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Master's Dissertation
DOI
https://doi.org/10.11606/D.76.2021.tde-03092021-114253
Document
Author
Full name
Cristiane Yumi Mise London
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2021
Supervisor
Committee
Boito, Diogo Rodrigues (President)
Nielsen, Marina
Oliveira, Emmanuel Gräve de
Title in English
Higher-order perturbative QCD in the Higgs decay to bottom quarks
Keywords in English
Higgs boson
Padé approximant
QCD
Renormalon
Abstract in English
In the absence of direct observation of physics beyond the Standard Model at the LHC, precise tests both in theory and experiment require higher precision. The perturbative QCD corrections to the decay width of the Higgs boson into bottom quarks is known up to fourth order in the strong coupling, αs. This series is divergent and assumed to be asymptotic and its properties are better analyzed if we consider its Borel transform. In this work, we employ the method of Padé approximants to the Borel transform to reconstruct the series of the imaginary part of the scalar quark- antiquark correlator, directly related to the decay width, and study its renormalons and higher-order corrections. We begin by testing this method in the large-β0 limit of QCD, where the perturbative series is known to all orders, using it as a testing ground to determine the best strategy to build the series at higher orders using only the first four coefficients. In this limit, we observe that varying the renormalization scheme of the strong coupling αs and also employing the D-log Padé approximants can improve the convergence to the original function. We apply this procedure in full QCD in order to predict some of the main features of the series at (yet unknown) higher orders. We estimate the coefficient of order α5s (six loops) in a model-independent way as −8200 ± 308 and we could conclude that, although very small, this correction is important to stabilize the series. Thus, at present, the limiting factors in the precision of the decay rate of Higgs into bb are the uncertainties of the strong coupling αs and the bottom-quark mass mb.
Title in Portuguese
QCD perturbativa em ordens altas no decaimento do Higgs em quarks bottom
Keywords in Portuguese
Aproximante de Padé
bóson de Higgs
QCD
Renôrmalon
Abstract in Portuguese
Na ausência de observação direta de física além do Modelo Padrão no LHC, testes precisos tanto da teoria quanto experimentais requerem maior precisão. As correções perturbativas em QCD do decaimento do bóson de Higgs em quarks bottom é conhecido até quarta ordem no acoplamento forte, αs. Essa série é divergente e assumida assintótica e suas propriedades são melhor analisadas se considerarmos sua transformada de Borel. Nesse trabalho, empregamos o método dos aproximantes de Padé na transformada de Borel para reconstruir a série da parte imaginária do correlator escalar quark-antiquark, que está diretamente relacionado à taxa de decaimento, e estudar seus renôrmalons e suas correções de ordens mais altas. Iniciamos testando esse método no limite large-β0 da QCD, onde a série perturbativa é conhecida em todas as ordens, usando-o como um laboratório para determinar a melhor estratégia para reconstruir a série em ordens mais altas usando somente os quatro primeiros coeficientes. Nesse limite, observamos que variar o esquema de renormalização do acoplamento forte αs e aplicar os chamados D-log Padés podem melhorar a convergência à função original. Aplicamos o procedimento na QCD completa a fim de prever algumas das características principais da série em ordens superiores (ainda desconhecidas). Estimamos o coeficiente de ordem α5s (seis loops) independente de modelo como −8200 ± 308 e pudemos concluir que, apesar de ser muito pequena, essa correção é importante para estabilizar a série. Portanto, atualmente os fatores limitantes na precisão da taxa de decaimento do Higgs em bb são as incertezas do acoplamento forte αs e da massa do quark bottom mb.
 
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Publishing Date
2021-09-17
 
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