Searches for CP violation in D decays ... - Agenda (Indico) · Y. Grossman, A. L. Kagan and Y. Nir,...

Searches for CP violation in D0 decays from BABAR and Belle

Maurizio Martinellion behalf of the BABAR Collaboration

Università degli Studi di Bari and INFNFPCP 2010 - May 27 2010, Torino ITALY

Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010

• Standard Model: CP violation from KM phase in CKM quark mixing matrix:

• Charmed Mesons:

• CP violation is CKM suppressed O(10-3)

• Experimental Sensitivity O(10-2)

CP violation in D0 decays

1% Signal = New Physics2

1− λ2

2 λ Aλ3(ρ− iη + i2ηλ2)

−λ 1− λ2

2 − iηA2λ4 Aλ2(1 + iηλ2)Aλ3(1 − ρ− iη) −Aλ2 1


New Physics Scenario

• Direct CP violation at tree level («1%)

• extra quarks in SM vector-like representations• supersymmetry without R-parity models• two Higgs doublet models

• Direct CP violation at one-loop (1%)

• QCD penguin and dipole operators• FCNCs in supersymmetric flavor models.

CPV ~ 1% Strong Evidence for non-SM processes

Details:Y. Grossman, A. L. Kagan and Y. Nir, Phys. Rev. D75, 036008 (2007)I. I. Bigi, hep-ph/0104008 (2001)

Singly Cabibbo Suppressed (CS) decays are uniquely sensitive toCabibbo Favoured and Double CS are not

3

c→ uqq


Charm & B-factories• Why search for CP violation at B-factories:

• Υ(4S): ccbar cross section = 1/4 total

• require p*(D) > 2.5 GeV/c to reduce background

• D*+→D0π+ provides D0 flavor

• Drawback: Electroweak Forward-Backward asymmetry

4

(GeV/c)lab

sig] p(D*)+-K0, D0D[D*0 1 2 3 4 5

)2Ev

ents

/(100

MeV

/c

0

100

200

300

400

500BBcc

uds

p(D*) > 2.5 GeV/c

MC


Experimental Searches

• Direct CP violation

• Dalitz Plot analysis

• Time dependent

• T odd correlations

5


ACP =RD0 −RD0

RD0 + RD0, with R =

ΓCS

ΓCF

• In asymmetric detectors like BABAR and Belle, forward-backward asymmetry could bias these measurements

• FB asymmetry = EW+EM currents interference

• Two solutions:• estimate FB asymmetry contribution• normalize CP asymmetry to CF channels

Nc/Nc = f(cos θ∗)

ACP =ΓD0 − ΓD0

ΓD0 + ΓD0

Direct CP violation

6

Γ = yields


ACP =RD0→K+π−(nπ)

WS −RD0→K+π−(nπ)WS

RD0→K+π−(nπ)WS + RD0→K+π−(nπ)

WS

, with RWS =Γ(K+π−(nπ))Γ(K−π+(nπ))

• D* tagged

• Identification of Right Sign and Wrong Sign decay using K charge

• Both are DCS, using ratio DCS/CF yields

• 2D binned maximum likelihood fit to (m(D0), ∆m)

Doubly Cabibbo Suppressed D0→K+π-(nπ)

ACPKπππ = -0.006±0.053

RS

WS ACPKππ = -0.018±0.044

RS

WS

Phys. Rev. Lett. 95, 231801 (2005)Belle (281fb-1)

syst. < 0.01

NDtot=1978±104 NDtot=1721±757

D0→K+π-π0 D0→K+π-π+π-


AhhCP,dir = Ahh

CP + AFB + Aπs

ACP =Γ(D0 → h+h−)− Γ(D0 → h+h−)Γ(D0 → h+h−) + Γ(D0 → h+h−)

= AhhCP,dir + Ahh

CP,ind

Cabibbo Suppressed Decays: D0→h+h-

• Major issue: asymmetry in D0 tagging

• FB asymmetry

• soft pion(πs) reconstruction asymmetry

Need to separate contributions to ACP

from mixing analysis

8



• map the πs asymmetry using D0→K-π+ tagged and untagged data to retrieve the weighting factors to correct D0 yield

• measure ACP in cosθ bins in order to isolate production asymmetry

• measure ACP from χ2 fit over cosθ bins

even: ACP uniform over cosθ

odd: AFB asymmetric over cosθ

9

a±(cos θ∗) =nD0(±| cos θ∗|)− nD0(±| cos θ∗|)nD0(±| cos θ∗|) + nD0(±| cos θ∗|)

ACP �[a+(cos θ∗) + a−(cos θ∗)]/2AFB �[a+(cos θ∗)− a−(cos θ∗)]/2



0 0.2 0.4 0.6 0.8-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8-0.06

-0.04

-0.02

0

0 0.2 0.4 0.6 0.8-0.06

-0.04

-0.02

0

0 0.2 0.4 0.6 0.8-0.06

-0.04

-0.02

0

0 0.2 0.4 0.6 0.8-0.06

-0.04

-0.02

0

(a) (b)

(c) (d)

aKK

FBaK

KCP

a!! FB

a!!

CP

| cos !CMSD0 | | cos !CMSD0 |

| cos !CMSD0 | | cos !CMSD0 |

BABAR (385fb-1)Phys. Rev. Lett. 100, 061803 (2008)

Category ∆ACPKK ∆ACPππ

2-dim PDF shapes

πs corrections

ACP corrections

Quadrature sum

±0.04% ±0.05%

±0.08% ±0.08%

±0.09% ±0.20%

±0.13% ±0.22%

Systematic errors

ResultsACPKK = (0.00±0.34stat±0.13syst)%

ACPππ = (-0.24±0.52stat±0.22syst)%

two-dimensional fit to D0 and ∆mSample Size

K-π+ untag

K-π+ tag

K+K-

π+π-

6.6x106

1.5x106

130x103

64x103

10

D0→K+K- D0→π+π-



Belle (540fb-1)Phys. Lett. B670.190 (2008)

|cos *|

AC

P

a) K+K-

|cos *|

AC

Pb) + -

|cos *|

AFB c) K+K-

|cos *|

AFB d) + -

-0.04

-0.03-0.02

-0.01

0

0.01

0.020.03

0.04

0 0.2 0.4 0.6 0.8-0.04

-0.03-0.02

-0.01

0

0.01

0.020.03

0.04

0 0.2 0.4 0.6 0.8

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0 0.2 0.4 0.6 0.8

Category ∆ACPKK ∆ACPππ

Signal Counting

πs corrections

ACP extraction

Quadrature sum

±0.04% ±0.06%

±0.10% ±0.10%

±0.03% ±0.04%

±0.11% ±0.12%

Systematic errors

ResultsACPKK = (-0.43±0.30stat±0.11syst)%

ACPππ = (+0.43±0.52stat±0.12syst)%

one-dimensional fit to D0 mass spectrum

Sample Size Purity

K-π+ untag

K-π+ tag

K+K-

π+π-

6.3x106 80%

1.3x106 99%

120x103 97%

51x103 91%

11

D0→K+K- D0→π+π-


Dalitz Plot Analysis

• Quantities that can be measured:

• Asymmetry on the Dalitz Plot

• Asymmetry in the angular moments

• Asymmetry in the amplitudes (model dependent)

• Phase Space integrated asymmetry

12


Cabibbo Suppressed Decay D0→π+π-π0

Belle (532fb-1)Phys. Lett. B662.102 (2008)

Source MC stat. Tracking Fit KS veto PID Binning AFB Total

σ(%) 0.24 1.01 0.58 0.23 0.15 0.05 0.15 1.23

ACP = (0.43±0.41stat±1.30syst)%

Phase Space integrated asymmetry measurement

Sample Yields

π+π-π0 2.4x106

13

peaking background from D0+random πs

fit PDF from MC

Systematics


χ2/ν =

�ν�

i=1

∆2i

�/ν

Cabibbo Suppressed Decay D0→h+h-π0

BABAR (385fb-1)Phys. Rev. D78, 051102(R) (2008)

) 4/c2) (GeV0-(2m0 1 2 3

) 4/c2

) (G

eV0

+(2

m

1

2

3

-4

-3

-2

-1

0

1

2

3

4

(a)

) 4/c2) (GeV0-(K2m1 2

) 4/c2

) (G

eV0

+(K2

m

0

1

2

-4

-3

-2

-1

0

1

2

3

4

(b)

∆ ∆

|0DCM| cos

0 0.2 0.4 0.6 0.8

CP

0a

-0.01

0

0.01 (a)

|0DCM| cos

0 0.2 0.4 0.6 0.8

CP

0K

Ka

-0.02

0

0.02

0.04 (b)

Normalized Residuals

R = efficiency corrected ND0bar/ND0

CL(no CPV) = 32.8% CL(no CPV) = 16.6%

average on cosθ to cancel FB asymmetry

Search for asymmetries in the Dalitz plot

ACPKKπ=(1.00±1.67stat±0.25syst)%ACPπππ=(-0.31±0.41stat±0.17syst)%

Sample Size Purity

K+K-π0

π+π-π0

11x103 98%

82x103 98%

14

∆ =(nD0 −R · nD0)�

σ2nD0+R2·σ2

nD0

CL = one sided gaussian Confidence Level for consistency with no CPV hypothesis

(b)D0→K+K-π0(a)D0→π+π-π0


Cabibbo Suppressed Decay D0→h+h-π0

BABAR (385fb-1)Phys. Rev. D78, 051102(R) (2008)

No CPV found in Dalitz amplitudes comparing amplitudes, phases and fractions

Study of the Angular Moments to search for asymmetries

15

continued

)2) (GeV/c-+m(0.26 1.01 1.76

0X

-2

0

2

)2) (GeV/c-+m(0.26 1.01 1.76

1X

-2

0

2

)2) (GeV/c-+m(0.26 1.01 1.76

2X

-2

0

2

)2) (GeV/c0+m(0.26 1.01 1.76

0X

-2

0

2

)2) (GeV/c0+m(0.26 1.01 1.76

1X

-2

0

2

)2) (GeV/c0+m(0.26 1.01 1.76

2X

-2

0

2

)2) (GeV/c-K+m(K1 1.5

0X

-2

0

2

)2) (GeV/c-K+m(K1 1.5

1X

-2

0

2

)2) (GeV/c-K+m(K1 1.5

2X

-2

0

2

)2) (GeV/c0+m(K0.6 1 1.4

0X

-2

0

2

)2) (GeV/c0+m(K0.6 1 1.4

1X

-2

0

2

)2) (GeV/c0+m(K0.6 1 1.4

2X

-2

0

2

D0→π+π-π0 D0→K+K-π0

particlecombination π+π- π+π0 K+K- K+π0

CL (No CPV) 28.2% 28.4% 63.1% 23.8%


∆Y =τKπ

τhhAτ

τhh =τ+hh + τ−hh

2Aτ =

τ+hh − τ−hh

τ+hh + τ−hh

τ+hh =τKπ [1 + rm (y cosϕf − x sin ϕf )]−1

τ−hh =τKπ

�1 + r−1

m (y cosϕf − x sin ϕf )�−1

Time Dependent (TD)

• D0 mixing affects D0 decay times (h=K,π)

• defining

• ∆Y is a probe for CP violation in decay times

(SM: ∆Y=0)16

for a definition of x, y, rm and φf see Nicola’s talk on D0 mixing

(rm=1,φf =0)


t = mD0�L · �p/p2

Cabibbo Suppressed Decay D0→h+h- (TD)Belle (540fb-1)Phys. Rev. Lett. 98.211803 (2007)

Source Acceptance Equal t0 M window Sig/SB bkg Bkg B(t) Res Func Selection Binning Total

σ(%) 0.07 0.08 <0.01 0.06 0.07 0.01 0.05 0.01 0.15

Aτ = (0.01±0.30stat±0.15syst)%

• D* tagged events• many systematics cancel in lifetime ratio

t (fs)

Even

ts p

er 6

1.5

fs (a) KK

t (fs)

Even

ts p

er 6

1.5

fs (b) K

t (fs)

Even

ts p

er 6

1.5

fs (c)

t (fs)

(NK

K+N

)/NK (d)

1

10

10 2

10 3

10 4

-2000 0 2000 400010

10 2

10 3

10 4

10 5

-2000 0 2000 4000

1

10

10 2

10 3

-2000 0 2000 40000.1

0.11

0.12

0.13

0.14

0.15

0.16

0 2000 4000

Sample Size Purity

K-π+

K+K-

π+π-

111x103 98%

1220x103 99%

49x103 92%

AτKK=(0.15±0.35stat)%Aτππ=(-0.28±0.57stat)%

yCP≠0

17

Systematics


Cabibbo Suppressed Decay D0→h+h- (TD)

17

Aτ = (-0.26±0.36stat±0.08syst)%

BABAR (385fb-1)Phys. Rev. D78.011105 (2008)

Source Sig Model Charm Bkg Comb Bkg Selection Detector Model Total

σ(%) KK

σ(%) ππ

σ(%) average

0.072 0.001 0.001 0.083 0.054 0.122

0.265 0.002 0.005 0.172 0.040 0.318

0.062 0.001 0.002 0.011 0.054 0.083

t (ps)-2 -1 0 1 2 3 4

Nor

m.

Res

idua

l

-22

Even

ts/0

.06

ps

1

10

210

310

1

10

210

310

DataSignal

Charm

Comb.

*-D+K-K

t (ps)-2 -1 0 1 2 3 4

Nor

m.

Res

idua

l

-22

Even

ts/0

.06

ps

1

10

210

310

1

10

210

310

DataSignal

Charm

Comb.

*+D+K-K

t (ps)-2 -1 0 1 2 3 4

Nor

m.

Res

idua

l

-22

Even

ts/0

.06

ps

1

10

210

310

1

10

210

310DataSignal

Charm

Comb.

*-D+-

t (ps)-2 -1 0 1 2 3 4

Nor

m.

Res

idua

l

-22

Even

ts/0

.06

ps

1

10

210

310

1

10

210

310DataSignal

Charm

Comb.

*+D+-

Sample Size Purity

K-π+

K+K-

π+π-

731x103 99.9%

67x103 99.6%

31x103 98.0%

AτKK=(-0.40±0.44stat±0.12syst)%Aτππ=(0.05±0.64stat±0.32syst)%

• D* tagged events• many systematics cancel in lifetime ratio

18

Systematics


AT =Γ(�v1 · (�v2 × �v3) > 0)− Γ(�v1 · (�v2 × �v3) < 0)Γ(�v1 · (�v2 × �v3) > 0) + Γ(�v1 · (�v2 × �v3) < 0)

T odd correlations

• Asymmetry in T-odd observable→T violation→CPV (assuming CPT invariance)

• T-odd observable (v = spin or momentum)

• Final State Interactions could fake the measure producing AT≠0

• Remove FSI effects

AT =12

�AT − AT

�

W. Bensalem, A. Datta and D. London, Phys. Rev. D66, 094004 (2002)W. Bensalem and D. London, Phys. Rev. D64, 116003 (2001)W. Bensalem, A. Datta and D. London, Phys. Lett. B538, 309 (2002)

T violating observable

19

measured on D0

measured on D0


CT = �pK+ · (�pπ+ × �pπ−)

D0→K+K-π+π-

• T-odd correlation observable (CT) can be built using final state particle momenta:

I. I. Bigi, hep-ph/0107102 (2001)

-p

+p

+Kp

-Kp

-p × +pTC

rest frame0D

20

AT =Γ(D0, CT > 0)− Γ(D0, CT < 0)Γ(D0, CT > 0) + Γ(D0, CT < 0)

AT =Γ(D0,−CT > 0)− Γ(D0,−CT < 0)Γ(D0,−CT > 0) + Γ(D0,−CT < 0)


AT = (1.0± 5.1stat ± 4.4syst)× 10−3

AT =(−68.5± 7.3stat ± 5.8syst)× 10−3

AT =(−70.5± 7.3stat ± 3.9syst)× 10−3

)2Ev

ents

/ ( 0

.8 M

eV/c

0

200

400

600

800

1000)2Ev

ents

/ ( 0

.8 M

eV/c

0

200

400

600

800

1000

0

dataSignalBackground

>0)T

(C0D <0)T

(C0D

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Pull

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Pull

-3 0

+3

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

)2Ev

ents

/ ( 0

.8 M

eV/c

0

200

400

600

800

1000)2Ev

ents

/ ( 0

.8 M

eV/c

0

200

400

600

800

1000

0

>0)TC (0D <0)TC (0D

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Pull

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Pull

-3 0

+3

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

BABAR

Pre

limin

ary

BABAR (470fb-1)hep-ex/1003.3397 (submitted to PRL)

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Even

ts/ (

0.8

0 M

eV/c

^2)

0

1000

2000

3000

4000

)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9

Even

ts/ (

0.8

0 M

eV/c

^2)

0

1000

2000

3000

4000dataSignal

peaking0Dm peaking

Combinatoric+sD

BABARpreliminary

)2 m (GeV/c0.14 0.145 0.15

Even

ts/ (

0.1

5 M

eV/c

^2)

0

5000

10000

)2 m (GeV/c0.14 0.145 0.15

Even

ts/ (

0.1

5 M

eV/c

^2)

0

5000

10000dataSignal

peaking0Dm peaking

Combinatoric+sD

BABARpreliminary

Pull

Pull

-3 0+3

Pull

Pull

-3 0+3

• D* tagged events• 2D fit to (m(D0), ∆m)• 47000 signal events

Effect signal PDF ∆m peak PDF bin size PID p*(D0) cosθ* fit bias mistag det asym Total

σ(x10-3) 0.2 0.5 0.2 3.5 1.7 0.9 1.4 0.0 1.1 4.4

fit projections signal region

21

Cabibbo Suppressed Decay D0→K+K-π+π-

Systematics:


Conclusions• D0 and charm decays provide a

powerful probe for non SM processes involving CPV

• Experimental sensitivity comparable to higher SM predictions

• Many experimental techniques developed by BABAR and BELLE

• No evidence of CPV found yet

• Is the best yet to come?

22

)-2 10× (CPA-10 -8 -6 -4 -2 0 2 4 6 8 10

Belle(2005) 0-+ K 0DBelle(2005) -+-+ K 0DBelle(2007) -+ 0DBelle(2007) -K+ K 0DBaBar(2008) -+ 0DBaBar(2008) -K+ K 0DBaBar(2008) -+ 0DBaBar(2008) -K+ K 0DBelle(2008) -+ 0DBelle(2008) -K+ K 0DBelle(2008) 0-+ 0DBaBar(2008) 0-+ 0DBaBar(2008) 0-K+ K 0DBaBar(2010) -+-K+ K 0D

Searches for CP violation in D decays ... - Agenda (Indico) · Y. Grossman, A. L. Kagan and Y. Nir,...

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Transcript of Searches for CP violation in D decays ... - Agenda (Indico) · Y. Grossman, A. L. Kagan and Y. Nir,...