QCD corrections to double J/psi production in e+e- annihilation at sqrt[s]=10.6 GeV

Next-to-leading-order (NLO) QCD corrections to double J/psi production in e+e- annihilation at sqrt[s]=10.6 GeV are calculated. We find that they greatly decrease the cross section, with a K factor (NLO/LO) ranging from -0.31 to 0.25 depending on the renormalization scale. Although the renormalization scale dependence indicates a large uncertainty, when combined with the NLO QCD corrections to J/psi+etac production, it can explain why the double J/psi production could not be found at B factories while the J/psi+etac production could, despite the fact that cross section of the former is larger than that of the latter at LO by a factor of 1.8.     

Next-to-leading-order QCD correction to e(+)e(-)-->J/psi+eta(c) at sqrt[s]=10.6 GeV

One of the most challenging open problems in heavy quarkonium physics is the double charm production in e+e- annihilation at B factories. The measured cross section of e+e- --> J/psi + eta(c) is much larger than leading order (LO) theoretical predictions. With the nonrelativistic QCD factorization formalism, we calculate the next-to-leading order (NLO) QCD correction to this process. Taking all one loop self-energy, triangle, box, and pentagon diagrams into account, and factoring the Coulomb-singular term into the cc bound state wave function, we get an ultraviolet and infrared finite correction to the cross section of e+e- --> J/psi + eta(c) at sqrt[s] = 10:6 GeV. We find that the NLO QCD correction can substantially enhance the cross section with a K factor (the ratio of NLO to LO) of about 1.8-2.1; hence, it greatly reduces the large discrepancy between theory and experiment.     

e+ e- annihilation into J/psi + J/psi

Recent measurements by the Belle Collaboration of the exclusive production of two charmonia in e(+)e(-) annihilation differ substantially from theoretical predictions. We suggest that a significant part of the discrepancy can be explained by the process e(+)e(-)-->J/psi+J/psi. Because the J/psi+J/psi production process can proceed through fragmentation of two virtual photons into two cc pairs, its cross section may be larger than that for J/psi+eta(c) by about a factor of 3.7, in spite of a suppression factor alpha(2)/alpha(2)(s) that is associated with the QED and QCD coupling constants.     

Hunting for glueballs in electron-positron annihilation

We calculate the cross section for the exclusive production of J(PC)=0(++) glueballs G0 in association with the J/psi in e(+)e(-) annihilation using the perturbative QCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative Upsilon decay. The cross section for e(+)e(-)-->J/psi+G0 at sqrt[s]=10.6 GeV is similar to exclusive charmonium-pair production e(+)e(-)-->J/psi+h for h=eta(c) and chi(c0), and is larger by a factor of 2 than that for h=eta(c)(2S). As the subprocesses gamma(*)-->(cc)(cc) and gamma(*)-->(cc)(gg) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e(+)e(-)-->J/psiX may actually be due to the production of charmonium-glueball J/psiG(J) pairs.     

QCD corrections to J/psi and Upsilon production at hadron colliders

We calculate the cross section for hadroproduction of a pair of heavy quarks in a (3)S(1) color-singlet state at next-to-leading order in QCD. This corresponds to the leading contribution in the nonrelativistic QCD expansion for J/psi and Upsilon production. The higher-order corrections have a large impact on the p(T) distributions, enhancing the production at high p(T) at both the Fermilab Tevatron and the CERN Large Hadron Collider. The total decay rate of a (3)S(1) into hadrons at next-to-leading order is also computed, confirming for the first time the result obtained by Mackenzie and Lepage in 1981.     

J/Psi production in pp collisions at square root = 200 GeV at the BNL relativistic heavy ion collider

We study J/psi production in pp collisions at BNL Relativistic Heavy Ion Collider (RHIC) within the PHENIX detector acceptance range using the color singlet and color octet mechanism which are based on perturbative QCD and nonrelativistic QCD. Here we show that the color octet mechanism reproduces the RHIC data for J/psi production in pp collisions with respect to the p(T) distribution, the rapidity distribution, and the total cross section at square root = 200 GeV. The color singlet mechanism leads to a relatively small contribution to the total cross section when compared to the octet contribution.     

Precision Calculations for the T-Odd Quark Pair Production at the CLIC e+e- Linear Collider

We perform the precision calculations for the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes up to the QCD next-to-leading order (NLO) including full weak decays for the final T-odd mirror quarks in the littlest Higgs model with T-parity (LHT) at the Compact Linear Collider (CLIC). We show the dependence of the leading order (LO) and NLO QCD corrected cross sections on the colliding energy √s, and provide the LO and QCD NLO kinematic distributions of final particles. The results show that the LO cross section can be enhanced by the NLO QCD correction and the K-factor increases obviously when the threshold of the on-shell q_q_-pair production approaches the colliding energy √s. The K-factor value varies in the range of 1.04 ～ 1.41 in our chosen parameter space. We find that a simple approximation of multiplying the LO kinematic distribution with the integrated K-factor is not appropriate for precision study of the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes, since the NLO QCD corrections are phase space dependent. It is necessary to calculate the differential cross sections including full NLO QCD corrections to get reliable results.     

QCD Correction to σ(e+e-→ZH→Zbb)

We study the QCD corrections to the calculated values of σ(e⁺e^-→ZH→Zbb), and find that for M_H<100 GeV, the process can be measured at the LEP energy to extract information of Higgs and the QCD corrections are negligible, namely the tree-level calculation is sufficiently aciurate for the energy range, while for M_H > 100 GeV, the Higgs-involved subprocess can only be investigated at NLC, and then the QCD correction becomes as large as 45%. For M_H > 2mt, considering the subprocess e⁺e^-→ZH→Ztt, the QCD corrections are also important and must be taken into account for the cross section evaluation.     

Largep T prompt photon production at HERA

We examine the possibility of using direct photon production at HERA as a means of obtaining information about the photon structure and fragmentation functions. Estimates of the cross section for inclusive prompt photon production at theep collider HERA are made completely in next-to-leading order QCD. Using parton distributions for the photon evolved in next-to-leading order QCD for the first time, we show that theO( _s ) corrections to the processes involving these functions are significant in the regions where they dominate. This can have important consequences for the possibility of measuring the gluon content of the photon using these processes at HERA. Moreover, we show that it may not be straightforward to separate the various contributions to the cross section in theep lab frame.     

微扰QCD对Drell-Yan过程能量损失效应的修正

利用Glauber模型以及DGLAP方程下的核内核子的部分子分布函数, 在次领头阶QCD下计算了Drell-Yan过程中的能量损失效应, 计算表明QCD修正并不能改善理论结果与试验结果的符合, 尤其是p-W与p-Be以x₁为变量的微分截面比. 原因是所用的核内核子部分子的分布函数是以领头阶近似为基础并通过演化方程得到的. 于是利用在次领头阶微扰QCD下得到的核遮蔽效应核内核子的部分子分布函数重新计算了次领头阶QCD修正对Drell-Yan过程能量损失的贡献. 计算结果表明康普顿散射过程与湮没过程中应该有更多的能量损失.     

Single slepton production associated with a top quark at LHC in NLO QCD

Single slepton production in association with a top quark at the CERN Large Hadron Collider (LHC) is one of the important processes in probing the R-parity violation couplings. We calculate the QCD next-to-leading order (NLO) corrections to the $pp \to t\tilde{\ell}^{-}(\bar{t}\tilde{\ell}^{+})+X$ process at the LHC and discuss the impacts of the QCD corrections on kinematic distributions. We investigate the dependence of the leading order (LO) and the NLO QCD corrected integrated cross section on the factorization/renormalization energy scale, slepton, stop-quark and gluino masses. We find that the uncertainty of the LO cross section due to the energy scale is obviously improved by the NLO QCD corrections, and the exclusive jet event selection scheme keeps the convergence of the perturbative series better than the inclusive scheme. The results show that the polarization asymmetry of the top-quark will be reduced by the NLO QCD corrections, and the QCD corrections generally increase with the increment of the $\tilde{t}_{1}$ or $\tilde {g}$ mass value.     

Upsilon production at Fermilab Tevatron and LHC energies

We update the theoretical predictions for direct Upsilon(nS) hadroproduction in the framework of nonrelativistic QCD. We show that the next-to-leading order corrections in alpha(S) to the color-singlet transition significantly raise the differential cross section at high p(T) and substantially affect the polarization of the Upsilon. Motivated by the remaining gap between the next-to-leading order yield and the cross-section measurements at the Fermilab Tevatron, we evaluate the leading part of the alpha(S)(5) contributions, namely, those coming from Upsilon(nS) associated with three light partons. The differential color-singlet cross section at alpha(S)(5) is in substantial agreement with the data, so that there is no evidence for the need of color-octet contributions. Furthermore, we find that the polarization of the Upsilon(nS) is longitudinal. We also present our predictions for Upsilon(nS) production at the LHC.     

Top—Higgs and the Process e^＋e^— → vvtt

We discuss the contributions of the top-Higgs ht^0 proedicted by topcolor-assisted technicolor (TC2) models to the process e^ e^-→vvtt.We find that the contributions are very large.For mht=400 GeV and ε=0.01,the production cross section of this process can reach 11.2fb,which may be detected in the future high energy e^ e^- collider experiments.The process e^ e^-→vvtt can be used to test experimentally the signal of TC2 models.     

Hard- and soft-fermion-pole contributions to single transverse-spin asymmetry for Drell-Yan process

We study the single transverse-spin asymmetry for the Drell-Yan lepton pair production based on the twist-3 mechanism in the collinear factorization. We calculate all the hard-pole (HP) and the soft-fermion-pole (SFP) contributions to the single-spin-dependent cross section originating from the quark-gluon correlation functions in the transversely polarized nucleon in the leading order with respect to the QCD coupling constant. Combined with the soft-gluon-pole (SGP) contribution, this completes the corresponding twist-3 cross section. In the real photon limit, where all the HP contributions are transformed into the SFP contribution, we find that the SFP partonic hard cross section for the two independent quark-gluon correlation functions coincides in each scattering channel, as in the case of the inclusive light-hadron production. Our result enables one to extract the quark-gluon correlation functions from the forthcoming experiments at several facilities such as RHIC and J-PARC.     

The total cross section for the production of heavy quarks in hadronic collisions

We present the results of a full calculation of the QCD O(α_S³) radiative corrections to the total cross section for the production of a heavy quark pair. We find large contributions for parton subenergies near threshold and well above threshold. The implications for the production of top and bottom quarks at collider energies are discussed.     

W Boson production cross section at the Large Hadron cCllider with Omicron(alpha(2)(s)) corrections

We compute the Omicron(alpha(2)(s)) QCD corrections to the fully differential cross section pp --> WX --> lnuX, retaining all effects from spin correlations. The knowledge of these corrections makes it possible to calculate with high precision the boson production rate and acceptance at the CERN Large Hadron Collider (LHC), subject to realistic cuts on the lepton and missing energy distributions. For certain choices of cuts we find large corrections when going from next-to-leading order (NLO) to next-to-next-to-leading order in perturbation theory. These corrections are significantly larger than those obtained by parton-shower event generators merged with NLO calculations. Our result may be used to assess and significantly reduce the QCD uncertainties in the many studies of boson production planned at the LHC.     

Next-to-leading-order QCD corrections to J/psi polarization at Tevatron and Large-Hadron-Collider energies

We calculate the next-to-leading-order QCD corrections to J/psi polarization at the Fermilab Tevatron and CERN Large Hadron Collider. Our results show that the J/psi polarization status drastically changes from transverse-polarization dominant at leading order to longitudinal-polarization dominant at next-to-leading order. Although the theoretical evaluation predicts a larger longitudinal polarization than the value measured at the Tevatron, it may provide a solution towards the previous large discrepancy for J/psi polarization between theoretical predication and experimental measurement.     

Gluino-pair production at the Tevatron

The next-to-leading order QCD corrections to the production of gluino pairs at the Tevatron are presented in this paper. Similar to the production of squark-antisquark pairs, the dependence of the cross section on the renormalization/factorization scale is reduced considerably by including the higher-order corrections. The cross section increases with respect to the lowest-order calculation which, in previous experimental analyses, had been evaluated at the scale of the invariant energy of the partonic subprocesses.     

QCD corrections to γγ→ZZ at small scattering angles

QCD corrections to the electroweak cross section of γγ→ZZ at high energies and small scattering angles have been calculated. The dominant contributions are due to t-channel gluon exchange, i.e., photons dissociate into quark–antiquark pairs giving rise to two colour dipoles which interact through gluons. Corrections resulting from the leading log BFKL amplitude are of the order of a few percent close to the forward region already at the 1 TeV energy range and are rising with the scattering energy. We also considered the helicity non-conserving cases in which the QCD corrections in comparison to the electroweak part of the amplitude strongly grow with energy. The helicity non-conserving scattering process is of particular interest since it is sensitive to the Higgs sector.