Nuclear Theory·nucl-th

Monday·October 11, 2021

11 papers—3 primary·8 cross-listed

01
Evidence of a higher nodal band $α$ + $^{44}$ Ca cluster state in fusion reactions and $α$ clustering in $^{48}$ Ti
S. Ohkubo
In the nucleus $^{48}$ Ti, whose structure is essential in evaluating the half-life of the neutrinoless double- $β$ decay ( $0 ν β β$ ) of $^{48}$ Ca, the existence of the $α$ cluster structure is shown for the first time. A unified description of scattering and structure is performed for the $α$ + $^{44}$ Ca system. By using a global potential, which reproduces experimental $α$ + $^{44}$ Ca scattering over a wide range of incident energies, $E_{α}$ =18 - 100 MeV, it is shown that the observed $α$ + $^{44}$ Ca fusion excitation function at $E_{α}$ =9 -18 MeV is described well. The bump at $E_{α}$ =10.2 MeV is found to be due to a resonance which is a $7^{-}$ state of the higher nodal band with the $α$ + $^{44}$ Ca cluster structure in $^{48}$ Ti. The local potential $α$ + $^{44}$ Ca cluster model locates the ground band of $^{48}$ Ti in agreement with experiment and reproduces the enhanced $B (E 2)$ values in the ground band well. This shows that collectivity due to $α$ clustering in $^{48}$ Ti should be taken into account in the evaluation of the nuclear matrix element in the $0 ν β β$ double- $β$ decay of $^{48}$ Ca.
nucl-thnucl-exPRC(2021)·1 citation
02
Bayesian parameter estimation in $χ$ EFT using Hamiltonian Monte Carlo
Isak Svensson🇸🇪 · Andreas Ekström🇸🇪 · Christian Forssén🇸🇪
The number of low-energy constants (LECs) in chiral effective field theory ( $χ$ EFT) grows rapidly with increasing chiral order, necessitating the use of Markov chain Monte Carlo techniques for sampling their posterior probability density function. For this we introduce a Hamiltonian Monte Carlo (HMC) algorithm and sample the LEC posterior up to next-to-next-to-leading order (NNLO) in the two-nucleon sector of $χ$ EFT. We find that the sampling efficiency of HMC is three to six times higher compared to an affine-invariant sampling algorithm. We analyze the empirical coverage probability and validate that the NNLO model yields predictions for two-nucleon scattering data with largely reliable credible intervals, provided that one ignores the leading order EFT expansion parameter when inferring the variance of the truncation error. We also find that the NNLO truncation error dominates the error budget.
nucl-thPRC(2022)·24 citations
03
Fast emulation of quantum three-body scattering
Xilin Zhang🇺🇸 · R.J. Furnstahl🇺🇸
We develop a class of emulators for solving quantum three-body scattering problems. They are based on combining the variational method for scattering observables and the recently proposed eigenvector continuation concept. The emulators are first trained by the exact scattering solutions of the governing Hamiltonian at a small number of points in its parameter space, and then employed to make interpolations and extrapolations in that space. Through a schematic nuclear-physics model with finite-range two and three-body interactions, we demonstrate the emulators to be extremely accurate and efficient. The computing time for emulation is on the scale of milliseconds (on a laptop), with relative errors ranging from $1 0^{- 13}$ to $1 0^{- 4}$ depending on the case. The emulators also require little memory. We argue that these emulators can be generalized to even more challenging scattering problems. Furthermore, this general strategy may be applicable for building the same type of emulators in other fields, wherever variational methods can be developed for evaluating physical models.
nucl-thhep-latphysics.atom-phphysics.comp-ph+1PRC(2022)·45 citations
04
Coulomb and nuclear excitations of $^{70}$ Zn and $^{68}$ Ni at intermediate energy
S. Calinescu🇷🇴 · O. Sorlin (GANIL)🇫🇷 · I. Matea🇫🇷 · F. Carstoiu🇷🇴 · D. Dao🇫🇷 · F. Nowacki🇫🇷 · G. de Angelis🇮🇹 · R. Astabatyan🇷🇺 · S. Bagchi🇳🇱 · C. Borcea🇷🇴 · R. Borcea🇷🇴 · L. Cáceres🇫🇷 and 39 other authors
The reduced transition probabilities $B (E 2; 0_{g . s .}^{+} \to 2_{1}^{+}, 2_{2}^{+})$ in $^{70}$ Zn and the full $B (E 2; 0_{g . s .}^{+} \to 2^{+})$ strength up to S $_{n}$ =7.79 MeV in $^{68}$ Ni have been determined at the LISE/GANIL facility using the Coulomb-excitation technique at intermediate beam energy on a $^{208}$ Pb target. The $γ$ rays emitted in-flight were detected with an array of 46 BaF $_{2}$ crystals. The angles of the deflected nuclei were determined in order to disentangle and extract the Coulomb and nuclear contributions to the excitation of the 2 $^{+}$ states. The measured $B (E 2; 0_{g . s .}^{+} \to 2_{1}^{+})$ of 1432(124) e $^{2}$ fm $^{4}$ for $^{70}$ Zn falls in the lower part of the published values which clustered either around 1600 or above 2000 e $^{2}$ fm $^{4}$ , while the $B (E 2; 0_{g . s .}^{+} \to 2_{2}^{+})$ of 53(7) e $^{2}$ fm $^{4}$ agrees very well with the two published values. The relatively low $B (E 2; 0_{g . s .}^{+} \to 2_{1}^{+})$ of 301(38) e $^{2}$ fm $^{4}$ for $^{68}$ Ni agrees with previous studies and confirms a local magicity at $Z = 28, N = 40$ . Combining the results of the low-energy spectra of $^{68}$ Ni and $^{70}$ Zn and their shell-model interpretations, it is interesting to notice that four different shapes (spherical, oblate, prolate and triaxial) are present. Finally, a summed $E 2$ strength of only about 150 e $^{2}$ fm $^{4}$ has been found experimentally at high excitation energy, likely due to proton excitations across the $Z = 28$ gap. The experimental distribution of this high-energy $E 2$ excitation agrees with SM calculations, but its strength is about two times weaker.
↳ nucl-exnucl-thPRC(2021)·5 citations
05
Study of the jet transport coefficient at the Large Hadron Collider energies using Color String Percolation Model
Dushmanta Sahu🇮🇳 · Aditya Nath Mishra🇭🇺 · Raghunath Sahoo🇮🇳
In order to have a better understanding of the matter formed in ultra-relativistic collisions, we estimate the jet transport coefficient, $q^$ , within the Color Sting Percolation Model (CSPM) for various multiplicity classes in proton-proton collisions and centrality classes in nucleus-nucleus collisions at the Large Hadron Collider energies. We study $q^$ as a function of final state charged-particle multiplicity and initial percolation temperature. Finally, we compare our obtained results with those calculated from the JET collaboration.
↳ hep-phhep-exnucl-exnucl-thPoS(2021)·1 citation
06
Extension of Glauber-like model for Proton-Proton collisions using anisotropic and inhomogeneous density profile
Suman Deb🇮🇳 · Golam Sarwar🇮🇳 · Dhananjaya Thakur🇮🇳 · Pavish S.🇩🇪 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳
Results from proton-proton ( $pp$ ) collisions have routinely been used as a baseline to analyze and understand the production of QCD matter expected to be produced in nuclear collisions. But recent studies of small systems formed in $pp$ collisions at the LHC energies hint at the possibility of producing medium with collective behavior. Therefore, results from $pp$ collisions required more careful investigation to understand whether QCD matter is produced in high multiplicity $pp$ collisions. With this motivation, the Glauber model traditionally used to study the heavy-ion collision dynamics at high energy is applied here to understand the dynamics of $pp$ collisions. We have used anisotropic and inhomogeneous quark/gluon-based proton density profile, a realistic picture obtained from deep inelastic scattering results and this model explains the charged particle multiplicity distribution of $pp$ collisions at LHC energies very well. Collision geometric properties like impact parameter and mean number of binary collisions ( $⟨ N_{co l l} ⟩$ ), mean number of participants ( $⟨ N_{p a r t} ⟩$ ) at different multiplicities are determined for $pp$ collisions. We further used these collision geometric properties to estimate average charged-particle pseudorapidity density ( $⟨ d N_{c h} / d η ⟩$ ) and found it to be comparable with the experimental results. Knowing $⟨ N_{co l l} ⟩$ , we have obtained nuclear modification-like factor ( $R_{pp}$ ) in $pp$ collisions which has not been done before to the best of our knowledge.
↳ hep-phhep-exnucl-exnucl-thPoS(2021)·1 citation
07
Analysis of OPAL Bose-Einstein Correlation at $Z^{0}$ -pole by the second conventional formula
Takuya Mizoguchi🇯🇵 · Seiji Matsumoto🇯🇵 · Minoru Biyajima🇯🇵
We can obtain a second conventional formula ( $C F_{II}$ ) with two components by extending the conventional formula $C F_{I}$ with one component for Bose-Einstein Correlation (BEC). We used $C F_{II}$ to analyze the BEC at $Z^{0}$ -pole as part of the OPAL collaboration. $R_{1} (G) = 0.91 \pm 0.03$ fm ( $λ_{1} = 0.61 \pm 0.03$ ) and $R_{2} (G) = 2.57 \pm 0.44$ fm ( $λ_{1} = 0.35 \pm 0.09$ ) are the estimated interaction region, where $λ_{1}$ and $λ_{2}$ are the degrees of coherence, and G is the Gaussian distribution, respectively. Long range correlation (LRC) is also studied.
↳ hep-phhep-exnucl-thInt.J.Mod.Phys.A(2022)·2 citations
08
Predictions on global properties in O+O collisions at the Large Hadron Collider using a multi-phase transport model
Debadatta Behera🇮🇳 · Neelkamal Mallick🇮🇳 · Sushanta Tripathy🇮🇹 · Suraj Prasad🇮🇳 · Aditya Nath Mishra🇭🇺 · Raghunath Sahoo🇮🇳
Oxygen ( $^{16}$ O) ions are planned to be injected at the Large Hadron Collider (LHC) in its next runs, and a day of physics run is anticipated for O+O collisions at $s_{NN}$ = 7 TeV. As the system size of O+O collisions has the final state multiplicity overlap with those produced in pp, p+Pb and Pb+Pb collisions, the study of global properties in O+O collisions may provide a deeper insight into the heavy-ion-like behavior observed in small collision systems and its similarities/differences with a larger system like Pb+Pb collisions. In the present work, we report the predictions for global properties in O+O collisions at $s_{NN}$ = 7 TeV using a multi-phase transport model (AMPT). We report the mid-rapidity charged-particle multiplicity, transverse mass, Bjorken energy density, pseudo-rapidity distributions, squared speed of sound, transverse momentum ( $p_{T}$ ) spectra, the kinetic freeze-out parameters, and $p_{T}$ -differential particle ratio as a function of collision centrality. Further, we have studied the transverse momentum-dependent elliptic flow of charged particles. The results are shown for Woods-Saxon and harmonic oscillator nuclear density profiles. In addition, we have compared the results with an $α$ -clustered structure incorporated inside the oxygen nucleus. Average charged-particle multiplicity and the Bjorken energy density show a significant increase in most central collisions for the harmonic oscillator density profile, while other global properties show less dependence on the density profiles considered in this work. The results from the $α$ -clustered structure incorporated inside the oxygen nucleus show similar initial energy density and final charged-particle multiplicity as observed for the harmonic oscillator density profile.
↳ hep-phhep-exnucl-exnucl-thEPJA(2022)·46 citations
09
Implementation of machine learning techniques to predict impact parameter and transverse spherocity in heavy-ion collisions at the LHC
Aditya Nath Mishra🇭🇺 · Neelkamal Mallick🇮🇳 · Sushanta Tripathy🇮🇹 · Suman Deb🇮🇳 · Raghunath Sahoo🇮🇳
Machine learning techniques have been quite popular recently in the high-energy physics community and have led to numerous developments in this field. In heavy-ion collisions, one of the crucial observables, the impact parameter, plays an important role in the final-state particle production. This being extremely small (i.e. of the order of a few fermi), it is almost impossible to measure impact parameter in experiments. In this work, we implement the ML-based regression technique via Gradient Boosting Decision Trees (GBDT) to obtain a prediction of impact parameter in Pb-Pb collisions at $s_{N N}$ = 5.02 TeV using A Multi-Phase Transport (AMPT) model. After its successful implementation in small collision systems, transverse spherocity, an event shape observable, holds an opportunity to reveal more about the particle production in heavy-ion collisions as well. In the absence of any experimental exploration in this direction at the LHC yet, we suggest an ML-based regression method to estimate centrality-wise transverse spherocity distributions in Pb-Pb collisions at $s_{N N}$ = 5.02 TeV by training the model with minimum bias collision data. Throughout this work, we have used a few final state observables as the input to the ML-model, which could be easily made available from collision data. Our method seems to work quite well as we see a good agreement between the simulated true values and the predicted values from the ML-model.
↳ hep-phhep-exnucl-exnucl-thPoS(2021)·0 citations
10
Transverse spherocity dependence of azimuthal anisotropy in heavy-ion collisions at the LHC using a multi-phase transport model
Neelkamal Mallick🇮🇳 · Raghunath Sahoo🇮🇳 · Sushanta Tripathy🇮🇹 · Antonio Ortiz🇲🇽
One of the event shape observables, the transverse spherocity ( $S_{0}$ ), has been studied successfully in small collision systems such as proton-proton collisions at the LHC as a tool to separate jetty and isotropic events. It has a unique capability to distinguish events based on their geometrical shapes. In this work, we report the first implementation of transverse spherocity in heavy-ion collisions using a multi-phase transport model (AMPT). We have performed an extensive study of azimuthal anisotropy of charged particles produced in heavy-ion collisions as a function of transverse spherocity ( $S_{0}$ ). We have followed the two-particle correlation (2PC) method to estimate the elliptic flow ( $v_{2}$ ) in different centrality classes in Pb-Pb collisions at $s_{NN}$ = 5.02 TeV for high- $S_{0}$ , $S_{0}$ -integrated and low- $S_{0}$ events. We found that transverse spherocity successfully differentiates heavy-ion collisions event topology based on their geometrical shapes, i.e., high and low values of spherocity. The high- $S_{0}$ events have nearly zero elliptic flow, while the low- $S_{0}$ events contribute significantly to the elliptic flow of spherocity-integrated events.
↳ hep-phhep-exnucl-exnucl-thPoS(2021)·1 citation
11
Testing the impact of electromagnetic fields on the directed flow of constituent quarks in heavy-ion collisions
Ashik Ikbal Sheikh🇺🇸 · Declan Keane🇺🇸 · Prithwish Tribedy🇺🇸
It has been proposed that strong electromagnetic fields produced in the early stages of heavy-ion collisions can lead to splitting of the rapidity-odd directed flow of positive and negative hadrons. For light hadrons, the interpretation of such measurements is complicated by the low magnitude of directed flow as well as by ambiguities arising from transported quarks. To overcome these complications, we propose measurements using only hadrons carrying produced quarks ( $u ˉ, d ˉ, s, s ˉ$ ). We discuss how to identify the kinematics where such hadrons are produced via the coalescence mechanism and therefore their flow is the sum of the flow of their constituent quarks. With this sum rule verified for certain combinations of hadrons, the expected systematic violation of this rule with increasing electric charge can be measured, which could be a consequence of the electromagnetic fields produced in the collisions. Our approach can be tested with the high statistics data from Phase II of the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC).
↳ nucl-exhep-phnucl-thPRC(2022)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE