Search for CP Violation in B 0 h decays and B 0 h decays with B A B AR

Search for CP Violation in B0h decays

and B0h decays with BABAR

International Europhysics Conference on High Energy Physics ,July 17th-23rd, 2003, Aachen, Germany

Christophe Yèche (CEA-Saclay, DAPNIA/SPP)

Outline:• CP asymmetries in +- and +K- (PRL, 89, 281802 (2002))

• Decay rates for +0 and 00 (submitted to PRL, hep-ex/0303028)

• CP asymmetries in +- and +K- (submitted to PRL, hep-ex/0306030)

• Decay rates for +0, 0+ and 00(BABAR-CONF-03/014)

Ch. Yèche EPS 2003 Aachen, 18 July, 2003

CP Violation in Standard Model

2

tbtstd

cbcscd

ubusud

CKM

VVV

VVV

VVV

V

VtdVtb*

VudVub*

VcdVcb*

B,

BJ/KSBDK

• CP symmetry can be violated in any field theory with at least one non-trivial phase in the Lagrangian

• This condition is satisfied in the SM through the three-generation CKM quark-mixing matrix

• Unitary constraint 0*** tbtdcbcdubud VVVVVV

Representation with Unitary Triangle:• The angles (,,) are related to CPviolating asymmetries in specific B decays

• is already measured with good precision: Sin2 = 0.734 ± 0.055

• Next step: “measurement” of sin2


CP Violation in B0+ -

tmCtmSBBA dd cossin)/(00

2

2

||1

||1

C

2||1

Im2

S

C0, S= Im () =sin2

i

f eA

A

p

q 2

C 0, S= sin2eff

For single weak phase With an additional weak phase

Penguin diagramTree diagram

|A(penguin)/A(tree)|~ 30%

| | 1 must fit for direct CPIm () sin2 need to relate asymmetry to C 0, S= sin2eff

Vub

Vtd

*

3


z

0tagB

ee

S4

K

0recB

Inclusive Reconstruction B-Flavor Tagging

Exclusive B Meson Reconstruction

CP eigenstates

Flavor eigenstates

(flavor eigenstates) Resolution function and mistags

(CP eigenstates) CP analysis

00flavrec BB

00CPrec BB

PEP-2 (SLAC)

Experimental technique

4


Background suppression- Discriminating variables

5

2*2beamES

*BpEm *

beam* EEE B

(mES) 2.6 MeV/c2 (E) 26 MeV

mES: powerful variable to separate signal from light-quark continuum

E: some separation power for final states with different K/ composition

mES and E are used in the likelihood


Continuum suppression- Discriminating variables

6

uuee

“Jets”

ππBBee 00

*iθ

candidate

candidate candidate

candidate

• Spherical B events vs jet-like continuum: Techniques exploiting event topology and angular distributions

• Fisher variable: Combine two “monomials”,

where the sum is over the tracks i of the “Rest-Of-Event”

Use as a discriminating variable in the Likelihood

i

ipL *0

iiipL

2**2 )cos(and

“Rest-Of-Event”


PID: K/ Separation

7

KDDD 00* ,

K hypothesis hypothesis

DIRC: Cherenkov light emitted by the track around a cone with

Photons are captured by internal reflection in the bar and transmitted to a PMT matrix.

Resolution (c) = 2.5 mrad (e+e-+-)

n/1cos c

Cherenkov angle c is used in the likelihoodto separate , K, KK

8 at 2GeV/c2.5 at 4GeV/c

K/ momentum:2 4 GeV/c


B0+ -/ K+ - / K+K-

Branching Fractions

8

6

0

10)2.06.07.4()(BF

B

6

0

10)7.09.09.17(

)(BF

KB

The yields are extracted from a maximum likelihood fitbased on the variables:mES, E, F and c

)CL 90%(106.0)(BF 60 KKB

Continuum e+e- q q

Continuum

B0+-B0+-

B0K+-B0K+-

K

N(B0 +-) = 157 ± 19 ± 7

N(B0 K+-) = 589 ± 30 ± 17

Projection plots


CP Asymmetry Results for -+ / -K+

ACP (K) = -0.102 0.050 0.016C = -0.30 0.25 0.04S = 0.02 0.34 0.05

)cos()sin()/(00 tmCtmSBBA

9

The CP parameters are extracted from a maximum likelihood fit based on the variables: mES, E, F , c and t (for C and S)

1-ps)05.052.0(

ps)07.056.1(

dm

Cross-checks:Float and md

B0K+-

No Observation of CP Violation

A(B

0 /B

0 )


Constraint on : Isospin Analysis•The decays B +-, +0, 00 are related by isospin

Two relations (one for B0, one for B0) Neglecting EW penguins, B+ +0 is pure tree diagram Representation with a triangle with a common side. Need to measure separate BF for B0/B0 and B+/B-

Triangle relations allow determination of penguin-induced shift in

• Bound on penguin pollution “Back up” solution if the BF(00) is too small for isospin analysis!!!

22 eff

)(

)/()(sin

0

0000

eff2

BBF

BBBF

)(A~

)(A 00 BB

M. Gronau and D. London,Phys. Rev. Lett., 65, 3381 (1990)

Y. Grossman and H.R. Quinn,Phys. Rev., D58, 017504 (1998)

10


B 00 /+0 BF

Fit region

Continuum

Continuum e+e- q q

• B++0 decays

Likelihood fit with mES, E, F and c

Potential +- background suppressed

with a tight cut on E

• B000 decays

Likelihood fit with mES, E, F T

Potential +0 background suppressedwith a cut on M(+0) and on E(+0 0)

• Bound on penguin pollution

60.19.0

0 10)6.05.5()(BF

B

C.L. %[email protected])/(BF

10)6.1()/(BF

60000

66.0 7.03.0 6.0

0000

BB

BB

C.L. %90@51eff

11


Interpretation• Isospin Analysis

Large upper limit for BF(B000)Confidence levels obtained with the BABAR measurements of C, S,,BF(B000) and BF(B++0) Independent of models but no constraint in (,) plane

• QCD factorization

The phase and the magnitude of the treeand penguin amplitudes are predicted bythe QCD factorization. Confidence levels obtained with the BABAR measurements of C and S. Very strong constraint in (,) plane.

BBNS, Nucl. Phys., B606, 245 (2001)

12


How to measure with B0 ?

• Two final states: Same diagrams as B0- +, related to angle Final states are not CP eigenstates Two parameters (C, S) Four parameters (C, S, C, S) + charge asymmetry -/+

• Comparison with B0- + :Larger Branching Fractions (4) Smaller ratio |A(penguin)/ A(tree)|

13


• Time probability of the B0 /K

Parameters measured in the the /K analysis

)cos()()sin()(1))(1()(

)cos()()sin()(1))(1()(

/||

/||

0

0

tmCCtmSSehAtf

tmCCtmSSehAtf

hhhht

CPh

B

hhhht

CPh

B

14

Parameterization similar to B0+-

• 4 CP Violation Parameters: Direct CP Violation with the charge asymmetries (+/-) ACP0 for K and .

Summing over the charge, we have the “usual” (B0/B0) asymmetry:

Direct CP Violation: C 0

CP in interference between decay and mixing: S 0

• 2 Dilution Parameters: C can be different from zero (naïve factorizationC~0.3). S can be different from zero, no prediction for this term. if C=0 (P(B0/B0+-)=P(B0 /B0-)) and S=0

no dilution of sin(2eff) when S is measured!

)cos()sin()/()()/( 0000

00 tmCtmSNNNNBBABBBB


Overview of /K analysis

15

• Analysis very similar to /K analysis: Same data set (19992002) ~ 81 fb-1. Tagging and resolution function studied with fully reconstructed events. Simultaneous fit of and K events. Extraction of a the CP parameters with a maximum Likelihood fit using the same kind of variables mES, E, F /NN, c and t.

• Features specific to /K analysis : Continuum Suppression: NN with L0, L2 and two additional variables

o Mass (mass of the pair (±0)).o Helicity (angle between 0 and B in rest frame).

Modeling of true-signal and misreconstructed-signal. Modeling of charm and charmless B backgrounds.


B0/K Branching Fractions

Continuum

Continuum + B backgroundContinuum

Continuum + B background

16

Continuum

Continuum + B backgroundContinuum


K K

6

00

10)2.28.16.22(

)/(BF

BB

63.12.1

0

10)3.13.7()(BF

KB

Projectionplots

1834428

)(N

2521120

)(N

K


CP AsymmetryResults for /K

ACP () = -0.18 0.08 0.03ACP (K) = 0.28 0.17 0.08

C = 0.36 0.18 0.04C = 0.28 0.18 0.04

S = 0.19 0.24 0.03S = 0.15 0.25 0.03

)/(00 BBA

17

Continuum + B backgroundB background

See P-F Giraud’s Talk, about direct CP Violation. By combining C, C and ACP

() a little more than a 2 effect for direct CP Violation.


B 00 /+0/ 0+ BF• Principle of the analyses

Approach very similar to B0+-

Likelihood fit with mES, E, NN and (t)

• Next steps

Isospin analysis (more complicated)Two triangles Two pentagons Interpretation with QCD factorization For a first attempt, see next slide. (0-+) Dalitz plot analysis.

C.L. %[email protected])(BF

10)5.07.09.0()(BF

10)8.00.12.9()(BF

10)9.19.10.11()(BF

6000

6000

60

60

B

B

B

B

First observation !!!


Continuum

Continuum

Continuum +B background

B+ +0

B0 00

18


Interpretation with QCD factorization• Direct CP with QCD factorization

In recent papers, computation of QCDfactorization for PV decays (,…) QCD Factorization predicts very small direct CP violation for +-, better agreement with charming penguin.

• Mixing-induced CP Violation C.L. in (,) plane the BaBar results for the S and S withthe computation of QCD factorization for PV decays

R. Aleksan et al., Phys. Rev. D67, 094019 (2003)

See S. Safir Talk

BABAR QCDFQCDF +

Ch. penguin

ACP() -0.18 ±0.09 -0.015 -0.115

C 0.36 ±0.18 0.019 0.092

C 0.28 ±0.18 0.250 0.228

19


Conclusions

• BABAR results: No observation of CP Violation in B0+-. A “hint” of direct CP Violation in B0+-. No observation of B000 and B000 decays. First observation of B++0 decay.

• Prospects The isospin analysis does not constrain yet. QCD factorization may give very strong constraint on but still needs to be validated. The redundancy in experimental measurements (B0+-, B0+-, and B0+-) may provide a solid framework to test theoretical models and to extract .

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Documents

Search for CP Violation in B 0 h decays and B 0 h decays with B A B AR