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Register a new userAn Updated Study for $Upsilon$ Production and Polarization at the Tevatron and 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.
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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.
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 extend our previous analysis on inclusive heavy quarkonia hadroproduction to the whole Upsilon(nS) (n=1,2,3) resonance family. We use a Monte Carlo framework with the colour-octet mechanism implemented in the PYTHIA event generator. We include in our study higher order QCD effects such as initial-state emission of gluons and Altarelli-Parisi evolution of final-state gluons. We extract some NRQCD colour-octet matrix elements relevant for Upsilon(nS) (n=1,2,3) hadroproduction from CDF data at the Fermilab Tevatron. Then we extrapolate to LHC energies to predict prompt bottomonia production rates. Finally, we examine the prospect to probe the gluon density in protons from heavy quarkonia inclusive hadroproduction at high transverse momentum and its feasibility in LHC general-purpose experiments.
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.
This paper provides a review of the experimental studies of processes with a single top quark at the Tevatron proton-antiproton collider and the LHC proton-proton collider. Single top-quark production in the t-channel process has been measured at both colliders. The s-channel process has been observed at the Tevatron, and its rate has been also measured at the center-of-mass energy of 8 TeV at the LHC in spite of the comparatively harsher background contamination. LHC data also brought the observation of the associated production of a single top quark with a W boson as well as with a Z boson. The Cabibbo-Kobayashi-Maskawa matrix element |Vtb| is extracted from the single-top-quark production cross sections, and t-channel events are used to measure several properties of the top quark and set constraints on models of physics beyond the Standard Model. Rare final states with a single top quark are searched for, as enhancements in their production rates, if observed, would be clear signs of new physics.
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