Measurement of B→r/wg and study
of B→K*g with BaBar
Kevin Yarritu
Stanford Linear Accelerator Center
on behalf of the
BABAR collaboration
DPF2006
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Charge conjugate states implied throughout talk
b→s,d transitions

Flavor changing neutral current
 Exists in Standard Model only through
quantum corrections
- BF ~10-6 (rg) , ~10-5 (K*g )
 Top quark dominates in loop (SM)
Vtb
V*ts/d
Leading order short distance contribution
- Amplitude proportional to VtbV*ts/d
 Non-Standard Model particles can contribute in the loop
2
Quantities Obtained from Measurements
 Extract
Vtd
with B→rg and B→K*g
Vts
Vtd
- compare with other measurements of
(Bs mixing)
Vts
Annihilation amplitude
corrections
R = 0.1±0.1
Vtd
Vts
Ali, Lunghi, Parkhomenko
PLB 595, 323 (2004)
1(.5) for r±(r0)
Form factor ratio 1/ = 1.17±0.09
hep-ph/0603232
 Hadronic uncertainties partially cancel in ratios
 Direct CP and isospin asymmetry
measurements of B→K*g are sensitive to new
physics
SM: ACP < 1% , Δ0+ = +(2.6 ± 0.8) x 10-2 Matsumori, Sanda, Keum PRD 72, 014013 (2005)
3
Previous publications from Babar
B→rg
uses 191 fb-1
SM: (1.38±0.42) x 10-6
hep-ph/0405075
Combined BF:
PRL 94, 011801 (2005)
B→K*g
CP
uses 81.9 fb-1
Isospin asymmetry: -0.046 < Δ0- < 0.146 90% C.L.
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PRD 70 112006 (2004)
Experimental Techniques

Reconstruct B→r/w g with modes r+/0→p+p0/- , w→p+p-p0

Major sources of background
- events
- continuum (light qq)
- B→K*g (BF ~ 40 times higher)

Apply selection criteria
- 1.5 GeV < Eg* < 3.5 GeV
- use of DIRC for particle
identification ( p/K separation )
- r/w mass selection
- apply veto for g’s coming
from p0’s and h’s
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Experimental Techniques 2
 Suppress background using different topology, angular information
 Combine background suppression variables using Neural Net
 Define variables to reconstruct B meson
mES 

(E *
2
beam
* 2
- | pB |
*
) E *  EB* - Ebeam
Use multidimensional maximum likelihood fit with different components for
signal and background ( q q , B B )
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p0/ h veto likelihood
 combine high energy g candidate with all other g candidates in the event and
determine consistency with p0/h
Two-photon mass
Photon energy
signal
 form 2 dimensional
likelihood ratio (LR)
 also consider
p0
converted photons
and make selection
based on M(ge+e-)
h
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simulated signal and background
prev. analysis
p0
signal efficiency
h efficiency
p0 efficiency
p0/h veto performance
prev. analysis
h
signal efficiency
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B→r/wg continuum suppression
background rejection

Neural net contains 33 input variables
- Event shape variables ( 2nd Fox-Wolfram moment, angle between g and thrust axis….) (11)
- Variables that detect the presence of flavor in rest of event (4)
- Kinematic properties of e, m, K in rest of event (18)
New
Prev. analysis +
add. input
r0
Previous
Analysis (14)
r+
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signal efficiency
B→r/wg likelihood fit

Optimize cuts by maximizing signal significance in fit region defined by
E * < 0.3 and mES > 5.22

Four dimensional fit for rg and five for wg
- Fit variables: mES , E* , transformed NN output, cosθhelicity
+ cosθdalitz (wg)
θhelicity(rg) = angle between p+ and B in r rest frame
θhelicity(wg) = angle between the normal of p+p- plane and B in w rest frame
θdalitz = angle between p0 and p+ in p+p- rest frame
transformed
NN output

r0g fit has K*0g and K*+g as separate components
r+g treats K*+g (K*+→K+p0) separately
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Events / ( 0.1 )
Events / ( 0.85 )
Events / ( 0.0053 GeV )
B+→r+g fit projections
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Preliminary results
Isospin asymmetry:
( B  r g )
- 1  -0.36  0.27
0
0
2( B  r g )
+
+
isospin weighted
Simultaneous fit result:
BF[B  ( r , w )g ]  (1.01  0.21  0.08) 10-6
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Vtd
Vts
comparisons
Vtd
018
017
 0.171+-00..021
(exp) +-00..014
(theory)
Vts
BR(B→(ρ/ω)γ)/BR(B→K*γ)
BaBar ICHEP 2006
Belle 2005
B-Factories average
CDF measurement
(mS)
CKM fitter code w/o Δms
Global fit excludes ms and Br(w)g
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B→K*g (in progress)



Reconstruct in modes: K*0 → K+p- , KS p0 / K*+→ K+p0 , KS p+
use same framework as B → rg (use p0/h likelihood ratios)
Neural Net (13 inputs)
- event shape variables in addition to variables that detect presence of flavor
K*→ K+p0
K*→K+p-
New analysis
Previous
analysis
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B→K*g (K*→K+p-)
81.9 fb-1
Previous mass peak
288 fb-1
New mass peak
 Background subtracted using mES sidebands
 P-wave relativistic Breit-Wigner line shapes used to represent data
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Conclusions


Improved upon previous B→r/wg analysis
Babar observes the decay B0  ρ0g now , and finds the
first evidence for the decay B+→ ρ+ g. The combined
branching fraction from Babar is
____
BF[ B  ( r / w )g ]  (1.01  0.21  0.08) 10-6
which is the most precise measurement of this decay rate.
This is used to obtain
Vtd
018
017
 0.171+-00..021
(exp) +-00..014
(theory)
Vts

stay tuned for result from the B→K*g analysis
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