Abstract
We have done the exploratory study of bottom tetraquarks ($[bq\bar b \bar q];{q\in u,d}$) in the diquark-antidiquark framework with the inclusion of spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction. Our focus here is on the $Y_b$(10890) and other exotic states in the bottom sector. We have predicted some of the bottom counterparts to the charm tetraquark candidates. Our present study shows that if $Z_b(10610)$ and $Z_b(10650)$ are diquark-diantiquark states then they have to be first radial excitations only and we have predicted $Z_b(10650)$ state as first radial excitation of tetraquark state $X_b$ (10.143-10.230). We have identified $X_b$ state with $J^{PC}= 1^{+-}/0^{++}$ as being the analogue of $Z_c(3900)$. An observation of the $X_b$ will provide a deeper insight into the exotic hadron spectroscopy and is helpful to unravel the nature of the states connected by the heavy quark symmetry. We particularly focus on the lowest P wave $[bq][\bar b\bar q]$ states with $J^{PC}=1^{--}$ by computing their leptonic, hadronic and radiative decay widths to predict the status of still controversial $Y_b$(10890) state. Apart from this, we have also shown here the possibility of mixing of P wave states. In the case of mixing of $1^{--}$ state with different spin multiplicities, we found that predicted masses of the mixed P states differ from $Y_b$(10890) state only by $\pm20$ MeV energy difference which can be helpful to resolve further the structure of $Y_b$(10890).
Highlights
In recent years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic new quarkonia states, narrow resonances, called X, Y, Z particles, which do not seem to have a simple qqstructure. Their masses and decay modes show that they contain a heavy quark–antiquark pair, but their quantum numbers are such that they must contain a light quark–antiquark pair [17]
There are most likely many more which are yet unknown and many of them should reflect in the bbsector according to heavy quark symmetry
The CMS experiment searched for the bottomonium partner of X (3872) at hadron colliders [22] in the Υ(1S)π π decay mode and found no evidence for the Xb state, while the ratio of the cross section Xb to Υ(2S) shows an upper limit in the range of (0.9–5.4) % at 95 % confidence level for Xb masses between 10–11 GeV
Summary
In recent years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic new quarkonia states, narrow resonances, called X, Y, Z particles, which do not seem to have a simple qqstructure. Motivated by the BaBar discovery of a large Y (4260) → π + π + J/ψ signal in the charmonium mass region, the Belle experiment has searched for a similar state in the bottomonium sector [23] They observed partial decay widths Υ(5S) → π + π + Υ(nS) (n = 1, 2, 3) associated with the peak in the π + π + Υ(nS) cross section hundreds of times larger than the theoretical predictions [1] and the corresponding measured rates for the Υ(4S) [24]. The experimental search for tetraquark states is a very difficult problem, since exotic candidates are nothing but the resonances immersed in the excited hadron spectra and, they usually decay to several hadrons Their mass and decay products put them in the category of quarkonia-like resonances but their masses do not fit into the conventional quark model spectrum of quark–antiquark mesons [38,39].
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