arXiv subjects

Z. Rajabi Najjar

Publications and source records attributed to Z. Rajabi Najjar.

6 recordsLinked to original sources

arXiv2026

Phenomenology of Hypothetical Single-Top Hadronic States

We present a comprehensive theoretical study of the masses of possible baryonic and mesonic configurations containing a single top quark. Our analysis includes the baryons $Λ_t$, $Ξ_t$, $Σ_t$, $Ξ'_t$, $Ω_t$, $Ω_{tcc}$, and $Ω_{tbb}$, together with the pseudoscalar and vector mesons $T_{t\bar n}^{\mathrm{Ps}}$, $T_{t\bar n}^{\mathrm{V}}$, $T_{t\bar s}^{\mathrm{Ps}}$, $T_{t\bar s}^{\mathrm{V}}$, $T_{t\bar c}^{\mathrm{Ps}}$, $T_{t\bar c}^{\mathrm{V}}$, $T_{t\bar b}^{\mathrm{Ps}}$, and $T_{t\bar b}^{\mathrm{V}}$. Motivated in part by recent experimental indications of a pseudoscalar enhancement near the $t\bar t$ threshold reported by the CMS and ATLAS collaborations, this study is carried out within the framework of two-point QCD sum rules to determine the corresponding ground-state masses by including perturbative contributions and nonperturbative condensates up to dimension eight. For several channels, including the $Λ_t$, $Ξ_t$, $Σ_t$, $T_{t\bar b}^{\mathrm{Ps}}$, and $T_{t\bar b}^{\mathrm{V}}$ states, the extracted central masses lie slightly below the corresponding sums of constituent quark masses, which may indicate nontrivial binding dynamics or near-threshold multiquark configurations within the uncertainties of the method. Moreover, when the full theoretical uncertainties are taken into account in a conservative manner, a larger subset of the investigated states exhibits a consistent tendency toward weak binding behavior, suggesting that the possibility of loosely bound configurations cannot be excluded for most of the considered baryonic and mesonic channels. These results provide useful first-principles theoretical benchmarks for possible top-containing hadronic systems, which may support future searches at the LHC, along with sensitivity analyses for next-generation facilities such as the FCC.

hep-ph↗

arXiv2026

Masses of Purely Top-Quark Bound States: Toponium and the Triply-Top Baryon

We investigate the pseudoscalar ($η_t$) and vector ($ψ_t$) toponium states, as well as the triply-top baryon ($Ω_{ttt}$), using the QCD sum-rule method. This study was motivated by the recent observation of a pseudoscalar enhancement near the $t\bar{t}$ threshold, reported by the CMS and ATLAS collaborations with a statistical significance exceeding $5σ$. In the calculations, we consider both the perturbative and nonperturbative contributions, with the nonperturbative operators taken into account up to dimension eight. The results obtained for the pseudoscalar toponium provide a theoretical estimate that is consistent with the near-threshold events observed in recent experimental studies. The calculated negative binding energy for both the pseudoscalar and vector toponium states reflects the strong correlation within the $t\bar{t}$ system and can be interpreted as $t\bar{t}$ bound states, while the calculated central mass for the $Ω_{ttt}$ slightly exceeds the central value of the sum of the constituent top-quark masses. The results of this study can provide a precise theoretical guide for future experimental investigations of these states, which are composed entirely of top quarks, at high-energy colliders such as the LHC and future facilities like the FCC.

hep-ph↗

arXiv2025

Study of the semileptonic decay $Λ\to p\,\ell\,\barν_{\ell}$ in QCD

We conduct a comprehensive study of the semileptonic decay process $Λ\to p\,\ell\,\barν_{\ell}$, focusing on the determination of all six vector and axial-vector form factors that govern the low-energy hadronic matrix elements of the underlying theory. These invariant form factors constitute the essential inputs for describing the decay, and their dependence on the momentum transfer $q^{2}$ is analyzed across the entire physical kinematic region. To parametrize the $q^{2}$dependence, we adopt both the $z$-expansion formalism and a polynomial fitting approach. Utilizing parametrizations, we compute the exclusive decay widths for both the electron and muon channels, and subsequently extract the corresponding branching ratios. Furthermore, we evaluate the ratio of decay widths between the muon and electron channels defined as $R^{μe} \equiv \frac{Γ(Λ\to p\,μ\,\barν_μ)}{Γ(Λ\to p\,e\,\barν_{e})}$ obtaining $R^{μe} = 0.196^{+0.009}_{-0.012}$ from the polynomial fit and $R^{μe} = 0.174^{+0.002}_{-0.005}$ from the $z$ expansion. While both ratios are compatible with previously reported values in the literature, the result from the $z$ expansion exhibits particularly strong agreement with the averages reported by the Particle Data Group.

hep-ph↗

arXiv2025

Investigation of triply heavy spin-3/2 baryons in their ground and excited states

We calculate the masses and residues of triply heavy baryons with spin-3/2, including $Ω^*_{ccc}$, $Ω^*_{ccb}$, $Ω^*_{bbc}$ and $Ω^*_{bbb}$, using the QCD sum rules method. Our calculations primarily focus on obtaining the masses of the first three resonances, that is, the ground state (1S), the first orbital excited state (1P), and the first radial excited state (2S), for the mentioned baryons. We additionally determine the residues of these baryons, which serve as key parameters for studying their possible decay channels and interactions with other particles. To achieve higher accuracy compared to previous studies, we consider nonperturbative operators up to eight mass dimensions. We present our calculated outcomes in two distinct energy schemes, referred to as pole and $\mathrm{\overline{MS}}$. Given the absence of experimental data for these states, we compare our results with previous theoretical calculations that are reported in relevant studies employing various approaches. These results may provide valuable insights for experimental groups searching for the triply heavy baryons.

hep-ph↗

arXiv2025

Semileptonic decay of the triply heavy $Ω_{ccb}$ to the observed $Ξ^{++}_{cc}$ state

We investigate the weak semileptonic decay of the $ Ω^{+}_{ccb} \rightarrow Ξ^{++}_{cc} ~{\ell}\barν_{\ell}$, where a triply heavy baryon with spin 1/2 decays into the observed doubly heavy baryon with spin 1/2, using QCD sum rule method in all lepton channels. We compute the six relevant vector and axial vector form factors entering the low energy matrix elements in full theory. The invariant form factors are building blocks, using the fit faction of which in terms of $ q^2 $ in whole physical region, we calculate the exclusive widths in three lepton channels. Our predictions may help the present and future experiments in the course of their search for doubly and triply heavy baryons.

hep-ph↗

arXiv2024

Properties of the ground and excited states of triply heavy spin-1/2 baryons

We study the triply heavy spin-1/2 baryons with quark contents $ ccb $ and $ bbc $, and calculate their mass and residue using QCD sum rules. In the calculations, we consider the ground (1S), first orbitally excited (1P) and first radially excited (2S) states. Aiming to achieve higher accuracies in the results, we perform the computations by taking into account the non-perturbative operators up to eight mass dimensions. We compare our results with the predictions of other theoretical studies existing in the literature. The obtained results may help experimental groups in their search for these yet unseen, but previously predicted by the quark model, interesting particles.

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