Radiative Penguins @ B Factories

1
Radiative Penguins_at_ B Factories

• V. Erkcan Özcan
• University College London

2
Radiative Penguin FamilyFlavor Changing Neutral
Currents
For Bs penguins, see talk by R. V. Kooten.
b?sg penguin BF, CPV, E-spectrum
b?dg penguin BF, CPV, E-spectrum
RARE!

3
Experimental Challenge
Analyses of all radiative penguins impeded by
huge BGs.

• Continuum Backgrounds
• ee-?qq(g) or ll(g).

• Penguins as signal BG
• One signal mode is the BG of another.

Signal and Backgrounds vs. photon energy for
inclusive B?Xsg.
4
A Signal Event
Isolated high-E EM deposition in the
calorimeter. p0/hs vetoed.
B-tagging High-P lepton from other B meson.
BG suppression not enough Psedo-reconstruction,
event weighting, BG subtraction, peaking BG fits
etc. needed!
Isotropic BB event topology.
5
B Factories
KEKB (KEK)
PEP-II (SLAC)
Asymmetric-energy beams Hermetic
detectors High-granularity EM CAL Excellent
vertex resolution Data _at_ Y(4S) resonance and
off-resonance (10)
Total 560fb-1
Total 330fb-1
Analyses based on 111-386 M BB
Analyses based on 88-232 M BB
6
Exclusive b?sgas of Summer 05
First baryonic channel
Reconstructing particular exclusive decay.
Experimentally cleaner. BF calculations depend on
form factors, so theoretically less
precise. Other observables, like CP violation
parameters, to be compared to those from
tree-level B decays. Some surprises of 2005
K1(1270)g / Kpp0g as large as K(892)g, pLg
observed. 40 of total rate.
Resonance structure in Kppg could tell about g
polarization
Comparable to K(892)
Branching Ratio 106
7
B?Kh()g
First studied by Belle (275 M BB). New BaBar
results consistent (232 M BB).
5.3s observation
TD CP violation can be studied like B?K0p0g.
First upper limits
Expected to be suppressed due to destructive
interference
hep-ex/0603054, submitted to PRL
8
Inclusive b?sg Constraints on NP
Total branching fraction very sensitive decay to
NP. Two techniques Sum-of-exclusive (K(np)g),
fully inclusive (reconst. g only). World average
in good agreement with SM theory. gt Strong
constraints on NP.
BaBar sum-of-exclusive value statistically
systematically independent of BaBar fully
inclusive value (not in HFAG). BaBar fully
inclusive value to be updated very soon.
BaBar Physics Reach Study
Combined constraint
Constraints to H mass in 2hdm. (following Hou,
PRD 48 2342, 1993 and Gambino-Misiak
hep-ph/0104034)
b?sg constraint
b?tn constraint (pre-FPCP)

• Exp. world average (HFAG)

Eg gt 1.6 GeV
SM prediction (NLO)
Experimental errors already smaller than
theory. NNLO calculation expected to
significantly reduce error.
Hurth et. al., Nucl. Phys. B, 704, 56 (2005)
9
b?sg Photon Spectrum
1st Moment
2nd Moment
(Momentum of b)2
Motion of b inside B, Fermi motion, is
universal so information from B?Xsg can be
used in studying other B decays (ex. extracting
Vub).
preliminary
CLEO
sum-of-exclusive
fully inclusive
10
Moments of the Photon Spectrum
Moments as a function of minimum Eg. Good
agreement among experiments and with theory
predictions.
Theory is Bigi,Benson and Uraltsev (Nucl Phys B
710 371 2005) using BaBar measured B-gtXcln
moments PRL 93 011803 (2004).
(Moments at higher E from Belle not shown
also consistent.)
11
Fits to HQE Parameters
Fits from O. Buchmüller, H. Flächer,
hep-ph/0507253. Thanks to H. Flächer for plot.

• Fits performed to obtain bquark mass and Fermi
  momentum in kinetic scheme (Benson, Bigi,
  Uraltsev) and SF scheme (Lange, Neubert, Paz).
• Fits to b?cln moments, b?sg moments or b?sg
  spectra are consistent.

mb (GeV) mp2 (GeV2)
Kin. 4.5900.039 0.4010.040
SF 4.6040.038 0.1890.038
mb error less than 1!
12
Direct CP AsymmetryInclusive B?Xg
CP Asymmetry measured in many exclusive
modes. Even time-dependent asymmetry studied in
channels like Ks0p0g (see talk by H. Kakuno).
For inclusive b?sg
For inclusive untagged b?(sd)g
BaBar lepton-tagged fully-inclusive (89 M BB)
13
b?dgFirst Observation
386 M BB
hep-ex/0506079

• Requires strong BG suppression
• Flavor-tagging, vertex displacement from other B,
  K veto, r/w helicity cuts
• Fit for signal, continuum, Kg, other B BGs.
• Central values show big isospin violation!
• Combined fit, assuming isospin.

14
b?dgComparison with BaBar
211 M BB
PRL 94 011801 2005
Combined fit, assuming isospin
15
b?dg Vtd/Vts
Ratio of form factors ?2 0.85 0.10
SU(3) breaking ?R 0.1 0.1
UTfit to all modes
UTfit to r0 data only
Earlier BaBar result
Independent constraint on CKM ?ms of B
Factories
16
b?sllC7, C9 C10
Exclusive Kll and Kll
Inclusive (Sum-of-exclusive)
Gambino et.al., PRL 94 061803 (2005)
q2 range 1-6 GeV2 gt4mm2
2004 1.80.9 5.62.0
2005 1.50.6 4.11.1
exp. avg. 1.60.5 4.51.0
SM 1.60.2 4.40.7
C7-C7SM 3.30.3 8.81.0
BF (10-6)

• Established in all individual modes except K
  modes K0ee mode.
• Kll smallest B decay measured at 5s.

3s away from exp.
Kll
preliminary
17
B?Kll _at_ Belle
386 M BB
hep-ex/0603018

• 113.6 13.0 Kll events (44 purity).
• Fix A7-0.33 (SM) and fit for A9/A7 and A10/A7.
• Repeat for A70.33.
• Use Kll for null test.

A9/A7 -12.33 A10/A7 12.82
SM
18
B?Kll _at_ BaBar
229 M BB
preliminary

• BaBar follows broader approach.
• C1-C10 would not account for pseudoscalar/scalar
  particles that can replace g/Z.
• In presence of such scalar contribution, FS, AFB
  can be non-zero even for B?Kll.

Fits are performed to obtain both AFB FS.
Consistent with zero (SM).
19
B?Kll _at_ BaBar
229 M BB

• For Kll decay, in addition to AFB, another
  quantity of interest longitudinal polarization
  FL of K.
• FL sensitive to left-handed currents with
  complex phases or right-handed currents in g
  penguin amplitude.

preliminary
SM inconsistent with AFB fit at low-q2 !!! (98
CL)
Wrong sign C9C10 excluded! (consistent with Belle)
FL fit consistent with SM. With 1 ab-1 could
exclude wrong-sign C7.
20
Summary

• Extracted BFs / CPV / AFB almost all in agreement
  with SM.
• BaBar AFB (B?Kll) measurement at low q2 away
  from SM would be useful to average BaBar and
  Belle measurements.
• Developed techniques highly scaleable,
  experimental errors to be reduced significantly
  as B factories collect more data.
• Inclusive modes
• NNLO theoretical calculation to reduce theory
  errors (as much as a factor of two) in two years.
• Measured HQE parameters quantify universal
  motion of b quark in B meson. Useful in
  extracting Vub and Vcb from semileptonic decays.
• Exclusive modes
• b?d penguin observed. CKM fits with rare
  radiative decays
• Wilson coefficients are now experimental
  observables. With even 1ab-1 data important
  discoveries are at hand.

21
Backup Slides
22
PEP-II _at_ SLAC KEKB _at_ KEK
Design Peak
3 10.0
10 16.3
1033cm-2s-1 1 BB pair / sec
Enough energy to create bquark pairs, but not
enough for B-meson pairs.
Off-resonance data _at_ 10.54/10.52 GeV CM no BB
pairs, only continuum BG
23
Thanks to I. Bizjak.
Belle Detector
Aerogel Cherenkov cntr.
n1.0151.030
SC solenoid 1.5T
3.5 GeV e
CsI(Tl) 16X0
ToF cntr.
8 GeV e-
Central Drift Chamber small cell He/C2H6
m / KL detection 14/15 lyr. RPCFe
Si vertex det. 3/4 layer DSSD
24
BABAR Detector
Electromagnetic Calorimeter 6580 CsI(Tl) crystals
1.5 T Solenoid
e (3.1 GeV)
Cherenkov Detector (DIRC) 144 fused-silica
bars 11000 PMTs
e- (9 GeV)
Drift Chamber 40 radial layers
Instrumented Flux Return steel / RPCs (muon /
neutral hadrons)
Silicon Vertex Tracker 5 layers, double sided
strips

• SVT 15 mm z hit resolution (inner
  layers, perp. tracks)
• SVTDCH 98 efficiency, ?(pT)/pT 0.13 ?
  pT 0.45
• DIRC K-? separation 4.2? _at_ 3.0 GeV/c ?
  gt3.0? _at_ 4.0 GeV/c
• EMC ?E/E (2.3 ? E-1/4 ? 1.9), ??
  ? (3.9 ? E-1/2) mrad

25
Box Diagrams Z-Mediated Penguins
26
Continuum Backgroundsvs. Lepton Tag
20 of all B decays are Xl?.

• Continuum BGs still dominate over signal after
  previous cuts!
• Requiring a lepton tag strongly suppresses what
  remains (signal efficiency 5, but continuum
  suppressed by ?1300!).
• Tag High-momentum lepton, not back to back with
  photon, missing energy due to neutrino
• MC tagging rate corrected from independent
  measurements of inclusive lepton spectra.
• What remains is subtracted with off-resonance
  data.

27
B?Xsg Sum-of-Exclusive

• Reconstruct B candidate in one of 38 modes.
• Use event shape to reduce continuum BG.
• Fit mES (for each mXS bin) to extract signal
  yield.
• Use observed yields in different modes to correct
  MC fragmentation.

28
Wilson CoefficientsOperator Product Expansion
Common framework Effective theory. New physics
expected to change Ci(?).
29
B?Kll