Search for lepton flavour violation in Z decays

Adriani, O.; Aguilar-Benı́tez, M.; Ahlen, S. P.; Alcaraz, J.; Aloisio, A.; Alverson, G.; Alviggi, M. G.; Ambrosi, G.; An, Q.; Anderhub, H.; Anderson, A.L.; Andreev, V.; Angelescu, T.; Antonov, L.; Antreasyan, D.; Arce, P.; Arefiev, A.; Atamanchuk, A.; Azemoon, T.; Aziz, T.; Baba, P.V.K.S.; Bagnaia, P.; Bakken, J. A.; Ball, R. C.; Banerjee, S.; Bao, J.; Barillère, R.; Barone, L.; Basçhirotto, A.; Battiston, R.; Bay, A.; Becattini, F.; Bechtluft, J.; Becker, R. H.; Becker, U.; Behner, F.; Behrens, J.; Bencze, G.; Berdugo, J.; Berges, P.; Bertucci, B.; Betev, B.L.; Biasini, M.; Biland, A.; Bilei, G. M.; Bizzarri, R.; Blaising, J. J.; Bobbink, G. J.; Böck, R.; Böhm, A.; Borgia, B.; Bosetti, M.; Bourilkov, D.; Bourquin, M.; Boutigny, D.; Bouwens, B.; Brambilla, E.; Branson, J. G.; Brock, I. C.; Brooks, M. L.; Bujak, A.; Burger, J. D.; Burger, W. J.; Busenitz, J.; Buytenhuijs, A.; Cai, X. D.; Capell, M.; Caria, M.; Carlino, G.; Cartacci, A. 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doi:10.1016/0370-2693(93)90348-l

Cited by 37 publications

(13 citation statements)

References 20 publications

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“…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][8][9][10]. The most stringent upper limit is BðZ → eμÞ < 1.7 × 10 −6 at the 95% confidence level (C.L.)…”

Section: Introductionmentioning

confidence: 99%

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
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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Section: Introductionmentioning

confidence: 99%

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
7
96
0
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“…4 Owing to the unitarity of the mixing matrix, the amplitudes vanish for massless or degenerate virtual neutrinos, in exact analogy with the GIM cancellation in the quark sector [23].…”

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confidence: 99%

Charged lepton flavor violation from massive neutrinos inZdecays

2001

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Present evidences for neutrino masses and lepton flavour mixings allow to predict, in the Standard Model with light neutrinos, branching rates for the decays Z → eµ, µτ, eτ of less than 10 −54 , while present experimental exclusion limits from LEP 1 are of order 10 −5 . The GigaZ option of the TESLA Linear Collider project will extend the sensitivity down to about 10 −8 . We study in a systematic way some minimal extensions of the Standard Model and show that GigaZ might well be sensitive to the rates predicted from these scenarios. *

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“…On the high energy side, interesting searches have been performed at LEP in the context of LFV decays of the Z boson [23][24][25][26], and further improvements have either been made or are expected from the ATLAS [27] and CMS [28] experiments at the LHC collider. Moreover, after the discovery of the Higgs boson [29,30], new limits on the H → τμ BR are currently under investigation [31,32].…”

Section: Introductionmentioning

confidence: 99%

Lepton-flavour violating decays in theories with dimension 6 operators

Pruna

Signer

2016

EPJ Web of Conferences

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Abstract. Despite a large experimental effort, so far no evidence for flavour-violating decays of charged leptons such as l i → l j γ and l i → l j l k l k has been found. The absence of a signal puts very severe constraints on many extensions of the Standard Model. Here we apply a model independent approach by studying such decays in the Standard Model effective field theory. Going beyond leading order in the Standard Model couplings and considering all dimension 6 operators that might lead to lepton-flavour violation, we are able to extract limits on a large number of Wilson coefficients of such operators. We are also able to compare the impact of particular searches and find, for example, that flavour-violating decays of the Z-boson Z → μe are much more constrained from low-energy experiments μ → eγ than from the limits of current and future direct searches at high energy.

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Search for lepton flavour violation in Z decays

Cited by 37 publications

References 20 publications

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
7
96
0
View full text Add to dashboard Cite

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
7
96
0
View full text Add to dashboard Cite

Charged lepton flavor violation from massive neutrinos inZdecays

Lepton-flavour violating decays in theories with dimension 6 operators

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Search for lepton flavour violation in Z decays

Cited by 37 publications

References 20 publications

Search for the lepton flavor violating decayZ→eμinppcollisions atsAad1, Abbott2, Abdallah3 et al. 2014Phys. Rev. DSelf Cite1147960View full textAdd to dashboardCite

Search for the lepton flavor violating decayZ→eμinppcollisions atsAad1, Abbott2, Abdallah3 et al. 2014Phys. Rev. DSelf Cite1147960View full textAdd to dashboardCite

Charged lepton flavor violation from massive neutrinos inZdecays

Lepton-flavour violating decays in theories with dimension 6 operators

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Product

Resources

About

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
7
96
0
View full text Add to dashboard Cite

Search for the lepton flavor violating decayZ→eμinppcollisions ats
Aad¹,
Abbott²,
Abdallah³
et al. 2014
Phys. Rev. D
Self Cite
114
7
96
0
View full text Add to dashboard Cite