W and Z/γ ∗ boson production in association with a bottom-antibottom pair

Journal of High Energy Physics (Impact Factor: 6.11). 06/2011; 9(9). DOI: 10.1007/JHEP09(2011)061
Source: arXiv


We present a study of l\nu b\bar{b} and l+ l- b\bar{b} production at hadron
colliders. Our results, accurate to the next-to-leading order in QCD, are based
on automatic matrix-element calculations performed by MadLoop and MadFKS, and
are given at both the parton level, and after the matching with the Herwig
event generator, achieved with aMC@NLO. We retain the complete dependence on
the bottom-quark mass, and include exactly all spin correlations of final-state
leptons. We discuss the cases of several observables at the LHC which highlight
the importance of accurate simulations.

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Available from: Valentin Hirschi
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    • "[9] [10] [11]. W b ¯ b production is also available in NLO+partonshower (NLO+PS) event generators such as the POWHEG BOX [12] and MC@NLO [8]. "
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    ABSTRACT: We present a next-to-leading order plus parton-shower event generator for the production of a W boson plus two bottom quarks and a jet at hadron colliders, implemented in the POWHEG BOX framework. Bottom-mass effects and spin correlations of the decay products of the W boson are fully taken into account. The code has been automatically generated using the two available interfaces to MadGraph4 and GoSam, the last one updated to a new version. We have applied the MiNLO prescription to our Wbbj calculation, obtaining a finite differential cross section also in the limit of vanishing jet transverse momentum. Furthermore, we have compared several key distributions for Wbbj production with those generated with a next-to-leading order plus parton-shower event generator for Wbb production, and studied their factorization- and renormalization-scale dependence. Finally, we have compared our results with recent experimental data from the ATLAS and CMS Collaborations.
    Full-text · Article · Feb 2015 · Journal of High Energy Physics
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    • "Finally, all terms of O(α 4 S ) have been ignored here; note that at least those proportional to y 2 t are usually seen as NNLO contributions to the gluon-fusion cross section. The fully automated MadGraph5 aMC@NLO [27] program can handle 4FS b ¯ bH production rather straightforwardly – the calculation is of a complexity similar to that of Zb ¯ b production, which could be studied [46] even with a version of the code much less powerful than the present one. However, the default treatment of Yukawa couplings in the code is that of an on-shell scheme renormalisation, which is not optimal in the case of b ¯ bH production, where the MS scheme has to be preferred [47]. "
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    ABSTRACT: We study the production of a Higgs boson in association with bottom quarks in hadronic collisions, and present phenomenological predictions relevant to the 13 TeV LHC. Our results are accurate to the next-to-leading order in QCD, and matched to parton showers through the MC@NLO method; thus, they are fully differential and based on unweighted events, which we shower by using both Herwig++ and Pythia8. We perform the computation in both the four-flavour and the five-flavour schemes, whose results we compare extensively at the level of exclusive observables. In the case of the Higgs transverse momentum, we also consider the analytically-resummed cross section up to the NNLO+NNLL accuracy. In addition, we analyse at ${\cal O}(\alpha_S^3)$ the effects of the interference between the $b\bar{b}H$ and gluon-fusion production modes.
    Full-text · Article · Sep 2014 · Journal of High Energy Physics
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    • "Full particle-level predictions have existed at LO for some time, obtained by matching parton shower generators to LO multi-leg matrix elements in the 4FNS [5] [6], 5FNS [7], or both [8]. More recently, a full particle-level prediction for Z+ ≥ 2 b-jets at NLO in the 4FNS with matched parton shower has become available [9] [10]. The same framework can also be used to provide a full particle-level prediction for Z+ ≥ 1 b-jet at NLO in the 5FNS. "
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    ABSTRACT: Measurements of differential production cross-sections of a $Z$ boson in association with $b$-jets in $pp$ collisions at $\sqrt{s}=7$ TeV are reported. The data analysed correspond to an integrated luminosity of 4.6~fb$^{-1}$ recorded with the ATLAS detector at the Large Hadron Collider. Particle-level cross-sections are determined for events with a $Z$ boson decaying into an electron or muon pair, and containing $b$-jets. For events with at least one $b$-jet, the cross-section is presented as a function of the $Z$ boson transverse momentum and rapidity, together with the inclusive $b$-jet cross-section as a function of $b$-jet transverse momentum, rapidity and angular separations between the $b$-jet and the $Z$ boson. For events with at least two $b$-jets, the cross-section is determined as a function of the invariant mass and angular separation of the two highest transverse momentum $b$-jets, and as a function of the $Z$ boson transverse momentum and rapidity. Results are compared to leading-order and next-to-leading-order perturbative QCD calculations.
    Preview · Article · Jul 2014
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