Quark Research Articles

Three-zero texture of quark-mass matrices as a solution to the strong CP problem

The strong charge-parity (CP) problem has been a long-standing problem in particle physics since 1976, illustrating the small CP-violation phase in quantum chromodynamics (QCD). The axion, based on the Peccei–Quinn mechanism, is the most popular solution to the problem. In this paper, we propose an alternative solution based on the three-zero texture of quark mass matrices without additional heavy quark states, which has been shown to fit data well. We show that the required three-zero texture is naturally constructed in a six-dimensional spacetime with a T2/Z3 orbifold compactification.

Productions of bottom and bottom-strange mesons in pion and kaon induced reactions

In the present work, we propose to explore the productions of the bottom and bottom-strange mesons in the high-energy pion and kaon-induced reactions on a proton target. The cross sections are evaluated with an effective Lagrangian constructed by the heavy-quark limit and chiral symmetry. Our estimations show that at Pπ=80\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_\\pi =80$$\\end{document} GeV, the cross sections for B(5279), B∗(5325)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^*(5325)$$\\end{document}, B0∗(5722)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_0^*(5722)$$\\end{document}, B1′(5716)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_1^\\prime (5716)$$\\end{document}, B1(5721)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_1(5721)$$\\end{document} and B2∗(5747)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_2^*(5747)$$\\end{document} production processes are estimated to be 3.19–86.26, 1.86–51.29, 0.88–24.33, 0.86–23.69, 162.35–4477.66, and 57.16–1604.43 nb, respectively, where uncertainties arise from the model parameter. In addition, the cross sections for the corresponding bottom-strange mesons production processes are very similar. From the heavy quark effective theory point of view, the ratios between the cross sections for bottom mesons and bottom-strange mesons should be similar and the present estimations are consistent with the expectation of heavy quark limit. In particular, the cross-section ratios related to the states in the same doublets are of order one. The cross sections related to the states in the T doublets are about two orders larger than those related to the states in the S doublets.

Repulsive Vector Couplings and Massive Strange Stars

ABSTRACTWe describe in this work the hypothetical nuclear matter QCD phase composed of up, down and strange quarks, introducing repulsive vector interactions, which yield an enhanced MIT bag model (vMIT). Repulsive interactions seem a crucial ingredient to describe stable (and massive hybrid) compact star configurations, to comply with recent observations of pulsars with masses above . The motivation of our study, based on a known and widespread theoretical approach, is to review some of its foundations in view of recent observational advances on pulsar properties with a higher precision measurements. We address in this contribution the stability of compact stars with vector interactions, highlighting also the role of the bag constant and its impact on the stellar incompressibility. Therefore we reassess the proposal formulated by Bodmer, Terazawa, Witten, Farhi, and Jaffe, which suggests that strange quark matter may actually be more stable than ordinary hadronic matter. On this line of investigation, we analyze the dimensionless tidal deformability constraints of the intriguing central compact object (CCO) within the supernova remnant HESS J1731‐347 and the GW170817 event as strange matter candidates.

Heavy Quark Contributions in Bjorken Sum Rule with Analytic Coupling

We consider heavy quark contributions to the polarized Bjorken sum rule. We found good agreement between the experimental data and the predictions of analytic QCD. To satisfy the limit of photoproduction, we use new representation of the perturbative part of the polarized Bjorken sum rule, recently proposed.

Hybrids, tetraquarks, pentaquarks, doubly heavy baryons, and quarkonia in Born-Oppenheimer effective theory

The discovery of XYZ exotic states in the hadronic sector with two heavy quarks represents a significant challenge in particle theory. Understanding and predicting their nature remains an open problem. In this work, we demonstrate how the Born-Oppenheimer (BO) effective field theory (BOEFT), derived from quantum chromodynamics (QCD) on the basis of scale separation and symmetries, can address XYZ exotics of any composition. We derive the Schrödinger coupled equations that describe hybrids, tetraquarks, pentaquarks, doubly heavy baryons, and quarkonia at leading order, incorporating nonadiabatic terms, and present the predicted multiplets. We define the static potentials in terms of the QCD static energies for all relevant cases. We provide the precise form of the nonperturbative low-energy gauge-invariant correlators required for the BOEFT: static energies, generalized Wilson loops, gluelumps, and adjoint mesons. These are to be calculated on the lattice, and we calculate here their short-distance behavior. Furthermore, we outline how spin-dependent corrections and mixing terms can be incorporated using matching computations. Lastly, we discuss how static energies with the same BO quantum numbers mix at large distances leading to the phenomenon of avoided level crossing. This effect is crucial to understand the emergence of exotics with molecular characteristics, such as the χc1(3872). With BOEFT both the tetraquark and the molecular picture appear as part of the same description. Published by the American Physical Society 2024

Doubly heavy tetraquark bound and resonant states

We calculate the energy spectrum of the S-wave doubly heavy tetraquark systems, including the QQ(′)q¯q¯, QQ(′)s¯q¯, and QQ(′)s¯s¯ (Q(′)=b, c and q=u, d) systems within the constituent quark model. We use the complex scaling method to obtain bound states and resonant states simultaneously, and the Gaussian expansion method to solve the complex-scaled four-body Schrödinger equation. With a novel definition of the root-mean-square radii, we are able to distinguish between meson molecules and compact tetraquark states. The compact tetraquarks are further classified into three different types with distinct spatial configurations: compact even tetraquarks, compact diquark-antidiquark tetraquarks, and compact diquark-centered tetraquarks. In the I(JP)=0(1+) QQq¯q¯ system, there exists the D*D molecular bound state with a binding energy of −14 MeV, which is the candidate for Tcc(3875)+. The shallow B¯*B¯ molecular bound state is the bottom analog of Tcc(3875)+. Moreover, we identify two resonant states near the D*D* and B¯*B¯* thresholds. In the JP=1+ bbq¯q¯(I=0) and bbs¯q¯ systems, we obtain deeply bound states with a compact diquark-centered tetraquark configuration and a dominant χ3¯c⊗3c component, along with resonant states with similar configurations as their radial excitations. These states are the QCD analog of the helium atom. We also obtain some other bound states and resonant states with “QCD hydrogen molecule” configurations. Moreover, we investigate the heavy quark mass dependence of the I(JP)=0(1+) QQq¯q¯ bound states. We strongly urge the experimental search for the predicted states. Published by the American Physical Society 2024

Power corrections to quasidistribution amplitudes of a heavy meson

It has been recently demonstrated that light cone distribution amplitudes (LCDAs) for a heavy meson, defined in the heavy quark limit, can be extracted by simulating quasidistribution amplitudes on the lattice with a large meson momentum Pz. This extraction involves a two-step procedure. In the first step, the quasidistribution amplitudes are matched onto the QCD LCDAs in the large Pz limit. In the second step, the QCD LCDAs are matched onto the desired LCDAs defined in heavy quark effective theory. In this work, we present the mH2n/(Pz)2n and ΛQCD2/(xPz)2 and ΛQCD2/((1−x)Pz)2 corrections in the first step with mH being the heavy meson mass and x being the momentum fraction of the light quark. To account for mH2n/(Pz)2n corrections, we employ two methods: the moment relation that can provide mass corrections to all orders, and a leading-twist projector that gives the leading-order mass corrections. For the ΛQCD2/(Pz)2 corrections, we employ a renormalon model that addresses the renormalon ambiguity stemming from the divergence of the perturbative series. We adopt two parametrizations for QCD LCDAs to conduct a numerical analysis. The results suggest that these corrections are typically smaller than 20% in the region 0.2<x<0.8, and should be included in a precision analysis. These findings will serve as a valuable guide for future studies on heavy meson LCDAs, particularly in the context of lattice QCD, where accounting for such corrections is crucial for improving the accuracy and reliability of the results. Published by the American Physical Society 2024

Detecting the flavor content of the vacuum using the Dirac operator spectrum

We compute the overlap Dirac spectrum on three gauge ensembles generated using 2+1-flavor domain wall fermions. The three ensembles have different lattice spacings, and two of them have quark masses tuned to the physical point. The spectral density is determined up to λ∼100 MeV with subpercentage statistical uncertainty. We find that the density is close to a constant below λ∼20 MeV as predicted by chiral perturbative theory (χPT) and then increases linearly due to the strange quark mass. By fitting to the next-to-leading order χPT form and using the nonperturbative renormalization using the regularization independent momentum subtraction scheme, the SU(2) (keeping the strange quark mass at the physical point) and SU(3) chiral condensates at MS¯ 2 GeV are determined to be Σ=(265.4(0.5)(4.2) MeV)3 and Σ0=(234.3(0.5)(25.8) MeV)3, respectively. The pion decay constants are also determined to be F=84.1(1.9)(8.0) and F0=58.6(0.5)(10.0) MeV. The systematic errors are carefully estimated including the effects of fitting ranges and the uncertainty of low-energy constant L6. We also show that one can resolve the sea flavor content of the sea quarks and constrain their masses with ∼10%–20% statistical uncertainties using the Dirac spectral density. Published by the American Physical Society 2024

Challenges in the extraction of physics beyond the Standard Model from electron scattering

Abstract Precise measurements of electron and positron scattering, including parity violation, offer great promise in the search for physics beyond the Standard Model. In this context it is crucial to understand the corrections which might arise from charge symmetry violation, as well as the less well known strange and charm quark distributions. Our analysis, using state of the art parton distributions, suggests that these contributions lead to corrections in the extraction of the weak couplings $g^{eq}_{AV}$ and $g^{eq}_{VA}$ of the order $(1-2)\%$, while they are as large as $4\%$ for $g^{eq}_{AA}$, at a typical scale of $Q^2 = 10\ {\rm GeV}^2$. These results underline the importance of carrying out high precision measurements, which will not only provide information on physics beyond the Standard Model but also reduce the current uncertainties on our knowledge of the strange and charm quark distributions in the proton.

2B or not 2B, a study of bottom-quark-philic semi-visible jets

Semi-visible jets arise in strongly interacting dark sectors, resulting in jets overlapping with the missing transverse momentum direction. The implementation of semi-visible jets is done using the Pythia Hidden Valley module to mimic the QCD sector showering in so-called dark shower. In this work, only heavy flavour Standard Model quarks are considered in dark shower, resulting in a much less ambiguous collider signature of semi-visible jets compared to the democratic production of all five quark flavours in dark shower. The constraints from available searches on this signature are presented, and it is shown the signal reconstruction can be improved by using variable-radius jets. Finally a search strategy is suggested.

Heavy quark mass near the phase transition

Abstract Assuming that the number densities of heavy flavor in hadron gas and in QGP are same at $T_c$, we obtain the effective mass of heavy quark at $T_c$ from the comparison with the hadron resonance gas model which well describes particle yield in heavy-ion collisions. We find that charm quark mass at vanishing baryon chemical potential is around 1.8 GeV which is much heavier than QCD bare mass and close to $D$ meson mass. The mass slightly increases with increasing baryon chemical potential and then decreases.
On the other hand, anticharm quark mass constantly decreases with increasing baryon chemical potential. Bottom quark mass has a similar pattern. Extending the hadron resonance gas model to a bit higher temperature beyond $T_c$, the effective masses of charm and bottom quarks decrease with increasing temperature.

Hard-scattering approach to strongly hindered electric dipole transitions between heavy quarkonia

The conventional wisdom in dealing with electromagnetic transition between heavy quarkonia is the multipole expansion, when the emitted photon has a typical energy of order quarkonium binding energy. Nevertheless, in the case when the energy carried by the photon is of order typical heavy quark momentum, the multipole expansion doctrine is expected to break down. In this work, we apply the “hard-scattering” approach originally developed to tackle the strongly hindered magnetic dipole (M1) transition [Y. Jia , ] to the strongly hindered electric dipole (E1) transition between heavy quarkonia. We derive the factorization formula for the strongly hindered E1 transition rates at the lowest order in velocity and αs in the context of the nonrelativistic QCD, and conduct a detailed numerical comparison with the standard predictions for various bottomonia and charmonia E1 transition processes. Published by the American Physical Society 2024

QCD corrections at subleading power for inclusive nonleptonic b→cu¯d decays

In this paper we compute the next-to-leading order (NLO) QCD corrections for the inclusive nonleptonic decay rates of B hadrons at subleading power of the heavy quark expansion. In particular, we discuss the coefficient of the chromomagnetic moment parameter μG, which has a large uncertainty at leading order due to its dependence on the renormalization scale. We find that the renormalization-scale dependence of this coefficient is significantly reduced, thereby reducing the theoretical uncertainty of the coefficient and, consequently, the rates. The sign of the coefficient becomes stable, and we estimate that the NLO corrections will increase the decay rates by around 2%. Published by the American Physical Society 2024

Improved analysis of strong-interaction-stable doubly bottom tetraquarks on the lattice

We update earlier lattice results for the binding energies of the flavor antitriplet of strong-interaction-stable doubly bottom, JP=1+ tetraquarks, employing an extended sink construction which produces significantly improved ground-state effective-mass plateaus, as well as new, larger-volume ensembles which reduce possible finite-volume effects at lighter pion masses. The updated bindings are 115(17) MeV for the I=0 member of the antitriplet and 47(8) MeV for its I=1/2 partner. We also provide an update of our earlier study of the variable heavy mass dependence of binding in the 1+ channel and new results on this dependence for binding in the 0+ channel, accessible when the two heavy quarks have unequal masses. Implications of these results of potential relevance to experimental searches for signals of the production of doubly bottom tetraquarks and/or a possible bottom-charm partner of the Tcc are also discussed. Published by the American Physical Society 2024

Tetraquarks at large M and large N

We study tetraquarks in large N QCD with heavy quarks, in the domain where non-relativistic quantum mechanics offers an adequate approximation. Within the regime of validity of the Born-Oppenheimer approximation, we systematically study and explicitly construct tetraquark states. At leading order in the 1/N expansion, the bound spectrum consists of free mesons, while the 1/N corrections give rise to a Born-Oppenheimer potential that can bind the mesons into tetraquarks. We find two different types of tetraquarks, each endowed with distinct color-spatial wavefunctions. These states arise in the presence of an O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(N) mass hierarchy between the quarks and the antiquarks. We provide a quantitative argument indicating that only for such a hierarchy is the ground state of the system a tetraquark. We discuss what the extrapolation of our results to realistic values of the parameters may imply for the QCD tetraquark states.

Tetraquarks made of sufficiently unequal-mass heavy quarks are bound in QCD

Tetraquarks, bound states composed of two quarks and two antiquarks, have been the subject of intense study but are challenging to understand from first principles. We apply variational and Green’s function Monte Carlo methods to compute tetraquark ground-state energies in potential nonrelativistic QCD using a wide range of color and spatial wave functions. We find no evidence for bound tetraquarks composed of equal-mass quarks and antiquarks. Conversely, we find clear evidence for the existence of bound tetraquarks for sufficiently unequal quark/antiquark mass ratios at all overall mass scales where our effective theory results are applicable. We predict the critical mass ratios for bound state formation and study tetraquark bound states’ spatial and color structure at leading order and next-to-leading order in potential nonrelativistic QCD. Published by the American Physical Society 2024

Vetting quark-star models with gravitational waves in the hierarchical Bayesian framework

The recent discovery of gravitational waves (GWs) has opened a new avenue for investigating the equation of state (EOS) of dense matter in compact stars, which is an outstanding problem in astronomy and nuclear physics. In the future, next-generation (XG) GW detectors will be constructed, deemed to provide a large number of high-precision observations. We investigate the potential of constraining the EOS of quark stars (QSs) with high-precision measurements of mass m and tidal deformability Λ from the XG GW observatories. We adopt the widely-used bag model for QSs, consisting of four microscopic parameters: the effective bag constant B eff, the perturbative quantum chromodynamics correction parameter a 4, the strange quark mass m s , and the pairing energy gap Δ. With the help of hierarchical Bayesian inference, for the first time we are able to infer the EOS of QSs combining multiple GW observations. Using the top 25 loudest GW events in our simulation, we find that, the constraints on B eff and Δ are tightened by several times, while a 4 and m s are still poorly constrained. We also study a simplified 2-dimensional (2-d) EOS model which was recently proposed in literature. The 2-d model is found to exhibit significant parameter-estimation biases as more GW events are analyzed, while the predicted m–Λ relation remains consistent with the full model.

Experimental studies of in-medium modification of [formula omitted] meson mass through [formula omitted] decays

ϕ meson is an ideal probe to explore mass modification inside the nucleus due to partial restoration of chiral symmetry with its narrow width. The modification of ϕ mass is related to the strange-quark condensate 〈s̄s〉 in a finite density. J-PARC E88 has been proposed as an experiment to study the modification of ϕ mass inside nuclei in proton–nucleus collisions. Complementary to ϕ→e+e− decay measurements at J-PARC E16, E88 will measure high-statistics ϕ→K+K− decays of about 1 M in p+C, p+Cu, and p+Pb collisions by deploying kaon identification detectors at forward angles in the E16 spectrometer. Utilizing the high-statistics data, the momentum and polarization dependence of mass modification will be studied to evaluate the strange quark condensate in nucleons, and Lorentz-symmetry breaking effects. In this paper, we will discuss physics goals, the experimental design and feasibility, the performance of kaon identification detectors, and the timeline of the E88.

Limits on scalar dark matter interactions with particles other than the photon via loop corrections to the scalar-photon coupling

There is limited information about the interaction strength of a scalar dark matter candidate with hadrons and leptons for a scalar particle mass exceeding 10−3 eV while its interaction with photon is well studied. The scalar-photon coupling constant receives quantum corrections from one-loop Feynman diagrams which involve the scalar-lepton, scalar-quark, and scalar-W-boson vertices. We calculate these one-loop quantum corrections and find new limits on the scalar particle interactions with electron, muon, tau, quarks, nucleons, gluons, Higgs, and W-bosons by repurposing the results of experiments measuring the scalar-photon interaction. Limits on interactions of heavy leptons and quarks have been obtained for the first time, and limits on other interactions in certain mass intervals are 2 to 15 orders of magnitude stronger than those presented in previous publications and exclude the resolution of the muon g−2 anomaly with scalar particle. Published by the American Physical Society 2024

Three loop QCD corrections to the heavy-light form factors: fermionic contributions

We present analytic results for three-loop fermionic corrections to the heavy-light form factors in perturbative quantum chromodynamics. Specifically, we present all light quark contributions and contributions from two heavy quark loops. We use the method of differential equations to compute all relevant three-loop master integrals. The results for all these contributions are expressed in terms of harmonic polylogarithms and generalized harmonic polylogarithms.