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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
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
13/06/2007Frank Deppisch LFV in the Era of the LHC33//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC44//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC55//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC66//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC77//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC88//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC99//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1010//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1111//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1212//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1313//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1414//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1515//2626
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
µ e
µ→eγ µ N→e N
long-range
short-range
γ
13/06/2007Frank Deppisch LFV in the Era of the LHC1616//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1717//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1818//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC1919//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2020//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2121//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2222//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2323//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2424//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2525//2626
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
13/06/2007Frank Deppisch LFV in the Era of the LHC2626//2626
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