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Register a new user$Upsilon$ electroproduction at HERA, EIC, and LHeC within the nonrelativistic QCD framework
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Zhan Sun
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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.
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$Upsilon(nS)$ and $chi_b(nP)$ (n=1,2,3) production at the LHC is studied at next-to-leading order in $alpha_s$ in nonrelativistic QCD. Feeddown contributions from higher $chi_b$ and $Upsilon$ states are all considered for lower $Upsilon$ cross sections and polarizations. The long distance matrix elements (LDMEs) are extracted from the yield data, and then used to make predictions for the $Upsilon(nS)$ polarizations, which are found to be consistent with the measured polarization data within errors. In particular, the $Upsilon(3S)$ polarization puzzle can be understood by a large feeddown contribution from $chi_b(3P)$ states. Our results may provide a good description for both cross sections and polarizations of prompt $Upsilon(nS)$ and $chi_b(nP)$ production at the LHC.
High-accuracy $Upsilon$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $gamma ptoUpsilon p$, from which the absolute value of the $Upsilon p$ scattering length, $|alpha_{Upsilon p}|$, can be extracted using a Vector-Meson Dominance model. For this evaluation, we used $Upsilon$-meson photoproduction quasi-data from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|alpha_{Upsilon p}|$ with the recently determined scattering lengths for $omega p$, $phi p$, and $J/psi p$ using the A2, CLAS, and GlueX experimental data are performed. The role of the young vector-meson effect is evaluated.
We calculate cross sections for inclusive dijet photoproduction in electron-nucleus scattering in the kinematics of the future EIC and the possible LHeC, HE-LHeC, and the FCC using next-to-leading order (NLO) perturbative QCD and nCTEQ15 and EPPS16 nuclear parton density functions (nPDFs). We make predictions for distributions in the dijet average transverse momentum ${bar p}_T$, the average rapidity $bar{eta}$, the observed nuclear momentum fraction $x_A^{rm obs}$, and the observed photon momentum fraction $x_{gamma}^{rm obs}$. Comparing the kinematic reaches of the four colliders, we find that an increase of the collision energy from the EIC to the LHeC and beyond extends the coverage in all four considered variables. Notably, the LHeC and HE-LHeC will allow one to probe the dijet cross section down to $x_A^{rm obs} sim 10^{-4}$ (down to $x_A^{rm obs} sim 10^{-5}$ at the FCC). The ratio of the dijet cross sections on a nucleus and the proton, $sigma_A/(Asigma_p)$, depends on $x_A^{rm obs}$ in a similar way as the ratio of gluon densities, $g_A(x_A,mu^2)/[A g_p(x_A,mu^2)]$, for which current nPDFs predict a strong suppression due to nuclear shadowing in the region $x_A^{rm obs} < 0.01$. Dijet photoproduction at future lepton-nucleus colliders can therefore be used to test this prediction and considerably reduce the current uncertainties of nPDFs.
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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.
To resolve the long-standing discrepancy between the precision measurement of bottom quark forward-backward asymmetry at LEP/SLC and the Standard Model prediction, we propose a novel method to probe the $Zbbar{b}$ coupling by measuring the single-spin asymmetry $A_e^b$ of the polarized lepton cross section in neutral current DIS processes with a $b$-tagged jet at HERA and EIC. Depending on the tagging efficiency of the final state $b$-jet, the measurement of $A_e^b$ at HERA can already partially break the degeneracy found in the anomalous $Zbbar{b}$ coupling, as implied by the LEP and SLC precision electroweak data. In the first year run of the EIC, the measurement of $A_e^b$ can already break the degeneracy, due to its much larger luminosity and higher electron beam polarization. With enough integrated luminosity collected at the EIC, it is possible to either verify or exclude the LEP data and resolve the $A_{rm FB}^b$ puzzle. We also discuss the complementary roles between the proposed $A_e^b$ measurement at EIC and the measurement of $gg to Zh$ cross section at the HL-LHC in constraining the anomalous $Zbbar{b}$ coupling.
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