Lepton Flavor Violation at LHC
Warintorn Sreethawong (SOKENDAI, KEK)ICEPP Meeting

April 1-3, 2009

In collaboration with J. Hisano and M. M. Nojiri, arXiv:0812.4496

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP MeetingIntroduction & Motivation
I The LFV processes are important discovery channels of BSM.
I Current experimental upper bounds on LFV processes:

Br (µ → eγ) < 1.2 × 10−11

MEGA,

(1)

−8

Belle(BaBar),

(2)

−7

Belle(BaBar).

(3)

MEG,

(4)

superB factory.

(5)

Br (τ → µγ) < 4.5(6.8) × 10

Br (τ → eγ) < 1.2(1.1) × 10
I Prospects:

Br (µ → eγ) ∼ 10−13Br (τ decay) ∼ 10−9−10− 10I LHC plays a complementary role to identify new physics anddetermine LFV parameters. ⇐ esp. in light slepton scenario
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meetingµ → eγ
Right-handed LFV ⇒ Cancellation among dominant diagrams-8Br(µ -> e !)Current bound
MEGlog10(Branching Ratio)-9-10-11-12-13-14-15-16150200µ250300J. Hisano, T. Moroi, K. Tobe, M. Yamaguchi, Phys. Lett. B 391, 341 (1997)
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

500

µme
meRm!Lm!2450
400

At the cancellation point,411µ22 −2 f1 ( 2 ) ∼ 0.
2ml̃
ml̃
ml̃

350

LR(6)

R300

In the plot,i) m1/2 = 300 GeV, tan β = 10250200ii) mSUGRA-like relations are assumed
among M1 , M2 , and slepton masses

150100050100 150 200 250 300 350 400iii) µ is free (NUHM)

m0I µ∼ml̃L along the cancellation line

I µ is smaller as m0 decreases ⇒ DM relic density is smalland χ̃04 → ẽL and χ̃02 → ẽR are always kinematically allowed.
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Non-universal Higgs Mass Model (NUHM)
H. Baer, A. Mustafayev, S. Profumo, A. Belyaev, X. Tata, Phys. Rev. D71, 095008 (2005).
J. Ellis, K. A. Olive, Y. Santoso, Phys. Lett. B539, 107 (2002).
M. Drees et al., Phys. Rev. D63, 035008 (2001).
J. Hisano, R. Kitano, M. M. Nojiri, Phys. Rev. D65:116002 (2002).

We took mHU > mHD = m0 , particularly with M1 < M2 < µ ∼ m1/2 anddark matter relic density consistent with observations.
Moreover, we took the choice mχ̃0 < mẽR < mχ̃0 < mẽL < mχ̃0 when both1
2
4
left- and right-handed sleptons can be directly produced via neutralino
decay.

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP MeetingLFV Model
J.L. Feng, C.G. Lester, Y. Nir, Y. Shadmi, arXiv:0712.0674

Consider a horizontal U(1) × U(1) symmetry where each U(1) is explicitly
broken by a scalar singlet spurion carrying the corresponding charge -1.
⇒ Slepton masses:
MeL2 = meL2 + xm02 XeL0 ,where
0 4 8
XeL0 ∼  4 0 4  ,8 4 0Mẽ2 = mẽ2 + xm02 Xẽ0 ,(7)

0 2 4Xẽ0 ∼  2 0 2  ,4 2 0(8)and  = symmetry breaking parameter ∼ |Vus | ∼ 0.2
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Contents
1. A model point with correct DM relic density ⇒ the cancellation point
2. Sparticle masses and parameters determination from endpoint
information
3. Flipping solution exercises
Key observables:
I 2 jets + missing ET
I relative edge heights
I charge asymmetry

4. LFV and DM density

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP MeetingMC Study
ISAJET v7.75 + HERWIG 6.5 + AcerDet# of generated events = 5 × 106 → ∼ 300 fb −1 of integrated luminositypoint A:ũL → χ̃02ũL → χ̃04ũL → χ̃+
2m0mHDA0100
1000m1/2mHUtan βA
25.4
7.8
13.1

mSUGRA
31.6
1.3
1.830038010⇒χ̃02 → ẽRχ̃04 → ẽRχ̃04 → ẽLχ̃+2 → ν̃Lµ = 271 GeVΩDM h2 = 0.1179
A
13.5
0.7
2.3
7.4

mSUGRA
3.1
0.3
1.02.1(µ = 397.3 GeV for mSUGRA point)⇒ For point A, χ̃04 and χ̃+
2 have more Wino component.
⇒ Enhancement in Br (ũL → χ̃04 /χ̃+2 ) by at least factor 6.
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

OSSF dilepton invariant mass distribution
Entries
Mean
RMS

20000

51114252.23
22.96+
χ̃+
2 → ν̃L → χ̃1Entries
Mean
RMS

700

511142
129.2
29.63

600

17500

500

15000

χ̃02 → ẽR → χ̃01

12500
10000

χ̃04 → ẽR → χ̃01

400300χ̃04 → ẽL → χ̃01

7500
200
5000
100
2500
000

20

40

60

80100 120 140 160 180 200

100120mll

140160180200220240mllmax
I Including mjll, mjlmax , mjlmin , one can resolve mq̃L , mχ̃0 , mχ̃0 , mχ̃0 , mẽL , mẽR .
4

2

1I A study of four-lepton (2OSSF) events reveals mllmax (χ̃04 → ẽL → χ̃02 ).
+0.45
I mẽL − mχ̃0 = 124.92 +0.65−0.65 GeV, mẽR − mχ̃0 = 15.68 −0.49 GeV
1Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

1

ICEPP Meeting

Flipping Solutions mũL , mχ̃04 , mχ̃02 (mχ̃03 for A3), mχ̃01 , mẽL , mẽR
are degenerate between three points(point A2) ⇒ endpoints from their cascade decay
will be the same(point A3)(1)

M1 < M2 < µ (point A)(2)

M1 < µ < M2

(3)

µ < M1 < M2

We investigate whether three solutions can be discriminated @ the LHC.
For point A2,I χ̃04 and χ̃+
2 have more Wino component ⇐ Branching ratios
I χ̃02 has less Wino component ⇐ Charge asymmetry

For point A3,
I χ̃01 is Higgsino-like ⇐ 2 jets + missing ET
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting2 jets + missing ET
C. G. Lester and D. J. Summers, Phys. Lett. B463, 99 (1999)
A. Barr, C. Lester and P. Stephens, J. Phys. G29, 2343 (2003)

8< 0.940.89
Br (q̃R → χ̃01 ) =:0.16

point A
point A2
point A3

For pp → q̃R q̃R → q χ̃01 q χ̃01 events, their signature is two high-pT jets +large E/T .
/miss; mtest ) ≡mT 2 (pjT1 , pjT2 , pT

minβ/pα+p/T =p/missTThoinj2/β/αmax mT (pjT1 , pT ; mtest ), mT (pT , pT ; mtest )“”jj
222mT(pjT , p/α/α/αT ; mtest ) ≡ mj + mtest + 2 ET E
T − pT · p
T .
mT 2 (mtest = mχ̃0 ) ≤ mq̃R1PointA
A3

No. of Signal
1341
133

No. of SM Background
180
180

S/BSM
7.5
0.7

√
S/ BSM
100.0
9.9
CERN-OPEN-2008-020

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meetingµ → eγx = 0.3
A-8-10-11-12-13-14-15-16Br(µ -> e !)Current bound
MEG-9log10(Branching Ratio)-9log10(Branching Ratio)

A2-8Br(µ -> e !)Current boundMEG-10-11-12-13-14-15150200µ250300-16150200µ250300

I Point A and A2 have Br (µ → eγ) differ by two orders of magnitude.
I Only point A is in the cancellation region and then gives Br (µ → eγ) below

the current experimental upper bound.
I A precise determination of µ parameter is important for determination offlavor mixing parameter.
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

OSSF Dilepton Invariant Mass Distribution
AA2
Entries
Mean
RMS

20000

51114252.23
22.96

Entries
Mean
RMS

20000

17500

17500

15000

15000

12500

12500

10000

10000

7500

7500

5000

5000

55409957.52
29.89

A2: χ̃04 and χ̃+
2 have more
Wino component

2500

2500
0020406080

100 120 140 160 180 200

0020406080

mll

mll
Entries
Mean
RMS

700

100 120 140 160 180 200

511142
129.2
29.63

600

Entries
Mean
RMS

1200

554099
136.8
29.84

1000

500

⇒ Enhancement in edges
from0χ̃+2 → ν̃L → χ̃1 (factor 2)
and800χ̃04 → ẽL → χ̃01 (factor 4)relative to edge ofχ̃02 → ẽR → χ̃01

400
600300400200200

10000100120

140160180200220240mll

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

100120140160180200220240mll

ICEPP MeetingCharge Asymmetry
A. J. Barr, Phys. Lett. B596, 205 (2004)
T. Goto, K. Kawagoe, M. M. Nojiri , Phys. Rev. D70, 075016 (2004)
J. M. Smillie, B. R. Webber, JHEP 0510:069,2005.

Example
4jet

qL
qL

3.5

lRl-R (far)q̃Ll̃R−0!12l -q

1.50.5

θ = angle between quark andlepton in the χ̃02 rest frame

0l+
Lepton Flavor Violation at LHCl q

2.51χ̃02

Warintorn Sreethawong (SOKENDAI, KEK)

dP/ds!/2!02+3+lR (near)

00.2

0.4

s!/2

0.6

0.8

1

⇒ positive charge asymmetry
ICEPP Meeting

Spin correlation in Herwig, G. Corcella et al, arXiv:hep-ph/0011363v3.
AA2

7060

60
50

40

4030

20200100-20-10-200100

200300m jh l

400500600

0100200300m jh l

400500600

The difference between mjh l + and mjh l − distributions as a function of mjh l(jh is defined by mjh ll ≡ max(mj1 ll , mj2 ll ))Assuming that L-R slepton mixing is negligible, the flatness of charge asymmetry
distribution suggests the contribution from q̃R → χ̃02 decay.
⇒ χ̃02 for point A2 must have smaller Wino component.
⇒ M1 < µ < M2
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP MeetingM2/M12.14 2.16 2.18
0.6

2.2

2.22 2.24 2.26 2.28

R≡0.5

⇒The ratio R depends on µ/M1
stronger than on M2 /M1 .

R

0.4

R(µ/M1)

0.3
0.2

R(M2/M1)0.1
01.8 1.9

2Br (ũR → χ̃02 )Br (ũL → χ̃02 )2.1 2.2 2.3 2.4 2.5 2.6 2.7⇒ As µ/M1 is smaller, mixing
between neutralino states islarger and the charge
asymmetry receives more q̃Rcontribution.

µ/M1

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Parametersµ < M1 , M2
M1 < µ < M2mẽL ↔ mẽR

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

Resolving Methods
mT 2 methodcharge asymmetry + branching ratio
charge asymmetry

ICEPP Meetingµ → eγ
1e-10

0.02

MEGA

1e-11! (ml )12/mlr

1e-12

r

0.01

MEG

1e-13!m/m

Branching Ratio

0.015

Br(µ -> e ")

0.005
1e-14

1e-15

0.1

0.2

0.3

0.4

0.5

0.6

0.7

00.8

x+0.45
Recall mẽL − mχ̃01 = 124.92 +0.65−0.65 GeV, mẽR − mχ̃01 = 15.68 −0.49 GeV.

I The mass difference of order one percent, corresponding to 1 ∼ 2 GeV, isallowed by MEGA bound (Br (µ → eγ) < 1.2 × 10−11 ).
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meetinglog 10 (Branching Ratios)-10-11Br( μBr(μe γ)

3e)-12-13-14Br(μ-15-16200

220e; Ti)

260
240
μ (GeV)280

300

I The µ → e conversion rate shows strong sensitivity to the SUSY parameters

at different µ values from Br (µ → eγ) and Br (µ → 3e).
I µ = 271.33 +6.89−6.81 GeV
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Finally, precise SUSY parameter determination is also important for thedetermination of DM density and DM scattering cross section.

AA2A3observation/exp. upper boundΩDM h2
0.11790.08170.00960.122

SI (10−8 pb)
σpχ
1.6
3.2
17.5
4.6

(WMAP & SDSS)(CDMS)

SI
Uncertainties in σpχ
:I nucleon matrix element of strange quark
SII σpχ|A−exchange ∝tan2 βmA4Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

ICEPP Meeting

Conclusions
I We studied the the one-parameter-extended NUHM, mHU 6= mHD = m0 ,particularly with M1 < M2 < µ ∼ m1/2 and dark matter relic density consistent
with cosmological and astrophysical observations.
I We are also interested in the region where cancellation among leading
contributions to Br (µ → eγ) occurs in the models with right-handed LFV masses.
Therefore, we took the choice mχ̃0 < mẽR < mχ̃0 < mẽL < mχ̃0 when both left124
and right-handed sleptons can be directly produced via neutralino decay.
0+I In the region when M1 < M2 < µ ∼ m1/2 , χ̃4 and χ̃2 are a mixed states withrather large Wino component and their various decay patterns are expectable atthe LHC.
I When the relation M1 < M2 , µ is kept, we showed three solutions with similar mass
spectrum but different ordering of M1 , M2 and µ. We showed that by looking into
2 jets + missing ET signature, relative height of mll edges and charge asymmetry,the degeneracy can be lifted.
I We emphasized that a precise µ parameter determination is an important key forresolving cancellation point of LFV processes, determination of the LFV parameterand determination of DM density and DM scattering cross section.
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP Meeting

Mass Spectrum (point A)
mg̃
mũL
md̃L
mũR
md̃R

719.67665.19670.29648.85642.47mν̃mẽLmẽRmτ̃2mτ̃1224.37239.62130.38238.89128.07mχ̃+2mχ̃+1mχ̃04mχ̃03mχ̃02mχ̃01Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

321.62
196.30323.23278.87
197.82114.70ICEPP MeetingSelection criteria:
I an OSSF dilepton pair where both leptons have p l > 10 GeV andT|η| < 2.5.
I more than 4 jets with pjj
T ,1 > 100 GeV, pT ,2,3,4 > 50 GeV.

I Meff ≡ pT ,1 + pT ,2 + pT ,3 + pT ,4 + E/I E/

T > 400 GeV.

T > max(100, 0.2Meff ).

Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHCICEPP MeetingEstimated error of sparticle masses and SUSY parameters
Sparticle Massmχ̃01mẽR − mχ̃01mχ̃0 − mχ̃021
mẽL − mχ̃01mχ̃0 − mχ̃041mq̃L − mχ̃0Central value
114.7015.68
83.12
124.92208.53551.19mẽR − mµ̃R
mẽL − mµ̃L

1.00
2.00

1ParameterµM1
M2µ/M1M2 /M1
Warintorn Sreethawong (SOKENDAI, KEK)
Lepton Flavor Violation at LHC

Central value
271.33122.49230.892.215
1.885

Estimated error (1-σ)+6.7−6.3+0.45
−0.49
+0.75
−0.62+0.65
−0.65
+0.77
−0.64
+4.64
−4.47
+0.04
−0.04
+0.48
−0.49

Estimated error (1-σ)
+6.89
−6.81
+7.16
−7.17
+6.57
−6.54
+0.084−0.078+0.063−0.057ICEPP Meeting