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Register a new user$Dbar{D}^*$ scattering and $chi_{c1}(3872)$ in nuclear matter
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We study the behaviour of the $chi_{c1}(3872)$, also known as $X(3872)$, in dense nuclear matter. We begin from a picture in vacuum of the $X(3872)$ as a purely molecular $(D bar D^*-c.c.)$ state, generated as a bound state from a heavy-quark symmetry leading-order interaction between the charmed mesons, and analyze the $D bar D^*$ scattering $T-$matrix ($T_{D bar D^*}$) inside of the medium. Next, we consider also mixed-molecular scenarios and, in all cases, we determine the corresponding $X(3872)$ spectral function and the $D bar D^*$ amplitude, with the mesons embedded in the dense environment. We find important nuclear corrections for $T_{D bar D^*}$ and the pole position of the resonance, and discuss the dependence of these results on the $D bar D^*$ molecular component in the $X(3872)$ wave-function. These predictions could be tested in the finite-density regime that can be accessed in the future CBM and PANDA experiments at FAIR.
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Prompt $chi_c$ production at hadron colliders may provide a unique test for the color-octet mechanism in nonrelativistic QCD. We present an analysis for the polarization observables of $chi_{c1}$ and $chi_{c2}$ at next-to-leading order in $alpha_S$, and propose to measure them at the LHC, which is expected to be important for testing the validity of NRQCD.
Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $Lambda_b^0to chi_{c1}(3872)pK^-$ with $chi_{c1}to J/psipi^+pi^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58pm15)%$ of the decays proceed via the two-body intermediate state $chi_{c1}(3872)Lambda(1520)$. The~branching fraction with respect to that of the $Lambda_brightarrowpsi(2S)p K^{-}$ decay mode, where the $psi(2S)$~meson is reconstructed in the $J/psi pi^+pi^-$ final state, is measured to be: begin{equation*} frac{Lambda_b^0tochi_{c1}(3872)pK^-}{Lambda_btopsi(2S)p K^-} times frac{mathcal{B}(chi_{c1} to J/psi pi^+pi^-)}{mathcal{B}(psi(2S)to J/psi pi^+pi^-)} = left(5.4 pm 1.1 pm 0.2right)times 10^{-2},, end{equation*} where the first uncertainty is statistical and the second is systematic.
A study of the lineshape of the $chi_{c1}(3872)$ state is made using a data sample corresponding to an integrated luminosity of $3,$fb$^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7 and 8,TeV with the LHCb detector. Candidate $chi_{c1}(3872)$ and $psi(2S)$ mesons from b-hadron decays are selected in the $ J/psi pi^+ pi^-$ decay mode. Describing the {mbox{lineshape}} with a Breit--Wigner function, the mass splitting between the $chi_{c1}(3872)$ and $psi(2S)$ states, $Delta m$, and the width of the $chi_{c1}(3872)$ state, $Gamma_{mathrm{BW}}$, are determined to be begin{eqnarray*} Delta m & = & 185.598 pm 0.067 pm 0.068, mathrm{MeV} ,, Gamma_{mathrm{BW}} & = & phantom{00}1.39phantom{0} pm 0.24phantom{0} pm 0.10phantom{0} mathrm{MeV} ,, end{eqnarray*} where the first uncertainty is statistical and the second systematic. Using a Flatte-inspired model, the mode and full width at half maximum of the lineshape are determined to be begin{eqnarray*} mathrm{mode} & = 3871.69^{,+,0.00,+,0.05}_{,-,0.04,-,0.13} &mathrm{MeV} mathrm{FWHM} & = 0.22^{,+,0.07,+,0.11}_{,-,0.06,-,0.13}& mathrm{MeV} . end{eqnarray*} An investigation of the analytic structure of the Flatte amplitude reveals a pole structure, which is compatible with a quasi-bound $D^0bar{D}^{*0}$ state but a quasi-virtual state is still allowed at the level of $2$ standard deviations.
Using a total of $9.0~mathrm{fb}^{-1}$ of $e^+e^-$ collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes $e^+e^-to gamma X(3872)$ with $X(3872)topi^0chi_{cJ}$ for $J=0,1,2$. We report the first observation of $X(3872)topi^{0}chi_{c1}$, a new decay mode of the $X(3872)$, with a statistical significance of more than 5$sigma$. Normalizing to the previously established process $e^+e^-to gamma X(3872)$ with $X(3872)topi^+pi^-J/psi$, we find ${cal B}(X(3872) to pi^0 chi_{c1})/{cal B}(X(3872) to pi^+pi^- J/psi) = 0.88^{+0.33}_{-0.27}pm0.10$, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to $pi^0chi_{c0}$ and $pi^0chi_{c2}$ of 19 and 1.1, respectively.
The production of $chi_{c1}(3872)$ and $psi(2S)$ hadrons is studied as a function of charged particle multiplicity in $pp$ collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2 fb$^{-1}$. For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of $chi_{c1}(3872)$ to $psi(2S)$ cross-sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in $b$-hadron decays. This behavior is consistent with a calculation that models the $chi_{c1}(3872)$ structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the $chi_{c1}(3872)$ state are discussed.
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