Nuclear Theory

We report a new determination of q ^ , the jet transport coefficient of the Quark-Gluon Plasma. We use the JETSCAPE framework, which incorporates a novel multi-stage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the MATTER and LBT jet quenching models, are compared to experimental measurements of inclusive hadron suppression in Au+Au collisions at RHIC and Pb+Pb collisions at the LHC. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of q ^ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. In the multi-stage approach, the switch between MATTER and LBT is governed by a virtuality scale Q 0 . Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of q ^ / T 3 extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature T , with 90\% Credible Region (CR) depending on the specific choice of model configuration. The choice of MATTER+LBT, with switching at virtuality Q 0 , has 90\% CR of 2< q ^ / T 3 <4 for p jet T >40 GeV/c. The value of Q 0 , determined here for the first time, is in the range 2.0-2.7 GeV.

We present a method to determine the leading-order (LO) contact term contributing to the nn?�pp e ??e ??amplitude through the exchange of light Majorana neutrinos. Our approach is based on the representation of the amplitude as the momentum integral of a known kernel (proportional to the neutrino propagator) times the generalized forward Compton scattering amplitude n( p 1 )n( p 2 ) W + (k)?�p( p ??1 )p( p ??2 ) W ??(k) , in analogy to the Cottingham formula for the electromagnetic contribution to hadron masses. We construct model-independent representations of the integrand in the low- and high-momentum regions, through chiral EFT and the operator product expansion, respectively. We then construct a model for the full amplitude by interpolating between these two regions, using appropriate nucleon factors for the weak currents and information on nucleon-nucleon ( NN ) scattering in the 1 S 0 channel away from threshold. By matching the amplitude obtained in this way to the LO chiral EFT amplitude we obtain the relevant LO contact term and discuss various sources of uncertainty. We validate the approach by computing the analog I=2 NN contact term and by reproducing, within uncertainties, the charge-independence-breaking contribution to the 1 S 0 NN scattering lengths. While our analysis is performed in the MS ¯ ¯ ¯ ¯ ¯ ¯ ¯ scheme, we express our final result in terms of the scheme-independent renormalized amplitude A ν (|p|,| p ??|) at a set of kinematic points near threshold. We illustrate for two cutoff schemes how, using our synthetic data for A ν , one can determine the contact-term contribution in any regularization scheme, in particular the ones employed in nuclear-structure calculations for isotopes of experimental interest.

By relating the charge multiplicity distribution and the temperature of a de-exciting nucleus through a deep neural network, we propose that the charge multiplicity distribution can be used as a thermometer of heavy-ion collisions. Based on an isospin-dependent quantum molecular dynamics model, we study the caloric curve of reaction 103 Pd + 9 Be with the apparent temperature determined through the charge multiplicity distribution. The caloric curve shows a characteristic signature of nuclear liquid-gas phase transition around the apparent temperature T ap = 6.4 MeV , which is consistent with that through a traditional heavy-ion collision thermometer, and indicates the viability of determining the temperature in heavy-ion collisions with multiplicity distribution.

Hexaquarks constitute a natural extension of complex quark systems like also tetra- and pentaquarks do. To this end the current status of d ∗ (2380) in both experiment and theory is shortly reviewed. Recent high-precision measurements in the nucleon-nucleon channel and analyses thereof have established d ∗ (2380) as an indisputable resonance in the long-sought dibaryon channel. Important features of this I( J P )=0( 3 + ) state are its narrow width and its deep binding relative to the Δ(1232)Δ(1232) threshold. Its decay branchings favor theoretical calculations predicting a compact hexaquark nature of this state. We review the current status of experimental and theoretical studies on d ∗ (2380) as well as new physics aspects it may bring in the future. In addition, we review the situation at the Δ(1232)N and N ∗ (1440)N thresholds, where evidence for a number of resonances of presumably molecular nature have been found -- similar to the situation in charmed and beauty sectors. Finally we briefly discuss the situation of dibaryon searches in the flavored quark sectors.

We discuss the "sheet structure" of compressed baryonic matter possibly present in massive compact stars in terms of quantum Hall droplets and skyrmions for baryons in medium. The theoretical framework is anchored on a generalized scale symmetric hidden local symmetry that encompasses standard nuclear effective field theory ( s EFT) and can access the density regimes relevant to massive compact stars. It hints at a basically different, hitherto unexplored structure of the {\it densest} baryonic matter stable against collapse to black hole. Hidden scale symmetry and hidden local symmetry together in nuclear effective field theory are seen to play a potentially crucial role in providing the hadron-quark duality in compressed baryonic matter.

Both the incompressibility \Ka of a finite nucleus of mass A and that ( K ??) of infinite nuclear matter are fundamentally important for many critical issues in nuclear physics and astrophysics. While some consensus has been reached about the K ??, accurate theoretical predictions and experimental extractions of K ? characterizing the isospin dependence of \Ka have been very difficult. We propose a differential approach to extract the \Kt and \Ki independently from the \Ka data of any two nuclei in a given isotope chain. Applying this novel method to the \Ka data from giant monopole resonances in even-even Sn, Cd, Ca, Mo and Zr isotopes taken by U. Garg {\it et al.} at the Research Center for Nuclear Physics (RCNP), Osaka University, Japan, we find that the 106 Cd- 116 Cd and 112 Sn- 124 Sn pairs having the largest differences in isospin asymmetries in their respective isotope chains measured so far provide consistently the most accurate up-to-date \Kt value of K ? =??16±59 MeV and K ? =??23±86 MeV, respectively, largely independent of the remaining uncertainties of the surface and Coulomb terms in expanding the K A .

An investigation of the calculated α decay half-lives of super heavy nuclei (SHN) reveals that the diffuseness parameter is a great bottleneck for achieving accurate results and predictions. In particular, when universal proximity function is adopted for nuclear potential, half-life is found to vary significantly and nonlinearly as a function of diffuseness parameter. To overcome this limiting hurdle, a new semiempirical formula for diffuseness that is dependent on charge and neutron numbers is proposed in this work. With the model at hand, half-lives of 218 SHN are computed, for 68 of which there exists available experimental data and 150 of which are predicted. The calculations of half-lives for 68 SHN are compared against experimental data and the calculated data obtained by using deformed Woods-Saxon, deformed Coulomb potentials model, and six semiempirical formulas. The predictions of 150 SHN are compared against the predictions of seven of the current best semiempirical formulas. Calculations of the present study are in good agreement with the experimental half-lives outperforming all but ImSahu semiempirical formula. Moreover, the predictions of our model are consistent with predictions of the semiempirical formulas. We strongly conclude that more attention should be directed toward obtaining accurate diffuseness parameter values for using it in nuclear calculations.

We use the microscopic GiBUU transport model to calculate dilepton ( e + e − ) production in heavy-ion collisions at SIS18 energies focusing on the effect of collisional broadening of the ρ -meson. The collisional width of the ρ -meson at finite temperature and baryon density in nuclear matter is calculated on the basis of the collision integral of the GiBUU model. A systematic comparison with HADES data on dilepton production in heavy-ion collisions is performed. The collisional broadening of the ρ improves the agreement between theory and experiment for the dilepton invariant-mass distributions near the ρ pole mass and for the excess radiation in Au+Au at 1.23A GeV. We furthermore show that some remaining underprediction of the experimental dilepton spectra in C+C at 1A GeV and Au+Au at 1.23A GeV at intermediate invariant masses 0.2−0.4 GeV can be accounted for by adjusting the pn bremsstrahlung cross section in a way to agree with the inclusive dilepton spectrum from dp collisions at 1.25A GeV.

Strong electromagnetic fields are expected to be generated in off-central relativistic heavy ion collisions, which can induce a splitting of the directed flow of charged particles and anti-particles ( Δ v 1 ). Such a splitting manifests even for neutral charmed mesons pairs ( D 0 , D ¯ 0 ), hence being a direct probe of the formation of deconfined phase with charm quarks as degree of freedom. In the limit of large p T and weak interaction with the QGP, a formula of Δ v 1 ( p T , y z ) of charged particles and anti-particles as a function of p T and rapidity y z can be obtained, which is found to be related to the spectra of charged particles and the integrated effect of the Lorentz force. This formula is expected to be valid to heavy quarks and leptons at high p T , where the modification to their equations of motion due to the interaction with both QGP and electromagnetic fields is small, and should have a general application. We also proposed a measurement of Δ v 1 ( p T , y z ) of leptons from Z 0 decay and its correlation to that of D mesons, which would be a strong probe determining whether the large splitting measured in experiments has the electromagnetic origin.

At least three length scales are important in gaining a complete understanding of the physics of nuclei. These are the radius of the nucleus, the average inter-nucleon separation distance, and the size of the nucleon. The connections between the different scales are examined by using examples that demonstrate the direct connection between short-distance and high momentum transfer physics and also that significant high momentum content of wave functions is inevitable. The nuclear size is connected via the independent-pair approximation to the nucleon-nucleon separation distance, and this distance is connected via the concept of virtuality to the EMC effect. An explanation of the latter is presented in terms of light-front holographic wave functions of QCD. The net result is that the three scales are closely related, so that a narrow focus on any given specific range of scales may prevent an understanding of the fundamental origins of nuclear properties. It is also determined that, under certain suitable conditions, experiments are able to measure the momentum dependence of wave functions.