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 massiveν

s

and lepton mixing (UPMNS), the theoretical predictions for leptonic rare Z decays lie beyond experimental reach BR(Z → e± µ⌥) ∼ BR(Z → e± τ ⌥) ∼ 1054 BR(Z → e± µ⌥) ∼ BR(Z → e± τ ⌥) ∼ 1054 BR(Z → e± µ⌥) ∼ BR(Z → e± τ ⌥) ∼ 1054 BR(Z → µ± τ ⌥) ∼ 1060 BR(Z → µ± τ ⌥) ∼ 1060 BR(Z → µ± τ ⌥) ∼ 1060 Detection of rare decay modes

BR(Z ! `±

i `⌥ j )

(i 6= j) BR(Z ! `±

i `⌥ j )

(i 6= j) BR(Z ! `±

i `⌥ j )

(i 6= j)

provides indisputable evidence of New Physics!

BR(Z → e± µ⌥) < 7.5 × 107 BR(Z → e± µ⌥) < 7.5 × 107 BR(Z → e± µ⌥) < 7.5 × 107 BR(Z → e± τ ⌥) < 9.8 × 106 BR(Z → e± τ ⌥) < 9.8 × 106 BR(Z → e± τ ⌥) < 9.8 × 106 BR(Z → µ± τ ⌥) < 1.2 × 105 BR(Z → µ± τ ⌥) < 1.2 × 105 BR(Z → µ± τ ⌥) < 1.2 × 105

Current experimental bounds:

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

Several (well-motivated) new physics models allow for the rare leptonic decays

Z l1 l2

NP SUSY (MSSM, RpV), Little Higgs, ... In our work we consider SM extensions via sterileν

s

Sterileν

s

: appear in neutrino mass models experimentally & observationally motivated can lead to modified charged currents Observable effects

LFV , LFU, meson decays, rare leptonic decays, anomalous magnetic moments, neutrinoless double beta decay, ... , rare Z decays !

W ` ⌫ W ` ⌫ W ` ⌫

... 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; ...

LFV in rare Z-decays: sterile neutrinos

Z l1 l2

ν

s

Z

Z

Z

ν i are physical states i=1,2,3,...,3+N N = extra Majorana states

mN ∼ 10−10 − 103 GeV mN ∼ 10−10 − 103 GeV mN ∼ 10−10 − 103 GeV

Old Giga-Z studies

Wilson, DESY-EFCA LC workshop (1998-1999)

• J. I. Illana and T. Riemann, Phys. Rev. D63 (2001) 053004

Flores-Tlalpa, et al. Phys. Rev. D65 (2002) 073010

• D. Delepine and F. Vissani, Phys. Lett. B522 (2001) 95
• M. A. Perez et al., Int. J. Mod. Phys. A19 (2004) 159

...

Text

must be revisited:

• prior toθ

13 and other neutrino data

`i → `j `i → `j `i → `j

• new contributions of sterile states

are severely constrained radiative decays 3-body decays cosmology neutrinoless double beta decays invisible Z-width ....

`i → `j `j `j `i → `j `j `j `i → `j `j `j

MEG !

We have done a first study: @ FCC-ee emphasizing complementary with cLFV (low-energies)

Z → `i`j

LFV in rare Z-decays: “3+1” toy model

Ad-hoc extension; 4th state encodes contributions of arbitrary number of sterileν s

• exp. excluded

cosmo X cosmo OK

within reach of future 0vββ decay exps.

LC FCC-ee

COMET

Super B Babar

FCC-ee: assumed BR(Z → `i`j) & 10−13

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)

• exp. excluded

cosmo X cosmo OK

within reach of future 0vββ decay exps.

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)

FCC-ee LC Super B Babar

What next? Some ideas to discuss??

Leptons at high-energy ee-machines

Look for sterile states produced in e+e- collisions

Search forν s in e+e-➞ν

R

ν ➞ Wν ➞ jjν

µ µ

Studies done for LC @ 500GeV , 500fb-1 & polarised beams

[del Aguila et al, 0502189]

Look for direct Z➞ν

s

ν

s Can this contribution be disantagled from background? e+e-➞2 jets + same sign leptons

@ Hadron colliders: [Rajaraman and Whiteson, 1001.1229]

Leptons at high-energy ee-machines

Probe the Majorana nature of neutrinos: lepton number violating processes (LNV)

Inverse neutrinoless double beta decay... explore e-e- mode 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

excluded by bounds on neutrinoless double beta decay

Not very promising... ISS P r e l i m i n a r y

“3+1 toy model”

Preliminary

5 events @ 80fb-1

What next? Some ideas to discuss??

cLFV experimental status

cLFV Process Present Bound Future Sensitivity µ → eγ 5.7 × 10−13 [33] 6 × 10−14 [76] τ → eγ 3.3 × 10−8 [77] ∼ 3 × 10−9 [78] τ → µγ 4.4 × 10−8 [77] ∼ 3 × 10−9 [78] µ → eee 1.0 × 10−12 [79] ∼ 10−16 [80] τ → µµµ 2.1 × 10−8 [81] ∼ 10−9 [78] τ → eee 2.7 × 10−8 [81] ∼ 10−9 [78] µ−, Ti → e−, Ti 4.3 × 10−12 [82] ∼ 10−18 [83] µ−, Au → e−, Au 7 × 10−13 [84] µ−, Al → e−, Al 10−15 − 10−18 [85]

10-8 10-6 10-4 10-2 100 102 104 106 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100

m4 (GeV) sin2θ14

10-8 10-6 10-4 10-2 100 102 104 106 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100

m4 (GeV) sin2θ34

“3+1 toy model”: a brief look on the parameter space

Experiment Ref. |mee| (eV) EXO-200 (4 yr) [89,90] 0.075 - 0.2 nEXO (5 yr) [92] 0.012 - 0.029 nEXO (5 yr + 5 yr w/ Ba tagging) [92] 0.005 - 0.011 KamLAND-Zen (300 kg, 3 yr) [91] 0.045 - 0.11 GERDA phase II [88] 0.09 - 0.29 CUORE (5 yr) [93,94] 0.051 - 0.133 SNO+ [95] 0.07 - 0.14 SuperNEMO [96] 0.05 - 0.15 NEXT [97,98] 0.03 - 0.1 MAJORANA demo. [99] 0.06 - 0.17

0ν 2beta decays: future sensitivity