charged leptons as probes of the standard model

Charged Leptons as Probes of the Standard ModelJ. Michael Roney

University of Victoria (BABAR Collaboration Member)

Lepton-Photon SymposiumDaegu, South Korea August 13-18, 2007

Charged Leptons as Probes of the Standard Model J.M.Roney, Victoria2

What Standard Model sectors can we probe with charged leptons and how useful is that probing?

• Appropriate questions, especially for the LEPTON-photon symposium…

• There are recent very high precision measurements at low energy of interest but nothing new for LP07 (see Sven Heinemeyer’s review from

Monday morning) the tension between data and SM persists in muon g-2 PRL 97, 030801(2006) Odom et al electron g-2: defines to 0.7ppb EDMs: continue to heavily constrain any physics beyond the SM

• Lets start with the basics where new results are in: Quantum Field Theory has CPT invariance built into it: translates into equal masses &

lifetimes for each particle and antiparticle … SM silent on particular masses, but foundations crumble if e.g. + and - have different

masses or lifetimes charged leptons are the only bare fermions allowing such probes


SM is silent on actual values of the masses and lifetimes

• Some are used to define the SM parameter space because of their high precision whereas the absolute values are required for less foundational probing… such as the assumption of charged current universality Present new results on

lifetime masses and CPT tests


Precision lifetime at PSI byMuLan Collaboration Phys. Rev. Lett. 99, 032001 (2007)

• “Defines” GF : fundamental SM parameter

• GF

9ppm 0.0007ppm 23ppm

,...

2

2

2 5

3

182

1

19

( ,

2

)tF

W

F

H

G g

M

G m

r m m

weak int’n loop corrections e.g.

van Ritbergen & Stuart full 2-loop QEDcorrections (1999) allow determination ofGF from lifetime at 0.3ppm level

(Nucl.Phys.B564:343-390,2000)


(from D. Hertzog, Moriond’07)


(from D. Hertzog, Moriond’07)

(MuLan)

5 -2F

=2.197013(24) s (11ppm)

G 1.166372(6) 10 GeV (5ppm)


CPT test from lifetime Dominated by lifetime of s

(Bardin 94)

don’t expect much improvement on testing CPT

5

5

2.197 025(155) s - 2.197 013(24) s/ =

2.197019(21) s

0.5 71 10

PDG 2 8 10cf


CPT• what about Lifetime:

1st CPT on lifetime from BABAR (Lusiani, TAU04)

THIS TEST WOULD BENEFIT FROM HIGH

STATISTICS AS MANY SYSTEMATICS WOULD CANCEL


CPT Mass: BELLE published using 5.8x106 pair

events: in 414/fb of data PRL 99,011801(2007) (hep-ex/0608046)

2

2

4

1776.61 0.13 0.35MeV/c

0.05 0.23 0.14 MeV/c

2.8 10 @90%CL

m

m m

m mm

2

min 2( )( )

3

X beam X X XM M E E E P

X


0

CPT• Mass: future? A SuperB factory with ~100/ab would yield a

statistical error of 0.023MeV on the mass difference ~ 6 x smaller than 0.14MeV systematic error BELLE now quotes.(Reach 0.15MeV at 2.3/ab)

To fully exploit 100/ab, would need charge asymmetric momentum scales controlled at 10-5 level. VERY CHALLENGING DETECTOR SYSTEMATICS PROBLEM

Would get CPT test to 2x10-5 level of sensitivity and would be most sensitive CPT mass difference test after K0(10-18), proton and electron (10-8).


1

New preliminary mass from KEDR Collaboration at the VEPP-4M Collider in Novosibirsk (hep-ex/0611046)

0.29 20

0.25 20.23

.26177

1776.80 0.15

6.99 MeV/c (PDG06, BES dominated)

MeV/c (KEDR preliminary)

m

m

using e,,,K,– vs - e -pair events


2

The mass is needed for probes of charged current universality involving the but …to probe the SM in and e- universality further requires higher precision measurements of BR(eand BR( and improved lifetime measurements


3

Charged Current Lepton universality • Charged current universality: tau decays

e

Branching ratios: (+ Lifetime, mass):

g g1.0000 0.0020

( ) 17.82 0.05 % [0.3%] PDG'07 Avera

1.0004 0g g

ges( ) 17.33 0.05 % [0.3%]

BR e

BR

.0022


4

Lepton universality in Kaon Decays New results from KLOE at Frascati’s DANE phi factory for LP07

KR ( ) / ( )K e K

can have deviations from SM frome.g. multi-Higgs effects inducing aneffective pseudoscalar interaction upto the few % level in K decays(A. Masiero, P. Paradisi, R. Petronzio, PRD74 (2006) 011701)


5

KLOE Universality results• Using 1.7fb-1 at the

• Compare RK to a SM calculation (M. Finkemeier, PLB 387 (1996) 391) which includes internal brem photons (IB) and ignores contributions from structure-dependent direct photon emission (DE). Requires care!

IB IB+DE

K e

6499 10 events

~8000 events

K

K e


6

KLOE Universality results

2 22

2 2 2 2

1 1

: efficiencies

C: corrections to MC efficiencies

: Fraction of IB component accepted (via

TRG TRKK KTRKKe

K TRG TRK IBPID PIDK Ke Ke KeMC MC

MC

IB

NR C

N C

MC

5K

SM 5K

SMK K

R 2.55 0.05 0.05 10

R = 2.472 0.001 10

RATIO: R /R

MC

1.032 0.0 9

)

2

cf


7

Probing the CKM Matrix with leptons• CKM Unitarity implies:

• strange decays of provides an additional way of probing |Vus | with a technique having uncorrelated experimental and theoretical errors

+ +

3

2 2

u

2

0.97377 0.00027

from 0 0 nuclear decay and neutron decay

= 4.40 0.34 10

from e.g. inclusive B X (numerically negligible role)

Unitar

1

ity 0.22 0. 75

ud

ub

ud us ub

us

V V V

V

V

V

0012


8

Strange and non-Strange -Decays

1= e

ee

Br hadrons B BR

BBr e

Strangenon,Strange, RRR


9

Extracting |Vus|The weighted spectral functions may be written as:

When one takes the flavour breaking difference:

the D=0 terms cancel leaving D 2. So:

19

02

0 0

0 0

0

( )

( ( ) ) ( )

where ( ) must be calculated and (

Note: because D=0 >>D 2 contribution, eve

) me

n a large relative

uncertainty o

asur

n ( )

e

yi

d

wus

us w wud ud OPE

w wO

wOP

PE i

E

j

R s

R

VR s V R s

R s R s

s

uselds a small uncertainty on V

0

,, 0

0

( ) ( ) ( )

s

ijwij

dRR s ds w s ij ud or us

ds

, 0 , 00 2 2

( ) ( )( )

| | | |

w ww ud us

ud us

R s R sR s

V V

2 2 2 2(0) ( ) ( ), 0

2

( ) 3 1w kl kl D kl Dij EW ud us ud ud us us

D

R s S V V V V


0

BABAR Branching Ratio for -K-0(uses 230/fb)

(2.267±0.008)%

NData 78,112±280

NBkg 38,247±159

qq

-+

arXiv:0707.2922 [hep-ex]

submitted PRD-RC


1

#pair(351/fb)

310M

~6%

NSignal 53110

Purity 79%

arXiv:0706.223 [hep-ex] submitted to PLB

not in average

0

0 0

( ) 0.404 0.002 0.013 %

( ) 2 ( )

= 0.808 0.004 0.026 %

PDG 07 = 0.90 0.04 %

S

S

B K

B K B K

BELLE:BR, Mass & Width: - KS-


2

BELLE: BR -K-,-K-0(K*-); --0

-K-

-K-0

--0

#signal 1387 270 5959

BR

(1.620.10)x10-4

(1.610.050.09)x10-4

(1.650.160.10) x10-4

(4.71.10.4)x10-5

(1.390.030.07)x10-3

preliminary: decays with

arXiv:0708.0733 [hep-ex]


3

BELLE (preliminary) Use -K-0sample to get- K*-) through the K*-(892)K-0modeusing BR(K*-(892)K-0

-K*- BELLE~1.9 lower than

PDG 07(CLEO)

BR (1.130.19 0.07)x10-4

(2.900.800.42)x10-4


4

BABAR Branching Ratios for -h-h-h+

Particle Identification (PID) Efficiency Matrix

Candidates Decay Modes (MC Truth)

--+ K--+ K--K+ K-K-K+

--+ 97.40% 22.49% 4.73% 1.02%

K--+ 1.42% 74.87% 16.43 6.38%

K--K+ 0.01% 0.49% 59.63% 25.54%

K-K-K+ 0.26% 50.87%

Characteristic Efficiency (excluding PID)

2.8% 3.1% 3.5% 3.9%

)NN(MN

)NN(NM

)MC(Bkgi

Datai

iij

1Sigj

)MC(Bkgi

Datai

Sigj

jij

L2

NBr

Sigj

ji=Channels Selectedj=Decay Mode

arXiv:0707.2981 [hep-ex] Submitted PRL


5

BABAR Branching Ratios for -h-h-h+

--

+

K--K+

K--+

K-K-K+


6

Some Updates to |Vus| from

UPDATED

-K-0arXiv:0707.2922 [hep-ex]-K--+arXiv:0707.2981 [hep-ex]

-K0-arXiv:0706.2231 [hep-ex]


7


UPDATED

-K-0arXiv:0707.2922 [hep-ex]-K--+arXiv:0707.2981 [hep-ex]

-K0-arXiv:0706.2231 [hep-ex]


8

About the tension…• Comment 1: B-factory experimental program to

measure all strange decays of the in progress: many modes still to be measured by BABAR and BELLE, |Vus| analysis assumed modes not yet measured are negligibly small…

• Comment 2:Theory errors for R00 require some care (Maltman & Wolfe hep-ph/0603215): poor convergence properties of the integrated D=2 OPE series for R00

argues for better behaved weighted spectral functions – even so, difference is not diminished using ALEPH spectral functions re-scaled with B-factory BRs even with better behaved weighted SF

• Comment 3: The updated |Vus| analysis doesn’t yet include the new -K-,-K-0(K*-) results from Belle… these lower values will increase the tension further

• very active area for both experimentalists and theorists


9

Lepton Flavour Violation:A bit of history…the importance of being earnest in seeing nothing

1947: muon established as lepton, excited electron ruled out by absence ofe

1958: G. Feinberg: “leptonic GIM” argument establishes two neutrino types:

Early weak theory: BR(e)~10-4 expected but BR(e)<10-5

1950’s: first -Ne-N conversion experiments Ee=m-Binding Energy~105MeV

and eee searches


0

History of e-muon LFV SearchesB(μeγ) < 1.2x10-11 (MEGA/LAMPF) Brooks et al PRL 83 1521 (1999)

μTieTi < 4x10-12

MEG

‘MECO’(?)

hadronic decays


1

SNO, SuperK, K2K: all see neutrino mixing implying massive neutrinos

We even have parts of the mixing matrix … experiments, such as T2K, preparing to measure So the SM extended to include massive neutrinos predicts LFV in the charged lepton sector as well:

well below any conceivable experimental sensitivity…

OPPORTUNITY: CHARGED LFV IS UNAMBIGUOUS SIGNAL OF NEW PHYSICS

Pham EPJ C 8 (1999) 513

2314

22 1

( ) ln 10kk k

k

mBR l l U U

m

222 5423

232

2 -3 2(for max. mixing and =3 10 eV )23

e.g.Lee & Shrock, PRD 16,144(1977)

3( ) sin 2 ( ) 10

128

Similarly for and

w

m

mBR BR

m

e e

By beginning of 21st Century: Lepton Flavour Violation established!


2

Many SM extensions predict observable Charged LFV• If see-saw mechanism responsible for

small mass, natural to get large Charged LFV

• Heavy Neutrinos• Supersymmetry• …

e.g.SO(10) inspired model with SUSYimbedded in GUTCalibbi et al PRD 74(2006)

univ. gaugino mass


3

e

(requires ~107 /sec)


4

The present status of the MEG experiment (T. Mori)

Drift Chambers:

Installed and ready at the beam line; cosmic ray test soon

Liquid Xenon Gamma-Ray Detector:

All phototubes installed inside the cryostat; final preparations to start operation toward the end of August

Timing Counters:

Final assembly in Italy; Installation planned at the end of August


5

The whole MEG detector will be ready in September 2007

Plan to start an engineering run with muons after calibration runs in October.

Expect to start taking some physics data toward the end of the year

STATUS

of

MEG


6

Focus on Lepton Flavour Violation in decays

• lepton-mass dependent couplings • parameter space in some models touch current limits • different sensitivity to 2-body & 3-body decays – which mode will be discovered first is unknown (e.g. some mSUGRA+Seesaw

(PRD66) has parameters having : = 1.5:1.0:8.4) • Well motivated searches: complementary to potential LHC

discoveries: Limits (or discovery!) will better constrain theories

LFV expected in many SM-extensions lll

SM + mixingLee, Shrock, PRD 16 (1977) 1444Cheng, Li, PRD 45 (1980) 1908

Pham EPJ C8 (1999) 513

10-54 – 10-40

10-14

SUSY HiggsDedes, Ellis, Raidal, PLB 549 (2002) 159

Brignole, Rossi, PLB 566 (2003) 51710-10 10-7

SM + heavy Maj R

Cvetic, Dib, Kim, Kim , PRD66 (2002) 034008 10-9 10-10

Non-universal Z’ Yue, Zhang, Liu, PLB 547 (2002) 252 10-9 10-8

SUSY SO(10)Masiero, Vempati, Vives, NPB 649 (2003) 189

Fukuyama, Kikuchi, Okada, PRD 68 (2003) 03301210-8 10-10

mSUGRA + Seesaw

Ellis, Gomez, Leontaris, Lola, Nanopoulos, EPJ C14 (2002) 319

Ellis, Hisano, Raidal, Shimizu, PRD 66 (2002) 11501310-7 10-9


7

General approach in Search for LFV @ e+e- colliders

SM decay(1- or 3- prong)

(1 or 2 )

CM frame

Signal decayLFV: no pmiss

Lab frame

• e+e- +- clean environment+- back-to-back (CM frame), jet-likeeasy BB bkgd rej through event shape variables

• Event easily divided in 2 hemispheres in CM: signal and tag decay• Signal (LFV) decay is neutrinoless: no missing momentum• Tag (SM) tau decay: 1- or 3- prong (+ 1 or 2 )

(depending on signal and dominant non bkgd)


8

Signal: no neutrinos powerful mass and beam energy informationmass: mm

Babar uses beam energy constrained mass & vertex at μ point of closest approach to beamspot in x,y(MEC)~9MeV(cf no mass or vertex constraint ~24MeV)

Beam Energy:E = E -Ebeam ~ 0

(E)~50MeV

signal region typically defined as 2 box or ellipse


9

-

mode

Belle BaBar

Br, 10-8 Lum. fb-

1 Br, 10-8 Lum. fb-1

<4.5 535 <6.8 232

e- <12 535 <11 232

e+ <2.4 535 <5.6 376

e+e- <2.8 535 <8.0 376

<3.4 535 <5.3 376

e- <4.3 535 <3.7 376

+ee <2.1 535 <5.8 376

e-ee <3.6 535 <4.3 376

Summary of γ,


0

BaBar

New Babar (prelim) & Belle (prelim) results on

Signal Mode

e-e+e- μ-e+e- e-

μ+e-e-

e+

Dominant Background

uds

Bhabhaeeee

ee

uds

optimize event selections for each signal mode separately accounting for different background compositions


1

New prelim Belle result on

Belle update to 535fb-1increase in lumi by 6.1 fold

Efficiency:6.0-12.5%<Bkgnd>:0.01-0.40 eventsTotal <Bkgnd>=0.590.31evNobs=0 events

90%CL limits:BR()<(2.0-4.1)x10-8

5-7 fold improvement overprevious limit


2

New prelim BABAR results on BABAR update to 376fb-1

for LP07 increase in lumi by 4.3 fold

•Background PDFshapes fromMC or controlsamples•PDFs summedand fit to datain sidebands•<Bkgd> fromintegral of PDFover signal box


3

New prelim Babar results on

Efficiency:5.5-12.4%<Bkgnd>:0.3-1.3 events; total=4.20.8 eventsTotal Nobs=6 events

90%CL limits:BR()<(3.7-8.0)x10-8

2-5 fold lower limits over previous Babar results


4

New Belle results on V0 using 543fb-1

Efficiency:2.5-4.0%<Bkgnd>:0.0-0.2 eventsTotal <Bkgnd>=0.780.29evNobs=3 events

90%CL limits:BR(V0)<(6.1-18)x10-8


5

NEW ’hep-ex/0610067 PRL 98.061803 (2007)BaBar

expected background/channel ~ 0.1-0.3Total expected background=3.1, Observed=2


6

Some intepretations within benchmark models

compilation by S. Banerjee (Tau06,hep-ex/0702017)


7

LFV in tau decays: How far we can go?It depends on “irresidual background”

levels… not currently a limiting factor

: future sensitivity will be affected by e+e- tag irreducible background. When that limit hit, sensitivity will scale as 1/sqrt(Lumi) . For ~75/ab as with SuperB might expect O(10-9) level

, hh’: sensitivity not likely limited by irreducible backgrounds so might expect sensitivity to scale as 1/Lumi .For SuperB might expect O(10-10) level


8

Summary• Charged leptons are probing many sectors

of the SM CPT CC Universality LFV CKM unitarity with |Vus| - watch this space EDM g-2 – possible hint of something beyond SM?

• Look forward to more precision data from MEG, MuLan, Babar, Belle, KEDR, BES, KLOE


9

Additional Slides


050

, where or us

ij

ij

e

Br hadronsR ij ud

Br e

Strange and non-strange Hadronic Width

May be written in terms of the spectral density function

or in terms of the 2 point correlator function

2 2

22 (1) (0)2 2 2

0

2( ) 12 1 1 ( ) ( )

m

ij EW ij ij ij

s s dsR s S V s s

m m m

2 2

2 (1) (0)2 2 2

0

2( ) 12 1 1 ( ) ( )

m

ij EW ij ij ij

s s dsR s S V s s

m m m

Extracting |Vus| from -Spectral Function


1

Extracting |Vus|

51

0

0

)()(2

1)()(

)(~)(

2

s

s ssS thth

dssswi

dssswdsqs

ss

0

,, 2 2

0

1k ls

ijklij

dRs sR ds

m m ds

A set of ‘spectral moments’ has been used in the FESR as the particular weight functions w

For (k,l)=(0,0), R00 is obtained from the BR of strange decays


2


from S. Banerjee (Kaon07)


3

Belle result on summer ’06 result submitted to PLB

2 projection

signaldata

blinded region

Unbinned Extended Maximum Likelihood fit

94 events in 535 fb-1

within 2 ellipse, eff=5.1%

s(90% CL) = 2.0 events Br<4.5x10-8 at 90%C.L

3.63.2

6.0

( )

1

4.8

UEML fit to data in 2 ellipse

#signal events, 3.9

# background e

NOTE: P(s<-3.9)

vents, b 13.9

=25%10;

( )!

s b N

i ii

eL

N

s bB

s

SN

0705.0650[hep-ex] submitted to PRB


4

Belle result on esummer ’06 result submitted to PLB

2 projection

20 events within 5 in 535 fb-1

within 2 ellipse, eff=3%

UEML fit in 2 ellipse # signal events = -0.14 (P(n<-0.14)=48%)

# background evts=5.14

s(90% CL) = 3.34 events

Br<1.2x10-7 at 90%C.L

Unbinned Extended Maximum Likelihood fit0705.0650[hep-ex] submitted to PRB


5

Summary of l, l0, l, l’, lK0S

L (fb-1)

L (fb-1)

90% CLUL (10-7)

90% CLUL (10-7)

LumUL

Red

Blue


6

Summary of lhh’L (fb-1)90% CL

UL (10-7)

L (fb-1)90% CLUL (10-7)

Red

Blue


7

Current exp UL’s vs BSM scenarios

Excluded

BaBar (L=232 fb-1)Belle (L=535 fb-1)preliminary

SUSY SO(10) + seesawMasiero et al. – NJP 6 (2004) 202

23

22 4

( ) tanlij

j iF SUSY

BR l lG m

charged leptons as probes of the standard model

Documents

cancelcpt t mass

new preliminary t mass

charged leptons

8x106 tpair events

sm frome

cpt testsprecision

cpt invariance

antiparticle sm silent