FCC-ee lepton flavour violation V . De Romeri, S. Monteil, J. - PowerPoint PPT Presentation

FCC-ee lepton flavour violation V . De Romeri, S. Monteil, J. Orloff, A. Teixeira (LPC) & A. Abada (LPT) arXiv:1412.6322 [hep-ph], to appear in JHEP

LFV in rare Z-decays: new physics effects In minimal (ad-hoc) SM extensions with massive ν and s lepton mixing (U PMNS ), the theoretical predictions for leptonic rare Z decays lie beyond experimental reach BR( Z → e ± µ ⌥ ) ∼ BR( Z → e ± τ ⌥ ) ∼ 10 � 54 BR( Z → e ± µ ⌥ ) ∼ BR( Z → e ± τ ⌥ ) ∼ 10 � 54 BR( Z → e ± µ ⌥ ) ∼ BR( Z → e ± τ ⌥ ) ∼ 10 � 54 BR( Z → µ ± τ ⌥ ) ∼ 10 � 60 BR( Z → µ ± τ ⌥ ) ∼ 10 � 60 BR( Z → µ ± τ ⌥ ) ∼ 10 � 60 Detection of rare decay modes BR( Z ! ` ± BR( Z ! ` ± BR( Z ! ` ± i ` ⌥ i ` ⌥ i ` ⌥ j ) ( i 6 = j ) j ) j ) ( i 6 = j ) ( i 6 = j ) provides indisputable evidence of New Physics! Current experimental bounds: BR( Z → e ± µ ⌥ ) < 7 . 5 × 10 � 7 BR( Z → e ± µ ⌥ ) < 7 . 5 × 10 � 7 BR( Z → e ± µ ⌥ ) < 7 . 5 × 10 � 7 BR( Z → e ± τ ⌥ ) < 9 . 8 × 10 � 6 BR( Z → e ± τ ⌥ ) < 9 . 8 × 10 � 6 BR( Z → e ± τ ⌥ ) < 9 . 8 × 10 � 6 BR( Z → µ ± τ ⌥ ) < 1 . 2 × 10 � 5 BR( Z → µ ± τ ⌥ ) < 1 . 2 × 10 � 5 BR( Z → µ ± τ ⌥ ) < 1 . 2 × 10 � 5 OPAL Collaboration, R. Akers et al., Z. Phys. C67 (1995) 555 L3 Collaboration, O. Adriani et al., Phys. Lett. B316 (1993) 427 DELPHI Collaboration, P. Abreu et al., Z. Phys. C73 (1997) 243 ATLAS, CERN-PH-EP-2014-195 (2014)

LFV in rare Z-decays: FCC-ee l 1 Several (well-motivated) new physics Z models allow for the rare leptonic decays NP l 2 SUSY (MSSM, RpV), Little Higgs, ... In our work we consider SM extensions via sterile ν s Sterile ν : appear in neutrino mass models s experimentally & observationally motivated can lead to modified charged currents W ` ⌫ W ` ⌫ W ` ⌫ Observable effects LFV , LFU, meson decays, rare leptonic decays, anomalous magnetic moments, neutrinoless double beta decay, ... , rare Z decays ! ... Akhmedov et al., JHEP 1305 (2013) 081; Abada et al., JHEP 1402 (2014) 091; Antusch et al., [hep-ph/1407.6607]; Abada, De Romeri,Teixeira, JHEP 1409 (2014) 074; ...

ν ν LFV in rare Z-decays: sterile neutrinos Old Giga-Z studies l 1 Z Wilson, DESY-EFCA LC workshop (1998-1999) J. I. Illana and T. Riemann, Phys. Rev. D63 (2001) 053004 Z Flores-Tlalpa, et al. Phys. Rev. D65 (2002) 073010 D. Delepine and F. Vissani, Phys. Lett. B522 (2001) 95 s M. A. Perez et al., Int. J. Mod. Phys. A19 (2004) 159 ... l 2 must be revisited: Z - prior to θ 13 and other neutrino data - new contributions of sterile states i are physical states Text are severely constrained i=1,2,3,...,3+N radiative decays MEG ! ` i → ` j � ` i → ` j � ` i → ` j � 3-body decays ` i → ` j ` j ` j ` i → ` j ` j ` j ` i → ` j ` j ` j cosmology Z N = extra Majorana states neutrinoless double beta decays invisible Z-width m N ∼ 10 − 10 − 10 3 GeV m N ∼ 10 − 10 − 10 3 GeV m N ∼ 10 − 10 − 10 3 GeV .... We have done a first study: @ FCC-ee Z → ` i ` j emphasizing complementary with cLFV (low-energies)

LFV in rare Z-decays: “3+1” toy model Ad-hoc extension; 4th state encodes contributions of arbitrary number of sterile ν s Super B Babar COMET LC FCC-ee exp. excluded within reach of future cosmo X FCC-ee: assumed BR( Z → ` i ` j ) & 10 − 13 0v ββ decay exps. cosmo OK Steriles with mass above 80 GeV and mixings θ ` 4 ∼ O (10 − 5 ÷ − 4 ) within FCC reach Low-energy experiments (COMET) more powerful to probe sector µ − e FCC-ee more powerful than Babar (SuperB) to probe sector µ − τ Full simulations (to be carried)

LFV in rare Z-decays: Inverse Seesaw ISS: theoretically well motivated SM extension (SM + 3 RH + 3 steriles) Super B Babar LC FCC-ee within reach of future exp. excluded cosmo X 0v ββ decay exps. cosmo OK Only heavy steriles (mass above 1 TeV) within FCC reach FCC-ee more powerful than flavour-dedicated experiments to probe sector µ − τ Full simulations (to be carried) What next? Some ideas to discuss??

ν ν Leptons at high-energy ee-machines Look for sterile states produced in e + e - collisions in e + e - ➞ ν ➞ W ν ➞ Search for ν s jj ν R µ µ Studies done for LC @ 500GeV , 500fb -1 & polarised beams [del Aguila et al, 0502189] Look for direct Z ➞ ν s s e + e - ➞ 2 jets + same sign leptons Can this contribution be disantagled from background? @ Hadron colliders: [Rajaraman and Whiteson, 1001.1229]

Leptons at high-energy ee-machines Probe the Majorana nature of neutrinos: lepton number violating processes ( LNV ) Inspiration from hadron collisions; would this be feasible in e + e - ? 1st: likely not final state missing energy 2nd: e + e - ➞ jet + same sign leptons 5 events @ 80fb -1 ISS y r a Inverse neutrinoless double beta decay... n i m explore e - e - mode i l e r P “3+1 toy model” Preliminary Not very promising... excluded by bounds on neutrinoless double beta decay

What next? Some ideas to discuss??

cLFV experimental status 0 ν 2beta decays: future sensitivity Experiment Ref. | m ee | (eV) cLFV Process Present Bound Future Sensitivity 5 . 7 × 10 − 13 [33] 6 × 10 − 14 [76] EXO-200 (4 yr) [89,90] 0.075 - 0.2 µ → e γ 3 . 3 × 10 − 8 [77] ∼ 3 × 10 − 9 [78] nEXO (5 yr) [92] 0.012 - 0.029 τ → e γ nEXO (5 yr + 5 yr w/ Ba tagging) [92] 0.005 - 0.011 4 . 4 × 10 − 8 [77] ∼ 3 × 10 − 9 [78] τ → µ γ KamLAND-Zen (300 kg, 3 yr) [91] 0.045 - 0.11 1 . 0 × 10 − 12 [79] ∼ 10 − 16 [80] µ → eee GERDA phase II [88] 0.09 - 0.29 2 . 1 × 10 − 8 [81] ∼ 10 − 9 [78] τ → µµµ CUORE (5 yr) [93,94] 0.051 - 0.133 2 . 7 × 10 − 8 [81] ∼ 10 − 9 [78] τ → eee SNO+ [95] 0.07 - 0.14 4 . 3 × 10 − 12 [82] ∼ 10 − 18 [83] µ − , Ti → e − , Ti SuperNEMO [96] 0.05 - 0.15 7 × 10 − 13 [84] µ − , Au → e − , Au NEXT [97,98] 0.03 - 0.1 10 − 15 − 10 − 18 [85] MAJORANA demo. [99] 0.06 - 0.17 µ − , Al → e − , Al “3+1 toy model”: a brief look on the parameter space 10 6 10 6 10 4 10 4 10 2 10 2 m 4 (GeV) m 4 (GeV) 10 0 10 0 10 -2 10 -2 10 -4 10 -4 10 -6 10 -6 10 -8 10 -8 10 -14 10 -12 10 -10 10 -8 10 -6 10 -4 10 -2 10 0 10 -14 10 -12 10 -10 10 -8 10 -6 10 -4 10 -2 10 0 sin 2 θ 14 sin 2 θ 34