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Study of CP Violation in B 0   +  –  0 / K S Decays. Jinwei Wu Harvard University. Aug 21 st , 2006 . CP violation Extraction of α from B  ρ  decay Extraction of β from B  K S  decay Conclusion. Direct CP Asymmetry. . . . . no CPV.

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study of cp violation in b 0 0 k s decays
Study of CP Violation in B0+–0/KS Decays

Jinwei Wu

Harvard University

Aug 21st, 2006

  • CP violation
  • Extraction of α from B  ρ decay
  • Extraction of β from B  KS decay
  • Conclusion
slide2

Direct CP Asymmetry

no CPV

  • Sources of direct CP asymmetries:

Interference between two decay amplitudes (Ai) with different strong (i) and weak phases (i)

CPV

slide3

Time-dependent CP Asymmetry

B0

fCP

no oscillation

oscillation

B0

B0

fCP

no oscillation

B0

oscillation

slide4

Mixing induced CPV in Charmless B Decay

  • Decay-amplitude weak-phase structure for b → uud :
  • Time dependent asymmetry probes eff:
slide5

Quasi-two-body Analysis

R. Aleksanet al, 1990

free

Penguin

scenario

  • Quasi-two-body approximation, ignore interference effect
  • 6 observables through a time-dependent fit:

Measure CP violation, but not necessarily phase 

snyder quinn method

A3 = f+A+ + fA+ + f0A00

A3 = f+A+ + fA+ + f0A00

00

+–

+

Snyder-Quinn Method

Quinn, Snyder

PRD 48, 2139, (1993)

Idea: Extract  and the strong phases

using the interference between B0  +0 amplitudes

+0amplitude parameterization:

m(0)2 (GeV2)

  • The f+, ,0 are relativistic

Breit-Wigner form factors

m(+0)2 (GeV2)

fit projection plots
Fit Projection Plots

Strong signal with 347M BBbar

ρ(770) dominate

extract physics parameters
Extract physics parameters
  • Time-dependent Dalitz plot approach should supersede the previous quasi-two-body analysis, with interference among resonances taken into account.

hep-ex/0608002

* Using a Q2B approach and 144fb-1 data, BELLE measured:

probing direct cp violation

ρ



=?

B0

+

ρ+

B0

ρ+

+

=?

B0



ρ

B0

Probing Direct CP Violation

Define physically more intuitive quantities:

3.0

Large Direct CPV not expected…

road to
Road to 

Dalitz plot specific measurements:

  • What is the strong phase between B0ρ+ and B0ρ+?
  • What is ?
slide12

Measuring sin2β with Charmless B decay

decays are tree and penguin diagrams, with equal dominant weak phases

decays are pure “internal” and “flavor-singlet” penguin diagrams

High virtual mass scales involved: believed to be sensitive to New Physics

Both decays dominated by single weak phase

BR~ 10-3

B0J/yK0

Tree:

sin2b=0.69±0.03

B0fK0

Penguin:

BR~ 10-5

New Physics?

3

?

slide13

Sources of Standard Model Pollution

There are many modes that dominantly decay via bs(qq)…but not all modes were created equal

There are various estimates for the deviation from sin2β due to SM pollution…most of them expect a larger value!

This is ok; still gives

sin2b in SM.

c,t

b

s

K0

B0

d

d

d

w,p0,r0,h’(?),f0(?)…

d

b

u

w,p0,r0,h’(?),f0(?)…

B0

u

s

CKM and color suppressed..

but will lead to slight deviation.

K0

d

d

slide14

sin2β from B0KS Final State

  • quite a few CP events in this decay including r0KS and f0KS
  • also a higher (f?) resonance ~1500 MeV
  • there is a possible tree diagram which contaminates the sin2b measurement
  • time-dependent CP has been measured for f0Ks and r0Ks

Last summer, Belle presented a (time and tag independent) Dalitz Plot analysis of this mode…this approach will be important in the future!

slide15

B0KS Final State

  • A Dalitz plot with rich structures, apart from CP eigenstates, there are also flavor eigenstates.
  • K*(890)π, K*0(1430)π are important for testing QCD factorization and other schemes.
  • Can look for direct CP violation and test SU(3) symmetry in the B→ PV decays
  • Interference with flavor eigenstates can help lift the degeneracy in the sin2β measurement

K*(890)

K*(1430)

slide16

B0f0KS

ML fit :

  • Systematic errors dominated by
  • Fit bias & interference with other modes
slide17

B0ρ0 KS

  • Complications
  • high level of bkg
  • ρ is broad
  • Interference with ππ s-wave at both high mass and low mass

BaBar:

S=0.17±0.52±0.26

C=0.64±0.41±0.25

slide18

Analysis of B0KS Dalitz Plot

Similar analysis technique, need to handle additional flavor eigenstates

f0

r0

f???

Strong signal with 347M BBbar

conclusion
Conclusion
  • Extraction of α from B ρπ
    • The isospin analysis appears hopeless for the near future
    • There is hope for the Dalitz plot analysis although it’s technically difficult.
    • Extract α with no ambiguities. Especially useful when combined with other experiments or other measurements of α.
    • Latest result in hep-ex/0608002
  • Pioneered time-dependent Dalitz plot analysis for B decays. Framework setup to study other three-body B decays.
    • Already tested on B0→K+–0
    • Close to finish CP measurement of B0→K0+–,where CP violation in s-penguin decay and direct CP violation will be tested
    • Foresee preliminary results in September.