Nuclear Theory·nucl-th

Friday·April 17, 2020

10 papers—3 primary·7 cross-listed

01
Momentum-kick model application to high multiplicity pp collisions at $s = 13 TeV$ at the LHC
Beomkyu Kim🇰🇷 · Hanul Youn🇰🇷 · Soyeon Cho🇰🇷 · Jin-Hee Yoon🇰🇷
In this study, the momentum-kick model is used to understand the ridge behaviours in dihadron $Δ η$ -- $Δ φ$ correlations recently reported by the LHC in high-multiplicity proton-proton (pp) collisions. The kick stand model is based on a momentum kick by leading jets to partons in the medium close to the leading jets. The medium where partons move freely is assumed in the model regardless of collision systems. This helps us apply the method to small systems like pp collisions in a simple way. Also, the momentum transfer is purely kinematic and this provides us a strong way to approach the ridge behaviour analytically. There are already several results with this approach in high-energy heavy-ion collisions from the STAR and PHENIX at RHIC and from the CMS at LHC. The momentum-kick model is extended to the recent ridge results in high-multiplicity pp collisions with the ATLAS and CMS at LHC. The medium property in high-multiplicity pp collisions is diagnosed with the result of the model.
nucl-thhep-phInt.J.Theor.Phys.(2021)·3 citations
02
Convergence of Eigenvector Continuation
Avik Sarkar🇺🇸 · Dean Lee🇺🇸
Eigenvector continuation is a computational method that finds the extremal eigenvalues and eigenvectors of a Hamiltonian matrix with one or more control parameters. It does this by projection onto a subspace of eigenvectors corresponding to selected training values of the control parameters. The method has proven to be very efficient and accurate for interpolating and extrapolating eigenvectors. However, almost nothing is known about how the method converges, and its rapid convergence properties have remained mysterious. In this letter we present the first study of the convergence of eigenvector continuation. In order to perform the mathematical analysis, we introduce a new variant of eigenvector continuation that we call vector continuation. We first prove that eigenvector continuation and vector continuation have identical convergence properties and then analyze the convergence of vector continuation. Our analysis shows that, in general, eigenvector continuation converges more rapidly than perturbation theory. The faster convergence is achieved by eliminating a phenomenon that we call differential folding, the interference between non-orthogonal vectors appearing at different orders in perturbation theory. From our analysis we can predict how eigenvector continuation converges both inside and outside the radius of convergence of perturbation theory. While eigenvector continuation is a non-perturbative method, we show that its rate of convergence can be deduced from power series expansions of the eigenvectors. Our results also yield new insights into the nature of divergences in perturbation theory.
nucl-thcond-mat.str-elcs.NAhep-lat+2PRL(2021)·58 citations
03
Quantifying uncertainties and correlations in the nuclear-matter equation of state
C. Drischler🇺🇸 · J. A. Melendez🇺🇸 · R. J. Furnstahl🇺🇸 · D. R. Phillips🇺🇸
We perform statistically rigorous uncertainty quantification (UQ) for chiral effective field theory ( $χ$ EFT) applied to infinite nuclear matter up to twice nuclear saturation density. The equation of state (EOS) is based on high-order many-body perturbation theory calculations with nucleon-nucleon and three-nucleon interactions up to fourth order in the $χ$ EFT expansion. From these calculations our newly developed Bayesian machine-learning approach extracts the size and smoothness properties of the correlated EFT truncation error. We then propose a novel extension that uses multitask machine learning to reveal correlations between the EOS at different proton fractions. The inferred in-medium $χ$ EFT breakdown scale in pure neutron matter and symmetric nuclear matter is consistent with that from free-space nucleon-nucleon scattering. These significant advances allow us to provide posterior distributions for the nuclear saturation point and propagate theoretical uncertainties to derived quantities: the pressure and incompressibility of symmetric nuclear matter, the nuclear symmetry energy, and its derivative. Our results, which are validated by statistical diagnostics, demonstrate that an understanding of truncation-error correlations between different densities and different observables is crucial for reliable UQ. The methods developed here are publicly available as annotated Jupyter notebooks.
nucl-thastro-ph.HEhep-phnucl-exPRC(2020)·165 citations
04
$^{12}$ C(e,e'pN) Measurements of Short Range Correlations in the Tensor-to-Scalar Interaction Transition Region
I. Korover · J. R. Pybus · A. Schmidt · F. Hauenstein · M. Duer · O. Hen · E. Piasetzky · L.B. Weinstein · D.W. Higinbotham · the CLAS Collaboration
High-momentum configurations of nucleon pairs at short-distance are probed using measurements of the $^{12}$ C $(e, e^{'} p)$ and $^{12}$ C $(e, e^{'} pN)$ reactions (where $N$ is either $n$ or $p$ ), at high- $Q^{2}$ and $x_{B} > 1.1$ . The data span a missing-momentum range of 300--1000 MeV/c and are predominantly sensitive to the transition region of the strong nuclear interaction from a Tensor to Scalar interaction. The data are well reproduced by theoretical calculations using the Generalized Contact Formalism with both chiral and phenomenological nucleon-nucleon ( $N N$ ) interaction models. This agreement suggests that the measured high missing-momentum protons up to $1000$ MeV/c predominantly belong to short-ranged correlated (SRC) pairs. The measured $^{12}$ C $(e, e^{'} pN)$ / $^{12}$ C $(e, e^{'} p)$ and $^{12}$ C $(e, e^{'} pp)$ / $^{12}$ C $(e, e^{'} p n)$ cross-section ratios are consistent with a decrease in the fraction of proton-neutron SRC pairs and increase in the fraction of proton-proton SRC pairs with increasing missing momentum. This confirms the transition from an isospin-dependent tensor $N N$ interaction at $\sim 400$ MeV/c to an isospin-independent scalar interaction at high-momentum around $\sim 800$ MeV/c as predicted by theoretical calculation.
↳ nucl-exhep-phnucl-thPLB(2021)·48 citations
05
Neutrinoless Double Beta Decay from Lattice QCD: The Long-Distance $π^{-} \to π^{+} e^{-} e^{-}$ Amplitude
W. Detmold🇺🇸 · D.J. Murphy🇺🇸
Neutrinoless double beta decay ($ 0 \nu \beta \beta $) is a hypothetical nuclear decay mode with important implications. In particular, observation of this decay would demonstrate that the neutrino is a Majorana particle and that lepton number conservation is violated in nature. Relating experimental constraints on $0 \nu \beta \beta$ decay rates to the neutrino masses requires theoretical input in the form of non-perturbative nuclear matrix elements which remain difficult to calculate reliably. This work marks a first step toward providing a general lattice QCD framework for computing long-distance $0 \nu \beta \beta$ matrix elements in the case where the decay is mediated by a light Majorana neutrino. The relevant formalism is developed and then tested by computing the simplest such matrix element describing an unphysical $ \pi^{-} \rightarrow \pi^{+} e^{-} e^{-} $ transition on a series of domain wall fermion ensembles. The resulting lattice data is then fit to next-to-leading-order chiral perturbation theory, allowing a fully-controlled extraction of the low energy constant governing the transition rate, $g_{\nu}^{\pi \pi}(\mu = 770 \,\, \mathrm{MeV}) = -10.78(12)_{\rm stat}(51)_{\rm sys}$. Finally, future prospects for calculations of more complicated processes, such as the phenomenologically important $n^{0} n^{0} \rightarrow p^{+} p^{+} e^{-} e^{-}$ decay, are discussed.
↳ hep-lathep-phnucl-th40 citations
06
Roper-like resonances with various flavor contents and their two-pion emission decays
A. J. Arifi🇯🇵 · H. Nagahiro🇯🇵 · A. Hosaka🇯🇵 · K. Tanida🇯🇵
We study the three-body decay of the newly observed bottom baryon $Λ_{b}^{*} (6072)$ by LHCb; $Λ_{b}^{*} (6072) \to Λ_{b} π π$ . Its mass about 500 MeV above the ground state $Λ_{b}$ and a broad width imply that the state could be an analogue of the Roper resonance of the nucleon $N (1440)$ . In terms of sequential processes going through $Σ_{b}$ and $Σ_{b}^{*}$ , we find that the observed invariant mass distribution is reproduced assuming its spin and parity $J^{P} = 1/ 2^{+}$ . We discuss that the ratio of the two sequential processes and angular correlation of two pions are useful for the determination of spin and parity. We suggest further studies for the Roper resonance analogue in various flavor contents, raising an interesting and important question in baryon spectroscopy.
↳ hep-phnucl-thPRD(2020)·21 citations
07
The chiral magnetic effect and the chiral spin symmetry in QCD above Tc
L. Ya. Glozman🇦🇹
The chiral magnetic effect (CME) is an exact statement that connects via the axial anomaly the electric current in a system consisting of interacting fermions and gauge field with chirality imbalance that is put into a strong external magnetic field. Experimental search of the magnetically induced current in QCD in heavy ion collisions above a pseudocritical temperature hints, though not yet conclusive, that the induced current is either small or vanishing. This would imply that the chirality imbalance in QCD above $T_{c}$ that could be generated via topological fluctuations is at most very small. Here we present the most general reason for absence (smallness) of the chirality imbalance in QCD above Tc. It was recently found on the lattice that QCD above Tc is approximately chiral spin (CS) symmetric with the symmetry breaking at the level of a few percent. The CS transformations mix the right- and left-handed components of quarks. Then an exact CS symmetry would require absence of any chirality imbalance. Consequently an approximate CS symmetry admits at most a very small chirality imbalance in QCD above Tc. Hence the absence or smallness of an magnetically induced current observed in heavy ion collisions could be considered as experimental evidence for emergence of the CS symmetry above Tc.
↳ hep-phhep-lathep-thnucl-th1 citation
08
Inelasticity resulting from rapidity spectra analysis
Zbigniew Włodarczyk🇵🇱 · Maciej Rybczyński🇵🇱
In this work we study the pseudorapidity spectra o charged particles produced in proton+proton and proton+antiproton interactions in a wide energy range using the non-extensive Tsallis approach. We evaluate the inelasticity coefficients of the discussed reactions which remain approximately independent of the collision energy.
↳ hep-phnucl-thNew J.Phys.(2020)·1 citation
09
Direct Astrophysical Tests of Chiral Effective Field Theory at Supranuclear Densities
Reed Essick🇺🇸 · Ingo Tews🇺🇸 · Philippe Landry🇺🇸 · Sanjay Reddy🇺🇸 · Daniel E. Holz🇺🇸
Recent observations of neutron stars with gravitational waves and X-ray timing provide unprecedented access to the equation of state (EoS) of cold dense matter at densities difficult to realize in terrestrial experiments. At the same time, predictions for the EoS with reliable uncertainty estimates from chiral effective field theory ( $χ$ EFT) bound our theoretical ignorance. In this work, we analyze astrophysical data using a nonparametric representation of the neutron-star EoS conditioned on $χ$ EFT to directly constrain the underlying physical properties of the compact objects. We discuss how the data alone constrain the EoS at high densities when we condition on $χ$ EFT at low densities. We also demonstrate how to exploit astrophysical data to directly test the predictions of $χ$ EFT for the EoS up to twice nuclear saturation density, and estimate the density at which these predictions might break down. We find that the existence of massive pulsars, gravitational waves from GW170817, and NICER observations of PSR J0030+0451 favor $χ$ EFT predictions for the EoS up to nuclear saturation density over a more agnostic analysis by as much as a factor of 7 for the quantum Monte Carlo (QMC) calculations used in this work. While $χ$ EFT predictions using QMC are fully consistent with gravitational-wave data up to twice nuclear saturation density, NICER observations suggest that the EoS stiffens relative to these predictions at nuclear saturation density. Additionally, we marginalize over the uncertainty in the density at which $χ$ EFT begins to break down, constraining the radius of a $1.4 M_{⊙}$ neutron star to $R_{1.4} = 11.4 0_{- 1.04}^{+ 1.38}$ ( $12.5 4_{- 0.63}^{+ 0.71}$ ) km and the pressure at twice nuclear saturation density to $p (2 n_{sat}) = 14. 2_{- 8.4}^{+ 18.1}$ ( $28. 7_{- 15.0}^{+ 15.3}$ ) MeV/fm $^{3}$ with massive pulsar and gravitational-wave (and NICER) data.
↳ astro-ph.HEnucl-thPRC(2020)·154 citations
10
QZE and IZE in a simple approach and the neutron decay
Francesco Giacosa🇵🇱
We discuss a simple and analytically solvable measurement model which describes the famous Quantum Zeno Effect (QZE) and Inverse Zeno Effect (IZE), that correspond to the slow down and to the increase of the decay rate caused by measurements (or, more in general, by the interaction of an unstable state with the detector and the environment). Within this model one can understand quite general features of the QZE and IZE: by considering an unstable quantum state, such as an unstable particle, whose decay width as function of energy is $Γ (ω) = g^{2} ω^{α},$ then -- under quite general assumptions -- the QZE occurs for $α \in (0, 1)$ , while the IZE for $α \in (- \infty, 0) \cup (1, \infty) .$ This result is valid also for more realistic measurement models than the one described in this work. We then apply these considerations to the decay of the neutron, for which $α = 5.$ Hence, the realization of the IZE for the neutron decay (and for the majority of weak decays) is in principle possible. Indeed, trap experiments find a lifetime that is $8.7 \pm 2.1$ s shorter than beam experiments, suggesting that the IZE could have taken place.
↳ hep-phnucl-thquant-phActa Phys.Polon.B(2020)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE