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Search for Lepton-Flavor Violation in Tau Decays at BaBar
May 14nd, 2005 NW APS Section Meeting University of Victoria

Eric Torrence University of Oregon

Eric Torrence

1/25

May 2005


Outline

Brief Introduction Lepton Flavor Violation Ç - l-l+l- Ç - Å- + Ç - l- hÁ h

-

Rare Hadronic Decays Ç - 3 h - 2 h + (5-prong) Ç - 4 h - 3 h + ( 0 ) (7-prong) Summary of other BaBar tau results Ç Tau Lifetime Ç - ( 3 )-20 Ç - K -0


All results are preliminary, unless otherwise noted!
Eric Torrence 2/25 May 2005


The BaBar Experiment

Asymmetric e+e- "B-factory" also a Tau-charm factory ( e + e - BB ) = 1.05 nb ( e + e - + - ) = 0.89 nb
Eric Torrence 3/25 May 2005


Luminosity History
260 240 220 200 Integrated Luminosity (fb ) 180 160 140 120 100 80 60 40 20 0
1 May 1 Mar 1 Jan 1 Nov 1 Sep1 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep1 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep1 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep1 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep1 Jul 1 May 1 Mar 1 Jan 1 Nov
-1

BA B

AR

PEP-II Delivered 259.63/fb BABAR Recorded 249.81/fb BABAR off-peak 22.68/fb

96% Efficiency 220 million events!

1999 2000

2001

2002

2003

2004 2005
May 2005

Eric Torrence

4/25


Lepton Flavor Violation Limits on Lepton Flavor Changing Decays before BaBar/Belle Ç B ( Å e ) < 1.2 ç10 Ç B ( Å ) < 1.1 ç10
- 11

at 90% CL [MEGA/LAMPF] at 90% CL [SINDRUM] at 90% CL [CLEO] at 90% CL [CLEO]

Ç B ( Å eee ) < 1.0 ç10

- 12

-6 -6

Ç B ( Å ÅÅ ) < 1.9 ç10

Forbidden in SM, but no good theoretical motivation Neutrino Oscillations



-

Å

Å

-

W
-
Å

Å

-



LFV allowed in principle, but rate is very, very small. O(10-40)? Signature of new physics!
Eric Torrence 5/25 May 2005


LFV in Tau Decays Å- - Å
+

-



Å+ -



Å-

Natural part of many models of new physics, particularly those trying to explain neutrino data Theory Grab Bag Model SM + lepton CKM MSSM + seesaw MSSM + RH Maj. SUSY SO(10) SUSY GUT Gauge Mediated SUSY MSSM + universal soft breaking Seesaw w/ extra dim.
Eric Torrence

B( Å Å ) 10-40 10-7 10-10 10-8 10-8 10-8 10-7 10-11
6/25

Reference hep-ph/9810484 hep-ph/0206110 hep-ph/0306195 hep-ph/0209303 hep-ph/0307393 hep-ph/0310148 hep-ph/9911459 hep-ph/0210021
May 2005


B(Å->e)

B(->Å)

10 10

-10

M1/2=50

Å Å e

Tau vs. Muon Decays
10
-4 M1/2=50

Å Å

Experimental Bound
-12

10
-14 M1/2=200

-6

Experimental Bound 10
-8 M1/2=200

10 10 10

-16 M = 2 x 1016 GeV -18

10 400 500 M0 (GeV)

-10

M = 2 x 1016 GeV

100

200

300

100

200

300

400 500 M0 (GeV)

String inspired, heavy R SUSY [King and Oliveira, 1999] Current tau limits are often more sensitive Different models predict widely different hierarchies Å Å Å Å ÅÅ vs. Å e vs. Å vs. Å ÅÅ vs. Å KK

Search for everything, observation potentially very constraining...
Eric Torrence 7/25 May 2005


LFV Signature 1-prong "tag" Å 1-prong "tag"

lll

Ç One prong on "tag" side ( , , e , Å ,...) ~ 85% Ç Strict lepton identification Ç No missing momentum on 0.4 signal side - -> Å-e-e+ 0.2 "Neutrinoless" Decay m = m E = E
E (GeV)
rec

-m



0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2 0.4 M (GeV)

rec

-E

beam

Smeared by resolution and radiative effects Count events in signal region

All BaBar LFV analyses have been blinded...
Eric Torrence 8/25 May 2005


LFV Backgrounds - Å - Backgrounds - - Å - Å Å-

Irreducable at some level, mass/energy resolution important More significant is e + e - Å + Å - (Particle ID, kinematics) Backgrounds present a challenge - l - l + l - Backgrounds e+ e- e+ e- ,e+ e- e+ e- ,e+ e- Å+ Å Kinematics, photon conversions Generic tau decays - Particle ID Backgrounds generally lower than Å lhh somewhere in between
Eric Torrence 9/25 May 2005

-

3 leptons


Å lll analysis
E, GeV

qq
0.2 0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2 0.4

E, GeV

0.4

0.4

QED
0.2 0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2 0.4

M, GeV E, GeV E, GeV
0.4 0.4

M, GeV


0.2 0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2 0.4

data
0.2 0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2 0.4

M, GeV

M, GeV

Require 1-3 topology, reject conversions, Particle ID, plus specific cuts per channel against major backgrounds 3 background PDFs, shape from MC/control, rate from data
Eric Torrence 10/25 May 2005


BaBar Å lll LFV Limits
E (GeV)

- e-e+e0.2 -0

- Å+e-e-

- e-Å+Å-

BABAR

-0.2 -0.4 -0.6

- Å-e+e0.2 -0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0 0.2

- e+Å-Å-

- Å-Å+Å-

-0.4

-0.2

0

0.2

-0.4

-0.2

0

0.2

0.4
2

M (GeV/c )

Mode e-e+e- Å+e-e- Å-e+e- e+Å-Å- e-Å+Å- Å-Å+Å- Eff [%] 7.3 Á 0.2 11.6 Á 0.4 7.7 Á 0.3 9.8 Á 0.5 6.8 Á 0.4 6.7 Á 0.5 Nbgd 1.51 Á 0.11 0.37 Á 0.08 0.62 Á 0.10 0.21 Á 0.07 0.39 Á 0.08 0.31 Á 0.09 Nobs 1 0 1 0 1 0 9 BU0 2.0 ç 10-7 1.1 ç 10-7 2.7 ç 10-7 1.3 ç 10-7 3.3 ç 10-7 1.9 ç 10-7 L

No excess found! Limits ( 1 - 3 ) ç10 @ 90% CL L = 91.6 fb-1, = 0.89 nb PRL 92, 121801 (2004)
Eric Torrence 11/25 May 2005

-7


Å Å Selection NN Common Inputs Ç Ç Ç Ç Ç event missing mass highest tag-side p Å helicity angle missing pT signal-side m

Separate Tunings (by tag mode) Ç Ç Ç Ç Ç Ç electron electron gamma muon hadron hadron gamma 3-prong

Critical to efficiently suppress different background classes

Eric Torrence

12/25

May 2005


Å Å Results

L = 232.2 fb-1, = 0.89 nb (~400 million tau decays)

In 2 sigma signal ellipse: BGD expected: 6.2 Á 0.5 Data observed: 4 = ( 7.4 Á 0.5 ) % Improved limit by taking 2 sigma band in E Fit for signal (and background) in M = ( 9.4 Á 0.6 ) % B ( Å ) = ( - 5.6
-8 + 8.3 - 6.3

) ç10

-8

BF Limit 6.8 ç10 @ 90% CL (Frequentist) 30% chance to get a better limit in background-only hypothesis Submitted to PRL [hep-ex/0502032]
Eric Torrence 13/25 May 2005


BaBar Å lhh LFV Limits
E (GeV)
0.2 -0 -0.2 -0.4 -0.6 0.2 -0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 -0 0.2 -0.6 -0.4 -0.2 -0 0.2 -0.6 -0.4 -0.2 -0 0.2 -0.6 -0.4 -0.2 -0 0.2

- e-K+K

-

- e-K +-

- e-+K

-

- e-+-

- e+K-K

-

- e+K--

- e+--

- Å-K+K

-

- Å-K+-

- Å-+K

-

- Å-+-

- Å+K-K

-

- Å+K--

- Å+--

M (GeV/c )
2

-0.6 -0.4 -0.2 -0 0.2

-0.6 -0.4 -0.2 -0 0.2

-0.6 -0.4 -0.2 -0 0.2

+ - l- hÁ h

-

where h = or K (LFV or L = Á 2 )

Less help from particle ID, more backgrounds L = 221.4 fb-1, = ( 2.1 - 3.8 ) %, N
bgd

= ( 0 - 3 ) events (Å worst)

Total in 14 channels: 10 observed, 11.3 expected Limits: ( 0.7 - 4.8 ) ç10
-7

@ 90% CL

BaBar Preliminary [hep-ex/0409036] Factor of 20 improvement over CLEO results

Eric Torrence

14/25

May 2005


Belle Å Å Result

L = 86.3 fb-1, = ( 11.0 Á 0.5 ) % Expected: 20.2 Á 2.1 Observed: 19 BF Limit 3.1 ç10
-7

@ 90% CL

PRL 92, 171802 (2004)

Eric Torrence

15/25

May 2005


World LFV limits (x 10-7) @ 90% CL B( ) B( - e- ) B( - Å-Å+Å- ) B( - e-e+e- ) B( - l-l+l- ) B( - e-+- ) B( - Å-+- ) B( - e-K +K - ) B( - Å-K +K - ) B( - l-h+h- ) B( - l+h-h- ) B( - ( Å / e )-0 ) B( - ( Å / e )- ) B ( - ( Å / e ) - ' )
Mode - Å- BaBar Belle

0.7 1.9 2.0 (1-3) 1.2 2.9 1.4 2.5 (1-3) (0.7-5)

3.4 3.8 2.0 3.5 (2-4) 8.4 2.8 3.0 12 (3-16) (2-8) 4.1/1.9 1.5/2.3 4.7/10

Orders of magnitude improvements over previous CLEO limits! Could approach few 10-8 in clean modes by end of decade
Eric Torrence 16/25 May 2005


Combined tau decay SUSY limits tan

?
M0

Not nearly as easy as exclusive production!
e + e
- - Å+ -

+

Single diagrams leads to single exclusion contour

Single diagrams not enough, must sum ALL amplitudes

Results probably ready for Summer conferences
Eric Torrence 17/25 May 2005


Synergy with other Rare Decays

Junji Hisano TAU04 SUSY GUT relations give non-trivial predictions for various rare decays SUSY SU(5):

Important to compute loop contributions in "big picture" Some progress on more generalized framework...
Eric Torrence 18/25 May 2005


Hadronic Tau Decays




W



e+ e/Z

Tau Decays provide a clean laboratory to study QCD 5-prong modes suffer from lack of statistics 7-prong modes never seen...
200
Events/(0.1 GeV/c2)

50

CLEO
100

1pr tag
3h-2h+


lept tag
CLEO saw 295 events 25 (1.7 fb-1) PRL 73, 934 (1994)

0

0

2

4

0

2

4 M5 (GeV/c2)

0

Eric Torrence

19/25

May 2005


BaBar 5-prong Analysis 3 h - 2 h + mass compared to TAUOLA (phase space)

- 3h-2h+



1-5 topology, lepton tag, thrust, Pt/Emiss, no kaon id (yet) veto e-, 0, and conversions from signal side

Efficiency: 7.7%, Purity: 79%, Events: 34,849, Lumi: 232 fb-1 Backgrounds mostly from other tau decays with 0 or Ks
Eric Torrence 20/25 May 2005


BaBar 5-prong Results
BaBar 8.5 Á 0.4

B ( 3 h 2 h ) = ( 8.56 Á 0.05 Á 0.42 ) ç10 Also observation of - f 1 ( 1285 ) -


-

-

+

-4

Preliminary

Opal Aleph

9.1 Á 1.5 8.0 Á 1.7 7.7 Á 1.0 8.2 Á 0.6
6 8 10 12 + -4 B(3h 2h ) [10 ]

B ( - f 1 - ) = ( 3.9 Á 0.7 Á 0.5 ) ç10 CLEO: ( 5.8 Á 1.4 Á 1.8 ) ç10
-4

-4

(via f1Å)

Cleo PDG

Theory: 2.91 ç10

-4

Submitted to PRL hep-ex/0505004

2+2-
Eric Torrence 21/25 May 2005


BaBar 7-prong search L = 232.2 fb-1

1-7 topology, use pseudo-mass to distinguish e + e - qq , fit backgrounds
Mode Efficiency Bgd Expected Observed BF limit (10-7)

- 4-3+ - 4-3+0 - 4-3+( 0 )

5.5 3.6 9.3/9.4

3.9 8.2 21.6

8 7 24

4.3 2.5 3.0

Order of magnitude improvement on 7 (0) First limit on exclusive 7, 7 0 Theory prediction: < 6 ç10
- 11

(phase space) (Nussinov, Purohit, 2002)

Nearly submitted to PRD-RC
Eric Torrence 22/25 May 2005


Tau Lifetime Ç Very clean 1-3 sample Ç Reconstruct r- decay length from primary IP to 3-track vertex Ç Use simple mean <> to reduce syst.
decay_length_allcuts_unblinded_tau

1-prong 3-prong

Entries Entries

110245 145675 0

Events per 100 Åm

10

4

BABAR
preliminary

Mean Underflow RMS

Overflow

0.0240731 0 0.0406002

10

3

10

2

Data tau uds cc bb

BaBar
10

289.4 Á 1.3 291.4 Á 3.0 293.2 Á 2.5 289.2 Á 2.1 290.1 Á 1.9 289.0 Á 4.9 290.6 Á 1.1
290

Preliminary

1 -0.3 -0.2 -0.1 0 0.1 0.2

Delphi



0.3 cm

L3 Opal

Lifetime with 80 fb-1 289.40 Á 0.91 ( stat ) Á 0.90 ( syst ) fs (prelim.)

Aleph Cleo PDG
285

295 Tau Lifetime (fs)
May 2005

Eric Torrence

23/25


Other BaBar Tau Results 2- + 20 B(
- -+-00

) = ( 4.51 Á 0.07 Á 0.56 ) ç10
-3 -3

-3

B ( - - 0 ) = ( 1.71 Á 0.12 Á 0.16 ) ç10 B (
- - -0

) = ( 3.66 Á 0.10 Á 0.31 ) ç10
-0

B (

) < 4.5 ç10

-4

90% CL

L=124.4 fb-1 BaBar Preliminary - 0 B ( - K - 0 ) = ( 4.38 Á 0.04 Á 0.22 ) ç10 L=124.4 fb-1 BaBar Preliminary
-3

Improvements to be made to tau decay models Starting to look at hadronic structure

Eric Torrence

24/25

May 2005


Conclusions

Lepton Flavor Violation Searches BaBar (and Belle) have searched in wide variety of final states Limits now pushed below 10-7

Rare hadronic decays First results on rare hadronic decays are huge improvements over previous CLEO results. Much more to do here.

Other tau results Large number of interesting analyses underway. Many new results now or coming soon...

6 talks given at Tau04, September 2004

Eric Torrence

25/25

May 2005