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Register a new user$b bar b$ Kinematic Correlations in Cold Nuclear Matter
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R. Vogt
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Background: The LHCb Collaboration has studied a number of kinematic correlations between $B$-hadron pairs through their subsequent decays to $J/psi$ pairs at 7 and 8 TeV for four minimum values of the $J/psi$ $p_T$. Purpose: In this work, these measurements are compared to calculations of $b bar b$ pairs and their hadronization and inclusive decays to $J/psi J/psi$ are compared to the same observables. Potential cold matter effects on the $b bar b$ pair observables are discussed to determine which are most likely to provide insights about the system and why. Methods: The calculations, employing the exclusive HVQMNR code, assume the same intrinsic $k_T$-broadening and fragmentation as in [R. Vogt, Phys. Rev. C {bf 98} (2018) 034907]. The pair distributions presented by LHCb are calculated in this approach, both for the parent $b bar b$ and the $J/psi J/psi$ pairs produced in their decay. The sensitivity of the results to the intrinsic $k_T$ broadening is shown. The theoretical uncertainties due to the $b$ quark mass and scale variations on both the initial $b bar b$ pairs and the resulting $J/psi$ pairs are also shown. Possible effects due to the presence of the nucleus are studied by increasing the size of the $k_T$ broadening and modification of the fragmentation parameter. Results: Good agreement with the LHCb data is found for all observables. The parent $b bar b$ distributions are more sensitive to the $k_T$ broadening than are the final-state $J/psi$ pairs. Conclusions: Next-to-leading order calculations with $k_T$ broadening, as in [R. Vogt, Phys. Rev. C {bf 98} (2018) 034907], can describe all correlated observables. Multiple measurements of correlated observables are sensitive to different nuclear effects which can help distinguish between them.
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In this work, we preform a systematic investigation about hidden heavy and doubly heavy molecular states from the $D^{(*)}bar{D}^{(*)}/B^{(*)}bar{B}^{(*)}$ and $D^{(*)}D^{(*)}/bar{B}^{(*)}bar{B}^{(*)}$ interactions in the quasipotential Bethe-Salpeter equation (qBSE) approach. With the help of the Lagrangians with heavy quark and chiral symmetries, interaction potentials are constructed within the one-boson-exchange model in which we include the $pi$, $eta$, $rho$, $omega$ and $sigma$ exchanges, as well as $J/psi$ or $Upsilon$ exchange. Possible bound states from the interactions considered are searched for as the pole of scattering amplitude. The results suggest that experimentally observed states, $Z_c(3900)$, $Z_c(4020)$, $Z_b(10610)$, and $Z_b(10650)$, can be related to the $Dbar{D}^{*}$, $D^*bar{D}^{*}$, $Bbar{B}^{*}$, and $B^*bar{B}^{*}$ interactions with quantum numbers $I^G(J^P)=1^+(1^{+})$, respectively. The $Dbar{D}^{*}$ interaction is also attractive enough to produce a pole with $0^+(0^+)$ which is related to the $X(3872)$. Within the same theoretical frame, the existence of $Dbar{D}$ and $Bbar{B}$ molecular states with $0(0^+)$ are predicted. The possible $D^*bar{D}^*$ molecular states with $0(0^+, 1^+, 2^+)$ and $1(0^+)$ and their bottom partners are also suggested by the calculation. In the doubly heavy sector, no bound state is produced from the $DD/bar{B}bar{B}$ interaction while a bound state is found with $0(1^+)$ from $DD^*/bar{B}bar{B}^*$ interaction. The $D^*D^*/bar{B}^*bar{B}^*$ interaction produces three molecular states with $0(1^+)$, $0(2^+)$ and $1(2^+)$.
We perform a quantitative analysis of the $bbbar{b}bar{b}$ tetraquark decays into hidden- and open-bottom mesons and calculate, for the first time, the $bbbar{b}bar{b}$ tetraquark total decay width. On the basis of our results, we propose the $bbbar{b}bar{b} to B^{+} B^{-} (B^0 bar{B}^0) (B_s^0 bar{B}_s^0) to l^{+} l^{-}+text{X}$ decays as the most suitable channels to observe the $bbbar{b}bar{b}$ tetraquark states, since the calculated two-lepton cross section upper limit, $simeq 39 $ fb, is so large as to be potentially detectable with the 2018 LHCb sensitivity, paving the way to the observation of the $bbbar{b}bar{b}$ tetraquark in the future LHCb upgrade. The $4mu$ signal for the ground state, $J^{PC}=0^{++}$, is likely to be too small even for the upgraded LHCb, but it may not be hopeless for the $J^{PC}=2^{++}$ fully-bottom state.
Background: It has been proposed that the azimuthal distributions of heavy flavor quark-antiquark pairs may be modified in the medium of a heavy-ion collision. Purpose: This work tests this proposition through next-to-leading order (NLO) calculations of the azimuthal distribution, $dsigma/dphi$, including transverse momentum broadening, employing $<k_T^2>$ and fragmentation in exclusive $Q bar Q$ pair production. While these studies were done for $p+p$, $p + bar p$ and $p+$Pb collisions, understanding azimuthal angle correlations between heavy quarks in these smaller, colder systems is important for their interpretation in heavy-ion collisions. Methods: First, single inclusive $p_T$ distributions calculated with the exclusive HVQMNR code are compared to those calculated in the fixed-order next-to-leading logarithm approach. Next the azimuthal distributions are calculated and sensitivities to $<k_T^2>$, $p_T$ cut, and rapidity are studied at $sqrt{s} = 7$ TeV. Finally, calculations are compared to $Q bar Q$ data in elementary $p+p$ and $p + bar p$ collisions at $sqrt{s} = 7$ TeV and 1.96 TeV as well as to the nuclear modification factor $R_{p {rm Pb}}(p_T)$ in $p+$Pb collisions at $sqrt{s_{NN}} = 5.02$ TeV measured by ALICE. Results: The low $p_T$ ($p_T < 10$ GeV) azimuthal distributions are very sensitive to the $k_T$ broadening and rather insensitive to the fragmentation function. The NLO contributions can result in an enhancement at $phi sim 0$ absent any other effects. Agreement with the data was found to be good. Conclusions: The NLO calculations, assuming collinear factorization and introducing $k_T$ broadening, result in significant modifications of the azimuthal distribution at low $p_T$ which must be taken into account in calculations of these distributions in heavy-ion collisions.
We compute the mass-spectra of all bottom tetraquarks [$bb][bar{b}bar{b}$] and heavy-light bottom tetraquarks [$bq][bar{b}bar{q}$] (q=u,d), that are considered to be compact and made up of diquark-antidiquark pairs. The fully bottom tetraquark [$bb][bar{b}bar{b}$] has been studied in $eta_{b}(1S)eta_{b}(1S)$, $eta_{b}(1S)Upsilon(1S)$ and $Upsilon(1S)Upsilon(1S)$ S-wave channels, as well as a few orbitally excited channels, with masses ranging from 18.7 GeV to 19.8 GeV. The masses of heavy-light bottom tetraquarks are studied in the $B^{pm}B^{pm}$, $B^{pm}B^{*}$ and $B^{*}B^{*}$ channels, with masses ranging from 10.4 GeV to 10.5 GeV. Two charged resonances, $Z_{b}(10610)$ and $Z_{b}(10650)$, both with the quantum number $1^{+-}$, have also been investigated.
We have evaluated the decay modes of the $Upsilon(4s), Upsilon(3d), Upsilon(5s), Upsilon(6s)$ states into $Bbar B, Bbar B^*+c.c., B^* bar B^*, B_s bar B_s, B_s bar B^*_s +c.c., B^*_s bar B_s^* $ using the $^3P_0$ model to hadronize the $bbar b$ vector seed, fitting some parameters to the data. We observe that the $Upsilon(4s)$ state has an abnormally large amount of meson-meson components in the wave function, while the other states are largely $bbar b$. We predict branching ratios for the different decay channels which can be contrasted with experiment for the case of the $Upsilon(5s)$ state. While globally the agreement is fair, we call the attention to some disagreement that could be a warning for the existence of more elaborate components in the state.
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