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Search for long-lived particles decaying to e(+/-)mu(-/+)nu

Long-lived particles decaying to e(+/-) mu(-/+)nu, with masses between 7 and 50 GeV/c(2) and lifetimes between 2 and 50 ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using 5.4 fb(-1) of pp collisions collected with the LHCb detector at a centre-of-mass energy of root s = 13 TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of 125 GeV/c(2), and the charged current production from an on-shell W boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.

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Hossein Afsharnia, Liupan An, Vladislav Balagura, Aurelio Bay, Violaine Bellée, Federico Betti, Marc-Olivier Bettler, Frédéric Blanc, Alexey Boldyrev, Maxim Borisyak, Sara Celani, Chunhui Chen, Serhii Cholak, Peter Clarke, Victor Coco, Tommaso Colombo, Adam Davis, Michel De Cian, Hans Dijkstra, Paolo Durante, Dipanwita Dutta, Surapat Ek-In, François Fleuret, Christoph Frei, Elena Graverini, Marco Guarise, Guido Haefeli, Xiaoxue Han, Plamen Hristov Hopchev, Maxim Karpov, Veronica Sølund Kirsebom, Almagul Kondybayeva, Yiming Li, Ho Ling Li, Xuan Li, Hao Liu, Shuai Liu, Vladimir Macko, Pietro Marino, Maurizio Martinelli, Simone Meloni, Tatsuya Nakada, Tara Nanut, Matthew Needham, Niko Neufeld, Preema Rennee Pais, Anton Petrov, Guillaume Max Pietrzyk, Renato Quagliani, Gerhard Raven, Federico Leo Redi, Olivier Schneider, Maxime Schubiger, Sebastian Schulte, Lesya Shchutska, Evgenii Shmanin, Pavol Stefko, Maria Elena Stramaglia, Liang Sun, Zhipeng Tang, Frédéric Teubert, Mark Tobin, Minh Tâm Tran, Carina Trippl, Mingkui Wang, Zheng Wang, Yi Wang, Jian Wang, Rui Wang, Zhirui Xu, Yong Yang, Hang Yin, Ettore Zaffaroni, Yi Zhang, Lei Zhang, Yu Zheng, Xiaoqing Zhou, Yao Zhou
SPRINGER, 2021
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Abstract

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https://infoscience.epfl.ch/record/285265?ln=en

About this result

Related concepts (10)

Related concepts

Related publications (58)

Related publications

Standard Model

The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions – excluding gravity) in the universe and cla

LHCb experiment

The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designe

Mass

Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found th

Search for lepton-flavour violating decays of a Higgs-like boson at LHCb

Chitsanu Khurewathanakul

This thesis presents the search for a charged-lepton flavour violation via a model-independent Higgs-like boson decaying to a muon and a tau lepton,

H\rightarrow\mu\tau

. The validation of high-

p_T

tau lepton identification is performed with the measurement of

Z\rightarrow\tau^+\tau^-

production cross-section, using 2;

fb^{-1}

of integrated luminosity from

pp

collisions at

\sqrt{s}=8\;

TeV collected by the LHCb experiment at the LHC in 2012. The tau leptons are reconstructed in both leptonic and hadronic decay channels. The cross-section, restricted to events with both tau leptons having a transverse momentum greater than 20 GeV/c and a pseudorapidity between 2 and 4.5, and with a tau pair invariant mass between 60 and 120 GeV/

c^2

, is measured to be

\sigma_{Z\rightarrow\tau^+\tau^-}} = 95.20 \pm 2.13 \pm 4.79 \pm 0.17 \pm 1.10 \pb.

The uncertainties are statistical, systematic, from the LHC beam energy, and from the integrated luminosity. The results are compatible with the lepton universality hypothesis in

Z

decays, and are in agreement with NNLO Standard Model predictions. Using the validated tau-lepton identification and detection efficiencies, the search for

H\rightarrow\mu\tau

covering 99% of tau decay modes found no statistically significant excess. The upper limit on the cross-section times branching fraction,

\sigma_{gg\rightarrow H\rightarrow\mu\tau

, at 95% confidence level is set, ranging from about 22 pb for

m_H = 45

GeV/

c^2

to 4 pb at 195 GeV/

c^2

. Assuming the Standard Model Higgs, the limit on the braching fraction is

\mathcal{B}(H\rightarrow\mu\tau) < 25.7\%

, corresponding to a Yukawa coupling of

\sqrt{|Y_{\mu\tau}|^2 + |Y_{\tau\mu}|^2} < 1.69\times10^{-2}

EPFL2017

Search for a pseudoscalar boson decaying into a Z boson and the 125 GeV Higgs boson in $ℓ^+ℓ^−b\overline{b}$ final states

Muhammad Ahmad, Ahmed Ali, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, Giovanni Bianchi, Roberto Castello, Juan Ramon Castiñeiras De Saa, Yixing Chen, Tian Cheng, Giuseppe Codispoti, Alessandro Degano, Charles Dietz, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Daniel Gonzalez, Ruchi Gupta, Csaba Hajdu, Alexis Kalogeropoulos, Viktor Khristenko, Ji Hyun Kim, Donghyun Kim, Vineet Kumar, Ajay Kumar, Sanjeev Kumar, Ekaterina Kuznetsova, Wei Li, Ho Ling Li, Shuai Liu, Hao Liu, Werner Lustermann, Bibhuprasad Mahakud, 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, Marco Trovato, Andromachi Tsirou, Paul Turner, Joao Varela, Rui Wang, Qian Wang, Zheng Wang, Jian Wang, Siyuan Wang, Matthias Weber, Matthias Wolf, Fan Xia, Meng Xiao, Zhirui Xu, Fan Yang, Yong Yang, Kai Yi, Hang Yin

Results are reported on a search for decays of a pseudoscalar A boson into a Z boson and a light scalar h boson, where the Z boson decays into a pair of oppositely-charged electrons or muons, and the h boson decays into bb¯ . The search is based on data from proton–proton collisions at a center-of-mass energy s=8 TeV collected with the CMS detector, corresponding to an integrated luminosity of 19.7 fb−1 . The h boson is assumed to be the standard model-like Higgs boson with a mass of 125 GeV. With no evidence for signal, upper limits are obtained on the product of the production cross section and the branching fraction of the A boson in the Zh channel. Results are also interpreted in the context of two Higgs doublet models.

2015

Precise determination of the mass of the Higgs boson and tests of compatibility of its couplings with the standard model predictions using proton collisions at 7 and 8 $\,\text {TeV}$

Muhammad Ahmad, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, 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, Viktor Khristenko, Donghyun Kim, Ji Hyun 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, Rui Wang, Qian Wang, Zheng Wang, Jian Wang, Matthias Weber, Matthias Wolf, Meng Xiao, Zhirui Xu, Fan Yang, Yong Yang, Kai Yi, Lei Zhang

Properties of the Higgs boson with mass near 125

\,\text {GeV}

are measured in proton-proton collisions with the CMS experiment at the LHC. Comprehensive sets of production and decay measurements are combined. The decay channels include

\gamma \gamma

\mathrm{Z}\mathrm{Z}

\mathrm{W}\mathrm{W}

\tau \tau

\mathrm{b} \mathrm{b}

, and

\mu \mu

pairs. The data samples were collected in 2011 and 2012 and correspond to integrated luminosities of up to 5.1

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

at 7

\,\text {TeV}

and up to 19.7

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

at 8

\,\text {TeV}

. From the high-resolution

\gamma \gamma

and

\mathrm{Z}\mathrm{Z}

channels, the mass of the Higgs boson is determined to be

125.02\,^{+0.26-0.27} \,\text {(stat)} \,^{+0.14-0.15} \,\text {(syst)} \,\text {GeV}

. For this mass value, the event yields obtained in the different analyses tagging specific decay channels and production mechanisms are consistent with those expected for the standard model Higgs boson. The combined best-fit signal relative to the standard model expectation is

1.00\,\pm 0.09\,\text {(stat)} \,^{+0.08-0.07}\,\text {(theo)} \,\pm 0.07\,\text {(syst)}

at the measured mass. The couplings of the Higgs boson are probed for deviations in magnitude from the standard model predictions in multiple ways, including searches for invisible and undetected decays. No significant deviations are found.

2015