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

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

3 Shinya KANEMURA 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 SUSY (slepton mixing) Borzumati, Masiero Hisano, Moroi, Tobe, Yamaguchi Hisano, Moroi, Tobe, Yamaguchi Zee model for the ν mass Zee Zee model for the ν mass Zee Models of dynamical flavor violation Hill et al. Models of dynamical flavor violation Hill et al. Little Higgs models Little Higgs models

4 Shinya KANEMURA T au-associated LFV processes may be interesting at a collider experiment T au-associated LFV processes may be interesting at a collider experiment τ ⇔ e & τ ⇔ μ τ ⇔ e & τ ⇔ μ It is less constrained by current data as compared to theμ ⇔ e mixing 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. The Higgs mediated LFV is proportional to the Yukawa coupling ⇒ Tau-associated LFV processes. Different behavior from μe mixing case. Different behavior from μe mixing case. μ→eγ 1.2 ×10 ＾（－ 11 ） μ→ ３ e 1.1 ×10 ＾ （－ 12 ） μTi→eTi 6.1 ×10 ＾（－ 13 ） τ→μγ 3.1 ×10 ＾（－ 7 ） τ→ ３ μ ×10 ＾（－ 7 ） τ→μη 3.4 ×10 ＾（－ 7 ）

5 Shinya KANEMURA LFV in SUSY Slepton mixing induces LFV at loop. Gauge boson mediation Higgs boson mediation Form factors: A 1 L,R ij, A 2 L,R ij, … Form factors: κ ij Kitano, Koike Okada Babu, Kolda Dedes, Ellis, Raidal Bortzmati, Masiero Hisano, Moroi, Tobe, Yamaguchi

6 Shinya KANEMURA Experimental bounds on LFV parameters For κ 31, similar bound is obtained. The strongest bound on κ 32 comes from the τ→μη, τ→3μ results. the τ→μη, τ→3μ results. The strongest bound on (A 2 L,R ) ij comes from the μ→eγ,τ→eγ,τ→μγ results. the μ→eγ,τ→eγ,τ→μγ results. Gauge boson mediation Higgs boson mediation

7 Shinya KANEMURA A source of slepton mixing in 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 RGE

8 Shinya KANEMURA Decoupling property of LFV Gauge boson mediation : Higgs boson mediation : LFV Yukawa coupling NOT always decouple in the large M SUSY limit NOT always decouple in the large M SUSY limit Decouple in the large M SUSY limit

9 Shinya KANEMURA 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 M SUSY, 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 M SUSY limit.

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

11 Shinya KANEMURA Search for LFV at the ILC 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 S.K., T. Ota, K. Tsumura (THDM) 2005 LC Search: S.K., K. Matsuda, T. Ota, K.Tsumura,T. Shindou, E. Takasugi (MSSM) 2004 S.K., Y. Kuno, M. Kuze, T. Ota 2004 LHC search: Assamagan et al. (THDM) 2002 S.K., Y. Kuno, M. Kuze, T. Ota, T. Takai A. Brignole, A. Rossi (MSSM) 2003 K.Arganda., A. Curiel, M.Herrero, D. Temes, 2004 M. Sher, I. Turan (muon beam) 2003 M. Cannoni, St. Kolb, O. Penella 2003 N. Krasnikov 1996, N. Arkani-Hamed et al M. Hirouchi, M Tanaka 1998 J. Hisano et al M. Guchait, J. Kalinowski, P. Roy 2002

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

13 Shinya KANEMURA 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 )

14 Shinya KANEMURA Alternative process for search of the Higgs LFV coupling At future ν factories (μ colliders), muons of energy 50 GeV muons of energy 50 GeV ( GeV) can be available. ( GeV) can be available. DIS μ Ｎ →τ Ｘ process DIS μ Ｎ →τ Ｘ process At a LC (E cm =500GeV, L=10 34 /cm 2 /s) of 250GeV electrons available of 250GeV electrons available. DIS process e Ｎ →τ Ｘ process DIS process e Ｎ →τ Ｘ process A fixed target experiment option of ILC M. Sher S.K., Y. Kuno, M. Kuze, T. Ota

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

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

17 Shinya KANEMURA Number of produced taus Ee ＝ 250 GeV, Ee ＝ 250 GeV, L =10 34 /cm 2 /s, ⇒ electrons L =10 34 /cm 2 /s, ⇒ electrons In a SUSY model with |κ 31 |^2=0.3×10 -6 : In a SUSY model with |κ 31 |^2=0.3×10 -6 : σ=10 -3 fb = 2 x cm 2 σ=10 -3 fb = 2 x cm 2 N τ = ρ N A N e σ N τ = ρ N A N e σ 10 5 of τleptons are produced for 10 5 of τleptons are produced for the target of ρ=10 g/cm^2 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 coupling 2 by around 4 orders of magnitude 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 coupling 2 by around 4 orders of magnitude N A =6 x 10 23

18 Shinya KANEMURA High energy muon from tau cay be a signal Geometry (picture) ex) target ρ=10g/cm 2 Backgrounds Pion punch-through Pion punch-through Muons from Pion decay-in-flight Muons from Pion decay-in-flight Muon from the muon pair production Muon from the muon pair production ……. ……. e μ τ Hadron absorber Muon spectrometer (momentum measurement) (water) (iron) e elemag shower π Monte Carlo simulation is being done. GEANT4,… 10cm 6-10m target SK, Y. Kuno, M. Kuze, T. Ota, T. Takai dump

19 Shinya KANEMURASummary1 LFV is a clear signature for physics beyond the SM LFV is a clear signature for physics beyond the SM μ- e mixing strongly constrained by μ- e mixing strongly constrained by μ→eγ, μ-e conversion, …… μ→eγ, μ-e conversion, …… Collider experiments can be useful to search Collider experiments can be useful to search τ associated LFV processes. τ associated LFV processes. Various LFV process can be searched at ILC. LFV in LFV in LFV in Higgs boson decays LFV in Higgs boson decays LFV in DIS process at the fixed target option LFV in DIS process at the fixed target option These can be competitive to LFV searches at (Super) B factories Tsumura’s talk

20 Shinya KANEMURA Summary 2 DIS process e N →τX : Possibility of a fixed target experiment at a LC 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 The cross section is enhanced due to the sub-process of Higgs mediation with sea b-quarks At a LC with E cm =500GeV ⇒ σ ＝ fb At a LC with E cm =500GeV ⇒ σ ＝ fb L=10 34 /cm 2 /s ⇒ electrons available L=10 34 /cm 2 /s ⇒ electrons available 10^5 of taus are produced for ρ=10 g/cm 2 10^5 of taus are produced for ρ=10 g/cm 2 Non-observation of the signal (high-energy muons) Non-observation of the signal (high-energy muons) would improve the current limit by several orders. would improve the current limit by several orders. Realistic simulation: work in progress. Realistic simulation: work in progress.

21 Shinya KANEMURA Angular distribution eLeL τRτR θ Target Lab-frame Higgs mediation → chirality flipped → chirality flipped → （ 1 － cosθ SM ） 2 → （ 1 － cosθ SM ） 2  From the e L beam, τ R is emitted to the backward direction due to (1 ー cosθ CM ) 2 nature in CM frame.  In Lab-frame, tau is emitted forward direction with some P T.

22 Shinya KANEMURA Signal Backgrounds usual DIS Higgs boson mediation photon mediation Different distribution ⇒ BG reduction by E τ, θ τ cuts ⇒ BG reduction by E τ, θ τ cuts