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We update the theoretical predictions for direct Y(nS) hadroproduction in the framework of NRQCD. 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 pT and substantially affect the polarization of the Upsilon. Motivated by the remaining gap between the NLO yield and the cross section measurements at the Tevatron, we evaluate the leading part of the alpha_s^5 contributions, namely those coming from Y(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 Y(nS) is longitudinal. We also present our predictions for Y(nS) production at the LHC.
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Following the nonrelativistic QCD factorization scheme, by taking latest available measurement on $chi_b(3P)$ into consideration, we present an updated study on the yield and polarization of $Upsilon(1S,2S,3S)$ hadroproduction, and the fractions of $chi_b(mP)$ feed-down in $Upsilon(nS)$ production at QCD next-to-leading order. In the fitting, three schemes are applied with different choice of $chi_b(mP)$ feed-down ratios and NRQCD factorization scale. The results can explain the measurements on yield very well as in our previous work. The polarization puzzle to $Upsilon(3S)$ is now solved by considering the $chi_b(3P)$ feed-down contributions. The ratio of $sigma[chi_{b2}(1P)]/sigma[chi_{b1}(1P)]$ measurements from CMS can also be reproduced in our prediction. Among the different schemes, the results show little difference, but there are sizeable difference for the fitted long-distance color-octet matrix elements. It may bring large uncertainty when the values are applied in other experiments such as in $ee,~ep$ colliders.
Inclusive bottomonium hadroproduction at the Tevatron is firstly examined in a Monte Carlo framework with the colour-octet mechanism implemented in the event generation. We extract some NRQCD colour-octet matrix elements relevant for $Upsilon(1S)$ hadroproduction. Remarkably we find a quite small contribution (compatible with zero) from feeddown of $chi_{bJ}$ states produced through the colour-octet mechanism: $Upsilon(1S)$ indirect production via $chi_{bJ}$ decays should be mainly ascribed to the colour-singlet model. Finally we extrapolate to LHC energies to predict prompt $Upsilon(1S)$ production rates.
We demonstrate that in the back-to-back kinematics the production of four jets in the collision of two partons is suppressed in the leading log approximation of pQCD, compared to the hard processes involving the collision of four partons. We derive the basic equation for four-jet production in QCD in terms of the convolution of generalized two-parton distributions of colliding hadrons in the momentum space representation. Our derivation leads to geometrical approach in the impact parameter space close to that suggested within the parton model and used before to describe the four-jet production. We develop the independent parton approximation to the light-cone wave function of the proton. Comparison with the CDF and D0 data shows that the independent parton approximation to the light-cone wave function of the proton is insufficient to explain the data. We argue that the data indicate the presence of significant multiparton correlations in the light-cone wave functions of colliding protons.
We consider the transverse-momentum (q_T) distribution of Standard Model Higgs bosons produced by gluon fusion in hadron collisions. At small q_T (q_T<<m_H, m_H being the mass of the Higgs boson), we resum the logarithmically-enhanced contributions due to multiple soft-gluon emission to all order in QCD perturbation theory. At intermediate and large values of q_T (q_T <~m_H), we consistently combine resummation with the known fixed-order results. We use the most advanced perturbative information that is available at present: next-to-next-to-leading logarithmic resummation combined with the next-to-leading fixed-order calculation. We extend previous results including exactly all the perturbative terms up to order alphas^4 in our computation and, after integration over q_T, we recover the known next-to-next-to-leading order result for the total cross section. We present numerical results at the Tevatron and the LHC, together with an estimate of the corresponding uncertainties. Our calculation is implemented in an updated version of the numerical code HqT.
We review the status of the QCD corrected cross sections and kinematic distributions for the production of a Higgs boson in association with top quark or bottom quark pairs at the Fermilab Tevatron and at the LHC. Results for b-bbar-H production are presented in the Minimal Supersymmetric Model, where the rates can be greatly enhanced relative to the Standard Model rates. We place particular emphasis on theoretical uncertainties due to renormalization and factorization scale dependence and on the uncertainties coming from the Parton Distribution Functions.
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