LHC sensitivity to lepton flavour violating Z boson decays

Davidson, Sacha; Lacroix, Sylvain; Verdier, P.

doi:10.1007/jhep09(2012)092

Cited by 30 publications

(22 citation statements)

References 47 publications

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“…However, the Z penguins also contribute at one loop to μ → eγ and τ → μγ . And whereas the experimental constraint on τ → μγ [58,59] is consistent with Z → τ ± μ ∓ being detectable at the LHC, the bound from μ → eγ implies that aē Z / μ interaction, with coefficient of a magnitude that the LHC could detect, would overcontribute to μ → eγ by several orders of magnitude [54].…”

Section: The Vector Operatorsmentioning

confidence: 96%

“…These extra penguins are related to the common wisdom, that it is interesting for ATLAS and CMS to look for Z → τ ± μ ∓ and Z → τ ± e ∓ decays, but that they are unlikely to see Z → μ ± e ∓ [53]. The point [54] is that an interaction τ Z / μ would contribute at tree level to τ → μll, and at one loop to τ → μγ . To be within the sensitivity of the LHC, the coefficient of this coupling needs to exceed the naive bound from τ → μll.…”

Section: The Vector Operatorsmentioning

confidence: 99%

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$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

Davidson

2016

Eur. Phys. J. C

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Several experiments search for μ ↔ e flavour change, for instance in μ → e conversion, μ → eγ and μ → eēe. This paper studies how to translate these experimental constraints from low energy to a New Physics scale M m W . A basis of QCD × QED-invariant operators (as appropriate below m W ) is reviewed, then run to m W with one-loop Renormalisation Group Equations (RGEs) of QCD and QED. At m W , these operators are matched onto SU(2)-invariant dimension-six operators, which can continue to run up with electroweak RGEs. As an example, the μ → eγ bound is translated to the scale M, where it constrains two sums of operators. The constraints differ from those obtained in previous EFT analyses of μ → eγ , but they reproduce the expected bounds on flavour-changing interactions of the Z and the Higgs, because the matching at m W is pragmatically performed to the loop order required to get the "leading" contribution.

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Section: The Vector Operatorsmentioning

confidence: 96%

Section: The Vector Operatorsmentioning

confidence: 99%

$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

Davidson

2016

Eur. Phys. J. C

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“…(Although there is still a tension between the most recent Planck results on extra light neutrinos (relics) and reactor anomalies, in this work we focus on the rôle of (heavier) sterile fermions, which are not expected to contribute as light relativistic degrees of freedom [24].) Rare charged lepton flavour violating (cLFV) Z decays have been extensively discussed in the context of SM extensions involving massive (Majorana and/or Dirac) neutrinos [3,5,[25][26][27][28]; similar studies were carried using an effective theory approach [29][30][31][32], some also exploring a possible complementarity with low-energy cLFV searches.…”

Section: Jhep04(2015)051mentioning

confidence: 99%

Indirect searches for sterile neutrinos at a high-luminosity Z-factory

Abada

Romeri

Monteil

et al. 2015

J. High Energ. Phys.

101

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A future high-luminosity Z-factory will offer the possibility to study rare Z decays, as those leading to lepton flavour violating final states. Processes such as Z → ∓ 1 ± 2 are potentially complementary to low-energy (high-intensity) observables of lepton flavour violation. In this work we address the impact of new sterile fermions on lepton flavour violating Z decays, focusing on potential searches at FCC-ee (TLEP), and taking into account experimental and observational constraints on the sterile states. We consider a minimal extension of the Standard Model by one sterile fermion state, and two wellmotivated frameworks of neutrino mass generation, the Inverse Seesaw embedded into the Standard Model, and the νMSM. Our study shows that sterile neutrinos can give rise to contributions to BR(Z → ∓ 1 ± 2 ) within reach of the FCC-ee. We also discuss the complementarity between a high-luminosity Z-factory and low-energy charged lepton flavour violation facilities.

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“…There are stringent experimental limits on other charged lepton flavor violating processes, which can be used to derive an upper limit on the branching fraction for Z → eμ with some theoretical assumptions. For example, the upper limit on μ → 3e yields BðZ → eμÞ < 10 −12 [5] and on μ → eγ yields BðZ → eμÞ < 10 −10 [6]. The experiments at the Large Electron-Positron Collider (LEP) searched directly for the decay Z → eμ [7-10].…”

mentioning

confidence: 99%

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
110
7
96
0
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The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process Z → eμ in pp collisions using 20.3 fb −1 of data collected at ffiffi ffi s p ¼ 8 TeV. An enhancement in the eμ invariant mass spectrum is searched for at the Z-boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, Z → ee and μμ, significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z-boson mass, resulting in an upper limit on the branching fraction, BðZ → eμÞ < 7.5 × 10 −7 at the 95% confidence level. DOI: 10.1103/PhysRevD.90.072010 PACS numbers: 12.60.-i I. INTRODUCTIONLepton flavor conservation in the charged lepton sector is a fundamental assumption of the Standard Model (SM) but there is no associated symmetry. Thus, searches for lepton flavor violation (LFV) processes are good candidates for probing new physics. The observation of neutrino oscillations is a clear indication of LFV in the neutral lepton sector; however, such an oscillation mechanism cannot induce observable LFV in the charged lepton sector. All searches in the charged lepton sector have produced null results so far [1]. Lepton flavor violation in the charged lepton sector may have a different origin than LFV induced by neutrino oscillations and the search for this effect provides constraints on theories beyond the SM (see for example Refs. [2][3][4]).In this paper, a search for the lepton flavor violating decay Z → eμ is presented. There are stringent experimental limits on other charged lepton flavor violating processes, which can be used to derive an upper limit on the branching fraction for Z → eμ with some theoretical assumptions. For example, the upper limit on μ → 3e yields BðZ → eμÞ < 10 −12 [5] and on μ → eγ yields BðZ → eμÞ < 10 −10 [6]. The experiments at the Large Electron-Positron Collider (LEP) searched directly for the decay Z → eμ [7-10]. The most stringent upper limit is BðZ → eμÞ < 1.7 × 10 −6 at the 95% confidence level (C.L.) using a data sample of 5.0 × 10 6 Z bosons produced in e þ e − collisions at ffiffi ffi s p ¼ 88-94GeV [7]. The Large Hadron Collider (LHC) has already produced many more Z bosons in pp collisions, but with substantially more background. In this paper, the 20.3 AE 0.6 fb −1 [11] of data collected at ffiffi ffi s p ¼ 8 TeV by the ATLAS experiment corresponds to 7.8 × 10 8 Z bosons produced. Despite the larger background at the LHC, a more restrictive direct limit on the Z → eμ decay is reported in this paper. II. ATLAS DETECTORThe ATLAS detector [12] consists of an inner detector (ID) surrounded by a solenoid that produces a 2 T magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer (MS) immersed in a magnetic field produced by a system of toroids. The ID measures the trajectories of charged particles over the full azimuthal angle and in a pseudorapidity [13] range of jηj < 2.5 using silicon pixel, silicon microstrip, and straw-tube transitionradiation ...

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LHC sensitivity to lepton flavour violating Z boson decays

Cited by 30 publications

References 47 publications

$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

Indirect searches for sterile neutrinos at a high-luminosity Z-factory

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
110
7
96
0
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LHC sensitivity to lepton flavour violating Z boson decays

Cited by 30 publications

References 47 publications

$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

$$\mu \rightarrow e \gamma $$ μ → e γ and matching at $$\varvec{m_W}$$ m W

Indirect searches for sterile neutrinos at a high-luminosity Z-factory

Search for the lepton flavor violating decayZ→eμinppcollisions atsAad1, Abbott2, Abdallah3 et al. 2014Phys. Rev. D1107960View full textAdd to dashboardCite

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Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
110
7
96
0
View full text Add to dashboard Cite