Tue·Oct 6, 2020Tuesday·October 6, 2020

1. 01*

   Fine Structure of the Isovector Giant Dipole Resonance in ${}^{142-150}$Nd and ${}^{152}$Sm

   L. M. Donaldson🇿🇦 · J. Carter🇿🇦 · P. von Neumann-Cosel🇩🇪 · V. O. Nesterenko🇷🇺 · R. Neveling · P. -G. Reinhard🇩🇪 · I. T. Usman🇿🇦 · P. Adsley🇿🇦 · C. A. Bertulani🇺🇸 · J. W. Brümmer🇿🇦 · E. Z. Buthelezi · G. R. J. Cooper and 26 other authors

   Background: Inelastic proton scattering at energies of a few hundred MeV and very-forward angles including $0^{\circ }$ has been established as a tool to study electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Purpose: Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the IsoVector Giant Dipole Resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at iThemba LABS in Cape Town, South Africa. The scattering products were momentum-analysed by the K600 magnetic spectrometer positioned at ${\theta }_{\mathrm{Lab}}=0^{\circ }$. Using dispersion-matching techniques, energy resolutions of $\Delta E\approx 40-50$ keV were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photo-absorption cross sections using the equivalent virtual-photon method. Results: Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Comparisons with the Quasiparticle-Phonon Model (QPM) and Skyrme Separable Random Phase Approximation (SSRPA) predictions provide insight into the role of different giant resonance damping mechanisms. Conclusions: Fine structure is observed even for the most deformed nuclei studied. Fragmentation of the one particle-one hole ($1p1h$) strength seems to be the main source of fine structure in both spherical and deformed nuclei. Some impact of the spreading due to coupling of the two particle-two hole ($2p2h$) states to the $1p1h$ doorway states is seen in the spherical/transitional nuclei, where calculations beyond the $1p1h$ level are available.

   nucl-exPRC(2020)·16 citations
2. 02*

   Energy dependence of light neutral meson $p_{\mathrm{T}}$ spectrum produced in pp collisions at the LHC measured in ALICE

   Pooja Pareek (for the ALICE Collaboration)🇮🇳

   We present the measurement of light neutral mesons, ${\pi }^0$ and $\eta$, in pp collisions at different center-of-mass energies obtained with the ALICE experiment at the LHC. The ${\pi }^0$ and $\eta$ mesons are measured via photons reconstructed by the electromagnetic calorimeters and the central tracking system. The invariant cross-section of ${\pi }^0$ and $\eta$ mesons are measured in a broad $p_{\mathrm{T}}$ range at $\sqrt{s}=0.9,2.76,7,5.02$ and 8 TeV. The spectra of ${\pi }^0$ and $\eta$ mesons measured in pp collisions at different collision energies show $x_{\mathrm{T}}$-scaling at high $p_{\mathrm{T}}$ and violation of $m_{\mathrm{T}}$-scaling at low $p_{\mathrm{T}}$. The smaller $x_{\mathrm{T}}$-scaling exponents of our measurements compared to RHIC may hint at a reduced importance of higher twist processes at LHC.

   nucl-exhep-exPoS(2021)·0 citations
3. 03*

   Negative heat capacity for hot nuclei using formulation from the microcanonical ensemble INDRA Collaboration

   B. Borderie · S. Piantelli · E. Bonnet · R. Bougault · A. Chbihi · J.E. Ducret · J.D. Frankland · E. Galichet · D. Gruyer · M. Henri · M. La Commara · N. Le Neindre and 6 other authors

   By using freeze-out properties of multifragmenting hot nuclei produced in quasifusion central ${}^{129}$Xe+${}^{nat}$Sn collisions at different beam energies (32, 39, 45 and 50 AMeV) which were estimated by means of a simulation based on experimental data collected by the $4\pi$ INDRA multidetector, heat capacity in the thermal excitation energy range 4 - 12.5 AMeV was calculated from total kinetic energies and multiplicities at freeze-out. The microcanonical formulation was employed. Negative heat capacity which signs a first order phase transition for finite systems is observed and confirms previous results using a different method.

   nucl-excond-mat.stat-mechnucl-thEPJA(2020)·3 citations
4. 04*

   Patchy nuclear chain reactions

   Eric Dumonteil🇫🇷 · Rian Bahran🇺🇸 · Theresa Cutler🇺🇸 · Benjamin Dechenaux🇫🇷 · Travis Grove🇺🇸 · Jesson Hutchinson🇺🇸 · George McKenzie🇺🇸 · Alexander McSpaden🇺🇸 · Wilfried Monange🇫🇷 · Mark Nelson🇺🇸 · Nicholas Thompson🇺🇸 · Andrea Zoia🇫🇷

   Stochastic fluctuations of the neutron population within a nuclear reactor are typically prevented by operating the core at a sufficient power, since a deterministic behavior of the neutron population is required by automatic safety systems to detect unwanted power excursions. Recent works however pointed out that, under specific circumstances, non-Poissonian patterns could affect neutron spatial distributions. This motivated an international program to experimentally detect and characterize such fluctuations and correlations, which took place in 2017 at the Rensselaer Polytechnic Institute Reactor Critical Facility. The main findings of this program will indeed unveil patchiness in snapshots of neutron spatial distributions -- obtained with a dedicated numerical twin of the reactor -- that support this first experimental characterization of the 'neutron clustering' phenomenon, while a stochastic model based on reaction-diffusion processes and branching random walks will reveal the key role played by the reactor intrinsic sources in understanding neutron spatial correlations.

   ↳ physics.ins-detnucl-exnucl-th0 citations
5. 05*

   Lepton angular distribution of $W$ boson productions

   Yang Lyu🇺🇸 · Wen-Chen Chang🇹🇼 · Randall Evan McClellan🇺🇸 · Jen-Chieh Peng🇺🇸 · Oleg Teryaev🇷🇺

   The lepton angular distribution coefficients $A_i$ for $Z$ boson production in $pp$ and $\bar{p}p$ collisions have been measured at the LHC and the Tevatron. A recent study showed that many features of the measured angular distribution coefficients, including the transverse momentum ($q_T$) and rapidity dependencies and the violation of the Lam-Tung relation, can be well described using an intuitive geometric approach. In this paper, we extend this geometric approach to describe the angular distribution coefficients for $W$ boson produced in $\bar{p}p$ collisions at the Tevatron. We first compare the data with a perturbative QCD calculation at $\mathcal{O}({\alpha }_s^2)$. We then show that the data and QCD calculations can be well described with the geometric approach. Implications for future studies at the LHC energy are also discussed.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2021)·5 citations
6. 06*

   Measurements of ${\pi }^{\pm }$, $K^{\pm }$, $p$ and $\bar{p}$ spectra in ${}^7$Be+${}^9$Be collisions at beam momenta from 19$A$ to 150$A$ GeV/$c$ with the NA61/SHINE spectrometer at the CERN SPS

   NA61/SHINE Collaboration: A.Acharya🇵🇱 · H.Adhikary🇵🇱 · A.Aduszkiewicz🇵🇱 · K.K.Allison🇺🇸 · E.V.Andronov🇷🇺 · T.Antićić🇭🇷 · V.Babkin🇷🇺 · M.Baszczyk🇵🇱 · S.Bhosale🇵🇱 · A.Blondel🇫🇷 · M.Bogomilov🇧🇬 · A.Brandin🇷🇺 and 130 other authors

   The NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) studies the onset of deconfinement in hadron matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of ${\pi }^{\pm }$, $K^{\pm }$, $p$ and $\bar{p}$ produced in the 20$\%$ most $central$ ${}^7$Be+${}^9$Be collisions at beam momenta of 19$A$, 30$A$, 40$A$, 75$A$ and 150$A$ GeV/$c$. The energy dependence of the $K^{\pm }$/${\pi }^{\pm }$ ratios as well as of inverse slope parameters of the $K^{\pm }$ transverse mass distributions are close to those found in inelastic $p$+$p$ reactions. The new results are compared to the world data on $p$+$p$ and Pb+Pb collisions as well as to predictions of the EPOS, UrQMD, AMPT, PHSD and SMASH models.

   ↳ hep-exnucl-exEPJC(2021)·35 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.