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How can $X^{pm}(5568)$ escape detection?

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 Added by HongWei Ke
 Publication date 2018
  fields
and research's language is English




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Multi-quark states were predicted by Gell-Mann when the quark model was first formulated. Recently, numerous exotic states that are considered to be multi-quark states have been experimentally confirmed (four-quark mesons and five-quark baryons). Theoretical research indicates that the four-quark state might comprise molecular and/or tetraquark structures. We consider that the meson containing four different flavors $subar bbar d$ should exist and decay via the $X(5568)to B_spi$ channel. However, except for the D0 collaboration, all other experimental collaborations have reported negative observations for $X(5568)$ in this golden portal. This contradiction has stimulated the interest of both theorists and experimentalists. To address this discrepancy, we propose that the assumed $X(5568)$ is a mixture of a molecular state and tetraquark, which contributes destructively to $X(5568)to B_spi$. The cancellation may be accidental and it should be incomplete. In this scenario, there should be two physical states with the same flavor ingredients, with spectra of $5344pm307$ and $6318pm315$. $X(5568)$ lies in the error range of the first state. We predict the width of the second state (designated as $S_2$) as $Gamma(X_{S_2}to B_spi)=224pm97$ MeV. We strongly suggest searching for it in future experiments.



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199 - Hong-Wei Ke , Xue-Qian Li 2018
Discovery of $X(5568)$ brings up a tremendous interest because it is very special, i.e. made of four different flavors. The D0 collaboration claimed that they observed this resonance through portal $X(5568)to B_spi$, but unfortunately, later the LHCb, CMS, CDF and ATLAS collaborations reports indicate that no such state was found. Almost on the Eve of 2017, the D0 collaboration reconfirmed existence of $X(5568)$ via the semileptonic decay of $B_s$. To further reveal the discrepancy, supposing $X(5568)$ as a molecular state, we calculate the decay rate of $X(5568)rightarrow B_spi^+$ in an extended light front model. Numerically, the theoretically predicted decay width of $Gamma(X(5568)rightarrow B_spi^+)$ is $20.28$ MeV which is consistent with the result of the D0 collaboration ($Gamma=18.6^{+7.9}_{-6.1}(stat)^{+3.5}_{-3.8}(syst)$ MeV). Since the resonance is narrow, signals might be drowned in a messy background. In analog, two open-charm molecular states $DK$ and $BD$ named as $X_a$ and $X_b$, could be in the same situation. The rates of $X_ato D_spi^0$ and $X_bto B_cpi^0$ are estimated as about 30 MeV and 20 MeV respectively. We suggest the experimental collaborations round the world to search for these two modes and accurate measurements may provide us with valuable information.
Stimulated by the recent observation of the $X(5568)$, we study the $X(5568)$ and its partners under the tetraquark scenario. In the framework of the color-magnetic interaction, we estimate the masses of the partner states of the $X(5568)$ and discuss their decay pattern, which provide valuable information on the future experimental search of these states.
We consider the production of charmed baryons and mesons in the proton-antiproton binary reactions at the energies of the future $bar{P}$ANDA experiment. To describe these processes in terms of hadronic interaction models, one needs strong couplings of the initial nucleons with the intermediate and final charmed hadrons. Similar couplings enter the models of binary reactions with strange hadrons. For both charmed and strange hadrons we employ the strong couplings and their ratios calculated from QCD light-cone sum rules. In this method finite masses of $c$ and $s$ quarks are taken into account. Employing the Kaidalovs quark-gluon string model with Regge poles and adjusting the normalization of the amplitudes in this model to the calculated strong couplings, we estimate the production cross section of charmed hadrons. For $pbar{p}to Lambda_cbar{Lambda}_c$ it can reach several tens of $nb$ at $p_{lab}= 15 {GeV}$, whereas the cross sections of $Sigma_c$ and $D$ pair production are predicted to be smaller.
The problem of estimating the effect of missing higher orders in perturbation theory is analyzed with emphasis in the application to Higgs production in gluon-gluon fusion. Well-known mathematical methods for an approximated completion of the perturbative series are applied with the goal to not truncate the series, but complete it in a well-defined way, so as to increase the accuracy - if not the precision - of theoretical predictions. The uncertainty arising from the use of the completion procedure is discussed and a recipe for constructing a corresponding probability distribution function is proposed.
107 - R. Albuquerque 2016
We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order (LO) predicting the masses of the BK molecule and (su)bar(bd) four-quark states. We improve these results by adding NLO and N2LO corrections to the PT contributions giving a more precise meaning on the b-quark mass definition used in the analysis. We extract our optimal predictions using Laplace sum rule (LSR) within the standard stability criteria versus the changes of the external free parameters (tau-sum rule variable, t_c continuum threshold and subtraction constant mu). The smallness of the higher order PT corrections justifies (a posteriori) the LO order results + the uses of the ambiguous heavy quark mass to that order. However, our predicted spectra in the range (5173sim 5226) MeV, summarized in Table 7, for exotic hadrons built with four different flavours (buds), do not support some previous interpretations of the D0 candidate[1], X(5568), as a pure molecule or a four-quark state. If experimentally confirmed, it could result from their mixing with an angle: sin 2thetaapprox 0.15. One can also scan the region (2327~ 2444) MeV (where the D*_{s0}(2317) might be a good candidate) and the one (5173~ 5226) MeV for detecting these (cuds) and (buds) unmixed exotic hadrons (if any) via, eventually, their radiative or pi+hadrons decays.
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