Lepton Flavor Violation in the Era of the...

Lepton Flavor ViolationLepton Flavor Violationin the Era of the LHCin the Era of the LHC

Frank [email protected]

DESY Hamburg

Seminar, Graduiertenkolleg "Physik an Hadron-Beschleunigern" Freiburg, June 13, 2007

mailto:[email protected]

13/06/2007Frank Deppisch LFV in the Era of the LHC22//2626

OverviewOverview

● Lepton Flavor Violation● Supersymmetry● Neutrino Physics● Seesaw Mechanism● Low Energy Experiments● Collider Signals● Alternatives/Variations● Conclusion


Lepton Flavor ViolationLepton Flavor Violation

● Lepton Flavor is conserved in the Standard Model⇒ Clear sign for BSM physics

● Flavor Violation is seen in the quark and neutrino sector⇒ Strong case to look for charged Lepton Flavor Violation (LFV)

● LFV can shed light on– Grand Unification Models, Connection to quark flavor violation– Flavor Symmetries– Origin of Flavor

● Existing experimental boundsare stringent and will be improved in the near future


SupersymmetrySupersymmetry

Relates bosonic and fermionic degrees of freedom

Q Fermion → Boson , Q Boson → Fermion

⇒ Every Standard Model particle has a SUSY partner

● Solution to hierarchy problemSolution to hierarchy problem– Higgs mass not renormalized between Higgs mass not renormalized between

MMGUTGUT to to MMEWEW

● Radiative EW symmetry breakingRadiative EW symmetry breaking– Higgs potential can be derived Higgs potential can be derived

from SUSY from SUSY ● Gauge coupling unificationGauge coupling unification● Cold Dark MatterCold Dark Matter


SupersymmetrySupersymmetryThe MSSMThe MSSM

Minimal extension of the Standard Model with two Higgs doublets and conserved R-parity

Superpotential:

Phenomenology demands breaking of exact SUSY⇒ Additional terms in Lagrangian More than 100 free parameters⇒ Needed: Theoretical model for SUSY breaking

Boson Fermion Descriptiong g gluon/gluinoW W W boson/winoB B B boson/bino

, e L , e L L (s)sleptonseR∗ eL

c R (s)leptons u , d L u , d L L (s)quarksuR∗ uL

c R up-(s)squarksd R∗ d L

c R down-(s)squarkshu , hu

0L hu , hu

0L up-Higgs(inos)hd

0,hd−L hd

0, hd−L down-Higgs(inos)

W=ucT Y uQ⋅ H u

− d cT Y dQ⋅ H d

−ecT Y eQ⋅ H d

H u⋅ H d


SupersymmetrySupersymmetry● Theoretical framework for

SUSY breaking● SUSY breaking occurs in

hidden sector● Transmitted to observable fields

via gravitational interactions● Universality at MGUT

● No FCNC● Five free parameters

– m0 common scalar mass– m1/2 common gaugino mass– A0 common trilinear coupling– tanβ ratio of Higgs VEVs– signµ sign of Higgs mixing

● SUSY particle spectrum generated from RG evolution

Scenario SPS1a':m0 = 100 GeV, m1/2 = 250 GeV,A0 = -100 GeV, tanβ = 10, signµ = +

mSUGRAmSUGRA


NeutrinosNeutrinos

● Standard Model: Neutrinos are massless● Experimental observation of neutrino flavor oscillations

⇒ Neutrinos have masses and neutrino flavor is violated

● Measured mixing angles and mass differences

⇒ Nearly bi-maximal mixing ≠ Quark mixing

● Latest News: MiniBoone confirms this standard picture

U T mU=diag m1 ,m2 ,m3

U= c13c12 s12c13 s13e−i

−s12c23−s23 s13c12 c23c12−s23 s13 s12 s23c13s23 s12−s13c23 c12 −s23c12−s13 s12c23 c23c13 ×diag ei1 , ei2 ,1

sin212=0.30−0.050.04 ,sin223=0.50−0.12

0.14 ,sin213=0.000−0.0000.028 ,

m122 =8.1−0.60.6⋅10−5 eV2 ,m13

2 =±2.2−0.50.7⋅10−3eV2

OscillationsOscillations


NeutrinosNeutrinos● Oscillation experiments can not determine

absolute neutrino masses● Bound from Cosmology (WMAP)

● Bound (evidence?) from neutrinoless double beta decay (Heidelberg-Moscow)

● Absolute mass scale

... much lighter than other fermions

m1=00.5 eV

Absolute Mass ScaleAbsolute Mass Scale

n

n

p

p

e

e

d

d

u

u

e

e

W

W

ν

∑mi2eV

mee=∑U ei2 mi=0.24−0.58eV


SUSY SeesawSUSY Seesaw

● Add right-handed neutrinos to (MS)SM particle content, Seesaw Type I:

● Diagonalize seesaw matrix assuming super-heavy right-handed neutrinos

● Effective light neutrino mass matrix at low energies

MechanismMechanism

W=W MSSM−12RcT M R R

cRcT Y L⋅ H u

m=mDT M−1mD for mD≪M R m≈0.1eV mD

100GeV 2

M R

1014GeV −1

0 mDT

mD M R with mD=Y ⟨H u

0⟩≪M R L Lνc νc

H H

M

Susy Seesaw Teddy


SUSY SeesawSUSY SeesawExtensionsExtensions

● All three variations can emerge in SO(10) GUT models● SUSY Seesaw as effective model of neutrino sector

0 mDT

mD M R 0 mDT 0

mD 0 M RT

0 M R mL L mDT

mD M R

Seesaw I Seesaw II Seesaw III

i

e i , eic ,ic i

ei , eic ,ic i

ei , eic ,ic , S i

,mD≪M R⇒m=mD

T M RT−1M R

−1mD

mD≪M R⇒m=mD

T M−1mD

mD≪M R⇒m=mL L−mD

T M−1mD

m0.1eV

=mD2

100GeV 21014GeV

M R

m0.1eV

=mD2

100GeV 2

keV104GeV 2

M R2


SUSY SeesawSUSY SeesawNon-SUSY Seesaw● Ch. LFV is extremely suppressed by tiny ν masses, e.g. Br(µ→eγ) = 10-34

SUSY Seesaw● Neutrino flavor mixing radiatively induces slepton flavor mixing

from MGUT to the right-handed neutrino mass scales

● Correlation between slepton and neutrino flavor mixing

SleptonsSleptons

m L2 ij=−182 3m0A0Y LY ij

m R2 ij=0 L=logM GUT

M Riij

m LR2 ij=

−3 A082

Y e Y LY ij

Slepton mass matrix (6x6)

ml2=m L

2 m LR2

m LR2 m R

2

Origin ofcharged LFV


SUSY SeesawSUSY Seesaw

Light neutrino data,Choose R and Mi

Yν and Mi at MGUT

Slepton masses andmixings at MEW

mSUGRA condition: m0,A0MGUT

M3

M2

M1

MEW

Neutrino sector Slepton sector

Yν, M, mν

mL2, me

2, Ae

RenormalizationRenormalization Group Running Group Running


SUSY SeesawSUSY SeesawDetermination of Model ParametersDetermination of Model Parameters

m L2 ij=11 12 13

12∗ 22 2313∗ 23

∗ 33∝Y ⋅Y log MGUT /M R

● Problem of Standard Seesaw without SUSY:– Not Testable, Right-handed neutrinos too heavy– Only 9 parameters are (in principle) measurable

(light neutrino masses, mixing angles, CP phases)

– But: Model has 18 free parameters (Yν, MR)

● SUSY Seesaw:– Right-handed neutrinos are still too heavy – But: Corrections to the slepton mass matrix are in principle measurable

– ⇒ 9 potential observables

Slepton mass differences(Colliders)

∣12∣⇒Br e ,etc.

ℑij ⇒Electric dipole moments d e , d


SUSY SeesawSUSY SeesawLeptogenesisLeptogenesis

● Observed baryon asymmetry● Leptogenesis

– Right-handed neutrinos decay, violating CP and lepton number ⇒ lepton asymmetry η

L

– Transformation of ηL into baryon asymmetry η

B by SM sphaleron

processes (violating B+L)

– Use as additional constraint on model parameters

B=nB−nBn

=6.3±0.3⋅10−10

B= f Y , M 1 , for hierarchical M R

⇒M 15⋅109GeV


Rare LFV ProcessesRare LFV Processes● Current bounds and future sensitivities

– Br(µ→eγ) < 1.2⋅10-11 (MEGA) 10-13(MEG, 2009)– Br(τ→µγ) < 3.1⋅10-7 (Belle) 10-8 (Super-B Factory, LHC?)– Br(τ→eγ) < 3.7⋅10-7 (BaBar) 10-8 (Super-B Factory)– R(µ N→e N) < 7⋅10-13 (Sindrum) 10-18(PRIME) (µ−e conversion in nuclei)– µ→3e, τ→3µ (LHC), etc.

µ e

γ

µ e

qq

µ e

qq

µ→eγ µ N→e N

long-range

short-range

γ


Rare LFV DecaysRare LFV Decays

● Scattering of neutrino parameters● Fixed SUSY scenario SPS1a● Hierarchical (Degenerate) light

neutrinos● Degenerate heavy neutrinos Mνi=MR

● Strong dependence with MR

Br(li → ljγ)SUSY SeesawSUSY Seesaw

Br l i l j∝Y 2 2∝M R

2

m=Y 2 /M R

Br li l j≈3 tan2m8

ml i5

l i∣m L

2 ij∣2∝Y LY ij

2

m1=0

m1=0.3eV

current bound

future (MEG)

future


LFV at LHCLFV at LHC

pp q q , g q , g g

● Squark and gluino production

● ... followed by cascade decays via second lightest neutralino

● ... followed by LFV decay via sleptons(Agashe/Graesser, Hisano et al., Bartl et al.,Hinchliffe/Paige, Carvalho et al., Andreev et al.)

LFV Neutralino and Slepton DecaysLFV Neutralino and Slepton Decays

Br 20−e 1

0∝∣m L

2 12∣2

ml2 l

2 Br LFC

q g 20q g

● Edge structure of di-lepton invariant mass distribution

● Reach:

Br 20e 1

0=2−4% , L=30fb−1

Bar

tl et

al,

hep-

ph/0

5100

74


LFV at the LHCLFV at the LHC

● Possible signal signatures

● Main Background

● Exploit edge structure of signal invariant mass distribution

● Rough estimate:

Signals and BackgroundSignals and Background

pp l i l j2 jETmiss

l i l j3 jETmiss

l i l j l k l k2 jETmiss

pp t t ,WW , Z bb

minvmax l i

− l j2=m 2

02 1− ml

2

m 202 1−m 1

02

ml2

Andreev et al, hep-ph/0608176

N 20e 1

0=200 ⇒ 5@L=100 fb−1


Comparing sensitivity reach ● Fixed neutrino parameters: hierarchical light, degenerate heavy: MR

= 1014 GeV● Variation of m1/2, m0

(A0 = 0, tanβ = 10, signµ = +)

LFV at the LHCLFV at the LHCSUSY SeesawSUSY Seesaw

pres

ent b

ound

PS

I sen

sitiv

ity

Correlation with Br(µ→eγ)● Fixed mSUGRA scenario: SPS1a● Variation of neutrino parameters, deg L/Rdeg L/R, hier L/R and hier L/deg R neutrinos

MR≈1012-14GeV


LFV at LHCLFV at LHCLFV Neutralino and Slepton DecaysLFV Neutralino and Slepton Decays

Comparison of different flavor combinations● Fixed mSUGRA scenario: SPS1a● Variation of neutrino parameters, deg L/Rdeg L/R, hier L/R and hier L/deg R neutrinos

Within SUSY Seesaw, Br ecan be a more stringent bound on Br 2

0 10 than Br


LFV at the LHCLFV at the LHCGeneral Slepton Mixing (2 Flavor)General Slepton Mixing (2 Flavor)

Maximal left-handed slepton mixing

l 1l 2= cL sL

−sLcL⋅ eL

L ,L=4 , m=1GeV

Maximal right-handed slepton mixing

R=4, m=1GeV


LFV at LHCLFV at LHCGeneral Slepton Mixing (3 Flavor)General Slepton Mixing (3 Flavor)

● Random variation of right-handed slepton mass matrix, respecting all experimental limits (Bartl et al, hep-ph/0510074)

● Breakdown of mass-insertion approximation

Contribution from m R2 132 dominant,

m R2 12m R

2 23 strongly constrained

Loss of correlation, m R2 13m R

2 23 can be dominant over m R

2 122


LFV at LHCLFV at LHC● Drell-Yan Slepton-Pair Production

– Signal: di-leptons of different flavour and large missing pT

– Background: ttbar, WW, SUSY– Generally difficult but could be worthwhile– Reach for maximal LFV (S. Bityukov/N. Krasnikov, hep-ph/9712358):

● Slepton mass up to 250GeV● LSP mass ≤ 0.5 slepton mass

– Complementary to N2 decays

Other ChannelsOther Channels

pp l i l i l l 2 10

● Tau decays– τ →µγ (L. Serin / R. Stroynowski, ATL-PHYS-97-114):

● For 30fb-1 data: Br(τ →µγ) < 0.6 10-6

– τ →µµµ (CMS):● Br(τ →µµµ) < 10-8


LFV at the ILCLFV at the ILC● Slepton-pair production

● Clearer signal and easier background reduction

≈mt2 U

42 vu2 3m16

2 A02log

U2

M R32

● Precise slepton mass measurements possible down to few per mill level

● Determination of MνR3


Variations and AlternativesVariations and Alternatives

● SO(10) SUSY GUT (e.g. L. Calibbi et al, hep-ph/0605139)

– more predictive by fixing Yν

● Seesaw II (e.g. F. R. Joaquim and A. Rossi, hep-ph/0604083)

– neutrino mass generated by triplet Higgs term

● Long-lived stau NLSP (K. Hamaguchi/A. Ibarra, hep-ph/0412229)

– Stau can decay to µ, e in detector

● R-parity violating SUSY (e.g. M. Hirsch et al., hep-ph/0004115)

– can serve as neutrino mass generation mechanism– true alternative to Seesaw


ConclusionConclusion

● SUSY Seesaw introduces a rich phenomenology– Charged LFV in low energy experiments and colliders– Effective description emerging naturally from SO(10) GUT– Connecting Neutrino-, EW/SUSY- and GUT-scale physics– CP Violation effects, e.g. Leptogenesis, EDM's

● SUSY Seesaw induces charged LFV processes– Rare decays, e.g. Br(µ→eγ), and other low energy processes– Decays of second lightest neutralino at the LHC– Slepton pair production at the ILC– Correlations among these processes and neutrino parameters

● Determination of model parameters– SUSY Seesaw in principle testable– e.g. Br(µ→eγ) = 10-11 ⇒ MR ≈ 1012-14 GeV

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