The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e24330" altimg="si34.svg"><mml:mrow><mml:mi>X</mml:mi><mml:mi>Y</mml:mi><mml:mi>Z</mml:mi></mml:mrow></mml:math> states: Experimental and theoretical status and perspectives

Brambilla, Nora; Eidelman, S.; Hanhart, C.; Nefediev, A. V.; Shen, C. P.; Thomas, C.; Vairo, Antonio; Yuan, C. Z.

doi:10.1016/j.physrep.2020.05.001

Cited by 753 publications

(371 citation statements)

References 939 publications

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“…So far there is no conclusion on which interpretation is the correct one, see Refs. [3][4][5][6][7] for reviews of the experimental and theoretical status of the subject.…”

Section: Introductionmentioning

confidence: 99%

QCD spin effects in the heavy hybrid potentials and spectra

et al. 2020

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The spin-dependent operators for heavy quarkonium hybrids have been recently obtained in a nonrelativistic effective field theory approach up to next-to-leading order in the heavy-quark mass expansion. In the effective field theory for hybrids several operators not found in standard quarkonia appear, including an operator suppressed by only one power of the heavy-quark mass. We compute the matching coefficients for these operators in the short heavy-quark-antiquark distance regime, r ≪ 1=Λ QCD , by matching weakly coupled potential nonrelativistic QCD to the effective field theory for hybrids. In this regime the perturbative and nonperturbative contributions to the matching coefficients factorize, and the latter can be expressed in terms of purely gluonic correlators whose form we explicitly calculate with the aid of the transformation properties of the gluon fields under discrete symmetries. We detail our previous comparison with direct lattice computations of the charmonium hybrid spectrum, from which the unknown nonperturbative contributions can be obtained, and extend it to datasets with different light-quark masses.

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“…So far there is no conclusion on which interpretation is the correct one, see Refs. [3][4][5][6][7] for reviews of the experimental and theoretical status of the subject.…”

Section: Introductionmentioning

confidence: 99%

QCD spin effects in the heavy hybrid potentials and spectra

et al. 2020

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“…For reviews of these so-called XYZ mesons and related exotic states, see Refs. [2][3][4][5][6][7][8][9][10][11][12][13], and for a review dedicated to the Xð3872Þ, see Ref. [14].…”

Section: Introductionmentioning

confidence: 99%

Revisiting X(3872)→D0D¯0π0

2020

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The calculation of the decay Xð3872Þ → D 0D0 π 0 in effective field theory is revisited to include final state π 0 D 0 , π 0D0 and D 0D0 rescattering diagrams. These introduce significant uncertainty into the prediction for the partial width as a function of the binding energy. The differential distribution in the pion energy is also studied for the first time. The normalization of the distribution is again quite uncertain due to higher order effects but the shape of the distribution is unaffected by higher order corrections. Furthermore the shape of the distribution and the location of the peak are sensitive to the binding energy of Xð3872Þ. The shape is strongly impacted by the presence of virtual D Ã0 graphs which highlights the molecular nature of the Xð3872Þ. Measurement of the pion energy distribution in the decay Xð3872Þ → D 0D0 π 0 can reveal interesting information about the binding nature of the Xð3872Þ.

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“…During this time a plethora of new states have been observed, including candidates for four-quark (tetraquark) states, and more recently five-quark (pentaquark) states [1-3] (see Refs. [4][5][6] for recent reviews). In addition, a number of observations of peaking structures in the invariant-mass spectra of final states containing Ξ þ c K − [7], Ξ 0 b π − [8], Λ 0 b π − [9], and Λ 0 b π þ π − [10,11] have provided valuable experimental information to improve our understanding of quantum chromodynamics (QCD), the theory of the strong interaction.…”

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confidence: 99%

“…For example, in QCD, two quarks can exhibit attraction when in a J P ¼ 0 þ quantum state, giving rise to the notion that conventional baryons can be described as the bound state of a quark and a qq 0 diquark [15,16]. These ideas are naturally extensible to describe tetraquark and pentaquark candidates [4][5][6].…”

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confidence: 99%

First Observation of Excited Ωb− States

Aaij¹,

Beteta²,

Ackernley³

et al. 2020

Phys. Rev. Lett.

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We report four narrow peaks in the Ξ 0 b K − mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb −1 recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m½Ωwhere the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξ 0 b mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Γ½Ω b ð6316Þ − < 2.8 MeV, Γ½Ω b ð6330Þ − < 3.1 MeV and Γ½Ω b ð6340Þ − < 1.5 MeV. The natural width of the Ω b ð6350Þ − peak is 1.4 þ1.0 −0.8 AE 0.1 MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ω b ð6316Þ − and Ω b ð6330Þ − peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ω − b resonances.

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The XYZ states: Experimental and theoretical status and perspectives

Cited by 753 publications

References 939 publications

QCD spin effects in the heavy hybrid potentials and spectra

QCD spin effects in the heavy hybrid potentials and spectra

Revisiting X(3872)→D0D¯0π0

First Observation of Excited Ωb− States

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