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1. $$X(3872)$$transport in heavy-ion collisions

   https://doi.org/10.1140/epja/s10050-021-00435-6  

   Wu, Biaogang; Du, Xiaojian; Sibila, Matthew; Rapp, Ralf (April 2021, The European Physical Journal A)

   Abstract The production of the$$X(3872)$$ $X\left(3872\right)$ particle in heavy-ion collisions has been contemplated as an alternative probe of its internal structure. To investigate this conjecture, we perform transport calculations of the$$X(3872)$$ $X\left(3872\right)$ through the fireball formed in nuclear collisions at the LHC. Within a kinetic-rate equation approach as previously used for charmonia, the formation and dissociation of the$$X(3872)$$ $X\left(3872\right)$ is controlled by two transport parameters,i.e., its inelastic reaction rate and thermal-equilibrium limit in the evolving hot QCD medium. While the equilibrium limit is controlled by the charm production cross section in primordial nucleon-nucleon collisions (together with the spectra of charm states in the medium), the structure information is encoded in the reaction rate. We study how different scenarios for the rate affect the centrality dependence and transverse-momentum ($$p_T$$ $p_T$) spectra of the$$X(3872)$$ $X\left(3872\right)$. Larger reaction rates associated with the loosely bound molecule structure imply that it is formed later in the fireball evolution than the tetraquark and thus its final yields are generally smaller by around a factor of two, which is qualitatively different from most coalescence model calculations to date. The$$p_T$$ $p_T$ spectra provide further information as the later decoupling time within the molecular scenario leads to harder spectra caused by the blue-shift from the expanding fireball. 

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2. Measurement of χc1(3872) production in proton-proton collisions at $$ \sqrt{s} $$ = 8 and 13 TeV

   https://doi.org/10.1007/JHEP01(2022)131  

   Aaij, R.; Abdelmotteleb, A. S.; Abellán Beteta, C.; Abudinen Gallego, F. J.; Ackernley, T.; Adeva, B.; Adinolfi, M.; Afsharnia, H.; Agapopoulou, C.; Aidala, C. A.; et al (January 2022, Journal of High Energy Physics)

   A bstract The production cross-section of the χ c 1 (3872) state relative to the ψ (2 S ) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $$ \sqrt{s} $$ s = 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb − 1 , respectively. The two mesons are reconstructed in the J/ψπ + π − final state. The ratios of the prompt and nonprompt χ c 1 (3872) to ψ (2 S ) production cross-sections are measured as a function of transverse momentum, p T , and rapidity, y , of the χ c 1 (3872) and ψ (2 S ) states, in the kinematic range 4 < p T < 20 GeV/ c and 2 . 0 < y < 4 . 5. The prompt ratio is found to increase with p T , independently of y . For the prompt component, the double ratio of the χ c 1 (3872) and ψ (2 S ) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of p T and centre-of-mass energy. 

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3. Search for the $$ {B}_c^{+} $$ → χc1(3872)π+ decay

   https://doi.org/10.1007/JHEP06(2025)013  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (June 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> A search for the decay$$ {B}_c^{+} $$ $B_c^{+}$→ χ_c1(3872)π⁺is reported using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb⁻¹. No significant signal is observed. Using the decay$$ {B}_c^{+} $$ $B_c^{+}$→ψ(2S)π⁺as a normalisation channel, an upper limit for the ratio of branching fractions$$ {\mathcal{R}}_{\psi (2S)}^{\chi_{c1}(3872)}=\frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c1}(3872){\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to \psi (2S){\pi}^{+}}}\times \frac{{\mathcal{B}}_{\chi_{c1}(3872)\to J/\psi {\pi}^{+}{\pi}^{-}}}{{\mathcal{B}}_{\psi (2S)\to J/\psi {\pi}^{+}{\pi}^{-}}}<0.05(0.06), $$ $R_{\psi \left(2S\right)}^{{\chi }_{c1}\left(3872\right)}=\frac{B_{B_c^{+}\to {\chi }_{c1}\left(3872\right){\pi }^{+}}}{B_{B_c^{+}\to \psi \left(2S\right){\pi }^{+}}}\times \frac{B_{{\chi }_{c1}\left(3872\right)\to J/\psi {\pi }^{+}{\pi }^{-}}}{B_{\psi \left(2S\right)\to J/\psi {\pi }^{+}{\pi }^{-}}}<0.05\left(0.06\right),$ is set at the 90 (95)% confidence level. 

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4. Forming molecular states with hadronic rescattering

   https://doi.org/10.1140/epja/s10050-021-00650-1  

   Ilten, Philip; Utheim, Marius (January 2022, The European Physical Journal A)

   Abstract A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the$$\chi _{c1}(3872)$$ ${\chi }_{c1}\left(3872\right)$resonance, a possible tetraquark state, as well as three possible pentaquark states,$$P_c^+(4312)$$ $P_c^{+}\left(4312\right)$,$$P_c^+(4440)$$ $P_c^{+}\left(4440\right)$, and$$P_c^+(4457)$$ $P_c^{+}\left(4457\right)$. For the$$P_c^+$$ $P_c^{+}$states, the expected cross section from$$\Lambda _b$$ ${\Lambda }_b$decays is compared to the hadronic-rescattering production. The$$\chi _{c1}(3872)$$ ${\chi }_{c1}\left(3872\right)$cross section is compared to the fiducial$$\chi _{c1}(3872)$$ ${\chi }_{c1}\left(3872\right)$cross-section measurement by LHCb and found to contribute at a level of$${\mathcal {O}({1\%})}$$ $O\left(1\%\right)$. Finally, the expected yields of$$\mathrm {P_c^{+}}$$ $P_c^{+}$production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt$$\mathrm {P_c^{+}}$$ $P_c^{+}$signal from hadronic rescattering. 

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5. Higgs boson decay to charmonia via c-quark fragmentation

   https://doi.org/10.1007/JHEP08(2022)073  

   Han, Tao; Leibovich, Adam K.; Ma, Yang; Tan, Xiao-Ze (August 2022, Journal of High Energy Physics)

   A bstract We calculate the decay branching fractions of the Higgs boson to J / ψ and η c via the charm-quark fragmentation mechanism for the color-singlet and color-octet states in the framework of non-relativistic QCD. The decay rates are governed by the charm-quark Yukawa coupling, unlike the decay H → J / ψ + γ , which is dominated by the γ ∗ - J / ψ mixing. We find that the decay branching fractions can be about 2 × 10 − 5 for $$ H\to c\overline{c}+J/\psi $$ H → c c ¯ + J / ψ , and 6 × 10 − 5 for $$ H\to c\overline{c}+{\eta}_c $$ H → c c ¯ + η c . We comment on the perspective of searching for the Higgs boson to J / ψ transition at the High-Luminosity LHC for testing the charm-quark Yukawa coupling. 

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