Search for New Physics in Rare Decays

1
Search for New Physics in Rare Decays

• Sridhara DasuRepresenting BaBar
  CollaborationUniversity of Wisconsin - Madison

• Topics for this talk
• Flavor Changing Neutral Current Leptonic B
  decays
• B decay rate to rare final states
• Direct CP violation in rare decays
• B-factories also produce t and charm profusely
• Lepton Flavor Violation in t decays, D mixing
• Other B-Factory talks
• CP Violation in B system (Masashi Hazumis talk
  after the break)
• New physics effects in time-dependent
  asymmetries
• BaBar Rare B Decays Teela Pulliams talk this
  afternoon
• BaBar Asymmetries Giampiero Mancinellis talk
  this afternoon
• Global Unitarity Triangle Fits Maurizio
  Pierinis talk this afternoon

2
Weak B Decays
Vub Al3(r-ih)
New physics enters through loop effects
3
B-Factories e e- ? b b
ee? s(nb)
bb 1.05
cc 1.30
ss 0.39
uu 1.39
dd 0.35
tt 0.94
mm 1.16
ee 40
On peak ? B mesons Off peak ? Background
Although MU(4S) 2MB, U(4S) boost enables
time-dependent measurements
4
B-Factory Performance
Luminosity (cm-2 s-1) SLAC KEK
Design 3.0 x 1033 1.0 x 1034
Record Peak L 9.2 x 1033 1.4 x 1034
5
BaBar and Belle
High resolution energy and momentum measurement
down to 30 MeV with good particle ID g, e,
m, p, K, KL (direction only)? 4-vector
reconstruction
MB
6
EM Penguin Analyses

• Fully Inclusive Analysis (b?sg)
• Off resonance data subtraction
• B background subtraction using MC data
• Smallest B-meson model dependence
• Inclusive branching fraction well predicted
• Deviations point to new physics
• Extract B-meson model parameters, e.g., for
  improving Vub
• Semi-Inclusive (Sum of exclusive modes) Analysis
  (B?Xsg)
• B mass reconstruction (higher precision
  kinematics)
• Self flavor-tagging for direct CP asymmetry
• Many experimental and theoretical uncertainties
  cancel in ratio
• Exclusive Analysis (B?Kg, B?rg, B?wg)
• Cleaner signals, but have most model dependence
• Direct CP and isospin asymmetry
• Use ratios to obtain Vtd/Vts

7
Belle b?sg (140 fb-1)
Continuum
Signal
Photon E in c.m. (GeV)
Eg spectrum moments related to B-meson model
parameters - reduce Vub uncertainty
8
b?sg Branching Fraction
Semi-inclusive 20fb-1
Fully-inclusive (lepton tag) 50fb-1
Fully-inclusive others 9 fb-1
Fully-inclusive 140 fb-1
-4
A2,mlt0
0.8 TeV
tanb10

• Experimental results are consistent with SM
• Limits on SUSY parameter space
• Ellis, et al. hep-ph/0305212
• Green shaded exclusion region is due to b?sg

Universal sScalar mass
tanb8
1 TeV
Universal sFermion Mass
9
EM Penguins Direct CP Asymmetry
Weak phase difference
Strong phase difference

• Direct CP asymmetry can be non-zero when two or
  more amplitudes contribute to the decay process
• For b?sg, a single penguin amplitude dominates
• Predicted Standard Model asymmetry is 0 - new
  physics ?10
• A measurement significantly above zero, points to
  new physics!
• Many experimental and theoretical uncertainties
  cancel in ratios
• Semi-inclusive Analysis (B?Xsg)
• Exclusive Analysis (B?Kg, B?rg, B?wg)

10
BaBar Semi-inclusive B?Xsg
82 fb-1

• Reconstruct from sum of 12 exclusive hadronic
  modes
• Require K or Ks and up to 3 pions (np01)
• Extract signal in bins of hadronic mass Mhad
• Also useful for B-meson model parameter
  extraction
• Published only ACP so far

11

Direct CP asymmetry in b?sg
BaBar 82 fb-1
Belle 140 fb-1
Can be a clear sign of new physics
12
Exclusive Decay B ? Kg
82 fb-1
580
62
251
157
Teela Pulliams talkTime dependent CP

• First observation of B?K(892)g and B?K2(1430)g
  by CLEO (1993 and 2000)
• Much higher statistics now
• Theory errors are larger than experimental errors
• Study CP asymmetries and isospin asymmetry

13
Direct CP Isospin Asymmetry
DI improvement determines sign of C7
Standard Model ACP prediction is accurate and
smallMeasurements are consistent with zero,
dominated by statistical errors Future
measurements can point to new physics
14
B ? r g, B ? w g
No evidence w/ 78 fb-1

• Motivation
• Measure the least well known side of Unitarity
  Triangle
• Vtd/Vts alternative to DMd/DMs

B?rg, r?pp0
BaBar
B0?r0g, r0?pp-
B0?wg, w?pp-p0
15
B ? r g, B ? w g
Updated with L140 fb-1
16
B ? r g, B ? w g

• BaBar
  CLEO Theory
• PRL (92, 111801) (PRL 84, 5283)
  (Ali Parkhomenko)
• 
  Eur.Phys.J.
  C23 (2002) 89-112
• B(B0?r0g) lt 1.210-6 lt 1710-6
  (0.490.18)10-6
• B(B?rg) lt 2.110-6 lt 1310-6
  (0.900.34)10-6
• B(B0?wg) lt 1.010-6 lt 9.210-6
  (0.490.18)10-6

78 fb-1
9.2 fb-1
Previous Upper limits at 90 CL
New Belle Preliminary Results (140 fb-1)
Signal B0?r0g B?rg B0?w g
Yield 6.3 15.2 5.9
Efficiency 5.0 5.9 4.7
Branching Fraction 1.8 0.6 0.1 x 10-63.5 s significance 1.8 0.6 0.1 x 10-63.5 s significance 1.8 0.6 0.1 x 10-63.5 s significance
17
b ? s l l

• Complimentary to Bs?ll

AFB(NF-NB)/NFNB)
Y
Y
Forward l along BBackward l opp. B
Zero x-ing point
Mll2
Mll2
18
b ? s l l

• Exclusive Modes
• B?Kee, B?Kee, B?Kmm, B?Kmm
• Semi-inclusive
• Use sum of exclusive modes techniques a la b?s g
  analysis
• Hadronic component, Xs, has one K and up to 2 p

Belle 140 fb-1
MB
MB
MB
MB
BaBar 82 fb-1
LFV
K
K
s e m
s e es m m
MX
Mll
MB
MB
We are beginning to see higher hadronic mass
contribution
19
b ? s l l results

• Rarest B branching ratios observed consistent
  with SM predictions
• New observables (asymmetries) available for
  future studies
• New physics effects more dramatic

Complementary to Bs?mmCDF Limit B(Bs?mm)lt
5.8 x 10-7 _at_ 90 CL
20
B? ll

• Low SM predictions
• B(B?ee)10-15
• B(B? m m)10-10
• For B?em channel SM 0
• Sensitive to new physics, e.g., lepto-quarks

Mode Branching Fraction x 107 (_at_90 CL) Branching Fraction x 107 (_at_90 CL)
Mode Belle 78 fb1 BaBar 54 fb1
B?ee lt 1.9 lt 3.3
B?mm lt 1.6 lt 2.0
B?em lt 1.7 lt 2.1
CDF Limit B(Bd?mm) lt 1.5 x 107 _at_ 90
21
B?mn
22
B?tn

• Experimentally more challenging
• Recoil B technique
• Fully reconstruct one B
• Semi-leptonic B??D()ln
• Hadronic B??D()X
• Study the other B

23
B?Knn

• SM Predictions are more accurate than for B?Kll
• More sensitive to new physics
• Experimentally more challenging
• Recoil B technique
• Fully reconstruct one B
• Study the other

24
BaBar Invisible decay B?nn

• B(B?nn) suppressed by(mn/mb)2
• B(B?nng) SM prediction is lt 10-9
• Reconstruct one B - study other B
• 126K B ?Dln events reconstructed
• 82 fb-1 data used
• Search for events with extra energy

25
Lepton Flavor Violation t?lll

• Neutrino less decay - highly suppressed in SM
• ee- ? t(?lnn) t(?lll)
• Some new physics models allow rates within
  reach
• Six modes considered
• t?eee, t?emm, t?emm
• t?mmm, t?mee, t?mee
• Previous limits lt 10-6

t
l
l
X
l
26
LFV t?lll
MC signal clusters at 0 in both DM (measured
PDG t mass) and DE (measured t energy beam
energy)
No data (black dots) seen in the signal box for
all six modes searched
Upper limits lt x 10-7 _at_ 90 CL
Mode t-? eee mee mee emm mmm
BaBar 2.0 1.1 2.7 1.3 3.3 1.9
Belle 3.5 2.0 2.0 1.9 2.0 2.0
e mm
92 fb1
87 fb1
27
LFV t?mg
MC Signal Expectation
Belle Data
28
Hadronic Charmless Decays

• Numerous final states possible
• B?pp, B?pK
• B?rp, B?rr
• B?hK, B?fK
• Multiple diagrams
• Find penguin dominated channels
• Especially, those suppressed otherwise in SM
  isolate new physics effects
• CP asymmetries most sensitive observables
• Time-dependent studies for CP eigen states
  (M.Hazumi)

29
Rare Hadronic Decays
30
Direct CP Asymmetry
Belle (140fb-1) Cpp 0.58 0.15
0.07 (direct CPV _at_ 3.2s !)
Consistent with zero for almost all modes - lt 2s
effects
31
D Mixing
Mixing implies that the physical states are not
pure flavor states
SM Mixing box diagram
d, s, b
Vci
Vui
u
c
D0
D0
W
W
Charm mixing values most often quoted using
scaled parameters x, y
d, s, b
u
c
Vuj
Vcj
Standard Model x, y predictions are small
Rmix1010 (Datta Kumbhakar, Z.Phys. C27, 515,
1985) Rmix1010 (Petrov, PRD 56, 1685,
1997) Recent SM predictions can accommodate high
(1) mixing rate (Falk et al, PRD, 65,
054034, 2002,
hep-ph/0402204, 2004)
SM di-penguin diagram
Opportunity to search for new physics
Vci
W
Vui
c
u
Few mixing possible (Petrov, hep-ph/0311271)
d, s, b
D0
D0
g
d, s, b
u
c
Vci
Vui
W
32
D Mixing Results
with dKp being the relative strong phase between
DCS and mixing amplitudes
Year Exper. y (95 CL) x2/2 (95 CL)
2003 Babar -5.6 lt y lt 3.9 lt 0.11
2001 FOCUS -12.4lt ylt -0.5 lt 0.076
2000 CLEO -5.8 lt y lt 1.0 lt 0.041
Year Exper. Final State(s) Rmix (95 CL)
2002 FOCUS Km-n lt 0.13
2002 CLEO Ke-n lt 0.86
2004 Babar Ke-n (incl.) 0.12 (1s sens.)
2004 Babar Ke-n (incl.double tag) 0.06 (1s sens.)
Plot courtesy of G. Burdman I. Shipsey
No mixing seen yet
33
Summary

• Electro-weak penguins (b ? sg) are sensitive to
  new physics
• Branching Fractions (especially inclusive modes)
• Consistent with Standard Model - limits on SUSY
• CP asymmetries (deviations from SM0 ? new
  physics)
• Will remain of interest for a while
• Evidence for b ? dg
• Allows measurement of Vtd/Vts complementary to
  DMd/DMs
• Discovered b ? s l l- (More data needed to test
  new physics)
• Forward-backward asymmetry is sensitive to new
  physics
• No new physics seen in other search windows
• Pure leptonic B decays, lepton flavor violating t
  decays, D mixing
• Many more analysis in progress
• Integrated Luminosity 250 fb-1 by 2004 and
  500 fb-1
  by 2006!