Heavy Flavor Quarks Research Articles

Investigation on the bottom analogs Tbb− of Tcc+

We investigate the doubly bottom state Tbb− composed of two bottom mesons with JP=1+. The potentials are obtained using the one-boson exchange model. With the heavy quark flavor symmetry, all the parameters in the model are determined by fitting the experimental data of doubly charmed state Tcc+ from our previous work. Our analysis indicates that the isospin symmetry is well preserved. We identify a deeply bound Tbb− state with quantum numbers I(JP)=0(1+), in contrast to the loosely bound Tcc+. Additionally, we discover a resonant Tbb− state with I(JP)=1(1+). Furthermore, our investigation into the B¯B¯*−B¯*B¯* coupled channel effect reveals its important impact. The binding energy of the bound I(JP)=0(1+) states becomes deeper, while the resonant Tbb− state with I(JP)=1(1+) remains nearly unchanged. Published by the American Physical Society 2024

Electric dipole moments in 5+3 flavor weak effective theory

A fully generic treatment of electric dipole moments (EDMs) is presented in the CP-violating and flavor-conserving weak effective field theory (WET) with five flavors of quarks and three flavors of leptons. We systematically analyze leading contributions to EDMs originating from QCD and QED renormalization group running between the electroweak scale and low energy scales of about 2 GeV. We include the full one-loop anomalous dimension and a subset of two-loop corrections, as well as threshold corrections at the bottom, charm and τ masses. This allows us to derive master formulae in the space of generic WET for the neutron and proton EDMs, for EDMs of diamagnetic atoms, and for the precession frequencies constrained in molecular EDM experiments, from which bounds on the electron EDM are extracted. In particular, our master formulae capture the contributions of WET CP-violating operators with heavy quark and lepton flavors. As an application, we study EDM constraints on the Yukawa couplings of the Higgs boson, in both the linear and non-linear realizations of electroweak symmetry breaking.

Jet substructure

Jet substructure observables hold the keys to identifying the inner working of the quark–gluon plasma through its imprints in jet modification patterns. Because of the multi-scale nature of jet evolution, the strategy has focused on developing jet reclustering-based and jet shape-based observables to specifically probe different stages of jet evolution, which provide multi-dimensional quantification of jet particle distribution phase spaces. The developments of jet substructure in the past few years allowed us to explore the correlations among jet observables. The richer information beyond single-observable modifications could give provides a crucial step beyond the energy loss paradigm. This review surveys the theory and phenomenology of modern jet substructure observables, which help constraining the energy scales of medium interactions and identifying heavy flavor quarks within jets. Also, the peculiar soft activities point to more refined studies of medium responses to jets.

Production of Xb via radiative transition of ϒ(10753)

We studied the radiative transitions between the ϒ(10753), the S−D mixed state of the ϒ(4S) and ϒ1(3D13), and the Xb, the heavy quark flavor symmetry counterpart of the X(3782) in the bottomonium sector. The radiative transition was assumed to occur through the intermediate bottom mesons, including P-wave B1(′) mesons as well as the S-wave B(*) ones. The consideration of the B1(′) mesons leads to the couplings to be in S-wave, and hence enhances the contributions of the intermediate meson loops. The radiative decay width for the ϒ(10753)→γXb is predicted to be order of 10 keV, corresponding to a branching fraction of 10−4. Based on the theoretical results, we strongly suggest to search for the Xb in the e+e−→γXb with Xb→ππχb1 near s=10.754 GeV, and it is hoped that the calculations here could be tested by the future Belle II experiments. Published by the American Physical Society 2024

Exotic Tetraquarks at the HL-LHC with JETHAD: A High-Energy Viewpoint

We review the semi-inclusive hadroproduction of a neutral hidden-flavor tetraquark with light and heavy quark flavor at the HL-LHC, accompanied by another heavy hadron or a light-flavored jet. We make use of the novel TQHL1.0 determinations of leading-twist fragmentation functions to describe the formation mechanism of a tetraquark state within the next-to-leading order perturbative QCD. This framework builds on the basis of a spin physics-inspired model, taken as a proxy for the lowest-scale input of the constituent heavy-quark fragmentation channel. Then, all parton-to-tetraquark fragmentation functions are consistently obtained via the above-threshold DGLAP evolution in a variable-flavor number scheme. We provide predictions for a series of differential distributions calculated by the hands of the JETHAD method, well-adapted to NLL/NLO+ hybrid-factorization studies, where the resummation of next-to-leading energy logarithms and beyond is included in the collinear picture. We provide corroborating evidence that high-energy observables sensitive to semi-inclusive tetraquark emissions at the HL-LHC exhibit a fair stability under radiative corrections, as well as MHOU studies. Our analysis constitutes a prime contact point between QCD resummations and the exotic matter.

Regge trajectories for the heavy-light diquarks

We attempt to apply the Regge trajectory approach to the heavy-light diquarks composed of one heavy quark and one light quark. However, we find that the direct application of the usual Regge trajectory formula for the heavy-light mesons and baryons fails. In order to correctly estimate the masses of the heavy-light diquarks, it is needed to consider the light quark mass correction and the parameter C in the Cornell potential within the Regge trajectory formula. By using the modified Regge trajectory formulas, we are able to estimate the masses of the heavy-light diquarks (cu), (cs), (bu) and (bs), which agree with other theoretical results. It is illustrated that the heavy-light diquarks satisfy the universal descriptions irrespective of heavy quark flavors, similar to other heavy-light systems such as the heavy-light mesons, the heavy-light baryons composed of one heavy quark (diquark) and one light diquark (quark), and the heavy-light tetraquarks composed of one heavy diquark (antidiquark) and one light antidiquark (diquark). The diquark Regge trajectory provides a new and very simple approach for estimating the spectra of the heavy-light diquarks.

Inclusive production of J/ψ, ψ(2S), and Υ states in pNRQCD

Under some assumptions on the hierarchy of relevant energy scales, we compute the nonrelativistic QCD (NRQCD) long-distance matrix elements (LDMEs) for inclusive production of J/ψ, ψ(2S), and Υ states based on the potential NRQCD (pNRQCD) effective field theory. Based on the pNRQCD formalism, we obtain expressions for the LDMEs in terms of the quarkonium wavefunctions at the origin and universal gluonic correlators, which do not depend on the heavy quark flavor or the radial excitation. This greatly reduces the number of nonperturbative unknowns and substantially enhances the predictive power of the nonrelativistic effective field theory formalism. We obtain improved determinations of the LDMEs for J/ψ, ψ(2S), and Υ states thanks to the universality of the gluonic correlators, and obtain phenomenological results for cross sections and polarizations at large transverse momentum that agree well with measurements at the LHC.

X(3872) , X(4014) , and their bottom partners at finite temperature

The properties of the $X(3872)$ and its spin partner, the $X(4014)$, are studied both in vacuum and at finite temperature. Using an effective hadron theory based on the hidden-gauge Lagrangian, the $X(3872)$ is dynamically generated from the $s$-wave rescattering of a pair of pseudoscalar and vector charm mesons. By incorporating the thermal spectral functions of open charm mesons, the calculation is extended to finite temperature. Similarly, the properties of the $X(4014)$ are obtained out of the scattering of charm vector mesons. By applying heavy-quark flavor symmetry, the properties of their bottom counterparts in the axial-vector and tensor channels are also predicted. All the dynamically generated states show a decreasing mass and acquire an increasing decay width with temperature, following the trend observed in their meson constituents. These results are relevant in relativistic heavy-ion collisions at high energies, in analyses of the collective medium formed after hadronization or in femtoscopic studies, and can be tested in lattice-QCD calculations exploring the melting of heavy mesons at finite temperature.

Chromopolarizabilities of fully heavy baryons

We compute the chromopolarizabilities of the fully heavy baryons ${\mathrm{\ensuremath{\Omega}}}_{QQ{Q}^{\ensuremath{'}}}$ ($Q,{Q}^{\ensuremath{'}}=b$, $c$) in the framework of potential nonrelativistic quantum chromodynamics. At leading order, the fully heavy hadrons are considered as ground chromo-Coulombic bound states. We find that the chromopolarizability ${\ensuremath{\beta}}_{\mathrm{\ensuremath{\Omega}}}$ of a fully heavy baryon $QQQ$ is 2.6 times the chromopolarizability ${\ensuremath{\beta}}_{\ensuremath{\psi}}$ of the quarkonium $\overline{Q}Q$ with the same heavy quark flavor $Q$. This result is accurate up to the correction of the order 0.3 for $Q=b$ and provides an order-of-magnitude estimate for $Q=c$. We discuss the dependence of the ratio ${\ensuremath{\beta}}_{\mathrm{\ensuremath{\Omega}}}/{\ensuremath{\beta}}_{\ensuremath{\psi}}$ on the heavy quark mass ${m}_{Q}$ and the strong coupling constant ${\ensuremath{\alpha}}_{s}$ as well as on the ratio of the masses ${m}_{{Q}^{\ensuremath{'}}}/{m}_{Q}$, in the case not all quarks in the baryon are identical. Since the chromopolarizability of heavy hadrons defines the strength of their interaction at low energies mediated by soft gluons, which at long range hadronize into pairs of pions and kaons, our findings argue in favor of the existence of near-threshold states composed of pairs of fully heavy baryons.

The investigations of the P-wave Bs states combining quark model and lattice QCD in the coupled channel framework

Combining the quark model, the quark-pair-creation mechanism and B(*) overline{K} interaction, we have investigated the near-threshold P-wave Bs states in the framework of the Hamiltonian effective field theory. With the heavy quark flavor symmetry, all the parameters are determined in the Ds sector by fitting the lattice data. The masses of the bottom-strange partners of the {D}_{s0}^{ast }(2317) and {D}_{s1}^{ast }(2460) are predicted to be {M}_{B_{s0}^{ast }}={5730.2}_{-1.5}^{+2.4} MeV and {M}_{B_{s1}^{ast }}={5769.6}_{-1.6}^{+2.4} MeV, respectively, which are well consistent with the lattice QCD component. The two P-wave Bs states are the mixtures of the bare overline{b}s core and B(*) overline{K} component. Moreover, we find a crossing point between the energy levels with and without the interaction Hamiltonian in the finite volume spectrum in the 0+ case, which corresponds to a CDD (Castillejo-Dalitz-Dyson) zero in the T-matrix of the Boverline{K} scattering. This CDD zero will help deepen the insights of the near-threshold states and can be examined by future lattice calculation.

On Drell-Yan production of scalar leptoquarks coupling to heavy-quark flavours

Given the hints of lepton-flavour non-universality in semi-leptonic B decays, leptoquark (LQ) models with sizeable couplings to heavy-quark flavours are enjoying a renaissance. While such models are subject to stringent constraints from low-energy experiments also bounds from non-resonant dilepton searches at the Large Hadron Collider (LHC) turn out to be phenomenologically relevant. Based on the latest LHC dilepton analyses corresponding to an integrated luminosity of around 140 fb−1 of proton-proton collisions at sqrt{s} = 13 TeV, we present improved limits on the scalar LQ couplings that involve heavy-quark flavours and light or heavy dileptons. In particular, we show that effects beyond the leading order that are related to real QCD emissions are relevant in this context, since the inclusion of additional heavy-flavoured jets notably improves the exclusion limits that derive from the high-mass dilepton tails. The impact of electroweak corrections and interference effects between signal and background is also analysed. Within the POWHEG-BOX framework we provide a dedicated Monte Carlo code that allows for an on-the-fly signal event generation including all the LQ corrections considered in this article.

Recent heavy-flavour measurements with ALICE

In this contribution, an overview on the latest results of the ALICE Collaboration on the production of heavy-flavour hadrons in pp and Pb–Pb collision systems will be presented. Due to their large masses, heavy quarks are produced on shorter time scales than the typical QGP formation time, thus they participate to the system evolution and interact with the medium constituents making the heavy-flavour quarks a perfect probe to investigate the QGP properties. Heavy-flavour production measurements in pp collisions are a needed reference for Pb–Pb studies, to study the hadronization mechanisms in small colliding systems and to test perturbative QCD calculations at the LHC energies. The results presented report charm and beauty cross section measurements with an unprecedented precision down to very low momentum. In addition, results on heavy-flavour production highlight the non-universality of heavy-quark fragmentation fractions among different collision systems and energy scales.

Update on strong and radiative decays of the $$D_{s0}^*(2317)$$ and $$D_{s1}(2460)$$ and their bottom cousins

The isospin breaking and radiative decay widths of the positive-parity charm-strange mesons, $D^{*}_{s0}$ and $D_{s1}$, and their predicted bottom-strange counterparts, $B^{*}_{s0}$ and $B_{s1}$, as hadronic molecules are revisited. This is necessary, since the $B^{*}_{s0}$ and $B_{s1}$ masses used in Eur. Phys. J. A 50 (2014) 149 were too small, in conflict with the heavy quark flavour symmetry. Furthermore, not all isospin breaking contributions were considered. We here present a method to restore heavy quark flavour symmetry, correcting the masses of $B^{*}_{s0}$ and $B_{s1}$, and include the complete isospin breaking contributions up to next-to-leading order. With this we provide updated hadronic decay widths for all of $D^{*}_{s0}$, $D_{s1}$, $B^{*}_{s0}$ and $B_{s1}$. Results for the partial widths of the radiative deays of $D_{s0}^*(2317)$ and $D_{s1}(2460)$ are also renewed in light of the much more precisely measured $D^{*+}$ width. We find that $B_s\pi^0$ and $B_s\gamma$ are the preferred channels for searching for $B_{s0}^*$ and $B_{s1}$, respectively.

Machine learning classification for D0 meson signal extraction in d+Au collisions

In heavy-ion collisions at large particle colliders, such as LHC or RHIC, heavy-flavour (charm and beauty) quarks are produced mainly through initial hard scatterings. Therefore, they can serve as the probes of properties of the hot medium created in such collisions. Additionally, in small collision systems, such as d/p+Au collisions, cold nuclear matter effects can also affect the charm quark production with respect to p+p collisions. Hadrons, that contain heavy-flavour quarks, could not be directly detected, thus they are measured via reconstruction of their decay products. However, due to a large number of particles produced in such collisions, separation of the decay products from combinatorial background is challenging and advanced statistical analysis is needed. In this article, we exploit D0 (D0)→K- π+ (K+ π-) decay in order to investigate performance of several machine learning algorithms with different implementation approaches to find the most effective way how to separate signal from random combinatorial background. For this study, we use HIJING and STAR detector simulation of d+Au collisions at √(sNN)=200 GeV embedded to the collisions recorded with the STAR. In this paper we compare deep neural network implemented using Keras with TensorFlow backend, random forest model implemented using scikit-learn and boosted decision trees implemented by means of the Toolkit for Multivariate Data Analysis with ROOT. Described methods might be applied on reconstruction of any two-body decay in high-energy physics experiments.

Hunting for the heavy quark spin symmetry partner of Z_{cs}

The discovery of a charged strange hidden-charm state Z_{cs}(3985) implies another higher Z^*_{cs} state coupling to {bar{D}}_s^{*-}D^{*0} + c.c under the heavy quark spin symmetry. In this paper we discuss a possible hunt for it with data taken at existing facilities. We point out a hint for Z^*_{cs} in the data of {bar{B}}_s^0 rightarrow J/psi K^- K^+ at LHCb, though weak, in line with the production mechanism of pentaquark P_c. We also study the triangular singularity which would possibly enhance the production of Z^*_{cs} in electron-positron collision. Surprisingly, the production rate of Z^*_{cs} is expected to be maximum at the e^+ e^- center of mass energy of 4.648 GeV, which is lower than 4.681 GeV for Z_{cs} due to the inverted coupling hierarchy of D_{s1}{bar{D}}^* K and D_{s2}{bar{D}}K in the triangle diagrams. Their bottom analogue under heavy quark flavor symmetry is also discussed. Our theoretical analysis would confront with future experiment of LHCb, BESIII, and Bell II.

Study of heavy quark conserving weak decays in the quark model

Within the framework of a constituent quark model, we investigate the heavy quark conserving weak decays of Ξc and Ξb. This process involves elementary transitions of us→du or s→udu¯ with the heavy quark as a spectator, while for the charmed baryon in the initial state it can also occur via cs→dc to conserve the heavy quark flavor in the weak decays. It shows that the heavy quark symmetry (HQS) plays an essential role in the processes where the heavy quark acts as a spectator. For the Ξc decays, the dominance of the pole terms in the parity-conserving transitions is evident. This can naturally explain the sizable branching ratio for Ξc0→Λcπ− as recently reported by LHCb. The same mechanism predicts a large branching ratio for Ξc+→Λcπ0. In contrast, the decays of Ξb will only go through the parity-violating processes because of the HQS. In addition, the branching ratios of the Ξc+→Λcπ0 and Ξb0→Λbπ0 processes are also predicted for the further experimental measurement.

Open charm and beauty measurements from small to large systems

Heavy-flavor quarks (i.e. charm and beauty) are essential probes to investigate the properties of the quark-gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. The measurement of the nuclear modification factor (RAA) gives insight into the in-medium parton energy loss in heavy-ion collisions. Furthermore, the measurements of heavy-flavor elliptic flow (v2) provide crucial information about the degree of thermalization of heavy quarks in the QGP, the path-length dependence of heavy-quark in-medium energy loss, and possible recombination effects. The higher flow harmonics, such as the triangular flow (v3), provide further constraints on the effect of fluctuations in the initial state of the system. The measurements in proton-proton (pp) collisions allow for testing perturbative quantum chromodynamics (pQCD) calculations and are needed as a baseline for investigating the medium effects in heavy-ion collisions. In this contribution, recent results of open charm and beauty production measured with the ALICE detector are discussed.

Updates to the one-loop provider NLOX

We describe the 1.2 update to NLOX, a computer program for calculations in high-energy particle physics. New features since the 1.0 release and other changes are described, along with usage documentation.

Is X(7200) the heavy anti-quark diquark symmetry partner of X(3872)?

The D^{(*)}Xi _{cc}^{(*)} system and {bar{Xi }}_{cc}^{(*)}Xi _{cc}^{(*)} system can be related to the D^{(*)}{bar{D}}^{(*)} system via heavy anti-quark di-quark symmetry (HADS). In this work, we employ a contact-range effective field theory to systematically investigate the likely existence of molecules in these systems in terms of the hypothesis that X(3872) is a 1^{++}~D{bar{D}}^{*} bound state in the isospin symmetry limit, with some of the unknown low energy constants estimated using the light-meson saturation approximation. In the meson–meson system, a J^{PC}=2^{++}~{bar{D}}^{*}D^{*} molecule commonly referred to as X(4013) is reproduced, which is the heavy quark spin partner of X(3872). In the meson-baryon system, we predict two triply charmed pentaquark molecules, J^{P}=1/2^{-}~D^{*}Xi _{cc} and J^{P}=5/2^{-}~D^{*}Xi _{cc}^{*}. In the baryon-baryon system, there exist seven di-baryon molecules, J^{PC}=0^{-+}~{bar{Xi }}_{cc}Xi _{cc}, J^{PC}=1^{--}~{bar{Xi }}_{cc}Xi _{cc}, J^{PC}=1^{-+}~{bar{Xi }}_{cc}Xi _{cc}^{*}, J^{PC}=1^{--}~{bar{Xi }}_{cc}Xi _{cc}^{*}, J^{PC}=2^{-+}~{bar{Xi }}_{cc}Xi _{cc}^{*}, J^{PC}=2^{-+}~{bar{Xi }}_{cc}^{*}Xi _{cc}^{*}, and J^{PC}=3^{--}~{bar{Xi }}_{cc}^{*}Xi _{cc}^{*}. Among them, the J^{PC}=0^{-+}~{bar{Xi }}_{cc}Xi _{cc} molecule may contribute to the X(7200) state recently observed by the LHCb Collaboration, which implies that X(7200) can be related to X(3872) via HADS. As a byproduct, with the heavy quark flavor symmetry we also study likely existence of molecular states in the B^{(*)}{bar{B}}^{(*)}, {bar{B}}^{(*)}Xi _{bb}^{(*)}, and {bar{Xi }}_{bb}^{(*)}Xi _{bb}^{(*)} systems.

Photoproduction of strange hidden-charm and hidden-bottom states

Recently BESIII collaboration discovered a charged strange hidden-charm state Z_{cs}(3985) in the D_s^-D^{*0} + D_s^{*-}D^{0} spectrum. A higher Z'_{cs} state coupling to {bar{D}}_s^{*-}D^{*0} is expected by SU(3)-flavor symmetry, and their bottom partners are anticipated by heavy quark flavor symmetry. Here we study the photoproduction of these exotic states and investigate carefully the background from Pomeron exchange. Our results indicate that the maximal photoproduction cross section of strange partner is around 1–2 orders of magnitude smaller than that of the corresponding non-strange states. The possibility of searching for them in future electron-ion colliders (EIC) is briefly discussed.