QCD Next-to-leading Order Corrections Research Articles

Higgs boson pair production and decay at NLO in QCD: the bb¯γγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ b\\overline{b}\\gamma \\gamma $$\\end{document} final state

The Higgs boson pair production at the LHC provides a probe to the Higgs boson self-coupling. The higher-order QCD corrections in this process are sizable and must be taken into account in comparison with data. Due to the small cross section, it is necessary to consider at least one of the Higgs bosons decaying to bottom quarks. The QCD corrections to the decay processes would also be important in such cases. We present a full calculation of the total and differential cross sections for the bb¯γγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ b\\overline{b}\\gamma \\gamma $$\\end{document} final state with next-to-leading order (NLO) QCD corrections. After applying typical kinematic cuts in the final state, we find that QCD NLO corrections in the decay decrease the LO result by 19% and reduce the scale uncertainties by a factor of two. The QCD corrections to the invariant mass mjjγγ distribution, the transverse momentum spectra of the leading bottom quark jet and photon are significant and can not be approximated by a constant factor.

Signature of theγ+jetand dijet production mediated by an excited quark with QCD next-to-leading order accuracy at the LHC

We present a detailed study of the production and decay of the excited quark at the QCD next-to-leading order (NLO) level at the Large Hadron Collider, using the narrow width approximation and helicity amplitudes method. We find that the QCD NLO corrections can tighten the constraints on the model parameters and reduce the scale dependencies of the total cross sections. We discuss the signals of the excited quark production with decay mode $q^{\ast}\rightarrow q\gamma$ and $q^{\ast}\rightarrow qg$, and present several important kinematic distributions. Moreover, we give the upper limits of the excited quark excluded mass range and the allowed parameter space for the coupling constants and the excited quark mass.

NLO QCD corrections to Single Top and W associated photoproduction at the LHC with forward detector acceptances

In this paper we study the Single Top and W boson associated photoproduction via the main reaction $\rm pp\rightarrow p\gamma p\rightarrow pW^{\pm}t+Y$ at the 14 TeV Large Hadron Collider (LHC) up to next-to-leading order (NLO) QCD level assuming a typical LHC multipurpose forward detector. We use the Five-Flavor-Number Schemes (5FNS) with massless bottom quark assumption in the whole calculation. Our results show that the QCD NLO corrections can reduce the scale uncertainty. The typical K-factors are in the range of 1.15 to 1.2 which lead to the QCD NLO corrections of 15$%$ to 20$%$ correspond to the leading-order (LO) predictions with our chosen parameters.

Dark matter pair associated with a W boson production at the LHC in next-to-leading order QCD

We investigate the QCD next-to-leading order (NLO) corrections to the production of a pair of fermionic dark matter particles associated with a W boson production through a mediator which couples to standard model particles via either a vector or axial-vector coupling at the LHC. We find that the QCD NLO corrections reduce the dependence of the total cross sections on the factorization and renormalization scales, and the $K$-factors increase with the increment of the dark matter mass. We also provide the LO and QCD NLO corrected distributions of the transverse momenta $p_T^\mu$ of final muon and transverse mass $M_T$. We find that the LO cross section is significantly changed by the QCD NLO corrections.

Precise calculation for heavy gauge boson production in the LHT model

In the framework of the littlest Higgs model with T parity, we study the WH/Zh+q_ and WH-pair productions at the CERN Large Hadron Collider up to the QCD next-to-leading order (NLO). The kinematic distributions of final decay products and the theoretical dependence of the cross section on the factorization/renormalization scale are analyzed. We adopt the PROSPINO scheme in the QCD NLO calculations to avoid double counting and keep the convergence of the perturbative QCD description. By using the subtraction scheme, the QCD NLO corrections enhance the leading order cross section with a K-factor in the range of 1.00 ~ 1.43 for WH (ZH)q- production process, and in the range of 1.09 ~ 1.22 for the WH pair production process.

Searching for the signal of dark matter and photon associated production at the LHC beyond leading order

We study the signal of dark matter and photon associated production induced by the vector and axial-vector operators at the LHC, including the QCD next-to-leading order (NLO) effects. We find that the QCD NLO corrections reduce the dependence of the total cross sections on the factorization and renormalization scales, and the $K$ factors increase with the increasing of the dark matter mass, which can be as large as about 1.3 for both the vector and axial-vector operators. Using our QCD NLO results, we improve the constraints on the new physics scale from the results of the recent CMS experiment. Moreover, we show the Monte Carlo simulation results for detecting the $\gamma+\Slash{E}_{T}$ signal at the QCD NLO level, and present the integrated luminosity needed for a $5\sigma$ discovery at the 14 TeV LHC . If the signal is not observed, the lower limit on the new physics scale can be set.

Precise QCD predictions onWHZHproduction in the littlest Higgs model withTparity at the LHC

We investigate the effects of the littlest Higgs model with $T$ parity up to the QCD next-to-leading order (NLO) on the ${W}_{H}^{\ifmmode\pm\else\textpm\fi{}}{Z}_{H}$ productions at the CERN Large Hadron Collider (LHC), and discuss the kinematic distributions of final decay products and the theoretical dependence of the cross section on the factorization/renormalization scale. We find that the QCD NLO corrections reduce the scale uncertainty of the leading-order cross section in the case of ${\ensuremath{\mu}}_{F}={\ensuremath{\mu}}_{R}$. By adopting the prospino subtraction scheme [scheme (II)] in analysing the QCD NLO contributions, we obtain the numerical results which keep the convergence of the perturbative QCD description. Our results by adopting scheme (II) at the 14 TeV (8 TeV) LHC show that the $K$-factor for the ${W}_{H}^{+}{Z}_{H}$ production varies in the range of 1.01--1.10 (1.00--1.08), while the $K$-factor for the ${W}_{H}^{\ensuremath{-}}{Z}_{H}$ production varies in the range of 1.11--1.13 (1.11--1.12), when the global symmetry-breaking scale $f$ goes from 400 GeV to 1.5 TeV (1 TeV).

Signature of same-sign top pair production mediated by a nonuniversalZ′with QCD next-to-leading order accuracy at the LHC

We present a detailed study of the same-sign top pair production mediated by a nonuniversal ${Z}^{\ensuremath{'}}$ including production and decay at the Large Hadron Collider (LHC) at the QCD next-to-leading order (NLO) level, using the narrow width approximation and helicity amplitudes method. We find that the QCD NLO corrections can loosen the constraint on the model parameters and reduce the dependence of the total cross sections on the factorization scale significantly. We also study the signature and backgrounds of the process at the NLO level. In order to suppress the backgrounds, we further investigate the difference between the production rates of the positively and negatively charged dilepton at the LHC, and find that the same-sign dilepton signal of the new physics could be discovered more easily. Besides, we also discuss the uncertainty from the parton distribution at the NLO level.

Constraints on flavor-changing neutral-currentHtqcouplings from the signal oftHassociated production with QCD next-to-leading order accuracy at the LHC

We study a generic Higgs boson and a top quark associated production via model-independent flavor-changing neutral-current couplings at the LHC, including complete QCD next-to-leading order (NLO) corrections to the production and decay of the top quark and the Higgs boson. We find that QCD NLO corrections can increase the total production cross sections by about 48.9% and 57.9% for the $Htu$ and $Htc$ coupling induced processes at the LHC, respectively. After kinematic cuts are imposed on the decay products of the top quark and the Higgs boson, the QCD NLO corrections are reduced to 11% for the $Htu$ coupling induced process and almost vanish for the $Htc$ coupling induced process. Moreover, QCD NLO corrections reduce the dependence of the total cross sections on the renormalization and factorization scales. We also discuss signals of the $tH$ associated production with the decay mode $t\ensuremath{\rightarrow}b{l}^{+}{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$, $H\ensuremath{\rightarrow}b\overline{b}$, and $t\overline{t}$ production with the decay mode $\overline{t}\ensuremath{\rightarrow}H\overline{q}$, $t\ensuremath{\rightarrow}b{l}^{+}{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$. Our results show that, in some parameter regions, the LHC may observe the above signals at the $5\ensuremath{\sigma}$ level. Otherwise, the upper limits on the flavor-changing neutral-current $Htq$ couplings can be set.

WH-pair production in the littlest Higgs model withTparity in next-to-leading order QCD at the LHC

In the framework of the littlest Higgs model with $T$ parity, we study the $W_H$-pair production at the CERN Large Hadron Collider up to the QCD next-to-leading order (NLO). The kinematic distributions of final decay products and the theoretical dependence of the cross section on the factorization/renormalization scale are analyzed. We adopt the PROSPINO scheme in the QCD NLO calculations to avoid double counting and keep the convergence of the perturbative QCD description. Our numerical results show that the QCD NLO corrections significantly reduce the scale uncertainty, and enhance the leading order integrated cross section with a $K$-factor in the range of $1.10-1.22$ ($1.09-1.17$) with the symmetry breaking scale $f$ varying from $400 GeV$ ($400 GeV$) to $1.5 TeV$ ($1.0 TeV$) at the $14 TeV$ $(8 TeV)$ LHC. We find that it is possible to select the signal events of the $W_H$-pair production from the $pp\to W^+ W^- \to e^+ \mu^-\nu_{e}\bar{\nu}_{\mu}+X$ background with high ratio of signature over background by taking proper lower limits on transverse momenta, invariant mass of the final charged leptons and the missing transverse momentum.

Production of massive color-octet vector bosons at next-to-leading order

We report the first complete calculation of QCD corrections to the production of a massive color-octet vector boson. Our next-to-leading-order (NLO) calculation includes both virtual corrections as well as corrections arising from the emission of gluons and light quarks, and we demonstrate the reduction in factorization-scale dependence relative to the leading-order approximation used in previous hadron collider studies. We show that the QCD NLO corrections to coloron production are as large as 30%, and that the residual factorization scale-dependence is reduced to of order 2%. We also calculate the K-factor and the p_T spectrum for coloron production, since these are valuable for comparison with experiment. Our results apply directly to the production of the massive color-octet vector bosons in axigluon, topcolor, and coloron models, and approximately to the production of KK gluons in extra-dimensional models or color-octet technivector mesons in technicolor models.

QCD corrections to associated Higgs boson production with aWboson pair at LHC

The Higgs boson production in association with a pair of W bosons at the Large Hadron Collider (LHC) can be used to probe the coupling between the Higgs boson and vector gauge bosons and discover the signature of new physics. We describe the impact of the complete QCD next-to-leading order (NLO) radiative corrections and the gluon-gluon fusion subprocesses to the cross section of this process at the LHC and investigate the dependence of the leading order (LO) and QCD corrected cross sections on the factorization/renormalization energy scale and Higgs boson mass. We present the LO and QCD corrected distributions of the invariant mass of a W boson pair and the transverse momenta of the final W and Higgs boson. We find that the QCD NLO corrections and the contribution from a gluon-gluon fusion subprocess significantly modify the LO distributions, and the scale dependence of the QCD corrected cross section is badly underestimated by the LO results. Our numerical results show that the K-factor of the QCD correction varies from 1.48 to 1.64 when m{sub H} goes up from 100 GeV to 160 GeV. We find also the QCD correction from the gg{yields}H{sup 0}W{sup +}W{sup -} subprocess at the LHC is more » significant and should be considered in precise experiment. « less