Shinya Kanemura (Osaka Univ.) on behalf of

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

2. Contents • Introduction • Tau associated LFV processes • LFV Yukawa coupling • Search for tau associated LFV couplings via LFV-DIS processes • μN　→τＸ at a neutrino factory, a muon collider • e N →τX at a linear collider (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 Hisano et al. • Zee model for the ν mass Zee • Models of dynamical flavor violation Hill et al.

5. In this talk, we discuss tau-associated LFV in SUSY models τ⇔e & τ ⇔μ • The Higgs mediated LFV is proportional to the Yukawa coupling ⇒ Tau-associated LFV processes. Different behavior from μe mixing case. • It is less constrained by current data as compared to theμ⇔e mixing 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）　

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 MSUSY, 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 MSUSY limit

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

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

9. A source of slepton mixingin 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

10. Experimental bound on κ32, κ31 The strongest bound on κ32comes from the τ→μη result. For κ31,similar bound is obtained.

11. Current Data

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

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

14. Search for Higgs mediated τ- e & τ- μ mixing at future colliders • Tau’s rare decays at B factories. τ→eππ　（μππ） τ→eη (μη) τ→μe e (μμμ),…. In nearfuture, τ rare decay searches may improve the upper limit by about 1 order of magnitude. • We here discuss the other possibilities. • The DIS process μＮ (eN)→τＸ　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 (100-500GeV) can be available. DIS μＮ→τＸprocess • At a LC (Ecm=500GeV L=10^34/cm^2/s) 10^22 of 250GeV electrons available. DIS process eＮ→τＸprocess A fixed target experiment option of ILC

17. A Linear Collider　（LC） collision ILC （former JLC, TESLA, NLC） 1st stage 2nd 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 ～12TeV • Pseudo vectorτ→μπ 　 ～11TeV Black, Han, He, Sher, 2002

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

20. Enhancement of cross section in SUSY Higgs mediated process CTEQ6L • Each sub-process e q →τq is proportional to the down-type quark masses. • For the energy > 60 GeV, the total cross section is enhanced due to the b-quark sub-process E ＝50 GeV 10^(-5)fb 100 GeV10^(-4)fb 250 GeV10^(-3)fb

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

22. Angular distribution Higgs mediation →chirality flipped 　→　（1－cosθCM） 2 Lab-frame τR μL θ Target Lab-frame

23. Energy distribution for each angle 2 • From theμL beam, τR is emitted to the backward direction due to (1 ー cosθCM)nature in CM frame. • In Lab-frame, tau is emitted forward direction with some PT. Eμ＝50 GeV Eμ＝100 GeV Eμ＝500 GeV

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

25. Muon beam

26. Signal • # of tau for L =10^20 muons |κ32|^2=0.3×10^(-6): Eμ＝50 GeV 100×ρ[g/cm^2]τ’s 100 GeV 1000 500 GeV 50000 • Hadronic products τ→π、ρ, a1, …＋　missings • Hard hadrons emitted into the same direction as the parent τ’s τR　⇒　backward νL+ forward π,ρ、…. • # of hard hadrons ≒ 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] • Emitted to forwad direction without large PT due to Ratherford scattering 1/sin^4(θcM/2) • Energy cuts • Realistic Monte Carlo simulation is necessary to see the feasibility 4

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

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

30. Hadrons from μN→τXand backgrounds Eπ＞50GeV, θπ＞0.025rad ⊿μ0.01rad Takai Scattering angle ofμis small, it would be difficult to tag background events for reduction

31. Electron beam

32. Number of taus Ee＝250 GeV, L =10^34 /cm^2/s, ⇒10^22 electrons In a SUSY model with |κ31 |^2=0.3×10^(-6): σ=10^(-3) fb 10^5 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 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 • Muons from Pion decay-in-flight • Muon from the muon pair production • Monte Carlo Simulation • 50GeV electron beam • Event Generator Signal: modified LQGENEP Background: γＤＩＳ　　　σ=0.04μｂ • BG absorber, simulation for the pass through • Propability of e, π, μby using GEANT

34. 6-10m 10cm • High energy muon from tau is a signal • Geometry (picture) ex) target ρ=10g/cm^2 • Backgrounds • Pion punch-through • Muons from Pion decay-in-flight • Muons 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 by using GEANT

35. Summary • We discussed LFV via DIS processes μＮ　（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. • 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 ET • The signal is hard hadrons from τ→πν、ρν,a1ν, .... ,which go along the τdirection. • Main background: mis-ID of μ in μN→μX…. • DIS process e N →τX : • At a LC with Ecm=500GeV ⇒ σ＝10^(-3) fb L=10^34/cm^2/s ⇒ 10^22 electrons available 10^5 of taus are produced for ρ=10 g/cm^2 • Non-observation of the signal (high-energy muons) would improve the current limit by 10^4. • Realistic simulation: work in progress.