Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions

504

379

We present a general method that allows one to decay narrow resonances in Les Houches Monte Carlo events in an efficient and accurate way. The procedure preserves both spin correlation and finite width effects to a very good accuracy, and is therefore particularly suited for the decay of resonances in production events generated at next-to-leading-order accuracy. The method is implemented as a generic tool in the MadGraph5 framework, giving access to a very large set of possible applications. We illustrate the validity of the method and the code by applying it to the case of single top and top quark pair production, and show its capabilities on the case of top quark pair production in association with a Higgs boson.

“…single-t we used MSTW2008nlo68cl nf4 (v5.8.4) instead [24], where α S (M Z ) = 0.11490. The renormalization and factorization scales are set equal to the same scale µ.…”

Section: Spin Correlation Effects In Nlo Eventsmentioning

confidence: 99%

Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations

Artoisenet

Frederix

Mattelaer

et al. 2013

504

379

“…12 Note that we could also take into account the effects due to the bottom and charm quark masses on the PDFs. Indeed, a change in the fitted masses for these quarks may affect the gluon splitting and hence alter the shape of the gluon-gluon luminosity in gg → H. We have estimated quantitatively this effect by using the m b and mc dependent MSTW PDFs [89] with mc = 1.40 ± 0.15 GeV and m b = 4.75 ± 0.05 GeV. In the case of the charm quark, we obtain a ≈ 0.2% change at MH = 115 GeV and at most ≈ 1.5% change at MH = 500 GeV.…”

Section: Jhep03(2011)055mentioning

confidence: 99%

Higgs production at the lHC

Baglio

Djouadi

2011

172

194

Abstract:We analyze the production of Higgs particles at the early stage of the CERN large Hadron Collider with a 7 TeV center of mass energy (lHC). We first consider the case of the Standard Model Higgs boson that is mainly produced in the gluon-gluon fusion channel and to be detected in its decays into electroweak gauge bosons, gg → H → W W, ZZ, γγ. The production cross sections at √ s = 7 TeV and the decay branching ratios, including all relevant higher order QCD and electroweak corrections, are evaluated. An emphasis is put on the various theoretical uncertainties that affect the production rates: the significant uncertainties from scale variation and from the parametrization of the parton distribution functions as well as the uncertainties which arise due to the use of an effective field theory in the calculation of the next-to-next-to-leading order corrections. The parametric uncertainties stemming from the values of the strong coupling constant and the heavy quark masses in the Higgs decay branching ratios, which turn out to be non-negligible, are also discussed. The implications for different center of mass energies of the proton collider, √ s = 8-10 TeV as well as for the design energy √ s = 14 TeV, are briefly summarized. We then discuss the production of the neutral Higgs particles of the Minimal Supersymmetric extension of the Standard Model in the two main channels: gluon-gluon and bottom quark fusion leading to Higgs bosons which subsequently decay into tau lepton or b-quark pairs, gg, bb → Higgs → τ + τ − , bb. The Higgs production cross sections at the lHC and the decay branching ratios are analyzed. The associated theoretical uncertainties are found to be rather large and will have a significant impact on the parameter space of the model that can be probed.

“…The MSTW2008lo68cl [30] parton distribution functions (PDF) are used for generating the signal samples. The BlackMax and charybdis generators calculate the total cross section σ from geometric considerations, assuming that σ ∝ πr 2 S , where r S is the Schwarzschild radius [1,2].…”

Section: Event Reconstruction and Monte Carlo Samplesmentioning

confidence: 99%

Search for microscopic black holes in pp collisions at $$ \sqrt {s} = {\text{7TeV}} $$

Chatrchyan

Khachatryan

Sirunyan

et al. 2012

A search for microscopic black holes in pp collisions at a center-of-mass energy of 7 TeV is presented. The data sample corresponds to an integrated luminosity of 4.7 fb −1 recorded by the CMS experiment at the LHC in 2011. Events with large total transverse energy have been analyzed for the presence of multiple energetic jets, leptons, and photons, which are typical signals of evaporating semiclassical and quantum black holes, and string balls. Agreement with the expected standard model backgrounds, which are dominated by QCD multijet production, has been observed for various combined multiplicities of jets and other reconstructed objects in the final state. Model-independent limits are set on new physics processes producing high-multiplicity, energetic final states. In addition, new model-specific indicative limits are set excluding semiclassical and quantum black holes with masses below 3.8 to 5.3 TeV and string balls with masses below 4.6 to 4.8 TeV . The analysis has a substantially increased sensitivity compared to previous searches.