A Study on muon electron to tau conversion

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

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

Introduction Shinya KANEMURA 3

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. n SUSY (slepton mixing) Borzumati, Masiero Hisano, Moroi, Tobe, Yamaguchi n n n Zee model for the n mass Zee Models of dynamical flavor violation Hill et al. …. Shinya KANEMURA 4

LFV in SUSY Slepton mixing induces LFV at one loop. Gauge boson mediation Bortzmati, Masiero Hisano, Moroi, Tobe, Yamaguchi Form factors: A 1 L, Rij, A 2 L, Rij , … Higgs boson mediation Form factors: Babu, Kolda Dedes, Ellis, Raidal Kitano, Koike Okada κij Shinya KANEMURA 5

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

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 7

Tau-associated LFV t ⇔m n n &　 t ⇔　e 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→eg m→ 3 e　　　　　　 m Ti → e Ti　　　　 t →m g t → 3 m t →m h　　　　　　 Shinya KANEMURA 1. 2 × 10＾（－11）　　　　　　 　1. 1 × 10＾（－12） 6. 1 × 10＾（－13） 3. 1 × 10＾（－7） (1. 4 -3. 1) × 10＾（－7） 3. 4 × 10＾（－7）　 8

Experimental bounds on LFV parameters Gauge boson mediation The strongest bound on (A 2 L, R)ij comes from the μ →e γ , τ→ μγ results. Higgs boson mediation The strongest bound on k 32 (tau-mu mixing) comes from the , τ→ m h results. For k 31 (tau-e mixing) , similar bound is obtained from τ→ e h. Shinya KANEMURA 9

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 near future, τ rare decay searches may improve the upper limit by about 1 order of magnitude. We here discuss the alternative possibilities. n The DIS process μＮ (e. N)→τＸ　at a fixed target experiment at a neutrino factory and a LC Shinya KANEMURA 10

LFV Deep Inelastic Scattering Shinya KANEMURA 11

Deep inelastic scattering LFV process DIS μＮ→τＸ process: At a future neutrino factory (or a muon collider) , about 1020 muons/year of energy 50 Ge. V (or 100 -500 Ge. V) can be available. DIS process eＮ→τＸ process: At a LC (Ecm=500 Ge. V (or 1 Te. V), L=1034/cm 2/s) 1022 electrons/year of 250 Ge. V (or 500 Ge. V) electrons available. A fixed target experiment option of a LC Shinya KANEMURA 12

The cross section in SUSY Higgs mediated LFV process CTEQ 6 L Sub-process e- q →τ- q is proportional to the down-type quark mass. Probability for the b-quark is larger for higher energies. For Ee > 60 Ge. V, the total cross section is enhanced due to the b-quark sub-process Ee ＝ 50 Ge. V 10 -5 fb 100 Ge. V　 10 -4 fb 250 Ge. V　 10 -3 fb Shinya KANEMURA 13

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

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

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 mediated LFV ⇒　No bottom Yukawa enhancement At high energy DIS e N →τX　process is more sensitive to the Higgs mediation than the gauge mediation. Shinya KANEMURA 16

Experiments Target: muon beam 100 g/cm^2 electrom beam 10 g/cm^2 Near future n CERN μbeam (200 Ge. V) n SLAC LC (50 Ge. V) Future n n Nutrino Factory, muon collider ILC fixed targed option Shinya KANEMURA 17

Muon beam Shinya KANEMURA 18

Signal # of tau for L =1020 muons |κ 32|2=0. 3× 10 -6: Eμ＝ 50 Ge. V 　　　 100×ρ[g/cm 2]　　τ’s　 　　　　　　　100 Ge. V 1000 500 Ge. V 50000 　　 Hadronic products τ→π、ρ, a 1, …＋　missings Hard hadrons emitted into the same direction as the parent τ’s τR　⇒　backward νL　+ forward π, ρ、… Bullock, Hagiwara, Martin Shinya KANEMURA 19

Backgrounds Hard muons from DIS μN→μX may be a fake signal. n n Rate of mis-ID 　　　 　[machine dependent] Emitted to forwad direction without large PT due to Ratherford scattering 1/sin 4(θc. M/2) Energy cuts Hard hadrons from the target (N ) Realistic Monte Carlo simulation is necessary to see the feasibility Shinya KANEMURA 20

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

Monte Carlo Simulation 500 Ge. V muon beam Generator: Signal Modified LQGENEP (leptoquark generator) Bellagamba et al Background LEPTO γＤＩＳ 　　　　　Q 2>1. 69 Ge. V 2, σ=0. 17μｂ MC_truth level analysis Work in progress Shinya KANEMURA 22

Electron beam Shinya KANEMURA 23

Number of produced taus 　 Ee＝ 250 Ge. V, L =1034 /cm 2/s, ⇒　1022 electrons In a SUSY model with |κ 31 |^2=0. 3× 10 -6　: σ= 10 -3 fb　 = 6 x 10 -42 cm 2 N τ = 　ρ N A 　N e 　σ NA=6 x 1023 　 105 of τleptons are produced for 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 coupling 2 by around 4 orders of magnitude. Shinya KANEMURA 24

Signal/Backgrounds Signal: for example, μ from τ in e N→τX Backgrounds: n n n Pion punch-through Muons from Pion decay-in-flight Muon from the muon pair production Monte Carlo Simulation n 250 Ge. V-1. 5 Te. V electron beam Event Generator Signal: modified LQGENEP Background: LEPTO γＤＩＳ　　 BG absorber, simulation for the pass through probability of e, π, μ　by using GEANT Shinya KANEMURA 25

High energy muon from tau can be a signal Geometry (picture) ex) target ρ=10 g/cm 2 10 cm e 6 -10 m μ τ target e dump (water) π Hadron absorber (iron) elemag shower Backgrounds n n n Muon from g DIS Muon from pair paroduction (dilepton) Pion punch-through Muons from Pion decay-in-flight ……. Monte Carlo simulation Muon spectrometer (momentum measurement) LQGENEP, LEPTO, GEANT 4 Shinya KANEMURA 26

Cuts: Eμ, r, rgap, Q 2 μ τ e r μ rgap target Muon spectrometer (momentum measurement) Shinya KANEMURA 27

MC analysis (under study) (LQGENEP, LEPTO, GEANT 4) LC Ee=250 Ge. V, 500 Ge. V, 1 Te. V, 1. 5 Te. V L=1022 electrons per year Signal　　 　 muons from LFV DIS　 n n e N →τX　with 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. Q 2 cut: Q 2>10 Ge. V 2 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. 28 Shinya KANEMURA

Takai Values of the cross section Number of MC events 10, 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 29

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

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 Ge. V, 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. n n n In the SUSY model, 100 -10000 tau leptons can be produced for Eμ=50 -500 Ge. V. 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, 　a 1ν, . . , which go along the τdirection. Main background: mis-ID of μ in μN→μX…. DIS process e N →τX : n n At a LC with Ecm=500 Ge. V ⇒ σ＝ 10 -3 fb L=1034/cm 2/s ⇒ 1022 electrons available 105 of taus are produced for ρ=10 g/cm 2 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 31

Takai Shinya KANEMURA 32

A source of slepton mixing in 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 33

The gauge boson mediation v. s. the Higgs 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) Te. V, the gauge mediation becomes suppressed, while the Higgs mediated LFV can be large. Shinya KANEMURA 34

Hadrons from μN→τX　and backgrounds Eπ＞ 50 Ge. V, θπ＞ 0. 025 rad ⊿μ　0. 01 rad Takai Scattering angle ofμis small, it would be difficult to tag background events 35 for reduction　　　Work Shinya KANEMURA in progress

Prediction on LFV Yukawa Consider that m. SUSY is as large as O(1) Te. V with a fixed value of |μ|/m. SUSY Gauge mediated LFV is suppressed, while the Higgs-LFV coupling κij　 can be easily as large as the current experimental limit. Babu, Kolda; Brignole, Rossi m. SUSY ～　O(1) Te. V Shinya KANEMURA 36

Current Data for rare tau decays Shinya KANEMURA 37