Rare and Semileptonic Decays of B and K Mesons

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Rare and Semileptonic Decays of B and K Mesons

• Jeffrey D. Richman
• University of California, Santa Barbara
• BABAR Collaboration

Particles and Nuclei International
Conference Santa Fe, Oct. 27, 2005
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Outline

• Goals and challenges
• KL?p0 nn
• The kaon revolution KL ?pe- n, Vus, and the
  recalibration of kaon branching fractions
• Electroweak penguin/box diagram processes
  B?Kg, B?rg, B?Xs g
  and B?K ll-, B?K ll-
• Semileptonic B decays and the measurement of Vcb
  , Vub , mb, mc
• Leptonic B decays Bs?mm-, B?t nt
• Perspective and conclusions

Far too many topics to cover... my apologies!
Parallel session talks contain many more details
(Bizjak, Godang, Koeneke, Mohapatra,)
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Rare and Semileptonic Decays Goals
Rare decay loop/box process ? test SM at 1-loop
level ? new (heavy) particles can be produced
in virtual intermediate states can compete with
SM amps ? search for effects of new physics
Semileptonic decay tree diagram ? measure
Vij ? determine quark masses, QCD parameters
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Common theme understanding dynamics

• Amplitude factorizes ? single hadronic current
• Form factors/QCD parameters can sometimes be
  extracted from data or be calculated
• Precise rate predictions possible for some
  processes
• Methods HQET, heavy-quark expansions, lattice
  QCD,

Understanding dynamics is an important goal in
itself!
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CKM matrix b and s decays are both suppressed!
(Wolfenstein parametrization)
5 highlighted Vij discuss in this talk!
unitarity 6 triangles, all with same area
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BABAR
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KL?p0nn

• KL decay directly measures h (height of
  unitarity triangle)!
• SM prediction
• Use K?p0 e n measurement to compute hadronic
  current.

Buras, Schwab, Uhlig, hep-ph/0405132 very
small theory errors achievable.
E949, PRL 93, 031801 (2004)
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Preliminary results on KL?p0nn from KEK E391a
1. Measure g position and energy in CsI

• Prelim. result uses 1.14 x 109 KL decays
  e0.73x10-2
• So far, only very small fraction of data used.
  
• No events observed in signal box
• E391a goal
• Proposal in preparation for follow-on
  experiment at J-PARC

2. Reconstruct decay vertex assuming MggM(p0).
3. Signature z(vertex) and pt
Major backgrounds
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K?pen , Vus, and the kaon revolution
Review of Particle Properties, 2002
experiment BR, tK
KLen 1 Ken1/2
form factor theory q20 expt shape
I-spin corr. for K decay
long distance rad. corrections
short distance radiative corr.
Leutwyler Roos, Z.Phys.25, 91 (1984)
Cirigliano et al., Eur.Phys. J C35, 53
(2004) Andre, hep-ph/0406006
Sirlin, Nucl. Phys. B196, 83 (1982)
other work in progress
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Recalibration of KL branching fractions

• KTeV measured 6 largest KL modes PRL 93,
  181802-1 (2004)
• Account for 99.93 of decays 5 ratios of
  branching fractions
• 105-106 events/mode careful treatment of
  radiation from electrons.
• Measurement of KL semilep form factors
  (1.7-4.2 shifts) hep- ex/0406003, 0406006

E. Blucher, Lepton-Photon 2005
fit to all new meas.
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Extraction of Vus
E. Blucher, Lepton-Photon 2005

• Average of recent results
• KLOE, KTeV, NA48, ISTRA
• correlations taken into account

Competing method G(K?m n) KLOE,
hep-ex/0509045 lattice MILC, PRD70, 114501
(2004) Marciano, PRL93, 231803 (2004)
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Radiative penguin decays of B mesons
Now its a physics program!
Observation of B?K g CLEO II (1993) Loops in B
decays!
PRL 71, 674 (1993) cited gt500 times!
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Observation of the b?dg decays B?r (w) g
Belle, 386 M BB hep-ex/0506079
BABAR, 211M BB PRL 94, 011801 (2005)
8.2 evts
20.8 evts
Ali, Lunghi, Parkhomenko, PLB 595, 323 (2004)
5.9 evts
Belle
good agreement w/global CKM fit
Belle
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Inclusive B?Xs g Decay

• Canonical process for testing the SM at 1 loop
  level
• Provides powerful constraints on new physics
  models
• Major effort by theory community to compute QCD
  and EW corrections NLL calculation complete
  NNLL calculation forseen

Hurth, Lunghi, Porod, Nucl. Phys. B 704, 56
(2005) see also Neubert, Eur.Phys. J C40, 165
(2005)
Buras
et al., Nucl.Phys. B631, 219 (2002)
HFAG July 2005
Belle, PRL93, 061803 (2004)
fully incl.
sum of 38 excl. modes
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Moments of B?Xs g Photon Energy Spectrum
(see talk by Karsten Koeneke, Section VI.4)
Used in determination of mb, Vcb , and Vub
2nd Moment (GeV2)
1st Moment (GeV)
Minimum E? (GeV)
Minimum E? (GeV)
hep-ex/0507001
D. Benson, I.I. Bigi and N. Ultrasev Nucl. Phys.
B 710, 371-401 (2005)
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Electroweak penguins B?Kll- and B?Kll-

• With ll- pair, can produce both pseudoscalar
  and vector mesons
• New physics can affect both rate and kinematic
  distributions.

BABAR hep-ex/0507005 (229M BB)
Belle prelim. hep-ex/0410006, 0508009
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B?Kll- and B?Kll- branching fractions
Theory errors mainly due to form factors.
(rarest observed B decay)
pole at low q2
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B?Kll- Lepton F-B Asymmetry
Lepton angular distribution in l l- rest frame
Belle lepton A(FB) raw
386 M BB
hep-ex/0508009
SM
NP scenarios
?constraints on Wilson coeffs describing
short-distance physics
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Precision measurement of Vcb and the atomic
physics of B mesons

• inclusive semileptonic rate
• inclusive lepton-energy spectrum (moments)
• inclusive recoil hadron mass spectrum (moments)

Observables
Vcb, mb, mc, mp , mG , rD , rLS
Heavy-quark expansion theory params
BABAR, PRL 93, 011803 (2004)
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Vcb and inclusive parameters from B?Xcln and
B?Xs g

• Buchmuller and Flacher hep-ph/0507253
• Fit to moments of inclusive distributions in
  B?Xc l n and B?Xs g
• Experiments BABAR, Belle, CDF, CLEO, DELPHI

all moments
all moments
Dln zero rec.
lt2 errors
kinetic mass scheme
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Measuring Vub is hard, but the error is
shrinking
Large b?c background suppression cuts introduce
dependence on theory predictions for kinematic
distributions.
Fully reconstructed B recoil analysis
Lepton spectrum endpoint analysis
p
BABAR hep-ex/0509040
Breco
e-
D
e
n
Brecoil
continuum data (off res)
Xu
l
Belle
hep-ex/0505088
b?c subtraction
b?u
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Vub inclusive measurements
El endpoint

• Key CKM constraint
• Use mb and QCD parameters extracted from
  inclusive B?Xc l n and B?Xs g spectra.
• Many methods with uncertainties around 10.
• Uncertainty from mb has been reduced to 4.5.
• With more data, the Vub uncertainties could
  be pushed down to 5-6.5.

El vs. q2
mX
mX vs. q2
mb, theory
expt
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B0?p l- n form-factor predictions
Measuring Vub using B?p l n and lattice QCD
f(q2) is relevant form factor for B?p l n (le,
m)
Fermilab/MILC
HPQCD
At fixed q2, lepton momentum spectrum is
exactly known in this mode, since only one
form factor.
HPQCD hep-lat/0408019
restricted q2 range
Fermilab/MILC hep-lat/0409116
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B?p l n branching fraction and q2 distribution
Becher and Hill, hep-ph/0509090
Relatively flat distribution in spite of rapidly
changing form factor. Consequence of p3 factor
in decay rate.
HFAG averages
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Search for Bs?mm- and B0?ll-

• Highly suppressed in the SM
• Bd suppressed by Vtd/Vts2
• No SM signals expected at Tevatron or at B
  factories, but can have large enhancements from
  new physics.

Strong correlation with neutralino-proton
cross section in mSUGRA!
Beck,Kim,Ko hep-ph/0406033
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Perspective/Conclusions

• K Physics
• Early results from 1st dedicated KL?p0nn
  experiment
• KL branching fractions re-measured 5 to 8
  shifts
• Vus shift 3
• Unitarity of 1st row of CKM matrix looks better
  work in progress on Vud
• B Physics
• B?rg observed provides interesting constraint
  on Vtd/Vts
• Many b?sg and b?sll- modes observed studies of
  kinematic distributions are especially
  interesting
• Vcb measured to 2 via inclusive method mb
  well determined
• Vub precision now below 10.
• Keep pushing inclusive vs. exclusive crosscheck!
• Leptonic B decays providing interesting
  sensitivity to new physics
• B factories will push to 1 ab-1. Many more
  results to come!

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Backup slides
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Huge program on B decays to charmless hadronic
final states...
see H. Jawahery talk for hadronic b?s decays
(10-6)
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Observation of the b?dg decays B?r (w) g
Belle
BABAR
Note naïve expectation is G(B?rg)2
G(B0?r0g)2 G(B0?wg) BABAR/Belle discrepancy on
B0?r0g to be resolved with more data.
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BABAR
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B?Xs g New Physics Sensitivity

• Constraints on Two Higgs doublet models (Type
  II)
• mH charged Higgs mass
• tanb ratio of vacuum expectation values of the
  two doublets
• Hou PRD48, 2342 (1993), Gambino Misiak
  Nucl. Phys B611, 338 (2001), Neubert Eur.
  Phys. J C40, 165 (2005).

future projections
current BABAR data
90 C.L. allowed regions (above lines)
2 ab-1
1 ab-1
0.5 ab-1
combined
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Search for leptonic B- decays

• helicity suppressed
• CKM suppressed (Vub)
• annihilation diagram
• tree-level sensitivity to H-

Non-relativistic mesons (2 heavy quarks)
Predicted leptonic branching fractions (Vub
0.0039, fB 200 MeV)
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Search for B-?t- n
BABAR, hep-ex 0507069

• t reconstruction a major challenge
• fully reconstruct other B in event
• require lepton (or pion) and no additional
  observed energy (2-3n)

e-
Eextra
Belle, hep-ex/0507034
Backgrnd
e
Backgrnd
t-
nt
nt
Expected signal x10
e-
ne
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Search for Bs?mm- and B0?ll-

• Highly suppressed in the SM
• Bd suppressed by Vtd/Vts2
• No SM signals expected at Tevatron or at B
  factories, but can have large enhancements from
  new physics.

90 C.L.
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Bs?mm- and SUSY
Dermisek, Raby, Roszkowski, Ruiz de Austri,
hep-ph/0507233
Baek, Kim, Ko, hep-ph/0406033
Dark matter cross section s(cp) vs. B(Bs?mm-).
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Experiment vs. Lattice D?K l n form factor
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Measuring Vub using B?p l n
Projection to 1 ab-1 (data taken to be on BK fit
curve from present measurement).
BABAR
PRD 72, 051102 (2005)
In the high q2 region alone, we will measure the
branching fraction with an uncertainty of (6-7)
, or (3-3.5) uncertainty on Vub . Lattice
theorists expect to reach 6, so
exclusive/inclusive will be similar.
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Precision measurement of Vcb fits to moments
of lepton spectrum and hadron recoil spectrum
BABAR PRL 93011803 (2004)
? used, ? unusedin the nominal fit
mX moments
BABAR
El moments
Red line OPE fitYellow band theory errors
c 2/ndf 20/15
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Muon decay a prototype low-energy weak decay

• W-mediated b-quark transitions have several key
  features in common with muon decay.
• Very strong dependence of decay rate on mass!

(ignoring QED radiative corrections)