Shinya Kanemura Shinya Kanemura (Osaka Univ.)(Osaka Univ.)

on behalf ofon behalf of S.K., Y. Kuno, T. Ota, M. Kuze S.K., Y. Kuno, T. Ota, M. Kuze PLB607(2005)165

Search for LFV (tau-mu and tau-e) Search for LFV (tau-mu and tau-e) via DIS processes with high energy via DIS processes with high energy

intense muons and electronsintense muons and electrons

S.K., Y. Kuno, T. Ota, M. Kuze, T. Takai S.K., Y. Kuno, T. Ota, M. Kuze, T. Takai Work in progress

77thth International Workshop on Neutrino Factories and Superbeams International Workshop on Neutrino Factories and SuperbeamsLab Nazionali di Frascati, Frascati, (Rome), June 21-26, 2005Lab Nazionali di Frascati, Frascati, (Rome), June 21-26, 2005

ContentsContentsIntroductionIntroduction Tau associated LFV processesTau associated LFV processes LFV Yukawa couplingLFV Yukawa couplingSearch for tau associated LFV couplings viSearch for tau associated LFV couplings via LFV-DIS processes a LFV-DIS processes μNμN 　→　→ ττ Ｘ Ｘ at a neutrino factory, a muon collat a neutrino factory, a muon coll

ider ider e N →τX at a linear collidere N →τX at a linear collider (a fixed target experiment at ILC) (a fixed target experiment at ILC)

SummarySummary

PLB607(2005)165

IntroductionIntroduction

LFV is a clear signal for physics beyond the SM.LFV is a clear signal for physics beyond the SM.Neutrino oscillation may indicate the possibility of Neutrino oscillation may indicate the possibility of LFV in the charged lepton sector.LFV in the charged lepton sector.In new physics models, LFV can naturally appear.In new physics models, LFV can naturally appear. SUSY (slepton mixing) SUSY (slepton mixing) Borzumati, MasieroBorzumati, Masiero

Hisano et al.Hisano et al. Zee model for the ν mass Zee model for the ν mass ZeeZee Models of dynamical flavor violation Models of dynamical flavor violation Hill et al.Hill 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..

Different behavior from μe mixing case. Different behavior from μe mixing case. It is less constrained by current data as compared to theμ⇔It is less constrained by current data as compared to theμ⇔

e mixinge mixing 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 SUSYIt is known that sizable LFV can be induced at loop It is known that sizable LFV can be induced at loop due to slepton mixing due to slepton mixing Up to now, however, no LFV evidence has been obUp to now, however, no LFV evidence has been observed at experiments. served at experiments. μ→e γ, μ→eee, ….μ→e γ, μ→eee, ….

This situation may be explained by large MThis situation may be explained by large MSUSY, SUSY, so thso that the SUSY effects decouple.at the SUSY effects decouple.

Even in such a case, we may be able to Even in such a case, we may be able to search LFV through the Higgs boson search LFV through the Higgs boson mediation, which does not necessarily mediation, which does not necessarily decouple for a large Mdecouple for a large MSUSY SUSY limitlimit

Decoupling property of LFV Decoupling property of LFV

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 in SUSY models. Slepton mixing induces LFV 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

A source of slepton mixingA source of slepton mixingin the MSSM+RNin the MSSM+RN

Slepton mixing induces both the Higgs mediated Slepton mixing induces both the Higgs mediated LFV and the gauge mediation. LFV and the gauge mediation. Off-diagonal elements can be induced in the sleOff-diagonal elements can be induced in the slepton mass matrix at low energies, even when it ipton mass matrix at low energies, even when it is diagonal at the GUT scale.s diagonal at the GUT scale.RGERGE 　　

Experimental bound on κExperimental bound on κ32, 32, κκ3131

For κ31, 　 similar bound is obtained.

The strongest bound on κThe strongest bound on κ3232 　　 comes from comes from the τ→μη result.the τ→μη result.

Current DataCurrent Data

The correlation between the Higgs The correlation between the Higgs mediation and the gauge mediationmediation and the gauge mediation

For relatively low mFor relatively low mSUSY, SUSY, the Higgs mediated LFVthe Higgs mediated LFVis constrained by current data for the gauge mediated LFV.is constrained by current data for the gauge mediated LFV.

For mFor mSUSYSUSY > > 　　 O(1)TeV, the gauge mediation becomes O(1)TeV, the gauge mediation becomes suppressed, while the Higgs mediated LFV can be large. suppressed, while the Higgs mediated LFV can be large.

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

Gauge mediated LFVGauge mediated LFV is suppressedis suppressed,

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

Decoupling property of the Higgs LDecoupling property of the Higgs LFV coupling (κFV coupling (κij ij ))

Search for Higgs mediated τ- e & τ- μ mixinSearch for Higgs mediated τ- e & τ- μ mixing at future collidersg at future colliders

Tau’s rare decays at B factories.Tau’s rare decays at B factories.　　　　　　 τ→eππτ→eππ 　（　（ μππμππ ）） τ→eη τ→eη 　　　　 (μη)(μη)　　　　　　 τ→μe e (μμμ),τ→μe e (μμμ), 　…　… . .

In nearIn near future, τ rare decay searches may improve the uppefuture, τ rare decay searches may improve the upper limit by about 1 order of magnitude. r limit by about 1 order of magnitude.

We here discuss the other possibilities.We here discuss the other possibilities. The DIS process μThe DIS process μ Ｎ Ｎ (eN)→τ(eN)→τ Ｘ　Ｘ　 at a fixed tat a fixed t

arget experiment at a νfactory and a LC arget experiment at a νfactory and a LC

Search of the LFV Yukawa couplingSearch of the LFV Yukawa 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

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. DIS process DIS process ee Ｎ→Ｎ→ ττ ＸＸ process process

μ （e） τ

N

qq

h, H, A

X

A fixed target experiment option of ILCA fixed target experiment option of ILC

ILC ILC （（ former JLC, TESLA, NLCformer JLC, TESLA, NLC ））

A Linear ColliderA Linear Collider 　（　（ LCLC ））

collision

1st stage

2nd stage

Roadmap report JLC

Constraints on the new physics scale Constraints on the new physics scale via theτμcoupling from datavia theτμcoupling from data

Scalar coupling τ→μππ ΛScalar coupling τ→μππ Λ ～～ 2.6 TeV2.6 TeVPseudo scalar coupling τ→μη Pseudo scalar coupling τ→μη ～～ 12 TeV12 TeVVector τ→μρ Vector τ→μρ ～～ 1212 　　 TeVTeVPseudo vectorPseudo vector 　　　　 　　　　 τ→μπ τ→μπ 　 ～　 ～ 1111 　　TeVTeV 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

Black, Han, He, Sher, 2002Black, Han, He, Sher, 2002

The cross sectionThe cross sectionScalar coupling Scalar coupling ---several 10^(-1) fb---several 10^(-1) fb

In SUSY, In SUSY, scalar coupling = pseudo scalar scalar coupling = pseudo scalar

couplingcoupling10^(-4)-10^(-5) smaller than sc10^(-4)-10^(-5) smaller than scalar coupling boundalar coupling bound

CTEQ6LCTEQ6L

Enhancement of cross section in SUSYEnhancement of cross section in SUSY

CTEQ6L

Each sub-process Each sub-process e q →τq e q →τq is proportional to the down-type quaris proportional to the down-type quar

k masses.k masses.For the energy > 60 GeV, the total cFor the energy > 60 GeV, the total cross section ross section

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

e τ

N

q qh, H, A

X

Higgs mediated process

Contribution of the gauge boson mediation

e τ

N

q qγ ,Z

X

τ→eγτ→eγ 　　 results gives the upper bound results gives the upper bound on the tensor coupling, therefore on on the tensor coupling, therefore on the e N →τXthe e N →τX 　　 cross sectioncross section

Gauge coupling ⇒ 　 No bottom Yukawa enhancement

At high energy DIS e N →τX 　 process is more sensitive to the Higgs mediation than the gauge mediation.

Angular distribution

μL

τR

θ

Target

Lab-frame

Lab-frame

Higgs mediationHiggs mediation → → 　　 chirality flippedchirality flipped　→　（　→　（ 11 －－ cosθcosθCMCM ））

2

Energy distribution for each angleEnergy distribution for each angle From theFrom theμμLL beam, beam, ττRR is emitted to the backward direction du is emitted to the backward direction du

e to (1 e to (1 ー ー cosθcosθCMCM)) 　　 nature in CM frame. nature in CM frame.

In Lab-frame, tau is emitted forward direction with some PIn Lab-frame, tau is emitted forward direction with some PT.T.

EμEμ ＝＝ 50 GeV50 GeV EμEμ ＝＝ 100 GeV100 GeV EμEμ ＝＝ 500 GeV500 GeV

2

ExperimentsExperiments

Near futureNear future CERN μbeam (200GeV)CERN μbeam (200GeV)

SLAC LC (50GeV)SLAC LC (50GeV)

FutureFuture Nutrino Factory, muon colliderNutrino Factory, muon collider

ILC fixed targed optionILC fixed targed option

Target: Target: muon beam 100g/cm^2muon beam 100g/cm^2

electrom beam 10g/cm^2electrom beam 10g/cm^2

Muon beam Muon beam

SignalSignal# of tau for L =10^20 muons # of tau for L =10^20 muons

|κ32|^2=0.3×10^(-6):|κ32|^2=0.3×10^(-6): EμEμ ＝＝ 50 GeV 50 GeV 　　　 　　　 100×ρ[g/cm^2]100×ρ[g/cm^2] 　　　　 τ’sτ’s 　　　　　　　　　　　　　　　　 100 GeV 1000 100 GeV 1000 500 GeV 50000 500 GeV 50000 　　　　

Hadronic products Hadronic products τ→πτ→π 、、 ρ, aρ, a1, 1, …… ＋　＋　 missingsmissings

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

ττRR 　⇒　　⇒　 backward νbackward νLL 　　 + forward π,ρ+ forward π,ρ 、…、… ..

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

τ R ν L π

Bullock, Hagiwara, MartinBullock, Hagiwara, Martin

BackgroundsBackgroundsHard hadrons from the target (N) should not be sHard hadrons from the target (N) should not be so serious, and smaller for higher energies of the o serious, and smaller for higher energies of the initial muon beam.initial muon beam.

Hard muons from DIS μN→Hard muons from DIS μN→μμX may be a fake sigX may be a fake signal. nal. Rate of mis-ID Rate of mis-ID 　　　 　　　　 　 [machine dependen[machine dependen

t]t] Emitted to forwad direction without large PEmitted to forwad direction without large PT T due to due to

Ratherford scattering Ratherford scattering 1/sin^4(θc1/sin^4(θcMM/2) /2) Energy cutsEnergy cuts

Realistic Monte Carlo simulation is necessary to Realistic Monte Carlo simulation is necessary to see the feasibilitysee the feasibility

4

SignalSignal

BackgroundsBackgrounds

usual DISusual DIS

Higgs boson mediationHiggs boson mediation

photon mediationphoton mediation

Different distributionDifferent distribution 　　　　 ⇒　　　　　 ⇒　 BG reduction by EBG reduction by Eττ, θ, θττ 　　 cuts cuts

Monte Carlo SimulationMonte Carlo Simulation

500GeV muon beam500GeV muon beamGenerator: Signal Modified LQGENEP Generator: Signal Modified LQGENEP

(leptoquark generator) (leptoquark generator)

Bellagamba et alBellagamba et al Background LEPTO γBackground LEPTO γ ＤＩＳＤＩＳ　　　　　　　　　　　　　　　　　　　　 Q^2>1.69GeV^2,σ=0.17μQ^2>1.69GeV^2,σ=0.17μ

ｂｂ MC_truth level analysisMC_truth level analysis

Work in progressWork in progress

Takai

Eπ ＞ 50GeV, θπ ＞ 0.025rad⊿μ 　 0.01rad

Hadrons from μN→τX 　 and backgrounds

Scattering angle ofμis small, it would be difficult to tag background events for reduction

Electron beamElectron beam

Number of taus Number of taus 　 　 EeEe ＝＝ 250 GeV, 250 GeV, L =10^34 /cm^2/s, ⇒L =10^34 /cm^2/s, ⇒ 　　 10^22 electrons10^22 electrons In a SUSY model with |κIn a SUSY model with |κ3131 |^2=0.3×10^(-6): |^2=0.3×10^(-6): σ=10^(-3) fbσ=10^(-3) fb

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

Naively, non-observation of the high energy muons from tNaively, non-observation of the high energy muons from the tau of the e N → τ X process may improve the current he tau of the e N → τ X process may improve the current upper limit on the e-τ-Φcoupling^2upper limit on the e-τ-Φcoupling^2 by around 4 orders of by around 4 orders of magnitudemagnitude

Signal/BackgroundsSignal/BackgroundsSignal: μ from τ in e N→τXSignal: μ from τ in e N→τXBackgrounds: Backgrounds: Pion punch-throughPion punch-through Muons from Pion decay-in-flightMuons from Pion decay-in-flight Muon from the muon pair production Muon from the muon pair production

Monte Carlo SimulationMonte Carlo Simulation 50GeV electron beam50GeV electron beam Event Generator Signal: modified LQGENEPEvent Generator Signal: modified LQGENEP Background: γBackground: γ ＤＩＳ　　　ＤＩＳ　　　 σ=0.04μσ=0.04μ ｂｂ BG absorber, simulation for the pass through BG absorber, simulation for the pass through Propability of e, π, μPropability of e, π, μ 　　 by using GEANTby using GEANT

High energy muon from tau is a signalHigh energy muon from tau is a signalGeometry (picture) ex) target ρ=10g/cm^2Geometry (picture) ex) target ρ=10g/cm^2

BackgroundsBackgrounds Pion punch-throughPion punch-through Muons from Pion decay-in-flightMuons from Pion decay-in-flight Muons from the muon pair production Muons from the muon pair production …………. .

e

μτ

Hadron absorber

Muon spectrometer(momentum measurement)

(water) (iron)

eelemag shower

π

Monte Carlo simulation by using GEANTMonte Carlo simulation by using GEANT

10cm 6-10m

targetdump

Summary Summary We discussed LFV via DIS processes We discussed LFV via DIS processes μμ Ｎ　（Ｎ　（ e Ne N ） →） → τXτX using high ener using high energy muon and electron beams and a fixed target.gy muon and electron beams and a fixed target.For E > 60 GeV, the cross section is enhanced due to the sub-process of HiFor E > 60 GeV, the cross section is enhanced due to the sub-process of Higgs mediation with sea b-quarksggs mediation with sea b-quarksDIS DIS μN→τX μN→τX by the intense high energy muon beam.by the intense high energy muon beam.

In the SUSY model, 100-10000 tau leptons can be produced for Eμ=50-500 GeIn the SUSY model, 100-10000 tau leptons can be produced for Eμ=50-500 GeV.V.

No signal in this process can improve the present limit on the Higgs LFV coupling No signal in this process can improve the present limit on the Higgs LFV coupling by 10^2 – 10^4. by 10^2 – 10^4.

Theτ is emitted to forward direction with ETheτ is emitted to forward direction with ETT The signal is The signal is hard hadronshard hadrons from τ→πν from τ→πν 、、 ρν,ρν, 　　 aa11ν, .... ,which go along the τdireν, .... ,which go along the τdire

ction.ction. Main background: mis-ID of μ in μN→μX….Main background: mis-ID of μ in μN→μX….

DIS processDIS process e N →τX : e N →τX : At a LC with EAt a LC with Ecmcm=500GeV σ⇒=500GeV σ⇒ ＝＝ 10^(-3) fb10^(-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 (high-energy muons) Non-observation of the signal (high-energy muons) would improve the current limit by 10^4. would improve the current limit by 10^4. 　　　　

Realistic simulation: work in progress.Realistic simulation: work in progress.