Spectroscopy, lifetime and decay modes of the Tbb− tetraquark

Abstract

We present the first full-fledged study of the flavor-exotic isoscalar T − bb ≡ bbūd tetraquark with spin and parity J P = 1 + . We report accurate solutions of the four-body problem in a quark model, characterizing the structure of the state as a function of the ratio MQ/mq of the heavy to light quark masses. For such a standard constituent model, T − bb lies approximately 150 MeV below the strong decay threshold B −B * 0 and 105 MeV below the electromagnetic decay threshold B −B0 γ. We evaluate the lifetime of T − bb , identifying the promising decay modes where the tetraquark might be looked for in future experiments. Its total decay width is Γ ≈ 87 × 10 −15 GeV and therefore its lifetime τ ≈ 7.6 ps. The promising final states are B * − D * + ℓ −ν ℓ andB * 0 D * 0 ℓ −ν ℓ among the semileptonic decays, and among the nonleptonic ones. The semileptonic decay to the isoscalar J P = 0 + tetraquark T 0 bc is also relevant but it is not found to be dominant. There is a broad consensus about the existence of this tetraquark, and its detection will validate our understanding of the low-energy realizations of Quantum Chromodynamics (QCD) in the multiquark sector. * gajatee@usal.es † javier.vijande@uv.es ‡ valcarce@usal.es § j-m.richard@ipnl.in2p3.fr Hadronic physics has been much stimulated during the last two decades by the experimental discovery of several new resonances in the hidden-charm sector, resonances that are hardly accommodated in the traditional quark-antiquark or three-quark picture [1]. These are the so-called XY Z mesons and LHCb pentaquarks, which belong to the class of "exotic hadrons", although they are not flavor exotics. After several years of studies, no definite conclusion has been drawn as to whether such non-flavor exotic states correspond to multiquark structures or to hadron-hadron molecules. A similar situation was encountered in the light scalar meson sector, where a multiquark picture was first introduced [2] as an attempt to explain the inverted mass spectrum (inverted in comparison to the simple quarkantiquark structure favored by the naive quark model) exhibited by the low-lying scalar mesons, some of which were later on suggested to be meson-meson molecules [3].For years, the sector of flavor-exotic hadrons has been somewhat forgotten, as being less easily accessible than the hidden-flavor sector. However, already some decades ago, investigations on flavor-exotic multiquarks concluded that QQqq four-quark configurations become more and more deeply bound when the mass ratio M Q /m q increases [4]. There is nowadays a broad theoretical consensus about the existence of such unconventional tetraquark configurations for which all strong decays are energetically forbidden. The most promising candidate is an isoscalar tetraquark with double beauty and J P = 1 + quantum numbers, which is stable against strong and electromagnetic decays. The same conclusion about the stability of this state has been reached in a wide variety of theoretical approaches [4][5][6][7][8][9][10][11][12][13][14]. A nov...

Masses of doubly heavy tetraquarks TQQ′ in a relativized quark model

“…In Refs. [41,78], the authors also discussed the dependence of mass ratios between the heavy and light subsystems within nonrelativistic quark model, and showed the same behaviors with our relativized calculations. If one keeps reducing the mass ratios, the doubly heavy tetraquarks will become fully heavy tetraquarks.…”

“…Compared withBB Ã channel, the binding energy is 54 MeV and the decay width should be tiny enough. Although the binding energy is smaller than that of the nonrelativistic quark models[31,32,[37][38][39]63,67,71,73,78,79], we obtain the same conclusion about the stability of this state. The differences may arise from the relativized Hamiltonian, where the smearing potentials and relativistic corrections are included.…”

Double-heavy tetraquarks

“…The mass, lifetime, and decay modes of this tetraquark are investigated in Ref. [54]. A compact double-bottom tetraquark state with IJ P ¼ 01 þ is also presented in heavy-ion collisions at the LHC [55], and actually, in 1988, the dimeson TðbbūdÞ had already been proposed [56].…”

Hidden and Open Heavy-Flavor Hadronic States

“…For a representative state below all possible strong-decay thresholds, for example the T bb tetraquark discussed in Sect. 3.1, we have calculated its decay width due to all plausible semileptonic and nonleptonic decay modes [19]. Some of the corresponding processes are illustrated in Fig.…”