Shinya Kanemura (Osaka Univ.)

Shinya KANEMURA Shinya KANEMURA 11

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

Discovery of Higgs and SUSY to Pioneer Particle Physics in the Discovery of Higgs and SUSY to Pioneer Particle Physics in the 2121ststCentury@Univ. of Tokyo, Nov 24-25. 2005Century@Univ. of Tokyo, Nov 24-25. 2005

Yoshitaka Kuno Yoshitaka Kuno (Osaka), (Osaka), Toshihiko Ota Toshihiko Ota (TU Munich)(TU Munich)

Masahiro Kuze, Tomoyasu TakaiMasahiro Kuze, Tomoyasu Takai (Tokyo Inst. Tech.) (Tokyo Inst. Tech.)

A Study on muon (electron) to tau cA Study on muon (electron) to tau conversion in Deep Inelastic Scatteringonversion in Deep Inelastic Scattering

22

Shinya KANEMURA Shinya KANEMURA

ContentsContents

Introduction Introduction Physics Motivation Physics Motivation LFV Yukawa coupling (Higgs mediated LFV)LFV Yukawa coupling (Higgs mediated LFV) Tau associated LFV processTau associated LFV process

LFV Deep Inelastic Scattering processes LFV Deep Inelastic Scattering processes Cross sections and general featuresCross sections and general features Muon beamMuon beam Electron beamElectron beam

Summary Summary

33


IntroductionIntroduction

44


Physics MotivationPhysics Motivation

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

Neutrino oscillation may indicate the possibility of LFV iNeutrino oscillation may indicate the possibility of LFV in the charged lepton sector.n 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, Moroi, Tobe, YamaguchiHisano, Moroi, Tobe, Yamaguchi Zee model for the Zee model for the mass mass ZeeZee Models of dynamical flavor violation Models of dynamical flavor violation Hill et al.Hill et al. … …. .

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LFV in SUSYLFV in SUSYSlepton mixing induces LFV at one loop.Slepton mixing induces LFV at one loop.

Gauge boson mediation

Higgs boson mediation

Form factors: A1L,R

ij, A2L,R

ij , …

Form factors: κij

Kitano, Koike Okada

Babu, KoldaDedes, Ellis, Raidal

Bortzmati, MasieroHisano, Moroi, Tobe, Yamaguchi

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Decoupling property of LFVDecoupling property of LFV

Gauge boson mediation :Gauge boson mediation :

Higgs boson mediation : Higgs boson mediation : LFVLFV Yukawa couplingYukawa coupling

Not always decouple in the large MNot always decouple in the large MSUSYSUSY limit limit

Decouple in the large MDecouple in the large MSUSYSUSY limit limit

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LFV in SUSY scenarioLFV in SUSY scenario

It is known that sizable LFV can be induced at loop due tIt is known that sizable LFV can be induced at loop due to slepton mixing. o slepton mixing.

Up to now, however, no evidence for LFV has been obseUp to now, however, no evidence for LFV has been observed at experiments. rved at experiments. μ→eμ→e, μ→eee, …., μ→eee, ….

This situation may be explained by large MThis situation may be explained by large MSUSYSUSY, so that th, so that the SUSY effects decouple.e SUSY effects decouple.

Even in such a case, we may be able to search LFV Even in such a case, we may be able to search LFV via the Higgs boson mediation, which does not via the Higgs boson mediation, which does not necessarily decouple for a large Mnecessarily decouple for a large MSUSY SUSY limit.limit.

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TTau-associated LFV au-associated LFV

The tau associated LFV is interesting for Higgs mediatioThe tau associated LFV is interesting for Higgs mediatio

n, which is proportional to the Yukawa coupling n, which is proportional to the Yukawa coupling

(Different behavior from μe mixing case.)(Different behavior from μe mixing case.) Tau associated LFV is less constrained by current data as Tau associated LFV is less constrained by current data as

compared to theμ⇔e mixingcompared to theμ⇔e mixing → e 1.2 ×10 ＾（－ 11 ）　　　　　　→ 3e 　　　　　　　 1.1 ×10 ＾（－ 12 ）Ti → e Ti 　　　　 6.1 ×10 ＾（－13 ）→ 3.1 ×10 ＾（－ 7 ）→ (1.4-3.1) ×10 ＾（－7 ）→ 　　　　　　 3.4 ×10 ＾（－ 7 ）　

⇔ ⇔　 e

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Experimental bounds on LFV Experimental bounds on LFV parametersparameters

For 31 31 (tau-e mixing)(tau-e mixing) , similar bound is obtained from →→ee

The strongest bound on The strongest bound on (tau-mu mixing) comes from (tau-mu mixing) comes from the , τ→ the , τ→ results. results.

The strongest bound on (AThe strongest bound on (A22L,RL,R))ijij comes from comes from

the the →→ee→→ee→→ results. results.

Higgs boson mediation

Gauge boson mediation

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Search for Higgs mediated τ- e & τ- μ mixing at Search for Higgs mediated τ- e & τ- μ mixing at future collidersfuture 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 upper limit future, τ rare decay searches may improve the upper limit by about 1 order of magnitude. by about 1 order of magnitude.

We here discuss the alternative possibilities.We here discuss the alternative possibilities. The DIS process μThe DIS process μ ＮＮ (eN)→τ(eN)→τ Ｘ　Ｘ　 at a fixed target at a fixed target

experiment at a neutrino factory and a LC experiment at a neutrino factory and a LC

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LFV Deep Inelastic ScatteringLFV Deep Inelastic Scattering

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Deep inelastic scattering LFV process Deep inelastic scattering LFV process

DISDIS μ μ Ｎ→Ｎ→ ττ ＸＸ process: process: At a future neutrino factory At a future neutrino factory (or a muon collider) , about (or a muon collider) , about 10102020 muons/year of energy 50 GeV muons/year of energy 50 GeV (or 100-500 GeV) can be available. (or 100-500 GeV) can be available.

DIS process DIS process ee Ｎ→Ｎ→ ττ ＸＸ process: process: At a LC At a LC (E(Ecmcm=500GeV (or 1TeV), =500GeV (or 1TeV),

L=10L=103434/cm/cm22/s)/s) 10102222 electrons/year of electrons/year of 250GeV (or 500GeV) electrons available. 250GeV (or 500GeV) electrons available.

μ （e） τ

N

qq

h, H, A

X

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

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The cross section in SUSYThe cross section in SUSY

CTEQ6L

Sub-process Sub-process ee-- q →τ q →τ- - qq is proportio is proportional to nal to

the the down-typedown-type quark massquark mass..Probability for the b-quark is larger foProbability for the b-quark is larger for higher energies.r higher energies.For For Ee > 60 GeVEe > 60 GeV, ,

the total cross section is enhanced the total cross section is enhanced due to the due to the b-quark sub-processb-quark sub-process Ee Ee ＝＝ 50 GeV 1050 GeV 10-5 -5 fbfb

100 GeV100 GeV 　　 1010-4 -4 fb fb 250 GeV250 GeV 　　 1010-3-3fbfb

e τ

N

qq

h, H, A

X

Higgs mediated LFV process

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Angular distribution

μL

τR

θ

Target

Lab-frame

Lab-frame

Higgs mediationHiggs mediation → → 　　 chirality flippedchirality flipped　→　（　→　（ 11 －－ coscoscmcm ）） 22

From theFrom the μ μLL ( (eeLL) beam, ) beam, ττRR is emitted to the backward direction due is emitted to the backward direction due to (1 to (1 ーー cosθcosθCMCM))22 　　 nature in the CM frame. nature in the CM frame.

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

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Energy distribution for each angleEnergy distribution for each angle From theFrom the e eLL beam, beam, RR is emitted is emitted 　　　　 to the backward direction due to to the backward direction due to 　　　　 (1 (1 ーー coscos))22 nature in the CM frame. nature in the CM frame. In Lab-frame, In Lab-frame, tau is emitted forward 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

μ L

τ R

θ

Target

Lab-frame

EE ＝＝ 50 GeV50 GeV

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Contribution of the gauge boson mediation

e τ

N

qq

γ ,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 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.

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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

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Muon beamMuon beam

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SignalSignal# of tau for L =10# of tau for L =102020 muons muons

|κ32||κ32|22=0.3×10=0.3×10-6-6:: EμEμ ＝＝ 50 GeV 50 GeV 　　　　　　 100×ρ[g/cm100×ρ[g/cm22]] 　　　　 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 parent τ’sHard hadrons emitted into the same direction as the parent τ’s ττRR 　⇒　　⇒　 backward νbackward νLL 　　 + forward π,ρ+ forward π,ρ 、…、…

τ R ν L π

Bullock, Hagiwara, MartinBullock, Hagiwara, Martin

2020


BackgroundsBackgrounds

Hard muons from DIS μN→Hard muons from DIS μN→μμX may be a fake signal. X may be a fake signal. Rate of mis-ID Rate of mis-ID 　　　　　　　　 [machine dependent][machine dependent] Emitted to forwad direction without large PEmitted to forwad direction without large PT T due to Rathedue to Rathe

rford scattering rford scattering

1/sin1/sin44(θc(θcMM/2) /2)

Energy cuts Hard hadrons from the target (N )Energy cuts Hard hadrons from the target (N )

Realistic Monte Carlo simulation is necessary to see tRealistic Monte Carlo simulation is necessary to see the feasibilityhe feasibility

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SignalSignal

BackgroundsBackgrounds

Higgs boson mediationHiggs boson mediation

photon mediationphoton mediation

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

2222


Monte Carlo SimulationMonte Carlo Simulation

500GeV muon beam500GeV muon beam

Generator: Signal Modified LQGENEP Generator: Signal Modified LQGENEP

(leptoquark generator) (leptoquark generator)

Bellagamba et alBellagamba et al

Background LEPTO γBackground LEPTO γ ＤＩＳＤＩＳ　　　　　　　　　　　　　　　　　　　　 QQ22>1.69GeV>1.69GeV22,σ=0.17μ,σ=0.17μ ｂｂ

MC_truth level analysisMC_truth level analysisWork in progressWork in progress

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Electron beamElectron beam

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Number of produced taus Number of produced taus 　　 EeEe ＝＝ 250 GeV, 250 GeV, L =10L =103434 /cm /cm22/s, ⇒/s, ⇒ 　　 10102222 electrons electrons In a SUSY model with |κIn a SUSY model with |κ3131 |^2=0.3×10 |^2=0.3×10-6-6 　　 : : σ= 10σ= 10-3-3 fb fb 　　 = 6 x 10= 6 x 10-42 -42 cmcm22

NNττ== 　　 ρ Nρ NAA 　　 NNee 　　 σσ

　　 101055 of τleptons are produced 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 froNaively, non-observation of the high energy muons from the tau of the e N → τ X process may improve the cm the tau of the e N → τ X process may improve the current upper limit on the eτΦ couplingurrent upper limit on the eτΦ coupling22 by around 4 ord by around 4 orders of magnitude.ers of magnitude.

NA=6 x 1023

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Signal/BackgroundsSignal/Backgrounds

Signal: for example, μ from τ in e N→τXSignal: for example, μ from τ in e N→τX

Backgrounds: 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 250GeV-1.5 TeV electron beam250GeV-1.5 TeV electron beam Event Generator Signal: modified LQGENEPEvent Generator Signal: modified LQGENEP

Background: LEPTO γBackground: LEPTO γ ＤＩＳ　　ＤＩＳ　　 BG absorber, simulation for the pass through probabilBG absorber, simulation for the pass through probabil

ity of e, π, μity of e, π, μ 　　 by using GEANTby using GEANT

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High energy muon from tau can be High energy muon from tau can be a signala signalGeometry (picture) ex) target ρ=10g/cmGeometry (picture) ex) target ρ=10g/cm22

BackgroundsBackgrounds Muon from Muon from DIS DIS Muon from pair paroduction (dilepton)Muon from pair paroduction (dilepton) Pion punch-throughPion punch-through Muons from Pion decay-in-flightMuons from Pion decay-in-flight …………. .

e

μ

τ

Hadron absorber

Muon spectrometer(momentum measurement)

(water)(iron)

eelemag shower

π

Monte Carlo simulation LQGENEP, LEPTO, GEANT4Monte Carlo simulation LQGENEP, LEPTO, GEANT4

10cm 6-10m

targetdump

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μτ

targetMuon spectrometer(momentum measurement)

e

μ

r

rgap

Cuts: Eμ, r, rgap, Q2

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MC analysis (under study) MC analysis (under study) (LQGENEP, LEPTO, GEANT4)(LQGENEP, LEPTO, GEANT4)

LC Ee=250GeV, 500GeV, 1TeV, 1.5TeV LC Ee=250GeV, 500GeV, 1TeV, 1.5TeV L=10L=102222 electrons per year electrons per year

SignalSignal 　　　　　　 muons from LFV DISmuons from LFV DIS 　　 e N →τXe N →τX 　　 with τ→μννwith τ→μνν 　　 10104-54-5 muons/year muons/year

Background Background 　　 muons from γDIS, etc muons from γDIS, etc Kinematic cuts Kinematic cuts

1. E1. E (muon energy cut) (muon energy cut)

2. P2. PT T or or r (angle cut)r (angle cut) 3. rgap (extrapolate back cut)3. rgap (extrapolate back cut) 4. Q4. Q2 2 cut: Qcut: Q22>10GeV>10GeV22

But with 10But with 1088 MC events, MC events, the number of the MC background event is reduced to 1. the number of the MC background event is reduced to 1.

Simulation with more MC events (10Simulation with more MC events (109-109-10) is ) is work in progresswork in progress..

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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!

Takai

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

Takai

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Summary Summary We discussed LFV via DIS processes We discussed LFV via DIS processes μμ Ｎ　（Ｎ　（ e Ne N ） →） → τXτX using high energy mu using high energy muon and electron beams and a fixed target.on and electron beams and a fixed target.For E > 60 GeV, the cross section is enhanced due to the sub-process of Higgs mediFor E > 60 GeV, the cross section is enhanced due to the sub-process of Higgs mediation with sea b-quarksation 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 GeV.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 10No signal in this process can improve the present limit on the Higgs LFV coupling by 1022

– 10– 1044. . Theτ is emitted to forward direction with PTheτ is emitted to forward direction with PTT The signal is The signal is hard hadronshard hadrons from τ→πν from τ→πν 、、 ρν,ρν, 　　 aa11ν, .... , which go along the τdirection.ν, .... , which go along the τdirection. 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⇒ ＝＝ 1010-3-3 fb fb

L=10L=103434/cm/cm22/s 10⇒/s 10⇒ 2222 electrons available electrons available 101055 of taus are produced of taus are produced for ρ=10 g/cm for ρ=10 g/cm22

Non-observation of the signal (high-energy muons) Non-observation of the signal (high-energy muons) would improve the current limit by 10would improve the current limit by 1044. . 　　　　

Realistic simulation: work in progress (collecting more MC events).Realistic simulation: work in progress (collecting more MC events).

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Takai

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

Slepton mixing induces both the Higgs mediated LFV Slepton mixing induces both the Higgs mediated LFV and the gauge mediation. and the gauge mediation.

The off-diagonal elements in the slepton mass matrix The off-diagonal elements in the slepton mass matrix can be induced at low energies, even when it is diagocan be induced at low energies, even when it is diagonal at the GUT scale.nal at the GUT scale.

RGERGE 　　

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The gauge boson mediation v.s. The gauge boson mediation v.s. the Higgs mediationthe Higgs mediation

For relatively low mFor relatively low mSUSYSUSY, , 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.

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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 　　　 Work in progress

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mmSUSY SUSY ～　～　 O(1) TeVO(1) TeV

Consider that mConsider that mSUSYSUSY is as large as O(1) TeV with is as large as O(1) TeV with a fixed value of |μ|/ma 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 easily as large as the current expcan be easily as large as the current experimental limiterimental limit. . Babu,Kolda; Babu,Kolda; Brignole, RossiBrignole, Rossi

Prediction on LFV YukawaPrediction on LFV Yukawa

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Current Datafor rare tau decays

Shinya Kanemura (Osaka Univ.)

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