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Shinya Kanemura (Osaka Univ.)

A Study on muon (electron) to tau conversion in Deep Inelastic Scattering. Yoshitaka Kuno (Osaka), Toshihiko Ota (TU Munich) Masahiro Kuze, Tomoyasu Takai (Tokyo Inst. Tech.). Shinya Kanemura (Osaka Univ.).

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Shinya Kanemura (Osaka Univ.)

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  1. A Study on muon (electron) to tau conversion in Deep Inelastic Scattering Yoshitaka Kuno (Osaka), Toshihiko Ota (TU Munich) Masahiro Kuze, Tomoyasu Takai (Tokyo Inst. Tech.) Shinya Kanemura (Osaka Univ.) Discovery of Higgs and SUSY to Pioneer Particle Physics in the 21stCentury@Univ. of Tokyo, Nov 24-25. 2005 Shinya KANEMURA

  2. Contents • Introduction • Physics Motivation • LFV Yukawa coupling (Higgs mediated LFV) • Tau associated LFV process • LFV Deep Inelastic Scattering processes • Cross sections and general features • Muon beam • Electron beam • Summary Shinya KANEMURA

  3. Introduction Shinya KANEMURA

  4. Physics Motivation • LFV is a clear signature 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, Moroi, Tobe, Yamaguchi • Zee model for the n mass Zee • Models of dynamical flavor violation Hill et al. • …. Shinya KANEMURA

  5. LFV in SUSY Slepton mixing induces LFV at one loop. Gauge boson mediation Bortzmati, Masiero Hisano, Moroi, Tobe, Yamaguchi Form factors: A1L,Rij, A2L,Rij , … Higgs boson mediation Babu, Kolda Dedes, Ellis, Raidal Kitano, Koike Okada Form factors: κij Shinya KANEMURA

  6. Decoupling property of LFV • Gauge boson mediation : Decouple in the large MSUSY limit • Higgs boson mediation : LFVYukawa coupling Not always decouple in the large MSUSY limit Shinya KANEMURA

  7. LFV in SUSY scenario • It is known that sizable LFV can be induced at loop due to slepton mixing. • Up to now, however, no evidence for LFV has been observed at experiments. μ→eg, 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 via the Higgs boson mediation, which does not necessarily decouple for a large MSUSY limit. Shinya KANEMURA

  8. t⇔ m &t ⇔e Tau-associated LFV • The tau associated LFV is interesting for Higgs mediation, which is proportional to the Yukawa coupling (Different behavior from μe mixing case.) • Tau associated LFV is less constrained by current data as compared to theμ⇔e mixing m → e g 1.2 ×10＾（－11）　　　　　　m→3e1.1 ×10＾（－12） m Ti → e Ti6.1 ×10＾（－13） t → m g 3.1 ×10＾（－7） t → 3 m (1.4-3.1) ×10＾（－7） t → m h3.4 ×10＾（－7）　 Shinya KANEMURA

  9. Experimental bounds on LFV parameters Gauge boson mediation The strongest bound on (A2L,R)ij comes from the μ → e γ, τ→ e γ, τ→ μγ results. Higgs boson mediation The strongest bound on k32 (tau-mu mixing) comes from the , τ→ m h results. For k31 (tau-e mixing), similar bound is obtained from τ→ e h. Shinya KANEMURA

  10. 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 alternative possibilities. • The DIS process μＮ (eN)→τＸ　at a fixed target experiment at a neutrino factory and a LC Shinya KANEMURA

  11. LFV Deep Inelastic Scattering Shinya KANEMURA

  12. Deep inelastic scattering LFV process • DIS μＮ→τＸprocess: At a future neutrino factory (or a muon collider) , about 1020 muons/year of energy 50 GeV (or 100-500 GeV) can be available. • DIS process eＮ→τＸprocess: At a LC (Ecm=500GeV (or 1TeV), L=1034/cm2/s)1022 electrons/year of 250GeV (or 500GeV) electrons available. A fixed target experiment option of a LC Shinya KANEMURA

  13. The cross section in SUSY Higgs mediated LFV process CTEQ6L • Sub-process e- q →τ- q is proportional to the down-typequark mass. • Probability for the b-quark is larger for higher energies. • For Ee > 60 GeV, the total cross section is enhanced due to the b-quark sub-process Ee ＝50 GeV 10-5 fb 100 GeV10-4 fb 250 GeV10-3fb Shinya KANEMURA

  14. Angular distribution Higgs mediation →chirality flipped 　→　（1－cosqcm）2 Lab-frame τR μL θ Target Lab-frame • From the μL (eL) beam, τR is emitted to the backward direction due to (1 ー cosθCM)2nature in the CM frame. • In Lab-frame, tau is emitted forward direction with some PT. Shinya KANEMURA

  15. Energy distribution for each angle • From the eL beam, tR is emitted to the backward direction due to (1 ー cosq)2 nature in the CM frame. • In Lab-frame, tau is emitted forward direction but with large angle with a PT. E＝500 GeV E＝50 GeV E＝100 GeV Shinya KANEMURA

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

  17. 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 Shinya KANEMURA

  18. Muon beam Shinya KANEMURA

  19. Signal • # of tau for L =1020 muons |κ32|2=0.3×10-6: Eμ＝50 GeV 100×ρ[g/cm2]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、… Bullock, Hagiwara, Martin Shinya KANEMURA

  20. Backgrounds • 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/sin4(θcM/2) • Energy cuts Hard hadrons from the target (N ) • Realistic Monte Carlo simulation is necessary to see the feasibility Shinya KANEMURA

  21. Signal Higgs boson mediation Backgrounds photon mediation Different distribution ⇒BG reduction by Eτ, θτ cuts Shinya KANEMURA

  22. Monte Carlo Simulation • 500GeV muon beam • Generator: Signal Modified LQGENEP (leptoquark generator) Bellagamba et al Background LEPTO γＤＩＳ Q2>1.69GeV2,σ=0.17μｂ • MC_truth level analysis Work in progress Shinya KANEMURA

  23. Electron beam Shinya KANEMURA

  24. Number of produced taus Ee＝250 GeV, L =1034 /cm2/s, ⇒1022 electrons In a SUSY model with |κ31 |^2=0.3×10-6: σ= 10-3 fb= 6 x 10-42 cm2 Nτ=ρ NANeσ 105 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 eτΦ coupling2 by around 4 orders of magnitude. NA=6 x 1023 Shinya KANEMURA

  25. Signal/Backgrounds • Signal: for example, 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 • 250GeV-1.5 TeV electron beam • Event Generator Signal: modified LQGENEP Background: LEPTO γＤＩＳ　　 • BG absorber, simulation for the pass through probability of e, π, μby using GEANT Shinya KANEMURA

  26. 10cm 6-10m μ High energy muon from tau can be a signal • Geometry (picture) ex) target ρ=10g/cm2 • Backgrounds • Muon from g DIS • Muon from pair paroduction (dilepton) • Pion punch-through • Muons from Pion decay-in-flight • ……. τ e dump Hadron absorber (water) target (iron) π e elemag shower Muon spectrometer (momentum measurement) Monte Carlo simulation LQGENEP, LEPTO, GEANT4 Shinya KANEMURA

  27. Cuts: Eμ, r, rgap, Q2 μ τ r e μ rgap target Muon spectrometer (momentum measurement) Shinya KANEMURA

  28. MC analysis (under study) (LQGENEP, LEPTO, GEANT4) • LC Ee=250GeV, 500GeV, 1TeV, 1.5TeV L=1022 electrons per year • Signalmuons from LFV DIS • e N →τXwith τ→μνν • 104-5 muons/year • Background muons from γDIS, etc • Kinematic cuts 1. Em (muon energy cut) 2. PT or r (angle cut) 3. rgap (extrapolate back cut) 4. Q2 cut: Q2>10GeV2 • But with 108 MC events, the number of the MC background event is reduced to 1. • Simulation with more MC events (109-10) is work in progress. Shinya KANEMURA

  29. Takai Values of the cross section Number of MC events 10,000,000 Cross sections of produced taus (and muons from them) After the cuts by Et, r, rgap, the values where the number of the MC background event becomes 1 More MC events necessary! Shinya KANEMURA

  30. Takai Event number 100,000,000 (10 times greater) S/N where the MC events becomes 1. Shinya KANEMURA

  31. 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 102 – 104. • Theτ is emitted to forward direction with PT • 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=1034/cm2/s ⇒ 1022 electrons available 105 of taus are produced for ρ=10 g/cm2 • Non-observation of the signal (high-energy muons) would improve the current limit by 104. • Realistic simulation: work in progress (collecting more MC events). Shinya KANEMURA

  32. Takai Shinya KANEMURA

  33. A source of slepton mixingin 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 Shinya KANEMURA

  34. The gauge boson mediation v.s. the Higgs 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. Shinya KANEMURA

  35. 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 reductionWork in progress Shinya KANEMURA

  36. Prediction on LFV Yukawa 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 easily as large as the current experimental limit. Babu,Kolda; Brignole, Rossi mSUSY ～　O(1) TeV Shinya KANEMURA

  37. Current Data for rare tau decays Shinya KANEMURA

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