(Belle II Collaboration)€¦ · mixed charged bkg uds charm signal Belle II MC Continuum...

Measurement of CKM angle φ3 at Belle II

Niharika Rout

(Belle II Collaboration)

IIT Madras, India

Conference on Flavor Physics and CP ViolationMay 7, 2019

Niharika Rout Measurement of CKM angle φ3

Outline

1 Introduction

2 Current status of CKM parameters

3 Extraction of φ3 from B± → D(∗)K (∗)±

4 Belle II outlook

5 Future prospects

6 Summary

Niharika Rout Measurement of CKM angle φ3 2

Introduction

Unitaritycondition

=⇒(1st � 3rd)

Measuring SM CP violation ⇒ Measure complex phase of CKM el-ements.

φ1/β ≡ arg(−VcdV∗cb

VtdV∗tb

)

φ2/α ≡ arg(− VtdV∗tb

VudV∗ub

)

φ3/γ ≡ arg(−VudV∗ub

VcdV∗cb

)

Definition of φ3 does not dependon coupling to top quark.

Thus measurable via treelevel decays ⇒ theoreticallycleaner [O(10−7)] [1].

Precise measurement providesSM benchmark.1

J. Brod, J. Zupan, arxiv:1308.5663


Current status of CKM parameters

Figure : Constraints on CKM parameters [2]

Direct measurements

(φ3)combined = (73.5+4.2−5.1)◦

Indirect extrapolation

(φ3)combined = (65.3+1.0−2.5)◦

φ3 is an excellent probe to NP.

Testing of direct vs indirectdisagreement.

Need to improve precision on direct

measurement.

Figure : Constraints on “tree-level” processes (left) and “loop-level” processes (right)

2Image source: http://ckmfitter.in2p3.fr/


Extraction of φ3

φ3: Only CKM angle accessible at tree level.

Sensitivity to φ3 arises from the interference of b → u and b → cquark transitions.

Classic mode: B± → DK±.

Interference occurs when D0 and D0

decay to the same final state f .

rB = |Asup

Afav| ∼ |VubV

∗cs

VcbV ∗us| ×CcolorSupp ∼ 0.1 for B± → DK± decays [3].

δB is the strong phase difference between favoured and suppressedmodes; φ3 is the weak phase.

3HFLAV16, Y. Amhis et al. (Heavy Flavor Averaging Group), Eur. Phys. J. C 77 (2017)895 [arXiv:1612.07233 [hep-ex]]


Common final states: primary methods

GLW [Phys. Lett. B 253, 483]

Both D0 and D0 decays to same CP eigenstates such as K+K−, π−π+ (CP-even), K0Sπ

0

(CP-odd).4 observables (RCP± ,ACP± )No need of external inputs.

ADS [Phys. Rev. Lett. 78, 3257]

D from a favoured amplitude decays to adoubly-Cabibbo-suppressed state.

2 Observables (RADS,AADS)

External charm factory inputs (rD andδD).

GGSZ [Phys. Rev. D 68, 054018] parameters to extract: φ3 , rB and δB

Uses multi-body D(K0Sh−h+) final states.

Sensitivity to φ3 by comparing D Dalitzdistributions for B+ and B−

Fit D Dalitz plot with full amplitudemodel.

AB = A(m2−,m

2+)+rBe

i(δB+φ3)A(m2+,m

2−)

m2± = squared invariant masses of K0

Sh±

: D Dalitz plot variables.Figure : Dalitz plots of B+ → DK+ (left) and

B− → DK− (right) arXiv:1806.01202v1 [hep-ex]


GGSZ: Binned model-independent approachOptimal binning of the D Dalitz plot which gives the maximum sensitivity to φ3.Number of events in ith bin is a function of x±/y±:

N±i = hB [K±i + r2BK∓i +

√KiK−i (x±ci ± y±si )].

hB : Normalization constant. Ki : Number of events in the ith bin of a flavourtagged D decay (obtained using a sample of D∗± → Dπ± decays).Fit simultaneously in each bin,

(x±, y±) = rB(cos(±φ3 + δB), sin(±φ3 + δB))

ci and si : amplitude-averaged strong phase difference between D0 and D0 over ith

bin and are obtained from external charm factories like CLEO and BESIII.

Figure : Optimal binning of D Dalitz plot and comparison of phase terms ci , si measured by CLEO and Belle [4]

4Phys. Rev. D 85, 112014 (2012)


φ3: world averages (HFLAV)

From all measurements of B → D(∗)K (∗) from GLW, ADS, and GGSZ

(Belle + BaBar + LHCb)

0

0.2

0.4

0.6

0.8

1

CL

−1

0 50 100 150]° [γ

GLW

ADS

GGSZ

Combined

GLW

ADS

GGSZ

Combined

68.3%

95.5%

HFLAVCKM 2018

0

0.2

0.4

0.6

0.8

1

CL

−1

0 50 100 150]° [γ

+K−sD→0

sB+*K0D→+B+K0*D→+B0*K0D→0B

+K0D→+BCombined

+K−sD→0

sB+*K0D→+B+K0*D→+B0*K0D→0B

+K0D→+BCombined

68.3%

95.5%

HFLAVCKM 2018

(φ3)combined = (73.5+4.2−5.1)◦ [8]

(φ3)Belle = (73+13−15)◦

(φ3)BaBar = (69+17−16)◦ [6]

(φ3)LHCb = (74+5.0−5.8)◦ [7]

6[PRD 87 052015 (2013)]

7[LHCb-CONF-2017-004]

8http://www.slac.stanford.edu/xorg/hflav/triangle/moriond2018/index.shtml


Belle II @SuperKEKB

Super KEKB: 4 GeV e+ and 7 GeV e− asymmetric collider at KEK, Japan.Belle II detector is at the interaction point.

The center-of-mass energy is close to the mass of Υ(4S), which decays to BB pair.

Figure : Belle II detector [9]

9Image source: PoS EPS-HEP2017 (2017) 223


Status of Belle II experiment

Phase I (complete)

Accelerator commissioningwith single beam.

Phase II (complete)

Taken data with partialdetector (with small part ofvertex detector).Accumulated ∼ 0.5 fb−1

data.Physics studies are going on.

Phase III (“Run I” started)

SuperKEKB becameoperational on March 11th forphase III data taking.First collision was on March25th.

Ultimate goal: 50 ab−1 Figure : SuperKEKB luminosity projection


Glimpse from phase II data taking

D∗± → D0(K0Sπ

0)π±

M∆

0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 0.156 0.158 0.16

)2E

ntrie

s/ (

0.00

06 G

eV/c

0

5

10

15

20

25

30

35 +π)0π0

S(K0 D→ *+D

Belle II 2018 (preliminary)

-1L dt = 472 pb∫

0π0SK

M

1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1

)2E

ntrie

s/ (

0.01

33 G

eV/c

0

5

10

15

20

25

30 +π)0π0

S(K0 D→ *+D


-1 L dt = 472 pb∫

D∗± → D0(K0Sπ

+π−)π±

M∆

0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 0.156 0.158 0.16

)2E

ntrie

s/ (

0.00

06 G

eV/c

0

20

40

60

80

100 +π)+π-π0

S(K0 D→ *+D


-1L dt = 472 pb∫

0π0SK

M

1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1)2

Ent

ries/

(0.

0133

GeV

/c0

20

40

60

80

100

120+π)+π-π0

S(K0 D→ *+D


-1L dt = 472 pb∫

Better reconstruction, selection and tagging algorithm.Improved PID performance.Good neutral (K 0

S , π0) reconstruction efficiency.



Mbc =√

E2beam − (Σ−→pi )2, Mbc > 5.27 GeV/c2, ∆E = ΣEi − Ebeam, |∆E | < 0.05 GeV.

E (GeV)∆-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Ent

ries

/ (16

MeV

)

0

10

20

30

40

50

60

70

80

90±π)ππ0

S,K0π

S,KK,K0ππ,Kπ,K3π->D(K±B

±ρ)π, K3π->D(K±B±π)0ππ, Kπ, K3π(K*0->D±B

±

π)0ππ, Kπ, K3π(K±*

->D0B

±

ρ)π, K3π(K±*

->D0B

±

π)ππ(K±->D0B

±

ρ)ππ(K±->D0B

(S)

(*)) K-µ+µ, -e+(eψ->J/0B


-1L dt = 472 pb∫

)2 (GeV/cbcM5.2 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29

)2E

ntrie

s /

(4 M

eV/c

0

20

40

60

80

100

120

140 ±π)ππ0S

,K0πS

,KK,K0ππ,Kπ,K3π->D(K±B±ρ)π, K3π->D(K±B

±π)0ππ, Kπ, K3π(K*0->D±B

±

π)0ππ, Kπ, K3π(K±*

->D0B

±

ρ)π, K3π(K±*

->D0B

±

π)ππ(K±->D0B

±

ρ)ππ(K±->D0B

(S)

(*)) K-µ+µ, -e+(eψ->J/0B


L dt ∫ -1= 472 pb

More than 200 B candidates from hadronic modes!!


B± → DK± @Belle II

ADS, GLW and GGSZ can all bereproduced at Belle II.

Ongoing analyses (D final states)

KK , ππ: CP-even.K0Sπ

0: CP-odd.

K0Sππ: GGSZ

Need to focus on:

PID improvements.Continuum suppression.

Tracking, K0S selection.

Figure : K0S reconstruction at Belle II

E (GeV)∆

0.2− 0.1− 0 0.1 0.2

Ent

ries

/ 4 M

eV

0

100

200

300

400

500

600

700mixedcharged bkgudscharmsignal

Belle II MC Continuumsuppression

=⇒95% bkg rej30% sig loss

E (GeV)∆

0.2− 0.1− 0 0.1 0.2

Ent

ries

/ 4 M

eV

0

20

40

60

80

100

120

140

160

180

200

220mixedcharged bkgudscharmsignal

Belle II MC


Future prospects

Expect Belle II and LHCb upgrade to match each other’sperformance!δ(φ3) < 2◦ by 2027.

Due to Belle II unbiased trigger it will be better in Dalitz plot analysisand sensitivity to the neutrals will allow to include more D modes.LHCb will clearly have more precise results in fully-charged finalstates.


Summary

Precision measurement of φ3 is very crucial.

Current uncertainty on φ3 ∼ 5◦

Combined sensitivity of 1.6◦ isexpected:

Including more D(∗) modes!Integrated luminosity = 50ab−1

Input from Charm factory Figure : fit extrapolated to the 50 ab−1 for anSM-like scenario [B2TIP report]

Assuming BESIII will collect 10 fb−1, D0 hadronic parametersmeasured at BESIII will play vital role.

Uncertainty on indirect prediction of φ3 already ∼ 1◦

Many modes can be added to improve the uncertainity.


Backup


φ3 sensitivity studies with Belle II

Goal is to go up-to precision ≈ 1◦.B± → D0(K 0

Sπ−π+)K±: Golden mode to determine φ3!

Large branching fraction involved.

Significant overlap between D0 and D0 amplitudes which gives a large interferenceterm sensitive to φ3.

Rich resonant structure which provides large variations of the strong phase in D

decay: sesnsitive to φ3.

* GLW like states: Interference of B− → DK− , D → K 0Sρ

* ADS like states: Interference of B− → DK− , D → K∗π

Figure : Expected uncertainty on φ3 (based on toy MonteCarlo studies) versus luminosity

Figure : Dalitz binning used for D → K0Sππ analysis

δ(φ3)50ab−1= 1.6◦ when Belle GLW

+ ADS + GGSZ extrapolated.Niharika Rout Measurement of CKM angle φ3 18


D∗± → D0(K−π+)π±

0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆

0

20

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)2E

ntrie

s / (

0.42

MeV

/c

+π)+π-(K0D→*+D


-1L dt = 472 pb∫

1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c+π-M(K

0

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)2E

ntrie

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5 M

eV/c +π)+π-(K0D→*+D


-1L dt = 472 pb∫

D∗± → D0(K−π+π0)π±

0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆

0

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ntrie

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+π)0π+π-(K0D→*+D


-1L dt = 472 pb∫

1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c0π+π-M(K

0

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500)2E

ntrie

s / (

5 M

eV/c

+π)0π+π-(K0D→*+D


-1L dt = 472 pb∫

D∗± → D0(K−π+π−π+)π±

0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆

0

50

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)2E

ntrie

s / (

0.42

MeV

/c

+π)+π-π+π-(K0D→*+D


-1L dt = 472 pb∫

1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c+π-π+π-M(K

0

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)2E

ntrie

s / (

5 M

eV/c +π)+π-π+π-(K0D→*+D


-1L dt = 472 pb∫


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