arXiv subjects

Alessandro Giachino

Publications and source records attributed to Alessandro Giachino.

10 recordsLinked to original sources

arXiv2025

Strange pentaquarks with a hidden heavy quark-antiquark pair

The strange pentaquarks with hidden heavy quark pair ($q^3c\bar c$ and $q^3b \bar b$) are investigated by the coupled-channel quark cluster model. Two types of the $q^3$ color-octet configurations are found to provide the attraction, which makes bound states, sharp resonances, and cusps in the baryon meson scattering. A resonance appears at around 4500 MeV in the strange hidden charm sector. Such structures are more clearly seen in the hidden bottom systems.

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arXiv2024

Fully charmed tetraquark production at the LHC experiments

We develop the formalism for production of a fully heavy tetraquark and apply it to the calculation of $pp\to T_{4c}+X$ cross-sections. We demonstrate that the production cross-section of a fully heavy tetraquark, even if it is a diquark-antidiquark cluster, can be obtained in the meson-like basis, for which the spin-color projection technique is well established. Prompted by the recent LHCb, ATLAS and CMS data, we perform a pQCD calculation of ${\cal O}(α_s^5)$ short-distance factors in the dominant channel of gluon fusion, and match these to the four-body $T_{4c}$ wave functions in order to obtain the unpolarized $T_{4c}(0^{++},1^{+-},2^{++})$ cross-sections. The novelty in comparison with the recently published article~\cite{Feng:2023agq} lies in the fact that we predict the absolute values as well as the $dσ/dp_T$ spectra in the kinematic ranges accessible at the ongoing LHC experiments. From the comparison with the signal yield at LHCb we derive the constraints on the $Φ\cdot\text{Br}(J/ψ\,J/ψ)$ (reduced wave function times branching) product for the $T_{4c}$ candidates for $X(6900)$ and observe that $X(6900)$ is compatible with a $2^{++}(2S)$ state.

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arXiv2024

A new subtraction scheme at NLO exploiting the privilege of kT-factorization

We present a subtraction method for the calculation of real-radiation integrals at NLO in hybrid kT-factorization. The main difference with existing methods for collinear factorization is that we subtract the momentum recoil, occurring due to the mapping from an (n+1)-particle phase space to an n-particle phase space, from the initial-state momenta, instead of distributing it over the final-state momenta.

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arXiv2023

One-loop gauge invariant amplitudes with a space-like gluon

Nowadays the particle physics has entered an era where high precision calculations are required in order to compare the theoretical predictions with the experimental data. In this paper, we explicitly compute the virtual contributions for the space-like one-jet processes, $\procgg,\procqq,\procH$ and $\procee$ within the auxiliary parton method. Our results, which are expected to play an important role in high precision description of small $x$ physics, explicitly confirm the conjecture developed in Ref. \cite{vanHameren:2022mtk}, thus helping to bridge the gap between lowest order calculations and NLO corrections within hybrid $k_T$-factorization scheme.

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arXiv2022

Rich structure of the hidden-charm pentaquarks near threshold regions

The recent abundant observations of pentaquarks and tetraquarks by high-energy accelerator facilities indicate the realization of the conjecture by Gell-Mann and Zweig, and by De Rujula, Georgi and Glashow [1-3]. We construct a coupled-channel model for the hidden-charm pentaquarks with strangeness whose quark content is $udsc \bar c$, $P_{cs}$, described as $ Λ_c \bar{D}_s^{(*)}, Ξ_c^{('*)} \bar{D}^{(*)}$ molecules coupled to the five-quark states. These molecules are formed by the suitable cooperation of heavy quark and chiral symmetries. We reproduce the experimental mass and quantum numbers $J^P$ of $P_{cs}(4338)$ for which LHCb has just announced the discovery. We make other predictions for new $P_{cs}$ states as molecular states near threshold regions that can be studied by LHCb.

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arXiv2021

Masses and decay widths of $Ξ_{c/b}$ and $Ξ^\prime_{c/b}$ baryons

In this article, we present a complete classification of the negative parity $Ξ'_{c/b}$ and $Ξ_{c/b}$ $P$-wave states: 7 belonging to the $SU(3)$ flavor sextet and 7 to the flavor anti-triplet, the calculation of the $Ξ'_{c/b}$ and $Ξ_{c/b}$ strong partial decay widths into $^2Σ_c \bar{K}$, $^2Ξ_c^{'} π$, $^2Σ_c \bar{K}$, $^4Ξ_c^{'} π$, $Λ_c^{'} \bar{K}$, $Ξ_c^{} π$ and $Ξ_c^{} η$ channels both within the Elementary Emission Model (EEM) and the $^3P_0$ model, and the calculation of the electromagnetic decay widths for $Ξ'_{c/b}$ and $Ξ_{c/b}$ radiative decays. By means of the equal-spacing mass rule and by the analysis of the strong partial decay widths, we suggest possible assignments for the new LHCb $Ξ_{c}(2923)$, $Ξ_{c}(2939)$, and $Ξ_{c}(2965)$ states, as well as for the $Ξ_{c}$'s previously reported by Belle and BaBar. Our results can be tested by future experiments, at LHCb and Belle, disentangling the remaining missing piece of information, {\it i.e.} the quantum numbers. Finally, a comparison is made between a three-quark and a quark-diquark description of $Ξ_c$ states. Very recently the LHCb collaboration reported the observation of two new $Ξ_b$ states, namely $Ξ_b(6327)^{0}$ and $Ξ_b(6333)$, in $Λ_b^0 K^{-} π^{+}$ channel with a statistical significance larger than nine standard deviations. The experimental masses and widths of these two states are consistent with our mass and width predictions for the doublet of D-wave excitations of the $Ξ_b$ system with $J^{P}_{Ξ_b(6327)^{0}}=\frac{3}{2}^{+}$ and $J^{P}_{Ξ_b(6333)^{0}}=\frac{5}{2}^{+}$.

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arXiv2020

Heavy Hybrid Decays in a Constituent Gluon Model

A constituent gluon model that is informed by recent lattice field theory is developed. The model is then used to compute hybrid strong decay widths, that can be useful for the GlueX collaboration at Jefferson Lab and the PANDA collaboration at FAIR. Commensurately, forthcoming data from GlueX and PANDA will test the model. Widths tend to be large except for those of the lightest hybrid $S$-wave multiplet. Selection rules, extensions, limitations, and applications are discussed.

hep-ph↗

arXiv2020

$P_c$ pentaquarks with chiral tensor and quark dynamics

We investigate the hidden-charm pentaquarks as superpositions of $Λ_c \bar{D}^{(*)}$ and $Σ_c^{(*)} \bar{D}^{(*)}$ (isospin $I = 1/2$) meson-baryon channels coupled to a $uudc\bar{c}$ compact core by employing an interaction satisfying the heavy quark and chiral symmetries. Our model can consistently explain the masses and decay widths of $P_c^+(4312)$, $P_c^+(4440)$ and $P_c^+(4457)$ with the dominant components of $Σ_c \bar D$ and $Σ_c \bar D^\ast$ with spin parity assignments $J^P = 1/2^{-}, 3/2^{-}$ and $1/2^{-}$, respectively. We analyze basic properties of the $P_c$'s such as masses and decay widths, and find that the mass ordering is dominantly determined by the quark dynamics while the decay widths by the tensor force of the one-pion exchange.

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arXiv2018

Hidden-charm and bottom meson-baryon molecules coupled with five-quark states

In this paper, we investigate the hidden-charm pentaquarks as $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ molecules coupled to the five-quark states. Furthermore, we extend our calculations to the hidden-bottom sector. The coupling to the five-quark states is treated as the short range potential, where the relative strength for the meson-baryon channels is determined by the structure of the five-quark states. We found that resonant and/or bound states appear in both the charm and bottom sectors. The five-quark state potential turned out to be attractive and, for this reason, it plays an important role to produce these states. In the charm sector, we need the five-quark potential in addition to the pion exchange potential in producing bound and resonant states, whereas, in the bottom sector, the pion exchange interaction is strong enough to produce states. Thus, from this investigation, it emerges that the hidden-bottom pentaquarks are more likely to form than their hidden-charm counterparts; for this reason, we suggest that the experimentalists should look for states in the bottom sector.

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arXiv2017

Compact pentaquark structures

We study the possibility that at least one of the two pentaquark structures recently reported by LHCb can be described as a compact pentaquark state, and we give predictions for new channels that can be studied by the experimentalists if this hypothesis is correct. We use very general arguments dictated by symmetry considerations, in order to describe the pentaquark states within a group theory approach. A complete classification of all possible states and quantum numbers, that can be useful both to the experimentalists, for new finding, or to theoretical model builders, are given, without the introduction of any particular dynamical model. Some prediction are finally given using a Guersey-Radicati inspired mass formula. We reproduce the mass and the quantum numbers of the lightest pentaquark state reported by LHCb ( 3/2^-), with a parameter free mass formula, fixed on the well established baryons. We predict others pentaquark resonances (giving their masses, and suggesting possible decay channels) which belong to the same multiplet of the lightest one.Finally, we compute the partial decay widths for all the predicted pentaquark resonances.

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