Search for tau-e (tau-mu) flavor Search for tau-e (tau-mu) flavor mixing at a linear collider mixing at a linear collider

Shinya KANEMURA Shinya KANEMURA (Osaka Univ.)(Osaka Univ.)

withwith

Yoshitaka KUNO, Toshihiko OTAYoshitaka KUNO, Toshihiko OTA 　　 (Osaka Univ)(Osaka Univ)Masahiro Kuze (Tokyo Inst. Tech.)Masahiro Kuze (Tokyo Inst. Tech.)

ACFA’07, Nov 11. 2004, at National Taiwan UniversityACFA’07, Nov 11. 2004, at National Taiwan University

IntroductionIntroduction

LFV is a clear signal for physics beyond the SM.LFV is a clear signal for physics beyond the SM.

e ⇔μe ⇔μ 　　　　　　 μ⇔τμ⇔τ 　　　　　　 τ⇔eτ⇔e 　　

Neutrino oscillation may indicate LFV among charged leptons.Neutrino oscillation may indicate LFV among charged leptons.

In SUSY models, LFV can naturally appear.In SUSY models, LFV can naturally appear. Borzumati, MasieroBorzumati, Masiero

Hisano et al.Hisano et al.

In this talk, we discuss tau-associated LFV in SIn this talk, we discuss tau-associated LFV in SUSY modelsUSY models

ττ⇔e ⇔e 　　 & & ττ ⇔μ ⇔μ

The Higgs mediated LFV is proportional to the Yukawa couplThe Higgs mediated LFV is proportional to the Yukawa coupling ing

⇒ ⇒ Tau-associated LFV processesTau-associated LFV processes.. It is less constraind by current data as compared to theμ⇔e It is less constraind by current data as compared to theμ⇔e

mixingmixing

μ→eγ 1.2 ×10 ＾（－ 11 ）　　　　　　　

μ→ ３ e 　　　　　　　　　　 1.1 　 ×10＾（－ 12 ）

μTi→eTi 　　　　　　　　 6.1 ×10 ＾（－ 13 ）

τ→μγ 3.1 ×10 ＾（－ 7 ）τ→ ３ μ 1.4-3.1 ×10 ＾（－

7 ）τ→μη 　　　　　　 　　　 3.4 ×10 ＾

（－ 7 ）　

LFV in SUSYLFV in SUSYLFV is induced at one loop due to slepton mixingLFV is induced at one loop due to slepton mixing

Gauge mediation :Gauge mediation :

Higgs mediation :Higgs mediation :

Higgs mediation does not decouple in the large MHiggs mediation does not decouple in the large MSUSYSUSY limit limit

LFV Yukawa coupling LFV Yukawa coupling

Slepton mixing induces LFV Slepton mixing induces LFV in SUSY models. in SUSY models.

Babu, Kolda;Babu, Kolda;Dedes,Ellis,Raidal;Dedes,Ellis,Raidal;Kitano, Koike, OkadaKitano, Koike, Okada

κκijij 　　 = Higgs LFV parameter= Higgs LFV parameter

mmSUSY SUSY ～　～　 O(1) TeVO(1) TeV

Consider that MConsider that MSUSYSUSY is as large as O(1) TeV is as large as O(1) TeV with a fixed value of |μ|/M with a fixed value of |μ|/MSUSY SUSY

While gauge mediated LFVWhile gauge mediated LFV is suppressedis suppressed,

the Higgs-LFV coupling κthe Higgs-LFV coupling κijij 　　 can be sufficiently large . can be sufficiently large . Babu,Kolda; Babu,Kolda; Brignole, RossiBrignole, Rossi

Search for Higgs mediated Search for Higgs mediated τ- e & τ- μ mixingτ- e & τ- μ mixing

Tau’s rare decays Tau’s rare decays 　　　　　　 τ→eππτ→eππ 　（　（ μππμππ ）） τ→eη τ→eη 　　　　 (μη)(μη)　　　　　　 τ→μe e (μμμ)τ→μe e (μμμ) 、　…、　… . . In nearIn near future, τ decay searches will improve the upper limit future, τ decay searches will improve the upper limit

by 1-2 orders of magnitude.by 1-2 orders of magnitude.

Other possibilities ?Other possibilities ? Higgs decays into a tau-mu or tau-e pairHiggs decays into a tau-mu or tau-e pair The DIS process The DIS process e e Ｎ （Ｎ （ μμ Ｎ） →Ｎ） → ττ ＸＸ　　 by a fixed target experiment at a LC (μby a fixed target experiment at a LC (μ ＣＣ ))

Higgs boson decayHiggs boson decay

After the Higgs boson is found, we can consider the possAfter the Higgs boson is found, we can consider the possibility to measure the LFV Higgs couplings ibility to measure the LFV Higgs couplings directlydirectly from t from the decay of the Higgs bosons.he decay of the Higgs bosons. LHCLHC Assamagan et al; Brignole, RossiAssamagan et al; Brignole, Rossi

LC LC Kanemura, Ota, et al., Kanemura, Ota, et al.,

PLB599(2004)83.PLB599(2004)83.

Search for h →τμ (τe) atSearch for h →τμ (τe) at LC:LC: Simple kinematic structure (Esp. Higgssrahlung procSimple kinematic structure (Esp. Higgssrahlung proc

ess)ess) Precise measurements: Precise measurements:

property (mproperty (mhh,Γ,σ,Br,…) will be thoroughly measured,Γ,σ,Br,…) will be thoroughly measured Less backgrounds Less backgrounds

Higgs Production at a LCHiggs Production at a LC　　　　　　　　　　　　　　　　　　　　

～ 10^5 Higgs produced

Decay branching ratio (h→τμ)Decay branching ratio (h→τμ)

The branching ratio of 10^(-4) – 10^(-3) is possible.

SignalSignalThe process can be identified by using Z reThe process can be identified by using Z re

coil:coil:

Theτmomentum is reconstructed by Theτmomentum is reconstructed by

using Eusing Ecmcm, m, mhh, p, pZZ 　　 and pand pμμ

It is not required to measure It is not required to measure ττ

The # of the signalThe # of the signal eventevent

11 event for leptonic decay of Z11 event for leptonic decay of Z118 event for hadronic decay118 event for hadronic decay

BackgroundsBackgrounds

FeasibilityFeasibility

Resolution of Z momentum Resolution of Z momentum

Signal / FakeSignal / Fake

118 / 230 events118 / 230 events

(Z →jj(Z →jj 、 、 δδ ＝３＝３ GeV)GeV)

11 / 8 events 11 / 8 events

(Z→ll, δ(Z→ll, δ ＝＝ 1GeV)1GeV)

For some specific parameter region, For some specific parameter region, h →h → 　　 τμτμ 　（　（ τeτe ） ） can be studied at a LC.can be studied at a LC.No big advantage, although it depends on machine. No big advantage, although it depends on machine.

Alternative process for search of the Higgs Alternative process for search of the Higgs LFV coupling?LFV coupling?

At future ν factories (μ colliders) ,At future ν factories (μ colliders) , 10^20 muons of energy 50 GeV 10^20 muons of energy 50 GeV (100-500GeV) can be available. (100-500GeV) can be available. DISDIS μ μ Ｎ→Ｎ→ ττ ＸＸ processprocess Sher, Turan, PRD69(2004)302Sher, Turan, PRD69(2004)302 Kanemura, et al, hep-ph/0410044Kanemura, et al, hep-ph/0410044

At a LC At a LC (Ecm=500GeV L=10^34/cm^2/s)(Ecm=500GeV L=10^34/cm^2/s)

10^22 of 250GeV electrons available. 10^22 of 250GeV electrons available. We here consider the LFV DIS processes We here consider the LFV DIS processes

　　 ee Ｎ→Ｎ→ ττ ＸＸ 　 　 by using the electron (positron) beam of a LCby using the electron (positron) beam of a LC

μ （e） τ

N

qq

h, H, A

X

A fixed target experiment option of LCA fixed target experiment option of LC

Cross section in SUSY modelCross section in SUSY model

CTEQ6L

Each sub-process Each sub-process e q (μq) →τq e q (μq) →τq is proportional to the d-type is proportional to the d-type

quark masses.quark masses.

For the energy > 60 GeV, thFor the energy > 60 GeV, the total cross section e total cross section

is enhanced due to is enhanced due to the b-quark sub-processthe b-quark sub-process

EμEμ ＝＝ 50 GeV 10^(-5)fb50 GeV 10^(-5)fb 100 GeV100 GeV 　 　 10^(-4)fb 10^(-4)fb

250 GeV250 GeV 　 　 10^(-3)fb10^(-3)fb

μ （e） τ

N

qq

h, H, A

X

Energy distribution for each angleEnergy distribution for each angle From theFrom the ll LL beam, beam, ττRR is emitted is emitted 　　　　 to the backward direction due to to the backward direction due to 　　 　　 (1 (1 ー ー cosθcosθCMCM)) 　 　 nature in the CM frame. nature in the CM frame. In Lab-frame, tau is emitted forward In Lab-frame, tau is emitted forward 　 　 direction but with large angle with a Pdirection but with large angle with a PT.T.

EE ＝＝ 100 GeV100 GeV EE ＝＝ 500 GeV500 GeV

2 μ L

τ R

θ

Target

Lab-frame

SignalSignalNumber of taus (case of electron beam) Number of taus (case of electron beam)

　 　 EE ＝＝ 250 GeV, L =10^34 /cm^2/s, ⇒250 GeV, L =10^34 /cm^2/s, ⇒ 　　 10^22 electrons (positrons) 10^22 electrons (positrons) in a SUSY model with |κin a SUSY model with |κ3i3i |^2=0.3×10^(-6): σ=10^(-3) fb |^2=0.3×10^(-6): σ=10^(-3) fb

　　 　　 10^5 of τleptons are produced10^5 of τleptons are produced for the target of ρ=10 g/cm^2 for the target of ρ=10 g/cm^2 　　　　　　　　

Naively, Naively, non-obervation of the e N → τ X process may improve the currenon-obervation of the e N → τ X process may improve the current upper limit on the e-τ-Φnt upper limit on the e-τ-Φ 　　 coupling by around 4-5 orders of magnitudecoupling by around 4-5 orders of magnitude

We may consider its hadronic products as the signal We may consider its hadronic products as the signal τ→(πτ→(π 、、 ρ, aρ, a11, , …)…) ＋　＋　 missingsmissings

# of hadrons # of hadrons 0.3×(# of tau)≒ 0.3×(# of tau)≒

Hard Hard hadrons emitted into the same direction as the parent τ’s hadrons emitted into the same direction as the parent τ’s

τ R ν L π

Bullock, Hagiwara, MartinBullock, Hagiwara, Martin

BackgroundsBackgrounds

Hadrons from the target (N) should be softer, anHadrons from the target (N) should be softer, and more unimportant for higher energies of the inid more unimportant for higher energies of the initial e or μ beam.tial e or μ beam.

Hard leptons from Hard leptons from ll N→ N→ ll X would be be a fake siX would be be a fake signal via mis-ID of gnal via mis-ID of ll as π. ( as π. (ll = e or μ)= e or μ) Rate of mis-ID Rate of mis-ID 　　　 　　　　 　 Emitted to forwad direction without large PEmitted to forwad direction without large PT T due to the due to the

Rutherford scattering Rutherford scattering

1/sin^4(θc1/sin^4(θcMM/2) ⇒/2) ⇒ 　 　 PPTT cuts cuts Other factors to reduce the fakeOther factors to reduce the fake

Realistic Monte Carlo simulation is necessary.Realistic Monte Carlo simulation is necessary.

SummarySummary

Possibility of measuring LFV via Possibility of measuring LFV via e N→τX e N→τX by using thby using the high energy electron beam of a LC with ae high energy electron beam of a LC with a fixed-targe fixed-target.t.EEcmcm=500GeV σ⇒=500GeV σ⇒ ＝＝ 10^(-3) fb 10^(-3) fb

L=10^34/cm^2/s 10^22 electrons available ⇒L=10^34/cm^2/s 10^22 electrons available ⇒ 10^5 of taus are produced10^5 of taus are produced for ρ=10 g/cm^2 for ρ=10 g/cm^2

Non-observation of the signal would improve the curreNon-observation of the signal would improve the current limit on the τ-e-Φ coupling by 10^(4-5). nt limit on the τ-e-Φ coupling by 10^(4-5). The signal would be The signal would be hard hadronshard hadrons from τ→πν from τ→πν 、、 ρν, aρν, a11

ν, .... , which go along the τdirection.ν, .... , which go along the τdirection.Main background: mis-ID of e from eN→eX.Main background: mis-ID of e from eN→eX.Background simulation will be done.Background simulation will be done.