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Register a new userInclusive production of heavy quarkonium $eta_Q$ via $Z$ boson decays within the framework of nonrelativistic QCD
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In the paper, the inclusive production of heavy quarkonium $eta_Q$ ($Q=b$ or $c$) via $Z$ boson decays within the framework of nonrelativistic QCD (NRQCD) effective theory are studied. The contributions from the leading color-singlet and color-octet Fock states are considered. Total and differential decay widths for the inclusive decays $Z to eta_c+X$ and $Z to eta_b+X$ are presented. It is found that the decay $Zto eta_Q +X$ is dominated by the $^3S_1^{[8]}$ component, so the decays can be inversely adopted to determine the values of the long-distance matrix elements $langle {cal O}^{eta_{c}}(^{3}S_{1}^{[8]})rangle$ and $langle {cal O}^{eta_{b}}(^{3}S_{1}^{[8]})rangle$ respectively. The numerical results show that at an $e^+e^-$ collider running at the $Z$ pole with a high luminosity around $10^{35}{rm cm}^{-2}{rm s}^{-1}$ (a super $Z$ factory), there are about $4.5times 10^7$ $eta_c$ meson events and $6.2times 10^5$ $eta_b$ meson events to be produced per operation year, and the inclusive decays may be used for clarifying some problems on the heavy quarkonium $eta_Q$ and NRQCD.
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We compute the color-singlet and color-octet nonrelativistic QCD (NRQCD) long-distance matrix elements for inclusive production of $P$-wave quarkonia in the framework of potential NRQCD. In this way, the color-octet NRQCD long-distance matrix element can be determined without relying on measured cross section data, which has not been possible so far. We obtain inclusive cross sections of $chi_{cJ}$ and $chi_{bJ}$ at the LHC, which are in good agreement with data. In principle, the formalism developed in this Letter can be applied to all inclusive production processes of heavy quarkonia.
We consider a different power counting in potential NRQCD by incorporating the static potential exactly in the leading order Hamiltonian. We compute the leading relativistic corrections to the inclusive electromagnetic decay ratios in this new scheme. The effect of this new power counting is found to be large (even for top). We produce an updated value for the $eta_b$ decay to two photons. This scheme also brings consistency between the weak coupling computation and the experimental value of the charmonium decay ratio.
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Hong-Fei Zhang (College of Big Data Statistics
, Guizhou University ofn Finance
, Economics
2019
We study the $eta_c$ photoproduction in $ep$ collisions in this paper. The short-distance coefficients for $cbar{c}(^1S_0^{[1]})$, $cbar{c}(^1S_0^{[8]})$, $cbar{c}(^3S_1^{[8]})$, and $cbar{c}(^1P_1^{[8]})$ photoproductions are evaluated at leading order in $alpha_s$ expansion, where the color-singlet contribution is achieved for the first time. We have carefully analyzed different kinematic distributions of the cross sections and found that the color-singlet contribution is considerably suppressed comparing with the color-octet parts. This feature renders the $eta_c$ photoproduction process an ideal laboratory to test the color-octet mechanism in nonrelativistic QCD. By taking different sets of long-distance matrix elements, we have observed some apparently distinguishable predictions, which can be utilized to scrutinize the validity of these matrix elements.
The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $xi$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributions to the quantum anomalous energy, mass radius, spin and mechanical pressure in the proton. We use the recent GlueX data on the $J/psi$ photoproduction to illustrate the potential physics impact from the high-precision data from future JLab 12 GeV and EIC physics program.
Based on the nonrelativistic QCD framework, we study the $Upsilon$ production in semi-inclusive deep inelastic electron-proton scattering (SIDIS) at HERA, EIC, and LHeC, with the main aim of assessing the viability of observing $Upsilon$ electroproduction at the three colliders. The color-octet (CO) contributions are found to have a crucial effect on both the integrated and differential cross sections, serving to further establish the significance of the CO mechanism. By setting the kinematic cuts to $p_{t,Upsilon}^{star 2}>1~textrm{GeV}^{2}$, $W>50$ GeV, $2<Q^2<100~textrm{GeV}^2$, and $0.3<z<0.9$, only a few electroproduced $Upsilon$ events can be generated at HERA, partially accounting for its lack of measured $Upsilon$ electroproduction. However, under the same cut conditions, the EIC and LHeC can accumulate about $8.7times10^{2}$ and $3.7times10^{4}$ reconstructed $Upsilon$ events in one operation year, respectively, which manifestly indicates the prospect of detecting the $Upsilon$-related SIDIS processes at the two forthcoming $ep(eA)$ colliders.
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