Baryon States Research Articles

Multi-differential pattern of low-mass e+e− excess from [formula omitted] Au+Au collisions with HADES

The matter formed in central heavy-ion collisions at a few GeV per nucleon is commonly understood as resonance matter, a gas of nucleons and excited baryon states with a substantial contribution from mesonic, mostly pionic excitations. Yet, in the initial phase of the reaction the system is compressed to beyond nuclear ground state density and hence substantial modifications of the hadron properties are expected to occur. The spectral distribution of virtual photons measured in Au+Au collisions at 2.4 GeV center of mass energy indicates strong medium effects beyond pure superposition of individual NN collisions. We present multi-differential distributions of low-mass electron pairs. This radiation is remarkably well described assuming emission from a thermalized system. To gain deeper understanding of the microscopic origin of the radiation, we extracted the centrality dependent true (not blue-shifted) temperature, its azimuthal distribution, as well as mass-dependent effective slope parameter. Virtual photon spectra are confronted with available model calculations.

Exotics at BESIII

With a collected integrated luminosity of about 12 fb−1, useful data set for XYZ new resonances, BESIII continues the exploration of these exotic charmonium-like states. In this proceeding, recent results on the measurements of the line-shape of e+e− → π+π−ψ(3868) and π+D0D*−, as well as the JP determination of ZC (3900) will be presented. An abundance of Y will be reported in several decay channels. Finally the present BESIII data above the ${e^ + }{e^ - }\, \to \,{\Lambda _C}{\bar \Lambda _C}$ threshold will be shortly discussed because they are barely in agreement with the current Belle data on the candidate charmed baryonium state Y(4660). A BEPCII upgrade, that will allow to settle this open question, has been funded.

Aspects of baryon spectroscopy at ELSA

A renaissance in hadron specroscopy in both meson and baryon sectors was triggered by the discovery of the enigmatic X, Y, Z states. Meanwhile, the discussion on unconventional quark-gluon compositions to understand their internal structure expanded to baryonic states in the charm sector, i.e. the pentaquark candidates observed at LHCb. Old problems and recent findings in the strange sector may suggest similar structures to exist there as well. In this light recent results and the ongoing new BGO-OD experiment at ELSA are discussed.

Heavy baryon spectroscopy

Masses of heavy baryons are calculated in the relativistic quarkdiquark picture. Obtained results are in good agreement with available experimental data including recent measurements by the LHCb Collaboration. Possible quantum numbers of excited heavy baryon states are discussed.

Decuplet to octet baryon transitions in chiral perturbation theory

We have systematically investigated the decuplet (T) to octet (B) baryon (Trightarrow Bgamma ) transition magnetic moments to the next-to-next-to-leading order and electric quadruple moments to the next-to-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. Throughout our calculation, we have adopted the small-scale scheme and have not considered the 1/M recoiling corrections directly. We count the octet and decuplet baryon mass splitting delta , the small momenta p, and the pion mass m_{phi } as the same order small-scale parameter, which was denoted as epsilon . Our results for the transition magnetic moments show reasonably good convergence of the chiral expansion. The analytical expressions may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.

Ξ* photoproduction from threshold to W=3.3GeV

The doubly strange Ξ baryons provide an effective way to study a puzzle called the missing-baryons problem where both quark models and lattice gauge theory predict more baryon excited states than are seen experimentally. However, few of these excited states have been observed with any certainty. Here, high-mass Ξ* states have been searched for in photoproduction with the detector of the CLAS Collaboration, and upper limits for the total cross sections have been established from threshold to W=3.3GeV. In addition, the total cross sections of the ground-state Ξ−(1320) and first excited state Ξ−(1530) are presented, extending significantly the center-of-mass energy range of previous data.Received 5 September 2018DOI:https://doi.org/10.1103/PhysRevC.98.062201©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle interactionsPhotonuclear reactionsQCD in nuclear reactionsQuark modelNuclear Physics

Baryons under strong magnetic fields or in theories with space-dependent θ -term

Baryonic states are sufficiently complex to reveal physics that is hidden in the mesonic bound states. Using gauge/gravity correspondence we study analytically and numerically baryons in theories with space-dependent $\theta$-term, or theories under strong magnetic fields. Such holographic studies on baryons are accommodated in a generic analytic framework we develop for anisotropic theories, where their qualitative features are common irrespective of the source that triggers the anisotropy. We find that the distribution of the quarks forming the state, depends on the angle between the baryon and the anisotropic direction. Its shape is increasingly elliptic with respect to the strength of the field sourcing the anisotropy, counterbalancing the broken rotational invariance on the gluonic degrees of freedom. Strikingly, the baryons dissociate in stages with a process that depends on the proximity of the quarks to the anisotropic direction, where certain quark pairs abandon the bound state first, followed by the closest pairs to them as the temperature increases. This observation may also serve as a way to identify the nature of certain exotic states. Finally, we investigate holographic baryons with decreased number of quarks and explain why in theories under consideration the presence of anisotropy does not modify the universal stability condition in contrast to the usual trend.

Analysis of the doubly heavy baryon states and pentaquark states with QCD sum rules

In this article, we study the doubly heavy baryon states and pentaquark states with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension 7 and 13 respectively in a consistent way. In calculations, we separate the contributions of the negative parity and positive parity hadron states unambiguously, and study the masses and pole residues of the doubly heavy baryon states and pentaquark states in details. The present predictions can be confronted to the experimental data in the future.

Structure of baryon states from non-perturbative methods

In this approach we have adapted non-perturbative many-body methods to describe baryon-like states built from effective quarks, antiquarks degrees of freedom and collective RPA states. As starting point, we have used the QCD Hamiltonian written in the Coulomb gauge, and considered a confining interaction to describe the non-perturbative effects of dynamical gluons. The effective Hamiltonian used is expressed in terms of the effective quark-antiquark, di-quarks and di-antiquark excitations and approximately diagonalized by mapping quark-antiquark pairs and di-quarks (di-antiquarks) onto phonon states. For the structure of the vacuum of the theory, color-scalar- and color-vector-structures are introduced to account for ground state correlations. We present the structure of the baryon-like states, beyond the common three constituent quarks, describe their interactions and present a simple calculation to illustrate the method.

The S- and P-Wave Low-Lying Baryons in the Chiral Quark Model

The $1S$, $2S$, $1P$ and $2P$ states of light baryons are investigated within the chiral quark model, paying particular attention to the well-known order reverse problem of $1P$ and $2S$ states. Besides a nonperturbative linear-screened confining interaction and a perturbative one-gluon exchange between quarks, we incorporate the Goldstone-boson exchanges taking into account not only the full octet of pseudoscalar mesons but also the scalar one. The scalar meson exchange potential simulates the higher order multi-pion exchange terms that appear in the chiral Lagrangian and its omission has been already admitted as a deficiency of the original model in describing, for instance, the $\rho-\omega$ splitting. The numerical approach to the three body bound state problem is the so-called Gau\ss ian expansion method, which is able to get a precision as good as Faddeev calculations. With a set of parameters fixed to different hadron and hadron-hadron observables, we find that the chiral potential could play an important role towards the issue on the mass order reverse problem. We extend our calculation to the $qqQ$ and $qQQ$ sectors (with $q$ representing a light $u$-, $d$-, or $s$-quark and $Q$ denoting the charm quark or the bottom one) in which many new states have been recently observed. Some tentative assignments are done attending to the agreement between theoretical and experimental masses; however, we admit that other sources of information are needed in order to make strong claims about the nature of these states.

Holographic three flavor baryon in the Witten\u2013Sakai\u2013Sugimoto model with the D0\u2013D4 background

With the construction of the Witten–Sakai–Sugimoto model in the D0–D4 background, we systematically investigate the holographic baryon spectrum in the case of three flavors. The background geometry in this model is holographically dual to Uleft( N_{c}right) Yang–Mills theory in large N_{c} limit involving an excited state with a nonzero theta angle or glue condensate leftlangle mathrm {Tr}mathcal {F}wedge mathcal {F}rightrangle =8pi ^{2}N_{c}tilde{kappa }, which is proportional to the charge density of the smeared D0-branes through a parameter b or tilde{kappa }. The classical solution of baryon in this model can be modified by embedding the Belavin–Polyakov–Schwarz–Tyupkin instanton and we carry out the quantization of the collective modes with this solution. Then we extend the analysis to include the heavy flavor and find that the heavy meson is always bound in the form of the zero mode of the flavor instanton in strong coupling limit. The mass spectrum of heavy-light baryons in the situation with single- and double-heavy baryon is derived by solving the eigen equation of the quantized collective Hamiltonian. Afterwards we obtain that the constraint of stable baryon states has to be 1<b<3 and the difference in the baryon spectrum becomes smaller as the D0 charge increases. It indicates that quarks or mesons can not form stable baryons if the theta angle or glue condensate is sufficiently large. Our work is an extension of the previous study of this model and also agrees with those conclusions.

Covariance Matrix for Helicity Couplings

The helicity couplings at $$Q^2=0$$ for excited baryonic states have been determined in the past, but no information is available regarding their correlations that are relevant for comparison to theory. We present here our calculation of such correlations between the helicity couplings. They contain information for quantitative comparisons with theoretical values, they can be used to quantify the impact of polarization observables, and can help design new experiments.

Non-perturbative RPA-method implemented in the Coulomb gauge QCD Hamiltonian: From quarks and gluons to baryons and mesons

Starting from an algebraic model based on the QCD-Hamiltonian and previously applied to study meson states, we have developed an extension of it in order to explore the structure of baryon states. In developing our approach we have adapted concepts taken from group theory and non-perturbative many-body methods to describe states built from effective quarks and anti-quarks degrees of freedom. As a Hamiltonian we have used the QCD Hamiltonian written in the Coulomb Gauge, and expressed it in terms of effective quark-antiquark, di-quarks and di-antiquark excitations. To gain some insights about the relevant interactions of quarks in hadronic states, the Hamiltonian was approximately diagonalized by mapping quark-antiquark pairs and di-quarks (di-antiquarks) onto phonon states. In dealing with the structure of the vacuum of the theory, color-scalar and color-vector states are introduced to account for ground-state correlations. While the use of a purely color-scalar ground state is an obvious choice, so that colorless hadrons contain at least three quarks, the presence of coupled color-vector pairs in the ground state allows for colorless excitations resulting from the action of color objects upon it.

Pentaquarks with hidden charm as hadroquarkonia

We consider hidden charm pentaquarks as hadroquarkonium states in a QCD inspired approach. Pentaquarks arise naturally as bound states of quarkonia excitations and ordinary baryons. The LHCb P_c(4450) pentaquark is interpreted as a psi '-nucleon bound state with spin-parity J^P=3/2^-. The partial decay width varGamma (P_c(4450)rightarrow J/psi +N)approx 11 MeV is calculated and turned out to be in agreement with the experimental data for P_c(4450). The P_c(4450) pentaquark is predicted to be a member of one of the two almost degenerate hidden-charm baryon octets with spin-parities J^{P}=1/2^-,3/2^-. The masses and decay widths of the octet pentaquarks are calculated. The widths are small and comparable with the width of the P_c(4450) pentaquark, and the masses of the octet pentaquarks satisfy the Gell-Mann–Okubo relation. Interpretation of pentaquarks as loosely bound varSigma _cbar{D}^* and varSigma _c^*bar{D}^* deuteronlike states is also considered. We determine quantum numbers of these bound states and calculate their masses in the one-pion exchange scenario. The hadroquarkonium and molecular approaches to exotic hadrons are compared and the relative advantages and drawbacks of each approach are discussed.

Lattice study of the scalar and baryon spectra in many-flavor QCD

In the search for a composite Higgs boson in walking technicolor models, many flavor QCD, in particular with [Formula: see text], is an attractive candidate, and has been found to have a composite flavor-singlet scalar as light as the pion. Based on lattice simulations of this theory with the HISQ action, we will present our preliminary results on the scalar decay constant using the fermionic bilinear operator, and on the mass of the lightest baryon state which could be a dark matter candidate. Combining these two results, implications for dark matter direct detection are also discussed.

First Observation of the Rare Purely Baryonic Decay B^{0}→pp[over ¯

The first observation of the decay of a B^{0} meson to a purely baryonic final state, B^{0}→pp[over ¯], is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8TeV and corresponds to an integrated luminosity of 3.0 fb^{-1}. The branching fraction is determined to be B(B^{0}→pp[over ¯])=(1.25±0.27±0.18)×10^{-8}, where the first uncertainty is statistical and the second systematic. The decay mode B^{0}→pp[over ¯] is the rarest decay of the B^{0} meson observed to date. The decay B_{s}^{0}→pp[over ¯] is also investigated. No signal is seen and the upper limit B(B_{s}^{0}→pp[over ¯])<1.5×10^{-8} at 90%confidence level is set on the branching fraction.

Non-leptonic two-body weak decays of Λc(2286)

We study the non-leptonic two-body weak decays of Λc+(2286)→BnM with Bn (M) representing as the baryon (meson) states. Based on the SU(3) flavor symmetry, we can describe most of the data reexamined by the BESIII Collaboration with higher precisions. However, our result of B(Λc+→pπ0)=(5.6±1.5)×10−4 is larger than the current experimental limit of 3×10−4 (90% C.L.) by BESIII. In addition, we find that B(Λc+→Σ+K0)=(8.0±1.6)×10−4, B(Λc+→Σ+η′)=(1.0−0.8+1.6)×10−2, and B(Λc+→pη′)=(12.2−8.7+14.3)×10−4, which are accessible to the BESIII experiments.

Traversable asymptotically flat wormholes in Rastall gravity

There are some gravitational theories in which the ordinary energy–momentum conservation law is not valid in the curved space–time. Rastall gravity is one of the known theories in this regard, which includes a non-minimal coupling between geometry and matter fields. Equipped with the basis of such theory, we study the properties of traversable wormholes with flat asymptotes. We investigate the possibility of exact solutions by a source with the baryonic matter state parameter. Our survey indicates that Rastall theory has considerable effects on the wormhole characteristics. In addition, we study various case studies and show that the weak energy condition may be met for some solutions. We also give a discussion regarding traversibility of such wormhole geometry with phantom sources.

The Λc(2860), Λc(2880), Ξc(3055) and Ξc(3080) as D-wave baryon states in QCD

In this article, we tentatively assign the Λc(2860), Λc(2880), Ξc(3055) and Ξc(3080) to be the D-wave baryon states with the spin-parity JP=32+, 52+, 32+ and 52+, respectively, and study their masses and pole residues with the QCD sum rules in a systematic way by constructing three-types interpolating currents with the quantum numbers (Lρ,Lλ)=(0,2), (2,0) and (1,1), respectively. The present predictions favor assigning the Λc(2860), Λc(2880), Ξc(3055) and Ξc(3080) to be the D-wave baryon states with the quantum numbers (Lρ,Lλ)=(0,2) and JP=32+, 52+, 32+ and 52+, respectively. While the predictions for the masses of the (Lρ,Lλ)=(2,0) and (1,1) D-wave Λc and Ξc states can be confronted to the experimental data in the future.

Instability of baryonic matter in relativistic mean-field models

In this article we evaluate some of the properties of strongly interacting hadronic matter using non-linear Walecka model in relativistic mean-field approximation. We find that due to the coupling of baryons and bosons, baryonic matter develops instability that is characterised by the appearance of baryonic state with negative entropy density. In the region of instability of baryonic matter we find no evidence of negative in-medium mass of baryons or any signal of kaon condensation. Further we find that this instability of baryonic matter can halt the process of first order phase transition from strongly interacting hadronic matter consisting of coupled baryons and bosons to a weakly interacting quark–gluon plasma phase.