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Register a new userProduction of the bottomonium-like states $Z_b$ states at $e$-$h$ and ultraperipheral $h$-$h$ collisions
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The photoproduction of bottomonium-like states $Z_{b}(10610)$ and $Z_{b}(10650)$ via $gamma p$ scattering is studied within an effectiv Lagrangian approach and the vector-meson-dominance model. The Regge model is employed to calculate the photoproduction of $Z_{b}$ states via $t$-channel with $pi$ exchange.The numerical results show that the values of the total cross-sections of $Z_{b}(10610)$ and $Z_{b}(10650)$ can reach 0.09 nb and 0.02 nb, respectively, near the center of mass energy of 22 GeV. The experimental measurements and studies on the photoproduction of $Z_{b}$ states near energy region around $Wsimeq 22$ GeV is suggested. Moreover, with the help of eSTARlight and STARlight programs, one obtains the cross-sections and event numbers of $Z_{b}(10610)$ production in electron-ion collision (EIC) and Ultraperipheral collisions (UPCs). The results show that a considerable number of events from $Z_{b}(10610)$ can be produced on the relevant experiments of EICs and UPCs. Also, one calculates the rates and kinematic distributions for $gamma prightarrow Z_{b}n$ in $ep$ and $pA$ collisions via EICs and UPCs, and the relevant results will provide an important reference for the RHIC, LHC, EIC-US, LHeC, and FCC experiments to search for the bottomonium-like $Z_{b}$ states.
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We search for rare decays of $D$ mesons to hadrons accompany with an electron-positron pair (h(h)$e^+e^-$), using an $e^+e^-$ collision sample corresponding to an integrated luminosity of 2.93 fb$^{-1}$ collected with the BESIII detector at $sqrt{s}$ = 3.773 GeV. No significant signals are observed, and the corresponding upper limits on the branching fractions at the $90%$ confidence level are determined. The sensitivities of the results are at the level of $10^{-5} sim 10^{-6}$, providing a large improvement over previous searches.
Heavy quarkonium production in ultraperipheral nuclear collisions is described within the QCD dipole formalism. Realistic quarkonium wave functions in the rest frame are calculated solving the Schrodinger equation with a subsequent Lorentz boost to high energy. We rely on several selected $Qbar Q$ potentials, which provide the best description of quarkonium spectra and decay widths, as well as data on diffractive electroproduction of quarkonia on protons. Nuclear effects are calculated with the phenomenological dipole cross sections fitted to DIS data. Higher twist effect related to the lowest $Qbar Q$ Fock component of the photon, as well as the leading twist effects, related to higher components containing gluons, are included. The results for coherent and incoherent photoproduction of charmonia and bottomonia on nuclei are in a good accord with available data from the recent UPC measurements at the LHC. They can also be verified in future experiments at the planned electron-ion colliders.
The dominant contributions to W-+ H+- production at the LHC are the tree-level b anti-b annihilation and the gg fusion. We perform for the case of the complex MSSM a complete calculation of the NLO EW corrections to the b anti-b annihilation channel and a consistent combination with other contributions including the standard and SUSY QCD corrections and the gg fusion, with resummation of the leading radiative corrections to the bottom-Higgs couplings and the neutral Higgs-boson propagators. We observe a large CP-violating asymmetry, arising mainly from the gg channel.
The extremely neutron-rich system $^{6}$H was studied in the direct $^2text{H}(^8text{He},{^4text{He}})^{6}$H transfer reaction with a 26 $A$ MeV secondary $^{8}$He beam. The measured missing mass spectrum shows a broad bump at $sim 4-8$ MeV energy relative to the $^3$H+$3n$ decay threshold. This bump can be interpreted as a broad resonant state in $^{6}$H at $6.8(5)$ MeV. The population cross section of such a presumably $p$-wave state (or may be few overlapping states) in the energy range from 4 to 8 MeV is $dsigma/dOmega_{text{c.m.}} simeq 190(40)$ $mu$b/sr in the angular range $5^{circ}<theta_{text{c.m.}}<16^{circ}$. The obtained missing mass spectrum is practically free of the $^{6}$H events below 3.5 MeV ($dsigma/dOmega_{text{c.m.}} lesssim 5$ $mu$b/sr in the same angular range). The steep rise of the $^{6}$H missing mass spectrum at $sim 3$ MeV allows to derive the lower limit for the possible resonant state energy in $^{6}$H of $4.5(3)$ MeV. According to the paring energy estimates, such a $4.5(3)$ MeV resonance is a realistic candidate for the $^{6}$H ground state (g.s.). The obtained results confirm that the decay mechanism of the $^{7}$H g.s. (located at 2.2 MeV above the $^{3}$H+$4n$ threshold) is the true (or simultaneous) $4n$ emission. The resonance energy profiles and the momentum distributions of fragments of the sequential $^{6}$H$ ,rightarrow , ^5$H(g.s.)+$n, rightarrow , ^3$H+$3n$ decay were analyzed by the theoretically-updated direct four-body-decay and sequential-emission mechanisms. The measured momentum distributions of the $^{3}$H fragments in the $^{6}$H rest frame indicate very strong dineutron-type correlations in the $^{5}$H ground state decay.
Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He I spectrum are needed to determine the primordial helium abundance to a precision of $< 1$% in order to constrain Big Bang Nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H I, we showed that differences in $l$-changing collisional rate coefficients predicted by three different theories can translate into 10% changes in predictions for H I spectra. Here we consider the more complicated case of He atoms, where low-$l$ subshells are not energy degenerate. A criterion for deciding when the energy separation between $l$ subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by Pengelly & Seaton (1964) is not sufficiently accurate. We introduce a simple modification of this theory which leads to rate coefficients which agree well with those obtained from pure quantal calculations using the approach of Vrinceanu et al. (2012). We show that the $l$-changing rate coefficients from the different theoretical approaches lead to differences of $sim 10$% in He I emissivities in simulations of H II regions using spectral code Cloudy.
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