Standard Model Higgs Boson Searches in the Weak Boson Decay Channels with the ATLAS Detector

The search of the Standard Model Higgs boson decaying into a pair of weak bosons with the subsequent leptonic decay of the W or Z bosons is presented. The contributions achieved by this work range from the réévaluation of Higgs boson normalisation cross-sections, to the development of the analysis strategies using detailed Monte Carlo simulations and the search results for the H -► ZZ -► l+l-ννbar decay mode based on 4.7 fb-1 of proton-proton collision data at sqrt(s) = 7 TeV taken during 2011 by the ATLAS detector. The computation of cross-sections values for Higgs boson production at centre-of-mass energies varying from 6 to 14 TeV, for the main production mechanisms at the LHC were documented for posterior usage among the Collaboration. Preliminary detector resolution studies on Z -► μμ events using early data collected by ATLAS are also described. Simulation studies for the H -► ZZ(*) -► l+l-l+l- and H — W+W- — l+νl-ν channels included feasibility checks used to quantify the expected sensitivity of the analyses for various scenarios with different centre-of-mass energy, luminosity and detector calibration conditions. These results were part of the input that the Collaboration used to feed the schedule and plans of the LHC. On the H -► ZZ -► l+l-ννbar channel, upper limits on the Higgs boson production cross-section in a mass range between 200 and 900 GeV are set. With this channel by itself, the Standard Model Higgs boson particle is excluded at 95% confidence level in the mass range between 319 and 558 GeV To complete the current picture of the Higgs boson searches in the ATLAS detector, a compilation of the different Higgs boson analyses performed by the ATLAS Collaboration are introduced. The Higgs boson existence is constrained to be in a narrow window between 122.5 GeV and 129 GeV with 95% confidence level; where an excess of 2.6 a local significance is observed.

Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s} = $ 8 TeV

Muhammad Ahmad, Benjamin William Allen, Georgios Anagnostou, Konstantin Androsov, Tagir Aushev, Michele Bianco, Roberto Castello, Yixing Chen, Xin Chen, Tian Cheng, Davide Cieri, Pratyush Das, Alessandro Degano, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Daniel Gonzalez, Seungkyu Ha, Csaba Hajdu, Peter Hansen, Ali Harb, Alexis Kalogeropoulos, Viktor Khristenko, Donghyun Kim, Ji Hyun Kim, Sanjeev Kumar, Vineet Kumar, Ajay Kumar, Ekaterina Kuznetsova, Ho Ling Li, Wei Li, Zhen Liu, Shuai Liu, Hao Liu, Werner Lustermann, Bibhuprasad Mahakud, Maren Tabea Meinhard, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Varun Sharma, Ashish Sharma, Lesya Shchutska, Muhammad Shoaib, Gurpreet Singh, Jan Steggemann, Xin Sun, Marco Trovato, Andromachi Tsirou, David Vannerom, Joao Varela, Hui Wang, Mingkui Wang, Rui Wang, Jian Wang, Siyuan Wang, Yi Wang, Qian Wang, Zheng Wang, Muhammad Waqas, Matthias Weber, Matthias Wolf, Fan Xia, Meng Xiao, Zhirui Xu, Yong Yang, Kai Yi

A study of the associated production of a

\mathrm{Z}

boson and a charm quark jet (

\mathrm{Z} + \mathrm{c}

), and a comparison to production with a

\mathrm{b}

quark jet (

\mathrm{Z} + \mathrm{b}

), in

\mathrm {p}\mathrm {p}

collisions at a centre-of-mass energy of 8

\,\text {TeV}

are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7

\,\text {fb}^{-1}

, collected with the CMS detector at the CERN LHC. The

\mathrm{Z}

boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of

\mathrm{c}

\mathrm{b}

flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with

p_{\mathrm {T}} ^{\ell } > 20\,\text {GeV}

{|\eta ^{\ell }|} < 2.1

71< m_{\ell \ell } < 111\,\text {GeV}

, and heavy flavour jets with

p_{\mathrm {T}} ^{\text {jet}} > 25\,\text {GeV}

and

{|\eta ^{ \text {jet}}|} < 2.5

. The

\mathrm{Z} + \mathrm{c}

production cross section is measured to be

\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{c} + X) \mathcal {B}(\mathrm{Z} \rightarrow \ell ^+\ell ^-) = 8.8 \pm 0.5\,\text {(stat)} \pm 0.6\,\text {(syst)} \,\text {pb}

. The ratio of the

\mathrm{Z} + \mathrm{c}

and

\mathrm{Z} + \mathrm{b}

production cross sections is measured to be

\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{c} + X)/\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{b} + X) = 2.0 \pm 0.2\,\text {(stat)} \pm 0.2\,\text {(syst)}

. The

\mathrm{Z} + \mathrm{c}

production cross section and the cross section ratio are also measured as a function of the transverse momentum of the

\mathrm{Z}

boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.

2018

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Muhammad Ahmad, Benjamin William Allen, Georgios Anagnostou, Konstantin Androsov, Tagir Aushev, Michele Bianco, Xin Chen, Yixing Chen, Tian Cheng, Davide Cieri, Giuseppe Codispoti, Pratyush Das, Abhisek Datta, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Daniel Gonzalez, Ruchi Gupta, Seungkyu Ha, Csaba Hajdu, Peter Hansen, Ali Harb, Miao Hu, Alexis Kalogeropoulos, Viktor Khristenko, Donghyun Kim, Ji Hyun Kim, Sanjeev Kumar, Ajay Kumar, Vineet Kumar, Ekaterina Kuznetsova, Jing Li, Lei Li, Wei Li, Ho Ling Li, Yiming Li, Zhen Liu, Hao Liu, Werner Lustermann, Bibhuprasad Mahakud, Maren Tabea Meinhard, Amr Mohamed, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Sourav Sen, Varun Sharma, Ashish Sharma, Lesya Shchutska, Wei Shi, Kun Shi, Muhammad Shoaib, Gurpreet Singh, Jan Steggemann, Marco Trovato, Andromachi Tsirou, David Vannerom, Joao Varela, Yi Wang, Mingkui Wang, Xiao Wang, Hui Wang, Qian Wang, Jian Wang, Zheng Wang, Siyuan Wang, Muhammad Waqas, Matthias Weber, Matthias Wolf, Fan Xia, Meng Xiao, Zhirui Xu, Yong Yang

Measurements are presented of associated production of a

\mathrm {W}

boson and a charm quark (

\mathrm {W}+\mathrm {c}

) in proton–proton collisions at a center-of-mass energy of 13

\,\text {Te}\text {V}

. The data correspond to an integrated luminosity of 35.7

\,\text {fb}^{-1}

collected by the CMS experiment at the CERN LHC. The

\mathrm {W}

bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of

{\mathrm {D}^{*}(2010)^{\pm }}

mesons that decay via

{\mathrm {D}^{*}(2010)^{\pm }}\rightarrow \mathrm {D}^0 + {\pi ^{\pm }}\rightarrow \mathrm {K}^{\mp } + {\pi ^{\pm }}+ {\pi ^{\pm }}

. A cross section is measured in the fiducial region defined by the muon transverse momentum

p_{\mathrm {T}} ^{\mu } > 26\,\text {Ge}\text {V}

, muon pseudorapidity

|\eta ^{\mu } | < 2.4

, and charm quark transverse momentum

p_{\mathrm {T}} ^{\mathrm {c}} > 5\,\text {Ge}\text {V}

. The inclusive cross section for this kinematic range is

\sigma (\mathrm {W}+\mathrm {c})=1026\pm 31\,\text {(stat)} \begin{array}{c} +76\\ -72 \end{array}\,\text {(syst)} \text { pb}

. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the

\mathrm {W}

boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.

Springer2019

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Measurements are presented of associated production of a

\mathrm {W}

boson and a charm quark (

\mathrm {W}+\mathrm {c}

) in proton–proton collisions at a center-of-mass energy of 13

\,\text {Te}\text {V}

. The data correspond to an integrated luminosity of 35.7

\,\text {fb}^{-1}

collected by the CMS experiment at the CERN LHC. The

\mathrm {W}

bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of

{\mathrm {D}^{*}(2010)^{\pm }}

mesons that decay via

{\mathrm {D}^{*}(2010)^{\pm }}\rightarrow \mathrm {D}^0 + {\pi ^{\pm }}\rightarrow \mathrm {K}^{\mp } + {\pi ^{\pm }}+ {\pi ^{\pm }}

. A cross section is measured in the fiducial region defined by the muon transverse momentum

p_{\mathrm {T}} ^{\mu } > 26\,\text {Ge}\text {V}

, muon pseudorapidity

|\eta ^{\mu } | < 2.4

, and charm quark transverse momentum

p_{\mathrm {T}} ^{\mathrm {c}} > 5\,\text {Ge}\text {V}

. The inclusive cross section for this kinematic range is

\sigma (\mathrm {W}+\mathrm {c})=1026\pm 31\,\text {(stat)} \begin{array}{c} +76\\ -72 \end{array}\,\text {(syst)} \text { pb}

. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the

\mathrm {W}

boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.

Springer2019

Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s} = $ 8 TeV

A study of the associated production of a

\mathrm{Z}

boson and a charm quark jet (

\mathrm{Z} + \mathrm{c}

), and a comparison to production with a

\mathrm{b}

quark jet (

\mathrm{Z} + \mathrm{b}

), in

\mathrm {p}\mathrm {p}

collisions at a centre-of-mass energy of 8

\,\text {TeV}

are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7

\,\text {fb}^{-1}

, collected with the CMS detector at the CERN LHC. The

\mathrm{Z}

boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of

\mathrm{c}

\mathrm{b}

flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with

p_{\mathrm {T}} ^{\ell } > 20\,\text {GeV}

{|\eta ^{\ell }|} < 2.1

71< m_{\ell \ell } < 111\,\text {GeV}

, and heavy flavour jets with

p_{\mathrm {T}} ^{\text {jet}} > 25\,\text {GeV}

and

{|\eta ^{ \text {jet}}|} < 2.5

. The

\mathrm{Z} + \mathrm{c}

production cross section is measured to be

\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{c} + X) \mathcal {B}(\mathrm{Z} \rightarrow \ell ^+\ell ^-) = 8.8 \pm 0.5\,\text {(stat)} \pm 0.6\,\text {(syst)} \,\text {pb}

. The ratio of the

\mathrm{Z} + \mathrm{c}

and

\mathrm{Z} + \mathrm{b}

production cross sections is measured to be

\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{c} + X)/\sigma (\mathrm {p}\mathrm {p}\rightarrow \mathrm{Z} + \mathrm{b} + X) = 2.0 \pm 0.2\,\text {(stat)} \pm 0.2\,\text {(syst)}

. The

\mathrm{Z} + \mathrm{c}

production cross section and the cross section ratio are also measured as a function of the transverse momentum of the

\mathrm{Z}

boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.

2018

Standard Model Higgs Boson Searches in the Weak Boson Decay Channels with the ATLAS Detector

Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s} = $ 8 TeV

Study of Final-State Radiation in Decays of Z Bosons Produced in $pp$ Collisions at 7 TeV

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Study of Final-State Radiation in Decays of Z Bosons Produced in $pp$ Collisions at 7 TeV

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s} = $ 8 TeV