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Search for Lepton Flavor Violation at the ILC

Search for Lepton Flavor Violation at the ILC. Shinya Kanemura (Osaka Univ.). 8th ACFA LC Workshop ＠ Taegue, Korea, July 11-14. 2005. Contents. Introduction Lepton Flavor Violation (LFV) LFV in SUSY Gauge boson mediation & Higgs boson mediation LFV search at a LC LFV in LFV in

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Search for Lepton Flavor Violation at the ILC

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  1. Search for Lepton Flavor Violation at the ILC Shinya Kanemura (Osaka Univ.) 8th ACFA LC Workshop＠Taegue, Korea, July 11-14. 2005 Shinya KANEMURA

  2. Contents • Introduction • Lepton Flavor Violation (LFV) • LFV in SUSY • Gauge boson mediation & Higgs boson mediation • LFV search at a LC • LFV in • LFV in • LFV in Higgs decays • LFV DIS process (a fixed target experiment at a LC) • Summary N. Krasnikov 1996, N. Arkani-Hamed et al. 1996 M. Hirouchi, M Tanaka 1998 J. Hisano et al. 1999 M. Guchait, J. Kalinowski, P. Roy 2002 M. Cannoni, St. Kolb, O. Penella 2003 S.K., K. Matsuda, T. Ota, K.Tsumura, T.Shindou, E. Takasugi (MSSM) S.K., T. Ota, K. Tsumura (THDM) S.K., Y. Kuno, M. Kuze, T. Ota Shinya KANEMURA

  3. Introduction • LFV is a clear signal for physics beyond the SM. • Neutrino oscillation may indicate the possibility of LFV in the charged lepton sector. • In many new physics models, LFV can naturally appear. • SUSY (slepton mixing) Borzumati, Masiero Hisano, Moroi, Tobe, Yamaguchi • Zee model for the ν mass Zee • Models of dynamical flavor violation Hill et al. • Little Higgs models Shinya KANEMURA

  4. Tau-associated LFV processes may be interesting at a collider experiment τ⇔e & τ ⇔μ • It is less constrained by current data as compared to theμ⇔e mixing • The Higgs mediated LFV is proportional to the Yukawa coupling ⇒ Tau-associated LFV processes. Different behavior from μe mixing case. μ→eγ 1.2 ×10＾（－11）　　　　　　　 μ→３e1.1×10＾（－12） μTi→eTi6.1 ×10＾（－13） τ→μγ 3.1 ×10＾（－7） τ→３μ 1.4-3.1 ×10＾（－7） τ→μη3.4 ×10＾（－7）　 Shinya KANEMURA

  5. LFV in SUSY Slepton mixing induces LFV at loop. Gauge boson mediation Bortzmati, Masiero Hisano, Moroi, Tobe, Yamaguchi Form factors: A1L,Rij, A2L,Rij , … Higgs boson mediation Babu, Kolda Dedes, Ellis, Raidal Kitano, Koike Okada Form factors: κij Shinya KANEMURA

  6. Experimental bounds on LFV parameters Gauge boson mediation The strongest bound on (A2L,R)ij comes from the μ→eγ,τ→eγ,τ→μγ results. Higgs boson mediation The strongest bound on κ32comes from the τ→μη, τ→3μ results. For κ31,similar bound is obtained. Shinya KANEMURA

  7. A source of slepton mixingin the MSSM+RN • Slepton mixing induces both the Higgs mediated LFV and the gauge mediation. • The off-diagonal elements in the slepton mass matrix can be induced at low energies, even when it is diagonal at the GUT scale. • RGE Shinya KANEMURA

  8. Decoupling property of LFV • Gauge boson mediation : Decouple in the large MSUSY limit • Higgs boson mediation : LFVYukawa coupling NOT always decouple in the large MSUSY limit Shinya KANEMURA

  9. Why no LFV found ? • It is known that sizable LFV can be induced at loop due to slepton mixing. • Up to now, however, no LFV evidence has been observed at experiments. μ→e γ, μ→eee, …. • Why? Maybe large MSUSY, so that the SUSY effects (including LFV phenomena) decouple? Even in such a case, we may be able to search LFV via the Higgs boson mediation, which does not necessarily decouple for a large MSUSY limit. Shinya KANEMURA

  10. The correlation between the gauge boson mediation and the Higgs mediation For relatively low mSUSY, the Higgs mediated LFV is constrained by current data for the gauge mediated LFV. For mSUSY >O(1)TeV, the gauge mediation becomes suppressed, while the Higgs mediated LFV can be substantial. Shinya KANEMURA

  11. Search for LFV at the ILC N. Krasnikov 1996, N. Arkani-Hamed et al. 1996 M. Hirouchi, M Tanaka 1998 J. Hisano et al. 1999 M. Guchait, J. Kalinowski, P. Roy 2002 • LFV in electron-positron (electron) collision • Direct LFV Yukawa determination via the Higgs boson decays • LFV in a deep inelastic scattering process at a fixed target experiment M. Cannoni, St. Kolb, O. Penella 2003 A. Brignole, A. Rossi (MSSM) 2003 K.Arganda., A. Curiel, M.Herrero, D. Temes, 2004 LHC search: Assamagan et al. (THDM) 2002 LC Search: S.K., K. Matsuda, T. Ota, K.Tsumura,T. Shindou, E. Takasugi (MSSM) 2004 S.K., T. Ota, K. Tsumura (THDM)2005 M. Sher, I. Turan (muon beam)2003 S.K., Y. Kuno, M. Kuze, T. Ota 2004 S.K., Y. Kuno, M. Kuze, T. Ota, T. Takai Shinya KANEMURA

  12. M. Cannoni, St. Kolb, O. Penella 2003 • R-conserving SUSY • 1-loop process due to slepton mix • Resonant effect enhances the cross section • better than • can probe a region of parameter space which is allowed by theτ→eγ results depending on the luminosity Search for is complementary with the μ→eγ、τ→eγ Shinya KANEMURA

  13. LFV in Higgs boson decays • Direct measurement of LFV Yukawa couplings. • At the LHC, a Higgs boson is expected at a LC. • Precision measurement of Higgs parameters will be done at the LHC and at a LC. • To measure Br(h→μτ) , a LC (a Higgs factory) has the advantage because of its kinematics (H-strahlung). • At a LC, LFV Yukawa couplings can be well constrained in a wide region of parameter space of the 2HDM. • Study in the MSSM and the 2HDM (Tsumura’s Talk ) Shinya KANEMURA

  14. Alternative process for search of the Higgs LFV coupling • At future ν factories (μ colliders) , 1020 muons of energy 50 GeV (100-500GeV) can be available. DIS μＮ→τＸprocess • At a LC (Ecm=500GeV, L=1034/cm2/s) 1022 of 250GeV electrons available. DIS process eＮ→τＸprocess M. Sher S.K., Y. Kuno, M. Kuze, T. Ota S.K., Y. Kuno, M. Kuze, T. Ota A fixed target experiment option of ILC Shinya KANEMURA

  15. Enhancement of cross section in SUSY Higgs mediated LFV process CTEQ6L • Sub-process e- q →τ- q is proportional to the down-typequark mass. • Probability for the b-quark is larger for higher energies. • For Ee > 60 GeV, the total cross section is enhanced due to the b-quark sub-process Ee ＝50 GeV 10-5 fb 100 GeV10-4 fb 250 GeV10-3fb Shinya KANEMURA

  16. Contribution of the gauge boson mediation τ→eγresults gives the upper bound on the tensor coupling, therefore on the e N →τXcross section Gauge mediated LFV ⇒No bottom Yukawa enhancement At high energy DIS e N →τXprocess is more sensitive to the Higgs mediation than the gauge mediation. Shinya KANEMURA

  17. Number of produced taus Ee＝250 GeV, L =1034 /cm2/s, ⇒1022 electrons In a SUSY model with |κ31 |^2=0.3×10-6: σ=10-3 fb= 2 x 10-42 cm2 Nτ=ρ NANeσ 105 of τleptons are producedfor the target of ρ=10 g/cm^2 Naively, non-observation of the high energy muons from the tau of the e N → τ X process may improve the current upper limit on the eτΦ coupling2 by around 4 orders of magnitude NA=6 x 1023 Shinya KANEMURA

  18. 6-10m 10cm • High energy muon from tau cay be a signal • Geometry (picture) ex) target ρ=10g/cm2 • Backgrounds • Pion punch-through • Muons from Pion decay-in-flight • Muon from the muon pair production • ……. μ τ e dump Hadron absorber (water) target (iron) π e elemag shower Muon spectrometer (momentum measurement) Monte Carlo simulation is being done. GEANT4,… SK, Y. Kuno, M. Kuze, T. Ota, T. Takai Shinya KANEMURA

  19. Summary1 • LFV is a clear signature for physics beyond the SM • μ- e mixing strongly constrained by μ→eγ, μ-e conversion, …… Collider experiments can be useful to search τ associated LFV processes. • Various LFV process can be searched at ILC. • LFV in • LFV in • LFV in Higgs boson decays • LFV in DIS process at the fixed target option These can be competitive to LFV searches at (Super) B factories Tsumura’s talk Shinya KANEMURA

  20. Summary 2 • DIS process e N →τX : • Possibility of a fixed target experiment at a LC • The cross section is enhanced due to the sub-process of Higgs mediation with sea b-quarks • At a LC with Ecm=500GeV ⇒ σ＝10-3 fb L=1034/cm2/s ⇒ 1022 electrons available 10^5 of taus are produced for ρ=10 g/cm2 • Non-observation of the signal (high-energy muons) would improve the current limit by several orders. • Realistic simulation: work in progress. Shinya KANEMURA

  21. Angular distribution Higgs mediation →chirality flipped 　→　（1－cosθSM）2 Lab-frame τR eL θ Target Lab-frame • From the eL beam, τR is emitted to the backward direction due to (1 ー cosθCM)2nature in CM frame. • In Lab-frame, tau is emitted forward direction with some PT. Shinya KANEMURA

  22. Signal Higgs boson mediation Backgrounds photon mediation usual DIS Different distribution 　　　　 ⇒　BG reduction by Eτ, θτcuts Shinya KANEMURA

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