Nuclear Theory·nucl-th

Thursday·September 16, 2021

10 papers—7 primary·3 cross-listed

08
[Submitted on 27 Jul 2021] (cross-list from hep-lat)
On the order of the QCD chiral phase transition for different numbers of quark flavours
Francesca Cuteri🇩🇪 · Owe Philipsen🇩🇪 · Alessandro Sciarra🇩🇪
The nature of the QCD chiral phase transition in the limit of vanishing quark masses has remained elusive for a long time, since it cannot be simulated directly on the lattice and is strongly cutoff-dependent. We report on a comprehensive ongoing study using unimproved staggered fermions with $N_{f} \in [2, 8]$ mass-degenerate flavours on $N_{τ} \in {4, 6, 8}$ lattices, in which we locate the chiral critical surface separating regions with first-order transitions from crossover regions in the bare parameter space of the lattice theory. Employing the fact that it terminates in a tricritical line, this surface can be extrapolated to the chiral limit using tricritical scaling with known exponents. Knowing the order of the transitions in the lattice parameter space, conclusions for approaching the continuum chiral limit in the proper order can be drawn. While a narrow first-order region cannot be ruled out, we find initial evidence consistent with a second-order chiral transition in all massless theories with $N_{f} \leq 6$ , and possibly up to the onset of the conformal window at $9 ≲ N_{f}^{*} ≲ 12$ . A reanalysis of already published $O (a)$ -improved $N_{f} = 3$ Wilson data on $N_{τ} \in [4, 12]$ is also consistent with tricritical scaling, and the associated change from first to second-order on the way to the continuum chiral limit. We discuss a modified Columbia plot and a phase diagram for many-flavour QCD that reflect these possible features.
Comments:
32 pages, 14 figures; improved error analysis and figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2107.12739 [pdf]
JHEP(2021)·130 citations
09
[Submitted on 15 Sept 2021] (cross-list from nucl-ex)
First Measurement of the $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ Transition Strength in $^{7}$ Be: Testing Ab Initio Predictions for $A = 7$ Nuclei
S. L. Henderson · T. Ahn · M. A. Caprio · P. J. Fasano · A. Simon · W. Tan · P. O'Malley · J. Allen · D. W. Bardayan · D. Blankstein · B. Frentz · M. R. Hall and 6 other authors
Electromagnetic observables are able to give insight into collective and emergent features in nuclei, including nuclear clustering. These observables also provide strong constraints for ab initio theory, but comparison of these observables between theory and experiment can be difficult due to the lack of convergence for relevant calculated values, such as $E 2$ transition strengths. By comparing the ratios of $E 2$ transition strengths for mirror transitions, we find that a wide range of ab initio calculations give robust and consistent predictions for this ratio. To experimentally test the validity of these ab initio predictions, we performed a Coulomb excitation experiment to measure the $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ transition strength in $^{7}$ Be for the first time. A $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ value of $26 (6) (3) e^{2} fm^{4}$ was deduced from the measured Coulomb excitation cross section. This result is used with the experimentally known $^{7}$ Li $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ value to provide an experimental ratio to compare with the ab initio predictions. Our experimental value is consistent with the theoretical ratios within $1 σ$ uncertainty, giving experimental support for the value of these ratios. Further work in both theory and experiment can give insight into the robustness of these ratios and their physical meaning.
Comments:
9 pages, 7 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2109.07312 [pdf]
PRC(2019)·20 citations
10
[Submitted on 15 Sept 2021] (cross-list from quant-ph)
Definitive Detection of Orbital Angular Momentum States in Neutrons by Spin-polarized $^{3}$ He
Terrence Jach (National Institute of Standards and Technology)🇺🇸 · John Vinson (National Institute of Standards and Technology)🇺🇸
A standard method to detect thermal neutrons is the nuclear interaction $^{3}$ He(n,p) $^{3}$ H. The spin-dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized $^{3}$ He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross-sections for neutrons in an $L = 1$ OAM state. The absorption of those neutrons results in compound states $J^{π} = 0^{-}$ , $1^{-}$ , and $2^{-}$ . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of $^{4}$ He after absorption, due to the fact that the compound state has odd parity. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross-sections and new channels of radioactive decay.
Subjects:
Quantum Physics (quant-ph); Nuclear Theory (nucl-th)
arXiv:
2109.07454 [pdf]
PRC(2022)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE

On the order of the QCD chiral phase transition for different numbers of quark flavours

First Measurement of the B(E2;3/2−→1/2−) Transition Strength in 7Be: Testing Ab Initio Predictions for A=7 Nuclei

Definitive Detection of Orbital Angular Momentum States in Neutrons by Spin-polarized 3He

Affiliations

First Measurement of the $B (E 2; 3/ 2^{-} \to 1/ 2^{-})$ Transition Strength in $^{7}$ Be: Testing Ab Initio Predictions for $A = 7$ Nuclei

Definitive Detection of Orbital Angular Momentum States in Neutrons by Spin-polarized $^{3}$ He