Nuclear Theory·nucl-th

Wednesday·May 1, 2024

7 papers—2 primary·5 cross-listed

01
Statistical Theory of Neutron-Induced Nuclear Fission and of Heavy-Ion Fusion
Hans A. Weidenmüller
For both reactions we use an approach similar to that of compound-nucleus reaction theory. For neutron-induced fission, we describe the compound system generated by absorption of the neutron and the nuclear system near the scission point as two statistically independent systems governed by random-matrix theory. The systems are connected either by a barrier penetration factor or by a set of transition states above the barrier. Each system is coupled to a different set of channels. An analogous model is used for heavy-ion fusion. Assuming that (seen from the entrance channel) the system on the other side of the barrier is in the regime of strongly overlapping resonances, we obtain for fixed spin and parity closed-form analytical expressions for the total probability for fission and for fusion. Parts of these expressions can be calculated reliably within existing compound-nucleus reaction theory. The remaining parts are the probabilities for passage through or over the barrier. These may be determined theoretically from the liquid-drop model or experimentally from total fission or fusion cross sections.
nucl-thPRC(2024)·2 citations
02
Exploring the potential of synthesizing unknown superheavy isotopes via cold-fusion reactions based on the dinuclear system model
Hao Wu · Peng-Hui Chen · Fei Niu · Zu-Xing Yang · Xiang-Hua Zeng · Zhao-Qing Feng
To assess the potential of cold-fusion for synthesizing superheavy nuclei (SHN) with proton numbers 104-113, we systematically calculated 145 naturally occurring projectile-target combinations within the DNS model. Reactions predominantly show maximum cross-sections in the 1n to 2n channels, peaking near the Coulomb barrier with a sum of barrier and Q-value within 30 MeV. The maximum cross-section occurs below the Bass barrier, suggesting either the Bass model's limitation or significant deformation reducing the effective Coulomb barrier. Our calculations align well with experimental data, revealing that more neutron-rich projectiles slightly enhance fusion, though the effect is minor. For fixed targets (Pb, Bi), evaporation residue cross-sections decrease linearly with increasing projectile proton number, attributed to reduced fusion probability and lower fission barriers in heavier SHN. The touching potential $V_{in}$ shows a linear trend with the product of projectile-target proton numbers, with neutron-rich systems exhibiting lower $V_{in}$ . Some reactions with $V_{in} < V_{S}$ may involve nucleon transfer before capture. Based on the DNS model, we identified optimal combinations and collision energies for synthesizing SHN with significant cross-sections. Collectively, our findings indicate that cold fusion is a promising avenue for creating proton-rich SHN around the drip line in the Z=104-113 region, offering distinct advantages over alternative mechanisms.
nucl-thPRC(2025)·0 citations
03
Alpha radioactivity deep-underground as a probe of axion dark matter
Carlo Broggini🇮🇹 · Giuseppe Di Carlo🇮🇹 · Luca Di Luzio🇮🇹 · Claudio Toni🇮🇹
We propose to investigate the time modulation of radioisotope decays deep underground as a method to explore axion dark matter. In this work, we focus on the $α$ -decay of heavy isotopes and develop a theoretical description for the $θ$ -dependence of $α$ -decay half-lives, which enables us to predict the time variation of $α$ -radioactivity in response to an oscillating axion dark matter background. To probe this scenario, we have recently constructed and installed a setup deep underground at the Gran Sasso Laboratory, based on the $α$ -decay of Americium-241. This prototype experiment, named RadioAxion- $α$ , will allow us to explore a broad range of oscillation's periods, from a micro-second up to one year, thus providing competitive limits on the axion decay constant across 13 orders of magnitude in the axion mass, ranging from $1 0^{- 9}$ eV to $1 0^{- 20}$ eV after one month of data collection, and down to $1 0^{- 22}$ eV after three years.
↳ hep-phhep-exnucl-exnucl-thPLB(2024)·9 citations
04
Strongly vs. weakly coupled in-medium showers: energy stopping in large- $N_{f}$ QED
Peter Arnold🇺🇸 · Omar Elgedawy🇺🇸 · Shahin Iqbal🇵🇰
Inside a medium, showers originating from a very high-energy particle may develop via medium-induced splitting processes such as hard bremsstrahlung or pair production. During shower development, two consecutive splittings sometimes overlap quantum mechanically, so that they cannot be treated independently. Some of these effects can be absorbed into an effective value of a medium parameter known as $q^$ . Previous calculations (with certain simplifying assumptions) have found that, after adjusting the value of $q^$ , the leftover effect of overlapping splittings is quite small for purely gluonic large- $N_{c}$ showers but is very much larger for large- $N_{f}$ QED showers, at comparable values of $N α$ . Those works did not quite make for apples-to-apples comparisons: the gluon shower work investigated energy deposition from a gluon-initiated shower, whereas the QED work investigated charge-deposition from an electron-initiated shower. As a first step to tighten up the comparison, this paper investigates energy deposition in the QED case. Along the way, we develop a framework that should be useful in the future to explore whether the very small effect of overlapping splitting in purely gluonic showers is an artifact of having ignored quarks.
↳ hep-phnucl-thJHEP(2024)·12 citations
05
CP Violation Problem
Nicolai Popov (LMU)🇩🇪 · William J. Briscoe (GWU)🇺🇸 · Igor Strakovsky (GWU)🇺🇸
The strong CP violation problem has a long history emanating from its discovery 60 years ago in the decay of neutral kaons and subsequent experimental and theoretical studies over several decades. We review herein experimental data that observe indirect CP violation of the order of $\sim 1 0^{- 3}$ , as well as the discovery of direct CP violation of the order of $\sim 1 0^{- 6}$ . Despite improved experimental methods over the past half a century, the original CP violation numbers have remained the same. Verification of the CP violation in the decay of charged kaons was also observed. Data reflecting CP violation in the decays of $B$ and $D$ mesons have become very important and are also discussed in this review. The question of CP violation only with the participation of $s s ˉ$ , $c c ˉ$ , and $b b ˉ$ quarks in the framework of the Standard Model or beyond it and its small magnitude remains open.
↳ hep-phhep-exnucl-exnucl-thBraz.J.Phys.(2025)·0 citations
06
Toward the application of large- $N$ deconfinement to SU(3) QCD
Hiromasa Watanabe🇯🇵
It is generally known for $U (N)$ gauge theory at finite temperature that phase transitions are manifested by taking the large- $N$ limit. Since the large- $N$ theory undergoes two thermodynamic phase transitions, a nontrivial intermediate phase can be realized in addition to the phases classified as the conventional confined and deconfined phases. In this talk, we discuss that a similar picture can be applied to QCD with $N = 3$ . In particular, we analyze the gauge configurations of lattice QCD calculations involving dynamical quarks and show the results of an analysis of the deviation due to finite-temperature effects from the Haar randomness expected at zero temperature in $SU (N)$ gauge theory, using physical pictures suggested by the large- $N$ theory.
↳ hep-thhep-lathep-phnucl-thPoS(2024)·0 citations
07
The Width of an Electron-Capture Neutrino Wave Packet
B.J.P. Jones🇺🇸 · E Marzec🇺🇸 · J. Spitz🇺🇸
We discuss the size of an electron neutrino wave packet emerging from an electron capture decay using the formalism of open quantum systems. This quantitative result is based on methodology that we have previously used to predict the width of an electron antineutrino wave packet from a beta-decaying nucleus, adapted for the different initial states in electron capture and beta decay. These predictions are now becoming relevant to experimental probes of the neutrino width, for example indirectly through precision spectroscopic studies of the nuclear recoil. We provide a translation between a recent Beryllium Electron capture in Superconducting Tunnel junctions Experiment (BeEST) measurement of the daughter nuclear recoil spectrum from $^{7} Be$ electron capture decay ( $e^{-} +^{7} Be \to^{7} Li + ν_{e}$ ) and a constraint on the outgoing neutrino width. According to our analysis, the direct limit on the neutrino wave packet width from electron capture decay using the recent BeEST result should map to $σ_{ν, x} > 6.2 pm$ . We determine that a hard upper limit on the wave packet width exists at $σ_{ν, x} \sim 2.7 nm$ , based on the relative momentum between the electron and nucleus. However, we find that the localization is most likely driven by the embedding of the decaying atom in the tantalum crystal lattice resulting in a width scale of approximately $σ_{ν, x} \sim 10$ ~pm, motivated by data from X-ray diffraction and M $o ¨$ ssbauer spectroscopy, which lies intriguingly close to the current bound.
↳ hep-phnucl-th5 citations

Affiliations

first authorsco-authorsvia INSPIRE

Statistical Theory of Neutron-Induced Nuclear Fission and of Heavy-Ion Fusion

Exploring the potential of synthesizing unknown superheavy isotopes via cold-fusion reactions based on the dinuclear system model

Alpha radioactivity deep-underground as a probe of axion dark matter

Strongly vs. weakly coupled in-medium showers: energy stopping in large-Nf​ QED

CP Violation Problem

Toward the application of large-N deconfinement to SU(3) QCD

The Width of an Electron-Capture Neutrino Wave Packet

Affiliations

Strongly vs. weakly coupled in-medium showers: energy stopping in large- $N_{f}$ QED

Toward the application of large- $N$ deconfinement to SU(3) QCD