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Evidence for the direct decay of the 125 GeV Higgs boson to fermions

The discovery of a new boson with a mass of approximately 125 GeV in 2012 at the LHC has heralded a new era in understanding the nature of electroweak symmetry breaking and possibly completing the standard model of particle physics. Since the first observation in decays to gamma gamma, WW, and ZZ boson pairs, an extensive set of measurements of the mass and couplings to W and Z bosons, as well as multiple tests of the spin-parity quantum numbers, have revealed that the properties of the new boson are consistent with those of the long-sought agent responsible for electroweak symmetry breaking. An important open question is whether the new particle also couples to fermions, and in particular to down-type fermions, since the current measurements mainly constrain the couplings to the up-type top quark. Determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays, as recently reported by the CMS experiment in the study of Higgs decays to bottom quarks and tau leptons. In this paper we report the combination of these two channels which results, for the first time, in strong evidence for the direct coupling of the 125 GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected.

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Muhammad Ahmad, Georgios Anagnostou, Konstantin Androsov, Giovanni Bianchi, Roberto Castello, Jie Chen, Yixing Chen, Tian Cheng, Giuseppe Codispoti, Alessandro Degano, Charles Dietz, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Yu Fu, Yifei Guo, Ruchi Gupta, Csaba Hajdu, Alexis Kalogeropoulos, Ji Hyun Kim, Donghyun Kim, Vineet Kumar, Ajay Kumar, Sanjeev Kumar, Ekaterina Kuznetsova, Ho Ling Li, Wei Li, Hao Liu, Shuai Liu, Werner Lustermann, Matteo Marone, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Sourav Sen, Ashish Sharma, Varun Sharma, Lesya Shchutska, Muhammad Shoaib, Michal Simon, Gurpreet Singh, Jan Steggemann, Wei Sun, Andromachi Tsirou, Paul Turner, Joao Varela, Jian Wang, Xiao Wang, Mingkui Wang, Qian Wang, Zheng Wang, Matthias Weber, Matthias Wolf, Wenjing Wu, Fan Yang, Yong Yang, Kai Yi, Lei Zhang, Yu Zheng
2014
Article

Résumé

Official source

https://infoscience.epfl.ch/record/274807?ln=fr

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Concepts associés (29)

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Publications associées (109)

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Modèle standard de la physique des particules

vignette|upright=2.0|Modèle standard des particules élémentaires avec les trois générations de fermions (trois premières colonnes), les bosons de jauge (quatrième colonne) et le boson de Higgs (cinqui

Quark bottom

Le quark bottom (souvent abrégé en quark b), ou quark beau (beauty quark en anglais), est un quark, une particule élémentaire de la physique des particules. Propriétés vignette|300px|Diag

Boson

En mécanique quantique, un boson est une particule subatomique de spin entier qui obéit à la statistique de Bose-Einstein. Le théorème spin-statistique différencie les bosons des fermions, qui ont un

Searches for heavy Higgs bosons in two-Higgs-doublet models and for $t→ch$ decay using multilepton and diphoton final states in $pp$ collisions at 8 TeV

Muhammad Ahmad, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, Giovanni Bianchi, Roberto Castello, Yixing Chen, Tian Cheng, Giuseppe Codispoti, Alessandro Degano, Charles Dietz, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Yifei Guo, Ruchi Gupta, Csaba Hajdu, Alexis Kalogeropoulos, Ji Hyun Kim, Donghyun Kim, Vineet Kumar, Ajay Kumar, Sanjeev Kumar, Ekaterina Kuznetsova, Wei Li, Ho Ling Li, Shuai Liu, Hao Liu, Werner Lustermann, Matteo Marone, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Sourav Sen, Ashish Sharma, Varun Sharma, Lesya Shchutska, Muhammad Shoaib, Michal Simon, Gurpreet Singh, Jan Steggemann, Wei Sun, Andromachi Tsirou, Paul Turner, Joao Varela, Rui Wang, Zheng Wang, Xiao Wang, Jian Wang, Qian Wang, Matthias Weber, Matthias Wolf, Fan Yang, Yong Yang, Kai Yi, Lei Zhang, Yu Zheng

Searches are presented for heavy scalar (

\mathrm{H}

) and pseudoscalar (

\mathrm{A}

) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of

\mathrm{p}\mathrm{p}

collisions collected with the CMS experiment at the LHC at a center-of-mass energy of

\sqrt{s} = 8~\mathrm{TeV}

and corresponding to an integrated luminosity of

19.5~\mathrm{fb}^{-1}

. The decays

\mathrm{H} \rightarrow \mathrm{h} \mathrm{h}

and

\mathrm{A} \rightarrow \mathrm{Z} \mathrm{h}

, where

\mathrm{h}

denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. The search results are presented in terms of the

\mathrm{H}

and

\mathrm{A}

production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% CL cross section upper limits of approximately

7~\mathrm{pb}

\sigma \mathcal{B}

for

\mathrm{H} \rightarrow \mathrm{h} \mathrm{h}

and

2~\mathrm{pb}

for

\mathrm{A} \rightarrow \mathrm{Z} \mathrm{h}

. Also presented are the results of a search for the rare decay of the top quark that results in a charm quark and an SM Higgs boson,

\mathrm{t} \rightarrow \mathrm{c} \mathrm{h}

, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% CL upper limit of 0.56% on

\mathcal{B}(\mathrm{t} \rightarrow \mathrm{c} \mathrm{h})

2014

Chargement

Search for neutral MSSM Higgs bosons decaying to a pair of tau leptons in pp collisions

Muhammad Ahmad, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, Giovanni Bianchi, Roberto Castello, Yixing Chen, Tian Cheng, Giuseppe Codispoti, Alessandro Degano, Charles Dietz, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Ruchi Gupta, Csaba Hajdu, Alexis Kalogeropoulos, Donghyun Kim, Ji Hyun Kim, Sanjeev Kumar, Vineet Kumar, Ajay Kumar, Ekaterina Kuznetsova, Wei Li, Ho Ling Li, Hao Liu, Shuai Liu, Werner Lustermann, Matteo Marone, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Sourav Sen, Ashish Sharma, Varun Sharma, Lesya Shchutska, Muhammad Shoaib, Michal Simon, Gurpreet Singh, Jan Steggemann, Wei Sun, Andromachi Tsirou, Paul Turner, Joao Varela, Zheng Wang, Jian Wang, Rui Wang, Qian Wang, Matthias Weber, Matthias Wolf, Fan Yang, Yong Yang, Kai Yi, Yu Zheng

A search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model (MSSM) decaying to tau-lepton pairs in pp collisions is performed, using events recorded by the CMS experiment at the LHC. The dataset corresponds to an integrated luminosity of 24.6 fb

^{−1}

, with 4.9 fb

^{−1}

at 7 TeV and 19.7 fb

^{−1}

at 8 TeV. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes the case where the Higgs boson is produced in association with a b-quark jet. No excess is observed in the tau-lepton-pair invariant mass spectrum. Exclusion limits are presented in the MSSM parameter space for different benchmark scenarios, m

_{h}^{max}

, m

_{h}^{mod +}

, m

_{h}^{mod −}

, light-stop, light-stau, τ-phobic, and low-m

_{H}

. Upper limits on the cross section times branching fraction for gluon fusion and b-quark associated Higgs boson production are also given.

2014

Chargement

Measurement of Top Quark-Antiquark Pair Production in Association with a W or Z Boson in pp Collisions at $\sqrt{s} = 8$ $\,\text {TeV}$

A measurement of the cross section for the production of top quark–antiquark pairs (

{\mathrm {t}}\overline{{\mathrm {t}}}

) in association with a vector boson V (W or Z) in proton-proton collisions at

\sqrt{s} = 8

\,\text {TeV}

is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb

^{-1}

recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and

\mu

) channels: a same-sign dilepton analysis targeting

{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}

events, and trilepton and four-lepton analyses designed for

{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}

events. In the same-sign dilepton channel, the

{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}

cross section is measured as

\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}} = 170 ^{+90-80}\,\text {(stat)} \pm 70\,\text {(syst)} \, \text {fb}

, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the

{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}

cross section,

\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}} = 200 ^{+80-70}\,\text {(stat)} ^{+40-30}\,\text {(syst)} \mathrm{fb}^{-1}

, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive

{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {V}}

process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

2014

Chargement