Search for lepton flavor violating μ Ｎ→ τ Ｘ reaction with high energy muons

1. Search for lepton flavor violating μＮ→τＸ　reaction with high energy muons Shinya KANEMURA (Osaka Univ.) with Yoshitaka KUNO, Masahiro KUZE, Toshihiko OTA TAU ‘04, Sep 16. 2004, Nara, JAPAN

2. 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 new physics models, LFV naturally appears. • SUSY (slepton mixing) Borzumati, Masiero Hisano et al. • Zee type models for the ν mass Zee • Models of dynamical flavor violation (Topcolor, Top seesaw etc)Hill et al.

3. Experimenal bounds on LFV processes process branching ratio • 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）　 Present experimental bounds on the tau associated processes are milder than those on the e-μLFV.

4. In this talk, we consider tau-associated LFV • The discovery of large mixing between νμandντ may be relatedto large LFV inthe μ-τsector • In SUSY models, the Higgs mediated LFV can contribute to the tau-associated process with the enhancement of the tau lepton mass.

5. Constraints on theτ-μeffective couplings from current data • Scalar coupling τ→μππ Λ～2.6 TeV • Pseudo-scalar coupling τ→μη ～12 TeV • Vector τ→μφ ～14TeV • Pseudo-vectorτ→μπ 　 ～11TeV Black, Han, He, Sher, 2002

6. (pseudo) vector coupling tensor coupling Higgs mediation = (pseudo) scalar coupling ∝lepton mass : →τ-associated process LFV in SUSY In SUSY model, effects of slepton mixing can induce LFV via loop diagrams gauge mediation=

7. Babu, Kolda; Dedes,Ellis,Raidal; Kitano, et al. LFV Yukawa coupling Slepton mixing induce LFV in SUSY models. κij= Higgs LFV parameter

8. Decoupling property • Gauge mediation (Dim=5) : decouple for large MSUSY • Higgs mediation (Dim=4) Does not decouple in the large MSUSY limit

9. Consider that MSUSY is as large as O(1) TeV with a fixed value of |μ|/MSUSY A sufficiently large Higgs mediated LFV coupling can be realized in a SUSY model, with the suppressed gauge mediated LFV. Babu,Kolda; Brignole, Rossi For mA=150GeV and tanβ=60,

10. Alternative process for the search of the Higgs LFV coupling • Future τ decay search may improve the upper limit by one or two orders of magnitude. • Do we have another way to measure the Higgs LFV coupling? • At future neutrino factories (muon colliders), Energy 50 GeV (100-500GeV) 10^20 muons can be available. • We here consider the DIS process μＮ→τＸ from such intense muon beam.

11. The DIS processμN→τX At either a neutrino factory or a muon collider • High energy muon beam(Eμ＝２０－３００ GeV) • Intensity （10＾20muons/year） μL τR h, H, A q q N X

13. CERN SPS muon beam S.N. Gninenko, et al., CERN-SPSC-2004-016 SPSC-EOI-004 SPS muon beam 10-100GeV Tau detection by NOMAD Quasi-Elastic scattering of μＮ→τＮ 　　　　　　　　　　　　　　　　　　　　　　 ↓　　　　 τ→μνν Details will be presented at the SPSC Villars Meeting 22-28 Sept’04

14. The cross section of μＮ→τＸ Effective scalar coupling 　 （using limit fromτ→μππ） σ　＜～ 0.5 fb Sher ⇒ 10^6×ρ[g/cm^3] tau’s from intensity 10^20 muons Pseudo-scalar coupling (using limit from τ→μη) σ　＜～　10^(-4) fb In SUSY, scalar coupling = pseudo-scalar coupling The cross section is 10^(-4)－10^(-5) smaller than the scalar coupling case

15. Enhancement of the SUSY cross section • Each sub-process μq→τq is proportional to the quark masses because of the Yukawa coupling. • For the energy > 50 GeV, the hadronic cross section is enhanced due to the b-quark sub-process Eμ＝50 GeV 10^(-5)fb 100 GeV10^(-4)fb 300 GeV10^(-3)fb • Importance of higher energy beam than 50 GeV CTEQ6L

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

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

18. Signal • Number of tau for L =10^20 muons in a SUSY model with |κ32|^2=0.3×10^(-6): Eμ＝50 GeV 100×ρ[g/cm^3]ofτleptons 100 GeV 1000 500 GeV 50000 • We can consider its hadronic products as the signal 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

19. Backgrounds • Hadrons from the target (N) should be softer, and more unimportant for higher energies of the initial muon beam. • Hard muons from μN→μX may be a fake signal via mis-ID of μas π. • Rate of mis-ID • Emitted to forwad direction without large PT due to the Rutherford scattering 1/sin^4(θcM/2) ⇒PT cuts • Other factors to reduce the fake • Realistic Monte Carlo simulation is necessary to see the feasibility

20. Summary • We discussed the possibility of measuring LFV via μN→τX by the intense high energy beam. • Non-observation of the signal can improve the present limit on the scalar LFV coupling by ～10^6. • In the SUSY model (scalar coupling=p-scalar coupling), 100-10000 tau leptons can be produced for Eμ=50-500 GeV. • For Eμ > 50 GeV, the cross section is enhanced due to the b-quark sub-process. • The signal is hard hadrons from τ→πν、ρν, a1ν, .... , which go along the τdirection. • Main background: mis-ID of μ from μN→μX. • Different distribution: PT cut may be effective. • Realistic background simulation should be done.

21. Note added • In the similar way, we can consider search for e-τconversion via the DIS process of e N →τ X. • At a linear collider (E=500GeV L=10^34/cm^2/s)10^22 electrons of E=250GeV available. The constraint on the (eτqq) coupling can be improved via e N →τ X by 10^8 as compared to that byτ→eππ.