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Register a new userKinematic distributions of the $eta_c$ photoproduction in $ep$ collisions within the nonrelativistic QCD framework
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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.
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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.
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.
Diffractive photoproduction of $eta_c$ is an important process to study the effect of Odderon, whose existence is still not confirmed in experiment. A detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also unclear.Taking charm quarks as heavy quarks, we can use NRQCD and take $eta_c$ as a $cbar c$ bound state. Hence, in the production of $eta_c$a free $cbar c$ pair is first produced and this pair is transformed into $eta_c$ subsequently.In the forward region of the kinematics, the $cbar c$ pair interacts with initial hadron through exchanges of soft gluons. This interaction can be studied with HQET, which provides a systematic expansion in the inverse of the $c$-quark mass $m_c$. We find that the calculation of the $S$-matrix element in the forward region can be formulated as the problem of solving a wave function of a $c$-quark propagating in a background field of soft gluons. At leading order we find that the differential cross-section can be expressed with four functions, which are defined with a twist-3 operator of gluons. The effect of exchanging a Odderon can be identified with this operator in our case. We discuss our results in detail and compare them with those obtained in previous studies. Our results and those from other studies show that the differential cross-section is very small in the forward region. We also show that the production through photon exchange is dominant in the extremely forward region, hence the effect of Odderon exchange can not be identified in this region.For completeness we also give results for diffractive photoproduction of $J/Psi$.
In this contribution, we study the inclusive and diffractive $eta_{c}$ photoproduction in $pp$ and $pPb$ ultra-peripheral collisions (UPCs) at the LHC Run 2 energies. The quarkonium production is studied using nonrelativistic quantum chromodynamics (NRQCD) formalism. We present predictions for rapidity and transverse momentum distributions for the $eta_c$ photoproduction and present our estimate for the total cross sections at the Run 2 energies.
We study the inclusive production of isolated prompt photons within the framework of the quasi-multi-Regge-kinematic approach, applying the quark Reggeization hypothesis. We describe accurately and without free parameters the transverse momentum and pseudorapidity spectra of prompt photons in the inclusive photoproduction at the HERA Collider. It is shown that the main mechanism of the inclusive prompt photon production in the gamma p collisions is the fusion of a Reggeized quark (antiquark) from the proton and a collinear antiquark (quark) from the photon into a photon, via the effective Reggeon-quark-gamma vertex. The fragmentation of the quark, which is produced via the gamma-Reggeon-quark and quark-Reggeon-quark vertices, into a photon is strongly suppressed by the isolation cone condition and it gives a significant contribution in the region of a large negative pseudorapidity only. At the stage of numerical calculations we use the Kimber-Martin-Ryskin prescription for unintegrated quark and gluon distribution functions, with the following collinear parton densities as input: MRST for a proton and GRV for a photon.
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