Kappert, Rosa

Onderwater, Cornelis

Pellegrino, Antonio

van Veghel, Maarten

Wiersema, Garbrand

English

The existence of three flavors of fundamental fermions is one of the great mysteries of the standard model of particle physics. At the same time it is at the basis of a variety of exciting phenomena, such as CP violation and neutrino flavor oscillations. Hints are mounting that the assumption of lepton universality and charged lepton flavour conservation, as currently incorporated in the standard model, may not be valid. We report on our test of charged lepton flavour conservation in the decay of B mesons, as measured at LHCb

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   University of GroningenB(s)→eμ: search for lepton flavour violation at LHCbOnderwater, Cornelis; Pellegrino, Antonio; Kappert, Rosa; Wiersema, Garbrand; van Veghel,MaartenIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2016Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Onderwater, C., Pellegrino, A., Kappert, R., Wiersema, G., & van Veghel, M. (2016). B(s)→eμ: search forlepton flavour violation at LHCb. Poster session presented at Physics@FOM, Veldhoven, Netherlands.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 21-06-2022  founded in 1614B(s)→eμ: search for lepton flavour violation at LHCbRosa Kappert, Gerco Onderwater, Antonio Pellegrino, Maarten van Veghel, Garbrand WiersemaUniversity of Groningen and NikhefIntroduction LFV Searches at LHCbExcellent particle identification and momentum resolution make LHCb an ideal environment to search for rare decays. We investigate LFV through decays of heavy B and D mesons into muon-electron pairs. Earlier LHCb results (90% CL) for the branching ratios were reported:● Br(B0→eμ)  < 2.8x10-9 (1 fb-1)● Br(Bs0→eμ) < 1.1x10-8 (1 fb-1)● Br(D0→eμ) < 1.3x10-8 (3 fb-1)The analysis of Br(B(s)→eμ) for the 2011 & 2012 3fb-1 data is expected to be finalized soon.Lepton (Flavour) UniversalityThe weak interaction strength is the same for all lepton flavours. This is referred to as lepton universality. Contrary to quark flavour mixing, lepton flavour mixing seems to be exclusive for the neutrinos, notably neutrino oscillations. Flavour mixing of the charged leptons has not been observed, and is predicted to be unmeasurably small by the Standard Model. Experimental observation of charged lepton flavour mixing would thus unambi-guously signal new physics.Flavour physics is the study of the interactions that distinguish between the three different copies of fundamental fermions. Within the Standard Model quarks, leptons, and neutrinos appear in three flavours, and only the interaction with the Higgs boson distinguishes these flavours, leading to flavour non-universality.Through the years a clear understanding of the underlying mechanism of flavour mixing and flavour non-universality has emerged, and this mechanism has been successfully verified in experiments.However, flavour physics still represents one of the most puzzling and, at the same time, interesting aspects of particle physics, summarized by two open questions:● What determines the observed pattern of masses and mixing angles of quarks and leptons?● Which are the sources of flavour symmetry breaking accessible at low energies?Answering these questions is a key part of the more general program of investigating the nature of physics beyond the Standard Model.Hints for Lepton Non-UniversalityRecent experimental data in high energy physics hint toward violation of Lepton Universality in semi-leptonic decays. The statistically most significant results are for (with ℓ=e,μ):● B→D*ℓνℓ3.8σ 1,2,3● B→Dℓνℓ2.0σ 1,2,3● B→Kℓ+ℓ– 2.6σ 3● h→μτ 2.5σ 4,51BaBar, 2Belle, 3LHCb, 4ATLAS, 5CMSViolation of lepton universality necessarily leads to lepton flavour violation, as no known symmetry principle can protect the one in the absence of the other.Implications & ProspectsSeveral models attempt to explain the observed non-universality, while meeting limits on decays such as B(s)0 → μμ and severe constrains from e.g. μ→eγ and μ→eee. Some of these models predict LFV signals within reach of LHCb†. Interesting links exist with the pp→γγ (750GeV) excess‡, and the (g-2)μ anomaly¶. New measurements will help to constrain these models.†e.g. Leptoquarks: Sahoo, Mohanta, arXiv:1512.04657; new interactions: Glashow, Guadagnoli, Lane, Phys. Rev. Lett. 114, 091801 (2015) ‡e.g. Two Higgs doublet: Bizot, Davidson, Frigerio, Kneur, arXiv:1512.08508¶,e.g. Doubly charged scalar: Chakrabortty,  Ghosh,  Mondal,  Srivastava, arXiv:1512.03581

B(s)→eμ: search for lepton flavour violation at LHCb

https://pure.rug.nl/ws/files/27849474/Physics_FOM_v2.pdf

B(s)→eμ: search for lepton flavour violation at LHCb

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