Measurements of the angle a: rr, rp (BaBar

1
Measurements of the angle a rr, rp (BaBar
Belle results)
WIN05, Delphi June 8, 2005

• Georges Vasseur

2
Outline

• Physics motivation
• Measurement of a in B?rr.
• Measurement of a in B?rp Dalitz.
• Summary on a.

3
CP violation

• CP violation is explained in the Standard Model
  by a phase in the CKM unitary matrix.
• In the Wolfenstein parameterization
• with l ? 0.22 , A ? 0.83
• CP violation if h ? 0.

4
The unitarity triangle
g phase of Vub (b?u transition)
b phase of Vtd (B0 mixing)
a
g
b
(0,0)
(0,1)

• a p-b-g process involving both B0 mixing and
  b?u transition

5
CP violation in the interference between mixing
and decay

• For a CP final state fCP, time-dependent
  asymmetry is
• With

B0
Mixing (q/p)
B0
fCP
from mixing
C ? 0 Direct CP violation
S ? 0 Indirect CP violation
6
CP violation in B0???-

• Access to a from the interference of a b?u decay
  (g) with B0B0 mixing (b).

• I

g
Tree only
Tree Penguin
T tree amplitude P penguin
amplitude d strong phase difference between
penguin and tree
Inc. penguin contribution
How can we obtain a from aeff ?
7
Isospin analysis

• Use SU(2) to relate amplitudes of all rr modes.

2?-?eff
Small amplitudes
Gronau, London PRL65, 3381 (1990)
8
Asymmetry measurement
t 0
fully reconstructed B
Coherent B0B0 production
B 0
tag
B 0

• Exclusive B meson reconstruction.
• Time measurement Dz 250 mm, s Dz 170 mm.
• B-flavor tagging Q S e(1-2w)2 30.
• with e efficiency and w mistag rate.

9
Common features of the analyses

• Kinematical signal identification with
• Beam energy substituted mass
• Energy difference
• Hadron ID (separation p/K).
• Event-shape variables combined in a neural
  network (NN) or Fisher discriminant to suppress
  jet-like continuum event.

10
B0???- analysis

• B???- not historically favored for measuring a
• 2 p0s in the final state.
• 3 amplitudes (VV decay) A0 (CP-even
  longitudinal), A (CP-even
  transverse), A- (CP-odd transverse).
• But turned out to be the best mode
• Large branching fraction.
• Penguin pollution much smaller than in B?pp.
• 100 longitudinally polarized! Pure CP-even
  state.

BaBar Preliminary
BaBar, Phys.Rev.Lett 93, 231801 (2004)
signal
232 MBB
bkgd
BaBar, hep-ex/050349, submitted to PRL
11
Details of the B0???- analysis

• Unbinned extended maximum likelihood fit on a
  data sample of 68703 events.
• Efficiency on signal 7.7.
• 8 observables mES, DE, Dt, NN, mpp (x2),
  cosQpphel (x2).
• Modelisation of signal (1 of fit sample),
  continuum (92 of fit sample), and 38 different
  modes of B-background (7 of fit sample).
• Extract signal yield, longitudinal polarization
  fraction, cosine and sine coefficients.

232 MBB
12
ACP(t) in B0?rr- decays
BaBar, hep-ex/0503049, submitted to PRL
Preliminary
232 MBB
signal
bkgd
13
B???0 analysis

• For isospin analysis, need other B?rr rates.
• B???0 was measured two years ago by both BaBar
  and Belle.

89 MBB
85 MBB
Phys.Rev.Lett 91, 171802 (2003)
Phys.Rev.Lett 91, 221801 (2003)
14
B0??0?0 analysis

• Limiting factor in the isospin analysis.
• Tree is color suppressed.
• No significant signal
• Penguin are smalls.
• Dominant systematic comes from the potential
  interference from B?a1p (22).

BaBar, Phys.Rev.Lett 94, 131801 (2005)
15
Isospin analysis with B???
Phys.Rev.Lett 93, 231801 (2004)
a-aeff lt 11
Phys.Rev.Lett 91, 171802 (2003) Phys.Rev.Lett 91,
221801 (2003)
Phys.Rev.Lett 94, 131801 (2005)
Error dominated by r0r0 measurement
BaBar, hep-ex/050349, submitted to PRL
16
B0?(?p)0 analysis

• Unlike rr-, rp- is not a CP eigenstate
• Must consider 4 configurations
• Equivalent "isospin analysis" not viable.
• However, a full time-dependent Dalitz plot
  analysis can constrain a.

Snyder, Quinn PRD 48, 2139 (1993)
Interference at equal masses-squared gives
information on strong phases between resonances
r0
p-
p0
p
?
p-
p0
r-
p
17
Time-dependent Dalitz analysis

• Extract ? and strong phases using interferences
  between amplitudes of decay.

• Assuming amplitude is dominated by r,r-and r0
  resonances

script ,-,0 refers to r,r-,r0

• The "f"s are functions of the Dalitz-plot and
  describe the kinematics of B?rp (S?VS).
• The "A"s are the complex amplitudes containing
  weak and strong phases. They are independent of
  the Dalitz variables.

18
Result with B?pp-p0

• Hint of direct CP-violation

• Likelihood scan of a using

k? ,-,0 T tree amp. P penguin
-
-
213 MBB
2.9 ?
Mirror solution not shown Weak constraint at
C.L.lt5
19
Combined a measurement

• The best individual measurement comes from rr.
• Mirror solution are disfavored, thanks to rp.
• Good agreement with global CKM fit.
• Combined value

http//ckmfitter.in2p3.fr
20
Summary

• CP violation has entered a phase of precision
  measurements thanks to the B-factories.
• The angle a of the unitarity triangle has been
  measured with an uncertainty of 10.
• Will still improve.

http//ckmfitter.in2p3.fr