We investigate the appearance of quark degrees of freedom in dense isospin-symmetric nuclear matter. We employ the parity doublet model to incorporate chiral dynamics. Specifically, we contrast quarkyonic matter, in which quarks occupy states above the nucleon Fermi surface, with baryquark matter, in which quarks populate states inside the nucleonic Fermi sea. We find that while baryquark matter is generally energetically favored over quarkyonic matter, the self-consistent treatment of the momentum-space shell reveals that purely hadronic matter provides the lowest free energy up to densities well beyond nuclear saturation. Consequently, the contribution of quarks is not relevant within the model's domain of applicability, even though chiral symmetry becomes restored. This demonstrates that the onset of quark degrees of freedom and the restoration of chiral symmetry need not coincide.

The evolution of the collectivity of tellurium isotopes from midshell towards $N=82$ is currently based mainly on properties of the first excited $2^{+}$ states. To extend structural information in this isotopic chain, in particular with respect to the balance of microscopic, seniority-type, and collective excitations, electric quadrupole transition strengths from $4^{+}$ states need to be considered. An experiment was performed to determine the $4_1^{+}$ lifetime of ${}^{132}\mathrm{Te}$ via the recoil-distance Doppler-shift method at the University of Cologne tandem accelerator. The isotope of interest was populated in the two neutron-transfer reaction ${}^{130}\mathrm{Te}$(${}^{18}\mathrm{O},{}^{16}\mathrm{O}$)${}^{132}\mathrm{Te}^{*}$. The $E2$ decay transition strength has been determined to be $B(E2;4_1^{+}\to 2_1^{+})=9.3\left(10\right)\text{W.u.}$ This value differs from literature data but compares favorably to shell model calculations.

In this study we examine the impact of the initial stage and dynamical evolution on final-state observables in heavy-ion collisions. For this goal we develop a novel approach, $\mathrm{EPOSir}+\mathrm{PHSDe}$, which employs energy-conserving multiple parallel scattering approach, accommodating factorization and saturation (EPOS) initial conditions as the starting point for parton and hadron evolution within the parton-hadron-string dynamics (PHSD) microscopic transport approach. By examining the space-time evolution of matter in this model and comparing to EPOS (which starts with an $S$-matrix approach for parallel scatterings for the initial conditions and uses a hydrodynamic evolution for the quark-gluon plasma stage with the UrQMD as afterburner) and PHSD (which starts with primary high-energy $NN$ scattering realized via the LUND string model and continues with fully microscopic transport dynamics for strongly interacting partonic and hadronic matter), we identify the key differences in the final particle distributions among the three approaches. Our analysis focuses on rapidity, transverse momentum spectra, and flow harmonics $v_2$ for $\mathrm{Au}+\mathrm{Au}$ collisions at the invariant energy of $\sqrt{s_{NN}}=200$ GeV. We find a dominant influence of dynamical evolution over the initial conditions on the final observables.

Hadronic resonances, with lifetimes of a few $\mathrm{fm}/c$ are key tools for studying the hadronic phase in high-energy collisions. This work investigates resonance production in pp collisions at $\sqrt{s}=13.6\mathrm{TeV}$ and in Pb-Pb collisions at $\sqrt{s_{NN}}=5.36\mathrm{TeV}$ using the EPOS4 model. The EPOS4 model provides the capability of switching the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) ON or OFF, allowing the study of final-state hadronic interactions in the hadronic phase. Although this study is primarily focused on understanding the production of hadronic resonances, we also investigate the production of strange and nonstrange hadrons in relation to rescattering, regeneration, baryon-to-meson production, and strangeness enhancement, using transverse momentum ($p_{\mathrm{T}}$) spectra and particle ratios. Rescattering effects and strangeness enhancement play an important role in the low-$p_{\mathrm{T}}$ region, where soft, nonperturbative processes dominate particle production. At intermediate $p_{\mathrm{T}}$, the baryon-to-meson yield ratios show an enhancement, and the strong mass-dependent radial flow observed for baryons in the most central Pb-Pb collisions reflects the interplay between hadronization dynamics and collective effects. The average $p_{\mathrm{T}}$ scaled with the reduced hadron mass (i.e., the mass divided by the number of valence quarks) is examined, revealing a deviation from a linear trend for short-lived resonances, attributed to hadronic phase effects. By analyzing the yield ratios of short-lived resonances to stable hadrons in pp and Pb-Pb collisions, the time duration ($\tau$) of the hadronic phase as a function of average charged multiplicity is estimated. The results show that $\tau$ increases with increasing multiplicity and system size, also exhibiting a nonzero value for high-multiplicity pp collisions. It is found that the production of baryons such as nonstrange ($p$), strange ($\mathrm{\Lambda }$), and multistrange ($\mathrm{\Xi }$, $\mathrm{\Omega }$) in the most central Pb-Pb collisions is influenced by competing processes of strangeness enhancement and baryon-antibaryon annihilation. Comparing these findings with measurements at energies available at the CERN Large Hadron Collider offers valuable insights into the underlying dynamics of the hadronic phase and their production dynamics.

The ${\pi }^{+}p$ elastic scattering process is studied, using an effective Lagrangian approach that incorporates the $s$-, $u$-, and $t$-channel amplitudes, including ${\mathrm{\Delta }}^{++}\left(1232\right), {\mathrm{\Delta }}^0\left(1232\right)$, neutron, and ${\rho }^0$ contributions. By constructing the spin-density matrices from the scattering amplitudes, the von Neumann (entanglement) entropy is derived and associated with the spin degrees of freedom of the initial and final state particles. The entropy is computed by performing a partial trace over the spin subsystems, and its behavior is analyzed as a function of the center-of-mass energy $W$ and scattering angle $\theta$. It is found that entropy exhibits nontrivial angular and energy dependences, reflecting the interplay among resonance contributions and background amplitudes. In particular, the ${\mathrm{\Delta }}^{++}$ region shows relatively low entanglement, suggesting spin coherence dominated by the specific resonant contribution, while the background contributions increase entropy due to mixed spin configurations. These results indicate that entanglement entropy can serve as a novel probe into the quantum structure of hadronic scattering amplitudes, providing complementary insights beyond conventional cross-section analyses.

Background: The development of SU(3) chiral effective-field theory (EFT) has opened the way to a systematic exploration of three-baryon forces (3BFs), a key ingredient in hypernuclear and dense matter physics. However, $\mathrm{\Xi }NN$ 3BF based on SU(3) chiral EFT has not been studied until now.

Purpose: We apply SU(3) chiral EFT to derive $\mathrm{\Xi }NN$ potentials in momentum space. Then, we investigate how the $\mathrm{\Xi }NN$ 3BF affects the correlation function of deuteron–${\mathrm{\Xi }}^{-}$ pair created through heavy-ion collisions.

Methods: To reduce the number of low-energy constants involved in the $\mathrm{\Xi }NN$ potentials, we employ the decuplet saturation approximation, by which only two of them remain unconstrained. The deuteron–${\mathrm{\Xi }}^{-}$ scattering is treated as an effective two-body problem with the $\mathrm{\Xi }NN$ 3BF incorporated into the potential between the deuteron and ${\mathrm{\Xi }}^{-}$.

Results: We found that the effect of the $\mathrm{\Xi }NN$ 3BF on the deuteron–${\mathrm{\Xi }}^{-}$ correlation function is at most about 4%. This small effect is not primarily due to the loosely bound nature of the deuteron. Instead, this is because the deuteron and ${\mathrm{\Xi }}^{-}$ interact with each other mainly at low momentum, corresponding to peripheral scattering, where the influence of the $\mathrm{\Xi }NN$ 3BF is limited.

Conclusions: Since the correlation function shows limited sensitivity to the short-range 3BF, complementary approaches may be necessary.

The complex scaling method is commonly used to describe decaying states, but its applications are limited because the Hamiltonian operator must contain only relative coordinates. This has hindered the use of complex scaling in models defined with laboratory single-particle coordinates, and in particular one of the most important model in low-energy nuclear physics, the no-core shell model. We will then present a straightforward procedure for introducing complex scaling in the no-core shell model in order to calculate nuclear resonance states. For that matter, the complex-scaled two-body matrix elements must first be determined, and the resulting many-body Hamiltonian complex symmetric matrix must be diagonalized afterwards. Applications pertain to the bound ground states of the lightest nuclei ${}^2\mathrm{H}$, ${}^3\mathrm{H}$, ${}^3\mathrm{He}$, and ${}^4\mathrm{He}$, as well as the resonance ground states of ${}^5\mathrm{He}$ and ${}^5\mathrm{Li}$, whereby the realistic interaction Daejeon16 is utilized.

We explore the impact of two-body currents (2BCs) at finite momentum transfer with a focus on magnetic-dipole properties in ${}^{48}\mathrm{Ca}$ and ${}^{48}\mathrm{Ti}$. To this end, we derive a multipole decomposition of 2BCs to fully include the momentum-transfer dependence in ab initio calculations. As application, we investigate the effects of 2BCs on the strong $M1$ transition at 10.23 MeV in ${}^{48}\mathrm{Ca}$ using the valence-space in-medium similarity renormalization group (VS-IMSRG) with a set of nonimplausible interactions as well as the 1.8/2.0 (EM) interaction. Experiments, such as $(e,e^{\prime })$ and $(\gamma ,n)$, disagree on the magnetic-dipole strength $B$($M1$) for this transition. Our VS-IMSRG results favor larger $B$($M1$) values similar to recent coupled-cluster calculations. However, for this transition there are larger cancellations between the leading pion-in-flight and seagull 2BCs, so that future calculations including higher-order 2BCs are important. For validation of our results, we investigate additional observables in ${}^{48}\mathrm{Ca}$ as well as $M1$ transitions in ${}^{48}\mathrm{Ti}$. For these, our results agree with experiment. Finally, our results show that for medium-mass nuclei 2BC contributions to $M1$ and Gamow-Teller transitions are, as expected, very different. Therefore, using similar quenching factors for both in phenomenological calculations is not supported from first principles.

The ${}^{15}\mathrm{N}(n,\gamma ){}^{16}\mathrm{N}$ reaction plays a vital role in affecting the fluorine abundance produced in asymptotic giant branch stars and Wolf-Rayet stars by competing with the production reaction ${}^{15}\mathrm{N}(\alpha ,\gamma ){}^{19}\mathrm{F}$. However, the current understanding of this reaction is hampered by substantial discrepancies in both the neutron spectroscopic factors for the low-lying states of ${}^{16}\mathrm{N}$ and the reaction rate of ${}^{15}\mathrm{N}(n,\gamma ){}^{16}\mathrm{N}$. To address these uncertainties, we employ the Gamow shell model to investigate the spectroscopic factors of ${}^{16}\mathrm{N}$. Our results reveal that all these states are single-particle levels. Subsequently, the Gamow shell model coupled-channel representation was utilized to derive the cross section of ${}^{15}\mathrm{N}(n,\gamma ){}^{16}\mathrm{N}$ reaction at low energies. The associated reaction rate is then calculated based on the obtained cross section. Our calculation aligns with the available experimental data overall.

We investigate the influence of the nuclear symmetry energy and its density slope parameter on the neutron dripline and neutron star properties using a semiclassical liquid drop model (LDM) and energy density functionals constrained by chiral effective field theory. To analyze finite nuclei and mass tables, the nuclear symmetry energy at saturation density is fixed, and the surface tension is determined to minimize the root-mean-square deviation of the total binding energy for 2208 nuclei. Correlations between symmetry energy parameters and neutron driplines, crust-core transition densities, and the radii of $1.4M_{\odot }$ neutron stars are explored using the LDM framework. Additionally, we examine the relationship between macroscopic properties, such as neutron star radii ($R_{1.4}$), and microscopic properties, including the number of isotopes and the last bound nucleus for $Z=28$, within the LDM context.

Magnetic dipole ($M1$) moments in nuclei neighboring the doubly magic core are investigated by self-consistent mean-field (SCMF) approaches that allow for the breaking of time-reversal symmetry. By the SCMF calculations with the M3Y-P6 interaction, which keeps realistic spin-isospin and tensor channels, the $M1$ moments are well reproduced, particularly those in the nuclei adjacent to $jj$-closed magicity. The results are in better agreement with the data than those with the Gogny-D1S interaction, slightly better than those of UNEDF1 supplemented by a spin-isospin channel adjusted to the $M1$ moments themselves, and comparable to the shell-model results with the chiral effective-field-theory ($\chi \mathrm{EFT}$) interaction. Analyses via quadrupole moments, occupation numbers, and the lowest-order perturbation theory elucidate the cooperative effects of quadrupole deformation and spin correlation on the displacement from the Schmidt values, which has been known in terms of the quenching of the spin matrix elements. It is shown that a significant portion of the spin correlation is carried by the spin-isospin and tensor channels in the effective interaction. However, while agreement is remarkable at ${}^{131}\mathrm{Sn}^m, {}^{133}\mathrm{Sn}$, and ${}^{209}\mathrm{Pb}$, discrepancies remain at the $Z=\mathrm{odd}$ nuclei ${}^{133}\mathrm{Sb}, {}^{207}\mathrm{Ti}$, and ${}^{209}\mathrm{Bi}$, as in the $\chi \mathrm{EFT}$-based shell-model results.

The study of the nuclear equation of state (EoS) is one of the primary goals of experimental and theoretical heavy-ion physics. The comparison of recent high-statistics data from the STAR Collaboration with transport models provides a unique possibility to address this topic in a yet-unexplored energy domain. Employing the microscopic $N$-body parton-hadron-quantum-molecular dynamics transport approach, which allows us to describe the propagation and interactions of hadronic and partonic degrees of freedom, including cluster and hypernucleus formation and dynamics, we investigate the influence of different EoS on bulk observables, the multiplicity, $p_T$, and rapidity distributions of protons, $\mathrm{\Lambda }\mathrm{s}$ and clusters up to $A$ = 4, as well as their influence on the collective flow. We explore three different EoS: two static EoS, dubbed “soft” and “hard,” which differ in the compressibility modulus, as well as a soft momentum-dependent EoS. We find that a soft momentum-dependent EoS reproduces most baryon and cluster observables, including the flow observables, quantitatively; however, hard EoS show a similar trend.

The relative distribution of isotopes produced during the big bang is a sensitive probe of cosmology. Uncertainties remain in the nuclear reactions between deuterium and ${}^7\mathrm{Be}$, which lead to a reduction in the ${}^7\mathrm{Li}$ yield. In two experiments using the ${}^{10}\mathrm{B}({}^3\mathrm{He},\alpha ){}^9\mathrm{B}$ reaction, the spectrum of ${}^9\mathrm{B}$ states above the deuteron threshold was investigated with the SE-SPS spectrograph and their decay through $\alpha , \mathrm{d}$, or $\mathrm{p}$ emission observed in coincidence with the SABRE silicon detector array. The dominant ${}^7\mathrm{Be}+\mathrm{d}$ resonance was measured at 299(13)-keV center-of-mass energy, and its decay branching ratios were determined. This resonance energy and resonance strength of 1.7(4) keV correspond to higher reaction rates and smaller uncertainties than a previous experiment, but do not alter the big-bang nucleosynthesis yield for ${}^7\mathrm{Li}$ significantly. An additional tentative peak at 150(12) keV was observed, but could not conclusively be attributed to the ${}^7\mathrm{Be}+\mathrm{d}$ channel and was not observed in other channels.

In many applications one has to deal with functions that depend on two directions. A convenient basis for function expansion is provided by bipolar harmonics that are given by an irreducible tensor product of the spherical functions with different arguments. The basis of biharmonic functions is overcomplete for a fixed total angular momentum and for arbitrary internal angular momenta. Bipolar harmonics with a small rank of total momentum often enter the final results while the ranks of the internal tensors can run over a wide (or infinite) range. But it is possible to decompose the bipolar harmonic using the smallest set of internal orbital momenta for a fixed total momentum. Here, the new method is applied for calculations of decomposition coefficients at low values of total angular momenta and arbitrary values of internal momenta. Basis functions from the minimal set are modified in two respects: 1. Expansion coefficients include total dependence on the angle between two directions and basis functions are independent from this angle. 2. New basis is orthogonal and normalized to the absolute value of unity. These tensors form the normalized orthogonal basis from the minimal set of bipolar harmonics. The basis and expansion coefficients are presented explicitly for total orbital momentum $L\le 3$.

Symmetries and their breaking mechanisms are fundamental in nuclear physics with spin symmetry (SS) and pseudospin symmetry (PSS) playing key roles in nucleon and antinucleon spectra. While PSS in nucleons has been extensively studied, the manifestation of SS in antinucleon resonances—critical for exotic nuclei, where resonant states dominate near drip lines—remains unexplored. Here, we present the first systematic investigation of SS in antineutron resonant states within nuclei using relativistic mean-field theory combined with the complex momentum representation method, focusing on ${}^{40}\mathrm{Ca}$ with Woods-Saxon potentials. Our results reveal pronounced near-degeneracy in energy and width for resonant spin doublets, confirming robust SS preservation in antineutron resonances. Dirac spinor analysis shows that upper components $f\left(r\right)$ exhibit near-perfect degeneracy. SS quality improves near the continuum threshold, aligning with threshold-driven symmetry restoration. Sensitivity analysis demonstrates that a shallower potential (reduced $|{\mathrm{\Sigma }}_0|$) enhances SS, while larger diffuseness ($a$) or radius ($R$) degrades it with $\mathrm{\Delta }\mathrm{\Gamma }$ exhibiting resonance-type-dependent trends. These results establish the first systematic evidence for SS in antineutron resonances, advancing our understanding of nuclear structure and providing benchmarks for future studies of antimatter-nucleus interactions at facilities like GSI-FAIR.

The Glauber model calculation of single-particle cross section ${\sigma }_{\mathrm{sp}}$ for one-proton removal ($-p$) from the $0p_{3/2}$ orbit of the ground state (g.s.) of ${}^7\mathrm{Li}$ on a ${}^9\mathrm{Be}$ target at $400\mathrm{MeV}/\mathrm{nucleon}$ is performed. The calculation takes valence proton wave function $R_l\left(r\right)$ and the residue (core) and target nucleon densities from a wide collection of theoretical approaches. $R_l\left(r\right)$ is extracted from the overlap $\langle {}^6\mathrm{He}_{\text{g.s.}}|{}^7\mathrm{Li}_{\text{g.s.}}\rangle$ calculated from a variety of theoretical approaches, which include no-core shell model (NCSM), variational Monte Carlo structure model (VMC), Green's function Monte Carlo structure model (GFMC), and Gamow shell model (GSM), by directly using the overlap (overlap), fitting the overlap with an eigenstate in a Woods-Saxon (WS) potential (WSFit), and by reproducing the root-mean-square (rms) radius of the overlap by an eigenstate in a WS potential (MFrms). The nucleon densities of the core ${\rho }_{\mathrm{c}}\left(r\right)$ and the target ${\rho }_{\mathrm{t}}\left(r\right)$ are taken from VMC, GFMC, Hartree-Fock (HF) calculation, and Gaussian distributions. The ${\sigma }_{\mathrm{sp}}({}^7\mathrm{Li}-p$) calculated with $R_l\left(r\right)$ from the MFrms and overlap methods are very close to that of the WSFit method, with a relative difference of less than 0.3%, 0.2%, 2.2%, and 3.4% for GSM, GFMC, NCSM, and VMC overlaps, respectively. As for the nucleon densities, the ${\sigma }_{\mathrm{sp}}({}^7\mathrm{Li}-p$) calculated using HF, VMC, and GFMC ${\rho }_{\mathrm{c}}\left(r\right)$ differ considerably from those using Gaussian ${\rho }_{\mathrm{c}}\left(r\right)$ with the same rms radii by a difference relative to the former of 15.8%, 16.4%, and 17.7%, respectively. This is less conspicuous for the cases of ${\rho }_t\left(r\right)$ from HF (7.3%) and VMC (2.2%). The above conclusions are checked to qualitatively hold for the cases of one-proton (-neutron) removal from the $0p_{1/2}$ and $0p_{3/2}$ orbits of the g.s. of ${}^7\mathrm{Be}$ (${}^7\mathrm{Li}$) at the same energy on the same target.

The synthesis of superheavy elements strongly relies on the competition of the quasifission and fusion fission dynamics in the fusion-evaporation reactions. The systematics on the formation of superheavy nuclei in the ${}^{48}\mathrm{Ca}, {}^{50}\mathrm{Ti}, {}^{51}\mathrm{V}$, and ${}^{54}\mathrm{Cr}$ induced fusion reactions on actinide nuclei ${}^{232}\mathrm{Th}, {}^{231}\mathrm{Pa}, {}^{238}\mathrm{U}, {}^{237}\mathrm{Np}, {}^{242,244}\mathrm{Pu}, {}^{243}\mathrm{Am}, {}^{245,248}\mathrm{Cm}, {}^{249}\mathrm{Bk}, {}^{249}\mathrm{Cf}$ has been thoroughly investigated with the dinuclear system model by including the cluster transfer and coupling to the dynamical evolution of the quadrupole deformation parameters. The uncertainties of the fusion-evaporation excitation functions with the mass models of FRDM2012, KTUY05, LDM1966, SkyHFB, WS4 are investigated and compared with the available experimental data from Dubna, GSI, Berkeley, and RIKEN, respectively. The production cross sections, optimal evaporation channels, and beam energies in the synthesis of superheavy elements $Z$ = 119 and 120 were predicted and compared for the different mass models in the reactions of ${}^{50}\mathrm{Ti}+{}^{249}\mathrm{Bk}, {}^{51}\mathrm{V}+{}^{248}\mathrm{Cm}, {}^{54}\mathrm{Cr}+{}^{243}\mathrm{Am}, {}^{50}\mathrm{Ti}+{}^{249}\mathrm{Cf}, {}^{51}\mathrm{V}+{}^{249}\mathrm{Bk}, {}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}$, respectively.

The effect of ${\mathrm{\Sigma }}^{*}\left(1385\right)$ baryon resonance on the time evolution of the $\mathrm{\Lambda }$ hyperon polarization in hadronic matter is studied using a spin-dependent kinetic approach. This approach explicitly includes the production of the ${\mathrm{\Sigma }}^{*}$ resonance from the $\mathrm{\Lambda }-\pi$ and $\mathrm{\Sigma }\left(1192\right)-\pi$ scatterings as well as its decay into $\mathrm{\Lambda }+\pi$ or $\mathrm{\Sigma }+\pi$, all including explicitly their spin dependence. The resulting coupled kinetic equations governing the time evolution of $\mathrm{\Lambda }, \mathrm{\Sigma }$, and ${\mathrm{\Sigma }}^{*}$ numbers and polarizations are solved for Au-Au collisions at $\sqrt{s_{NN}}=7.7$ GeV and 20–50% centrality, using initial values determined by their thermal yields and the thermal vorticity in the hadronic matter at chemical freeze-out temperature. As the hadronic matter expands and cools, the $\mathrm{\Lambda }$ polarization is found to increase slightly during early times and then decreases very slowly afterwards, while the $\mathrm{\Sigma }$ polarization remains nearly constant and the ${\mathrm{\Sigma }}^{*}$ polarization continuously decreases. Including feed-down contributions to the $\mathrm{\Lambda }$ polarization from the decays of partially polarized ${\mathrm{\Sigma }}^0, {\mathrm{\Sigma }}^{*}$, and $\mathrm{\Xi }\left(1322\right)$ hyperons, where the $\mathrm{\Xi }$ polarization is obtained by solving coupled kinetic equations for the $\mathrm{\Xi }$ and ${\mathrm{\Xi }}^{*}\left(1532\right)$ system, the resulting $\mathrm{\Lambda }$ polarization becomes smaller and decreases over time. In both cases, the time variation of the $\mathrm{\Lambda }$ polarization is, however, sufficiently small to support the assumption of an early freeze-out of $\mathrm{\Lambda }$ spin degree of freedom in relativistic heavy-ion collisions.

In heavy ion collisions particle distributions fluctuate from event to event. It is interesting to study local fluctuations of a specific particle species, e.g., baryons, in the transverse plane. Fluctuations of the harmonic flow provide an integrated measure of such fluctuations. An alternative approach is to study proton number fluctuations measured in a relatively narrow azimuthal angle window. Due to the transverse flow, particles registered in a narrow azimuthal angle window are emitted predominantly from a region located at the same side of the fireball as the observation window. Similarly, it is informative to measure the covariance of the number of protons emitted in two opposite windows of azimuthal angles. The main difficulty lies in distinguishing effects of local baryon density fluctuations in the transverse plane from global particle density and collective flow fluctuations. These global density and flow fluctuations can be estimated using some reference particles, e.g., charged mesons. Reliable estimates of such fluctuations can be constructed both for the second factorial cumulant of the proton number in an azimuthal angle window and for the covariance between two such windows. The simultaneous measurement of both quantities provides a sensitive probe of local baryon number fluctuations superimposed on top of a fluctuating fireball background density.