arXiv subjects

Robert J. Oakes

Publications and source records attributed to Robert J. Oakes.

At least 19 recordsLinked to original sources

arXiv2010

Next-to-leading order QCD predictions for graviton and photon associated production in the Large Extra Dimensions model at the LHC

We present the calculations of the complete next-to-leading order(NLO) QCD corrections to the inclusive total cross sections for the Kaluza-Klein(KK) graviton and photon associated production process $pp \to γG_{KK} + X$ in the large extra dimensions(LED) model at the LHC. We show that the NLO QCD corrections in general enhance the total cross sections and reduce the dependence of the total cross sections on the factorization and renormalization scales. When jet veto is considered, the NLO corrections reduce the total cross sections. We also calculate some important differential cross sections for this process at NLO: the missing transverse momentum distribution, the transverse momentum distribution and the pseudorapidity distribution of photon.

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arXiv2007

Threshold Resummation Effects in the Associated Production of Chargino and Neutralino at Hadron Colliders

We investigate the QCD effects in the associated production of the chargino and the neutralino, $\tildeχ^\pm_{1}$ and $\tildeχ^0_{2}$, in the Minimal Supersymmetric Standard Model (MSSM) at both the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. Our results show that, compared to the NLO predictions, the threshold resummation effects can increase the total cross sections by 3.6% and 3.9% for the associated production of $\tildeχ^+_{1}\tildeχ^0_{2}$ and $\tildeχ^-_{1}\tildeχ^0_{2}$ at the LHC, respectively, and by 4.7% for those of $\tildeχ^\pm_{1}\tildeχ^0_{2}$ at the Tevatron. In the invariant mass distributions the resummation effects are significant for large invariant mass. The threshold resummation reduces the dependence of the total cross sections at the LHC (Tevatron) on the renormalization/factorization scales to 5% (4%) from up to 7% (11%) at NLO.

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arXiv2005

Charged Higgs Production at Linear Colliders in Large Extra Dimensions

In the Two-Higgs-Doublet Model(2HDM) with large extra dimensions(LED), we study the contributions of virtual Kaluza-Klein(KK) gravitons to 2HDM charged Higgs production, especially in the two important production processes $e^+e^-\to H^+H^-$ and $e^+e^-\to H^-t\bar{b}$, at future linear colliders (LC). We find that KK graviton effects can significantly modify these total cross sections and also their differential cross sections compared to their respective 2HDM values and, therefore, can be used to probe the effective scale $Λ_T$ up to several TeV. For example, at $\sqrt{s}=2$ TeV, the cross sections for $e^+e^-\to H^+H^-$ and $e^+e^-\to H^-t\bar{b}$ in the 2HDM are 7.4fb for $m_{H^-}=150$ GeV and 0.003fb for $m_{H^-}=1.1$ TeV and $\tanβ=40$, while in LED they are 12.1fb and 0.01fb, respectively, for $Λ_T=4$ Tev.

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arXiv2005

Heavy Supersymmetric Particle Effects in Higgs Boson Production Associated with a Bottom Quark Pair at LHC and Tevatron

If all the supersymmetry particles (sparticles) except a light Higgs boson are too heavy to be directly produced at the Large Hadron Collider (LHC) and Tevatron, a possible way to reveal evidence for supersymmetry is through their virtual effects in other processes. We examine such supersymmetric QCD effects in bottom pair production associated with a light Higgs boson at the LHC and Tevatron. We find that if the relevant sparticles (gluinos and squarks) are well above the TeV scale, too heavy to be directly produced, they can still have sizable virtual effects in this process. For large $\tanβ$, such residual effects can alter the production rate by as much as 40 percent, which should be observable in future measurements of this process.

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arXiv2005

Next-to-leading order QCD predictions for pair production of neutral Higgs bosons at the CERN Large Hadron Collider

We present the calculations of the complete NLO inclusive total cross sections for pair production of neutral Higgs bosons through $b\bar b$ annihilation in the minimal supersymmetric standard model at the CERN Large Hadron Collider. In our calculations, we used both the DREG scheme and the DRED scheme and found that the NLO total cross sections in the above two schemes are the same. Our results show that the $b\bar b$-annihilation contributions can exceed ones of $gg$ fusion and $q\bar q$ annihilation for $h^0H^0$, $A^0h^0$ and $A^0H^0$ productions when $\tanβ$ is large. In the case of $μ>0$, the NLO corrections enhance the LO total cross sections significantly, which can reach a few tens percent, while for $μ<0$, the corrections are relatively small, and are negative in most parameter space. Moreover, the NLO QCD corrections can reduce the dependence of the total cross sections on the renormalization/factorization scale, especially for $μ<0$. We also use the CTEQ6.1 PDF sets to estimate the uncertainty of LO and NLO total cross sections, and find that the uncertainty arising from the choice of PDFs increases with the increasing $m_{A^0}$.

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arXiv2003

Supersymmetric effects in top quark decay into polarized W-boson

We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak (SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal or transverse W-boson. The corrections are presented in terms of the longitudinal ratio Γ(t-->W_L b)/Γ(t--> W b) and the transverse ratio Γ(t-->W_- b)/Γ(t--> W b). In most of the parameter space, both SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1% in magnitude and they tend to have opposite signs. The corrections to the total width Γ(t-->W b) are also presented for comparison with the existing results in the literature. We find that our SUSY-EW corrections to the total width differ significantly from previous studies: the previous studies give a large correction of more than 10% in magnitude for a large part of the parameter space while our results reach only few percent at most.

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arXiv2003

Higgs-boson production associated with a bottom quark at hadron colliders with SUSY-QCD corrections

The Higgs boson production p p (p\bar p) -> b h +X via b g -> b h at the LHC, which may be an important channel for testing the bottom quark Yukawa coupling, is subject to large supersymmetric quantum corrections. In this work the one-loop SUSY-QCD corrections to this process are evaluated and are found to be quite sizable in some parameter space. We also study the behavior of the corrections in the limit of heavy SUSY masses and find the remnant effects of SUSY-QCD. These remnant effects, which are left over in the Higgs sector by the heavy sparticles, are found to be so sizable (for a light CP-odd Higgs and large \tanβ) that they might be observable in the future LHC experiment. The exploration of such remnant effects is important for probing SUSY, especially in case that the sparticles are too heavy (above TeV) to be directly discovered at the LHC.

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arXiv2000

Supersymmetric Electroweak Corrections to Charged Higgs Boson Production in Association with a Top Quark at Hadron Colliders

We calculate the $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ and $O(α_{ew} m_{t(b)}^4/m_W^4)$ supersymmetric electroweak corrections to the cross section for the charged Higgs boson production in association with a top quark at the Tevatron and the LHC. These corrections arise from the quantum effects which are induced by potentially large Yukawa couplings from the Higgs sector and the chargino-top(bottom)-sbottom(stop) couplings, neutralino-top(bottom)-stop(sbottom) couplings and charged Higgs-stop-sbottom couplings. They can decrease or increase the cross section depending on $\tanβ$ but are not very sensitive to the mass of the charged Higgs boson for high $\tanβ$. At low $\tanβ(=2)$ the corrections decrease the total cross sections significantly, which exceed -12% for $m_{H^{\pm}}$ below $300GeV$ at both the Tevatron and the LHC, but for $m_{H^{\pm}}>300GeV$ the corrections can become very small at the LHC. For high $\tanβ(=10,30)$ these corrections can decrease or increase the total cross sections, and the magnitude of the corrections are at most a few percent at both the Tevatron and the LHC.

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arXiv1999

Implications of LEP/SLD Data for New Physics in Zbb_bar Couplings

The combined LEP/SLD data on the b\bar b forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the $Zb\bar b$ couplings. In general, the effect of new physics can be parameterized by $SU_C(3)\times SU_L(2)\times U_Y(1)$ invariant higher dimensional operators. By fitting the recently announced LEP/SLD data on A_b and R_b, the size of the coupling strengths of these operators can be determined. We also found that the new physics operators can be divided into two types, depending on their Higgs field content. The ones involving the Higgs have very mild effects at higher energy colliders, while the other type which do not contain the Higgs field can show significantly large effects on $b\bar b$ production at LEP II, $t\bar t$ production at the NLC and single top production at the Tevatron. The preliminary data from the LEP II measurements disfavors the second type of operators.

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arXiv1999

Yukawa Corrections to Charged Higgs Boson Production in Association with a Top Quark at Hadron Colliders

We calculate the Yukawa corrections of order $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ to charged Higgs boson production in association with a top quark at the Tevatron and the LHC. The corrections are not very sensitive to the mass of the charged Higgs boson and can exceed -20% for low values of $\tanβ$, where the contribution of the top quark is large, and high values of $\tanβ$ where the contribution of the bottom quark becomes large. These Yukawa corrections could be significant for charged Higgs boson discovery searches based on this production process, particularly at the LHC where the cross section is relatively large.

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arXiv1997

Supersymmetric QCD Corrections to Single Top Quark Production at the Fermilab Tevatron

We evaluate the supersymmetric QCD corrections to single top quark production via $q \bar q'\to t \bar b$ at the Fermilab Tevatron in the minimal supersymmetric model. We find that within the allowed range of squark and gluino masses the supersymmetric QCD corrections can enhance the cross section by a few percent. The combined effects of SUSY QCD, SUSY EW, and the Yukawa couplings can exceed 10% for the smallest allowed $\tanβ~ (\simeq 0.25)$ but are only a few percent for $\tanβ>1$.

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arXiv1997

Supersymmetric Electroweak Parity Nonconservation in Top Quark Pair Production at the Fermilab Tevatron

We evaluate the supersymmetric (SUSY) electroweak corrections to the effect of parity nonconservation in $q {\bar q} \to t {\bar t}$ production at the Fermilab Tevatron predicted by the Minimal Supersymmetric Model (MSSM). We find that the parity nonconserving asymmetry from the SUSY electroweak and SUSY Yukawa loop corrections predicted by the minimal supergravity (mSUGRA) model and the MSSM models with scenarios motivated by current data is about one percent. It will be challenging to observe such a small asymmetry at the Tevatron with 10 fb^{-1} of luminosity. It could however be observable if both the top- and bottom-squarks are light and $\tan β$ is smaller than 1, though theses parameters are not favored by mSUGRA.

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arXiv1996

SU(3) flavor symmetry breaking and semileptonic decays of heavy mesons

Assuming the ${\bar D}^0, D^-, D^-_s$ and $B^+, B^0, B_s^0$ mesons belong to triplets of SU(3) flavor symmetry, we analyse the form factors in the semileptonic decays of these mesons. Both quark and meson mass differences are taken into account. We find a number of relations, in agreement with the present data as well as with previous analyses, and predict certain ratios of form factors, not yet measured, most notably the D meson decay constant $f_D = 209 \pm 39$ MeV.

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arXiv1996

Supersymmetric Electroweak Corrections to Single Top Quark Production at the Fermilab Tevatron

We have calculated the $O(α_{ew} M_t^2/M_W^2)$ supersymmetric electroweak corrections to single top quark production via $q\bar q' \to t\bar b$ at the Fermilab Tevatron in the minimal supersymmetric model. The supersymmetric electroweak corrections to the cross section are a few percent for $tan β> 1$, and can exceed 10% for $tanβ<1$. The combined effects of SUSY electroweak corrections and the Yukawa corrections can exceed 10% for favorable parameter values, which might be observable at a high-luminosity Tevatron.

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arXiv1996

Yukawa Corrections to Single Top Quark Production at the Fermilab Tevatron in the Two-Higgs-Doublet Models

We calculate Yukawa corrections of order $α_{ew} M_t^2/M_W^2$ to single top quark production via $q \bar q'\rightarrow t \bar b$ at the Fermilab Tevatron in the two-Higgs-doublet models. In our calculation we also keep the terms proportional to $ M_b^2 \tan^2 β$ since their effects may become rather important for large $\tanβ$. The corrections can amount to more than a 15\% reduction in the production cross section relative to the tree level result in the general two-Higgs-doublet model, and a 10\% enhancement in the minimal supersymmetric model, which might be observable at a high-luminosity Tevatron.

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arXiv1996

Comparative Study of the Hadronic Production of $B_c$ Mesons

The full order $α_s^4$ perturbative QCD calculation of the production of $B_c$ mesons at the Tevatron is compared with the fragmentation approximation. The non-fragmentation diagrams, in which two or more quarks and/or gluons can simultaneously be nearly on-shell, are important unless $P_T\gg M_{B_c}$.

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arXiv1996

One-loop QCD Corrections to Top Quark Decay into a Neutralino and Light Stop

We calculate the one-loop QCD corrections to $t\rightarrow \tilde t_1 \tilde χ^0_j$ using dimensional reduction scheme, including QCD and supersymmetric QCD corrections. The analytic expressions for the corrections to the decay width are given, which can easily be extended to $t\rightarrow \tilde χ^+_j \tilde b_i $. The numerical results show that the correction amounts to more than a 10\% reduction in the partial width relative to the tree level result. We also compare the corrections in the no-mixing stop case with those in the mixing stop case.

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arXiv1996

Comparative Study of the Hadronic Production of $B_c$ Mesons

A comparative study of the full $α_s^4$ perturbative QCD calculation of the hadronic production of the $B_c$ and $B_c^*$ mesons and the fragmentation approximation is presented. We examined the various subprocesses in detail and the distribution $C(z)$, where $z$ is twice the fraction of the $B_c$ or $B_c^*$ meson energy in the center of mass of the subprocess, which proved insightful and revealed the importance of certain non-fragmentation contributions. We concluded that the condition for the applicability of the fragmentation approximation in hadronic collisions is that the transverse momentum $P_T$ of the produced $B_c$ and $B_c^*$ be much larger than the mass of the $B_c$ meson; i.e., $P_T\gg M_{B_c}$. Numerical results for the cross sections at the Fermilab Tevatron are also presented using updated parton distribution functions with various kinematic cuts.

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