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Search for lepton flavor violation via the intense high-energy muon beam

Search for lepton flavor violation via the intense high-energy muon beam. Shinya KANEMURA (Osaka Univ.) with. Yoshitaka KUNO, Masahiro KUZE, Toshihiko OTA. Nufact 2004, July 28, Osaka Univ., Osaka, JAPAN. Contents. Introduction LFV Experimental bounds Gauge mediation and Higgs mediation

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Search for lepton flavor violation via the intense high-energy muon beam

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  1. Search for lepton flavor violation via the intense high-energy muon beam Shinya KANEMURA (Osaka Univ.) with Yoshitaka KUNO, Masahiro KUZE, Toshihiko OTA Nufact 2004, July 28, Osaka Univ., Osaka, JAPAN

  2. Contents • Introduction • LFV • Experimental bounds • Gauge mediation and Higgs mediation • Parameters where Higgs mediated LFV becomes important • The DIS processμN→τN’ • High energy muon beam at a neutrino factory • The cross section of μN→τN’ in a SUSY model • The signal and backgrounds • Summary

  3. Introduction • Neutrino oscillation may suggest the possibility of LFV in the charged lepton sector. • LFV is a clear signature for the physics beyond the SM. • In many new physics models, LFV appears naturally. • SUSY (slepton mixing) • Models of dynamical flavor violation (Topcolor, Top seesaw etc)Hill et al.; He, Yuan • Zee type models Zee; Lim et al ;Cheung, Seto

  4. In this talk, we consider LFV inthe μ-τsector • The discovery of large mixing between νμandντ may be relatedto large LFV intheμ-τsector • In addition to the gauge mediation, the Higgs mediated LFV can also contribute: the LF-violating Yukawa couplings are proportional to masses of associated leptons. • The present experimental constraints for LFV of the τ-μ sector are relatively milder than those of the e-μsector.

  5. Current experimental search for LF violating processes process branching ratio • μ→eγ 4.2 ×10＾（－12）　　　　　　　 • 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. Higgs mediation =(pseudo) scalar coupling (pseudo) vector coupling tensor coupling 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,Koike,Okada Higgs mediation The LFV Higgs couplings appear, because the mass and the Yukawa coupling matrices cannot be diagonalized simultaneously. Higgs LFV parameter

  8. Constraint on κ32 The strongest constraint onκ32 comes from τ→μη result

  9. Decoupling property • Gauge mediation (Dim=5) • Higgs mediation (Dim=4)

  10. Consider that MSUSY is as large as O(1) TeV with a fixed value of μ/MSUSY The experimental upper limit for κ32can be realized in a SUSY model, with the suppressed gauge mediated LFV. Babu,Kolda; Brignole, Rossi; SK, Matsuda, Ota, Shindou, Takasugi, Tsumura For mA=150GeV and tanβ=60,

  11. The DIS processμN→τN’ M. Sher et al At a ν-factory • High energy muon beam(Eμ＝１０－１００GeV) • Intense luminosity （１０＾20muons/year） μ τ h, H, A q q N N’

  12. Sub-process μq→τqin the SUSY model Higgs mediation Photon mediation Small ! From now on, we only show the Higgs mediation contribution

  13. The cross section • Sub-process is proportional to mq^2 because of Yukawa coupling. • For higher energy than 50 GeV, the hadronic cross section is enhanced due to the b-quark process • Eμ＝50 GeV 10^(-5)fb • 100 GeV10^(-4)fb • 300 GeV10^(-3)fb • Importance of higher energy beam than 50 GeV CTEQ6L

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

  15. Energy distribution for each angle 2 • From theμR beam, τL 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

  16. Signal • # of tau for L =10^20 muons |κ32|^2=0.3×10^(-6): Eμ＝50 GeV 100×ρ[g/cm^3]taus 100 GeV 1000 500 GeV 50000 • Hadronic products τ→π、ρ,…＋　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

  17. Backgrounds • # of hard hadrons from the target (N) should not be too large, and smaller for higher energies of the initial muon beam. • Hard muons from μN→μN’ may be a fake signal. • Emitted to forwad direction without large PT due to 1/sin (θcM/2) like CM-distribution ⇒PT cuts • Rate of mis-ID [machine dependent] • Other factors to reduce the fake • Clearly, realistic Monte Carlo simulation is necessary to see the feasibility 4

  18. Summary • We discussed possibilities of measuring LFV via μN→τN’ by the intense high energy beam. • In the SUSY model, the cross section can be 10^(-5) fb to 10^(-3) fb for Eμ=50-500 GeV. • For Eμ > 50 GeV, the cross section is enhanced due to the b-quark sub-process. • Theτ is emitted to forward direction with ET • The signal is hard hadrons from τ→πν、ρν,aν, .... ,which goes along the τdirection. • Main background: mis-ID of μ in μN→μN’. • Different distribution: PT cut should be effective. • Realistic background simulation is necessary.

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