Quark Antiquark Research Articles

Physics of near-threshold resonances

In this paper, we present our approach to the treatment of final-state interaction of hadrons. It is based on the assumption that quark–antiquark pairs are produced at small distances, while the interaction of hadrons takes place at larger distances. As a result, the effects of final-state interaction are determined by the wave function of produced hadronic system. The account for final-state interaction within this approach allows us to successfully describe the energy dependence of cross-sections of many processes, as well as electromagnetic form factors of hadrons.

Probing gauge-Higgs unification models at the ILC with quark–antiquark forward–backward asymmetry at center-of-mass energies above the Z mass

The International Linear Collider (ILC) will allow the precise study of e-e+→qq¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^{-}e^{+} \\rightarrow q\\bar{q}$$\\end{document} interactions at different center-of-mass energies from the Z\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z$$\\end{document}-pole to 1 TeV. In this paper, we discuss the experimental prospects for measuring differential observables in e-e+→bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^{-}e^{+} \\rightarrow b\\bar{b}$$\\end{document} and e-e+→cc¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^{-}e^{+} \\rightarrow c\\bar{c}$$\\end{document} at the ILC baseline energies, 250 and 500 GeV. The study is based on full simulation and reconstruction of the International Large Detector (ILD) concept. Two gauge-Higgs unification models predicting new high-mass resonances beyond the Standard Model are discussed. These models predict sizable deviations of the forward–backward observables at the ILC running above the Z mass and with longitudinally polarized electron and positron beams. The ability of the ILC to probe these models via high-precision measurements of the forward–backward asymmetry is discussed. Alternative scenarios at other energies and beam polarization schemes are also discussed, extrapolating the estimated uncertainties from the two baseline scenarios.

Gluon–gluon fusion contribution to the productions of three gauge bosons at the LHC

Productions of multiple gauge bosons at the LHC are sensitive to triple or quartic gauge couplings and thus provide a sensitive test for the electroweak sector of the Standard Model and allow for a probe of new physics. In this work we calculate the gluon–gluon initiate state contribution to the productions of three gauge bosons (Zγγ,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\gamma \\gamma ,$$\\end{document}ZZγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ZZ\\gamma $$\\end{document} and W+W-γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W^+W^-\\gamma $$\\end{document}) at the LHC, which is formally part of NNLO effects compared to the LO quark–antiquark channels corrections. For each process we present the ratio between the gluon–gluon channels contribution and the quark–antiquark channels contribution. We found that such a ratio for Zγγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\gamma \\gamma $$\\end{document}(ZZγ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(ZZ\\gamma )$$\\end{document} is of the order of 10-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-3}$$\\end{document}(10-4),\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(10^{-4}),$$\\end{document} much smaller than the corresponding ratio for the diboson production due to the decrease of gluon PDF when more particles appear in the final states. These small ratios imply that gluon–gluon fusion contribution is phenomenological negligible for the productions of Zγγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\gamma \\gamma $$\\end{document} and ZZγ.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ZZ\\gamma .$$\\end{document} However, for W+W-γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W^+W^-\\gamma $$\\end{document} production, the ratio is about 5%, which is of the same order of magnitude as the ratio for W+W-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W^+W^-$$\\end{document} production due to the big cancellation between the amplitudes of quark–antiquark channels. While such an effect can be neglected currently at the LHC, it may be accessible at the HL-LHC.

Relaxation time for the alignment between quark spin and angular velocity in a rotating QCD medium

We compute the relaxation times for massive quarks and antiquarks to align their spins with the angular velocity in a rigidly rotating medium at finite temperature and baryon density. The rotation effects are implemented using a fermion propagator immersed in a cylindrical rotating environment. The relaxation time is computed as the inverse of the interaction rate to produce an asymmetry between the quark (antiquark) spin components along and opposite to the angular velocity. For conditions resembling heavy-ion collisions, the relaxation times for quarks are smaller than for antiquarks. For semicentral collisions, the relaxation time for quarks is within the possible lifetime of the QGP for all collision energies. However, for antiquarks, this happens only for collision energies sNN≳50 GeV. The results are quantified in terms of the intrinsic quark and antiquark polarizations, namely, the probability to build the spin asymmetry as a function of time. Our results show that these intrinsic polarizations tend to 1 with time at different rates given by the relaxation times with quarks reaching a sizable asymmetry at a faster pace. These are key results to further elucidate the mechanisms of hyperon polarization in relativistic heavy-ion collisions. Published by the American Physical Society 2024

Quantum Chromodynamics of the Nucleon in Terms of Complex Probabilistic Processes

Despite the obvious progress made by the Feynman, Ravndal, and Kislinger relativistic model in describing the internal motion of a system with confinement of quarks in a nucleon, it turned out to be insufficiently realistic for a number of reasons. In particular, the model does not take into account some cornerstone properties of QCD, namely, gluon exchange between quarks, the influence of the resulting quark sea on valence quarks, and the self-interaction of colored gluons. It is these phenomena that spontaneously break the chiral symmetry of the quark system and form the bulk of the nucleon. To eliminate the above shortcomings of the model, the problem of self-organization of a three-quark dynamical system immersed in a colored quark–antiquark sea is considered within the framework of complex probabilistic processes that satisfy the stochastic differential equation of the Langevin–Kline–Gordon–Fock type. Taking into account the hidden symmetry of the internal motion of a dynamical system, a mathematically closed nonperturbative approach was developed, which makes it possible to construct the mathematical expectation of the wave function and other parameters of the nucleon in the form of multiple integral representations. It is shown that additional subspaces arising in a representation characterized by a noncommutative geometry with topological features participate in the formation of an effective interaction between valence quarks against the background of harmonic interaction between them.

The effect of quark–antiquark confinement on the deflection angle by the NED black hole

In this study, we explore the influence of quark–antiquark confinement on the deflection angle within the framework of nonlinear electrodynamic (NED) black holes. To achieve this, we establish the appropriate optical spacetime metric and subsequently determine the Gaussian optical curvature. Utilizing the Gauss–Bonnet theorem, we investigate the impact of quark–antiquark confinement on the deflection angle exhibited by NED black holes. Additionally, we delve into the effects of a cold non-magnetized plasma medium and also axion-plasmon on gravitational lensing. Our findings highlight the significance of the axion-plasmon effect on the optical properties of NED black holes, particularly its influence on gravitational lensing. This exploration is particularly relevant in the context of the axion’s potential role as a dark matter candidate. The multifaceted interplay between quark–antiquark confinement, nonlinear electrodynamics, and plasma dynamics provides a nuanced understanding of gravitational lensing phenomena. These insights contribute to ongoing research in dark matter studies and offer avenues for further theoretical and observational investigations in astrophysics.

Factorial growth at low orders in perturbative QCD: control over truncation uncertainties

A method, known as “minimal renormalon subtraction” [Phys. Rev. D97 (2018) 034503, JHEP08 (2017) 62], relates the factorial growth of a perturbative series (in QCD) to the power p of a power correction Λp/Qp. (Λ is the QCD scale, Q some hard scale.) Here, the derivation is simplified and generalized to any p, more than one such correction, and cases with anomalous dimensions. Strikingly, the well-known factorial growth is seen to emerge already at low or medium orders, as a consequence of constraints on the Q dependence from the renormalization group. The effectiveness of the method is studied with the gluonic energy between a static quark and static antiquark (the “static energy”). Truncation uncertainties are found to be under control after next-to-leading order, despite the small exponent of the power correction (p = 1) and associated rapid growth seen in the first four coefficients of the perturbative series.

Search for the Zγ decay mode of new high-mass resonances in pp collisions at [formula omitted] TeV with the ATLAS detector

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.

A possibility of existence of a pseudovector-type quark–antiquark condensate in the quark matter and Nambu–Goldstone modes on that condensate in the Nambu–Jona–Lasinio model

A possibility of a pseudovector-type quark–antiquark condensed phase, which leads to a quark spin polarized phase, in the quark matter is investigated taking account of the vacuum effects leading to the chiral symmetry breaking by using the Nambu–Jona–Lasinio model. Also, possible Nambu–Goldstone modes on the pseudovector-type quark–antiquark condensate and the tensor-type quark–antiquark condensate, which also leads to the quark spin polarized phase, are investigated.

Unpolarized transverse-momentum-dependent sea quark asymmetries of light nuclei in nonperturbative QCD

We investigate the transverse-momentum dependence of sea quark asymmetries in helium and deuteron nuclei. Accordingly, we calculate the nuclear sea quark distributions, in the first step, based on the modified chiral quark exchange formalism at the low Q 2 scale (Q 2 = 0.35 GeV2) in the nonperturbative region of quantum chromodynamics. In this formalism, the sea quark distributions are not symmetric because of chiral symmetry breaking. In the next step, we compute the transverse-momentum dependence of sea quark distributions using the covariant parton model, in which the unpolarized transverse-momentum-dependent (TMD) quark distribution functions are related to corresponding integrated ones. Finally, we obtain TMD quark–antiquark asymmetry of the strange sea for 3 He and deuteron, and also asymmetry for 3 He. To study the European Muon Collaboration (EMC) effect in the 3 He nucleus, we determine the ratio of the TMD strange sea asymmetries of 3 He and deuteron.

Holographic imaginary potential of a quark antiquark pair in the presence of gluon condensation

For a moving heavy quark antiquark (QQ) in a quark gluon plasma (QGP), we use gauge/gravity duality to study both real and imaginary parts of the potential ( operatorname{Re}{V}_{Qoverline{Q}} and operatorname{Im}{V}_{Qoverline{Q}} respectively) in a gluon condensate (GC) theory. The complex potential is derived from the Wilson loop by considering the thermal fluctuations of the worldsheet of the Nambu-Goto holographic string. We calculate operatorname{Re}{V}_{Qoverline{Q}} and operatorname{Im}{V}_{Qoverline{Q}} in both cases where the axis of the moving Qoverline{Q} pair is transverse and parallel with respect to its direction of movement in the plasma. Using the renormalization scheme for the operatorname{Re}{V}_{Qoverline{Q}} , we find that the inclusion of GC increases the dissociation length while rapidity has the opposite effect. While for the operatorname{Im}{V}_{Qoverline{Q}} , we observe that by considering the effect of GC, the operatorname{Im}{V}_{Qoverline{Q}} is generated for larger distance thus decreasing quarkonium dissociation, while rapidity has opposite effect. In particular, as the value of GC decreases in the deconfined phase, the operatorname{Im}{V}_{Qoverline{Q}} is generated for smaller distance thus enhancing quarkonium dissociation, and at high temperatures it is nearly not modified by GC, consistent with previous findings of the entropic force.

Dihadron production in DIS at small x at next-to-leading order: Transverse photons

We calculate the next-to-leading order corrections to dihadron production in deep inelastic scattering (DIS) at small $x$ using the color glass condensate formalism for the case when the virtual photon is transverse polarized. Similar to the case of longitudinal photon exchange all UV and soft singularities cancel while the collinear divergences are absorbed into quark and antiquark-hadron fragmentation functions. Rapidity divergences lead to Jalilian-Marian, Iancu, McLerran, Wiegert, Leonidov, Kovner (JIMWLK) evolution of dipoles and quadrupoles which describe multiple scatterings of the quark antiquark dipole on the target proton/nucleus and contain all the QCD dynamics of the target leading to a finite final result for the dihadron production cross section.

Chiral symmetry restoration at high matter density observed in pionic atoms

According to quantum chromodynamics, vacuum is not an empty space, because it is filled with quark–antiquark pairs. The pair has the same quantum numbers as the vacuum and forms a condensate because the strong interaction of the quantum chromodynamics is too strong to leave the vacuum empty. This quark–antiquark condensation, the chiral condensate, breaks the chiral symmetry of the vacuum. The expectation value of the chiral condensate is an order parameter of the chiral symmetry, which is expected to decrease at high temperatures or high matter densities where the chiral symmetry is partially restored. Head-on collisions of nuclei at ultra-relativistic energies have explored the high-temperature regime, but experiments at high densities are rare. Here we measure the spectrum of pionic 121Sn atoms and study the interaction between the pion and the nucleus. We find that the expectation value of the chiral condensate is reduced at finite density compared to the value in vacuum. The reduction is linearly extrapolated to the nuclear saturation density and indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus. In quantum chromodynamics, the condensation of quark–antiquark pairs breaks the chiral symmetry of vacuum. Experiments with pionic tin atoms demonstrate that the symmetry is partially restored at high densities.

Higgs boson decay into gluons in a 4D regularization: IR cancellation without evanescent fields to NLO

Higgs decay using an effective Higgs–Yang-Mills interaction in terms of a dimension five operator as well as usual QCD interactions is revisited in the context of Implicit Regularization (IReg) and compared with conventional dimensional regularization (CDR), four dimensional helicity (FDH) and dimensional reduction (DRED) schemes. The decay rate for H rightarrow gg(g) is calculated in this strictly four-dimensional set-up to alpha _s^3 order in the strong coupling. Moreover we include joint processes that contribute at the same perturbative order in the real emission channels consisting of 3 gluons as well as gluon quark–antiquark final states with light (zero mass) quarks. Unambiguous identification and separation of UV from IR divergences is achieved putting at work the renormalization group scale relation inherent to the method. UV singularities are removed as usual by renormalization, the IR divergences are cancelled due to the method’s compliance with the Kinoshita–Lee–Nauenberg (KLN) theorem. Most importantly, we verify that no evanescent fields such as epsilon -scalars need be introduced as required by some mixed regularizations that operate partially in the physical dimension.

Hamiltonian formalism for Fermi excitations in a plasma with a non-Abelian interaction

The Hamiltonian theory for the collective longitudinally polarized colorless gluon excitations (plasmons) and for collective quark–antiquark excitations with abnormal relation between chirality and helicity (plasminos) in high-temperature quark–gluon plasma (QGP) is developed. For this purpose, Zakharov’s formalism for constructing the wave theory in nonlinear media with dispersion is used. A generalization of the Poisson superbracket involving both commuting and anticommuting variables to the case of a continuous medium is performed and the corresponding Hamilton equations are presented. The canonical transformations including simultaneously both bosonic and fermionic degrees of freedom of the collective excitations in QGP are discussed and a complete system of the canonicity conditions for these transformations is written out. An explicit form of the effective fourth-order Hamiltonians describing the elastic scattering of plasmino off plasmino and plasmino off plasmon is found and the Boltzmann-type kinetic equations describing the processes of elastic scattering are obtained. A detailed comparison of the effective amplitudes defined within the (pseudo)classical Hamiltonian theory, with the corresponding matrix elements calculated early in the framework of high-temperature quantum chromodynamics in the so-called hard thermal loop approximation, is performed. This enables one to obtain, in particular, an explicit form of the vertex and coefficient functions in the effective amplitudes and in the canonical transformations, correspondingly, and also to define the validity of a purely pseudoclassical approach in the Hamiltonian description of the dynamics of quark–gluon plasma. The problem of determining the higher-order coefficient functions in the canonical transformations of fermionic and bosonic normal variables is considered. With the help of the coefficient functions obtained, the totally symmetric effective amplitudes of the elastic scattering of plasmino off plasmon and plasmino off plasmino are written out.

Soft gluon–quark–antiquark emission in QCD hard scattering

We consider the radiation of a soft gluon (g) and a soft quark–antiquark (q{{bar{q}}}) pair in QCD hard scattering. In the soft limit the scattering amplitude has a singular behaviour that is factorized and controlled by a soft current, which has a process-independent structure in colour space. We evaluate the soft gq{{bar{q}}} current at the tree level for an arbitrary multiparton scattering process. The irreducible correlation component of the current includes strictly non-abelian terms and also terms with an abelian character. Analogous abelian correlations appear for soft photon–lepton–antilepton emission in QED. The squared current for soft gq{{bar{q}}} emission produces colour dipole and colour tripole interactions between the hard-scattering partons. The colour tripole interactions are odd under charge conjugation and lead to charge asymmetry effects. We consider the specific applications to processes with two and three hard partons, and we discuss the structure of the corresponding charge asymmetry contributions. We also generalize our QCD results to the cases of QED and mixed QCD times QED radiative corrections.

Open bottom mesons in magnetized matter: Effects of (inverse) magnetic catalysis

In-medium masses of the pseudoscalar and vector open bottom mesons ([Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], [Formula: see text]) are studied in the magnetized nuclear matter by considering the effects of Dirac sea, within the chiral effective model. The mass modifications arise due to the interactions of the open bottom mesons with the nucleons and the scalar mesons, calculated in terms of the scalar and number densities of the nucleons and the scalar fields fluctuations, within the chiral model. The effects of the magnetized Dirac sea lead to the considerable changes in the scalar fields with increasing magnetic field, which are related to the condensates of light quark–antiquark pairs. There is observed to be a (reduction) enhancement in the QCD light quark condensates with rising magnetic field, a phenomenon called (inverse) magnetic catalysis. The contribution of the magnetic field on the Fermi sea of nucleons is also taken into account through protons Landau energy levels and anomalous magnetic moments (AMMs) of the nucleons. The additional contribution of the lowest Landau level for the charged mesons is taken into account. In the presence of an external magnetic field, the spin–magnetic field interaction between the longitudinal component of the vector mesons and the pseudoscalar mesons ([Formula: see text], [Formula: see text] and [Formula: see text]) are studied, which lead to level repulsion between their masses with increasing magnetic field. The magnetic fields are observed to have significant contribution on the masses of the open bottom mesons through the Dirac sea effects taking into account the AMMs of nucleons. In vacuum, appreciable medium modifications are obtained due to the magnetized Dirac sea contribution with nonzero nucleonic AMMs.

Evidence for intrinsic charm quarks in the proton

The theory of the strong force, quantum chromodynamics, describes the proton in terms of quarks and gluons. The proton is a state of two up quarks and one down quark bound by gluons, but quantum theory predicts that in addition there is an infinite number of quark–antiquark pairs. Both light and heavy quarks, whose mass is respectively smaller or bigger than the mass of the proton, are revealed inside the proton in high-energy collisions. However, it is unclear whether heavy quarks also exist as a part of the proton wavefunction, which is determined by non-perturbative dynamics and accordingly unknown: so-called intrinsic heavy quarks1. It has been argued for a long time that the proton could have a sizable intrinsic component of the lightest heavy quark, the charm quark. Innumerable efforts to establish intrinsic charm in the proton2 have remained inconclusive. Here we provide evidence for intrinsic charm by exploiting a high-precision determination of the quark–gluon content of the nucleon3 based on machine learning and a large experimental dataset. We disentangle the intrinsic charm component from charm–anticharm pairs arising from high-energy radiation4. We establish the existence of intrinsic charm at the 3-standard-deviation level, with a momentum distribution in remarkable agreement with model predictions1,5.We confirm these findings by comparing them to very recent data on Z-boson production with charm jets from the Large Hadron Collider beauty (LHCb) experiment6.

Study of double J∕ψ production mechanisms at COMPASS

During the past 40 years, the production of pairs of [Formula: see text] mesons in high-energy hadron collisions has been studied by several experiments. Despite the experimental and theoretical efforts, the origin of the process and the relative weight of different production mechanisms remain unknown. Depending on the energy scale, the double [Formula: see text] production can be described by single- and/or double-parton scattering sub-processes and gluon–gluon fusion or quark–antiquark annihilation mechanisms. The process can also be related to the hypothesis of the intrinsic charm of hadrons and the existence of exotic tetraquark states which were predicted by various theoretical models and have recently been observed by the LHCb experiment. To study dimuon pair production, the COMPASS experiment at CERN uses a 190[Formula: see text]GeV/[Formula: see text] negative pion beam impinging on different nuclear targets. First preliminary COMPASS results on [Formula: see text] pair production will be presented. The search for possible signals from exotic resonances and the study of double [Formula: see text] production mechanisms will be discussed.

Non-leptonic decays of bileptons

We provide a detailed analysis of the decays of doubly-charged bilepton gauge bosons Y±±, as predicted in models based on a SU(3)C×SU(3)L×U(1)X symmetry. In addition to the decay modes into same-sign lepton pairs, which were already investigated in scenarios wherein each branching ratio was about one third, there are, depending on the mass spectrum, possible non-leptonic decays which reduce the leptonic rates. These non-leptonic decays are typically into a light quark (antiquark) and a heavy TeV-scale antiquark (quark), which carries double lepton number and decays via virtual bileptons. We choose two benchmark points to represent the particle spectrum and present a phenomenological analysis of such decays. We find that, while the LHC statistics are too low, even in the high-luminosity phase, they can lead to a visible signal at a future 100 TeV hadron collider (FCC-hh). A more exhaustive exploration with a rigorous inclusion of tagging efficiencies, detector simulations and higher-order corrections to the partonic cross section, aiming at assessing the reach of LHC and FCC-hh for bileptons as a function of the model parameters, as well as a recast of four-top searches in terms of the bilepton model, are deferred to future work.