Rare B and ? decays and searches for New Physics

1
Rare B and ? decays and searches for New Physics

• Roger Barlow
• Manchester University and

New (preliminary) results, mostly but not
entirely from the B factory experiments Belle
and BaBar.
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Why look for Rare Decays?
If new particles are to appear on-shell at high
energy colliders, they must appear in virtual
loops and affect amplitudes

• Our chance to see them is when the Standard Model
  amplitudes are small
• Rare decays

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What made it possible?

• Measuring Branching ratios of 10-6 needs
  millions of events
• Physics progress possible thanks to machine
  physicists at SLAC and KEK
• designed and built B factories operating in a new
  high-current regime,
• continually faced and overcame new problems and
  challenges.
• design luminosities met and exceeded.

4
Finding a needle in haystack.

• Huge backgrounds from other Bs
• and ee- ?q?q

?E(GeV)
Use of ?EEB-?Ei and MES?EB2-(?pi)2
Use data sidebands (rather than Monte Carlo) to
estimate background
Blind Analysis Tune cuts without looking in the
MES-?E signal box
MES(GeV/c2)
(taken from Sekulas talk. One of many)
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Other Experimental techniques
Continuum suppression from combined information
from shape variables
Single-B beam technique Reconstruct one
tag B in a common decay mode (hadronic or
semileptonic). Remaining particles must also
form a B
Limits from N? S b N small Uncertainties on ?,
b
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Contents

• B decays
• Leptonic
• Radiative
• b?s ? and b?s l l -
• b?d ? and b?d l l -
• Hadronic Charmless
• Branching Fractions
• Charge Asymmetries
• Polarisation
• Tau decays

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B Decays to leptons
Proceeds through one or two weak bosons with
strong CKM suppression door open for NP
particles to contribute Free of hadronic
uncertainties in final state
Plus many other diagrams

?b
?

?
d,s
?-
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B? ? ????
CP, Rare decays, CKM V Browder (Belle) Sekula
(BaBar)
Important as W (suppressed by Vub) can be
replaced by charged Higgs, etc
Difficult due to neutrinos in the final state
tag with fully reconstructed B mesons (180
channels) Tag with B?D()l?
SM prediction (1.59? 0.40) x 10-4 (depends
on fB and Vub)
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B? ? ????
CP, Rare decays, CKM V Browder (Belle) Sekula
(BaBar)

• Identify possible ? in common decay mode
• Look at extra calorimeter energy
• (validate with for Dln)

H?
Extra E(GeV)
Extra E(GeV)
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Results
(revised). 3.5 ? significance
(new) BF(B????) (0.88 ?0.11)
x10-4 BRlt 1.80 10-4 _at_ 90CL
0.68 -0.67
Belle and BaBar results are similar. Agree within
errors Can be combined (R. Faccini) to give
(1.36 ? 0.48)x10-4
BF(B????)
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Impact
CP, Rare decays, CKM V Browder (Belle)

• Limits on e.g. 2 Higgs doublet model W.S.Hou,
  PRD 48, 2342 (1993)
• SM prediction enhanced/reduced by factor rH

Or Within the SM, use the value of BF(B????)
to give a measurement of fB
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B? ?? ? ? and e ? ?
CP, Rare decays, CKM V Sekula (BaBar)

• Helicity Suppressed
• Use hadronic tags B fully reconstructed as B to
  D() X
• Lepton is monoenergetic in signal-B rest frame
• Limits (_at_ 90 CL)
• lt7.9 x10-6 for e? (SM 10-12)
• lt6.2 x10-6 for ? ? (SM 10-7)

Lepton momentum in B frame (GeV/)
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B0 to l l ?
CP, Rare decays, CKM V Sekula (BaBar)
(simulated)

• FCNC and helicity suppressed, but an initial
  state photon allows helicity flip
• SM predictions of order 10-10
• (10-15, 10-11 respectively without the ? )
• See 0 events for e, 3 events for ? (but
  compatible with background)
• Limits (at 90 CL)
• BR(B?ee?)lt 0.7 x 10-7
• BR(B?mm?)lt 3.4 x 10-7

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B ? K ???
CP, Rare decays, CKM V Browder (Belle)

• Tag on other B
• Identify K
• Look for extra energy
• SM prediction 1.3 x 10-5
• Signal is B?K missing mass. (Could be light
  dark matter particle publications by M. Pospelov
  et al.)

Extra Calorimeter Energy (GeV)
(at 90 C.L)
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B0 ? ??-
CP, Rare decays, CKM IV-V Farrington
(CDF) Strauss (DØ) Sivoklokov (ATLAS) Langenegger
(CMS) Ruf (LHCb)
SM predicts Bs(3.4?0.5)x10-9 Bd(1.0?0.1)x10-10
NP can boost this by 100
B0s ? ??- B0d ? ??-
Expected BG 0.88 1.86
Events seen 1 2
BF (95 CL) lt1.0x10-7 lt3.0x10-8
LHC experiments will do this very precisely
DØ analysis not yet complete. Combines Bs and Bd.
Expect limit 2 10-7 Have result on BR( B
????) BR lt 4.1 x10-6 _at_ 95
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Radiative B decays
FCNC process suppressed in SM sensitive to new
particles in loops b?s? Inclusive and many
exclusive measurements b?sll - More
information from kinematics b?d? strongly
suppressed but open to different physics b?d ll
- on the way
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B ? s ? inclusive
Heavy Quark Physics I III Hurth (Theory) Convery
(BaBar)
Branching Fraction now well measured. Theory and
experimental error similar
0.37 -0.49
NLO calculation (3.61 ) x10-4
result (Eg gt1.9GeV) (3.67 ?0.29 ? 0.34 ? 0.29)
x10-4

• Fully Inclusive and sum of exclusives (38
  modes)

Not much room for New Physics here Constrains
model builders
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B ? s ? exclusive
Heavy Quark Physics III Limosami (Belle)

• Lots of channels
• Branching Fractions measured
• CP violating asymmetries measured
• If nonzero these would be a signature of New
  Physics

Example B? K0s?0?
?t(ps)
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B ? Kl l B ? Kl l
CP, Rare decays, CKM VI Kovalskyi (BaBar) BSM
VI Hamel de Monchenault
Standard Model Amplitudes have 3 parts with
different kinematics. Check out each separately
through Wilson Coefficients Photon
C7 Vector EW C9 Axial EW
C10
CKM factors x ? Ci(q2) x local operators
B?Kll (46 events)
Dilepton mass q2
?E(GeV)
MES(GeV/c2)
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CP, Rare decays, CKM VI Kovalskyi (BaBar)
Angular variables e.g.? angle of l l pair in
their rest frame. C10 interferes with C7/C9 to
give asymmetry
Kll Asymmetry as a function of q2
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B ? d ?
CP, Rare decays, CKM VI Kovalskyi (BaBar)

• First observation of
• B ? ??

MES(GeV/c2)
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CP, Rare decays, CKM VI Kovalskyi (BaBar)
Compare with B?K?
Same CKM elements as mixing but a non-trivial
test
W
?b
?d,?s
t
t
W
b
d,s
ds
t
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B ? ?? l l -
CP, Rare decays, CKM VI Kovalskyi (BaBar)

• Prediction few 10-8
• Measure B ? ? l l - and B0 ? ? 0 l l -
• with l e or ? (and e - ? )
• Total limit 7.9 x 10 -8 at 90 CL for B
• ( twice B0)
• Amazing to be probing at this level

?E(GeV)
?E(GeV)
MES(GeV/c2)
MES(GeV/c2)
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Charmless Hadronic Decays

• Many modes
• Will present collected branching ratios
• Will present measurements of time-integrated CP
  violation ACP they follow on directly from
  differences in charge conjugate decay states
• from the B/B- difference - trivial
• From self-tagged neutral modes trivial
• From C part of CPmixing fit nontrivial but
  standard

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Examples
Heavy Quark Physics I Dragic (Belle) Bona (BaBar)
MES(GeV/c2)
MES(GeV/c2)
?E(GeV)
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2 body ?-K combinations
Heavy Quark Physics I Dragic (Belle) Bona (BaBar)
Results on many other decays. See talks by
Dragic, Bona, Latham and Schümann in Heavy Quark
Physics Session I
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(No Transcript)
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B? K?- /K-?
CP, Rare decays, CKM IV Di Marco (BaBar) Unno
(Belle)

• Direct CP violation
• Experiments agree
• BaBar
• ACP-0.108 ?0.024?0.007
• Bel
• ACP-0.093 ?0.018?0.008

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Direct CP in K ?

• Competing amplitudes with different strong and
  weak phases
• ACP should be the same for K?- and K?0 (Gronau
  hep-ph 0508047)
• Current averages (HFAG)
• ACP (K?-)-0.093 ? 0.015
• ACP (K?0)0.047 ? 0.026
• Difference 0.14 ? 0.03 a long way from zero
• Maybe colour-suppressed trees are responsible
• Maybe New Physics

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Lipkin Sum Rule

• RLipkin2 ?(B?K?0)?(B0?K0?0)
• ?(B?K0?)?(B0?K?-)

From isospin and assuming the b ?s penguin
diagram dominates R should be 1O(10-2) Obtain
(HFAG average) RLipkin1.06 ? 0.05 (Was 1.25 ?
0.10 in 2003)
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B?K ? ratios
Heavy Quark Physics I Dragic (Belle)

• Can form many ratios, especially
• (A Buras, R Fleischer et al, Phys J C 45
  (701-710) 2006)
• Rn?(K ?-) Rc2 ?(K ?0)
• 2 ?(K0?0) ?(K0?)

Obtain (HFAG averages) Rn0.99 ? 0.07 Rc1.11 ?
0.07
Agree with each other And with SM predictions The
K? puzzle is no more
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The Polarisation Puzzle

• B ?V V decays are spin 0 to spin1spin1
• Should be 100 longitudinally polarised (if tree
  or penguin dominates)
• Measurements confute this for heavier V
  especially
• Needs to be understood affects CP decomposition
• More data now available

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B ??0?0
CP, rare decays, CKM III Telnov (BaBar)
32 -31

• See 98 ?22 events
• - 3 ? significance
• BR (1.16 ?0.27)10-6

0.36 -0.37
?E(GeV)
Fit longitudinal polarisation fl 0.86 ?
0.05 Measurement needed for B 0 ???- , used for
alpha Informs penguin uncertainty in ??
determination
MES(GeV/c2)
0.11 -0.13
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B ? ? K and f(980)K
Heavy Quarks I Bona (BaBar)
fL around 0.5, as in B ? ? K as opposed to 1
from simple models
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More on B to V V
CP, rare decays, CKM VI Bussey (CDF)

• CDF measure longitudinal polarisation in ? K, ?
  K
• Confirm BaBar and Belle results that polarisation
  is not 100
• ? ? on the way

M(??K?) (GeV)
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Rare Tau Decays
BSM VI Hayasaka
The B factories are also ? factories ?(? ? -)
0.89 nb at ?s M(?) Total sample of 1.5
billion tau leptons

• Search for New Physics in decays with Lepton
  Flavour Violation

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Compendium of results
BSM VI Hayasaka
Mode x10-7 Mode x10-7
tgmg Belle 0.45 tglll 1.1-3.5
tgeg BaBar 1.1 t-gme-e- BaBar 1.1
tgmh Belle 0.65 t-gm-e-e Belle 1.9
tgeh Belle 0.92 tglhh BaBar 0.7-4.8
tgmh' Belle 1.3 t-gmp-p- BaBar 0.7
tgeh' Belle 1.6 tglV0 Belle 2.0-7.7
tgmp0 Belle 1.2 tgmr0 Belle 2.0
tgep0 Belle 0.80 t-gLp- BaBar 0.59
tgmKs Belle 0.52 t-gLp- BaBar 0.58
tgeKs Belle 0.60 t-gLK- BaBar 0.72
t-gLK- BaBar 1.5
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General techniques

• Divide event into two hemispheres
• Tag side usual 1prong (e, ?, ?, ?) or 3 prong ?
  decay.
• Different analyses use different tags, trading
  purity for numbers.
• Signal side with no neutrinos. Powerful
  energy/momentum constraint.

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???l ? ? ???l ? K0
BSM VI Hayasaka

• l ? is ?? or e?.
• Theoretical predictions vary from 10-40 for SM
  (with ? mixing) upwards

• New 90 CL limits
• Br (? - ? e - g ) lt 12 x 10-8
• Br (? - ? m- g ) lt 4.1 x 10-8
• Br (t - ? e - KS) lt 5.6 10-8
• Br (? - ? m - KS) lt 4.9 10-8
• (hep-ex/0605025)

Tan ?
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?? -???? -, ?? K -,?? -, ? K
BSM VI Hayasaka

• Look for B-L conserved processes as allowed in
  the Standard Model
• Look for B-L violating processes as Baryogenesis
  may need them

?E(GeV)

Channel B-L Background N _at_90 CL
?-???? - C 0.42?0.42 0 lt5.94 10-8
?-? ?? - V 0.56?0.56 0 lt5.76 10-8
?-???K - C 0.26?0.26 0 lt7.19 10-8
?-? ?K - V 0.12?0.12 1 lt14.6 10-8
Decays to non-strange baryons ruled out through
proton lifetime measurements
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????
BSM VI Hayasaka
MSSM prediction

• ? in ?? and 3? modes
• Limit 1.6 x10-7 _at_ 90 CL (BaBar)
• 0.65 x10-7 _at_ 90 from Belle

Tan ?
MA(GeV/c2)
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Y(1S)???
BSM VI Besson(CLEO)
CLEO result on Lepton flavour violation
Detect ? through decay to e??
???
pe/Ebeam
??(?e??)
BRlt 6.2 10-6 LFV Scale ?gt1 TeV
p?/Ebeam
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Putting it all together
BSM VI Hamel de Monchenault
An example MSSM parameter space Isidori and
Paradisi hep-ex 0605012 One set of Parameters
?,AU, sparticle masses Restrictions on MH,
Tan? Due to b?s? Bs ??? g-2 ?MB B???
Tan ?
M(H)
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Conclusion

• BaBar and Belle are probing physics at the TeV
  scale, exploring parameter spaces of proposed New
  Physics models
• Limits on Higgs Masses, Tan ?, SUSY particles.
• Precision Frontier and Energy Frontier are
  Complementary. LHC results will benefit from Rare
  Decay information.
• Standard Model beginning to be heavily stressed
• A SuperB factory would stress it even further

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Many more results at next years conference(s)

• We look forward to welcoming you to Manchester
  next year

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Backup slides
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Exp. Needs single B beams
Lots of modes have several n and need beams with
a single, monochromatic B B?tn, B?nn,
B?Knn, Fully reconstruct one of the Bs and study
the remaining of the event ? closed kinematics,
missing energy reconstruction
Tag types
Semileptonic D()l(np) 5K/fb-1 Hadronic
D() X 3K/fb-1
purity
efficiency
Xnpmp0pKqKs
Pioneered by BaBar
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New Physics Implications
CP, Rare decays, CKM IV Farrington (CDF)

• SO(10) model
• Dermisek et al

hep-ph/0507233
?(GeV)
M1/2(GeV)
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What is a rare decay?

• Experimental definition
• One which has not been seen, or only just been
  seen for the first time
• Theoretical definition
• One which, in the standard model, is either
  absolutely forbidden or strongly suppressed
  FCNC, helicity, small CKM element.
• (b?c is big, so everything else is small)

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HFAG ACP