Light flavon signals at electron-photon colliders

Transcription

1 Light flavon signals at electron-photon colliders based on: JHEP 1603 (2016) 192 and arxiv: Yu Muramatsu (CCNU), Takaaki Nomura (KIAS), Yusuke Shimizu (Hiroshima U.), Hiroshi Yokoya (KIAS, QUC)

2 Particles in the SM three kinds of particles fermionic matter u quark d lepton ν e e charge:(su 3 C, SU 2 L ) U 1 Y u c t q L (3,2)1 6 u d u R c (ത3, 1) 2 3 d R c (ത3, 1)1 3 l L (1,2) 1 2 e e c R (1,1) 1 gauge boson B W g B(1,1) 0 W(1,3) 0 g(8,1) 0 Higgs boson H H(1,2)1 2 final piece of the SM makes SM complete 01/18

3 rich flavor structure (masses and mixings) U CKM = U MNS = In the SM Y u, Y d, Y e +neutrino sector just parameters mystery of nature 02/18

4 Flavor symmetry discrete symmetry for lepton (especially neutrino) flavor structure other example Froggatt-Nielsen Mechanism modified Altarelli Feruglio model AF model (Altarelli, Feruglio 2005) SUSY A 4 discrete symmetric model A 4 triplet flavon maf model (Shimizu, Tanimoto, Watanabe 2011) charged-lepton sector M: flavon mass 03/18

5 m l = v T Λ y e v d y μ v d y τ v d Λ: cut-off scale ratio v T Λ is constrained usually in this work Λ~M Planck Λ~O(10) TeV v T ~M M EW observation of flavon is hopeless v T ~M~M EW possibility of flavon signal 04/18

6 flavon Yukawa interaction in charged lepton sector (mass basis) flavor-conserving interaction flavor-violating interaction two key points fixed coupling flavor-violating interaction 05/18

7 Current constraint for flavon mass Constraint from τ lepton flavor violating decay constraint from Belle when residual Z 3 symmetry forbid many flavor-violating processes e.g. μ eγ, μ eee 06/18

8 Flavon signal at LHC (proton proton collider) flavon product cross section flavon main decay mode but it is not possible to identify all of these tau-leptons 07/18

9 electron photon collider (from ILC) considerable option for ILC (electron positron collider) photons are provided as back-scattered photons from electron beams photon beam energy Ito, Moroi, Takaesu arxiv: luminosity LCC Physics Working Group arxiv:1607:03829.studied for disappeared di-photon excess 08/18

10 advantage of electron photon collider electron positron collider electron photon collider flavon main decay mode final state lepton number tau-jet low p T cut QED interaction order 09/18

11 e γ τ τ + e signal flavon signal SM m e τ + invariant mass σ e γ τ τ + e background m τ τ + invariant mass 10/18

12 significance for e γ τ τ + e signal three selection rule identify three leptons remove SM events remove events which have m τh τh +< M Z + α collect flavon signal events m e τ h + is around flavon mass selection rule for two invariant masses second special rule large significance 11/18

13 m τh τh +invariant mass cut why we use m τ τ + < M z + α cut? usually we use m τ τ + M Z < α cut. beam energy is GeV 2 comes from difference between beam energies 12/18

14 m e τ h + invariant mass plot : SM background + flavon signal : SM background beam energy is GeV fb 1 (ILC) sufficient discovery significance 13/18

15 at the luminosity upgraded ILC beam energy is GeV fb 1 v T = 2m φt1 = m φt2 = m φt3 = 150 GeV 14/18

16 e γ 3LFV processes small cross section, but SM background is strongly suppressed σ e γ τ + μ μ = σ(e γ μ + τ τ ) 15/18

17 ILC upgraded ILC beam energy is ( ) GeV 2 At the upgraded ILC we can expect O(10) 3LFVP events. become strong evidence 16/18

18 17/18

19 Summary Light flavons are allowed. Especially in the modified AF model O(100) GeV mass flavons are allowed because of residual Z 3 symmetry. The electron photon collider is favored for detecting such flavons. For e γ e τ τ + process, the SM background can be strongly suppressed by considering an invariant mass of τ + and e which is sensitive for a flavon detection. For e γ τ + μ μ, μ + τ τ processes, the SM background is extremely small because in the SM there are no such flavor-violating final states. Sufficient discovery significance can be obtained even if flavons are heavier than the lower limits from flavor constraints. 18/18

20 statue of famous Chinese hero Guan Yu ( 関羽 ) Thank you for your listening. human size

21 Back up

22 model for lepton masses and mixings modified Altarelli Feruglio model A 4 triplet flavon AF model (Altarelli, Feruglio 2005) maf model (Shimizu, Tanimoto, Watanabe 2011) charged-lepton sector neutrino sector (+ other flavons and driving fields) v T Τ Λ is constrained to realize lepton masses and mixings. Λ : cut-off scale typically O(10) TeV right flavons (small M) are acceptable 01/15

23 flavon Yukawa interaction in charged lepton sector (mass basis) flavor-conserving interaction flavor-violating interaction residual Z 3 symmetry forbid many flavor-violating processes e.g. μ eγ, μ eee 02/15

24 Current constraint for flavon mass Constraint from τ lepton flavor violating decay constraint from Belle Constraint from t-channel process e e + μ μ +, τ τ + when constraint from LEP 03/15

25 Flavon signal at LHC (proton proton collider) flavon product cross section flavon main decay mode s = 14 TeV beam energy candidate for flavon signal processes contain many tau-leptons. Can we identify all of these tau-leptons? No number of event in which all tau-leptons are identified τ τ + τ τ + final state : zero τ τ + τ ҧ (when 3000 fb 1 data are collected) ν τ final state : zero 04/15

26 electron photon collider (from ILC) ILC (electron positron collider) photons are provided as back-scattered photons from electron beams beam energy Ito, Moroi, Takaesu arxiv: the photon luminosity function which has a peak at s γγ 0.79 s ee. photon beam energy =0.8 electron beam energy luminosity LCC Physics Working Group arxiv:1607:03829 L γγ L e e 3.6% L e e L e + e 3 L e γ 0.036L e e L e + e integrated luminosity for electron photon collider =0.6 integrated luminosity for electron positron collider 05/15

27 advantage of electron photon collider electron positron collider electron photon collider flavon main decay mode four lepton final state three lepton final state low tau-jet momentum tau-jet are caught by low p T cut In a low flavon mass region we can expect large flavon production cross section, on the other hand leptons which comes from flavon decay tend to have low momentum QED interaction order : two QED interaction order : one small cross section large cross section 06/15

28 e γ τ τ + e signal flavon signal SM m e τ + invariant mass σ e γ τ τ + e background m τ τ + invariant mass 07/15

29 significance for e γ τ τ + e signal signal event rate / background event rate signal event number / background event number S cl : significance based on Poisson distribution To calculate N S and N BG we use luminosities 4800, 300, 300 fb 1 which are planned in ILC for , , GeV beam energy, respectively. 08/15

30 m τh τh +invariant mass cut why we use M Z + α < m τ τ + selection? usually we use m τ τ + M Z > α selection. m τh τh + vs event number plot flavon signal beam energy is GeV 2 after detector simulation (cut) tau-lepton p T vs m τ τ + plot before detector simulation (parton level) p T cut for tau-jet : 10 GeV 09/15

31 m e τ h + invariant mass plot : SM background + flavon signal : SM background beam energy is GeV 2 beam energy is GeV fb fb 1 sufficient discovery significance 10/15

32 at the beam energy upgraded ILC beam energy is GeV fb 1 at the luminosity upgraded ILC beam energy is GeV fb 1 v T = 2m φt1 = m φt2 = m φt3 = 150 GeV beam energy is GeV fb 1 v T = 2m φt1 = m φt2 = m φt3 = 100 GeV 11/15

33 e γ 3LFV processes cross section for lepton flavor conserving (LFC) processes m τ m τ 2 cross section for lepton flavor violating (LFV) processes m τ m μ 2 σ e γ τ + μ μ = σ(e γ μ + τ τ ) but SM background is strongly suppressed 12/15

34 ILC upgraded ILC beam energy is ( ) GeV 2 ignore FV processes which contain e because of SM background At the upgraded ILC we can expect O(10) 3LFVP events. become strong evidence 13/15

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