abriefreviewofleptonflavorviolationattheilcjillana/redilc2011.pdf · 2011. 5. 18. ·...
TRANSCRIPT
A brief review of Lepton Flavor Violation at the ILC
José I. Illana
CAFPE, U. Granada
1. Motivation
2. Lepton flavor violating processes
3. Lepton Flavor Violation from BSM Physics
4. Probing LFV at the ILC
José I. Illana (ugr) IV jornadas sobre la participación española en futuros aceleradores lineales, Granada, May 2011 1
Motivation
• Evidence of LFV: neutrinos oscillate
⇒ Neutrinos have a (small) mass and mix:
νLα≡ Uαiνi α = e, µ, τ i = 1, 2, 3
⇒ LFV in the charged sector: negligible (one loop, GIM suppressed) in the SM
ℓα → ℓβ :
∣
∣
∣
∣
∣
α
π ∑i
U ∗αiUβi
m2νi
M2W
∣
∣
∣
∣
∣
2
∼∣
∣
∣
∣
∣
α
πsin 2θ
∆m2ν
M2W
∣
∣
∣
∣
∣
2
∼ 10−54
• Opportunity for New Physics [m2νi/M2
W → f (m2Fi/Λ2
NP)]
– Most NP models suffer the flavor problem: new sources of flavor mixing
– Lepton sector is more clean
– Examples: SUSY, Little Higgs, . . .
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 2
LFV processes
• Where to look for LFV?
– Rare lepton decays: [µ: MEGA/MEG, SINDRUM (PSI) | τ: Belle, BaBar, LHC]
– radiative (ℓj → ℓiγ),
– leptonic (ℓj → ℓiℓkℓk, ℓj → ℓiℓi ℓk),
– semileptonic (τ → µη, τ → µρ, τ → µππ, . . . )
– µ − e conversion in nuclei [SINDRUM2]
– Decays of other standard particles:
– Z → ℓiℓj [. . . , LEP, GigaZ]
– H → ℓiℓj [. . . , LHC, ILC]
– D0 → ℓiℓj, B → µe, . . .
– Decays of non-standard particles: [LHC, ILC]
e.g. charged sleptons, sneutrinos, charginos, neutralinos
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 3
LFV processes
• Present and future limits:
LFV process Present best UL (90% CL) Future sensitivity
B(µ → eγ) 1.2× 10−11 [MEGA 1999]
2.8× 10−11 [MEG 2010] 10−13 − 10−14 [MEG]
B(τ → eγ) 3.3× 10−8 [BaBar 2010] 3× 10−9 [SuperB]
B(τ → µγ) 4.4× 10−8 [BaBar 2010] 2.4× 10−9 [SuperB]
B(µ → eee) 1× 10−12 [SINDRUM 1988] 10−13 − 10−14 [MEG]
B(τ → eee) 2.7× 10−8 [Belle 2010] 10−9 − 10−10 [SuperB]
B(τ → µµµ) 2.1× 10−8 [Belle 2010] 10−9 − 10−10 [SuperB]
B(τ → eµµ) 2.7× 10−8 [Belle 2010] 10−9 − 10−10 [SuperB]
B(τ → µee) 1.8× 10−8 [Belle 2010] 10−9 − 10−10 [SuperB]
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 4
LFV processes
• Present and future limits:
LFV process Present best UL (90% CL) Future sensitivity
R(µ → e, Au) 7.0× 10−13 [SINDRUM2 2004] 10−16 [Mu2E (Fermilab)]
R(µ → e, Al) 10−16 [COMET (J-PARC)]
R(µ → e, Ti) 4.3× 10−12 [SINDRUM2 2004] 10−18 [PRISM/PRIME (J-PARC)]
B(Z → µ±e∓) 1.7× 10−6 [LEP 1995] 2× 10−9 [GigaZ]
B(Z → τ±e∓) 9.8× 10−6 [LEP 1993] 6.5κ × 10−8 [GigaZ] κ ∈ [0.2, 1]
B(Z → τ±µ∓) 1.2× 10−5 [LEP 1997] 2.2κ × 10−8 [GigaZ]
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 5
LFV processes
• NP at 1-loop transitions:
∆F = 1 ∆F = 2
+
µ → eγ µ → eee
µ − e conversion in nuclei
τ → eγ τ → eee τ → eµµ τ → eeµ
τ → µγ τ → µµµ τ → µee τ → µµe
Z → µe, eµ
Z → τe, eτ ⇑ ⇑Z → τµ, µτ
H → µe, eµ
H → τe, eτ ⇑ ⇑H → τµ, µτ
e+e− → ℓiℓj , γγ → ℓi ℓj
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 6
Lepton Flavor Violation from BSM Physics
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 7
Lepton Flavor Violation Supersymmetry
• Origin of LFV: misalignment of fermion and sfermion mass matrices
– Charged sleptons: ℓLi and ℓRisuperpartners of ℓLi and ℓRi
M2ℓ=
m2LL m2†
LR
m2LR m2
RR
(m2LL)ij = (m2
L)ij +
[
m2ℓi+
(
−1
2+ sin2 θW
)
M2Z cos 2β
]
δij
(m2RR)ij = (m2
eR)ij + (m2
ℓi− M2
Z sin2 θW cos 2β)δij
(m2LR)ij = (Ae)ijv cos β/
√2−mℓiµ
∗ tan β δij
Slepton mass eigenstates:
Sℓ M2ℓSℓ
†= diag(m2
ℓX) X = 1, . . . , 6
ℓX = SℓXiℓLi + SℓX,i+3ℓRiX = 1, . . . , 6 i = 1, 2, 3
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 8
Lepton Flavor Violation Supersymmetry
• Origin of LFV: misalignment of fermion and sfermion mass matrices
– Sneutrinos: νLαsuperpartners of νLα
(M2ν)αβ = (m2
L)αβ +
1
2M2
Z cos 2β δαβ
Sneutrino mass eigenstates:
Sν M2ν Sν† = diag(m2
νX) X = 1, 2, 3
νX = SνXανLα = Sν
XαUαiνi X = 1, 2, 3 α = e, µ, τ i = 1, 2, 3
⇒ Off-diagonal terms are responsible for LFV
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 9
Lepton Flavor Violation Supersymmetry
• LFV vertices ig (cLiAX PL + cRiAX PR) where iAX label mass eigenstates
.
ℓi
χ0
A(χ−
A)
νX(ℓX)
ν†X ¯χ−Aℓi : c
L[C]iAX = −V∗
A1SνXαUαi
cR[C]iAX =
mℓi√2MW cos β
UA2SνXαUαi
ℓ†X ¯χ0Aℓi : c
L[N]iAX =
1√2(tan θWN∗
A1 + N∗A2) S
ℓXi −
mℓi√2MW cos β
N∗A3S
ℓX,i+3
cR[N]iAX = −
√2 tan θWNA1S
ℓX,i+3 −
mℓi√2MW cos β
NA3SℓXi
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 10
Lepton Flavor Violation Supersymmetry
• One-loop transitions: bubbles and triangles (∆F = 1) [µ → eγ]
[Z → eµ]
[Φ → eµ]
.
µ
e
νX(ℓX)
χ−
B(χ0
B)
χ−
A(χ0
A)
γ, Z
µ
e
χ−
A(χ0
A)
νY (ℓY )
νX(ℓX)
γ, Z
µ
e
e
νX(ℓX)
χ−
A(χ0
A)γ∗, Z
µ
e
νX(ℓX)
χ−
B(χ0
B)
χ−
A(χ0
A)
h,H,A
µ
e
χ−
A(χ0
A)
νY (ℓY )
νX(ℓX)
h,H,A
µ
e
e
νX(ℓX)
χ−
A(χ0
A)h,H,A
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 11
Lepton Flavor Violation Supersymmetry
• One-loop transitions: boxes (∆F = 1 and ∆F = 2)
ee
χ−A(χ
0A)
χ−B(χ
0B)
νY (ℓY )
µ e
νX(ℓX)
ee
νX(ℓX)
νY (ℓY )
χ−B(χ
0B)
µ e
χ−A(χ
0A)
[µ → eee]
eµ
χ−A(χ
0A)
χ−B(χ
0B)
νY (ℓY )
τ µ
νX(ℓX)
eµ
νX(ℓX)
νY (ℓY )
χ−B(χ
0B)
τ µ
χ−A(χ
0A)
[τ → µµe]
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 12
Lepton Flavor Violation Supersymmetry
• Tree level chain decays:
Production and decay of charged sleptons, sneutrinos, charginos and neutralinos
e+e− → ℓ+X ℓ−Y → τ±µ∓χ0
1χ01
νX νY → τ±µ∓χ+1 χ−
1
χ0Aχ0
B → τ±µ∓χ01χ0
1
χ+A χ−
B → τ±µ∓χ±1 χ∓
1
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 13
Lepton Flavor Violation Little Higgs
• The model(s)
– The Higgs is a pseudo-Goldstone boson of an approximate global symmetry
broken at a scale f ∼TeV
– The global symmetry (partly gauged) gets explicitly broken by gauge and
Yukawa interactions, giving the Higgs a mass and non-derivative couplings,
still preserving the cancellation of one-loop quadratic corrections
(collective breaking)
– This introduces extra fermions and gauge fields (and extra Higgses):
new source of flavor mixing
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 14
Lepton Flavor Violation Littlest Higgs with T Parity
Assume the most popular model: Littlest Higgs with T Parity
The SM spectrum (T-even) is supplemented with:
⋆ T-odd fermion SU(2)L doublets lHL ≡ (νHL, ℓHL) and lHR ≡ (νHR, ℓHR)
⋆ T-odd gauge bosons WH, AH, ZH
• Origin of LFV: missalignment of T-even and T-odd fermion mass matrices
LYHgenerates heavy masses inducing heavy-light mixings:
√2 f l
0HLYHl
0HR
diag−→ l0HL = VH lHL l0HR = UHlHR
⇒ LLHT ∼ g l0HL/G
†Hl
0L = g (νHLV
†H , ℓHLV
†H) /G
†H
U νL
ℓL
V†HU ≡ VHν
V†H ≡ VHℓ
⇒ ViαHℓ νiHL/W
†Hℓ
αL CC and Viα
Hℓ ℓiHL{/AH, /ZH}ℓα
L NC
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 15
Lepton Flavor Violation Littlest Higgs with T Parity
• LFV vertices ig (gL PL + gR PR)
.
ℓα
νiH(ℓ
iH)
WH(AH , ZH)
W+H νiHℓ
α AH ℓiHℓ
α ZH ℓiHℓ
α
gL1√2sW
ViαHℓ
(
1
10cW− xH
2sW
v2
f 2
)
ViαHℓ −
(
1
2sW+
xH10cW
v2
f 2
)
ViαHℓ
gR 0 0 0
⇑Identical to SM with heavy neutrinos, replacing VHℓ by U and WH by W
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 16
Lepton Flavor Violation Littlest Higgs with T Parity
• One-loop transitions: bubbles and triangles (∆F = 1) [µ → eγ]
[Z → eµ]
[Φ → eµ]
.
µ
e
WH(AH , ZH)
νiH(ℓ
iH)
νjH(ℓ
jH)
γ, Z
µ
e
νiH(ℓ
iH)
WH(AH , ZH)
WH(AH , ZH)
γ, Z
µ
e
e
WH(AH , ZH)
νiH(ℓ
iH)γ∗, Z
µ
e
WH(AH , ZH)
νiH(ℓ
iH)
νjH(ℓ
jH)
h,H,A
µ
e
νiH(ℓ
iH)
WH(AH , ZH)
WH(AH , ZH)
h,H,A
µ
e
e
WH(AH , ZH)
νiH(ℓ
iH)h,H,A
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 17
Lepton Flavor Violation Littlest Higgs with T Parity
• One-loop transitions: boxes (∆F = 1 and ∆F = 2)
ee
νiH(ℓiH)
νiH(ℓjH)
WH(AH , ZH)
µ e
WH(AH , ZH)
ee
νiH(ℓiH)νiH(ℓ
jH)
WH(AH , ZH)µ e
WH(AH , ZH)
[µ → eee]
eµ
νiH(ℓiH)
νiH(ℓjH)
WH(AH , ZH)
τ µ
WH(AH , ZH)
eµ
νiH(ℓiH)νiH(ℓ
jH)
WH(AH , ZH)τ µ
WH(AH , ZH)
[τ → µµe]
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 18
Probing LFV at the ILC
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 19
Probing LFV at the ILC Supersymmetry
• Guchait, Kalinowski, Roy [EPJC 21 (2001) 163]
Deppisch, Päs, Redelbach, Rückl, Shimizu [PRD 69 (2004) 054014]
Production and decay of sleptons, charginos and neutralinos (SUSY seesaw)
e+e− → ℓ+i ℓ−j → ℓ+α ℓ
−β χ0
1χ01 Signal = ℓ+α ℓ
−β + 6ET
νiνcj → ℓ+α ℓ
−β χ+
1 χ−1 ℓ+α ℓ
−β + 4jets+ 6ET
χ0aχ
0b → ℓ+α ℓ
−β χ0
1χ01 ℓ+α ℓ
−β + ℓ+ 2jets+ 6ET
χ+a χ−
b → ℓ+α ℓ−β χ±
1 χ∓1 (purely leptonic overwhelmed by bkgd)
(Background from e+e− → ttg reduced by appropriate cuts)
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 20
Probing LFV at the ILC Supersymmetry
• Hohenwater-Sodek, Kernreiter [JHEP 06 (2007) 071]
Effects of LFV on chargino production
– σ(e+e− → χ+a χ−
b ) at√s = 500 GeV and assuming beam polarization enhanced
up to a factor 2 within limits from τ → µγ due to LFV νX exchange (t-channel)
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 21
Probing LFV at the ILC Supersymmetry
• Ibarra, Roy [JHEP 05 (2007) 059]
Sensitivity of future e+e and e−e− colliders to LFV in scenarios with a stau NLSP
– Signal: two heavily ionizing tracks due to the long-lived staus accompanied by
two (LFV in production) or four (LFV in selectron decay) charged leptons
– Sensitivity (better e−e− than e+e−) competitive with the present and projected
sensitivities to LFV from rare tau decays, although not from µ → eγ
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 22
Probing LFV at the ILC Supersymmetry
• Kanemura et al [PLB 599 (2004) 2004]
Search for LFV in Higgs boson decay at a Linear Collider
e+e− → Z∗ → Zh0 → Zτ±µ∓
– After taking appropriate kinematic cuts, the number of background events is
considerably reduced, so that the signal can be visible when the branching
ratio of h0 → τ±µ∓ is larger than about 10−4 (10−3 in the 2HDM)
(Energy tuned to optimize Higgsstrahlung (√s = MZ + 2mh) and L = 1 ab−1)
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 23
Probing LFV at the ILC Supersymmetry
• Canoni, Panella, Kolb [LCWS 04]
Majorana neutrino and light sneutrino contributions to e−e− → µe, τe
Majorana ν <∼ 2− 3 TeV feasible, and σ ∼ 10−2 fb in SUSY reachable (polariz.)
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 24
Probing LFV at the ILC Supersymmetry
• JI, Masip [PRD 67 (2003) 035004]
LFV Z decays from SUSY
– GigaZ: Z → µe invisible due to µ → eγ constraint, but Z → µe at reach
Probing LFV at the ILC Heavy neutrinos
• JI, Riemann [PRD 63 (2001) 053004]
LFV Z decays from heavy neutrinos
– GigaZ: Z → ℓ±i ℓ∓j visible if heavy neutrinos are lighter than the TeV and mix
enough to light neutrinos
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 25
Probing LFV at the ILC Little Higgs
• Wei Ma, Chong-Xing Yue, Jiao Zhang, and Yan-Bin Sun [1010.0052]
Jinzhong Han, Xuelei Wang, Bingfang Yang [1101.3598]
e+e− → ℓ±i ℓ∓j and γγ → ℓ±i ℓ
∓j and in the LHT at the ILC
(mediated by LFV in γℓiℓj and Zℓiℓj and constrained by rare lepton decays)
– σ(e+e− → ℓ±i ℓ∓j ) can reach several fb
– σ(γγ → ℓ±i ℓ∓j ) can reach 0.1− 1 fb
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 26
Probing LFV at the ILC Little Higgs
• Chong-Xing Yue and Shuang Zhao [EPJ C50 (2007) 897]
Signals of the LHT doubly charged scalar triplet Φ from e+e− → ℓ±i ℓ∓j
(mediated by the tree level subprocess e−e− → Φ−− → ℓ−i ℓ−j )
– At√s = 500 GeV the LFV contribution is small
but Φ can give a significant contribution to e+e− → ℓ±i ℓ∓i
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 27
Probing LFV at the ILC Model independent
• Ferreira, Guedes, Santos [PRD 75 (2007) 055015]
Different LFV decay widths and the cross sections σ(e+e− → ℓ±i ℓ∓j ) are compared
using dimension-six effective operators
– ILC (√s = 1 TeV, L = 1 ab−1) explores Λ <∼ 100 TeV.
– Limits from Z → ℓ±i ℓ∓j allow enough events in e+e− → ℓ±i ℓ
∓j even from future
bounds, but if the four-fermion coupling is dominant B(µ → eee) < 10−12
already kills e+e− → e±µ∓
– σ(γγ → ℓ±i ℓ∓j ) exceedingly small from constraints on ℓj → ℓiγ
– GigaZ will improve the limits on the LFV Z decays but is insensitive to the
four-fermion operators
José I. Illana (ugr) A brief review on Lepton Flavor Violation at the ILC 28