Physical Sciences: Colloquia Announcement

[TRIUMF Physical Sciences]

Dear Physical Sciences Division member,

We wish to invite you to attend two special seminars next week. Dates, times, titles, and abstracts are below for your information.

We hope to see you there!

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Monday, 29 March 2021, at 10 am
Ragnar Stroberg (U Washington)
Title: Are you sure? The quest for error bars in nuclear theory

Abstract: Perhaps the greatest benefit of the recent advances in ab initio nuclear theory is the possibility to make predictions with meaningful uncertainties. This is especially valuable for quantities that are difficult or impossible to access experimentally, such as those that arise in astrophysics or in searches for physics beyond the standard model. However, just because uncertainty quantification is possible does not mean that it is easy. In many cases, converged ab initio calculations of the quantities of interest, in the nuclei of interest, have only recently been achieved and efforts at rigorous uncertainty quantification are still in early stages. I will discuss some developments which enabled the ab initio calculations to be done at all and some initial efforts to make good on the promise of error bars for nuclei.

https://ca01web.zoom.us/j/66543046629?pwd=aVh4aWs4ZjlxOUFPOGhVNWVoM3Fxdz09

Wednesday, 31 March 2021, at 10 am
Gaute Hagen (ORNL)
Title: Advances in ab initio computations of nuclei
Abstract:
High performance computing, machine learning techniques, many-body methods with polynomial scaling, and ideas from effective-field-theory have revolutionized computations of nuclei. In addition, with a lot of interest and funding coming from industry and research institutions, fault tolerant quantum computers could potentially transform the way ab-initio computations are performed in the future. Here I report on recent advances in ab-initio coupled-cluster computations of nuclei starting from chiral Hamiltonians with two- and three-nucleon forces. Using state-of-the-art ab-initio methods we addressed a 50-year old quenching puzzle of β-decays in nuclei [1]. Performing a systematic study of this decay in light and medium-mass nuclei including the heavy nucleus 100Sn, we showed that this quenching can be explained by a proper treatment of two-body currents and many-body correlations. Continuing along these lines we have computed the neutrino-less double-beta decay in 48Ca [2]. We found a relatively small matrix element for the neutrino-less double-beta decay, while the two-neutrino matrix element is consistent with data. I will also show predictions for radii and binding energies of exotic neon and magnesium isotopes using a deformed coupled-cluster approach with chiral interactions with delta degrees of freedom [3]. Using this approach, we provided support for the discovery of a two-neutron halo in 29F [4], and recent charge radii measurements in neutron-rich potassium isotopes [5]. The measurements challenge ab initio theory and the magic character of the neutron shell closures at N = 20 and N = 32. Last, but not least, I will present a new method that emulates exact coupled-cluster computations and allows for the computation of nuclear properties for millions of different model parameters in less than one hour on a standard laptop, once the emulator is trained. The equivalent set of ab-initio coupled-cluster computations would require about 20 years. This speedup enables statistical computing of the chiral nuclear Hamiltonian, and entirely new ways to use experimental data across the nuclear chart to generate new knowledge about the strong nuclear interaction [6].
[1] P. Gysbers, et al, Nature Physics 15, 428–431 (2019)
[2] S. J. Novario, et al., arXiv:2008.09696 (2020)
[3] S. J. Novario, et al., Phys. Rev. C 102, 051303(R) (2020)
[4] S. Bagchi, et al., Phys. Rev. Lett. 124, 222504 (2020)
[5] Á. Koszorús, et al., Nature Physics, Open Access (2021)
[6] A. Ekström and G. Hagen, Phys. Rev. Lett. 123, 252501 (2019)

https://ca01web.zoom.us/j/67452392983?pwd=T1AzSVlmSFoxL25wRjFlaTdNV0wrQT09

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Allayne McGowan
Administrative Assistant – Physical Sciences Division
Assistant to Dr. Jens Dilling – Associate Laboratory Director
t   604-222-7438
amcgowan at triumf.ca<mailto:amcgowan at triumf.ca>
sciencediv at triumf.ca<mailto:sciencediv at triumf.ca>

TRIUMF Canada’s particle accelerator centre
www.triumf.ca<http://www.triumf.ca/> @TRIUMFLab

4004 Wesbrook Mall
Vancouver, BC  V6T 2A3

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