Tue·Jun 30, 2020Tuesday·June 30, 2020

1. 01*

   Strong QCD Insights from Excited Nucleon Structure Studies with CLAS and CLAS12

   D.S. Carman🇺🇸 · K. Joo🇺🇸 · V.I. Mokeev🇺🇸

   Studies of the spectrum of hadrons and their structure in experiments with electromagnetic probes offer unique insight into many facets of the strong interaction in the regime of large quark-gluon running coupling, {\it i.e.} the regime of strong QCD. The experimental program within Hall~B at Jefferson Laboratory based on data acquired with the CLAS spectrometer using electron and photon beams with energies up to 6~GeV has already considerably extended the scope of research in hadron physics in joint efforts between experiment and phenomenological data analysis. Impressive progress in relating the hadron structure observables inferred from the data to the strong QCD mechanisms underlying hadron mass generation has been achieved in the past decade. These results will be considerably extended with data from the experimental program with the new CLAS12 spectrometer that has begun data taking using electron beams with energies up to 11~GeV. With this extended kinematic reach the structure of nucleon resonances will be probed at the highest photon virtualities ever achieved in the studies of exclusive electroproduction, which will allow for the exploration of the distance scale where $>$98\% of light hadron mass emerges from QCD in the transition of the strong interaction from the regime of quark-gluon confinement to perturbative QCD.

   nucl-exhep-phFew Body Syst.(2020)·49 citations
2. 02*

   Initial fluctuations and power spectrum of flow anisotropies in relativistic heavy-ion collisions

   Shreyansh S. Dave🇮🇳 · Saumia P.S.🇷🇺 · Ajit M. Srivastava🇮🇳

   Flow has emerged as a crucial probe for the properties of the thermalized medium produced in relativistic heavy-ion collisions. The evolution of initial state fluctuations leaves imprints on the power spectrum of flow coefficients. Therefore flow coefficients are a crucial probe of initial state fluctuations arising from the parton distributions of the colliding nuclei. This has a very strong correspondence with the physics of power spectrum of cosmic microwave background radiation (CMBR) anisotropies which directly probes initial inflationary fluctuations. Much work has been done to probe these interesting interconnections, in particular, in developing techniques for the measurements of higher flow coefficients. We present a short review of these developments. The effect of initial magnetic field on these features will also be reviewed. All this acquires special importance in view of upcoming electron-ion collider which will directly probe initial parton distribution of the colliding nucleus.

   ↳ nucl-thhep-phnucl-exEur.Phys.J.ST(2021)·2 citations
3. 03*

   Excitation Functions of Tsallis-like Parameters in High-Energy Nucleus-Nucleus Collisions

   Li-Li Li🇨🇳 · Fu-Hu Liu🇨🇳 · Khusniddin K. Olimov🇺🇿

   The transverse momentum spectra of charged pions, kaons, and protons produced at mid-rapidity in central nucleus-nucleus (AA) collisions at high energies are analyzed by considering particles to be created from two participant partons which are assumed to be contributors from the collision system. Each participant (contributor) parton is assumed to contribute to the transverse momentum by a Tsallis-like function. The contributions of the two participant partons are regarded as the two components of transverse momentum of the identified particle. The experimental data measured in high-energy AA collisions by international collaborations are studied. The excitation functions of kinetic freeze-out temperature and transverse flow velocity are extracted. The two parameters increase quickly from $\approx 3$ to $\approx 10$ GeV (exactly from 2.7 to 7.7 GeV) and then slowly at above 10 GeV with the increase of collision energy. In particular, there is a plateau from near 10 GeV to 200 GeV in the excitation function of kinetic freeze-out temperature.

   ↳ hep-phhep-exnucl-exnucl-thEntropy(2021)·31 citations
4. 04*

   Precision determination of pion-nucleon coupling constants using effective field theory

   P. Reinert🇩🇪 · H. Krebs🇩🇪 · E. Epelbaum🇩🇪

   The pion-nucleon coupling constants determine the strength of the long-range nuclear forces and play a fundamental part in our understanding of nuclear physics. While the charged- and neutral-pion couplings to protons and neutrons are expected to be very similar, owing to the approximate isospin symmetry of the strong interaction, the different masses of the up- and down-quarks and electromagnetic effects may result in their slightly different values. Despite previous attempts to extract these coupling constants from different systems, our knowledge of their values is still deficient. In this Letter we present a precision determination of these fundamental observables with fully controlled uncertainties from neutron-proton and proton-proton scattering data using chiral effective field theory. To achieve this goal, we use a novel methodology based on the Bayesian approach and perform, for the first time, a full-fledged partial-wave analysis of nucleon-nucleon scattering up to the pion production threshold in the framework of chiral effective field theory, including a complete treatment of isospin-breaking effects and our own determination of mutually consistent data. The resulting values of the pion-nucleon coupling constants are accurate at the percent level and show no significant charge dependence. These results mark an important step towards developing a precision theory of nuclear forces and structure.

   ↳ nucl-thhep-lathep-phnucl-exPRL(2021)·67 citations
5. 05*

   Theoretical study of the $\Omega (2012)$ state in the ${\Omega }_c^0\to {\pi }^{+}\Omega (2012{)}^{-}\to {\pi }^{+}(\bar{K}\Xi {)}^{-}$ and ${\pi }^{+}(\bar{K}\Xi \pi {)}^{-}$ decays

   Chun-Hua Zeng🇨🇳 · Jun-Xu Lu🇨🇳 · En Wang🇨🇳 · Ju-Jun Xie🇨🇳 · Li-Sheng Geng🇨🇳

   We report on a theoretical study of the newly observed $\Omega (2012)$ resonance in the nonleptonic weak decays of ${\Omega }_c^0\to {\pi }^{+}\bar{K}{\Xi }^{\ast }(1530)(\eta \Omega )\to {\pi }^{+}(\bar{K}\Xi {)}^{-}$ and ${\pi }^{+}(\bar{K}\Xi \pi {)}^{-}$ via final-state interactions of the $\bar{K}{\Xi }^{\ast }(1530)$ and $\eta \Omega$ pairs. The weak interaction part is assumed to be dominated by the charm quark decay process: $c(ss)\to (s+u+\bar{d})(ss)$, while the hadronization part takes place between the $sss$ cluster from the weak decay and a quark-antiquark pair with the quantum numbers $J^{PC}=0^{++}$ of the vacuum, produces a pair of $\bar{K}{\Xi }^{\ast }(1530)$ and $\eta \Omega$. Accordingly, the final $\bar{K}{\Xi }^{\ast }(1530)$ and $\eta \Omega$ states are in pure isospin $I=0$ combinations, and the ${\Omega }_c^0\to {\pi }^{+}\bar{K}{\Xi }^{\ast }(1530)(\eta \Omega )\to {\pi }^{+}(\bar{K}\Xi {)}^{-}$ decay is an ideal process to study the $\Omega (2012)$ resonance. With the final-state interaction described in the chiral unitary approach, up to an arbitrary normalization, the invariant mass distributions of the final state are calculated, assuming that the $\Omega (2012)$ resonance with spin-parity $J^P=3/2^{-}$ is a dynamically generated state from the coupled channels interactions of the $\bar{K}{\Xi }^{\ast }(1530)$ and $\eta \Omega$ in $s$-wave and $\bar{K}\Xi$ in $d$-wave. We also calculate the ratio, $R_{\bar{K}\Xi }^{\bar{K}\Xi \pi }=\mathrm{Br}[{\Omega }_c^0\to {\pi }^{+}\Omega (2012{)}^{-}\to {\pi }^{+}(\bar{K}\Xi \pi {)}^{-}]/\mathrm{Br}[{\Omega }_c^0\to {\pi }^{+}\Omega (2012{)}^{-}\to {\pi }^{+}(\bar{K}\Xi {)}^{-}$]. The proposed mechanism can provide valuable information on the nature of the $\Omega (2012)$ and can in principle be tested by future experiments.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2020)·36 citations
6. 06*

   Medium effects on ${\Xi }^{-}$ production in the nuclear ($K^{-}$, $K^{+}$) reaction

   Toru Harada🇯🇵 · Yoshiharu Hirabayashi🇯🇵

   We study theoretically medium effects on ${\Xi }^{-}$ production in the ($K^{-}$, $K^{+}$) reaction, using the optimal Fermi-averaging procedure which describes the Fermi motion of a nucleon on the on-energy-shell $K^{-}p\to K^{+}{\Xi }^{-}$ reaction condition in nuclei. The result shows the strong energy and angular dependence of the in-medium $K^{-}p\to K^{+}{\Xi }^{-}$ cross section,which affects significantly the shape and magnitude of the production spectrum for ${\Xi }^{-}$ hypernuclear states in the ($K^{-}$, $K^{+}$) reaction on a nuclear target.The application to the ${\Xi }^{-}$ quasi-free production via the ($K^{-}$, $K^{+}$) reaction on a ${}^{12}$C target is also discussed in a Fermi gas model.

   ↳ nucl-thhep-thnucl-exPRC(2020)·4 citations
7. 07*

   Observable signatures of initial state momentum anisotropies in nuclear collisions

   Giuliano Giacalone🇫🇷 · Bjoern Schenke🇺🇸 · Chun Shen🇺🇸

   We show that the correlation between the elliptic momentum anisotropy, $v_2$, and the average transverse momentum, $[p_T]$, at fixed multiplicity in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+\textsc{Music}+UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the Color Glass Condensate, predicts a characteristic sign change of the correlator $\hat{\rho }(v_2^2,[p_T])$ as a function of charged particle multiplicity in p+Au and d+Au collisions at $\sqrt{s}=200\mathrm{GeV}$, and p+Pb collisions at $\sqrt{s}=5.02\mathrm{TeV}$. This sign change is absent in calculations without initial state momentum anisotropies. The model further predicts a qualitative difference between the centrality dependence of $\hat{\rho }(v_2^2,[p_T])$ in Au+Au collisions at $\sqrt{s}=200\mathrm{GeV}$ and Pb+Pb collisions at $\sqrt{s}=5.02\mathrm{TeV}$, with only the latter showing a sign change in peripheral events. Predictions for O+O collisions at different collision energy show a similar behavior. Experimental observation of these distinct qualitative features of $\hat{\rho }(v_2^2,[p_T])$ in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the Color Glass Condensate effective theory.

   ↳ nucl-thhep-phnucl-exPRL(2020)·71 citations
8. 08*

   Telling Solar Neutrinos from Solar Axions When You Can't Shut Off the Sun

   Pilar Coloma🇪🇸 · Patrick Huber🇺🇸 · Jonathan M. Link🇺🇸

   The XENON1T experiment recently reported an excess of events at low electron recoil energies, which may be due to interactions of solar neutrinos inside the detector via a large neutrino magnetic moment. We point out that a ${}^{51}$Cr neutrino source placed close to the detector can directly test this hypothesis.

   ↳ hep-phhep-exnucl-ex19 citations
9. 09*

   Pileup corrections on higher-order cumulants

   Toshihiro Nonaka🇯🇵 · Masakiyo Kitazawa🇯🇵 · ShinIchi Esumi🇯🇵

   We propose a method to remove the contributions of pileup events from higher-order cumulants and moments of event-by-event particle distributions. Assuming that the pileup events are given by the superposition of two independent single-collision events, we show that the true moments in each multiplicity bin can be obtained recursively from lower multiplicity events. In the correction procedure the necessary information are only the probabilities of pileup events. Other terms are extracted from the experimental data. We demonstrate that the true cumulants can be reconstructed successfully by this method in simple models. Systematics on trigger inefficiencies and correction parameters are discussed.

   ↳ physics.data-anhep-phnucl-exnucl-thNucl.Instrum.Meth.A(2020)·18 citations
10. 10*

    Insights on pion production mechanism and symmetry energy at high density

    Yangyang Liu🇨🇳 · Yongjia Wang🇨🇳 · Ying Cui🇨🇳 · Chen-Jun Xia🇨🇳 · Zhuxia Li🇨🇳 · Yongjing Chen🇨🇳 · Qingfeng Li🇨🇳 · Yingxun Zhang🇨🇳

    The $N\Delta \to NN$ cross sections, which take into account the $\Delta$-mass dependence of M-matrix and momentum $p_{N\Delta }$, are applied on the calculation of pion production within the framework of the UrQMD model. Our study shows that UrQMD calculations with the $\Delta$-mass dependent $N\Delta \to NN$ cross sections enhance the pion multiplicities and decrease the ${\pi }^{-}/{\pi }^{+}$ ratios. By analyzing the time evolution of the pion production rate and the density in the overlapped region for Au+Au at the beam energy of 0.4A GeV, we find that the pion multiplicity probes the symmetry energy in the region of 1-2 times normal density. The process of pion production in the reaction is tracked including the loops of $NN\leftrightarrow N\Delta$ and $\Delta \leftrightarrow N\pi$, our calculations show that the sensitivity of ${\pi }^{-}/{\pi }^{+}$ to symmetry energy is weakened after 4-5 N-$\Delta$-$\pi$ loops in the pion production path, while the ${\pi }^{-}/{\pi }^{+}$ ratio in reactions at near threshold energies remains its sensitivity to the symmetry energy. By comparing the calculations to the FOPI data, we obtain a model dependent conclusion on the symmetry energy and the symmetry energy at two times normal density is $S(2{\rho }_0)$=38-73 MeV within $1\sigma$ uncertainties. Under the constraints of tidal deformability and maximum mass of neutron star, the symmetry energy at two times normal density is reduced to $48-58$ MeV and slope of symmetry energy $L=54-81$ MeV, and it is consistent with the constraints from ASY-EOS flow data.

    ↳ nucl-thnucl-exPRC(2021)·44 citations
11. 11*

    Hawking radiation from acoustic black holes in relativistic heavy ion collisions

    Arpan Das🇵🇱 · Shreyansh S. Dave🇮🇳 · Oindrila Ganguly🇮🇳 · Ajit M. Srivastava🇮🇳

    We propose a new analogue model of gravity - the evolving quark gluon plasma (QGP) produced in relativistic heavy ion collisions. This quark gluon plasma is the "most inviscid" fluid known. Such low kinematic viscosity is believed to reflect strongly correlated nature for QGP in these experiments. Hence, it may provide a good example of a quantum fluid naturally suited to studies of acoustic Hawking radiation. Due to rapid longitudinal expansion, presence of a sonic horizon is also naturally guaranteed here, though, in general, this horizon is not static. Using Ultra relativistic quantum molecular dynamics (UrQMD) simulations, we show that, under certain conditions, the longitudinal velocity of the plasma, near the sonic horizon, can become time independent for a short span during the evolution of the system. During this period, we can have a conformally static acoustic metric with a (conformal) Killing horizon coinciding with the apparent horizon. An asymptotic observer will then see a thermal flux of phonons, constituting the Hawking radiation, coming from the horizon. For the relatively low energy collision considered here, where the resulting QCD system is governed by non-relativistic hydrodynamics, we estimate the Hawking temperature to be about 4-5 MeV (with the temperature of the QCD fluid being about 135 MeV). We discuss the experimental signatures of this Hawking radiation in terms of a thermal component in the rapidity dependence of the transverse momentum distribution of detected particles. We also discuss extension to ultra-relativistic case which should lead to a higher Hawking temperature, along with the effects of dynamical horizon leading to blue/red shift of the temperature.

    ↳ gr-qchep-phhep-thnucl-ex+1PLB(2021)·7 citations
12. 12*

    Systematic Analysis of Flow Distributions

    Hadi Mehrabpour🇮🇷

    The information of the event-by-event fluctuations is extracted from flow harmonic distributions and cumulants, which can be done experimentally. In this work, we employ the standard method of Gram-Charlier series with the normal kernel to find such distribution, which is the generalization of recently introduced flow distributions for the studies of the event-by-event fluctuations. Also, we introduce a new set of cumulants $j_n\{2k\}$ which have more information about the fluctuations compared with other known cumulants. The experimental data imply that not only all of the information about the event-by-event fluctuations of collision zone properties and different stages of the heavy-ion process are not encoded in the radial flow distribution $p(v_n)$, but also the observables describing harmonic flows can generally be given by the joint distribution $\mathcal{P}(v_1,v_2,...)$. In such a way, we first introduce a set of joint cumulants ${\mathcal{K}}_{nm}$, and then we find the flow joint distribution using these joint cumulants. Finally, we show that the Symmetric Cumulants $SC(2,3)$ and $SC(2,4)$ obtained from ALICE data are explained by the combinations ${\mathcal{K}}_{22}+\frac{1}{2}{\mathcal{K}}_{04}-{\mathcal{K}}_{31}$ and ${\mathcal{K}}_{22}+4{\mathcal{K}}_{11}^2$.

    ↳ nucl-thhep-phnucl-exPRC(2020)·5 citations
13. 13*

    Nucleon Polarizabilities and Compton Scattering as a Playground for Chiral Perturbation Theory

    Franziska Hagelstein (AEC Bern)🇨🇭

    I give a summary of recent results on nucleon polarizabilities, with emphasis on chiral perturbation theory. The predictive calculations of Compton scattering off the nucleon are compared to recent empirical determinations and lattice QCD calculations of the polarizabilities, thereby testing chiral perturbation theory in the single-baryon sector.

    ↳ nucl-thhep-lathep-phnucl-exSymmetry(2020)·13 citations
14. 14*

    Reaction Rate Sensitivity of the Production of $\gamma$-ray Emitting Isotopes in Core-Collapse Supernova

    Kirby Hermansen · Sean M. Couch🇺🇸 · Luke F. Roberts🇺🇸 · Hendrik Schatz🇺🇸 · MacKenzie L. Warren

    Radioactive isotopes produced in core-collapse supernovae (CCSNe) provide useful insights into the underlying processes driving the collapse mechanism and the origins of elemental abundances. Their study generates a confluence of major physics research, including experimental measurements of nuclear reaction rates, astrophysical modeling, and $\gamma$-ray observations. Here we identify the key nuclear reaction rates to the nucleosynthesis of observable radioactive isotopes in explosive silicon-burning during CCSNe. Using the nuclear reaction network calculator SkyNet and current REACLIB reaction rates, we evolve temperature-density-time profiles of the innermost $0.45M_{\odot }$ ejecta from the core collapse and explosion of a $12M_{\odot }$ star. Individually varying 3403 reaction rates by factors of 100, we identify 141 reactions which cause significant differences in the isotopes of interest, namely, ${}^{43}$K, ${}^{47}$Ca, ${}^{44,47}$Sc, ${}^{44}$Ti, ${}^{48,51}$Cr, ${}^{48,49}$V, ${}^{52,53}$Mn, ${}^{55,59}$Fe, ${}^{56,57}$Co, and ${}^{56,57,59}$Ni. For each of these reactions, we present a novel method to extract the temperature range pertinent to the nucleosynthesis of the relevant isotope; the resulting temperatures lie within the range $T=0.47$ to $6.15$GK. Limiting the variations to within $1\sigma$ of STARLIB reaction rate uncertainties further reduces the identified reactions to 48 key rates, which can be used to guide future experimental research. Complete results are presented in tabular form.

    ↳ astro-ph.SRastro-ph.HEnucl-exApJ(2020)·18 citations
15. 15*

    Requirements, Status, and Plans for Track Reconstruction at the sPHENIX Experiment

    Joseph D. Osborn (for the sPHENIX Collaboration)🇺🇸

    sPHENIX is a new experiment that is being constructed at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The primary physics goals of sPHENIX are to measure jets, their substructure, and the upsilon resonances in $p$$+$$p$, $p$+Au and Au+Au collisions. To realize these goals, a tracking system composed of a time projection chamber and several silicon detectors will be used to identify tracks that correspond to jets and upsilon decays. However, the sPHENIX experiment will collect approximately 200 PB of data utilizing a finite-sized computing center; thus, performing track reconstruction in a timely manner is a challenge due to the large occupancy of heavy-ion collisions. The sPHENIX experiment, its track reconstruction, and the need for implementing faster track -fitting algorithms, such as that provided by the A Common Tracking Software package, into the sPHENIX software stack are discussed.

    ↳ physics.ins-dethep-exnucl-exphysics.data-an4 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.