Article

# Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data

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Università di Parma Dipartimento di Fisica 43100 Parma Italy
(Impact Factor: 5.08). 12/2009; 66(3). DOI: 10.1140/epjc/s10052-010-1251-4
Source: arXiv

ABSTRACT We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed. Comment: Report of the "Working Group on Radiative Corrections and Monte Carlo Generators for Low Energies"; 99 pages, submitted to EPJC

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Available from: Andrej Arbuzov, Sep 25, 2015
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• "Let us stress that Helac-Phegas has been already extensively used and tested, see e.g. [19] [20] [21] [22] [23] [24]. Moreover, both libraries compute relevant contributions in a very efficient way, using off-shell recursive equations and avoiding a multiple evaluation of recurring building blocks. "
##### Article: Hadronic top-quark pair production in association with two jets at Next-to-Leading Order QCD
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ABSTRACT: We report on the calculation of the next-to-leading order QCD corrections to the production of ttbar pairs in association with two hard jets at the Fermilab TeVatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the TeVatron and 15% for the LHC. In case of the TeVatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to A_FB = -10.3% at leading order and A_FB = -4.6% at next-to-leading order. All results presented in this paper have been obtained with the help of the HELAC-NLO package.
Physical review D: Particles and fields 08/2011; 84(11). DOI:10.1103/PhysRevD.84.114017 · 4.86 Impact Factor
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• "Our LO results have been generated with the Helac- Dipoles [42] package and cross checked with Helac-Phegas [43] [44], a generator for all parton level processes in the Standard Model, which has, on its own, already been extensively used and tested in phenomenological studies see e.g. [45] [46] [47] [48] [49]. The integration over the fractions x 1 and x 2 of the initial partons is optimized with the help of Parni [50]. "
##### Article: Complete off-shell effects in top quark pair hadroproduction with leptonic decay at next-to-leading order
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ABSTRACT: Results for next-to-leading order QCD corrections to the pp( p[(p)] ) ® t[(t)] ® W+ W- b[(b)] ® e+ nem- [(n)]m b[`(b)] + X pp\left( {p\bar{p}} \right) \to t\bar{t} \to {W^{+} }{W^{-} }b\bar{b} \to {e^{+} }{\nu_e}{\mu^{-} }{\bar{\nu }_\mu }b\bar{b} + X processes with complete off-shell effects are presented for the first time. Double-, single-and non-resonant top contributions of the order O( as3a4 ) \mathcal{O}\left( {\alpha_s^3{\alpha^4}} \right) are consistently taken into account, which requires the introduction of a complex-mass scheme for unstable top quarks. Moreover, the intermediate W bosons are treated off-shell. Comparison to the narrow width approximation for top quarks, where non-factorizable corrections are not accounted for is performed. Besides the total cross section and its scale dependence, several differential distributions at the TeVatron run II and the LHC are given. In case of the TeVatron the forward-backward asymmetry of the top is recalculated afresh. With inclusive selection cuts, the forward-backward asymmetry amounts to AFBt = 0.051±0.0013 A_{FB}^t = 0.051\pm 0.0013 . Furthermore, the corrections with respect to leading order are positive and of the order 2.3% for the TeVatron and 47% for the LHC. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty due to higher order corrections is 8% for the TeVatron and 9% for the LHC. KeywordsJets–NLO Computations–Hadronic Colliders–QCD
Journal of High Energy Physics 02/2011; 2011(2):1-30. DOI:10.1007/JHEP02(2011)083 · 6.11 Impact Factor
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##### Article: Monte-Carlo generator photon jets for the process e + e −→γγ
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ABSTRACT: Monte-Carlo generator with photon jets radiation in collinear regions for the process e +e −→γγ is described in detail. Radiative corrections in the first order of α are treated exactly. Large leading logarithmic corrections coming from collinear regions are taken into account in all orders of α by applying the Structure Function approach. Theoretical precision of the cross section with radiative corrections is estimated to be 0.2%. This process is considered as an additional tool to measure luminosity in forthcoming experiments with the CMD-3 detector at the e +e − collider VEPP-2000.
European Physical Journal C 06/2011; 71(6). DOI:10.1140/epjc/s10052-011-1597-2 · 5.08 Impact Factor