Sanjay Swain, SLAC on behalf of BABAR Collaboration 22 nd Sept 2007 Outline Lepton flavor violation (LFV) Search for LFV at BABAR Constraints on new physics Baryon number violation Future sensitivity Summary Search for Baryon and Lepton Number Violation in BABAR Search for baryon and lepton number violations workshop, LBNL slepton gaugino

LFV in  -decays In the Standard Model, lepton flavor is conserved for each generation e.g  is not allowed L   L   L  ≠ 0  L  =0 L   1  L  ≠ 0 but L = 0 But neutrino oscillation implies:  e  Lepton Flavor is violated but in neutral sector This flavor oscillation in neutral sector induces LFV in charged leptons e     e -     L e =1 L   L   L = L e + L  + L  m w  eV  m  2  eV 2 Lee, Shrock, Phys. Rev. D 16, 1444 (1977)

New physics phenomena in  -decays Now B  )   M MxMx   2  M and M x have different (higher) mass scale ~ ~ 2 ~~  The branching fraction can be enhanced significantly in large tan  region 1.Improving the rate for LFV process 2.Mediation through H 0 or A 0 (heavy scalar or pseudoscalar) 2 M. Sher, PRD 66, (2002) Replacing A 0 with H 0      New particles carrying lepton flavor numbers, which have very large mass and simultaneously mix among themselves (sleptons). LFV coupling H slepton gaugino tan  v u,d are VEVs of neutral higgs coupled to up-type or down-type fermion fields

New physics phenomena in  -decays (cont.) If observed  signature of new physics if not observed  strong constraint on the nature of new physics, which is expected to be present above EW scale. Question: can we search for these LFV modes in B-factories; if yes, how ?  l  lll

Asymmetric energy B-factory Cherenkov Detector (DIRC) 144 fused silica bars K,  separation Electromagnetic Calorimeter 6580 CsI crystals e ± ID,  , K L and  reco Drift Chamber 40 layers Tracking + dE/dx Instrumented Flux Return 19 layers of RPC/LSTs   and K L ID Silicon Vertex Tracker 5 layers of double- sided silicon strips Tracking + dE/dx e + [3.1 GeV] e - [9 GeV] 9GeV (e  )  3.1GeV (e + ) Peak luminosity: 1.12  cm  2 s  1

PEP-II and BABAR performance July 2006 Cross Section    1.05 nb   0.92 nb Integrated luminosity  500 fb -1 > 500/fb (Sept 07) ~ 1 billion (10 9 )  ’s

How do we search for LFV in  -decay ? Divide the event space by the plane perpendicular to the thrust axis into two hemispheres: tag-side, in which SM  decay ( 1 or 3 prong) is observed and signal-side, in which a neutrinoless  decay is reconstructed e+e+ e-e- ++ -- --  tag-track(1 or 3) Neutrino (1 or 2) Signal-side hemisphere Tag-side hemisphere thrust axis Signal side Tag side  phase space MC simulation KK2f for  production TAUOLA for  decay

The variables used to identify the signal  Signal MC The beam-energy constrained  mass: M EC The energy difference  E = E  - recon – E beam For signal events: M EC  M    E  0 signal events mostly populated in signal region Signal region: As these decays are very rare  mostly background is detected on the signal-side. Various kinematical, topological and particle identification cuts are applied to suppress the background. Compare different distributions in data with MC to make sure the background is well understood. Blind the signal region  optimize all the selection criteria using MC BLIND ANALYSIS:

  simulated event in BABAR detector r-  view x-z view IFR hits of the muon trackPhoton energy deposition in calorimeter Electron from tag-side  decay

BABAR results for  l  Efficiency=(4.7±0.3)% BF (    e   )  11 X PRL 96, (2006) Background expected =1.9±0.4 No. of observed events = 1 Dominant backgrounds: Bhabha,      e  with ISR, FSR  e  Efficiency=(7.4±0.7)% BF (      )  6.8 X Background expected =6.2±0.5 No. of observed events = 4 Dominant backgrounds: dimuon (     ),      with ISR, FSR  PRL 95, (2005)  is considered to be the golden mode for the search for LFV BABAR used 232 fb-1 data to look for both  e 

MSSM with seesaw: Results from  l  and impact on new physics The current measurements start probing predicted new physics effect 12E-8/

New physics constraints Excluded SUSY SO(10) + seesaw Masiero eta l. NJP 6 (2004) 202 BABAR limit Allowed region Reaching a sensitivity of 10  for B  ) would probe the SUSY spectrum up to M 1/2 = 700GeV (M 1/2 is the gaugino mass)  SUSY SU(5) GUT Hisano eta l. Phys. Lett. B565 (2003) 183 SUSY SU(5) GUT with right handed neutrino  The current bound on B (  ) constraints the allowed region for S  ks ksks 200GeV<m 0 <1TeV m  = 5 x eV M N = 5 x GeV 

 ' '' Signal Mode  e-e+e-e-e+e-e-e+e-e-e+e- μ-e+e-μ-e+e-e-e-μ-e+e-μ-e+e-e-e- μ+e-e-μ+e-e-e+e+μ+e-e-μ+e-e-e+e+DominantBackgroundudsBhabhaeeee ee  uds optimize event selection for each signal mode separately accounting for different background composition Searched modes:    e  e  e         e        e  e    e  e   e       ll'l'' ( l, l', or l'' = e,  )

Efficiency: % Expected background events: depending on mode Total estimated background = 4.2  0.8 events Total number of observed events =6 90%CL limits: BR(  ' '' )<( )x fold lower limits over previous BABAR results  ll'l'' ( l, l', or l'' = e,  ) NEW 376 fb -1 BABAR data used arXiv: v1 (submitted to PRL) (Preliminary results)

Signal box (±2  in  E and M EC ) Estimated background : depending on mode Total estimated background = 3.1 Total observed events = 2  l P 0 ( l = e,  and P 0 =    ' ) Using 339 fb -1 data PRL 98, (2007)  decay mode UL (10 -7 )  decay mode UL (10 -7 ) eeee1.3   1.1 e  2.5  1.9 e    5.4   ) 4.5 e  (combine) 1.6  (combine) 1.5 e  '  '  5.8  '  '  3.6 e  '  '  4.2  '  '  2.7 e  ‘ (combine) 2.4  '  (combine) 1.4

The left plot shows the exclusion regions obtained in the m A and tan  plane by different experiments New result from BABAR Competitive with the direct Higgs searches at CDF and D0 95% C.L.) Constraining new physics using  result M. Sher, PRD 66, (2002) CDF: pp  H      pb   _ D0: pp  H  bb   pb   _ _      pb -1  S. Banerjee, Nucl. Phys. Proc. Suppl. 169, 199 (2007)

The baryon asymmetry of the universe (BAU) is one of the pressing questions today. Why do we see a large imbalance of matter and anti-matter in today’s universe ? SM assumes both lepton number L and baryon number B, and (B-L) conservation. However, many supersymmetry and superstring models allow B and L violation. We searched for two kinds of baryon instabilities:  (B-L) =0 or 2. So, the conservation or violation of (B-L) determines the mechanism of baryon instability. Baryon number violating  -decay Two modes considered here: (one can replace   with K  )       pp pp B: 0   L: +1   (B-L): -1  1 -1  -1 (B-L) conserving(B-L) violating

Baryon number violating decay              90% c.l. upper limit for signal yield 237 fb -1 BABAR data used for this analysis. (hep-ex: ) Elliptical signal region Signal MC with arbitrary normalization (Preliminary results)

Future sensitivity The upper limit on branching fraction depends on background BF UL 90  N sig 90  1 L 1 L 1 LL In the absence of background, the BF UL 90 varies as In presence of background, the BF UL 90 varies as An example: for , the irreducible background is    ISR (which is 1/5 th of the total background) So, the B UL 90 with irreducible background would be (1-2) X 10  with 1/ab data For  lll or l hh, no significant irreducible background. So, the BF UL 90 is expected to be ~10  Depending on background and decay mode, the Super B-factory with 100 ab  1 data would bring the limits to 10  - 10 

Summary BABAR has looked in many channels for evidence of LFV in  -decay No signal for LFV decay has been observed yet The limits are probing branching ratios around 10  well inside the parameter space of several new physics models, therefore imposing significant constraints The upper limit on branching fraction will improve as the B-factories accumulate more and more data However, it would be slow improvement due to the background for some modes, e.g.  e  There is still lots of data to come : at BABAR we expect about 750 fb-1 by end of next year Look forward to interesting limits (or something very interesting) from combined BABAR/Belle full data set