Shinya Kanemura

1
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 21stCentury_at_Univ. of Tokyo, Nov
24-25. 2005
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

3
Introduction
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.
• .

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 ?ij
6
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
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.
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• 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

t ? m t ? e
m ? e g 1.2 10(-11)
m?3e 1.1 10(-12) m Ti ? e Ti
6.1 10(-13) t ? m g 3.1
10(-7) t ? 3 m (1.4-3.1)
10(-7) t ? m h 3.4 10(-7)
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Experimental bounds on LFV parameters
Gauge boson mediation
The strongest bound on (A2L,R)ij comes from
the µ ? e ?, t? e ?, t? µ? results.
Higgs boson mediation
The strongest bound on k32 (tau-mu mixing) comes
from the , t? m h results.
For k31 (tau-e mixing) , similar bound is
obtained from t? e h .
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Search for Higgs mediated t- e t- µ mixing at
future colliders

• Taus rare decays at B factories.
• t?epp (µpp)
• t?e? (µ?)
• t?µe e (µµµ), .
• In near future, t 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)?tX at a fixed target
  experiment at a neutrino factory and a LC

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LFV Deep Inelastic Scattering
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Deep inelastic scattering LFV process

• DIS µN?tX process
• 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?tX process
• At a LC (Ecm500GeV (or 1TeV),
• L1034/cm2/s) 1022 electrons/year of
• 250GeV (or 500GeV) electrons available.

A fixed target experiment option of a LC
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The cross section in SUSY
Higgs mediated LFV process
CTEQ6L

• Sub-process e- q ?t- q is proportional to
• the down-type quark mass.
• Probability for the b-quark is larger for higher
  energies.
• For Ee gt 60 GeV,
• the total cross section is enhanced
• due to the b-quark sub-process
• Ee 50 GeV 10-5 fb
• 100 GeV 10-4 fb
• 250 GeV 10-3fb

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Angular distribution
Higgs mediation ? chirality flipped ?
(1-cosqcm)2
Lab-frame
tR
µL
?
Target
Lab-frame

• From the µL (eL) beam, tR is emitted to the
  backward direction due to (1 ? cos?CM)2 nature
  in the CM frame.
• In Lab-frame, tau is emitted forward direction
  with some PT.

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Energy distribution for each angle

• From the eL beam, tR is emitted
• to the backward direction due to
• (1 ? cosq)2 nature in the CM frame.
• In Lab-frame, tau is emitted forward
• direction but with large angle with a PT.

E500 GeV
E100 GeV
E50 GeV
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Contribution of the gauge boson mediation
t?e? results gives the upper bound on the
tensor coupling, therefore on the e N ?tX cross
section
Gauge mediated LFV ? No bottom Yukawa
enhancement
At high energy DIS e N ?tX process is more
sensitive to the Higgs mediation than the gauge
mediation.
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Experiments
Target muon beam 100g/cm2 electrom beam
10g/cm2

• Near future
• CERN µbeam (200GeV)
• SLAC LC (50GeV)
• Future
• Nutrino Factory, muon collider
• ILC fixed targed option

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Muon beam
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Signal

• of tau for L 1020 muons
• ?3220.310-6
• Eµ50 GeV 100?g/cm2 ts
• 100 GeV 1000
• 500 GeV 50000
• Hadronic products
• t?p??, a1, missings
• Hard hadrons emitted into the same direction as
  the parent ts
• tR ? backward ?L forward p,??

Bullock, Hagiwara, Martin
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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(?cM/2)
• Energy cuts Hard hadrons from the target (N )
• Realistic Monte Carlo simulation is necessary to
  see the feasibility

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Signal
Higgs boson mediation
Backgrounds
photon mediation
Different distribution ?BG reduction by Et, ?t
cuts
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Monte Carlo Simulation

• 500GeV muon beam
• Generator Signal Modified LQGENEP
• (leptoquark
  generator)
• 
  Bellagamba et al
• Background LEPTO ?DIS
• Q2gt1.69GeV2,s0.17µb
• MC_truth level analysis

Work in progress
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Electron beam
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• Number of produced taus
• Ee250 GeV,
• L 1034 /cm2/s, ? 1022 electrons
• In a SUSY model with ?31 20.310-6
• s 10-3 fb
  6 x 10-42 cm2
• Nt ? NA Ne s
• 105 of tleptons are produced for
• the target of ?10 g/cm2
• Naively, non-observation of the high energy
  muons from the tau of the e N ? t X process may
  improve the current upper limit on the etF
  coupling2 by around 4 orders of magnitude.

NA6 x 1023
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Signal/Backgrounds

• Signal for example, µ from t in e N?tX
• 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 ?DIS
• BG absorber, simulation for the pass through
  probability of e, p, µ by using GEANT

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• High energy muon from tau can be a signal
• Geometry (picture) ex) target ?10g/cm2
• Backgrounds
• Muon from g DIS
• Muon from pair paroduction (dilepton)
• Pion punch-through
• Muons from Pion decay-in-flight
• .

10cm
6-10m
µ
t
e
dump
Hadron absorber
(water)
target
(iron)
p
e
elemag shower
Muon spectrometer (momentum measurement)
Monte Carlo simulation LQGENEP, LEPTO,
GEANT4
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• Cuts Eµ, r, rgap, Q2

µ
t
r
e
µ
rgap
target
Muon spectrometer (momentum measurement)
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MC analysis (under study)
(LQGENEP, LEPTO, GEANT4)

• LC Ee250GeV, 500GeV, 1TeV, 1.5TeV
• L1022 electrons per year
• Signal muons from LFV DIS
• e N ?tX with t?µ??
• 104-5 muons/year
• Background muons from ?DIS, etc
• Kinematic cuts
• 1. Em (muon energy cut)
• 2. PT or r (angle cut)
• 3. rgap (extrapolate back cut)
• 4. Q2 cut Q2gt10GeV2
• 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.

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

• We discussed LFV via DIS processes µN (e N) ?tX
  using high energy muon and electron beams and a
  fixed target.
• For E gt 60 GeV, the cross section is enhanced due
  to the sub-process of Higgs mediation with sea
  b-quarks
• DIS µN?tX by the intense high energy muon beam.
• In the SUSY model, 100-10000 tau leptons can be
  produced for Eµ50-500 GeV.
• No signal in this process can improve the present
  limit on the Higgs LFV coupling by 102 104.
• Thet is emitted to forward direction with PT
• The signal is hard hadrons from t?p????, a1?,
  .... , which go along the tdirection.
• Main background mis-ID of µ in µN?µX.
• DIS process e N ?tX
• At a LC with Ecm500GeV ? s10-3 fb
• L1034/cm2/s ? 1022 electrons
  available
• 105 of taus are produced for
  ?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).

32
Takai
33
A source of slepton mixingin the MSSMRN

• 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

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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 gt O(1) TeV, the gauge mediation
becomes suppressed, while the Higgs mediated LFV
can be large.
35
Hadrons from µN?tX and backgrounds
Epgt50GeV, ?pgt0.025rad ?µ 0.01rad
Takai
Scattering angle ofµis small, it would be
difficult to tag background events for reduction
Work in progress
36
Prediction on LFV Yukawa
Consider that mSUSY is as large as O(1) TeV with
a fixed value of µ/mSUSY
Gauge mediated LFV is suppressed, while the
Higgs-LFV coupling ?ij can be easily as large as
the current experimental limit. Babu,Kolda
Brignole, Rossi

mSUSY O(1) TeV
37
Current Data for rare tau decays