Exploring the Origin of Light Heavy Elements

Bridging experiments, theory, and observations

 

Thanassis Psaltis
Triangle Universities Nuclear Laboratory & North Carolina State University
psaltis.tha@duke.edu
 

September 11, 2023
BRIDGCE-IReNA Annual Meeting


 

Image Credit: NASA/CXC/SAO

Acknowledgements


Almudena Arcones   Melina Avila   Camilla Juul Hansen  

Peter Mohr   Fernando Montes   Wei Jia Ong Hendrik Schatz


The periodic table from
a Galactic Chemical Evolution perspective

C. Kobayashi, A. Karakas and M. Lugaro, Astrophys. J 900, 179 (2020)
See talk by A. Cameron on GCE

 

 

 

 

 

 

 

HD 122563 (DSS2/ Aladin Sky Atlas)

What do the ancient stars show us?


See also: C. Sneden, J. J. Cowan and R. Gallino, Annu. Rev. Astron. Astrophys. 46, 241 (2008)
See talks by T. Beers and T. Hansen on observations of r-process stars • ‼️ r-process = total solar - s-process - γ-process

How many processes contribute to the production of elements between
strontium and silver?

The periodic table from
a Galactic Chemical Evolution perspective

C. Kobayashi, A. Karakas and M. Lugaro, Astrophys. J 900, 179 (2020)

The weak $r$-process

  • Where?

    In neutrino-driven outflows of explosive environments (ccSNe or NSMs)

  • When?

    During the expansion of the hot and dense outflows ($Y_e \equiv n_p/(n_p+n_n),s,\tau$)

  • How?

    After an $\alpha$-rich freeze-out from NSE at T= 5-2 GK $(\alpha,n)$ reactions produce heavy elements

  • What?

    Can synthesize heavy elements around Z = 47 (silver) found in metal-poor stars

S. Woosley & R.D. Hoffman, Astrophys. J 395, 202 (1992) • S. Wanajo et al., Astrophys. J. 554, 578 (2001) • A. Arcones & F. Montes, Astrophys. J 731, 5 (2011)

How important are the $\mathbf{(\alpha,xn)}$ reactions in the weak $r$-process?

How much do we know the $(\alpha,xn)$ reaction rates?

The $(\alpha,xn)$ reaction rates are sensitive to the $\alpha$-nucleus potential
and their uncertainties can be up to two orders of magnitude.


 
J. Pereira and F. Montes, Phys. Rev. C 93, 034611 (2016) • P. Mohr, Phys. Rev. C 94, 35801 (2016)

Framework of the sensitivity study

A. Parikh et al., Astrophys. J., Suppl. Ser. 178, 110 (2008)
N. Nishimura et al., Mon. Not. R. Astron. Soc 489, 1379 (2019)
J. Bliss et al., Phys. Rev. C 101, 055807 (2020)
P.A. Denissenkov et al., Mon. Not. R. Astron. Soc 503, 3913 (2021)
  • Relevant thermodynamic profiles spanning the astrophysical phase-space ($Y_e$, $s$, $\tau$)
    J. Bliss et al., Astrophys. J 855, 135 (2018)

  • $(\alpha, xn)$ reaction rates based on the Atomki-v2 $\alpha$-nucleus potential
    P. Mohr et al., At. Data Nucl. Data Tables 132, 101453 (2021)
  • MC sampling of the $(\alpha,xn)$ reaction rates (104 calculations)

  • Find the most impactful $(\alpha,xn)$ reactions and compare with observations
For more details: A. Psaltis et al., Astrophys. J 935, 27 (2022)

The impact of updated $(\alpha,n)$ reaction rates to elemental abundances

Same model, but different $(\alpha, xn)$ reaction rates!

A. Psaltis et al., Astrophys. J 935, 27 (2022)

The impact of new $(\alpha,n)$ reaction rates to elemental abundance ratios

A. Psaltis et al., Astrophys. J 935, 27 (2022)

Combine observations, astrophysical modeling and nuclear physics uncertainties

Which are the most important $\mathbf{(\alpha,xn)}$ reactions for the weak $r$-process?

Finding the most important $(\alpha,n)$ reactions for the weak $r$-process

Search for the (anti)correlations! 🔍

The most important $(\alpha,n)$ reactions for the weak $r$-process

N=50 shell closure is a bottleneck for T= 4-5 GK due to the $(n,\gamma) \leftrightarrow (\gamma,n)$ equilibrium

Can we study the most important
$\mathbf{(\alpha,xn)}$ reactions in the lab?

Most of the relevant beams are accessible!


Expected FRIB ultimate beam rates

What has been measured so far?

  • $\mathrm{^{86}Kr(\alpha,n)}$, $\mathrm{^{96}Zr(\alpha,n)}$ and $\mathrm{^{100}Mo(\alpha,n)}$ at ATOMKI
    G.G. Kiss et al., Astrophys. J 908, 202 (2021) • T.N. Szegedi et al., Phys. Rev. C 104, 035804 (2021)

  • $\mathrm{^{75}Ga(\alpha,n)}$, $\mathrm{^{85,86}Kr(\alpha,xn)}$, $\mathrm{^{85}Br(\alpha,xn)}$ at NSCL/FRIB (HabaNERO/SECAR)
    F. Montes, J. Pereira et al.

  • $\mathrm{^{86}Kr(\alpha,xn)}$, $\mathrm{^{87}Rb(\alpha,xn)}$, $\mathrm{^{88}Sr(\alpha,xn)}$, $\mathrm{^{100}Mo(\alpha,xn)}$ at Argonne (MUSIC)
    M. L. Avila, C. Fougères et al.
    W. J. Ong et al., Phys. Rev. C 105, 055803 (2022)

  • $\mathrm{^{86}Kr(\alpha,n)}$ and $\mathrm{^{94}Sr(\alpha,n)}$ at TRIUMF (EMMA)
    C. Aa. Diget, A. M. Laird, M. Williams et al.
    C. Angus et al., EPJ Web of Conferences, NPA-X (2023)

First measurement of the $\boldsymbol{\mathrm{^{93}Sr}(\alpha,xn)}$ reaction at Argonne with MUSIC



Proposal #1923, PI: A. Psaltis, co-PI: W.J. Ong

$\mathrm{^{93}Sr}(\alpha,xn)$ at Argonne with MUSIC

M. L. Avila et al., NIM A 859, 63 (2017)

  • Re-accelerated $\mathrm{^{93}Sr}$ beam from $\nu$CARIBU.

  • MUSIC has close to 100% efficiency due to its segmented anode structure.

  • Use a single beam energy to measure a large range of excitation functions of angle integrated cross sections.

Which are the most favourable
conditions to produce the light heavy elements in neutrino-driven outflows?

We formed linear combinations using trajectories of various astrophysical conditions to compare with observations of metal-poor stars.

The case of HD122563

Results for HD122563 using two trajectories

Results using two trajectories for our star sample

Colored lines have $\chi^2_n<1$

Proton-rich conditions are more favourable than neutron-rich

High entropy and short expansion timescale is preferred

Can isotopic abundances from meteorites reveal neutrino-driven nucleosynthesis signatures?

Secrets in the stardust?

A. Psaltis, W.J. Ong et al. (in preparation)

What is on the horizon?


New experimental measurements of the key $(\alpha, xn)$ reactions and multi-messenger observations will help us constrain the contribution of neutrino-driven outflows to the production elements between strontium and silver.

Summary

  1. The weak $r$-process in neutrino-driven outflows can contribute to the production of elements between strontium and silver that are observed in Galactic metal-poor stars.

  2. We explored the impact of $(\alpha,xn)$ reactions to the weak $r$-process and identified the most important of them to motivate future experiments in stable and radioactive ion beam facilities.

  3. We investigated which are the most common astrophysical conditions of the neutrino-driven outflows that fit the observational patterns of metal-poor stars.

  4. Experiments in the current and next-generation RIB facilities, multimessenger observations and theoretical modeling will enhance our understanding of the origin of the light heavy elements.

Thank you!

Slides available at http://psaltisa.github.io/talks

Extra slides

Methods

We formed linear combinations using various astrophysical conditions ($Y_e, s, \tau$)
to compare with observations of metal-poor stars.

\[ P = \sum_{i=1}^N w_i Y_i \]

where $w_i>0$ is a multiplication factor and $Y_i$ is the abundance pattern of the $i^{th}$ trajectory.

Total number of unique combinations: $C_r = N! / r! (N - r)!$
for example 2 trajectories out of 46 yields 1035 unique combinations

Methods

\[ \mathrm{minimize}~ ||A w - O||^2 \] where $O$ is the observational pattern and \[ A = \begin{bmatrix} Y_{11} & \cdots & Y_{1k}\\ \vdots & \ddots & \vdots \\ Y_{N1} & \cdots & Y_{Nk} \end{bmatrix} , w = \begin{bmatrix} w_1 \\ \vdots \\ w_k \end{bmatrix} \]

Goal: solve the least-squares problem using $\texttt{sklearn}$