting from the decay of massive LLPs, and displaced jets, resulting from LLPs that decay inside the HCAL. This approach significantly increases sensitivity to LLP signatures with soft hadronic final states, including exotic decays of the Higgs boson. I review the trigger implementation, calibration, and performance, showing results from recent HCAL timing scans that produce artificially delayed jets. The data collected with the new triggers provides a first look at the capabilities to capture softer events and expand the phase space accessible in LLP searches.

Michele Atzeni

Selected results in b->sll transitions at LHCb - Tales from the (charm-)loop

Abstract:
Transitions where a b-quark decays into two oppositely charged leptons and a s-quark are very rare in the Standard Model (SM). This makes them an ideal laboratory for probing potential contributions from New Physics indirectly. Over the past decade, a consistent pattern of anomalous measurements has emerged in these transitions. In this talk, I will present recent results from the LHCb experiment that provide complementary insights into these intriguing tensions and explore whether they reflect genuine New Physics or underestimated QCD effects, likely dominated by charm-loop contributions.

Yen-Jie Lee

First evidence of the medium response to hard probes with Z-hadron correlations in PbPb and pp collisions at \sqrt{s_{NN}} =5.02 TeV

Abstract:
This seminar talk presents the first measurement of low-transverse-momentum (pT) charged-hadron distributions in pseudorapidity and azimuthal angle, relative to the momentum direction of \(Z\) bosons, in lead-lead (\PbPb) collisions at a nucleon-nucleon center-of-mass energy of \(\sqrt{s_\mathrm{NN}} = 5.02\) TeV. The analysis uses PbPb data from 2018 with an integrated luminosity of \(1.67 \pm 0.03\) nb\(^{-1}\), complemented by proton-proton (pp) data from 2017 with \(301 \pm 6\) pb\(^{-1}\). Events are selected with at least one \(Z\) boson having \(40 < p_\mathrm{T} < 350\) GeV, and charged-hadron distributions are examined in \(p_\mathrm{T}\) bins to investigate potential in-medium parton-shower modifications and medium-recoil effects.

A significant modification is observed in the azimuthal and pseudorapidity distributions of charged hadrons with \(p_\mathrm{T}\) in the range of 1–2 GeV in \PbPb\ collisions compared to pp references. These results align with phenomenological models, such as the HYBRID model that is developed at MIT CTP, that incorporate the positive and negative wake effects associated with the fast moving-quarks and gluons in the Quark-Gluon Plasma (QGP).

This analysis provides crucial new insights into the interplay between hard and soft particle production in heavy-ion collisions. By comparing PbPb data with pp baselines and theoretical predictions, the findings offer the first experimental evidence for medium-recoil and medium-hole effects induced by a hard probe, contributing to a deeper understanding of jet quenching mechanisms in the QGP.

Coming Soon!

Andrzej Novak

Boosted Jet Searches for New Physics and the Higgs Boson

Abstract:
Low-mass resonances with small interaction strengths are emerging as a compelling new physics model. Hadronic decays, including those of Higgs, W, and Z boson, can be particularly favored in different BSM models, but remain challenging to access. Recent advances in machine learning have enabled the CMS experiment to push beyond existing limits on detection of these resonances in the boosted regime. The regime is critical for understanding new physics effects as some interactions could be observed here, while remaining invisible at lower energies. Interestingly, we see a large excess in the Higgs boson production in this regime in recent measurement. As a result, we further explore this through new searches for single and pair decays to hadrons, reconstructed within large-radius jets, is presented within the context of existing CMS results.