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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Hidden-strangeness tetraquarks in the dynamical diquark model

The dynamical diquark model describes multiquark exotic hadrons in terms of diquark components nucleated by heavy quarks and successfully explains multiple features of hidden-charm and hidden-bottom exotics. Here, we apply the model to the marginally heavy case of hidden-strange states to probe whether mesons near 2 GeV with peculiar properties, such as 𝜙⁡(2170), 𝑓 2 ⁡(2340), and 𝑋⁡(2370), are possible tetraquark candidates. We calculate spin-multiplet average masses using potentials obtained through lattice simulations and quark models, and we also describe the detailed spectra of the expected multiplets as a diagnostic to discern the nature of future hadrons likely to be discovered in this mass region by experiments at facilities such as BESIII, JLab, and the EIC.

Bound states↗
DOE OSTI2025

The impact of $γN$ and $γ^∗N$ interactions on our understanding of nucleon excitations

We review recent progress in our understanding of the nucleon excitation spectrum. Thanks to dedicated efforts at facilities such as ELSA, MAMI and Jefferson Lab, several new nucleon resonances have been discovered, and evidence for previously elusive states has been significantly improved. Numerous decay channels have been observed for the first time, and resonance properties are being extracted from these data by several groups through coupled-channel analyses of varying complexity. Electroproduction experiments have provided further insights into the internal structure of light baryon resonances – for example, the long-debated Roper resonance N (1440) is observed as a three-quark state with a significant meson-cloud component. While the non-relativistic quark model remains a valuable tool for organizing the spectrum of nucleon and Δ resonances, a variety of theoretical frameworks have emerged to offer deeper understanding, including phenomenological quark models, holographic QCD, functional methods, effective field theories, and lattice QCD. We examine the interplay between these approaches, highlight their respective strengths and explore how they complement each other in shaping our knowledge of light baryon resonances. We address several open questions in baryon spectroscopy, including the nature of the enigmatic Λ (1405), ongoing searches for exotic states such as hybrid baryons and pentaquarks, and the dichotomy between microscopic descriptions of baryons in terms of quarks and gluons versus effective hadronic descriptions based on meson-baryon dynamics.

Baryon resonances↗
DOE OSTI2024

Search for Θ+ in KLp→K+n reaction in KLF at JLab

The possibility of the existence of multiquark hadrons made of 4-quarks for mesons and 5-quarks for baryons was predicted by Gell-Mann [Phys. Lett. 8, 214 (1964)]. The renewed interest for the search for exotic pentaquark states was initiated by the paper by Diakonov, Petrov, and Polyakov [Z. Phys. A 359, 305 (1997)]. The 2003 experimental reports on the observation of [Formula: see text] pentaquark with [Formula: see text] quark content created a great excitement and many following experiments have reported its observation [K. H. Hicks, Eur. Phys. J. H 37, 1 (2012)]. After high-statistics experiments at JLab, which did not confirm previous claims by the CLAS collaboration, the community concluded that the [Formula: see text] pentaquark either does not exist at all or has an extremely small cross-section, making it currently unobserved. There were different review papers on this subject, questioning the existence of [Formula: see text] or trying to explain the reasons why reaching a conclusion based on production experiments is challenging [M. Amaryan, Eur. Phys. J. Plus 137, 684 (2022)]. To address the challenge of minimal 3-body final states, a formation experiment with a projectile-kaon beam is proposed. In the following, we discuss how the [Formula: see text] could be observed in the [Formula: see text] reaction in the KLF experiment at JLab [M. Amaryan et al. [KLF Collaboration], arXiv:2008.08215 [nucl-ex]].

Astronomy & Astrophysics↗
DOE OSTI2026

Electromagnetic production of kaons on the nucleon

Studies of the electromagnetic production of strange quarks started in the 1950s as something of a curiosity that puzzled experimentalists and theorists alike. Eventually, a nascent understanding of these processes began to take shape through the first pioneering experiments dedicated to explore photo- and electroproduction that were carried out in the period from the 1950s to the 1980s. As the datasets increased, concomitant advances in theoretical models were realized. However, these initial studies also made clear that more precise data was essential to continue to move forward. A paradigm shift occurred in the 1990s with the development of second-generation facilities at ELSA, MAMI, SPring-8, and JLab. High-intensity, high duty-factor accelerators, coupled with novel detector systems and advances in computing and readout electronics, brought nuclear physics experiments forward by orders of magnitude in counting statistics compared to the first-generation efforts. This was an utter boon to strangeness physics investigations, and to date, more than 50 dedicated experiments in kaon photo- and electroproduction have been completed at facilities around the world, leading to a host of experimental observables that have enabled significant advances in the exploration of strongly interacting systems that decay via $s\bar{s}$ quark pair creation. These data have proven to be an essential complementary pathway to study the spectrum and structure of the excited states of the nucleon, and the search for missing and exotic baryon configurations. As well, investigations in these channels are requisite for exploring hypernuclear production as a probe of the $YN$ interaction and for studies of the electromagnetic form factors of strange mesons. This review was designed to provide the first-ever in-depth overview of both the experimental and theoretical progress in the field of the electromagnetic production of strangeness. This work looks back over 70 years of past developments, discusses ongoing work and near-term plans, and details future possibilities being considered for third-generation facilities. Extensive lists of the available datasets and theoretical models are provided, together with a comprehensive supporting bibliography of the field. Throughout this work, the primary impacts of these explorations are highlighted, along with connections to a wide range of related phenomenological applications. An important goal of this review is to provide a complete, (reasonably) self-contained guide into this field prepared at a level that is relevant for both new and seasoned scientists, whether experimentalists, phenomenologists, or theorists, to better understand what has been accomplished by so many dedicated folks-each building on what has come before-and to appreciate the exciting future potential for continued studies in this area.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

PHOTOPRODUCTION OF np^0 BY DOUBLE-REGGE EXCHANGE

The GlueX experiment is a photoproduction experiment based at Jeferson Lab in Newport News, Virginia. A major aim of GlueX is to look for hybrid mesons, which are a quark and an anti-quark bound by an excited gluonic field that contributes to the quantum numbers. The reaction ¿p ¿ ¿e0p is of particular interest since ¿e is a potential decay mode of states with exotic quantum numbers JPC =1¿+, which are forbidden in the constituent quark model. Finding such a resonance would be a clear sign of non-quark model physics. In concert with the Joint Physics Analysis Center we have developed a model for double-Regge interactions in this channel. These non-resonant processes generate asymmetries in the distributions of decay angles, which could be falsely attributed to the interference between exotic odd partial waves and even partial waves. In previous searches for light exotics we have seen evidence for the necessity of accounting for the presence of these non-resonant productions. We present a double-Regge model for photoproduction of ¿e0 and the application of it by measuring the asymmetry of ¿e0 production in the double Regge limit, as well as a comparison of the measured results to current theoretical predictions.

Barsotti, Rebecca [Indiana Univ. Southeast, New Al↗
DOE OSTI2023

Search for a Singly Strange Hexaquark Using Polarization Data From CLAS12 at Jefferson Lab Virginia

Recently hadron spectroscopy has seen a lot of success. There has been a large number of baryon and meson resonances discovered over the last two decades. There have also been several tetra and pentaquark candidates with experimental evidence but not confirmed. The first serious candidate was the X(3872), a potential tetraquark, leading to this rise in success for exotic hadron physics. This has brought about improvements in Quantum Chromo Dynamics (QCD), our current best description of interactions between quarks and gluons. QCD predicts the existence of hexaquark states, and then the d*(2380) was discovered. This thesis explores the rest of the d* Jp =3+ anti-decuplet by searching for experimental evidence of the ds hexaquark. This is the first analysis of the e'd ¿e'K+d0 s ¿e'K+¿n channel using the Py' measurements of the ¿ as a lens to perform this search. This observable was extracted from ¿ electroproduction events off a liquid deuterium target. From this an upper limit of the Breit-Wigner peak strength was extracted. This was done with the use of the CLAS12 detector system housed at Thomas Jefferson Laboratory in Virginia, USA. These polarization measurements are the first to be made on this data, and this is the first time the ds has been searched for in such a way.

Clash, Geraint↗
DOE OSTI2021

Self-interacting neutrinos: Solution to Hubble tension versus experimental constraints

Exotic self-interactions among the Standard-Model neutrinos have been proposed as a potential reason behind the tension in the expansion rate, H 0 , of the universe inferred from different observations. We constrain this proposal using electroweak precision observables, rare meson decays, and neutrinoless double-β decay. In contrast to previous works, we emphasize the importance of carrying out this study in a framework with full Standard-Model gauge invariance. We implement this first by working with a relevant set of Standard- Model-Effective-Field-Theory operators and subsequently by considering a UV completion in the inverse See-Saw model. We find that the scenario in which all flavors of neutrinos self-interact universally is strongly constrained, disfavoring a potential solution to the H 0 problem in this case. The scenario with self-interactions only among tau neutrinos is the least constrained and can potentially be consistent with a solution to the H 0 problem.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Latest D0 results on exotic hadrons produced in $p\bar p $ collision

Prompt and nonprompt productions of exotic multiquark states are studied using the $\sim$10.4~fb$^{-1}$ data sample collected by the D0 experiment in Tevatron $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV. The recent D0 results on the prompt and nonprompt production of the $X(3872)$ and $Z_c^+(3900)$ states and the $P_c$ pentaquarks at the 4450~MeV region are reported. Signals corresponding to these states are found in the nonprompt production, whereas only the $X(3872)$ state is seen in the prompt production. The ratio of prompt to nonprompt $X(3872)$ production is about three times larger in the D0 measurement than that obtained by the ATLAS experiment at 8 TeV. Theoretically, the production, formation, coalescence, and disassociation processes are expected to be quite different for conventional mesons with a spatial size of (0.4-0.8) fm, compact multiquark states such as tetraquarks with a size of a few fm, and spatially extended molecular states with a size of (4-10) fm. They can be differently affected in prompt hadron-hadron collisions where there are many additional particles emitted from the interaction point. Consequently, the prompt to nonprompt production ratio of spatially extended exotic states can be suppressed at LHC comparing with the Tevatron conditions, because of large difference in the hadron-hadron collisions particle multiplicity. The prompt production studies provide an opportunity to better understand the nature of exotic states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Glueballs at physical pion mass

Glueballs are investigated through gluonic operators on two $ N_f=2+1 $ RBC/UKQCD gauge ensembles at the physical pion mass. The statistical errors of glueball correlation functions are considerably reduced through the cluster decomposition error reduction (CDER) method. The Bethe-Salpeter wave functions are obtained for the scalar, tensor, and pseudoscalar glueballs by using spatially extended glueball operators defined through the gauge potential $ A_\mu(x) $ in the Coulomb gauge. These wave functions exhibit similar features of non-relativistic two-gluon systems and are used to optimize the signals of the related correlation functions at the early time regions, where the ground state masses are extracted. These masses are close to those from the quenched approximation and indicate the possible existence of glueballs at the physical point. The resonance feature of glueballs and the mixing with conventional mesons and multi-hadron systems should be considered in a more systematic lattice study.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Isotopic equilibrium constants for very low-density and low-temperature nuclear matter

Yields of equatorially emitted light isotopes, 1 ≤ Z ≤ 14, observed in ternary fission in the reaction 241 Pu(n th, f) are employed to determine apparent chemical equilibrium constants for low-temperature and low-density nuclear matter. The degree of equilibration and role of medium modifications are probed through a comparison of experimentally derived reaction quotients with equilibrium constants calculated using a relativistic mean-field model employing a universal medium modification correction for the attractive σ meson coupling. The results of these comparisons indicate that equilibrium is achieved for the lighter ternary fission isotopes. For the heavier isotopes experimental reaction quotients are well below calculated equilibrium constants. This is attributed to a dynamical limitation reflecting insufficient time for full equilibrium to develop. The role of medium effects leading to yield reductions is discussed as is the apparent enhancement of yields for 8 He and other very neutron rich exotic nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Baryon-baryon, meson-meson, and meson-baryon interactions in nonrelativistic QCD

Van der Waals potentials describing interactions between color-singlet mesons and/or baryons vanish at leading order in potential nonrelativistic quantum chromodynamics (pNRQCD). This result and constraints from Gauss’s law are used to prove that weakly coupled pNRQCD van der Waals potentials in generic non-Abelian gauge theories with only heavy quarks are too weak to form bound states whose color state is a product of color singlets. Quantum Monte Carlo calculations of four, five, and six quarks with equal masses provide numerical evidence that exotic color configurations are higher energy than products of color-singlet hadrons, suggesting that equal-mass fully heavy tetraquark, pentaquark, and hexaquark bound states do not exist at next-to-leading order in pNRQCD and at all orders in QCD-like theories in which all quark masses are asymptotically large. Mechanisms for generating hadron-hadron bound states are identified, which necessarily involve large quark-mass hierarchies, relativistic effects arising from the presence of sufficiently light quarks, or nonperturbative effects outside the scope of weakly coupled pNRQCD.

Effective field theory↗
DOE OSTI2020

Study of Heavy Flavor Mesons and Flavor-Tagged Jets with the CMS Detector

The goal of this research program is to implement heavy flavor meson triggers in heavy-ion collisions for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) at CERN, including algorithm design, timing studies, offline validation, and online performance monitoring. The physics analyses which can be achieved by data from these new triggers is to address one of the most important questions in the field: parton flavor dependence of jet-quenching for the understanding of the transport properties of the Quark-Gluon Plasma. This program will allow CMS to collect the highest statistics heavy flavor meson and jet data ever recorded in heavy-ion colliders. The program includes two objectives: (1) Build and maintain the heavy flavor meson and jet triggers for heavy-ion collisions and deploy the trigger algorithms for 2015-2018 PbPb and pPb run at the LHC; (2) Perform heavy flavor meson and jet physics analyses, which can be used to study the parton flavor dependence of jet quenching, to extract the elastic energy loss coefficient of the QGP, and to test whether massive quarks also participate in collective expansion dynamics in heavy-ion collisions. With the heavy flavor physics trigger developed in this project, a competitive heavy flavor physics program in heavy-ion collisions has been established in CMS. This program allows studies of the fully reconstructed and flavor identified charm, beauty, and exotic hadrons that cover the widest transverse momentum range. The novel measurements supported by the award provide new constraints on the size of the flavor dependence of parton energy loss, the value of the in-medium charm quark diffusion coefficient, the mechanism of charm and beauty quark hadronization, and provide new insights to the nature of the X(3872) hadron.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

First measurement of 𝑎$^{0}_{2}$⁡(1320) polarized photoproduction cross section

We measure for the first time the differential photoproduction cross section dσ/dt of the a 2 (1320) meson at an average photon beam energy of 8.5 GeV, using data with an integrated luminosity of 104 pb −1 collected by the GlueX experiment. We fully reconstruct the γp → ηπ 0 p reaction and perform a partial-wave analysis in the a 2 (1320) mass region with amplitudes that incorporate the linear polarization of the beam. This allows us to separate for the first time the contributions of natural- and unnatural-parity exchanges. Furthermore, these measurements provide novel information about the photoproduction mechanism, which is critical for the search for spin-exotic states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

$$\pi ^-p\rightarrow \eta ^{(\prime )}\, \pi ^- p$$ in the double-Regge region: Joint Physics Analysis Center

Abstract The production of $$\eta ^{(\prime )}\pi $$ η ( ′ ) π pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to $$\eta ^{(\prime )}\pi $$ η ( ′ ) π production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction $$\pi ^-p\rightarrow \eta ^{(\prime )} \pi ^- \,p$$ π - p → η ( ′ ) π - p measured by COMPASS. We show that the data in $$2.4< m_{\eta ^{(\prime )}\pi } < 3.0{\mathrm {\,GeV}} $$ 2.4 < m η ( ′ ) π < 3.0 GeV can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the $$\eta ' \pi $$ η ′ π channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Searching for leptoquarks at future muon colliders

A high energy muon collider can provide new and complementary discovery potential to the LHC or future hadron colliders. Leptoquarks are a motivated class of exotic new physics models, with distinct production channels at hadron and lepton machines. We study a vector leptoquark model at a muon collider with √s = 3, 14 TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe leptoquark masses up to an order of magnitude beyond √s with perturbative couplings. Additionally, we can also probe regions of parameter space unavailable to flavor experiments. In particular, all of the parameter space of interest to explain recent low-energy anomalies in B meson decays would be covered even by a √s = 3 TeV collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Higgs production in association with a dark-Z at future electron positron colliders

In recent years there have been many proposals for new electron–positron colliders, such as the circular electron–positron collider, the international linear collider, and the future circular collider in electron–positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the hZ threshold. However, there are proposals to run these colliders at the lower WW threshold and Z -pole energies. In this paper, we study a new search for Higgs physics accessible at lower energies: e + e – → hZ d , where Z d is a new light gauge boson such as a dark photon or dark- Z . Such searches can be conducted at the WW threshold, i.e. energies below the hZ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron–positron colliders, these searches will be sensitive to Z d masses below 1 GeV, which is lower than the current direct LHC searches. Here, we will show that at $\sqrt{s}=160$ GeV with 10 ab –1 , a search for e + e – → hZ d is sensitive to h – Z – Z d couplings of δ ~ 9 × 10 –3 and cross sections of $\sim 2-3$ ab for Z d masses below 1 GeV. The results are similar at $\sqrt{s}=240$ GeV with 5 ab –1 . These limits are better than those expected from limits on the HL-LHC limits on Higgs branching ratio into generic non-standard model final states and comparable to meson decay limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for π 0 decays to invisible particles

The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 10 9 tagged π0 mesons from K + → π + π 0 (γ), searching for the decay of the π 0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10 –9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K + → π + X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c 2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗