980 GeV/c2 p

CPV in the Charm Sector at CDF

Mark MattsonWayne State University

7th InternationalWorkshop on the CKM

Unitarity Triangle

30 Sept 2012

CDF

Fermilab, IL

980 GeV/c2 p

Overview

• Why are charm CPV measurements interesting?

• Time-integrated CP asymmetry with D0 -> h+h-

• Measurement of ∆ACP between D0 -> KK and D0 -> ππ

• Search for CPV in D0 -> Ksππ

2

Why is charm CPV interesting?

• Predicted to be small in the SM; can be a probe for new physics

• Before Nov 2011, many believed it would be << 1%

• Predictions for charm CPV are difficult

• Dominant terms are non-perturbative / model-dependent

• Precision measurements for charm CPV are difficult

• Detector effects can mimic the effects of CPV

• See previous talk by Chris Parkes “CPV and Mixing in the Charm Sector at LHCb”, and earlier talks by Ko (Belle), Cenci (BaBar) and Sun (CLEO).

3

Time-integrated CP violation measurements with D0 -> h+h-

(5.94 fb-1)

4

Phys. Rev. D 85, 012009 (2012)

http://www-cdf.fnal.gov/physics/new/bottom/100916.blessed-Dpipi6.0

Asymmetry with

5

• Use D*+ -> D0 π+ and c.c. decays, where the charge of the π tags the D0 production flavor

• To make precision measurement, need to correct for detector effects that can bias the asymmetry

• Start with the “raw” difference between the number of D*+ and D*- (with D0-> ππ), to get the difference between D0 and D0-bar

• The detector can cause an imbalance in the number of charged pions used to form the D*±. Use the “raw” D*± -> π± D0, D0->K π to correct for that.

• Lastly, make a correction to the previous correction, to account for detector systematics that affect K+π- / K-π+

• Make sure the events are weighted to match pT and η distributions.

€

ACPππ =

Γ(D0 →π−π +) −Γ(D 0 →π +π−)Γ(D0 →π−π +) + Γ(D 0 →π +π−)

D0 ! h+h�

]2-mass [GeV/c+/-Invariant K1.8 2 2.2 2.4

2C

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s pe

r 5 M

eV/c

0

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610× 3445±) = 7257239 +/

- KA0N(D/ndf = 250/2322r

)-1Data (5.9 fbFit

RS/ KAD WS/ KAD

// AD Multibody D decaysCombinatorial backg.

m/6

-202

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100

150

310×

/ndf = 385/3042r 2007±) = 2476700 +

s/) +/- KA (0 DA +N(D*

)-1Data (5.9 fb

Fit

Random pions

m/6

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0

2

]2-mass [GeV/cs/0Invariant D

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0

2000

4000

6000

8000/ndf = 325/3082r

352±) = 106169 +s/) -/+/ A (0 DA +N(D*

)-1Data (5.9 fb

Fit

Random pions

m/6

-202

Data Driven Corrections

6

* refers to D* tagged events ; no * means an untagged sampleRepeat the procedure for D0 -> KK

ACP (⇡⇡) = A⇤raw(⇡⇡)�A⇤

raw(K⇡) +Araw(K⇡)

Individual Mode Asymmetries

7

ACP = AdirCP +

Z 1

0ACP (t)D(t)dt ⇡ Adir

CP +< t >

⌧Aind

CP

Note: Measured CP asymmetry is a combination of direct and indirect CP asymmetries

) [%]-K+KA0(DindCPA

-1 -0.5 0 0.5 1) [

%]

- K+ KA0

(Ddi

rC

PA

-2

0

2CDF

2008RABAB

Belle 2008

No CPV

2-dim 68% CL2-dim 95% CL1-dim 68% CL

) [%]-/+/A0(DindCPA

-1 -0.5 0 0.5 1

) [%

]- /+ /

A0(D

dir

CP

A

-2

0

2

CDF

2008RABAB

Belle 2008

No CPV

2-dim 68% CL2-dim 95% CL1-dim 68% CL

Measurement of ∆ACP betweenD0 -> KK and D0 -> ππ

(9.7 fb-1)

8

Phys. Rev. Lett. 109, 111801 (2012)

http://www-cdf.fnal.gov/physics/new/bottom/120216.blessed-CPVcharm10fb

∆ACP Measurement

9

• For ∆ACP measurements, event selection can be loosened

• Also, data beyond 6 fb-1 was added

• Cross check with data binned in different η, phi regions

2.005 2.01 2.015 2.02

5

10

15

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310!

+s") -

"+

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D# +

D*

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D # -

D*

)-1Data (9.7 fb

Fit

multibody#0D

Random pions

2.005 2.01 2.0150

10

20

30

40

50

10!

+s")

-K

+ K# (

0 D#

+D*

2.005 2.01 2.015 2.020

10000

20000

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-K

+ K# (

0D #

-D*

]2-mass [GeV/cs"0Invariant D

2C

andid

ate

s per

0.1

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A⇤raw(⇡⇡)�A⇤

raw(K⇡) +Araw(K⇡)

� [A⇤raw(KK)�A⇤

raw(K⇡) +Araw(K⇡)]

�ACP = A⇤raw(K

+K�)�A⇤raw(⇡

+⇡�)

∆ACP Measurement

10

[%]indCPA

-5 0 5

[%]

dir

CP

A6

-2

0

2

CDF

2008RABAB

Belle 2008

No CPV

2-dim 68% CL2-dim 95% CL1-dim 68% CL

CDF(Δ(ACP(Measurement:(•  For(ΔACP(measurement,(selecFon(can(be(loosened,(and(full(data(set(used((more(than(doubling(the(staFsFcs.(

•  Cross(check(with(data(binned(in(different(η,(φ regions.(

7/23/2012( 33(

5

10

15

20

310×+s�) -�+� � (0 D� +D* -

s�) -�+� � (0

D � -D*

)-1Data (9.7 fbFit

D decaysMultibody

Random pions

CDF Run II Preliminary

2.005 2.01 2.0150

10

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50 +s�) -K+ K� (0 D� +D*

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ates

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�ACP = (�0.62± 0.21± 0.10)%arXiv:1207.2158(

Combined Measurement

• Can combine the ∆ACP result with the ACP(ππ) and ACP(KK) result

• remove events from the ∆ACP analysis that were used in the other analysis, to create a statistically independent sample

• roughly 15% improvement on uncertainty from the earlier ACP(ππ) and ACP(KK) result

11

ACP(D0->π+π-) = (+0.31 ± 0.22)%ACP(D0->K+K-) = (-0.32 ± 0.21)%

Heavy Flavor Averaging Group Combination of ∆ACP Results

12

ACP (indirect) = (-0.025 ± 0.231)% ∆ACP (direct) = (-0.656 ± 0.154)%

Search for CPV in D0 -> Ksπ+π-

(6.0 fb-1)

13

Phys. Rev. D 86, 032007 (2012)

http://www-cdf.fnal.gov/physics/new/bottom/111013.blessed-D0KSpipi_ACP

CP Asymmetry in D0 KSπ+π-

• SM expectation of these CP asymmetries is O(10-6), well below exp. sensitivity• Dalitz fit (employing the Isobar model for the involved resonances)• First time at a hadron collider using Dalitz plot technique

• Model-independent bin-by-bin comparison of the D0 and D0 Dalitz plots

14

CP Asymmetry in D0 KSπ+π-

• Overall ACP = -0.0005 ± 0.0057 ± 0.0054• Negligible effect from neutral kaon CPV

• Asymmetries determined for resonance modes (next page)

15

CP Asymmetries for Resonances

16

amplitude phase

Conclusion

• Recent CDF results testing charm sector CPV with 3 analyses

• Time-integrated CP violation measurements with D0 -> h+h-

• Measurement of ∆ACP between D0 -> KK and D0 -> ππ

• Search for CPV in D0 -> Ksππ

• ∆ACP measurement is 2.7 sigma from zero, and consistent with the LHCb result

• No hints of CPV for Ksππ

• Need to continue improving experimental results and predictions to test SM

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