Baryon Junction Research Articles

Dependence of net-hyperon production at mid-rapidity on beam energy and its implication on baryon number carrier

The conventional picture of baryon number is that each valence quark inside a baryon carries 1/3 unit of baryon number. However, an alternative picture exists where the center of a Y-shaped topology of gluon fields, called the baryon junction, carries 1 unit of baryon number. Previous analysis suggests that the nature of the baryon number carrier is sensitive to net-proton yields at mid-rapidity in heavy-ion collisions, and experimental measurements potentially challenge the conventional picture. In this study, we analyzed published data from the BES-I program at RHIC, which performed Au+Au collisions at center-of-mass energies ranging from 7.7 to 200 GeV. We investigated the rapidity dependence of net-hyperon yields after correcting for strangeness production suppression, and found that the net-hyperon yields at mid-rapidity follow an exponential dependence on the beam rapidity. This behavior is consistent with Regge model predictions. Moreover, the exponential slopes for net- Λ, net-Ξ, and net-Ω are consistent with each other, suggesting that the baryon transport is flavor blind. Conventional models like PYTHIA, which use valence quarks as the baryon number carrier, have difficulty reproducing this transport behavior.

Search for baryon junctions in e+A collisions at the electron ion collider

Constituent quarks in a nucleon are the essential elements in the standard “quark model” associated with the electric charge, spin, mass, and baryon number of a nucleon. Quantum chromodynamics (QCD) describes nucleon as a composite object containing current quarks (valence quarks and sea (anti-)quarks) and gluons. These subatomic elements and their interactions are known to contribute in complex ways to the overall nucleon spin and mass. In the early development of QCD theory in the 1970s, an alternative hypothesis postulated that the baryon number might manifest itself through a non-perturbative configuration of gluon fields forming a Y-shaped topology known as the gluon junction. In this work, we propose to test such hypothesis by measuring (i) the Regge intercept of the net-baryon distributions for e+(p)Au collisions, (ii) baryon and charge transport in the isobaric ratio between e+Ru and e+Zr collisions, and (iii) target flavor dependence of proton and antiproton yields at large rapidity, transported from the hydrogen and deuterium targets in e+p(d) collisions. Our study indicates that these measurements at the EIC can help determine what carries the baryon number.

Unveiling Baryon Charge Carriers through Charge Stopping in Isobar Collisions.

Utilizing a comprehensive (3+1)D relativistic hydrodynamic framework with multiple conserved charge currents and charge-dependent lattice-QCD-based equation of state, we study the baryon and electric charge number deposition at midrapidity in isobar Ru+Ru and Zr+Zr collisions at the center of mass energy sqrt[s_{NN}]=200 GeV. Comparing our predictions with upcoming experimental data from the Relativistic Heavy Ion Collider will shed light on the existence of baryon junctions.

Studying strangeness and baryon production mechanisms through angular correlations between charged Ξ baryons and identified hadrons in pp collisions at s = 13 TeV

The angular correlations between charged Ξ baryons and associated identified hadrons (pions, kaons, protons, Λ baryons, and Ξ baryons) are measured in pp collisions at s = 13 TeV with the ALICE detector to give insight into the particle production mechanisms and balancing of quantum numbers on the microscopic level. In particular, the distribution of strangeness is investigated in the correlations between the doubly-strange Ξ baryon and mesons and baryons that contain a single strange quark, K and Λ. As a reference, the results are compared to Ξπ and Ξp correlations, where the associated mesons and baryons do not contain a strange valence quark. These measurements are expected to be sensitive to whether strangeness is produced through string breaking or in a thermal production scenario. Furthermore, the multiplicity dependence of the correlation functions is measured to look for the turn-on of additional particle production mechanisms with event activity. The results are compared to predictions from the string-breaking model Pythia 8, including tunes with baryon junctions and rope hadronisation enabled, the cluster hadronisation model Herwig 7, and the core-corona model Epos-lhc. While some aspects of the experimental data are described quantitatively or qualitatively by the Monte Carlo models, no model can match all features of the data. These results provide stringent constraints on the strangeness and baryon number production mechanisms in pp collisions.

Baryon junction and string interactions

We study junctions between confining strings. We show that the effective theory of such junctions is very predictive, with only one new parameter, the junction’s mass, controlling the first couple of terms in the expansion in the system size. By open-closed string duality, these considerations about the baryon junction map to interaction vertices of closed strings. Therefore, we calculate the interaction vertices of closed strings in theories such as Yang-Mills theory. We find some surprising selection rules for string interactions in 3+1 dimensions. Requiring perturbative stability and that the string coupling is weak, we suggest constraints on the junction’s mass. Published by the American Physical Society 2024

Baryon-number — flavor separation in the topological expansion of QCD

Gauge invariance of QCD dictates the presence of string junctions in the wave functions of baryons. In high-energy inclusive processes, these baryon junctions have been predicted to induce the separation of the flows of baryon number and flavor. In this paper we describe this phenomenon using the analog-gas model of multiparticle production proposed long time ago by Feynman and Wilson and adapted here to accommodate the topological expansion in QCD. In this framework, duality arguments suggest the existence of two degenerate junction-antijunction glueball Regge trajectories of opposite C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{C} $$\\end{document}-parity with intercept close to 1/2. The corresponding results for the energy and rapidity dependence of baryon stopping are in reasonably good agreement with recent experimental findings from STAR and ALICE experiments. We show that accounting for correlations between the fragmenting strings further improves agreement with the data, and outline additional experimental tests of our picture at the existing (RHIC, LHC, JLab) and future (EIC) facilities.

Search for baryon junctions in photonuclear processes and isobar collisions at RHIC

During the early development of quantum chromodynamics, it was proposed that baryon number could be carried by a non-perturbative Y-shaped topology of gluon fields, called the gluon junction, rather than by the valence quarks as in the QCD standard model. A puzzling feature of ultra-relativistic nucleus-nucleus collisions is the apparent substantial baryon excess in the mid-rapidity region that could not be adequately accounted for in most conventional models of quark and diquark transport. The transport of baryonic gluon junctions is predicted to lead to a characteristic exponential distribution of net-baryon density with rapidity and could resolve the puzzle. In this context we point out that the rapidity density of net-baryons near mid-rapidity indeed follows an exponential distribution with a slope of -0.61±0.03\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-0.61\\pm 0.03$$\\end{document} as a function of beam rapidity in the existing global data from A+A collisions at AGS, SPS and RHIC energies. To further test if quarks or gluon junctions carry the baryon quantum number, we propose to study the absolute magnitude of the baryon vs. charge stopping in isobar collisions at RHIC. We also argue that semi-inclusive photon-induced processes (γ+p\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma +p$$\\end{document}/A) at RHIC kinematics provide an opportunity to search for the signatures of the baryon junction and to shed light onto the mechanisms of observed baryon excess in the mid-rapidity region in ultra-relativistic nucleus-nucleus collisions. Such measurements can be further validated in A+A collisions at the LHC and e+p\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e+p$$\\end{document}/A collisions at the EIC.

Signatures of baryon junctions in semi-inclusive deep inelastic scattering

Local gauge invariance of the baryon wave function leads to the emergence of a baryon junction, where three (or N, in SU(N) gauge theory) string operators merge. The existence of baryon junction dramatically affects the dynamics of baryon stopping at high energies, and the corresponding predictions are supported by the recent data from STAR Collaboration at the Relativistic Heavy Ion Collider. Here we outline the ways in which the baryon junctions can be tested in semi-inclusive deep inelasttic scattering at Jefferson Laboratory and the future Electron Ion Collider.

Correlations of baryon and charge stopping in heavy ion collisions* *Supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB34030000) and the National Key Research and Development Program of China (2022YFA1604900), the U.S. DOE Office of Science365 under contract (DE-SC0012704, DE-FG02-10ER41666, DE-AC02-98CH10886)

Baryon numbers are theorized to be carried by valence quarks in the standard QCD picture of the baryon structure. Another theory proposed an alternative baryon number carrier, a non-perturbative Y-shaped configuration of the gluon field, called the baryon junction in the 1970s. However, neither of these theories has been verified experimentally. Recently, searching for the baryon junction by investigating the correlation of net-charge and net-baryon yields at midrapidity in heavy-ion collisions has been suggested. This paper presents studies of such correlations in collisions of various heavy ions from oxygen to uranium with the UrQMD Monte Carlo model. The UrQMD model implements valence quark transport as the primary means of charge and baryon stopping at midrapidity. Detailed studies are also conducted for isobaric + and + collisions. We found a universal trend of charge stopping with respect to baryon stopping and discovered that the charge stopping is always greater than the baryon stopping. This study provides a model baseline in valence quark transport for what is expected in net-charge and net-baryon yields at the midrapidity of relativistic heavy-ion collisions.

Investigation of the high-pT strange baryon anomalies at RHIC

Results from RHIC have shown that there is an enhanced baryon/meson ratio in the intermediate transverse momentum range (2<pT<6 GeV/c) in Au+Au collisions at both \(\sqrt{s_{NN}}\) =130 and 200 GeV. This was initially demonstrated by measurements of the p/π- ratio which was then extended in pT by the Λ/K0S ratio. The data were successfully described by models utilising different hadronization mechanisms: those having recombination of quarks and others having an interplay between flow, jet quenching and incorporating baryon junction loops. The strange particle data from the first Au+Au run at \(\sqrt{s_{NN}}\) =200 GeV gave tantalising hints that the observed enhancement of baryons compared to mesons was diminished by a pT of 6 GeV/c, but a lack of statistics in this range made a definitive statement impossible. Here we present an extended analysis of identified strange baryons and mesons in Au+Au collisions at \(\sqrt{s_{NN}}\) =200 GeV using data obtained by the STAR experiment from the 2004 running period. The increase in statistics extends the measurement of Λ hyperons out to at least 7 GeV/c and K0S mesons out to 9 GeV/c. This data allows us to place limits on the range where in-vacuum fragmentation functions are applicable and the effect of baryon dominance is reduced. We also discuss the prospects for making these measurements using multiply-strange baryons and mesons (Ω and ϕ).

Stopping and Baryon Transport in Heavy Ion Reactions

In this report I will give an experimental overview on nuclear stopping in hadron collisions, and relate observations to understanding of baryon transport. Baryon number transport is not only evidenced via net-proton distributions but also by the enhancement of strange baryons near mid-rapidity. Although the focus is on high-energy data obtained from pp and heavy ions from RHIC, relevant data from SPS and ISR will be considered. A discussion how the available data at higher energy relates and gives information on baryon junction, quark-diquark breaking will be made.

Forward and midrapidity like-particle ratios from [formula omitted] collisions at [formula omitted

We present a measurement of π−/π+, K−/K+ and p¯/p from p+p collisions at s=200 GeV over the rapidity range 0<y<3.4. For pT<2.0 GeV/c we see no significant transverse momentum dependence of the ratios. All three ratios are independent of rapidity for y≲1.5 and then steadily decline from y∼1.5 to y∼3. The π−/π+ ratio is below unity for y>2.0. The p¯/p ratio is very similar for p+p and 20% central Au+Au collisions at all rapidities. In the fragmentation region the three ratios seem to be independent of beam energy when viewed from the rest frame of one of the protons. Theoretical models based on quark–diquark breaking mechanisms overestimate the p¯/p ratio up to y≲3. Including additional mechanisms for baryon number transport such as baryon junctions leads to a better description of the data.

Baryon junction loops and the baryon-meson anomaly at high energies

A new version, v2.0, of the $\mathrm{HIJING}∕B\overline{B}$ Monte Carlo nuclear collision event generator is introduced in order to explore further the possible role of baryon junctions loops in the baryon-meson anomaly $(2&lt;{p}_{T}&lt;5\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c)$ observed in $200A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ $\mathrm{Au}+\mathrm{Au}$ reactions at RHIC. We show that junction loops with an enhanced intrinsic ${k}_{T}\ensuremath{\approx}1\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c$ transverse momentum kick may provide a partial explanation of the anomaly as well as other important baryon stopping observables.

High- p T pion quenching versus anti+baryon enhancement in nucleus-nucleus collisions

Jet quenching of quarks and gluons in central A + A collisions suppresses the high- p T meson production and exposes novel baryon dynamics that we attribute to (gluonic) baryon junctions. This mechanism predicts baryon enhancement in a finite moderate- p T window that decreases with increasing impact parameter. We also extend recent calculations of the transverse momentum behavior of p/π + and p ¯ / π − to other baryon species and show that a similar pattern is expected for the K −/Λ and K + / Λ ¯ ratios. Within the framework of the model constant p ¯ / p and Λ ¯ / Λ ratios are found in central Au + Au collisions at RHIC energies up to p T ≅ 4 – 5 GeV.

Can one understand stopping in heavy ion collisions without an anomalous mechanism?

We show that the baryon stopping observed in heavy ion collisions both at CERN-SPS and at RHIC can be understood using the same mechanism as in proton–proton collisions. No increase in the size of the baryon junction component is required between small size ( pp) and large size ( AA) systems.

Jet quenching and thep¯≳π−anomaly in heavy ion collisions at relativistic energies

PHENIX data on Au+Au at root(s)_= 130 AGeV suggest that p-bar yields may exceed pi- at high p_T > 2 GeV/c. We propose that jet quenching in central collisions suppresses the hard PQCD component of the spectra in central A+A reactions, thereby exposing a novel component of baryon dynamics that we attribute to (gluonic) baryon junctions. We predict that the observed p-bar >= pi- and the p > pi+ anomaly at p_T ~ 2 GeV/c is limited to a finite p_T window that decreases with increasing impact parameter.

Antihyperon Enhancement through Baryon Junction Loops

The baryon junction exchange mechanism recently proposed to explain valence baryon number transport in nuclear collisions is extended to study midrapidity anti-hyperon production. Baryon junction-anti-junction (J anti-J) loops are shown to enhance anti-Lambda, anti-Xi, anti-Omega yields as well as lead to long range rapidity correlations. Results are compared to recent WA97 Pb + Pb -> Y + anti-Y + X data.

Baryon junction stopping at the SPS and RHIC via HIJING/B

Baryon stopping at the SPS and RHIC energies is calculated by introducing a new baryon junction mechanism into HIJING. The exchange of a baryon junction, according to Regge phenomenology, leads to a cosh[(y − y CM)/2] rapidity dependence and an 1/ 4s energy dependence of the inclusive baryon cross section. This baryon junction dynamics also leads naturally to enhanced p T broadening in pA and AA together with enhanced mid-rapidity hyperon production.