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In the paper, we present QCD predictions for γ + ηc production at an electron-positron collider up to next-to-next-to-leading order (NNLO) accuracy without renormalization scale ambiguities. The NNLO total cross-section for e+ + e− → γ + ηc using the conventional scale-setting approach has large renormalization scale ambiguities, usually estimated by choosing the renormalization scale to be the e+e− center-of-mass collision energy s . The Principle of Maximum Conformality (PMC) provides a systematic way to eliminate such renormalization scale ambiguities by summing the nonconformal β contributions into the QCD coupling αs(Q2). The renormalization group equation then sets the value of αs for the process. The PMC renormalization scale reflects the virtuality of the underlying process, and the resulting predictions satisfy all of the requirements of renormalization group invariance, including renormalization scheme invariance. After applying the PMC, we obtain a renormalization scale-and-scheme independent prediction, σ|NNLO,PMC ≃ 41.18 fb for s =10.6 GeV. The resulting pQCD series matches the series for conformal theory and thus has no divergent renormalon contributions. The large K factor which contributes to this process reinforces the importance of uncalculated NNNLO and higher-order terms. Using the PMC scale-and-scheme independent conformal series and the Padé approximation approach, we predict σ|NNNLO,PMC+Pade ≃ 18.99 fb, which is consistent with the recent BELLE measurement σ obs = 16.58 − 9.93 + 10.51 fb at s ≃ 10.6 GeV. This procedure also provides a first estimate of the NNNLO contribution. [ABSTRACT FROM AUTHOR]

The associated production of Higgs boson with a hard photon at lepton collider, i.e. , e + e − → H γ , is known to bear a rather small cross section in Standard Model, and can serve as a sensitive probe for the potential new physics signals. Similar to the loop-induced Higgs decay channels H → γ γ , Z γ , the e + e − → H γ process also starts at one-loop order provided that the tiny electron mass is neglected. In this work, we calculate the next-to-leading-order (NLO) QCD corrections to this associated H + γ production process, which mainly stem from the gluonic dressing to the top quark loop. The QCD corrections are found to be rather modest at lower center-of-mass energy range ( s < 300 GeV ), thus of negligible impact on Higgs factory such as CEPC. Nevertheless, when the energy is boosted to the ILC energy range ( s ≈ 400 GeV ), QCD corrections may enhance the leading-order cross section by 20 % . In any event, the e + e − → H γ process has a maximal production rate σ max ≈ 0.08 fb around s = 250 GeV , thus CEPC turns out to be the best place to look for this rare Higgs production process. In the high energy limit, the effect of NLO QCD corrections become completely negligible, which can be simply attributed to the different asymptotic scaling behaviors of the LO and NLO cross sections, where the former exhibits a milder decrement ∝ 1 / s , but the latter undergoes a much faster decrease ∝ 1 / s 2 . [ABSTRACT FROM AUTHOR]

We compute the O (α s 2) corrections to the exclusive channels e + e − → J / ψ + χ c J (J = 0 , 1 , 2) at s = 10.58 GeV within the nonrelativistic QCD (NRQCD) factorization framework. The validity of NRQCD factorization at O (α s 2) has been confirmed for these double-charmonium exclusive production processes. We analyze the impact of the O (α s 2) corrections on the polarized and unpolarized cross sections, as well as the J / ψ angular distributions, which largely reduce the renormalization scale dependence but increase the O (α s) NRQCD predictions to some extent for χ c 0 , 1. With high numerical accuracy, our predictions for σ (J / ψ + χ c 1 , 2) through O (α s 2) are compatible with the upper limit of the Belle measurement. Although the theoretical prediction for σ (J / ψ + χ c 0) is consistent with both Belle and BaBar measurements within uncertainties, there still exists serious tension between the predicted and the measured profiles for the J / ψ angular distribution. Regarding the bright observation prospect of the e + e − → J / ψ + χ c 1 , 2 channels in Belle 2 experiment, it is interesting to compare the future measurements with our NRQCD predictions. The more accurate measurement of e + e − → J / ψ + χ 0 at Belle 2 will also help to clarify the long-standing puzzle of J / ψ angular distribution. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate, up to QCD next-to-next-to-next-to-leading order, the B c ⁎ decay constant, which, within the nonrelativistic QCD (NRQCD) framework, is factorized as the product of the short-distance coefficient (SDC) and the long-distance matrix element. For the first time, the renormalization constant and the anomalous dimension for the NRQCD vector current composed of c b ¯ , which are functions of the charm quark mass m c , the bottom quark mass m b and the factorization scale μ Λ , are obtained analytically at O (α s 2) and O (α s 3). The SDC is calculated up to O (α s 3) in perturbative expansion. Explicitly, the O (α s 2) correction to the SDC is analytically calculated in terms of logarithmic and polylogarithmic functions of r ≡ m b / m c , and the O (α s 3) correction to the SDC is numerically calculated at a series of values of r , ranging from 2.1 to 4.0. Surprisingly, we find that the nontrivial part of the SDC at O (α s 3) can be well estimated by a linear function of r. In addition, we find that the O (α s 2) and O (α s 3) corrections to the decay constant and decay width are considerable and very significant, which indicates a very poor convergence for the perturbative expansion. [ABSTRACT FROM AUTHOR]

In this paper, we study the azimuthal asymmetry in the J/𝜓 leptoproduction in unpolarized ep collisions. There are two independent azimuthal asymmetry modulations, namely cos(𝜓) and cos (2 𝜓), where 𝜓 is the azimuthal angle of the lepton scattering plane with respect to the hadron-interacting plane. We calculate the two modulations as functions of four kinematic variables, and find that they provide a very good laboratory to distinguish several models describing the heavy quarkonium production, including the color-singlet (CS) model, the nonrelativistic QCD (NRQCD). In addition, this process can be used to test the magnitude of the 1 S 0 8 long-distance matrix element, which is extraordinarily large from various phenomenological extraction. In order to make definite conclusions, we restrict our calculation in a specific kinematic region, where the CS and CO mechanisms can be distinguished by scrutinizing the values of the cos(𝜓) modulation, while the 1 S 0 8 dominance picture can be tested by measuring the values of the cos (2 𝜓) modulation. Calculating their values and carrying out a meticulous statistical analysis, we find that at an integrated luminosity ℒ = 1000pb−1, the statistical uncertainties of the two quantities are small enough to tell the three models apart. When this experiment is implemented at the future ep colliders such as the EIC, crucial information for the J/𝜓 production mechanism might be discovered. [ABSTRACT FROM AUTHOR]

Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the long-awaited O (α s 2) corrections for the exclusive double charmonium production process at B factories, i.e. , e + e − → J / ψ + η c at s = 10.58 GeV. We confirm that NRQCD factorization does hold at next-to-next-to-leading-order (NNLO) for exclusive double charmonium production. It is found that including the NNLO QCD correction considerably reduces the renormalization scale dependence, and also implies the reasonable perturbative convergence behavior for this process. We also include both O (v 2) and O (α s v 2) corrections for this process. With all the available corrections lumped together, our most comprehensive prediction is consistent with both the BaBar and Belle measurement within errors. [ABSTRACT FROM AUTHOR]

We apply a novel factorization formula recently developed within NRQCD framework to analyze the exclusive production of the fully-charmed tetraquark T 4 c plus a hard photon at super B factory. For simplicity, in this work we have concentrated on the production of the 0 + + and 2 + + T 4 c associated with a photon. With some rough estimates about the unknown nonperturbative NRQCD matrix elements in a simplified diquark-antidiquark model, we predict the production rates of these types of exclusive production channels at s = 10.58 GeV and also assess their observation prospect at Belle 2 experiment. [ABSTRACT FROM AUTHOR]