1. Shinya Kanemura (Osaka Univ.) on behalf of S.K., Y. Kuno, T. Ota, M. Kuze PLB607(2005)165 Search for LFV (tau-mu and tau-e) via DIS processes with high energy intense muons and electrons S.K., Y. Kuno, T. Ota, M. Kuze, T. Takai Work in progress 7 th International Workshop on Neutrino Factories and Superbeams Lab Nazionali di Frascati, Frascati, (Rome), June 21-26, 2005

2. Contents Introduction Tau associated LFV processes Tau associated LFV processes LFV Yukawa coupling LFV Yukawa coupling Search for tau associated LFV couplings via LFV-DIS processes μN →τ Ｘ at a neutrino factory, a muon collider μN →τ Ｘ at a neutrino factory, a muon collider e N →τX at a linear collider e N →τX at a linear collider (a fixed target experiment at ILC) (a fixed target experiment at ILC)Summary PLB607(2005)165

3. Introduction

4. LFV is a clear signal for physics beyond the SM. Neutrino oscillation may indicate the possibility of LFV in the charged lepton sector. In new physics models, LFV can naturally appear. SUSY (slepton mixing) Borzumati, Masiero SUSY (slepton mixing) Borzumati, Masiero Hisano et al. Hisano et al. 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.

5. In this talk, we discuss tau-associated LFV in SUSY models In this talk, we discuss tau-associated LFV in SUSY models τ ⇔ e & τ ⇔ μ τ ⇔ e & τ ⇔ μ 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. 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 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 1.4-3.1 ×10 ＾（－ 7 ） τ→μη 3.4 ×10 ＾（－ 7 ）

6. LFV in SUSY 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, …. This situation may be explained by large M SUSY, so that the SUSY effects decouple. Even in such a case, we may be able to search LFV through the Higgs boson mediation, which does not necessarily decouple for a large M SUSY limit

7. Decoupling property of LFV Gauge mediation : Higgs mediation : Higgs mediation does not decouple in the large M SUSY limit

8. LFV Yukawa coupling Slepton mixing induces LFV in SUSY models. Babu, Kolda; Dedes,Ellis,Raidal; Kitano, Koike, Okada κ ij = Higgs LFV parameter

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

10. Experimental bound on κ 32, κ 31 For κ 31, similar bound is obtained. The strongest bound on κ 32 comes from the τ→μη result. the τ→μη result.

11. Current Data

12. The correlation between the Higgs mediation and the gauge 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 large.

13. m SUSY ～ O(1) TeV Consider that M SUSY is as large as O(1) TeV with a fixed value of |μ|/M SUSY Gauge mediated LFVis suppressed Gauge mediated LFV is suppressed, while the Higgs-LFV coupling κ ij while the Higgs-LFV coupling κ ij can be sufficiently large. Babu,Kolda; Babu,Kolda; Brignole, Rossi Brignole, Rossi Decoupling property of the Higgs LFV coupling (κ ij )

14. Search for Higgs mediated τ- e & τ- μ mixing at future colliders Tau’s rare decays at B factories. τ→eππ （ μππ ） τ→eππ （ μππ ） τ→eη (μη) τ→eη (μη) τ→μe e (μμμ), …. τ→μe e (μμμ), …. In near future, τ rare decay searches may improve the upper limit by about 1 order of magnitude. In near future, τ rare decay searches may improve the upper limit by about 1 order of magnitude. We here discuss the other possibilities. The DIS process μ Ｎ (eN)→τ Ｘ at a fixed target experiment at a νfactory and a LC The DIS process μ Ｎ (eN)→τ Ｘ at a fixed target experiment at a νfactory and a LC

15. Search of the LFV Yukawa coupling At future ν factories (μ colliders), 10^20 muons of energy 50 GeV 10^20 muons of energy 50 GeV (100-500GeV) can be available. (100-500GeV) can be available. DIS μ Ｎ →τ Ｘ process DIS μ Ｎ →τ Ｘ process At a LC (Ecm=500GeV L=10^34/cm^2/s) 10^22 of 250GeV electrons available. 10^22 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

17. ILC （ former JLC, TESLA, NLC ） A Linear Collider （ LC ） collision 1 st stage 2 nd stage Roadmap report JLC

18. Constraints on the new physics scale via theτμcoupling from data Scalar coupling τ→μππ Λ ～ 2.6 TeV Pseudo scalar coupling τ→μη ～ 12 TeV Vector τ→μρ ～ 12 TeV Pseudo vector τ→μπ ～ 11 TeV Pseudo vector τ→μπ ～ 11 TeV Black, Han, He, Sher, 2002

19. The cross section Scalar coupling ---several 10^(-1) fb ---several 10^(-1) fb In SUSY, scalar coupling = pseudo scalar coupling scalar coupling = pseudo scalar coupling 10^(-4)-10^(-5) smaller than scalar coupling bound CTEQ6L

20. Enhancement of cross section in SUSY CTEQ6L Each sub-process e q →τq e q →τq is proportional to the down-type quark masses. is proportional to the down-type quark masses. For the energy > 60 GeV, the total cross section is enhanced due to is enhanced due to the b-quark sub-process the b-quark sub-process E ＝ 50 GeV 10^(-5)fb E ＝ 50 GeV 10^(-5)fb 100 GeV 10^(-4)fb 100 GeV 10^(-4)fb 250 GeV 10^(-3)fb 250 GeV 10^(-3)fb Higgs mediated process

21. 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 coupling ⇒ No bottom Yukawa enhancement At high energy DIS e N →τX process is more sensitive to the Higgs mediation than the gauge mediation.

22. Angular distribution μLμL τRτR θ Target Lab-frame Higgs mediation → chirality flipped → chirality flipped → （ 1 － cosθ CM ） → （ 1 － cosθ CM ） 2

23. Energy distribution for each angle  From the μ L beam, τ R is emitted to the backward direction due to (1 ー cosθ CM ) nature in CM frame.  In Lab-frame, tau is emitted forward direction with some P T. Eμ ＝ 50 GeV Eμ ＝ 100 GeV Eμ ＝ 500 GeV 2

24. Experiments Near future CERN μbeam (200GeV) CERN μbeam (200GeV) SLAC LC (50GeV) SLAC LC (50GeV)Future Nutrino Factory, muon collider Nutrino Factory, muon collider ILC fixed targed option ILC fixed targed option Target: muon beam 100g/cm^2 electrom beam 10g/cm^2

25. Muon beam

26. Signal # of tau for L =10^20 muons |κ32|^2=0.3×10^(-6): |κ32|^2=0.3×10^(-6): Eμ ＝ 50 GeV 100×ρ[g/cm^2] τ’s Eμ ＝ 50 GeV 100×ρ[g/cm^2] τ’s 100 GeV 1000 100 GeV 1000 500 GeV 50000 500 GeV 50000 Hadronic products τ→π 、 ρ, a 1, … ＋ missings τ→π 、 ρ, a 1, … ＋ missings Hard hadrons emitted into the same direction as the parent τ’s τ R ⇒ backward ν L + forward π,ρ 、 …. τ R ⇒ backward ν L + forward π,ρ 、 …. # of hard hadrons ≒ 0.3 × (# of tau) ≒ 0.3 × (# of tau) Bullock, Hagiwara, Martin

27. Backgrounds Hard hadrons from the target (N) should not be so serious, and smaller for higher energies of the initial muon beam. Hard muons from DIS μN→μX may be a fake signal. Rate of mis-ID [machine dependent] Rate of mis-ID [machine dependent] Emitted to forwad direction without large P T due to Ratherford scattering Emitted to forwad direction without large P T due to Ratherford scattering 1/sin^4(θc M /2) 1/sin^4(θc M /2) Energy cuts Energy cuts Realistic Monte Carlo simulation is necessary to see the feasibility 4

28. 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

29. Monte Carlo Simulation 500GeV muon beam Generator: Signal Modified LQGENEP (leptoquark generator) (leptoquark generator) Bellagamba et al Bellagamba et al Background LEPTO γ ＤＩ Ｓ Background LEPTO γ ＤＩ Ｓ Q^2>1.69GeV^2,σ=0.17μ ｂ Q^2>1.69GeV^2,σ=0.17μ ｂ MC_truth level analysis MC_truth level analysis Work in progress

30. Takai Eπ ＞ 50GeV, θπ ＞ 0.025rad ⊿ μ 0.01rad Hadrons from μN→τX and backgrounds Scattering angle ofμis small, it would be difficult to tag background events for reduction

31. Electron beam

32. Number of taus Ee ＝ 250 GeV, Ee ＝ 250 GeV, L =10^34 /cm^2/s, ⇒ 10^22 electrons L =10^34 /cm^2/s, ⇒ 10^22 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 σ=10^(-3) fb 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 e-τ-Φcoupling^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 e-τ-Φcoupling^2 by around 4 orders of magnitude

33. Signal/Backgrounds Signal: μ from τ in e N→τX 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 Monte Carlo Simulation 50GeV electron beam 50GeV electron beam Event Generator Signal: modified LQGENEP Event Generator Signal: modified LQGENEP Background: γ ＤＩＳ σ=0.04μ ｂ Background: γ ＤＩＳ σ=0.04μ ｂ BG absorber, simulation for the pass through BG absorber, simulation for the pass through Propability of e, π, μ by using GEANT Propability of e, π, μ by using GEANT

34. High energy muon from tau is 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 Muons from the muon pair production Muons from the muon pair production ……. ……. e μ τ Hadron absorber Muon spectrometer (momentum measurement) (water) (iron) e elemag shower π Monte Carlo simulation by using GEANT Monte Carlo simulation by using GEANT 10cm 6-10m target dump

35. Summary We discussed LFV via DIS processes μ Ｎ （ e N ） →τX using high energy muon and electron beams and a fixed target. For E > 60 GeV, the cross section is enhanced due to the sub-process of Higgs mediation with sea b-quarks DIS μN→τX by the intense high energy muon beam. In the SUSY model, 100-10000 tau leptons can be produced for Eμ=50-500 GeV. In the SUSY model, 100-10000 tau leptons can be produced for Eμ=50-500 GeV. No signal in this process can improve the present limit on the Higgs LFV coupling by 10^2 – 10^4. No signal in this process can improve the present limit on the Higgs LFV coupling by 10^2 – 10^4. Theτ is emitted to forward direction with E T Theτ is emitted to forward direction with E T The signal is hard hadrons from τ→πν 、 ρν, a 1 ν,....,which go along the τdirection. The signal is hard hadrons from τ→πν 、 ρν, a 1 ν,....,which go along the τdirection. Main background: mis-ID of μ in μN→μX…. Main background: mis-ID of μ in μN→μX…. DIS process e N →τX : At a LC with E cm =500GeV ⇒ σ ＝ 10^(-3) fb At a LC with E cm =500GeV ⇒ σ ＝ 10^(-3) fb L=10^34/cm^2/s ⇒ 10^22 electrons available L=10^34/cm^2/s ⇒ 10^22 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 10^4. would improve the current limit by 10^4. Realistic simulation: work in progress.